BULGARIAN ACADEMY OF SCIENCES
ANNUAL
REPORT
CONTENTS
Projects No 4, 7, 10, 11, 14, 15, 16, 17, 18, 19, 22, 23, 24, 25 are financially supported in part by the Bulgarian National Science Fund of the Ministry of Education, Science and Technologies; No 8 - by the Commette of geology and mineral resourses; No 23, in addition, by the International Centre for Diffraction Data (ICDD-JCPDS), USA. INTRODUCTION This annual report presents the research activities of the Central Laboratory of Mineralogy and Crystallography during the second 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:
Among the most important achievements of applied character we would mention:
As a result of the expanded collaboration with foreign universities, joint projects were performed aiming on the one hand at the synthesis of new materials with interesting properties and potentials for practical applications, such as palladium and zeolite catalysts and different sensors, and, on the other hand, at the precise structural characterization of new substances for the International XRD data bases in the field of crystallography and mineralogy. It should be noted that in spite of the serious economic difficulties our research activity is comparable with that during the last year and the international collaboration is even extended. Scientific plan is now turning toward modern problems in the field of crystallography and mineralogy and its succssful realization depends mainly on financial shortages. Nikola Zidarov RESEARCH TOPICS: I. MINERAL SYSTEMS: 1. Magmatic and metamorphic minerals and mineral associations in the Serbo-Macedonian Massif (N. Zidarov, P. Nenova, D. Angelsky). The conditions and the processes of formation and metamorphic transformation of protoliths which build up the Central part of the Serbo-Macedonian Massif (SMM) on Bulgarian territory are in investigation.
2. Mineral forming processes and geogenetic models of the fluorite formation (B. Zidarova, N. Zidarov). The basic features, the development and the morphogenetic types of the fluorite mineralization in the greatest Bulgarian fluorite deposit Chiprovci-east, located in West Balkan Mt., was investigated [44]. It is established that fluorite is embedded in tectonically dismembered and hydrothermally carsted marble layers as well as in green-schists, from the basal parts of the Chiprovci thrust fault. The mineral bodies consist mainly of four varieties of fluorite (Fl), quartz (Q) and calcite (Cal), small amounts of ankerite, ferrodolomite, barite and sporadically occurring galena and pyrite. The structure and the spatial distribution of mineral aggregates put in evidence two main ways of formation of fluorite bodies - either by metasomatic substitution of marbles or by deposition in empty spaces within the collapse-breccia which fills the paleocarstic caverns. It is found that the metasomatic fluorite-bearing bodies are stratiform . They are zoned, usually in five well-separated successive zones: fluorite (rear) zone, in which Fl >80%; carbonate-fluorite zone with two subzones, the first containing Fl³Q>Cal and the second one Q>Fl>Cal; quartz (front) zone with small amounts of Fl and Cal; a zone of large blocked calcite. The mineralization is developed in one Fluorite stage, after deposition of silver-lead ores, but before the cinabre-barite mineralization, by three successive impulses of hydrothermal activity. Five morphogenetic types of fluorite mineralization are specified. Compact, nestiform and sporadic types corresponds to the fluorite, carbonate-fluorite and quartz zones of metasomatic bodies. Breccia-form type is characteristic for the pipe-form bodies filling the paleocarstic caverns. The vein-type is developed in tectonically influenced schists and marbles. Proposals are done on the industrial application of each type. The reconstruction of the temperature regime, the dynamics of the hydrotermal fluorite formation and the local geogenetic model of the deposit is in progress. 3.Sedimentary-hydrothermal ore-forming processes in the Kremikovtsi deposit (Z. Damyanov). Close relations between ore-forming processes and chemical compositions of siderites from more than 25 deposits have been established [49]. A summary on the geology, mineralogy (with chart of mineral variety), mineral resources (commercial and potential) and zoning of the Kremikovtsi deposit has been published [6]. A detailed analisis of genetic hypotheses for this deposit has been made [48,49]. A new sedimentary-exhalative model of primary ore formation has been proposed [5]. The main sources of ore matter (cratonized Paleozoic basement + subcrustal derivatives of basaltic magma) and ore solution (mixed seawater + meteoritic water, heated and mineralized during the process of crustal convection into the Paleozoic basement) have been suggested on the basis of C, O and Pb isotope study [5]. Stable isotope data have shown the dominant role of biogenic C, probably taken up by the ore-bearing fluids during their passage through underlying beds enriched in organic matter, on the siderite ore formation [5]. A reevaluation of the metallogenic potential of Middle Triassic carbonate rocks in Bulgaria and new exploration in the region has been proposed on the basis of the new data for the genesis of the Kremikovtsi deposit [48]. 4. Mineralogical studies of native metals and alloys from the oceanic rift zones (East Pacific Rise, 21° S and Mid-Atlantic Ridge, 26° N - TAG hydrothermal field) (V. Dekov, Z. Damyanov). Mineralogical features of native tin, silver-copper and tin-lead alloys from the East Pacific Rise metalliferous sediments were studied [7, 50]. An endogenous hypothesis of their formation at low ¦O2 and ¦S2 and high P-T conditions during the upper mantle pre-chamber evolution of basic and ultrabasic magmatic systems has been proposed [7, 50]. Mineralogical characteristics of native aluminum, native nickel and tin-copper-lead alloy from the TAG hydrothermal field (MIR zone, Mid-Atlantic Ridge, 26o) are now under investigation. Near sulfide mound sediments from the TAG field have also been studied. Phase identification of different sulfides, silica phases, smectites, iron oxides and hydroxides, atacamite, Mn-oxide crusts and micronodules has been made. Specific features of their morphology, chemical composition and physical characteristics have been established. Metalliferous sediment horizons and hydrothermal precipitates dispersed have been 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 the 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. 5. Hydrothermal-metasomatic formations in the Zvezdel-Pcheloyad ore deposit (Y. Tzvetanova). Zoned skarns from Zvezdel-Pcheloyad ore deposit have been studied in detail. The chemical compositions of garnets, pyroxenes, feldspars, epidotes, wollastonite and sphene were obtained by electron microprobe analysis. Based on the recalculation to formula contents, three varieties of garnets have been established with following average composition:
The chemical investigation shows the presence of pyroxenes from diopside-hedenbergite series in endoskarn zone with structural formulae varying from Ca0.996(Fe2+0.602,Mg 0.238,Ti0.027Fe3+0.120 ,Al0.011)0.998(Si1.814 ,Al0.186)2O6 to Ca1.01(Mg0.666,Fe2+ 0.227,Ti0.011,Fe3+ 0.075,Al0.011)0.99(Si 1.892,Al0.108)2O6 and to subsilicic aluminian ferrian diopsides (fassaites) with component ratios (Di54,Hd5)59S3(Al) 13Es20S4(Mg)8 in the exoskarn zone. The equilibrium constant of Fe in coexisting garnets and pyroxenes in the garnet-pyroxenes zone determines high alkaline conditions during the bimetasomatic process. 6. Chemical
peculiarities, relationships and physic-chemical formation conditions of
lead phosphate minerals from Brussevtzi deposit The chemical features, the relationships and the physic-chemical conditions of formation of lead phosphate minerals (pyromorphite, plumbogummite and corkite) were studied. The minerals were investigated by SEM, XRD, DTA and IR spectroscopy. The obtained data show the presence of two varieties of pyromorphite with structural formulae: 1.(Pb3.68,Ca1.32)(PO4)3Cl1.10; 2.Pb5.05(PO4)3Cl 1.12, with unit cell parameters a=9.886(2) c=7.236(1) and a=9.987 c=7.330, respectively. Plumbogummite has the following composition: Pb1.10(Al2.93,Fe0.01 ,Cu0.003)2.94[(PO4 )1.96(SO4)0.03(SiO 4)0.01](OH)5.05.H2O. DTA date indicate a two-step dehydration of plumbogummite, rewild by a shoulder at 420 °C. The DTA-curve of corkite is characterized by one dehydration step at 530 °C. The Infrared band frequencies (in cm-1) for (PO4)3- of the above mentioned minerals are as follows: According to the phase relation diagram of lead phosphates this minerals are formed at pH>7. 7.
Platinum-group minerals from alluvial placers of Blagoevgrad graben Sulfide minerals of platinum-group elements (PGM) presented by braggite (PtS) and members of laurite (RuS2) - erlichmanite (OsS2) solid-solution series are characterized. Braggite is tetragonal with elementary cell parameters: a = 6.382 Å and c = 6.574 Å. All grains are sized below 200 µm, almost isometric, with dark-grey colour and a dull lustre. They contain Pt (46.59-67.97 wt %), Pd (14.40-29.72 wt %) and Ni (4.29-8.54 wt %). The crystal-chemical formulae of the grains vary from (Pt0.46Pd0.34Ni0.12 )0.92S to (Pt0.62Pd0.22Ni0.13)0.97S. The minerals of the laurite-erlichmanite solid-solution series are cubic, with parameters: a = 5.6124 Å (laurite) and a = 5.615 Å (erlichmanite). Most of them are small in size (below 200 µm) and with an almost isometric habit. Laurite is dark-grey, with very weak yellow reflections, while erlichmanite is dark grey. The element composition of minerals is close to the theoretical one. Other elements in their composition are: Ir (to 33 mol % IrS2 in laurite), Fe (0.07-2.48 wt %) and Ni (0.58-2.73 wt %). Their crystal-chemical formulae are as follows: laurite - (Ru0.58Os0.19Ir0.16 Fe0.04Ni0.03)1.00S 2.00; erlichmanite - (Os0.49Ru0.35Ir0.14 Ni0.02)1.00S2.00. The phase compositions and the characteristics of silicates observed in the matrix of individual PGM grains were published in [33]. The major part of the heavy mineral concentrates present togetherwith PGM in the same sediments is dominated by magnetite, ilmenite, garnet, amphibole, epidote, zircon, apatite and rutile. Pyroxene, biotite, pyrite, chromite and gold are more weakly presented, while the rest minerals (Au-amalgam, titanite, cinnabar, chlorite, spinel, turmaline, anatase and scheelite) are rarely found. 8. A 1:25 000 mineralogical map of the heavy mineral concentrates in Bulgarian stream sediments (O.Vitov). During 1996 the existing mineralogical data base is supplemented by information on 28 000 samples (see the figure).
The data base for each sample contains: the sample number, geographic coordinates, contour of water supply area including the supply region and supply province, the number of the following sample, the mineral composition and the mineral concentrations. Mathematical (stochastic) models are created to estimate whether the sampling is representative and to found the correlation between minerals and mineral associations. The processed data are presented in a map with specification and distribution of areas and prospective mineral resources. The application of the models considered above are published in [43,97]. 9. Regularities in the distribution of minerals and mineral associations in alluvial environment (O.Vitov). To resolve this problem, an algorithm and a program (QBASIC, DOS) are created for quantitative recalculation of the concentration of heavy minerals, obtained after laboratory analysis of minerals from alluvial sands. As a result, the processed data give information on the concentration of heavy minerals in the samples, the quality of the laboratory analysis, the distribution of minerals and mineral groups. A more special attention is brought on the stability of mineral associations according to Momji and Shilo coefficients and through the employment of the emperical stability coefficient proposed by us. The program is supported by a initial data base. Additionally, the program could be usefull for calculating the mineral resource and for data storage and processing in each mineralogical laboratory. II. TECHNOGENIC MINERAL SYSTEMS: 10. Mineralogy and geochemistry of coal and coal products (S. Vassilev). The phase-mineralogical and chemical composition, microstructural and some genetic phase peculiarities of solid waste products from coal burning at 11 Bulgarian thermoelectric power stations (TPS) were characterized. Fly ashes, bottom ashes and lagooned ashes comprise inorganic and organic constituents. The inorganic part consists mainly of non-crystalline (amorphous) components and lesser amounts of crystalline components represented by various major, minor and accessory mineral phases. The organic constituent contains unburnt coal components represented by slightly changed, semicoked and coked coal particles. The origin of solid phases could be: primary - minerals and phases contained in coal and having undergone no phase transition (silicates, oxides, volcanic glass, coal particles); secondary - phases formed during burning (glass, semicoke, coke); or tertiary - minerals and phases formed during the transport and storage of fly ashes and. bottom ashes (sulphates, carbonates and oxyhydroxides) [38]. Some relationships between coal rank (respectively Cdaf) and mineral and chemical composition of coals and their high-temperature ashes from 41 deposits of Bulgaria, Australia, The United States, Japan, Canada, China, Russia, South Africa and Ukraine, were studied. Low-rank coals (Cdaf <75%) are enriched in W, VM, A, H, N, O, and S, and their ashes are abundant in MgO, CaO, and SO3. Coal ashes derived from higher-rank coals demonstrate increased contents of SiO2, Al2O3, Fe2O3, K2O, Na2O, and TiO2. It was found that the occurrence, abundance and origin of mineral matter in coal depends on the coal rank to a certain extent. Higher-rank coals are abundant in ash-forming elements associated with probable detrital minerals, while low-rank coals demonstrate an enrichment in ash-forming elements associated with probable authigenic minerals and organics. Different processes related to some changes in inorganic matter during degree of coalification are discussed. It was found that the metamorphic progression and leaching behaviour of different minerals, phases and elements from low- to high-rank coals caused essential changes in mineral and chemical composition of coals [39]. The effective use of mineral sorbents for purification of K, Na, Ca, Mg, Br, Cl and F in waste waters from 10 thermo-electric power stations (TPS) was studied. Mineral sorbents like mixed-layered clay, montmorillonite and clinoptilolite can be effectivelly used for purification of waste waters from TPS. They can be applied individually, and especially in a combination, depending on the chemical specification of different waste water. It could be supposed a good purifiying effect of clinoptilolite and clay minerals for the waste waters enriched in transitional siderophilic (Ti, V, Cr, Mn) and chalcophilic metals (Cu, Zn, Cd, Pb) which have been determined earlier in the waste waters from Bulgarian TPS [42]. The occurrence, abundance and origin of minerals in coals and coal ashes from 35 deposits worldwide were studied. Major minerals identified in the crystalline matter of coals are commonly quartz, kaolinite, illite, calcite, pyrite, plagioclase, K-feldspar and gypsum, and occasionally dolomite, ankerite, siderite, Fe oxyhydroxides and sulphates. A number of minor and especially accessory minerals are also present. Modes of occurrence and some genetic peculiarities of the minerals found are described and summarized. Minerals and phases of probable detrital origin include mainly silicates, volcanic glass, oxyhydroxides, and phosphates. Authigenic minerals of syngenetic origin may be sulphides, clay minerals, carbonates and rarely sulphates and phosphates. Epigenetic minerals, formed by infiltration of low-temperature hydrothermal solutions, may include sulphides, carbonates, sulphates, clay minerals, quartz, chlorides and probably alkaline-earth hydroxides and zeolites. Alteration products of detrital and authigenic minerals may be Fe and Al oxyhydroxides, sulphates, kaolinite, illite, chlorite, muscovite, zeolites, and calcite. The behaviour of minerals and phases during low- and high-temperature ashing are also discussed [37]. Some relationships between ash content in coal (Ad basis) and the mineral and chemical composition of coals and their high-temperature ashes from 41 deposits worldwide were studied. Low-ash coals (<10%) are enriched in moisture, volatile matter, fixed carbon, and minerals such as montmorillonite, Fe, Al and Mg oxyhydroxides, dolomite, witherite and Fe sulphates, while their ashes are abundant in MgO, CaO, Na2O and TiO2. High-ash coals (>20%) demonstrate increased contents of H, N, O, S, and minerals such as quartz, illite, calcite, pyrite and gypsum, while their ashes are enriched in SiO2, Fe2O3 and K2O. Various processes related to some changes in ash content and inorganic matter during coalification are discussed. The material supply and leaching behaviour of different minerals, phases and elements during peat forming and coal progress, as well as the divergent plant constituents, regional, depositional and paleoenvironmental conditions in coal deposits cause the most essential changes in the mineral and chemical composition of coals, respectively in ash content [79]. The geochemistry of coals, coal ashes and combustion wastes from coal-fired power stations was studied. Contents, concentration trends, and modes of occurrence of 67 elements in coals, coal ashes, and combustion wastes at 11 Bulgarian thermoelectric power stations (TPS) were characterized. A number of trace elements in coal and coal ash have concentrations greater than their respective worldwide average contents (Clarke values). The highest values in coal ash are displayed by elements such as Rb, Cs, Ba, Cu, Sb, Bi, U and Ag. Trace elements are concentrated mainly in the heavy accessory minerals and organic matter in coal. A number of trace elements in the waste products, similar to coal ashes, exceed known Clarke contents. Trace elements are mainly enriched in non-magnetic, heavy and fine-grained fractions of fly ash. They are commonly present as impurities in the glass phases, and are included in the crystalline components. Their accessory crystalline phases, element-organic compounds, liquid and gas forms, are of subordinate importance. Some elements from the chalcophile (Cu, Zn, Ga, Ge, Pb, As, Sb), lithophile (Be, Ba, Ce, Hf, Sr, La, Zr, Mo, U) and siderophile (Sc, Cr, V) groups may release into the atmosphere during coal burning. For others, the combustion process appears to be a powerful factor causing their relative enrichment in the fly ash and rarely in the bottom ash and slag. Considerable amounts of Hf, some chalcophile elements (Zn, As, Tl, Pb) and Ag from stack emissions have probably entered the soil near TPS. Trace elements can also occur in watersoluble forms in the fly ash (Li, Sr, Mo, Cs, V, Cr, Mn, As, Bi, B, F, Cl, Br, I) and probably contaminate the surface and subsoil waters. Some trace elements (Sr, Ba, Yb, Sc, Cd, Tl, Pb, Bi) may accumulate in the vegetation near TPS [78]. Chlorine and bromine in Bulgarian coals and their combustion wastes from 7 thermo-electric power stations were studied. The obtained data show that Cl contents are similar to Clarke value, while Br concentrations are highly enriched in Bulgarian coals. The Cl and Br contents in coal, bottom ash and fly ash from Bulgarian TPS indicate that the combustion wastes may be a considerable pollution of Cl and Br in the air, soil, water and vegetation near TPS. A detailed understanding of concentrations, modes of occurrence, origin and behaviour of Cl and Br in coals and combustion wastes are required. [80]. 11. Phase-mineralogical and chemical transformations and inter- actions in inorganic matter of coal during heating (S. Vassilev, C. Vassileva). A comparative characterization of chemical and mineral composition for Bulgarian coals was done. 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 comparative characterization of their composition was done. Major minerals identified in the crystalline matter of Bulgarian coals are commonly quartz, kaolinite, illite, calcite, pyrite, plagioclase, K-feldspar and gypsum, and occasionally dolomite, siderite, Fe oxyhydroxides and Fe sulphates. Some genetic features of the inorganic matter in coal and coal ash are described and compared. The coals studied show high detrital (P, B, BD, ME) or high authigenic (S, MW) mineral abundances 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 high (B, P, BD) or low (ME, MW, S) silicate mineral abundances with sulphate (B, P, ME, MW, S) or oxyhydroxide (BD) mineral tendencies. III. SYNTHESIS, CRYSTALLIZATION, STRUCTURE AND PROPERTIES OF MINERALS AND NEW CRYSTALLINE MATERIALS: 12. Thin
molecular sieve films on noble metal substrates (S. Mintova, Microporous materials such as molecular sieve zeolites have several applications as catalysts, sorbents, and ion exchangers. During the last decade numerous studies have focused on the preparation of molecular sieve layers, thin films, and membranes. Devices with high selectivity, sensitivity and short response times are potentially useful within the fields of sensor technology and electrochemistry. An essential component in these devices is a thin microporous film that offers minimal diffusion resistance and maximum selectivity on the molecular level. The utilization of these materials in various applications is greatly dependent upon the properties of the molecular sieve layer grown on the support and of the orientation of the individual crystals. A novel method for growing dense microporous films less than 300 nm thick was developed in order to prepare such films on noble metal substrates. This method was used to depose silicalite-1 films on a gold surface in a three step process. The gold surface is modified with silane coupling agent after which the silane is hydrolyzed to yield a negatively charged interface. Positively charged colloidal silicalite-1 crystals are readily adsorbed as a monolayer upon this surface and are induced to crystallize further in a separate hydrothermal treatment step to yield a dense zeolite film. The sorption of highly dilute hydrocarbon vapors into these zeolite films was measured with a quartz crystal microbalances (QCM). The high sensitivity to organic vapors, the fast response with sorbates having high diffusivity, the reversible uptake, and the high chemical and thermal stability make these zeolite modified QCM devices very promising chemical sensors for a variety of applications [62, 63, 64, 65]. 13. Synthesis
and investigation of titanium silicates ETS-4 and ETS-10 The progress in the hydrothermal synthesis of molecular sieves has resulted in a large number of structures that are crystalline three-dimensional microporous solids composed of interconnected tetrahedra. In recent years, interest has turned toward a potentially large class of novel molecular sieve materials composed of interconnected octahedral- and tetrahedral-oxide polyhedra. Titanium silicates ETS-4 and ETS-10 were synthesized from titanosilicate gels in the present of an organic template and different inorganic cations. Raman and IR absorption spectra of these materials were measured at room temperature in the frequency range 200-1400 cm-1. The peaks observed in the spectra were identified through model calculations of the internal modes of vibration for clusters typical of the structure of these materials. The crystallization of ETS-4 in Na-, Na/K-, Na/Li- and Na/Ca- containing gels is subjected to a kinetic analysis. It is found that the presence of potassium, calcium and lithium in the gel modifies substantially the crystallization process. Thus, the sodium cations have a structural directing effect in the formation of ETS-4, while the effect of potassium, lithium and calcium is rather structure-breaking than structure-directing. These cations change considerably the crystal morphology, which gives the possibility to control the synthesis of ETS-4 for obtaining products with previously specified crystal size and morphology [19, 36, 61, 93]. 14.
Crystallization of molecular sieves on vegetal fibers (S. Mintova, Zeolite A and Y on chemi-thermo-mechanical pulp (CTMP) fluff, linen and cotton substrates using two different methods of deposition was studied. The zeolite-vegetal fibers composites were characterized by SEM, XRD, and thermal analysis. In the first case a seed-film method was applied. This method involves surface charge modification of the substrates, adsorbtion of a monolayer of colloidal zeolite crystals onto the surfaces and subsequent growth of these colloidal zeolite crystals into a continuous zeolite film. Application of this method resulted in continuous films of zeolite on all substrates investigated. The second approach involved direct synthesis on substrates subjected to chemical or mechanical pretreatment in order to modify their surface properties. Chemical treatment was found to improve the crystallization on cotton and linen fibers, which is not the case on CTMP. The mechanical pretreatment enhanced the zeolite crystallization on the linen fibers but not on the other substrates [22, 23, 34, 35, 76]. 15.
Experimental studies of the growth form of some minerals - quartz, corundum,
fluorite, calcite and some sulphides. (G. K. Kirov, The inner morphology of the crystals of several minerals have been studied by means of the especially devised by the authors original method of fine hydrothermal etching. The method includes finding of convinient cuts of the crystals as well as choosing the best etching conditions to reveal the growth sheets and the sector boundaries in the crystal. On this ground one can speculate on the growth history of the crystal and to make attempts to connect the growth forms observed with the growth conditions. Experiments were made with natural and man-made crystals of quartz, corundum, calcite and fluorite [56]. Based on some observations on the etched quartz crystals it has been
assumed that the faces of the hexagonal prism m { Conditions of revealing the inner morphology of corundum, fluorite and calcite crystals have been found and the study of the inner morphology of natural and man-made crystals of these minerals are in progress. 16. Etching break surfaces of quartz crystals (M. Chr. Maleev, G. K. Kirov). Etching of parting surfaces as well as random break of quartz crystals in 10 to 20 % HF has shown that compared to the flat crystal faces these surfaces appear rather stable against etching. After expostere for 72 hours, when the flat faces are covered by large and deep etch-pits, the broken surfaces remain smooth and shining and no etch-pits can be discovered both macroscopically and under the optical microscope. Only in SEM and when the observed surfaces is tilted against the electron beam to 60¦ or more it is observed that they are covered with tiny steps and kinks. On the parting surfaces all the steps are roughly parallel and on the random break surfaces the steps are oriented in several directions. The performed observations show that etched broken crystal surfaces could be very informative in the study of steps forming, movement and bunching [57]. 17. New cell for hydrothermal synthesis and crystal growth (G. K. Kirov). A new cell construction for hydrothermal experiments is proposed, which is nondestructable and nearly fully prevents the damaging effects of mixing of the inner (corrosive, working) and outer (pressure compensating) solutions. The cell can be made of metal, glass or teflon. It is not tightly closed by a lid which only prevents the mechanical mixing of solutions. One or two small holes in the upper part of the cell enable the perpetual pressure equalization during the run through leaking of insignificant quantities of pure vapors in or out of the cell. The reliability of the new cell has been tested in experiments of etching quartz crystals, of synthesis and growth of iron sulfide and dolomite crystals and of preparation of monodisperse alumina gels. 18. The block-building principles in the structures of some lead- antimony chlorine sulphosalts (V. Kostov-Kytin). The undoubted establishment of chlorine in some natural Pb-Sb sulphosalts and successful experiments for synthesizing such unusual compounds inspired new investigations aiming at the determination of the positions of chlorine in their structures as well as to explain the mechanism of its incorporation. Up to now, the crystal structures of the mineral dadsonite - Pb10+xSb14-xS31-xCl x and of two synthetic phases - Pb12.65Sb11.35S28.35 Cl2.65 and Pb4Sb4S9Cl2 were successfully determined [47]. The latter one synthesized on several occasions during the study of phases and the phase relations in the system PbS-Sb2S3-PbCl2 (experiments and investigations are now in progress). Identical structural characteristics were observed in the crystal structures of the three sulphosalts related to the pure chlorine positions. The chlorine there in is in a planar square coordination of four Pb atoms thus forming planar Pb4Cl groups. The latter occupy central portions, in the paired regular three-capped trigonal coordination prisms of Pb, specific for these compounds interconnecting the independent truncated lozenge-shaped rods in the structures. The same planar Pb4Cl groups can also be observed in the structure of PbCl2, used as a starting material in most of the syntheses. Presumably, a rich chlorine-bearing medium favors the appearance of planar Pb4Cl groups, which further facilitate the formation of specific atomic configurations, the latter being a constituent part in the structures of some Pb-Sb Cl sulphosalts. Clearly, this hypothesis needs further modification. 19. Purification
techniques for the growth of laser-grade CaF2 crystals A new effective multi stage technique to produce highly quality CaF2 crystals in a modified Bridgman-Stockbarger (BS) furnace is developed. The technique consists of three stage precursors preparation: thermo-breakage, electro-chemical grinding and separation of carefully selected natural fluorite of different origin (first stage), optimized chemical treatment of the selected grained material (second stage), high temperature additional purification of the grained material (third stage) and melt crystallization of thus prepared precursors under improved growth conditions (growth stage). The chemical analysis at each stage of the precursor preparation as well as the optical characterization of the grown crystals are carried out for determining the efficiency of the proposed technique. It is shown [63] that the thermo-breakage and the electro-chemical grinding do not introduce unintentional impurities into the starting material and are expected to be technologically and economically profitable. The selected grained material is treated by two alternative original methods for removing of the rare-earth (RE) and/or oxygen impurities and preparation of the final precursors. Both techniques require a high temperature treatment in vacuum furnace (under pressures below 0.01 Pa) of the grained material mixed with 0.5 wt.% PbF2. The procedure is performed in a multi camera crucibles which design depends on the purification specificity. When the goal is the removing of the RE impurities, the loaded grained material is heated up to 50 °C above its melting point temperature within a crucible whose cameras are linked with its outer compartment by canals with appropriate gas permeability. Thus, an efficient control of the speed of the vaporization, the mass transfer and the sublimation processes is carried into effect and the molten material is separated into two parts, one (up to nine off cylindrical-shaped quenched precursors) highly purified from and another one (sublimated compactly on the bottom of the outer compartment) rich in RE elements. Besides, both parts are effectively purified from oxygen contaminants the majority of which react with the PbF2 vapor at about 900 °C while the remainder desorbs at higher temperatures and is removed by the vacuum system. When the purification is reduced to the level of oxygen contaminants removing, the type of the used multi camera crucible has a little importance and the temperature dwell do not exceed 1100C. At these conditions the grained material is purified from the oxygen contaminants without reaching a molten phase but the formed precursors have again a tight shrunk structure. The efficiency of the proposed additional purification techniques and the growth yield are significantly improved when the third stage melt purification is combined with growth stage. The growth stage optimum is localized by special experiments involving a determination of the axial temperature distribution in empty multi camera crucible and the position of quenched interfaces within the loaded cameras of the fixed crucible as well [23]. For the purpose, a system of additional molybdenum reflective sheaths is placed into BS furnace unit and its effect on the temperature field is estimated in order to achieve the growth optimum. A long liner into the diaphragm bore of the furnace and a number of thin rings slipped on the crucible stem are capable to provide a reproducible optimum on each stage of growing in single and multi camera crucibles at a relatively low level of power supply. The crystals grown in the central compartment have slightly better characteristics than those in the peripheral ones. Analyzing the results of these experiments, one can find the relationships governing the growing processes and the directions for their effective control. Depending on the precursors quality, which is determined by the efficiency of the applied purification technique, the crystals obtained at growth optimum are proved competitor-grade (when the third stage purification does not affect the RE impurities) or laser-grade (when RE purification scheme has been provided). The quality of the laser-grade crystals is proved based on the excimer laser damage characterization for their radiation hardness and optical damage threshold [22]. The spectroscopic indicator technique is used to answer a variety of questions concerning the mass- and the heat-transport processes during the purification as well as its kinetics. A special theoretical is developed for describing the transport processes which are clearly determined by apparatus and substantial factors. The theoretical is used for further optimization of the purification techniques aimed at their industrial applications for production of large scale CaF2 crystals including the laser-grade. The developed theoretical also explains the transport processes proceeding at high temperature under vacuum when crystal chemical reactions occur with participation of RE ions in molten crystalline fluoride compounds. These processes lead to either the purification of the compounds from RE elements, or to their concentration by these elements. This result is reliable background for new development of an efficient technique for growing of multi component crystal systems with fluoride structure, doped with RE elements by precise vapor phase control. 20. High temperature solutions suitable for the growth of NdAl3(BO3)4 crystals (D. Shumov, V. Nikolov, D. Nihtianova, J. Macicek, J. Georgieva, The concentration region of NdAl3(BO3)4 phase in the NdBO3 - AlBO3 - BaO. 2B2O3 system was determined. The experimental data obtained make possible the choice of the most suitable region of high - temperature solutions for the growth of NdAl3(BO3)4 single crystals. This region is between mole ratios of NdBO3 : AlBO3 = 1 : 2 and 1 : 3.The best quality crystals were grown from solution with mole ratio of NdBO3 : AlBO3 = 1 : 2 by spontaneous crystallization. The electron microscopy, X -ray powder diffraction and DTA characterization of the NdAl3(BO3)4 single crystals have been performed. 21.
Investigation of Pb5MoO8 crystal growth
in PbO-MoO3 system The concentration and temperature regions of the Pb5MoO8 compound are determined in the PbO-MoO3 phase diagram. The Pb5MoO8 is an incongruently melting compound with the temperature of decomposition 763 ¦C. The concentration and temperature regions are situated between 14 and 15.6 mol% of MoO3, and 744 °C and 763 °C, respectivly. This part of the phase diagram is investigated by the slow cooling method of high temperature solutions and the temperatures of crystallization of the Pb2MoO5 and Pb5MoO8 phases are determined. The Pb5MoO8 single crystals are obtained by spontaneous crystallization for the first time. The possibility for growth of Pb5MoO8 single crystals in the PbO-MoO3 system is discussed. 22. Structure
and properties of volcanic and synthetic glasses (N. Zotov, The content of water in silicate melts is very important for their physical and chemical propertis, such as the viscosity and density and, thus, influences the volcanic activity. Recent spectroscopic investigations have shown that water in silicate glasses and melts is in two different forms: molecular water (H2O) and OH ions. A number of problems like microscopic structure of the water-containing glasses and melts, the nature of their depolymerization, the interactions with various ions (e.g. Na, Ca, K). The aim of our study have been to understand the strucute of these glasses. As the natural water-containing glasses are multi-component systems, their investigation is sophisticated because of the lack of long-range order. Therefore, for their study, one needs, in addition to the simple model systems, a number of structurally sensitive methods. The Na2O-SiO2, Na2O-SiO2-H2O, and Si glasses have been studied as model systems. The main results obtained can be summarized as followes:
The Raman and IR study of these materials indicate that the mechaism of depolimerization depends on the water content. If it is less than 5%, the Si-O-Si bonds containing Si atoms bounded to 4 bridging O atoms are destroyed, while if the water content is higher than 5%, destroyed are Si-O-Si bonds in which one Si atom is bounded to 3 bridgind O atoms.
A theoretical approach based on the Green's function method is proposed for the investigation of disorder-induced mode coupling in glasses and its effect on the Raman and IR spectra [16, 17]. This approach is applied for studying the effect of disorder in the thtrahedral angles for Na2O.SiO2 glass on the Raman intensities. The obtained results anr in accordance with the Monte-Carlo simulations.
23. Investigation
of tribochemical reactions between natural zeolites and insoluble phosphates
for obteining compound fertilizers (A. Toneva, The systems natural clinoptilolite - Tunisian phosphorites and NH4 clinoptilolite - Tunisian phosphorites are investigated on two levels of tribochemical treatment - tribochemical mixing and tribochemical activation. The obtained mixtures are studied by X- ray powder diffraction, DTA, TG, IR absorption and extraction in 2% lemon acid. The extraction of P2O5 accessible for plants, which results from solid reactions between the zeolite and the phosphate rapidly increases during the tribochemical treatment. The conditions for almost 100% assimilation of the lemon soluble P2O5 are found on the lower energy level of tribochemical mixing. The obtained results can be used for ecologicaly cleaned NPK compound fertilizers for agricultural needs. 24. Structure of Al-pillared montmorillonites - EM study and numerical simulation (V. Dimov, A. Ilieva, N. Khaltakova). Clay minerals, belonging to the group of montmorillonites (phyllosilicates of structural type 2:1), have been widely used as embedding matrices in pillaring by polymeric metal oxyhydroxy cations. While the metods of synthesis and the sorbtion and catalytic properties of these PILC have been well studied, their structural characteristics are only sporadicaly addressed. The aim of this work is directed to study the structural changes resulting from the process of pillaring and the factors affecting the formation of thermaly stable inter-layer pillared montmorillonites. Three types of montmorillonite were characterized as starting material [53,75,11] and in each case two types of polymeric oxyhydroxy cations were used for pillaring: 1. Al-containing: - [AlO4Al12(OH)24H 2O12]7+; 2. Cr-containig: [(H2O)4Cr(OH)2Cr(OH) 4]4+, [Cr3(OH)4]5+, [Cr4(OH)6]6+. By morphological, crystal-chemical and structural analyses [9,75] the montmorillonite from white bentonite clays from Dimitrovgrad region was shown to be most suitable for the formation of a stable PILC. Among the three starting samples studied this montmorillonite is of the lowest iron content, with a domminant interlayer Ca - containing complex, and of the highest degree of crystallinity. For the tree aforesaid types of montmorillonite the intercallated and the pillared forms were syntesised and their thermal stability and specific surface area investigated. It was found that the montmorillonite from white bentonite clays can be used for pillaring without any prelliminary cation-exchange modification and without removing the mineral impurities out of the starting fractions sized below 2 mm [75]. The degree of ordering of the produced pillared forms was studied by TEM and the structures of the Al13-pillared forms modelled in the framework of a simple pillar geometry. On the basis of the modelled structure diffraction patterns are simulated along the three coordinate axes using the Multy slice method and a good accordance between the simulated and the mesured TEM-patterns was observed. In addition, an increase in the degree of ordering along the c-axis was found for this modification. The character of the pillars-layers bounding was specified by IR absorption spectroscopy and by modelling the IR-spectra of the AI13-pillared montmorillonite. 25. Physico-chemical
and structural transformations of tungsten phases under supergenic conditions:
experiment, analysis and modeling. Goethite containing adsorbed tungsten is an ultimate product in the evolution of the tungsten-bearing phases in supergene zone. Type of the adsorbed tungsten species, their arrangement and manner of the linkage with the goethite surface are poorly studied. It is assumed only that tungsten is organized in WO4 complexes. To investigate this problem, series of Raman spectra of natural and synthetic goethite with varying content of tungsten (0-20 wt% WO3) are recorded and interpreted in a small-cluster approximation. Four major peaks are observed in the Raman spectra: 390 cm-1 (typical for all samples), 223, 292 and 610 cm-1 (typical only for tungsten-bearing goethites). The structural modeling for tungsten incorporated in goethite and the Raman spectra modeling show that: 1) The adsorbed tungsten is organized in WO6 octahedra both apex- and face-shared with FeO6 octahedra in the (100) goethite surface. 2) The peaks at about 223 and 292 cm-1 related to the linking oxygen between WO6 and FeO6 octahedra indicate that the distribution of WO6 octahedra on the (100) goethite surface is similar to that of the perovskite-type WO3 in the plane (111). 3) The correlation between the intensity of the peak at about 610 cm-1 and the content of tungsten shows that the adsorbed tungsten atoms form a quasi-two-dimensional WO3 phase of perovskite-type structure epitactically developed on the (100) goethite surface. 26. Study of the degree of ion exchange in natural and modified sorbents. Purification of waste waters (B. Vassileva, A. Ilieva and O. Petrov). On the base of former studies on sorption of ions from model and industrial waste waters by natural sorbents four new natural composit filter materials were designed. Their selectivity in respect to a series of ions (namely, Zn2+, Cu2+, Pb2+, Ca2+, Na+, K+, NH4+, F-, Cl-, NO3-) was investigated as well as their effectivity. On this ground the total sorption capacity for both cations and anions was determined. The obtained experimental data showed possibility for complete sorption of the ions from the model waste waters (in some cases reaching 100% removal). The used sorbent combinations may find application in filtering of waste industrial waters; to be used as barriers in waste depositories where to prevent from entering of the waste waters (carrying ions, heavy metals, nitrates, etc.) into underground waters and in soils. Additionally, the experiments with mixed filters allowed to characterize the waste waters and their interaction with the filters in respect to type and degree of ion contamination. 27. Thermal stability of heulandite-clinoptilolite in zeolitized rocks - topological and topochemical features (O. Petrov). Profile-fitting analysis of diffraction lines of heulandite (Heu)-clinoptilolite (Cli) group zeolites in sedimentary rocks from Eastern Rhodopes subjected to thermal treatments showed a polyphase zeolite nature of the samples. It was proved that Heu and high-silica Heu are present in addition to the common Ca-Cli and Cli. Ca-Cli is dominating but there is a differentiation in the temperatures at which it is stable (in the temperature range 400-600 °C). Close to the typical Cli are the samples from drill-hole #228 and most thermally stable is Cli in sample #22. Rietveld structural analysis applied to powder X-ray diffraction data proved that the more thermally unstable zeolite phases are charcterized by more calcium content in the sublattice of exchangeable cations (position M2 is almost fully occupied) and vice versa, the more stable phases have greater occupation of the potassium position, M3. In spite of the typical for Cli ratio, Si/Al>4.50, (according to the classification scheme) it can be stated that the quantity and distribution of Ca cations in the structure are responsible for the specific thermal behaviour. 28. Quantitative
modeling of the mineral composition of rocks by powder X-ray diffraction
(a modification of the Rietveld method). (O. Petrov, The Rietveld petrological analysis gives acceptable modal mineral compositions for rocks. The method can be applied both for fine-grained and coarser-grained rock samples. The basic principles of the method were studied in detail and the main problems analysed. The obtained results are the following: 1. A series of samples were collected (fine- to coarse-grained; acid to ultrabasic representatives). The samples are well characterized by the classical petrological approach (with modal and normative analyses; data of colleagues-petrologists). 2. Different types of rocks (23 samples) were studied by powder X-ray diffraction (XRD) phase analysis and the mineral composition was determined. 3. Prefered orientation (texture) of the particles in the XRD pattern was eliminated by applying a pelletizing method. 4. The appropriate experimental XRD scanning conditions were studied and specified. 5. Experimental XRD data for samples of granite and granodiorite were obtained by a step-scanning technique and the files were formated for use with the Rietveld program. 6. Creation of a structural data base for rock-forming minerals was started. 7. The quantitative analyses on the first two rock samples were started. 29. Syntesis, structural and phase characterization of new crystalline materials. (J. Macicek, O. Angelova, R. Petrova, T. Todorov, Y. Georgieva, Large number miscellaneous crystalline phases were investigated in the X-Ray Laboratory. The crystal structure of non-centrosymmetric 2Sr(ReO4)2.3Urea.2H2O, a phase with potential valuable applied properties, was determined in [1]. The structures of several other molecular adducts of inorganic salts were reported in [4, 29, 30]. In [2, 3] the crystal chemical behaviours of methacryloylcholine iodide and complexes with amino acids were discussed, respectively. Fourteen crystalline phases were studied, including synthesis, determination of the crystal structures, registration and processing of the precise powder X-Ray data, definition of corrundum number (RIR). All experimental results - parameters of unit cells, sets of interplanar distances and Miller indices, Figures of Merit of type Fn and M20 , etc. - are prepared according to the requirements of the International Union of Crystallography. Part of these phases includes adducts of inorganic salts with organic molecules - MnBr2.2Gly.2H2O, CoSO4.Gly.5H2O, MgSO4.Gly.5H2O, ZnSO4.Gly.5H2O, 2Sr(ReO4)2.3Urea.2H2 O, 2Pb(ReO4)2.3Urea.2H2 O and Cd(ReO4)2.2Acrylamide. The rest contains simple and double selenates, selenites and hydroselenites - Pr2(SeO4)3.5H 2O, Ce2(SeO4)3.5H 2O, Nd2(SeO4)3.5H 2O, YbH(SeO3)2.2H2O, ScH(SeO3)2. The list of phases includes and L-argininium Hydrogen Squarate (C6H15N4O2 .C4HO4) and Nd2(Se2O5)3.H2SeO3.2H2O. In Set 46 of Powder Diffraction File (PDF) of International Centre for Diffraction Data (ICDD) were published cards for 26 phases under the numbers from 499 to 456, from 756 to 763, 46-843, 46-874, 46-911, 46-912, from 1565 to 1569 and 46-1793. 30. Geometrization
of the fundamentals of chemistry (V. Penev, A monograph on the "Geometrization of the base of chemistry" [69] has been completed. Some of the principal results in this study are: 1. Four relatively separated parts were isolated in the base of chemistry. 2. In the first part - the statics of the simple chemical objects - has been entirely geometrizated. Several geometrical models of the different kinds of simple chemical objects (atoms and elementary ions) were built and analyzed as geometrical models of the Periodical system. These models were built into a preliminary defined three-dimensional "Mendeleev's space", VM(3), in a specially chosen "Mendeleev's system of coordinates", KM. 3. The geometrization of the second part - (the simple chemical processes), consistes in using operators which act on the coordinates of the simple chemical objects in the Mendeleev's space VM(3). 4. The way is outlined for the geometrization of the third part, namely - the complex chemical objects (multiatoms ions, molecules, crystals), and of the fourth part, - the complex chemical processes (chemical reactions), using a presentation by six-dimensional radius vectors and operators in a Cartesian product of the Mendeleev's space VM(3) and the usual three-dimensional physical space. The monography is in press in the Riva Publishing House. Ph.D. THESISES 31. Calorimetric investigation of the formation and the properties of natural zeolites (N. Petrova) [28]. The enthalpy of formation of chabazite, heulandite and clinoptilolite are determined using the method of dissolution in melt by a high-temperature Calve-type calorimeter. The reported results are the first data on the standard enthalpy of formation of chabazite and clinoptilolite. The Gibbs free energies of these zeolites are calculated. On the basis of these parameters one can study the equilibrium mineralogical state using P-T diagrams of all phases of interest. The zeolitization of glasses is studied by low-temperature calorimeter for the first time. It is shown that the glass composition and experimental conditions influence the mineralogical composition of the synthesized products and the zeolitization kinetics and enthalpy. The processes involved in the zeolitization of glasses are exothermic, which determines the high heat of zeolitization, comparable with the heat of a cooling intrusion, and plays an important role in the formation and existence of natural hydrothermal systems. Heats of ion-exchange of monocation forms of clinoptilolite and mordenite with alkali and alkali-earth cations are measered at 30 and 95 °C. The heats of ion-exchange are studied as functions of the ion-exchange capacity and of the ionization potential of the exchanging ions. Both the ion-exchange capacity and the heats of ion-exchange depend on temperature. The heat effects of ion-exchange are explained by the hydration characteristics of the exchainging ions and by the zeolite structural data. In the case of comparative calorimetric investigation of clinoptilolite and mordenite the differences in the heats of ion-exchange are equal to that in the free energies of the exchanging ions in both structure. The heats of immersion in water and methylenblau solutions and the heats of ion-exchange of tribochemically activated samples of clinoptilolite are investigated. The highest effect on the heats of immersion and on the heats of ion-exchange is observed after the 1st hour of activation. This indicates the improved optimum for dispersion of the zeolite particles from the crack formation on the surface and from the separation of small fragments. 32.
Vibrational spectra of silicon-oxygen rings in silicates An original method is proposed for effective modelling of Raman and IR spectra of crystalline and amorphous materials with covalent or mixed ionic-covalent chemical bonds through calculating the vibrational spectra of small clusters with imposed boundary conditions. The effect of the environment on the vibrational modes of the cluster is taken into account by a shell including the first and the second neighbours of the peripheral cluster atoms and a corresponding modification of the cluster dynamical matrix. The influence of disorder on the vibrational spectra is modelled by averaging the mode frequencies and intensities over all possible configurations of the cluster and shell atoms. A complete set of independent structural parameters is defined to describe the geometry of a ring of tetrahedra. The dependencies of the vibrational spectra of a n-membered ring of SiO4 tetrahedra on its order, degree of puckering and topology as well as on the structure and chemical composition of the environment are investigated in detail for the first time. The obtained dependencies allow to analyze by vibrational spectroscopy the structure of the silicon-oxygen framework in silicates [20, 21, 59]. Using this method the modes generating the Raman and IR spectra of crystalline and amorphous phases of the chain-like silicate CaSiO3 are determined. The structure and the interatomic forces of the amorphous phase of CaSiO3 are analyzed using the changes observed in the vibrational spectra after vitrification. On the basis of Raman spectra of three types of tourmaline it is shown that the positions and intensities of the peaks arising from Si-O vibrations depend of the type of the non-tetrahedral cations in the material. This dependence makes it possible to develop an effective spectroscopic method for evaluating the occupancy of the nontetrahedral crystallographic positions in complex silicates [51, 60]. Raman and IR spectra of the newly synthesized microporous titanium silicates ETS-4 è ETS-10 are measured and the observed peaks identified. The obtained results indicate that the structure of the titanium-silicate network of ETS-4 is identical to that of the zorite [19, 36, 93]. 33.
Effect of the disorder on vibrational spectra of glasses The thesis presents an approach for modelling the experimental vibrational spectra of glasses and crystals with high degree of structural disorder using a method based on the Green's functions of small-sized clusters. For this purpose the following major problems are solved: 1. A theoretical approach is proposed for modelling the vibrational spectra of glasses by minimal-sized structural units describing the short- and intermediate-range ogder; 2. A theoretical approach, based on the Green's function method in mode representation, is proposed for investigating the effect of structural disorder in glasses on the widths, frequency position and spectral intensities of their vibrational bands; 3. The acoustic nature of the vibrational band at about 150cm-1 in the vibrational spectra of a-Si is directly determind and the Raman spectra of this material are calculated without fitting parameters; 4. The degree of structural disorder in Si-O bond lengths and bond angles of Na2O.SiO2 glass is quantitatively estimated on the basis of its Raman spectrum; 5. The Raman spectra of WO3.1/3H2O and ferritungstite are calculated and the peaks identified. INTERINSTITUTES PROGRAMS:
POSTDOCTORAL FELLOWS AND POSTGRADUATED STUDENTS:
PUBLISHED ARTICLES AND REPORTS:
1. Angelova, O. and J. Macicek. 1996. Structures of molecular adducts of inorganic salts. V. Non-centrosymmetric 2Sr(ReO4)2.3Urea.2H2 O. - Z. Kristallogr., 211, 513-517 2. Angelova, O., J. Macicek, K. Kossev and N. Kosseva. 1996. Trimethyl [2-(2-methyl-2-propenoyloxy)-ethyl]ammonium iodite (Methacryloyl-choline iodide). - Acta Cryst. C52, 2216-2218. 3. Angelova, O., R. Petrova, V. Radomirska and T. Kolev. 1996. Crystalline complexes involving amino acids.II (R)-(-)-1-Phenylglycinium hydrogen squarate monohydrate. - Acta. Cryst. C52, 2218-2220. 4. Angelova, O., J. Macicek, R. Petrova, T. Todorov andB. Mihailova. 1996. Structures of molecular adducts of inorganic salts.VI. Comparison of the Cd(ReO4)2.2Urea and Cd(ReO4)2.2H2O structures. - Z. Kristallogr., 211, 163-169. 5. Damianov, Z. 1996. Genetic model of primary ore formation in the Kremikovtsi carbonate-hosted submarine exhalative iron (+Mn)-barite(+base metals) deposit, West Balkan, Bulgaria. - In: Plate Tectonic Aspects of the Alpine Metallogeny in the Carpatho-Balkan Region, vol.1, 39-45. 6. Damianov, Z., S Bakardjiev and P. Popov. 1996. Mineralogy, geology and genesis of the Kremikovtsi carbonate-hosted submarine exhalative iron(+Mn)-barite(+base metals) deposit, West Balkan, Bulgaria. - In: Plate Tectonic Aspects of the Alpine Metallogeny in the Carpatho-Balkan Region,vol.1, 29-37. 7. Dekov, V., Z. Damyanov and E. Mandova. 1996. Native tin and tin alloys from axial metalliferous sediments of an ultra-fast spreading centre: East Pasific Rise, 21¦S survey area. - N. Jb. Miner. Mh., Abh.9, 385-405. 8. Dimitrov, R., N. Vardev, O. Vitov and V. Georgiev. 1996. Ore-formation in the Osogovo-Milevo region. - Rev. Bulg. Geol. Soc, 57, 35-46. (In Bulgarian with English abstract). 9. Dimov, V., L. Filizova, N. Khaltakova and A. Ilieva. 1996. Natural and Al-pillared montmorillonites: evaluation of the microcrystallite thickness. - 14th Confer. of Clay Miner. and Petrol., Banska Stiavnica, Slovakia, Sept. 2-6. 10. Georgieva, I., I. Ivanov and O. Petrov. 1996. X-ray podre diffraction data for Ba3MnSi2O8-a new phase in the system BaO-MnO-SiO2. - Powder Diffraction, 11, 26-27. 11. Ilieva, A. 1996. Mineralogical and chemical composition of the clay fractions of bulgarian bentonites. - 14th Confer. of Clay Miner. and Petrol., Banska Stiavnica, Slovakia, Sept. 2-6. 12. Kamenov. B., E. Tarassova., Z. Iliev and P. Petrov. 1996. The ore magmatic system of the Granitovo pluton, Eastern Bulgaria: 1. Ore mineralizations. - Ann. Univ. Sofia., Livre 1 - Geol, 89, 107-119. (In Bulgarian with English abstract). 13. Kostov-Kytin, V. 1996. Characteristic of gold from Chala ore deposit, Eastern Phodope. - Ann. Univ. Sofia, Livre 1 - Geol, 89, 161-174. 14. Koumanova, B. and B. Vassileva. 1996. Application of natural sorbents to the treatment of waters from thermo-electric power station. - J. Water Sci. and Technol., 605-611. 15. Marinova, I and O. Vitov. 1996. Geochemical evidence for the existence of collisional boundary in the Bosnek-Gorna Dikanya -Dren area. Western Srednogorie (Western Bulgaria). - Compt. rend. Acad. bulg. Sci., 49, 8. 16. Marinov, M., N. Zotov and L. Konstantinov. 1996. The effect of disorder-induced mode coupling on vibrational spectra of disordered solids. - Z. Phys. B., 101, 219-225. 17. Marinov M. 1996. Effect of the disorder on vibrational spectra of glasses (PhD thesis) 18. Mihailova B. 1996. Vibrational spectra of silicon-oxygen rings in silicates (PhD thesis) 19. Mihailova, B., V. Valtchev, S. Mintova and L. Konstantinov. 1996. Vibrational Spectra of ETS-4 and ETS-10. - Zeolites, 16, 22-25. 20. Michailova, B., E. Dinolova, B. Gasharova and L. Konstantinov. 1996. Structural study of minerals by vibrational spectroscopy. - Phys. Chem. Miner., 23, 215-216 21. Mihailova, B. and L. Konstantinov. 1996. Vibrational spectra of rings in continuos Si-O networks. - Phys. Chem. Glasses, 37, 27-32. 22. Mintova, S., V. Valtchev and B. Schoeman. 1996. In Situ Deposition of Silicalite-1 on ZrO2 Fibers. - J. Mater. Sci. Lett., 15, 840-846. 23. Mintova, S., V. Valtchev., B. Schoeman and J. Sterte. 1996. Preparation of zeolite Y-Vegetal Fiber Composite Materials. - J. Porous Materials, 3, 143-147. 24. Mouchovski, J. I. Haltakov and V. Lyutskanov. 1996. Growth of ultra-violet grade CaF2 crystals and their application for excimer laser optics. - J. Crystal Growth, 162, 79-82. 25. Mouchovski, J., V. Penev and R. Kuneva. 1996. Crystals by an improved Bridgman-Stockbarger technique. - Cryst. Res. Technol., 31, 727-732. 26. Opalchenova, G., E. Dyulgerova and O. Petrov. 1996. A study of the influence of biphase calcium phosphate ceramics on bacterial strains-in vitro approach. - J. BioMed. Mat. Res., 31, 219-226. 27. Opalchenova, G., E. Dyulgerova and O. Petrov. 1996. Effect of calcium phosphate ceramics on gram-negative bacteria resistant to antibiotics. - J. BioMed. Mat. Res., 32,115-121. 28. Petrova, N.1996. Calorimetric investigation of the formation and the properties of natural zeolites (PhD thesis) 29. Petrova, R., O. Angelova and J. Macicek. 1996. Molecular adducts of inorganic salts. VI The dimorphism of Cd(ReO4)2.2tu(tu-thiourea). - Acta Cryst. C52, 1935-1939. 30. Petrova, R., O. Angelova, S. Bakardjieva and J. Macicek. 1996. Molecular adducts of inorganic salts. VII Cd(ReO4)2.2tu(tu-thiourea). - Acta Cryst. C52, 2432-2434. 31. Tarassova E., M. Tarassov and Yu. Christova. 1996. Hydrothermal metasomatites related to the Polski Gradetz pluton, Eastern Srednogorie. - Rev. Bulg. Geol .Soc., 2, 69-75 (In Bulgarian with English abstract). 32. Tarassova. E., Z. Iliev. and R. Iliev. 1996. Tracer gold from the Malko Tirnovo ore field. - Anniv. book " Fifty years of the Geology speciality in Sofia University", 47-50. (In Bulgarian with English abstract). 33. Tsinsov, Z. and L. Grozdanov. 1996. Silicate Inclusions in Platinum-Group minerals isolated from sediments of the Blagoevgrad graben, SW Bulgaria. - Compt. rend. Acad. bulg. Sci., 49, 2, 49-52. 34. Tzvetanova, S., S. Mintova and S. Raicheva., 1996. Relation between the molecular structure and the protective capacity of some quaternar amonium cations for corrosion of steel in acid media. - Bull. Bulg. Electrochem. Soc., ads. V. Bostanov and N. Atanasov, 129-132. 35. Valtchev, V., B. Schoeman, J. Hedlund, S. Mintova and J. Sterte. 1996. Preparation and Characterization of Hollow Fibers on Silicalite-1. - Zeolites, 16, 408. 36. Valtchev, V., S. Mintova, B. Mihailova and L. Konstantinov. 1996. Comparison of physicochemical properties of zorite and ETS-4. - Mat. Res. Bull., 31, 163. 37. Vassilev, S. and C. Vassileva. 1996. Occurrence, abundance and origin of minerals in coals and coal ashes. - Fuel Processing Technology, 48, 85-106. 38. Vassilev, S. and C. Vassileva. 1996. Mineralogy of combustion wastes from coal-fired power stations. - Fuel Processing Technology, 47, 261-280. 39. Vassilev, S., K. Kitano and C. Vassileva. 1996. Some relationships between coal rank and chemical and mineral composition. - Fuel, 75, 1537-1542. 40. Vassileva, B. 1996. A comparative study of the sorbtion properties of bentonites from Bulgarian deposits. - 14th Confer. of Clay Miner. and Petrol., Banska Stiavnica, Slovakia, Sept. 2-6, Book of Abstr. 41. Vassileva, B. and B. Koumanova. 1996. Regularities of evolution of the Earth crust. - Int. Conference, Sankt Peterburg, Oct. 15-18, Book of Abstr. 42. Vassileva, B., S. Vassileva and C. Vassilev. 1996. Effective use of mineral sorbents for purification of waste waters from thermo-electric power stations. - Compt. rend. Acad. bulg. Sci., 49, 4, 59-62. 43. Vitov, O. and V. Yamakov. 1996. Furie model and summary of geochemical investigations in the Kjustendil region. - Geol. & Miner. Resources. 4, 25-29. (In Bulgarian with English abstract). 44. Zidarov, N. and B. Zidarova. 1996. Fluorite mineralization in Chiprovtci ore zone - peculiarities, development and morphogenetic types. - Rev. Bulg. Geol. Soc, 57, 3, 1-20. 45. Zotov, N., H. Keppler, A. Hannon and A. Soper. 1996. The effect of water on the structure of silicate glasses- A neutron diffraction study. - J. Non-Cryst. Solids, 202, 153-163. 46. Zotov, N., M. Marinov and L. Konstantinov. 1996. Degree of structural disorder in sodium metasilicate glass Raman spectroscopy study. - J. Non-Cryst. Solids, 197, 179-191. PUBLICATIONS IN PRESS:
47. Angelova, O., V. Velikova, T. Kolev and V. Radomirska. Crystalline complexes involving amino acids.I.L-Argininium hydrogen squarate. - Acta Cryst. 48. Damianov, Z. Genesis of the Kremikovtsi deposit and metallogenic perspectives of the Sredec iron ore region. - Geologica Balc., 26, 4. 49. Damianov, Z. Primari ore petrology, whole-rock chemistry and zoning of the Kremikovtsi carbonate-hosted sedimentary exhalative iron(+Mn)-barite-sulfide deposit, West Balkan, Bulgaria. - N.Jb. Miner. Abh. 50. Dekov, V. and Z. Damyanov. Native silver-copper alloy in metalliferous sediments from the East Pasific Rise axial zone (20¦30'-22¦10'). - Oceanologica Acta. 51. Gasharova, B., B. Mihailova and L. Konstantinov. Raman spectra of various types of tourmalines. - Eur. J. of Mineral. 52. Harizanov, O., S. Angelova and A. Iossifova. 1996. Sol-Gel TiO2 Coatings from Acetate-Acetylacetonate Solution. - Proc. of the 9th Int. 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of lowtemperature quartz crystals can grow within their own sectors only
when the crystal length/weight ratio along the main crystallographic axis,
lc, and the twofold axis, la, respectively is greater
then a certain critical value. This assumption was checked in a series
of hydrothermal experiments. Natural quartz crystals with different la/lc have been grown from 0,5 M NaOH solution at 360 °C and 85 % filling.
In the crystals with la/lc smaller or equal to unity
the m-face is growing only through the rhombohedral faces. On the
contrary, when this ratio is greater than 4 the same face forms its own
growth sectors and larger the ratio faster the growth. A cluster of three
crystals presenting a large area of entering angles was grown in a special
run and it seems that the impact of the entering angles is smaller then
the impact of the length ratio. The so obtained results contribute to the
resolving of the classical "Stenonn's enigma"