BULGARIAN ACADEMY OF SCIENCES
CENTRAL
LABORATORY
OF MINERALOGY
AND
CRYSTALLOGRAPHY
ANNUAL REPORT
No 3/1997
BULGARIAN ACADEMY OF SCIENCES
CENTRAL
LABORATORY
OF MINERALOGY
AND
CRYSTALLOGRAPHY
ANNUAL REPORT
No 3/1997
| Editor: Dr. Nikola Zidarov; E-mail: nzidarov@interbgc.com |
| © Central Laboratory of Mineralogy and Crystallography, 1998 | ISSN 3033-2206 |
CONTENTS
Projects No 4, 11, 13, 16, 19, 24, 25 and 28 are financially supported
in part by the Bulgarian National Science Fund of the Ministry of Education,
Science and Technologies; No 8 - by the Committee of geology and mineral
resources; No 12 - by "Arsenal" Ltd.
INTRODUCTION
This annual report presents the research activities of the Central Laboratory of Mineralogy and Crystallography during the third year of its existence.
The topics developed were in accordance with the preliminary specified scientific and applied priorities. The most significant results, published or reported at conferences, can be grouped as follows:
Various mineral systems and their products have been studied. The metamorphic evolutionary history of the Ograzden metagranitoids, the thermal regime of the Ciprovci fluorite mineralization and the syn- diagenetic ore-forming processes of the Kremikovtsi carbonate-hosted iron-barite-sulfide deposit have been reconstructed. In natural materials (metalliferous sediments from the TAG hydrothermal field, Mid-Atlantic Ridge), metal particles from the ternary Sn-Pb-Cu alloy, as well as Cu-Zn alloys, native Sn, Ni and Al have been described for the first time. These results, fundamental in their character, are also of important practical interest, being the basis for the development of geological-genetic models needed for the prognostic, prospecting, exploration and estimation of mineral deposits.
Spatial mathematical models for geometrization of the basis of chemistry are proposed for the first time, by which minerals of a simple chemical composition can be presented uniquely in a six-dimensional mathematical space. A model is proposed for the transport of the platinum - group minerals in an alluvial environment, as well as a mathematical model for describing the character of the distribution of gold in Eastern Rhodopes, confirmed in the practice.
The following new phases and compounds are synthesized and characterized: a K-Ti silicate phase, a synthetic analogue of the natural ferritungstite, chlorine sulfosalts and twenty new crystalline phases synthesized in CLMC and other institutes of BAS, mono-exchanged tiocarbamide derivatives, glicine adducts of zinc inorganic salts, of non-centrosymmetric compounds and complexes with organic ligands, etc. The structure of sodium silicate glasses is investigated by neutron diffraction and is modeled by reverse Monte-Carlo simulations. It is expected some of the newly synthesized phases to have interesting practical applications.
Among the most important achievements of practical character are:
It is found that Cl and Br, accumulated in the combustion wastes of seven Bulgarian thermal power stations are a considerable pollution of the soils, waters, air and vegetation around the stations, a fact of both ecological and technological importance.
Resource and qualitative estimation is performed for Cr-containing cyanogen-free galvanic sediments from the most important plants in Bulgaria, including the Sofia district, aiming at their recycling and usage.
A patent entitled "A zeolite-based sorbents for softening of potable and technological waters" is defended.
The expanded collaboration with foreign universities is realized in eight joint projects, four of which have started from the beginning of 1998. The investigations involved aim, on the one hand, at synthesizing new materials with interesting practical and application properties, such as Pd and zeolite-based catalysts, sensors and sorbents, and, on the other hand, at precise structural characterization of new phases for filling the International XRD data bases in the field of crystallography and mineralogy.
As a result of the collaboration with the Institute of Chemistry and Technology of Natural Products in Palermo, Italy, it is found that the natural glasses from the Eastern Rhodopes (Bulgaria) and the Lipari islands (Italy) are structurally and chemically similar, making it possible the synthesis on this base of palladium-organometalic precursors by low-temperature reduction. The catalytic systems prepared that way are effective in the catalysis of styrene.
During this year, in spite of the serious economic difficulties our research activity is comparable with that during 1996, and the international collaboration is even extended. The scientific plan continues to be rearranged and developed toward modern problems in the field of crystallography and mineralogy and its successful realization is still restricted due to financial shortages.
Nikola Zidarov
Sofia, January 1998
RESEARCH TOPICS:
I. MINERAL SYSTEMS:
1. Magmatic and metamorphic minerals and mineral associations in the Serbo-Macedonian Massif (N. Zidarov, L. Macheva, E. Tarassova, Y.Tzvetanova)
Different gneisses from the Ograzdenian Super Group cropping out in the Ograzden block of the Serbo-Macedonian Massif in SW Bulgaria are investigated. As usually, it is assumed that they are irregularly migmatized parametamorphic rocks.
Field observations and petrographic investigations have proved the magmatic origin of the huge part of this rocks, participating in different thrusted sheets of several tectonic units.
Three types of metagranitoids were distinguished: one with porphyritic and a second with equigranular structures, both with two feldspars, metamorphosed to augen-banded and banded gneisses with the same mineral composition, and a third, plagiogranites transformed to plagiogneisses. Their protoliths had been influenced by heterogenic ductile deformations and weak subsolidus migmatization. In some parts of the gneisses relics of magmatic K-feldspar, plagioclase and biotite are preserved. The porphyroclasts of K-feldspar in the porphyritic metagranitoids are sized up to 10 cm, euhedral, irregularly oriented in the foliation-plane, containing small plagioclase crystals in the growth zones. All types of metagranitoids contain melanocratic inclusions elongated in the foliation-plane, having peculiarities of tectonicaly thinned xenoliths, as well as aplite and pegmatite veins influenced by metamorphism.
The reconstruction of the conditions for the formation of protoliths and their metamorphic transformation are in progress.
2. Processes of mineral formation and geogenetic models of the Fluorite formation (B. Zidarova, N. Zidarov, M. Marinov)
The temperature regime of the hydrothermal process in the metasomatic fluorite bodies in Ciprovci deposit are investigated on the basis of the temperature of homogenization of the fluid inclusions in fluorite.
Metasomatic processes in carbonate rocks producing fluorite are experimentally studied in the temperature range found for the fluorite formation in the Ciprovci deposit. These results and previous data can be used for the establishment of the geogenetic model of the deposit.
A mathematical model, describing the growth of some fluorite aggregates under conditions far from equilibrium in the Slavianka fluorite deposit, is created. These aggregates preserve the dissipative structure of the deposition medium and are specific forms of the self-organization on a macro-level.
3.Sedimentary-hydrothermal ore-forming processes in the Kremikovtsi deposit (Z. Damyanov)
New data on the primary ore petrology, whole-rock chemistry and the zoning of the siderite and hematite iron formations, barite ore and sulfide mineralization from the Kremikovtsi carbonate-hosted sedimentary exhalative iron(+Mn)-barite-sulfide deposit, Western Balkan, Bulgaria, have been established and a new submarine exhalative ore-forming model has been proposed [46]. A comparative analysis between lead isotope data in galenas from the Kremikovtsi deposit and some polymetallic deposits in Bulgaria and all over the world has been made. The lead isotope data give a good reason to consider this deposit as a result of Middle Triassic metallogenesis and are compared with some carbonate-hosted deposits in Southeastern Alps. The mineralogical features of clay minerals in the Kremikovtsi primary ores have been studied. Kaolinite, illite, berthierine and chamosite have been identified. They are characterized by various morphological types and polymorphs, marking different stages of sedimentation and diagenesis and are good indicators of sedimentary-exhalative evolution of the primary ores in the deposit. A preliminary study of the content of Hg in sulfide minerals, barite and technological products from the Kremikovtsi deposit is still in progress in order to clarify its sources, behavior in the technological processes and the opportunities for restriction of the harmful effect on the environment and men.
4. Mineralogical studies of native metals and alloys from theoceanic rift zones (East Pacific Rise, 21o S and Mid-Atlantic Ridge, 26oN- TAG hydrothermal field) (V. Dekov, Z. Damyanov)
Optical microscopic, SEM, microprobe and XRD analytical techniques permitted a detailed mineralogical study of a hitherto unknown (in seafloor sediments, rocks and ores) Ag71.5Cu28.5 alloy from the axial metalliferous sediments of the East Pacific Rise [1]. According to the proposed endogenous hypothesis of its formation, native silver-copper grains are formed as ultra-accessory micro-segregations in a silicate matrix during the mantle pre-chamber evolution of the basic and ultrabasic systems beneath the spreading zones under high P-T and low ƒO2 - ƒS2 conditions. The alloy formation was probably realized with falling temperature in the following sequence: crystallization of copper crystals (T 785o C) crystallization of silver+copper eutectic mixture (T = 779.4o C) silver and copper exsolution (T < 779.4o C) to a final composition of Cu + Ag-Cu eutectic + AgII [1].
Near sulfide mound sediments from the TAG field have been studied [47]. Phase identification has been performed of different sulfides, silica phases, smectites, iron oxides and hydroxides, atacamite, Mn-oxide crusts and micronodules. Specific features of their morphology, chemical composition and physical characteristics have been established. Metalliferous sedimentary horizons and hydrothermal precipitates dispersed have formed as a result of direct precipitation from the hydrothermal fluids, collapse of active chimneys and mass wasting of the gossans. Oxidation, dissolution, remobilization, precipitation and recrystallization of the phases and bacterial action have played an important role in the formation of near sulfide mound sediments. Cyclic volcanic activity at discrete volcanic centers has contributed specific material in the sedimentary cycle and formed distinct layers rich in basaltic components [47].
Mineralogical features of native tin and ternary Sn-Pb-Cu alloy, Cu-Zn alloy, native nickel and native aluminium from the TAG hydrothermal field (Mid-Atlantic Ridge, 26o) have also been studied. Metal particles from the ternary Sn-Pb-Cu alloy have been established for the first time in natural materials and data for the alloy studied with a probable initial melt composition of Sn76Pb17Cu7 is absent, to our knowledge, in the basic references devoted to the Sn-Pb-Cu system in technical materials.
5. Phase composition and formation conditions of garnet-fassaite skarns from Zvezdel-Pcheloyad ore deposit (Y. Tzvetanova)
Calcic garnet-fassaite skarns are enclosed in monzonites from the second magmatic phase, which participates in the Zvezdel paleogenic pluton, East Rhodopes.
The skarns consist of the following zones: plagioclase-pyroxene, plagioclase-pyroxene-wollastonite, plagioclase-pyroxene-wollastonite-garnet ± scapolite, pyroxene-garnet and garnet.
The bulk chemical composition of the different zones are recalculated by the Lindgren method. The results show a relative decrease in the values of SiO2, MgO, Fe2O3, FeO, an increase in the content of CaO and a relatively stable tendency to decreasing Al2O3 and TiO2 towards the exoskarn (garnet-fassaite and garnet zone).
The phase relations in the simple system CaO-Al2O3-Fe2O 3-SiO2 (investigated experimentally by Huckenholz et al., 1974) suggest, that skarns from Zvezdel-Pcheloyad represent calcareous rocks which have been metamorphosed to a grandite+fassaite+wollastonite assemblage at temperature higher than 935o C. Further, with decreasing the temperature below 798o C this assemblage has been brought down to the more stable grossular-andradite one.
6.Indicatory properties, stability and transformations of minerals from the Me3O4 and (Me2+, Me4+)2O3 systems: Fe-Tioxides from the Oman-Fakija pluton (E. Tarassova)
The studied Fe-Ti oxides are the most widespread accessory minerals in the Oman-Fakija pluton, their amounts ranging from 1 to 8 % in the basic rocks (pyroxenite, gabbro and quartz-gabbro - I intrusive phase); <1-3% in the intermediate rocks (quartz-monzonite, monzonite, monzodiorite - II phase), and <<1-2% in the small bodies and dykes of quartzmonzodiorite-porphyrite, monzonite-porphyrite, and granodiorite-porphyrite (III phase). The Fe-Ti oxides in these rocks are encountered as magnetite with ilmenite exsolutions and as homogeneous magnetite. The relative content of magnetite with ilmenite exsolutions decreases from the early intrusive phase (50%) to the later one (5%).
The total content of the minor elements (Ti, Al, Si, V, Mg, Mn, Cr, Ca) in the magnetites studied is comparatively low (0,2-3,5 wt.%). The composition of the homogeneous magnetite and that from the magnetite-ilmenite intergrowths are very similar for each of the considered rock. This indicates that the formation of the former magnetite and the latest transformations in the coexisting magnetite and ilmenite have been performed simultaneously under the same physicochemical conditions. The higher contents of Ti and V (TiO2 - up to 1,8 wt.% and V2O3 - up to 1,1 wt.%) are established in the magnetites from the basic rocks; Al and Mg are encountered in increased amounts (Al2O3, MgO - up to 1.1 wt.%) in the magnetite from the intermediate rocks; Si (SiO2 up to 1.3 wt.%) is the most typical minor element for the magnetite from the latest rocks.
Increased and variable contents of MnO and Fe2O3 and low contents of other minor elements (Al, Si, Ca, Cr, Mg) are characteristic for the ilmenites studied. According to their composition, the minerals can be specified as Mn-bearing ilmenite (basic rocks), Mn-ilmenite and Fe-pyrophanite (the rocks of the II and III phases). The significant variations in the content of MnO and Fe2O3, observed in the minerals studied, are considered as resulting from unevenly developed postmagmatic fluid attacks on the rocks.
7. Platinum-group minerals from native or placer deposits: phase composition, indicator features and associations, conditions for occurrence and transformation (Z. Tsintsov)
Statistic data of 84 individual grains of PGM from sediments of Gotse Delchev graben are studied. All they are concentrated in classes <200 mm and are distinguished with high and very high degree of mechanical processing. These are dominated by sperrylite (63.10 %); the rest of the individual grains are PGE alloys (22.62 %) and Pt-Fe alloys (14.28 %). The sperrylite is homogenic, without variation in the values of the composing elements in different parts of its grains. However, variations in the composition of other minerals in the PGE alloys are observed. The PGE alloys contain inclusions of Pt-Fe alloys and chromite. Chromite (predominantly Fe-containing), bowieite, kashinite and quartz are proved in the Pt-Fe alloys, while sperrylite rarely contains inclusions of quartz and amphibole (gedrite ?).
In chromitites from Pletena village in Gotse Delchev region, a single inclusion of laurite is established which is distinguished with its almost isometric form, porous surface and dimensions of 8x10 mm. Its composition includes Os, unevenly distributed in the different parts of the grain. The mineral association accompanying the laurite is exhibited by chromite, pentlandite, included in grains of chromites, and also by silver, galena, chalcopyrite and barite, observed in the welding of the chromitites. These minerals are almost isometric and fine-sized (< 5 mm).
8. A1:25000 mineralogical map of the heavy mineral concentrates in Bulgaria (O.Vitov)
During 1997 the mineralogical data base is supplemented by information on 23 000 samples (the figure), thus the total number of samples reaching 67 731. Using Fourie analysis a mathematical model is developed for estimating the systematic arrangement of the anomaly bands of the heavy mineralconcentrates. The model is confirmed by additional sampling and is applied to process data from Eastern Rhodopes [41].
The computer program SCHLICH96/QBASIC-DOS for quantitative recalculation of the content of minerals and mineral associations, based on data of laboratory analysis of heavy mineral concentrates and for maintaining factograph data base is adopted at LGI-Sofia. The program is used for processing data from maps of Nikolovo and Ranilist, Eastern Rhodopes, and mineralogical maps scaled 1:25 000 are drawn.
9. Structural classification of the phosphate minerals (O. Angelova, R. Petrova, T. Todorov, V. Velikova)
The criteria for classification of minerals has changed throughout the years following the development of the mineralogical science. A new classification scheme for phosphate minerals is going to be proposed on the base of their atomic structure. In order to apply a general structural approach to minerals it is necessary to determine the various mineral structural types. This is the main part of the program of the Commission on Classification of Minerals of the International Mineralogical Association. The research proposal aims at the determination of the structural types of phosphate minerals. Its realization is based on a complete physico-chemical characterization of each mineral, determination of the atomic structure and creation of a corresponding structural formula according to the criteria formulated by Lima-de-Faria & Figueiredo (1976) and by Lima-de-Faria and al. (1990) and the requirements of the Commission on Crystallographic Nomenclature of the International Union of Crystallography.
The bond strenght distribution in a crystal structure may be relatively homogeneous, as in many oxides, halogenides, alloys and intermetallic compounds, where the bonds are predominantly nondirectional, and such structures are formed by close packing of large atoms with the smaller atoms occupying the interstices. The "skeleton" of this type of structure, i.e. the "structural unit", is formed by anions, while the cations are in the interstitials. But in structures, where the directional bonds are dominant, the bond strength distribution is usually heterogeneous and then, the structural units may form finite groups, infinite chains, infinite sheets or infinite frameworks. Hence there are five main categories of structural units: individual atoms, finite groups, infinite sheets and infinite frameworks and the corresponding main categories of structures are respectively called closed-packed, group (or cluster), chain, sheet (or layer) and framework structures. These categories are subdivided and ordered from the simplest to the more complex cases.
The structural types among the phosphate minerals based on their known atomic structures were determined.The specific goals of this project are as follows:
As a result the following particular tasks were realized [71, 76, 80]:
10. Mineralogy and geochemistry of coals and coal products (S. Vassilev)
Some relationships between the ash content and the mineral and chemical composition of coals and their high-temperature ashes from 41 deposits in Bulgaria and worldwide (Australia, USA, Japan, Canada, China, Russia, South Africa, and Ukraine) were studied [35]. The contents, concentration trends, and modes of occurrence of 67 elements in coals, coal ashes, and combustion wastes from 11 Bulgarian thermoelectric power stations (TPS) were characterized. A number of trace elements in the coals and coal ashes studied have concentrations greater than their respective worldwide average contents (Clarke values) [34]. Chlorine and bromine in Bulgarian coals (Maritsa-East, Maritsa-West, Sofia, Pernik, and Bobov dol) and their combustion wastes from 7 TPS were investigated. The Cl and Br content showed that the combustion wastes may be a considerable pollution of these elements in air, soil, water and vegetation near TPS [68]. Chlorine and bromine in coals from the Pirin deposit were also studied. It is supposed that the vegetation, water solutions and terrigenous materials are the main sources of Cl, while an additional source (most probably of volcanic activity) causes the observed considerable enrichment of Br [67].
11. Phase-mineralogical and chemical transformations and interactions in inorganic matter of coals during heating (S. Vassilev, C. Vassileva)
The mineralogy and chemical composition of lignitic, subbituminous and bituminous coal and coal-ash samples from six Bulgarian deposits, namely Maritza West (MW), Sofia (S), Maritza East (ME), Bobov dol (BD), Pernik (P) and Balkan (B), were studied and a model for comparative characterization of their composition is performed [67]. Major minerals identified in the crystalline matter of Bulgarian coals are commonly quartz, kaolinite, illite, calcite, pyrite, plagioclase, K-feldspar and gypsum, and occasional dolomite, siderite, Fe oxyhydroxides and Fe-sulphates. Some genetic features of the inorganic compounds in coals and coal ashes are described and compared. The coals studied show a high detrital (P, B, BD, ME) or high authigenic (S, MW) mineral abundance with sulphide-sulphate (P, BD, ME, MW) or mixed carbonate and sulphide-sulphate (B, S) authigenic mineral tendencies. The high-temperature ashes of these coals belong to sialic (P), sialoferricalcic (B, BD), sialoferric (ME) or ferricalsialic (MW, S) chemical types. They have a high (B, P, BD) or low (ME, MW, S) silicate mineral abundance with sulphate (B, P, ME, MW, S) or oxyhydroxide (BD) mineral tendencies [67].
12. Resource and qualitative estimates of Cr-containing cianogen-free galvanic sediments (S. Isakova, I. Isakov)
In the process of neutralization, rendering harmless and sedimentation of waste waters from the industry for metal coatings a solid phase is formed which belongs to the category of toxic wastes. Tens sources wastes in Bulgaria are investigated and their composition analyzed. On the basis of the results obtained an estimate of the quality of these resources is performed. New data on the chemical and phase composition of such wastes are obtained using optical methods, scanning and transmission electron microscopy, X-ray diffraction, differential thermal analysis, IR-absorption spectroscopy, etc. Based on these studies a method is proposed for their highly effective usage. In that way a practical application of the Cr-containing cianogen-free galvanic sediments is proposed for elimination of such toxic wastes, the preservation of which deteriorates the environment and requires expensive technologies.
13. Geometrization of the fundamentals of Chemistry: Spatial mathematical models ofcomplex chemical objects (V. Penev, L. Konstantinov, M. Marinov)
The problem of the geometrization of chemistry, to the best of our knowledge, has been formulated, grounded and partially solved for the first time in [23, 55]. In continuing the solution of this problem a logical analysis of the statics and dynamics of complex chemical objects was performed with the aim to determine the logical structure and the basic definitions of these parts of the chemistry language. Some of the definition were corrected. It was proved that:
1. Each complex chemical object can be mathematically simply represented in the space of the chemical structure, VS(6) = VM(3) x VE(3), by respective simple function which is defined in the ordinary three-dimensional physical space, VE(3), and accepts values in the space of Mendeleev, VM(3).
2. All types of complex chemical objects are represented mathematically in the space VS(6) with the help of discrete and uninvertible simple functions.
3. The complex chemical objects which have a periodical structure can be mathematically represented in the space of structures, VS(6) by the help of periodical functions.
It is proved that each complex chemical process (i.e. each chemical reaction) can be simply mathematically represented in the seven dimensional coordinated space, VP(7)=VM(3) x [VE(3) x VT(1)] by an appropriate function which is defined in the four-dimensional physical space-time, [VE(3) x VT(1)], and accepts values in the space of Mendeleev, VM(3).
It is shown that the determination and classification of the structures of the different types of complex chemical objects in principle is determination and classification of corresponding discrete and uninvertible simple functions in the space of the structures, VS(6), (i.e. of those figures in VS(6) which have a chemical sense).
14. Modal analysis of granodiorite by powder XRD (the Rietveld method) (O. Petrov)
Amphibole-biotite granodiorite from Vurshilski pluton, Bulgaria was studied by powder XRD. The sample was kindly supplied by Dr. B. Kamenov (Sofia University) together with data from its characterization by the standard petrological methods. The mineral mode of this sample was determined by a quantitative modification of the Rietveld method from CuKa X-ray powder diffraction step-scan data. The refinements reached acceptable discrepancy values: Rp=18.9%, Rwp=23.6%, but further improvement is expected after a more careful elimination of the texture of the sample before the diffraction experiment and addition of the less abundant secondary and accessory minerals. The mineral quantities obtained by XRD correlate with those of the petrological methods as follows: for plagioclase - 47.6 % by XRD/43.1 % by standard petrological approach; quartz - 22.1/23.7; K-feldspar - 19.4/19.3; biotite - 5.2/7.6.
The acceptable accuracy of the XRD method is due to the incorporation of the full diffraction profile in Rietveld analysis calculations and the elimination of preferred orientation. The advantage of this approach over the traditional "reference intensity" XRD methods is that the crystal chemistry of the individual phases can be adjusted during each individual analysis. This provides both accurate phase abundances and important information on the major minerals. Further studies on other rock types are to be performed and the results discussed from methodological and petrological viewpoint.
15. Thermal stability of natural and ion-exchanged heulandite-clinoptilolite (O. Petrov, V. Valentinov)
Profile fitting analysis of 020 powder diffraction line of heulandite-clinoptilolite (Heu-Cli) group zeolites in sedimentary tuffs subjected to thermal treatment helps to distinguish a more complex thermal response of the structure of these minerals [24].
To obtain a clear picture of what happened during the whole temperature range (250 to 750o C) of heat treatments the fitted profiles of each sample were combined in plots with preserved 2-theta (position) - I (intensity) scales.
The analysis of the profile fitted values of FWHM (full-width at half-maximum), I (peak intensity), and d (inter-planar spacing) of the 020 peak was performed separately assuming some criteria: the broadening of the peak with temperature is attributed to the presence of more than one Heu-Cli phases which contract (due to dehydration) differently. The more contracted phase(s) is a reason for this broadening. In some cases the profile attained a specific shape, even reaching a distinct splitting which allowed several peaks with close d-spacings to be resolved; in our experiments we obtained a wide range of d-spacings - from 9.90A to 8.23A and for them we assumed that at temperatures higher than 400o C, the values in the range 9.90-9.80A characterize a typical Cli, 9.80-9.60A values are of a contracted Cli I (I-intermediate phase in analogy with Heu behavior), and the registered d-spacings of 8.23A (sample heated at 750oC) and 8.465A we relate to the formation of CliB (contracted ); the intensity behavior of the samples with temperature is very complicated - a gradual intensity loss for all samples was registered, markedly expressed at temperatures below 400o C which proves the presence of Heu (and Ca-Heu) in addition to Cli and Ca-Cli which are common for the Beli Plast deposit. The intensity lowering in the temperature range 400-600o C is related to the destruction of less thermally stable Ca-Cli. The preserved crystallinity above 600o C is of a typical clinoptilolite (Cli).
Further, thermal stability tests on ion-exchanged samples were performed. Ba-, K-, and Cs-exchanged samples have increased thermal stability. Ba and K ions occupy the positions centering the eight-membered rings of C-channels of the zeolite framework and this prevents from structural collapse, while the big monovalent Cs cations entirely fill the channels and also play the same role. The last is of environmental importance as Cli is a potential radionuclide sorbent. Sr- and Pb-exchanged Heu-Cli are with lowered thermal stability. The crystal chemical elucidation of this fact is currently in progress.
16. Chemical and structural transformations of tungsten minerals under low-temperature (exogenic) conditions: experiment, analysis and modeling (M. Tarassov, N. Khaltakova, V. Dimov, M. Marinov, B. Mihailova, O. Petrov)
Two ways of formation of WO3.nH2O phases by sol-gel process and by acid decomposition of CaWO4, are experimentally studied and compared. Two types of sulfuric acid solutions without (1) and with (2) Fe2(SO4)3 were used. The compound Na2WO4.2H2O of analytical grade is used in the sol-gel experiments.
1) WO3.nH2O phases in the systems without Fe2(SO4)
The results obtained for the temperature range 25-120o C and pH from 0.5 to 3.0 are summarized in the Table. The consequent rows of the phases obtained by the sol-gel process, as shown in the Table, demonstrate alternation of the forming phases with increasing pH of the solutions. Under the same conditions the scheelite is pseudomorphously replaced by the following equilibrium phases: WO3.2H2O (<50oC), WO3.H2O (50-120oC), WO3.1/3H2O-rh (>120oC).
Table: Conditions and phase formation reactions.
2) WO3.nH2O phases in the systems with Fe2(SO4)3.
The presence of Fe2(SO4)3 in the sol-gel process provokes the following changes illustrated for a temperature of 70o C, solutions with Fe/W = 0.11.0 and pH = 0.55.0:
The crystalline phases WO3.H2O and WO3.1/3H2O-h are formed only when pH is below 1.0. The other products are X-ray amorphous.
The crystalline phases are disperse and contain Fe (Fe/W up to 0.15). The iron content in the X-ray amorphous products increases with the pH of the solution. At the same time, the materials obtained become more disordered. These data indicate an insignificant possibility the crystalline phase (W,Fe)(O,OH)3 with pyrochlore type of structure to form through direct crystallization from solution.
The presence of Fe2(SO4)3 in sulfuric acid solution attacks scheelite at 70o C leading to the following change:
The products of the acid alteration of scheelite are polyphase and include crystalline WO3.H2O and WO3.1/3H2O-rh which pseudomorphously replace scheelite, so the X-ray amorphous materials are analogues to those formed by the sol-gel process.
The presence of Fe3+ in the solutions leads to the conversion CaWO4WO3.1/3H2O-rh at lower temperatures..
3) Mechanisms of the transformation CaWO4®WO3.nH2O
The problem is studied using TEM and employing the approaches of modular crystallography. It is found that the alteration of scheelite to WO3.nH2O is a process controlled by the structural features, being more intense parallel to the {101} planes of CaWO4. The following orientation relationships between CaWO4 and WO3.nH2O phases are established:
for the conversion CaWO4®WO3H2O:
|
||||
|
for the conversion CaWO4®WO3.1/3H2O-rh:
|
Analysis of the obtained data and structural modeling show that the transition CaWO4®WO3.H2O is controlled by a dissolution-reprecipitation mechanism (orientated crystallization), while the transition CaWO4®WO3.1/3H2O-rh occurs as a topotactical process [61, 62]. The later mechanism is in a good agreement with the decreasing of temperature of the transition CaWO4®WO3.1/3H2O-rh when Fe3+ ions are present in the solutions.
17. Mathematical modelingof the structure of polycationic pillars in modified montmorillonite (V. Dimov, N. Khaltakova, A. Ilieva)
A data base is created for the atomic positions of different types of polymeric Cr-oxide-hydroxide cations modifications.
Electron diffraction patterns of natural montmorillonites from Dimitrovgrad, Bulgaria and Elchovi potok, Slovakia and their pillared with Cr-oxide-hydroxide cations modifications were obtained by TEM.
Hypothetical atomic models for the Cr-pillars and for the montmorillonite pillared by this structural units were created. On this basis electron diffraction patterns of Cr-pillared montmorillonite were simulated. A good accordance between the experimental and simulated electron diffraction patterns for the studied montmorilonites was observed which proved the validity of the chosen model in respect to the real atomic structure.
The used approach is useful in studying modified atomic structures.
18. Experimental modeling of the replacement: WO4 .nH2O®(W,Fe)(O,OH)3 (M. Tarassov)
Experimental modeling of the formation of the (W,Fe)(O,OH)3 phase which is characterized by pyrochlore type structure showed that:
1. Direct formation of (W,Fe)(O,OH)3 from the solution seems not possible, because X-ray amorphous materials are always formed.
2. This pyrochlore phase was obtained as a product of the replacement of WO3.H2O when treating the latter with W- and Fe3+-containing solutions with pH in the range of 3.5 - 6.0.
19. Hydrothermal synthesis of Fe-sulfides under strict P, T, pH, pO and pS conditions (G. Kirov, G. Kamenov)
A series of 36 experiments was performed aiming at hydrothermal synthesis of Fe-sulfides under controlled conditions. In order to avoid the reaction between the hydrothermal solutions and the autoclave walls a method for nonhermetical closing of the glass ampoule was designed. The experiments were conducted in the temperature range 240o-360oC at a vertical temperature gradient from 4o to 51oC and continued from 3 hours to 7 days.
The three most naturally abundant types of iron sulfides (pyrite, marcasite and pyrrhotite) were successfully synthesized in the more of 90% of the hydrothermal experiments. By varying temperature and the oxidation-reduction potential, a selective crystallization of pyrite, marcasite and pyrrhotite was achieved The maximum size of the synthesized crystals reached 1 mm. Optical microscopy and powder diffraction analysis were applied to control the obtained sulfide phases.
20. Effect of clinoptilolite for extraction of P2O5 during the tribochemical processing of phosphorite (A. Toneva, N. Petrova, S. Bakardjieva)
The processing of natural phosphates by the classical acid method to obtain phosphate fertilizers and salts create ecological problems. A nontraditional approach to solve these problems is the tribochemical treatment of phosphorite, leading to a structural collapse and to a state of P2O5 which is more readily absorbed by plants. The yield of P2O5 in such a form is enhanced by the addition of clinoptilolite to phosphorite and a subsequent tribochemical treatment. The ratio of clinoptilolite to phosphorite is an important factor for the tribochemical reaction which completed when the tribochemical mixing (TM) and activation (TA) are appropriately controlled. The structural changes were checked during the TM and TA of the ratio of the phase composition clinoptilolite/phosphorite (80:20; 70:30; 50:50 and 20:80) by powder X-ray diffraction analysis.
Almost complete transformation (about 95%) of P2O5 into a useful state is obtained for the composition 80 wt% clinoptilolite + 20 wt% phosphorite in the case of TM, while for TA this value is lower, namely 88%.
Each tribochemical reaction proceeds specifically depending on the applied tribochemical treatment. Further systematic studies by IR spectroscopy, chemical analysis and powder XRD are needed in order to explain the observed effects and interactions and to evaluate the obtained products from an ecological point of view [32].
21. Zeolite based sorbent for water softening (Bulg. Patent #99381/1997) (L. Filizova, B. Vassileva, S. Shopov)
The sorbent is a natural or synthetic zeolite with appropriate grain size of the material containing sodium, ammonium or hydrogen cations and loaded with OH- and/or HPO42- anionic groups which makes possible the fixation of calcium and magnesium cations. The sorbent is with a strongly developed surface and the modification procedures do not change its sorption, ion-exchange, catalytic and surface properties, rather enhance favourably the interaction with the other components and the environment. Passing of water with hardness 5Ho (2 meq/l) through the designed equipment results in both ion-exchange reactions which diminish the content of calcium and magnesium cations in the water and in in situ fixation of the hydrogen-carbonate ion in the form of CaCO3 upon the surface of the sorbent grains. Thus, a production of softened hot water for households is ensured.
IV. MICROPOROUS MINERALS AND ANALOGUES
22. Synthesis of microporous titanium silicate material (V. Valchev, S. Mintova)
A microporous titanium silicate, ETS-4, is synthesized from gels containing Na, K, Na-K, Na-Li and Na-Ca. It is shown that the partial replacement of Na by K changes the crystallization kinetic behaviour, the morphology of the crystals grown being dependent on the type of cations. A new phase of ion-exchanging titanium silicate was synthesized from a gel of composition 9K2O : TiO2 : 10SiO2 : 675 H2O. This phase is characterized crystallographically and the unit cell parameters are determined as well as the powder X-ray diffraction patterns identified. The new phase is investigated by IR absorption spectroscopy and differential thermal analysis and it is shown that the water in this material is strongly bound in two forms differing in their geometry and strength of bounding.
23. Calorimetric study of ion exchange in zeolites (N. Petrova)
Heats of ion exchange of Ba clinoptilolite are determined at 30 and 95o C. The exothermal effects accompanying the ion exchange reactions become weaker in the same order as the ion selectivity of clinoptilolite in solution:
Cs > Rb > K > Na > Ba > Sr > Ca, namely the reaction Ba-clinoptilolite - 1M KNO3 is more exothermal than Na clinoptilolite - 1M NaNO3.The presence of strongly hydrating Mg cation in the solution affects the heat effects of the reaction Ba-clinoptilolite - 1M MgSO4.7H2O [57].
V.
SYNTHESIS, COMPOSITION STRUCTURE AND PROPERTIES
OF NEW CRYSTALLINE MATERIALS:
24. Adducts of urea derivatives as potential nonlinear optical materials - design, synthesis and structure (O. Angelova, V. Velikova, R. Petrova, K. Kossev, S. Bakardjieva and T. Todorov)
The theoretical design as well as the chemical and structural characterization of new materials with potential for non-linear optical applications is the main subject of this study. Recently, using wet and tribochemical methods efforts have been made to synthesize assymetrical derivatives of urea with functioned aryl or pyridyl substituents with different inductive and p- donating properties, to prepare their adducts with inorganic salts, which contain highly polarizible ions. As a result, 2-pyridylurea (I), 2-pyridyliumurea perrhenate (II) and perchlorate (III) were synthesized and their crystal structures determined [36, 37, 38, 39].
 |
The phase I crystallizes as a layered structure. Each layer consists
of parallel zigzag ribbons of H-bonded molecules extended along the ab-diagonal.
The structure of the phase II consists of columns of centrosymmetric
cation dimmers and H-bonded anions. The differing kinds of hydrogen bonding
between the same cation dimmers and the ClO4- anions
in the phase III results in layers parallel to the 
direction. Plane-to-plane coupling of the organic molecules (ions) takes
place only in the I and II phases. Both the adjacent carbonyl
group and the pyridine ring in the phase I as well as the two antiparallel
carbonyl groups in the phase II are distanced at 3.31(6)A and 3.17(1)A,
respectively.
Summarized crystal data for the three phases studied:
I) C6H7N3 O, C2/c, a=13.339(4)A,
b=5.480(2)A, c=18.208(5)A,
b=93.73(2)o; R=0.039, wR=0.053;
II) C6H8N3 O+.ReO4-,
P
, a=5.215(1)A,
b=9.167(3)A, c=10.597(4)A,
a=74,61(3)o, b=84.65(2)o,
g=86.42(5)o;
R=0.045, wR=0.081;
III) C6H8N3 O+.ClO4-,
P21/n, a=5.946(2)A, b=16.441(4)A, c=9.582(2)A,
b=100.14(2)o, R=0.036, wR=0.073.
25. Structural and phase characterization of new crystalline materials (J. Macicek, O. Angelova, R. Petrova, T. Todorov, S. Bakardjieva, V. Velikova)
The search of new classes of organic compounds with large non-linear optical coefficients and photochemical resistance against laser light was directed towards obtaining compounds with high dipole moments, asymmetric conjugated p-electron systems and such assuring growth of non-centrosymmetric crystals. As a part of this investigation the crystal structure of L-Argininium Hydrogen Squarate and (R)-(-)-1-Phenylglycinium Hydrogen Squarate Monohydrate were determined.
The following systems were examined :
M(ReO4)2 - Thiourea - H2O, M = Cd, Pb
CoSO4 - glycine(gly) - H2O
CoX2 - gly - H2O, X = Cl, Br, I
NiX2 - gly - H2O, X = Cl, Br, I
MnX2 - gly - H2O, X = Cl, Br, I
ZnX2 - gly - H2O, X = Cl, Br, I
ZnNO3 - gly - H2O
In the system Cd(ReO4)2 - Thiourea - H2O, a new adduct with composition [Cd(CH4N2S)6](ReO 4)2.H2O was identified and its crystal structure was determined [25]. The new compound ZnNO3.gly.2H2O, crystallizing in the non-centrosymmetric space group P212121 was obtained in the ZnNO3 - gly - H2O system. The publication of this crystal structure of this phase is now in progress. The double salts Me+Br.Me2+Br2.6H2O (Me=K, NH4, Rb, Me2+=Co, Ni) [30] has a distorted perovskite type structure by analogy with the monoclinic magnesium carnallites.
26. New solvents in the BaO-B2O3 system for growth of NdAl3(BO3)4 (NAB) and YAl3(BO3)4 (YAB) single crystals (D. Shumov, A. Nenov)
The concentration region of NdAl3(BO3)4 in the phase diagram NdBO3 -AlBO3 -BaO.3B2O3 is between 1:19 to 1:1 mole ratios of NdBO3:AlBO3. The viscosity of the solutions is too high at temperatures < 1000o C. The most appropriate mole ratios of NdBO3:AlBO3 for growth of NAB single crystals are from 1:1.2 to 1:1.5, where the concentration of the solute is > 50%, and the temperature is in the range of 1050-1100o C. The temperature and concentration regions of YAl3(BO3)4 in the system YBO3 -AlBO3 -BaO.2B2O3 were determined for the first time. Good quality YAB single crystals may be grown in this system, independently of the relatively narrow concentration regions between mole ratios YBO3:AlBO3 from 1:7 to 1:9. YAl3(BO3)4 doping with Nd leads to broadening of the concentration region and to growth of good quality laser crystals NdxY(1-x)Al3(BO 3)4.
27. Raman Spectroscopic Study of Pb5MoO8 (B. Mihailova, D. Nihtianova, L. Konstantinov)
Pb5MoO8 material is synthesized and the phase diagram of its formation studied. This material is investigated by transmission electron microscopy, single X-ray diffraction and Raman spectroscopy.
Nonpollarized Raman spectra of Pb5MoO8 were measured at room temperature in the range 20-1100 cm-1 and discussed in terms of two structural models, one based on electron diffraction data and the other on single X-ray diffraction data, which differ in the proposed positions of the Mo atoms. The validity of the two models was tested by comparing the experimental Raman spectrum of Pb5MoO8 with the calculated spectra for clusters typical of the two models. It is shown that the experimental Raman spectrum is fitted very well by Raman-active modes of the structural units based on X-ray diffraction data, pointing to the correctness of the single X-ray diffraction model. According to this model, the structure of Pb5MoO8 can be considered to be built of Pb-O strips along the a-axis, Pb-O chains along the c-axis and two types of pairs of MoO4 tetrahedra embodied in the Pb-O network.
28. Investigationsin the PbS-Sb2S3-PbCl2 system (V. Kostov-Kytin)
Phase investigations in the system PbS - Sb2S3 - PbCl2 were conducted in the temperature range 450o- 600oC using evacuated glass capsule technique. The end members of the system were used as starting materials in over 30 syntheses in the most interesting, from a mineralogical point of view, portion of the ternary diagram (40-80 mol% PbS; 20-60 mol% Sb2S3; 2-25 mol% PbCl2).
The runs revealed mainly tiny acicular crystals or their aggregates producted by gas - transport reactions. The samples were studied by optical, microprobe, X-ray powder diffraction and single crystal structural methods. The experimental data were used to build a phase diagram of the crystallization. In addition, the results show that a complete solid solution form between 56 and 60 mol% PbS at 10 mol% PbCl2 and between 48 and 52 mol% PbS at 20 mol% PbCl2. In the temperature interval 450o - 600o C and within the mentioned compositional range dark-gray single phase needle-shaped crystals of Pb4Sb4S9Cl2 [51], long up to 5 mm and 0.1-0.5 mm thick grow at the cool end of the ampules.
The products of the experiments beyond the described compositional range are represented mostly by tiny acicular aggregates and show an increased amount of recrystalized starting materials. However, the microprobe analysis and the X-ray powder diffraction patterns of the final products indicate predominance of two or more Pb-Sb chlorine-sulfosalt phases with 3 - 5 wt % Cl content. The structural characteristics reveal their close relation to minerals and synthetic phases known to have, or being expected to contain chlorine in their compositions, e.g., robinsonite - 6PbS:5Sb2S3; launeite - 9PbS:5Sb2S3; synthetic phases: Pb4Sb4S9Cl2 ; Pb11Sb10S24Cl 4; Pb2Sb2S5.
29. Structure of sodium tetra-silicate glass (N. Zotov, N. Zidarov, M. Marinov, M. Tarassov, E. Dinolova, J. Muhovski)
Knowledge on the structure of silicate melts is of primary importance for understanding magmatic and volcanic processes. X-ray diffraction and Raman spectroscopy studies of silicate melts at magmatic temperatures are very scarce and still represent significant experimental challenge. On the other hand, it is generally assumed that structural data for glasses quenched from high temperatures can be applied to the melt structure at the glass transition temperature.
In the framework of this project the structure of the sodium tetra-silicate glass (NS4) is studied by Neutron diffraction from room temperature up to the glass-liquid transition at about 773K . The NS4 was used as a simple model for complicated geologically relevant glasses and melts. In order to obtain a three dimensional model of the NS4 structure at room temperature the Reverse Monte Carlo method was applied using high resolution neutron diffraction data [42, 43, 44, 78,]. It is found that below the glass transition temperature 773K the increase of temperature leads to gradual decrease of the intensity of the peaks at slightly broadens the Si-O and O-O peaks in the corresponding pair correlation functions. Above the glass transition temperature the static structure factors remain practically constant up to the onset of crystallization. The observed structural changes can be attributed to temperature-enhanced dynamic distortions of SiO4 tetrahedra and suggest that there is a little change in the short- and medium-range order in the NS4 glasses and melts around the glass-liquid transition.
Experiments were performed in a specially designed high temperature furnace, aiming at investigation of the processes of mass transport in melts of basalt under the action of a gradient electric field.
30. Synthesis and structural characterization of Pd-containing catalysts deposited on substrates of volcanic glasses from Lipari islands (Italy) and from Eastern Rhodopes (Bulgaria) (N. Zotov, O. Petrov, V. Valchev)
The chemical composition of volcanic glasses from Lipari islands (Italy) and Eastern Rhodopes (Bulgaria) is determined by X-ray-fluorescence and electron-microprobe studies. Carried out are also thermodynamic analysis of the glass samples and their IR absorption spectra are analyzed to obtain the content of water as well as the concentration and the chemical bond strengths of the OH groups. The averaged atomic structure of the glasses under study is found out by X-ray wide angle scattering. The specific surface area and the porosity of the glasses is measured by X-ray scattering at small angles [48].
31.Phase and structural relationships in the pseudobinary systems M(ReO4)2 - H2O, M = Ca, Sr, Ba, Pb, Cd (T.Todorov) [31]
Rhenium and rhenium compounds possess interesting properties for technological applications in space engineering as acid and heat resistant alloys, as metal passivation layers and in catalytic chemistry. The ability of rhenium to form in its compounds multiple Re-Re bonds results in interesting magnetic properties.
Pure perrhenates of metals, M, with large ionic radii can be obtained from water solution as hydrates M(ReO4)2.xH2O. So far, only the monoclinic crystal structure of Ca(ReO4)2.2H2O has been investigated. However, the content of crystal water in these hydrates was an object of controversy.
Thermochemical, X-ray phase and single crystal structure analyses indicate the exact water composition of all known hydrates from the studied systems. A new, unknown so far, Ba(ReO4)2.H2O crystal hydrate was proved to exist.
The structures of all hydrates investigated are constituted by oxygen polyhedra of the metal atoms M and ReO4 tetrahedra. MOx polyhedra are either isolated or coupled by common faces or edges. Contrary to the M - polyhedra the ReO4 tetrahedra are isolated. During the interpretation of the structures the "Bond Valence Method" was used in order to determine how the valence of a given atom is distributed between the bonds formed. All water molecules are coordinated with M atoms, except the interstitial water molecules in the structure of Ba(ReO4)2.4H2O. All H atoms participate in the formation of normal or bifurcated hydrogen bonds.
32. Platinum-group minerals in alluvial sediments from Blagoevgrad graben (Z. Tsintsov) [33]
The distribution of platinum-group minerals (PGM) is studied using statistic data of 9227 individual grains. These PGM are presented by native platinum, isoferroplatinum, iridium, osmium, ruthenium, rutheniridosmine as well as by sulphides and similar compounds as mertieite II, braggite, sperrylite, laurite and erlichmanite all totaling up to around 91.51 %.
The grains are mainly irregularly shaped and crystals of sperrylite, Pt-Fe alloy, ruthenium, cooperite and laurite are rarely observed (concentrated over 96.24 % in fractions below 200 mm ). Other PGM as cooperite, bowieite, kashinite, cuprorhodsite, irarsite and hollingworthite are observed as inclusions in the individual grains. Their heterogeneity shows that they are formed both from dissociation of solid solutions and from the capture of inclusions by the host mineral.
It is established that the exotermal effect on speryllite (400 - 550o C) occurs in result of the mineral dearsenization, accompanied by phase transformation at which pure Pt is generated.
On the basis of the data obtained, the ultramafic bodies from the surrounding massifs of the Blagoevgrad graben are considered as possible prime sources of the minerals observed.
33. Regional dividing and mineralogical prognoses based on heavy mineral concentrates, west of Struma river, Kjustendil region (O. Vitov) [40]
The thesis describes a new method for processing data and drawing mineralogical prognosis maps and mineralogical sectioning. The method is applied to archival data (1946-1974) on mineralogical sampling in the investigated region. The results obtained are compared with the contemporary viewpoint for the geological structure, geophysical and geochemical formations and information on the mineral resources.
The method differs from those still existing in predefining the main terms in the schlich approach, in the statistical data processing and in the probability data modeling. Using this method of areal presentation of the results from the investigation of the heavy mineral concentrates it is found that all peculiarities in the geophysical and geochemical fields in the region can be presented uniquely in the new proposed mineralogical maps. Our mineralogical prognoses and sectioning confirm the Rouen ore field in the Ossogovo mountain and facts are pointed for: its northwestwards continuation from the Polegan fault; anticipated gold-bearing polymetal mineralization and its transition into W-Mo one in depth; as well as Bi-specialization in the Osogovo mountain.
The method confirms that the Karamanishko ore field in Serbia continues in Bulgaria in two blocks: a relatively upthrow (Lomnishki) with perspectives of gold, W-Mo and polymetal industrial potentials and another one downthrow (Trekleno) with perspectives for gold, Hg and polymetal and phosphorous ores.
A new ore field in the region of the Vlachina mountain with marked zonality is pointed out, namely with a periphery containing Au, Hg, a core containing Au and polymetal ores and a central part containing Au and W-Mo reach ores.
INTERINSTITUTES PROGRAMS:
POSTDOCTORAL FELLOWS AND POSTGRADUATED STUDENTS:
1. Dekov, V. and Z. Damyanov. 1997. Native silver-copper alloy in metalliferous sediments from the East Pacific Rise axial zone (20o30'-22o10'). – Oceanologica Acta, 20, 501-512.
2. Donchev, I., K. Mitov. 1997. Mineralogy of clinker waste and opportunities for its useful components extraction. – Geol. and miner. res., 2-3; 26-29.
3. Gasharova, B., B. Mihailova and L. Konstantinov. 1997. Raman spectra of various types of tourmalines. – European Journal of Mineralogy, 9, 935-940.
4. Georgiev, G. and L. Konstantinov. 1997. Spectral characterization of non-collinear acousto-optic tunable filters. – Optics & Laser Technology, 29, 267-270.
5. Grigorova, M., V. Masheva, D. Nihtianova, V. Rusanov, L. Bozukov, V. Gerganov and M. Mikhov. 1997. Hysteresis loops and remanence curves of small -Fe2O3 particles with different packing densities. – In: Magnetic Hysteresis in Novel Magnetic Materials, Ed. G.H. Hadjipanayis, Kluwer Academic Publishers, Dordrecht / Boston / London, The Nederlands, NATO ASI Series, Series E: Applied Sciences , 338, 357-361.
6. Kostov-Kytin, V., R. Petrova, J. Macicek. 1997. Crystal structure of synthetic Pb4.32Sb3.68S8.68Cl 2.32. A chlorine-bearing alternative to Pb4Sb4S11. - Eur. J. Mineral., 9, 1191-1197.
7. Lilkov, V., E. Dimitrova, O. Petrov. 1997. Hydratation process of cement containing fly ash and silica fume: the first 24 hours. – Cem. Concr. Res., 27, 577-588.
8. Marinov, M. and N. Zotov. 1997. Model investigation of the Raman spectra of amorphous silicon. – Phys. Rev. B 55, 2938-2944.
9. Marinova, I. and O. Vitov. 1997. Geochemical evidence for the existence of collisional boundary in the Bosnek-Gorna Dikanya-Dren area, Western Srednogorie (Western Bulgaria). – Compt. rend. Acad. bulg. Sci., 50, 2, 59-62.
10. Mihailova, B., L. Konstantinov, D. Petrova and M. Gospodinov. 1997. Effect of doping on Raman spectra of Bi12SiO20. – Solid State Communications, 102, 441-444.
11. Mihailova, B., S. Stoyanov, V. Gaydarov, M. Gospodinov and L. Konstantinov. 1997. Raman spectroscopy study of pyrochlore Pb2Sc0.5Ta1.5O 6.5 crystals. – Solid State Communications , 103, 623-627.
12. Mihailova, B., V. Valtchev, S. Mintova and L. Konstantinov. 1997. Characterization of water in microporous titanium silicates. – Journal of Materials Science Letters ,16, 1303-1304.
13. Mihailova B. and L. Konstantinov. 1997. Dependence of vibrational spectra of rings of SiO4 tetrahedra on their structural parameters. – Solid State Communications, 101, 163-166.
14. Mihailova B. and L. Konstantinov. 1997. Vibrational spectra of rings in continuous Si-O networks. – Physics and Chemistry of Glasses, 38, 27-32.
15. Mintova, S., B. Schoeman, V. Valtchev, J. Sterte, Shangyi Mo and T. Bein. 1997. Growth of silicalite films on pre-assembled layers of nanoscale seed crystals on piezoelectric chemical sensors. – Advanced Materials ,9, 585-586.
16. Mintova, S., J. Hedlund, V. Valtchev, B. Schoeman, J. Sterte. 1997. Preparation of ZSM-5 films from template free precursors. – J. Matererials Chemistry, 7(12), 2341-2344.
17. Mintova, S., V. Valtchev, S. Angelova and L. Konstantinov. 1997. Kinetic investigation of the effect of Na, K, Li and Ca on the crystallization of titanium silicate ETS-4. – Zeolites ,18 , 269-273.
18. Mintova, S., V. Valtchev, V. Engstrom, B. Schoeman, J. Sterte. 1997. Growth of silicalite-1 films on gold substrates. – Microporous Materials, 11, 149-154.
19. Nenova, P. 1997. "Fe23": A computer program for calculating the number of Fe2+ and Fe3+ ions in minerals. – Computers & Geoscience, 23, 215-219.
20. Nihtianova, D., D. Shumov, S. Angelova, Ya. Dimitriev and L. Petrov. 1997. Investigation of Pb5MoO8 crystal growth in the PbO-MoO3 system. – Journal of Crystal Growth, 179, 161-167.
21. Nihtianova, D., I. Ivanov, J. Macicek, I. Georgieva. 1997. Crystallographic data for BaMnSiO4 - A new phase in the system BaO-MnO-SiO2. – Powder Diffraction, 12, 167-170.
22. Nihtianova, D., V. Ivanov and V. Yamakov. 1997. Structure investigation of Pb5MoO8 single crystals by selected area electron diffraction. – Zeitschrift f?r Kristallographie, 212, 191-196.
24. Petrov, O., V. Valentinov. 1997. Heulandite - clinoptilolite in zeoloite rocks: a profile-fitting analysis of 020 powder difraction peak. – Natural Zeolites. Proc. of Sofia Zeolite Meeting' 95, eds. G. N. Kirov, L. Filizova, O. E. Petrov, Pensoft, Sofia, 126-132.
25. Petrova, R., O. Angelova, J. Macicek. 1997. Molecular adducts of inorganic salts. VII. Cadmium tetraoxorhenium hexakis(thiourea) hydrate. – Acta Cryst., C53, 565-568.
26. Petrova N. 1997. Enthalpy of formation of chabazite heulandite and clinoptilolite. – Compt. rend. Acad. bulg. Sci., 50, 4, 69-72.
27. Radev D., V. Blaskov, D. Klissurski, I. Mitov and A. Toneva. 1997. Effect of the mechanical activation of the reagents on the solid phase synthesis of iron (III) molybdate. – Journal of Alloys and Compounds, 256, 108-111.
28. Shumov, D., V.S. Nikolov, D. Nihtianova, J. Macicek, J. Georgieva and A. Nenov. 1997. High-temperature solutions suitable for the growth of NdAl3(BO3)4 crystals. – Journal of Crystal Growth, 172, 478-485.
29. Sterte, J., S. Mintova, G. Zhang and B.J. Schoeman. 1997. Thin molecular sieve films on noble metal substrates. – Zeolites,18, 387-390.
30. Tepavitcharova, St., J. Macicek, Chr. Balarew, Chr. Tzvetkova, O. Angelova. 1997. The double salts Me+Br.Me2+Br2.6H 2O) (Me+ = K, NH4; Me2+ = Co, Ni). – J. Solid State Chem., 129, 200-205.
31. Todorov, T. 1997. Phase and structuralrelationshipsinthepseudobinarysystemsM(ReO4)2-H2O,M=Ca,Sr,Ba,Pb,Cd(Ph.D. thesis)
32. Toneva, A., N. Petrova and S.Bakardjieva. 1997. Tribochemical reactions between natural phosphates and zeolites. – Proc. Contact, 97, 45-56.
33. Tsintsov, Z. 1997. Platinum-group minerals inalluvialsedimentsfromBlagoevgradgraben(Ph.D. thesis)
34. Vassilev, S. and C. Vassileva. 1997. Geochemistry of coals, coal ashes and combustion wastes from coal-fired power stations. – Fuel Processing Technology, 51, 19-45.
35. Vassilev, S., K. Kitano and C. Vassileva. 1997. Relations between ash yield and chemical and mineral composition of coals. – Fuel, 76, 3-8.
36. Velikova, V., K. Kossev, O. Angelova. 1997. Molecular complex of 2-amino-5-nitro-pyridine and 3-nitro-2-pyridone. – Acta Cryst., C53, 1270-1273.
37. Velikova, V., O. Angelova, K. Kossev. 1997. N-(2-Pyridyl)urea. – Acta Cryst., C53, 1273-1275.
38. Velikova, V., O. Angelova, R. Petrova, K. Kossev. 1997. N-(2-Pyridinium)urea perchlorate. – Acta Cryst., C53, 971-973.
39. Velikova, V., R. Petrova, O. Angelova. 1997 N-(2-Pyridinium)urea perrhenate. – Acta Cryst., C53, 1230-1232.
40. Vitov, O. 1997. Regional dividing and mineralogical prognoses based on heavy mineral concentrates, west of Struma river, Kjustendil region (Ph.D. thesis)
41. Vitov, O. 1997. Mineralogical prognosis for gold ore-mineralization prospecting in the East Rhodopes by heavy mineral concentrates. – Geol. and miner. res., 6-7; 42-46 (In Bulgarian with English summary).
42. Zotov, N., F. Bellido, M. Dominguez, R. Jimenez-Garay, A.C. Hannon, R. Sonntag. 1997. Effect of copper on the structure and other physical properties of Cu-As-Te chalcogenide glasses. – J. Phys. Chem. Solids, 58, 1625-1630.
43. Zotov, N., R. Jimenez-Garay, F. Bellido, M. Dominguez, A.C. Hannon, R. Sonntag. 1997. Structure of Cu-As-Te glasses - neutron diffraction and reverse Monte Carlo simulations. – Physica B, 234-236, 424-425.
44. Zotov, N., Ch. Wagner, F. Bellido, L.M. Rodriguez, R. Jimenez-Garay. 1997. Thermal analysis of Ag-As-Se chalcogenide glases. – Thermochim. Acta, 296 , 23-29.
PUBLICATIONS IN PRESS:
45. Breskovska, V., V. Kostov-Kytin. Native elements: New finds for Bulgaria. – Compt. rend. Acad. bulg. Sci.
46. Damyanov, Z. Ore petrology, whole-rock chemistry and zoning of the Kremikovtsi carbonate-hosted sedimentary-exhalative iron(+Mn)-barite-sulfide deposit, Western Balkan, Bulgaria. – N. Jb. Miner. Abh.
47. Damyanov, Z., V. Dekov, A. Lisitsyn, Y. Bogdanov, G. Aidanliiski and V. Dimov. Mineralogical features of the near sulfide mound sediments: MIR zone, TAG hydrothermal field (Mid-Atlantic Ridge, 26oN). – N. Jb. Miner. Abh.
48. Deganello, G., L. Liotta, A. Longo, A. Martorana, Y.Yanev and N. Zotov. Structure of natural water-containing glasses from Lipari (Italy) and Eastern Rhodopes (Bulgaria):SAXS, WAXS and IR studies. – J.Non-Cryst.Solids.
49. Eskenazy, G., S. Vassilev and E. Karaivanova. Chlorine and bromine in the Pirin coal deposit, Bulgaria. – Rev. Bulg. Geol. Soc.
50. Ilieva, A. Layer charge determination of montmorillonites from Bulgarian bentonite clays. – Compt. rend. Acad. bulg. Sci., 49, 11.
51. Kostov-Kytin, V. Block-building principles in the structure of some lead-antimony chlorine sulphosalts. – Comp.rend.Acad.bulg.Sci.
52. Lilkov, V., O. Petrov. 1997. Hydratation of cement mixed with "Pozzolit" mineral additive. – Proc. 10th Int. Congr. Chem. Cement: Additives, Admixtures, Characterization Techniques; Gotheburg, Sweden, June 2-6.
53. Marinova, I., O. Vitov. 1998. Geochemical prognoses in prospecting for gold based on secondary dispersion aureoles (on the example of Bosnek-Gorna Dikanya-Dren area, Radomir district). – Geol. and miner. res., 1, 16-21.
54. Mintova, S., V. Valtchev, O. Petrov, V. Dimov, N. Khaltakova. Synthesis and Characterization of a new Phase in the System K2O-TiO2-SiO2-H 2O. – Zeolites.
55. Penev, V., L. Konstantinov, M. Marinov. Geometrization of Chemistry: Formulation of the problem. – Compt. rend. Acad. bulg. Sci.
56. Petrov, St., J.Churtchev, R.Mitova, L.Boyanova, M.Tarassov. Xantoma of the stomach - some morphometrical pecularity and scanning electron microscopy. – Hepato-Gastroenterology.
57. Petrova, N., L. Filizova and G. Kirov. 1997. Calorimetric study of ion-exchange of clinoptilolite and mordenite at different temperature. – Proc. Sofia Zeolite Meeting 95.
58. Podolesheva, I., V. Platikanova, I. Konstantinov, V. Dimov, M. Tarassov. Thermally induced processes in thin layers, obtained by coevaporation of TeO2 and Sn. – J. of Vac. Sci. and Tech.
59. Stancheva, M., R. Petrova, J. Macicek. Neodymium diselenite selenious acid dihydrate - structure and conformation of the Se2O5 group. – Acta Cryst.
60. Stanimirova, Tz. and N. Petrova. 1998. DTA and TG study of minerals from the hydrotalcite-takovite isomorphic series. Influence of Mg-Ni substitution. – Compt. rend. Acad. bulg. Sci., 51, 6.
61. Tarassov, M., V. Dimov, N. Khaltakova. Acid Alteration of Scheelite: I. TEM Study of the Conversion of Scheelite to WO3.1/3 H2O. – Compt. rend. Acad. bulg. Sci.
62. Tarassov, M., N.Khaltakova, V.Dimov. Acid Alteration of Scheelite: II. Using a Fundamental Building Blocks Approach to Conversion of Scheelite to WO3.1/3 H2O. – Compt. rend. Acad. bulg. Sci.
63. Todorov, T., R. Petrova, K. Kossev, J. Macicek, O. Angelova. Hexakis(urea)magnesium chlorate. – Acta Cryst.
64. Todorov, T., R. Petrova, K. Kossev, J. Macicek, O. Angelova. Magnesium sulfate urea hydrate. – Acta Cryst.
65. Tsintsov, Z. Sulphides of platinum-group elements in alluvial sediments of Blagoevgrad graben. – Compt. rend. Acad. bulg. Sci., 51, 6.
66. Valtcheva, E., A. Ilieva, L. Filizova. Interlayer pillaring of montmorillonites from Bulgarian deposits of bentonite clays. – Compt. rend. Acad. bulg. Sci., 51, 4.
67. Vassilev, S. and C. Vassileva. Comparative chemical and mineral characterization of some Bulgarian coals. – Fuel Processing Technology.
68. Vassilev, S., G. Eskenazy and E. Karaivanova. 1997. Chlorine and bromine in Bulgarian coals and their combustion wastes. – Compt. rend. Acad. bulg. Sci., 50, 5.
69. Vitov, O ., I. Marinova. Statistical model of gold distribution in secondary disseminated halos. – Geol. and miner. res.
70. Zotov, N., H. Keppler. The structure of sodium tetrasilicate glass from neutron diffraction, reverse Monte Carlo simulations and Raman spectroscopy. – Phys. Chem. Minerals.
ABSTRACTS AND POSTERS AT SCIENTIFIC EVENTS:
71. Angelova, O. 1997. Structural classification of the inorganic orthophosphates-principles and formulae. – Seventeenth European Crystallographic Meeting, Lisbon - Portugal, 24-28 August.
72. Buchvarov, I., P. Tzankov, V. Stoev, K. Demerdjiev, D. Shumov. 1997. Generation of high-power picosecont pulses by passively mode-locked Nd: YAG laser using frequency doubling mirror. – NATO ASI, Advanced photonic with second order optically nonlinear processes, 22. IX - 4. X 1997, Sozopol, Bulgaria
73. Jossifova, M., J. Georgieva, L. Petrov. 1997. Phase characterization of dry rests from water leachates of coals and their waste from coal treatment. Proceedings 9th International Conference on Coal Science, Essen, Germany, 7-12 September 1997, Eds. A. Ziegler, K. H. van Heek, J. Klein, W. Wanzl, P & W Druck und Verlag GmbH, 1755-1758.
74. Lilkov, V., O. Petrov. 1997. Hydratation of cement mixed with "Pozzolit" mineral additive. Proc. 10th Int. Congr. Chem. Cement: Additives, Admixtures, Characterization Techniques; Gotheburg, Sweden, June 2-6.
75. Mo, S., S. Mintova and T. Bein. 1997. Building of new QCM instrument for measuring of piezoelectric chemical sensors containing zeolites. Annual Report for Motorola.
76. Petrova, R. 1997. Structural classification of simple phosphate minerals. – Seventeenth European Crystallographic Meeting, Lisbon - Portugal, 24-28 August.
77. Podolesheva I., V. Dimov, P. Gushterova, V. Platikanova, I. Konstantinov. 1997. Diffusion Processes in Layers Obtained by Coevaporation of TeO2 and Sn. – Proc. of International School on Condensed Matter Physics, Varna 96, World Scientific Press.
78. Puerto, M., N. Zotov, F. Bellido, P. Villares, R. Jimenez-Garay. 1997. Structure of amorphous Ag0.07As0.40S0.53 by X-ray diffraction and reverse Monte Carlo simulations. – Boletin de la Sociedad Espanol de Ceramica y Vidrio, 36, 306-309.
79. Schoeman, B., J. Hedlund, S. Mintova, V. Valtchev, J. Sterte. 1997. Preparation of thin dense films with emphasis on surface chemistry. – ZMPC'97, Tokyo, Japan, 115-119.
80. Todorov, T., R. Petrova, O. Angelova. 1997. Structural motifs in halogen and hydroxyl-containing phosphate minerals. – Seventeenth European Crystallographic Meeting, Lisbon - Portugal, 24-28 August.
81. Toneva, A., N. Petrova and S. Bakardjieva. 1997. Tribochemical reactions between natural phosphates and zeolites. – Proc. Contact, 97, 31.10.1997, Sofia.
