BULGARIAN ACADEMY OF SCIENCES
CENTRAL LABORATORY
OF MINERALOGY AND CRYSTALLOGRAPHY
ANNUAL REPORT
No 4/1998
BULGARIAN ACADEMY OF SCIENCES
CENTRAL LABORATORY
OF MINERALOGY AND CRYSTALLOGRAPHY
ANNUAL REPORT
No 4/1998
| Editor: Dr. Nikola Zidarov; E-mail: nzidarov@interbgc.com |
| © Central Laboratory of Mineralogy and Crystallography, 1999 | ISSN 3033-2206 |
CONTENTS
Projects No 4, 11, 12, 14, 21, 23 and
27 are financially supported in part by the Bulgarian National Science
Fund of the Ministry of Education, Science and Technologies; No 7 – by
the Ministry of Environment and Waters, and No 10 - by the “Union minier
Pirdop copper”.
This annual report presents the research activities of the Central Laboratory of Mineralogy and Crystallography during the fourth 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:
The studies of the composition and phase relations in natural mineral systems made it possible to: (1) prove the successive formation of granulites and mafic eclogites during the metamorphism of basic dyke rocks in SW Bulgaria; (2) distinguish berthierine of different origins and the main factors controlling the formation of clay minerals in iron-ore deposits; (3) develop geological-genetic model for the fluorite deposit Chiprovci-east; (4) relate the associations of native metals and alloys found in metalliferous sediments from the oceanic rift zones with stages of their evolution; (5) develop theoretical model for thermal transfusion of gold in the rocks; (6) investigate features of minerals from Bulgarian deposits (Sr-containing chabazite, tourmalines, hydrotalcites, etc.); (7) model experimentally the conditions for formation of ferritungstite and Cl-containing lead-antimony sulphosalts.
As a results of investigations aiming at modification and processing of mineral and technogenic products in order to use them in practice found were: (1) the phase-mineral and chemical composition of char products formed during pyrolysis of municipal solid waste; (2) the degree of Sr exchange in clinoptilolite; (3) the structural changes and dissolution kinetic during tribochemical activation of natural phosphate and modified clinoptilolite are studied in order to produce highly efficient fertilizers.
Aiming at the production of new materials systematic investigations were carried out on: (1) nano-sized crystals of zeolite Beta and a substantial katalitic effect is found with decreasing their size; (2) thin films of aluminum phosphate on metal substrates; (3) two-layered zeolite-fiber composites; (4) the optimal conditions for growing single crystals of Nd-Al borates for laser optics and for industrial production of ecologically pure defoliants; (5) syntheses and structural characterization of new phases of Pb-Mo and Pb-Cd phosphates and modified thiocarbamide derivatives, adducts and thiocarbamide complexes of Cd salts; (6) the structure and properties of large sized single crystals of sillenite structure, perspective for applications in opto-electronics and processing of information, and of metal-containing boron-carbide ceramics as supper hard materials.
Among the most important achievements of practical character are:
A modern technological solution is found for transformation of volatile toxic elements into an inert state during incineration of municipal solid waste which can solve the problem of their processing in Bulgaria.
Mineralogical and technological investigations of products from the plant "Union minier Pirdop copper" for flotation of copper slags were carried out, on the basis of which recommendations were proposed for reconstruction and for increasing copper extraction above 90 %.
A digital model is created for the river network of Bulgaria on the basis of 220 maps scaled 1:25 000 and the data base is completed for purposes of the Ministry of Environment and Waters with information for 18 000 samples of heavy mineral concentrates
The expanded collaboration with foreign universities is realized in four joint projects, three of which have started from the beginning of 1998.
As a result of the collaboration with the Ben-Gurion University of Negev, Israel, a possibility is found for controlling the size of submicron crystals of zeolite Beta and for production of samples with homogeneous particles' distribution. It is found that the decrease in the particle size has a substantial catalytic effect.
In the framework of a joint project
with the University of Pordue, USA thin films of aluminum phosphate were
grown on acoustic wave sensors by microwave processing of alumophosphate
precursors (a US patent subbmited).
Nikola Zidarov
Sofia, January 1999
RESEARCH TOPICS:
I. MINERAL SYSTEMS:
1. Magmatic and metamorphic minerals and mineral associations in the Serbo-Macedonian Massif (N. Zidarov, L. Macheva, P. Nenova, E. Tarassova, Y. Tzvetanova)
New field observations permitted the augen gneisses from the Maleshevska Group, cropping out in the easternmost part of the Belasitza Mt., to be determined as heterogenous milonitized porphyritic metagranites similar to those from the Eastern part of the Ograzden Mt. Very often they contain well preserved porphyroclasts of K-feldspar. The metagranitoids are trusthed on the Troscovska group`s amphibolites.
The crystal chemistry is investigated for the main rock-forming minerals of the metagranitoids, plagiogneisses, plagioclase-bearing schists and metapelites from the Ograzden block of the Serbo-Macedonian Massif (SMM).
Microprobe analysis along profile lines on coarse K-feldspar porphyroclasts from the metagranitoids showed both oscillatory zoning and gradual decrease of the content of Ba from the core to the rim (1.04 to 0.63 wt %), thus indicating their magmatic origin.
By microstructural investigations syn- and late-kinematic garnets are distinguished in the metapelites and plagioclase-bearing schists, and the distribution of the major elements is studied, which shows normal to complex zoning. Garnet-biotite geothermometry indicates minimum temperatures at about 650o C for the peak of metamorphism and at about 550o C for its retrograde stage.
Three generations of white mica are distinguished in the metapelites, plagioclase-bearing schists and metagranites of the Ograzden block of SMM: The early kinematic micas are phengites and are characterized by a high content of celadonite molecule (up to 3.34 Si p.f.u.), with a low content of paragonite end-member (up to 0.12 Na p.f.u.) and a high amount of S(Fe+Mg) (up to 0.42 p.f.u.). The syn- and late-kinematic white micas are almost pure muscovites with low content of Si (3.00 - 3.18 p.f.u.), high content of paragonite molecule (0.13-0.22 Na p.f.u.) and low content of S(Fe+Mg) (0.11 - 0.18 p.f.u.). Based on phengite geobarometry a value of 5-6 kbar is determined for Pmin of its crystallization.
Investigated is the chemistry of biotite from all the studied rock types, of staurolite from the gneisses and metapelits, and of chloritoid from the metapelites. The biotite contains a higher amount of magnesium (up to 40-60 %) being in the phlogopite-annite range, while the other two minerals are highly ferroan (0.79-0.81 % for the staurolite and 0.83-0.88 % for the chloritoid).
Similar investigations are carried out for gneisses and schists from the Belasitza block of the SMM and the results correlate with those for the same rock types from the Ograzden block.
Studying of the geochemistry of fine-grained granitoids from Belasitza block shows that they are quartz-diorites with a high ratio of Na2O/K2O in the range 1.2-1.5, and I type according to the A/CNK coefficient. Following the discriminant diagrams of Hariss et al. (1986), the quartz-diorites have been formed in volcanic-arc environment.
| Investigated are the metamorphic products and the processes of transformation of gabbro-norite dykes to melanocratic eclogites in the Gega melange body. This transition is an isochemical process in a partly hydrated system, during which different pseudo-morphoses, corona and diablastic structures are formed. The crystal chemical evolution is marked by a change in the amphibole composition (e.g. formation of high-aluminum amphiboles), by formation of more acidic plagioclases, neoblastic clynopyroxenes and garnets. Two stages of metamorphic evolution are distinguished: the first one, M1, of granulitization (amphibolitic granulites are formed) has three substages (M1.1, M1.2, M1.3), while the second one, M2, reveals the eclogitization process (formation of melanocratic eclogites). As shown in the figure, the geothermobarometry of the equilibrium mineral phases determines a prograde PT-path (the fields of metamorphic facies for basaltic composition, according to Oh, 1992, are also shown). |  |
2. Mineral forming processes and geogenetic models of the Fluorite Formation (B. Zidarova, N.Zidarov)
The third local geogenetic model of the largest and not exploited so far Bulgarian fluorite deposit Chiprovci-east was developed [65].
The mineralforming processes are reconstructed as a function of the parameters of the specific geologic situation and the fluorite formation mechanism. The deposit is formed by multistage hydrothermal processes in the frame of the complicated tectonic zone. Its spatial developing is controlled by structural factors - Chiprovci thrust plane cross-cut by transverse strike-slip faults and by lithological composition of the wall rocks - marbles, diabases and green schists. The evolution of the deposit is connected with three subsequent impulses of hydrothermal activity which precipitated fluorite, calcite and quartz. The fluorite mineralization was located after the deposition of silver-lead ores, but before the pyrite-cinnabar mineralization. By this manner three contrasting mineral formations were telescopped one onto another, separated probably by a considerable time interval, whose localization is determined by the same structural factors.
The fluorite deposition results from infiltrational-metasomatic processes in carbonate medium (srtatiform bodies) and secretion processes in hydrothermal carsts (pipe bodies) or in cracks in marbles and schists (veinlet bodies).
The fluorite bodies of industrial interest were formed in the temperature interval 280o-170o C, in the most productive sites being between 220o-200o C.
This deposit belongs to the Calcite-quartz-fluorite mineral type of the Fluorite Formation.
3. Sedimentary-hydrothermal ore-forming processes in Kremikovtsi deposit, Bulgaria (Z. Damyanov)
Analysis of data known so far determines Kremikovtsi deposit as a zonal carbonate-hosted one of SEDEX-type, consisting of stratiform pyrite and barite ore (intermediate facies) and MECS-IF-type iron(±Mn) formations with low-grade strata-bound sulfide mineralization, accompanied by a layer silicate assemblage (distal facies), as well as of their respective stockwork and vein iron carbonate-barite-sulfide occurrences in underlying rocks and ores. The deposit was a product of polystage Middle Triassic metallogenesis located in the marginal parts of a second-order graben-shaped structure, adjacent to the West Balkan Early Paleozoic accreted block and related to an incipient rift setting [4].
The main features of the layer
silicate minerals from the siderite iron formation were studied by optical
microscopy, SEM, TEM, XRD, IRS and electron microprobe (see Table 1).
Table 1
The figure shows the diagnostic diagram created on the basis of the ratio Mg/Fe vs. Al/Si, which is based on both original and reference data. This diagram can be used to distinguish berthierines of different origin. The aforesaid indicates that phyllosilicate mineralogy of iron formations and ironstones is controlled by the source and composition of the ore-forming solutions rather than the specificity of the ore-forming processes.
The occurrence of precious and rare metals in some volcanogenic massive sulfide, porphyry copper, polymetallic vein and skarn deposits from the Central and East Srednogorie is also investigated [1]. |
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4. Mineralogical studies of native metals and alloys from the oceanic rift zones (East Pacific Rise, 21o S and Mid-Atlantic Ridge, 26o N - TAG hydrothermal field) (V. Dekov, Z. Damyanov)
The morphology, chemical and physical characteristics and the genetic constraints are studied for minerals forming the major hydrothermal constituents (yellow ochrous lumps, green colloform Fe-Si crusts, rusty red Fe-oxyhydroxide crusts, gel-like silica lumps and quartz crystals, colloform Mn-oxyhydroxide crusts and micronodules, green atacamite crusts, sulfides and iron oxides) of the near sulfide mound sediments from the TAG field [5].
For the first time native Ag-Cu and Sn-Pb-Cu alloys were found in natural objects and native Al, native Sn, native Ni, Sn-Pb, Sn-Cu and Cu-Zn alloys in the metalliferous sediments from the East Pacific Rise (EPR) and Mid-Atlantic Ridge (MAR) (Table 1).
Table 1. Distribution and chemical composition (in wt.%) of native metals
and alloys from the EPR and MAR.
Table 2.
The presence of native metals and alloys, dominated by native Al, native Sn and Sn alloys, in the metalliferous sediments from both EPR and MAR, similar in chemical composition and textural features is a proof of their probable regular formation at a distinctive evolutionary stage of such tectono-magmatic systems and it may be related to high- to moderate-temperature subcrustal mineral-forming processes.
5. Indicatory properties, stability and transformations of minerals in the Me3O4 and (Me2+,Me4+)2O3 systems: Fe-Ti oxides from the Malkoturnovo pluton, Eastern Srednogorie (E. Tarassova)
Accessory Fe-Ti oxides (magnetite and ilmenite) from the Malkoturnovo pluton, Eastern Srednogorie, are investigated by optical microscopy and electron probe microanalysis [15]. Their total content in plutonic rocks (pyroxenite, gabbro, monzonite, quartzsienite, granodioritic porphyrites) varies between 0.5% (in acid rocks) and 2% (in basic rocks). Two types of magnetites being with (1) and without (2) ilmenite inclusions are established in the rocks studied. The most widespread textural types of magnetite-ilmenite intergrowths are: (1) cross-hatched intergrowths of thin ilmenite lamellae in all {111} planes of the host magnetite and (2) sandwich intergrowths of thick ilmenite lamellae predominantly in one set of {111} planes of the magnetite. Impurities such as Ti (TiO2 up to 1.8 wt.%), Al (Al2O3 2.8 wt.%), V (V2O3 0.92 wt.%), Mg (MgO 0.64 wt.%), Mn (MnO 0.45 wt.%), and Cr (Cr2O3 2.0 wt.%), are common in all the magnetite samples studied. The content of Ti, Al and Cr is found to correlate with the petrochemical type of rocks, being lowest in the acidic rocks (TiO2 up to 0.46 wt.%, Al2O3 1.1 wt.% Cr2O3 0.19 wt.%). Typical minor elements in ilmenite are Mn, Mg and V, whose content also correlate well with the specified type of rocks: ilmenite from the basic rocks is found enriched in Mg (MgO up to 5.2 wt.%) and V (V2O3 1.6 wt.%), while Mn is the major impurity component in ilmenite from the acidic rocks (MnO 6.7-23,3 wt.%). It is shown that the significant variations in Mn content of ilmenite from the acidic rocks and the indications for the replacements of ilmenite by hematite, rutile and titanite can serve as an argument for the origin of Mn in ilmenite from acidic rocks. The composition of the coexisting magnetites and ilmenites in all the rocks studied demonstrates that during the oxidizing exsolution of the Ti-containing protospinel, Al and Cr are concentrated in magnetite, while Mg and Mn in ilmenite.
Thermobarometric investigations on several pairs of co-existing magnetite and ilmenite show temperatures lower than 500oC and values of ¦O2 below the magnetite-hematite buffer.
6. Platinum-group minerals from host sources and placer deposits: phase composition, indicative features and associations, origin and transformation conditions (Z. Tsintsov)
An investigation of massive chromite ores from the ultramafic body near Pletena village is performed and new for the deposit minerals of the platinum-group minerals (PGM), Os-Ir-Ru alloy (rutheniridosmine) and erlichmanite (OsS2), are found [58,59,60]. They are embedded in the unchanged chromite matrix. The grains are mainly with isometric or slightly prolonged shape, their boundary with the matrix being well outlined. The grain size reaches 12, sometimes 15 mm. Most of the grains have a porous surface. The erlichmanite composition includes considerable quantities of Ru in the form of an alloy and the mineral itself in some cases associates with laurite.
This study completes the known association of the ore minerals with the PGM: chalcopyrite - CuFeS2; argentite or/and acanthite (Ag2S); nickeline - NiAs; vaesite - NiS2; gersdorffite - NiAsS; galena - PbS; pyrite - FeS2; idaite - Cu3FeS4, and violarite FeNi2S4. A great part of these minerals are new for the investigated ultramafic body.
PGM were not found in the sampled placer materials in the region of the ultramafic massive near Dobromirtsi village. A specific feature of the concentrates is their wine-red color due to the unusually high presence of almandine (above 90%). Besides, two varieties of corundum, ruby and colorless, were distinguished.
PGM were not found also in compact chromite ores from the ultramafic body near Dobromirtsi village, while an association of pentlandite, pyrite, ilmenite, titanite and zircon was observed.
7. 1:25000 mineralogical map of the heavy mineral concentrates in Bulgaria (O. Vitov)
During 1998 the mineralogical data base is supplemented by information on 18 832 samples, thus the total number of samples reaching 86 563 (see the figure).
As a graphic module of the river network of Bulgaria 51 000 samples are used from the supplying areas and regions (220 maps in M 1:25 000).
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A prognosis is performed: for prospecting of gold ore deposits in the region of Radomir, namely Bosnek-Gorna Dikanya-Dren and a model is proposed for estimating the content of gold in rocks, which indicates a lower content in areas of high temperature in porous media [9, 20, 21]. On this basis a tendency is suggested for the distribution of gold under conditions of a temperature gradient. The migration of gold in rocks near a thermal source is considered as thermodifusion in a thermogradient field.
II. TECHNOGENIC MINERAL SYSTEMS:
9. Mineralogy and geochemistry of coals and coal products (S. Vassilev, C. Vassileva)
The phase-mineral and chemical composition of refuse-derived char (RDC) generated by thermolysis of municipal solid waste (MSW) from France is characterized. The occurrence, abundance and source of trace elements in this RDC are studied. The behavior, capture and inertization of some toxic and potentially toxic trace elements (Cr, Cu, Mn, Ni, Pb, Sb and Zn) plus Fe during combustion of RDC are also described. Perspective sorbents and inertants for a retention of the most volatile Pb, Sb and Cu in RDC ash are kaolinite and montmorillonite or coals enriched in these minerals. In the case of effective RDC washing (dechlorination and desulphurization) the use of sorbents for capture of some metals could be reduced or even avoided. Some recommendations are given for RDC producion and utilization [63]. Low cost catalytic sorbents for NOx reduction, based on coal chars doped with transition metals, were produced and characterized. Pyrolysed Spanish coal, subsequently impregnated with derived from petroleum products transition metals (mainly V, Fe and Ni), was used for the reduction of NOx gases. The preliminary results show that these sorbents are perspective for industrial application [2,13,69,71]. The content of chlorine and bromine in some Bulgarian coals (Maritza West, Sofia, Maritza East, Bobov Dol, Pernik and Pirin) and their combustion wastes from 7 thermo-electric power stations (TPS) are determined. The results reveal that these wastes may seriously pollute air, soil, and water near TPS with Cl and Br [29,62].
10. Mineralogy of products from the cycles of grinding and flotation of copper slags (I. Dontchev, B. Zidarova, Z. Damyanov, E. Tarassova)
A method is proposed for mineralogical investigation of more than 500 samples from various technological points of the plant of "Union minier Pirdop copper". The received data for the degree of dressing of the slag minerals in the grinding process permits the following more important practical results to be announced: (1) the developed method for determination of the degree of mineral recovery was practically verified; (2) it was established that copper in metallic state is shaped as fibres and wires during milling which does not allow the full recovering of Cu in the concentrates; (3) due to ineffectivå flotation reagents part of copper and copper-iron sulphides are not floated in the finer grades (-0.025 mm) rather stay in the chamber products, respectively in the waste; (4) the composition of the silicate and oxide minerals in the slags varies with the supplied copper concentrates and often Cu is included as structural or non structural impurities in these minerals. These conclusions are of a great importance for rationalizing the processes and equipment in the plant for dressing of copper slags [28].
III. MODELING AND MODIFICATION OF MINERAL SYSTEMS:
11. Geometrization of the Chemistry fundamentals: Spatial mathematical models of complex chemical objects (V. Penev, L. Konstantinov, M. Marinov)
In continuing the investigations on geometrization of the language of chemistry [45] the following was performed:
1. Studied were relations between the epistemological categories structure, composition, construction, and process and the taxonomic categories family, genus, species, and subspecies from one side and the corresponding groups of basic chemical notions from the other.
2. The definitions of some epistemological categories and basic chemical notions, needed for mathematical modeling of the static and dynamics of complex chemical objects were specified.
3. The study of the system of basic hypothesis on which the contemporary language of chemistry is based was started with the purpose to formulate this language in an axiomatic form.
4. It was demonstrated that there is a direct connection between the problem of constructing unique mathematical images of the various species of simple and complex chemical objects and processes (i.e. the problem of geometrization of the chemistry language) and the taxonomic problem in cybernetics (i.e. the cybernetic problem of image recognition).
5. It can be stated that each chemical reaction can be uniquely related (by use the constructed unique spatial mathematical models of the basic chemical notions and relations) to a corresponding abstract cybernetical system, whose state is uniquely described in the defined seven-dimensional space of chemical reactions VR(7) [the definition of the space VR(7) was presented in: Centr. Lab. of Crys. and Min., Ann. Rep. No 3, p. 23].
The main conclusions are:
12. Morphology of etch pits in man-made and natural quartz crystals under hydrothermal conditions (M. Chr. Maleev, G. K. Kirov)
A detailed study about the morphology of etch pits in natural and man-made quartz crystals under hydrotermal conditions in carbonate solutions (fig.1) and ammonium bifluorite (fig.2) were achieved.
Fig. 1. Typical etch pits on quartz in carbonate solution
Fig. 2. Typical etch pits on quartz in ammonium bifluorite solution
13. Distribution of Sr in natural zeolites (O. Petrov, G. Kamenov, V. Kostov-Kytin)
Natural occurrences of Sr-containing zeolites are rare met. Also, as Sr90 is a serious radionuclide pollutant, it is important to study its distribution in the structure of natural zeolites because of their strong sorption selectivity towards this cation.
An occurrence of Sr-chabazite from Kayryaka, Bourgas, Bulgaria, was found for the first time and studied by electron microprobe, powder XRD, SEM, DTA/TG, optical microscopy [34]. The microprobe analysis gave composition typical for chabazite, but with an overall presence of Sr (from 0.15 to 0.26 atoms per unit-cell). Powder XRD proved the examined crystals to be chabazite. Further studies might clarify the Sr source in the mineral forming processes in the deposit.
Sr-exchanged sedimentary clinoptilolite from Eastern Rhodopes, Bulgaria, was prepared and analyzed chemically. An almost full exchange was proved to result in profound intensity changes in the powder XRD pattern of the sample which can be used for structural location of Sr in clinoptilolite by the Rietveld method. This is important for evaluation of the sorption capacity of this zeolite in respect to Sr-polluted environment.
14. Chemical and structural transformations of tungsten minerals under low temperature (exogenic) conditions: experiment, analysis and modeling (M. Tarassov, N. Khaltakova, M.Marinov, B. Mihailova, V. Dimov, O. Petrov)
Experiments carried out using pure WO3.H2O precursor and solutions with variable Fe/W atomic ratio showed the existence of a definite pH boundary, above which only the new phase is formed (see the figure). At lower values of pH, only dissolution and recrystallization of WO3.H2O is observed. The new phase (W,Fe)(O,OH)3obtained under the specified conditions is of essentially lower content of iron (Fe/W<0.12) than that in natural ferritungstites (Fe/W>0.3). This suggests negligible contribution of the chemically pure tungsten trioxide hydrates (tungstite and hydrotungstite) to the formation of ferritungstite under supergenic conditions and indicates a substantional role of the non equilibrium iron-containing tungsten gels. This suggestion was confirmed by investigation of series of samples from supergenic zones of Grantcha-ritza (Bulgaria) and Bom-Gorhon (Russia) deposits. In the former deposit ferritungstite forms amorphous iron-containing tungsten ochre (Fe/W=0.2-0.45), while in the latter the mineral replaces dispersive tungstite and hydrotungstite which contain sorbed iron (Fe/W=0.03-0.16). It is noticeable that the Bom-Gorhon samples give evidence of simultaneous formation of ferritungstite and of well-crystallised chemically pure WO3.H2O (tungstite) which confirms the aforesaid. |
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15. Structural modeling of inhomogeneous tourmaline by TEM images (V. Dimov, Zl. Vergilov, Il. Vergilov)
Tourmalines from Vitosha mountain are characterized by growth inhomogeneities indicating crystallization from a metastable phase and subsequent subsolidus dissolution during cooling.
To clarity the processes the real structure of selected samples was studied by high resolution TEM images (HRTEMI) and selected area electron diffraction patterns (SAEDP).
The contrast differences in the images [64,76] can be considered as a result of Al-Fe ordering in Z1 and Z2 positions of the tourmaline structure which lowers the symmetry from R3m to R3. On this basis structural models can be created by varying the occupation of Z1 and Z2 positions by different cations. In this way 18 structural types were created for tourmalines with feruvite and scherl - dravite composition. The structural models can be checked by HRI modeling and comparison with HRTEMI.
A date base for the tourmaline structure is created for PC to help in HRI modeling and automatic identification of SAEDP.
16. Thermal decomposition of minerals from the hydrothalcite - takovite isomorphic series (N. Petrova, Ts. Stanimirova)
The layered double hydroxides with general formula, [M1-x2+Mx3+ (OH)2]x+Ax/mm -nH2O (M2+=Mg, Ni, Fe, Zn, etc.; M3+=Al, Cr, Fe, Mg, Am-=CO32-, SO42-, OH-, Cl-, and x ranges between 0.25 and 0.33) form an abundant mineral group. These minerals have interesting properties for potential applications such as ion-exchangers, fire retardant polymers, cellulose composites, and catalysts.
Samples synthesized by mixing acid solution containing Mg- or/and Ni(NO3)2 and AlCl3with alkali solution of NaOH and Na2CO3 were studied by DTA and TG [50,51,70]. Four endothermic peaks are registered in the DTA curves, paired to separate low- and high-temperature regions. The low-temperature effects are due to both interlayer water being expelled and decomposition of part of the OH groups connected with Al. The high-temperature effects correspond to decomposition of the rest OH groups and the CO3 radical. The temperature of the peak's maximum in the low-temperature region is not influenced by the Mg-Ni isomorphic substitution, rather depends on the Mg-Al ratio. The peaks' positions and intensities in the high-temperature region depend linearly on the Mg-Ni substitution. In the case of samples with various aluminum contents the dependence is more complicated, namely the established differences are due to both differences in the layer charge and various ordering of the cations in the layers. During thermal decomposition the Mg- rich samples expel more volatile compounds at higher temperature than the Ni - ones.
17. Chemical, XRD, IR, and DTA/TG investigations of tribochemically treated clinoptilolite and phosphorite compounds (A. Toneva, N. Petrova, S. Bakardjieva)
The present investigation [73] concerns new data about the possible solid-phase tribochemical reactions between natural phosphate and clinoptilolite. Various proportions of natural phosphate and NH4-form of clinoptilolite are tribochemically treated in two stages to obtain almost 100% transition of P2O5 into a form nutritious for plants.
The kinetics of solubility of nutrient elements is colorimetrically determined, and structural changes of both natural materials and their mixtures are determined by powder XRD, IR spectroscopy, DTA and TG analysis. Considerable differences between the initial and tribochemically treated mixtures are observed and the energy accumulated during the mechanical treatment is determined.
The obtained results are basis for production of highly efficient and harmless NPK fertilizers, improved by the zeolite ability to absorb selectively heavy metals, radioactive isotopes and other wastes.
IV. MICROPOROUS MINERALS AND ANALOGUES
18. Structural, physical and chemical properties of microporous titanosilicates (V. Valtchev, S. Mintova)
The investigation of ion-exchange properties of titanosilicates showed that the degree of ion exchange is directly related to exchanging cation' size and hydration radius. Stuctural analyses revealed that the newly synthesized titanosilicate is isostructural to the mineral umbite. Two cation positions were specified, the first one in a 8-member ring (M1) and the second one in a 7-member ring (M2) connected with the channel system. The occupation of these two positions by different cations depends on ion's properties. Small highly hydrated cations such as Li and Na occupy predominantly M1 positions, while large cations such as Rb and Cs are localized in M2 positions. Such material have interesting ion exchange properties [44,75].
Thin continuous films of zeolite ZSM-5 were synthesized on quartz substrates with surface modified and covered by a monolayer of colloidal silicalite-1 seed crystals. These crystals were grown into continuous films with thickness in the range 230-3500 nm by hydrothermal treatment in a synthesis gel free from organic templates. The preferential orientation of the crystals was with their c-axes nearly parallel to the substrate surface, while in the course of crystallization it changed for most of crystals to such rotated approximately at 65 deg. Films prepared by this method may be of importance for development of zeolite-based membranes [11].
Thin silicalite-1 films were grown on (100) Silicon wafers seeded with colloidal silicslite-1 crystals and hydrothermally treated in a precursor solution. The influence of the seed's size and the concentration of adsorbed crystals on the film formation process was studied. The prefered orientation of crystals on the substrate surface is determined for both thin and thick films and a mechanism is proposed to explain the observed features. It is shown that seeds' size and sticking on the surface can be used to control the prefered crystal orientation in the film [31,32].
Thin films of AlPO4-5 were prepared on acoustic wave devices by microwave treatment of aluminophosphate precursors. Prior to hydrothermal treatment the supports were seeded or modified with organophosphate layers. Optimal conditions for preparing nanosized crystals and thin molecular sieve films are reported. The thickness and the orientation of zeolite crystals in the film can be controlled by preliminary treatment of the support, the gel composition and the conditions of microwave processing [40,42].
Films of zeolite Y, silicalite-1 and Sapo-5 were grown on various metal and alloy substrates. The influence of chemical composition and surface imperfections on the film formation was studied and the results obtained indicate that the metal surface determines film's properties and thickness, and the size of deposited zeolite crystals. Film's adhesivity and thermal stability were studied and shown to be determined mainly by the interactions acting at the gel-substrates interface [12].
Nanosized AlPO4-5 molecular sieves and submicron films were synthesized by microwave treatment af aluminophosphate precursors. The effects of the initial solution's chemical composition and the condition of treatment were investigated. The syntheses were performed under hydrothermal conditions in a microwave oven at tempertures in the interval 90-160oC using various concentrations and aging times. The resulting bulk products were analyzed by a variety of methods and optimal film growth conditions were specified. Sorption isotherms for n-hexane and cyclohexane in such films are reported [41].
The factors influencing the size of zeolite Beta crystals were investigated and used to control the individual crystal size and to synthesize samples with homogeneous distribution of particles crystals as small 10-20 mm were synthesized and studied by various methods. A technology of particle separation and their embedding in a matrix of aluminum oxide was developed in order to evaluate the catalytic properties of nanocrystals. This technology makes possible the preparation of zeolite crystals in pallets in which the aggregates are disconnected to individual crystals preserved in the matrix. The reduction in crystal size was shown to lead to about two times higher catalytic activity with respect to technological samples [68].
V.
SYNTHESIS, COMPOSITION STRUCTURE AND PROPERTIES
OF NEW CRYSTALLINE MATERIALS:
Magnesium chlorate, widely used so far as defoliant in agrochemistry, is a highly hygroscopic compound which under ambient conditions exists as hexahydrate and demands special cares and handling upon storage and maintenance. The industrial methods for preparation of Mg(ClO3)2 involve mainly NaClO3 and MgCl2 as starting materials. A new method using MgSO4, NaClO3 and Urea is described which leads to production of Mg(ClO3)2 . 6Urea, a new defoliating agent with improved purity and biological activity [16]. The complete substitution of crystallization water molecules makes this salt more stable and resistant to atmospheric moisture. Moreover, the corresponding adducts possess combined activity as defoliant and fertilizing agents. The development of this new method prompted us to investigate the ternary system MgSO4-urea-H2O. The solubility diagram published by others has revealed only a compound, MgSO4 . Urea . H2O. Our structural investigations recognized two other compounds, namely MgSO4.4Urea.H2O [17] and MSO4.6Urea [56].
22. Structural and phase characterization of new crystalline materials (T. Todorov, R. Petrova, S. Bakardjieva, O. Angelova)
Three Cd(NO3)2 . ntu (n=2, 4) complexes were established in the system Cd(NO3)2 tu - H2O. For n=4 two polymorphs, stable under different conditions were obtained. The crystal structure of the bisthiourea adduct (see the figure) is composed of neutral [Cdtu2(NO3)2] centrosymetric complexes (a) containing two chalating nitro groups. Both of the polymorphs with n=4 are build up of isolated Cd - polyhedra and H - bonded NO3 groups. In the first one cadmium is four coordinated by thiourea molecules only to form regular tetrahedron (b). The second one is rare example of five coordinated cadmium with four thiourea molecules and one monocoordinated nitro group with Cd ... O = 2.919 A (c) [47].
 |
The structure determination of ammonium hydrogensquarate monohydrate [35] was carried out as part of a project investigating the non-linear optical properties of new classes of organic compounds. The crystal structures of L-argininium Hydrogen Squarate, R-(-)-1-phenylglycinium hydrogensquarate, guanidinium hydrogensquarate, 1-phenylethyl ammonium hydrogensquarate, ((L)-(-)-asparaginum hydrogensquarate) monohydrate, and L-(+)-serinium hydrogensquarate are discussed. Ammonium hydrogensquarate monohydrate crystallize in the monoclinic space group P2/c. The hydrogensquarate, ammonium and water molecules are stacked along b axis and held together by an extensive hydrogenbonding network. One of the squarate and one of the ammonium molecules are refined with disordered possitions for hydrogen atoms.
For rod-based sulphosalt structures based on the SnS or PbS archetype E. Makovicky has derived 12 layer types specifying their geometric and compositional characteristics. These layer types differ in the way the rods being connected and, in addition, the layers differ in thickness and width of the lozenge-shaped rods.
The solution of the crystal structure of two synthetic and one natural Pb-Sb Cl sulphosalts revealed their common structural characteristics: presence of identical structural layers (Type-5, according to the classification of Makovicky) and occupation of specific sites only by Cl atoms of fourfold planar coordination - Pb4Cl [Kostov-Kytin, 1997, Compt. rend. Acad. bulg. Sci., 50, 5, 55-58]. Type5, represented as layers in which the lozenges are interconnected by single rows of anions with a fourfold planar coordination, is of special interest since it has been observed in crystal structures of the mineral dadsonite, the synthetic phases as Pb12.65Sb11.35S28.35 Cl2.65 and Pb4Sb4S11, and the chlorine-containing structural analogue of the latter [36,67].
Based on the geometric approach of Makovicky and on some common structural and chemical characteristics of these compounds an attempt was made to predict possible rod-layer combinations for the structures of hypothetical or already existing Pb-Sb Cl-sulphosalts. A good starting point could be the alternation of Type 5 layers for Type 2, Type 6 or their derivatives [36,67]. Best results on verifying this approach could be achieved when applying it to sulphosalts for which only lattice parameters and symmetry are known. In addition, the basic rules for atomic site occupancy within the unit cell and data on interatomic distances of solved crystal structures should be considered.
24. Synthesis and structural characterization of new phases in the system lPbO-mAxO4-nP2O5, l>>m,n; A=Al, Sc, Zr, Nb, Mo, Ta, TR (S. Bakardjieva)
Phase diagrams of the systems lPbO-mAxOy-nP2O 5, A=Al, Sc were investigated by STA, SEM, powder and single crystal XRD. A new Mo (IV)-containing phase was synthesized with composition Pb5MoO4(PO4)2 . It was found by XRD that this compound has the appatite type structure 5 Pb0.GeO4. P2O5. A new scandium phosphate, Pb6Sc2P8O29 was synthesized and found to have Ca6Sc2V8O29 - type structure.
Large sized high quality lithium triborate crystals were grown by TSSG method using B2O3 as a flux and by slow cooling of the solution, with and without pulling [49]. Inclusions and cracks were found to be main growth defects in LBO crystals. As cracking may be attributed to the strong thermal expansion anisotropy of LBO crystals, low temperature gradients have to be used in the growth chamber. The inclusions may be minimized by: (1) choice of the content of B2O3 in the solution in the range of 90.5-91 wt %; (2) increase of the flow of solution in the crucible; (3) slow cooling of the solution (0.2-0.5oC/day) and precise temperature control in the furnace.
26. Copper substitution in braunite: A combined neutron and X-ray powder diffraction study (N. Zotov, R. Miletich, H. Boysen, H. Tietze, W. Kockelmann)
In order to study further the mechanism of Cu substitution in braunite, the cation distribution in two Cu-substituted braunite samples synthesized by solid-state reaction was determined by combined neutron and X-ray Rietveld refinements [79]. The samples with starting bulk composition CuMn6SiO12 (Sample I) and Cu0.5Mn6.5SiO12 (Sample II) were annealed at 1050oC for 12 days. The samples contain minor quantities of (Cu,Mn)3O4 spinel, Mn3O4, Mn2O3, a-quartz and b-cristobalite. The Rietveld refinements were carried out with the GSAS package.
The multiphase refinements gave reliability factors Rp = 6.2% for Sample I (a = 9.4200(2) A, c = 18.6181(4) A and Rp = 12.4% for Sample II (a = 9.4247(2) A, c = 18.6688(4) A. The change of the c parameter and the c/a ratio are in agreement with previous studies according to which c and c/a decrease with increasing copper content. The combined refinements show that in addition to the eight-fold coordinated M1 site, a significant fraction of Cu enters the M3 site. The selective substitution of copper only on the M3 site could be easily understood taking into account that Mn3+ in the M3 site has the strongest Jahn-Teller octahedral distortions.
27. Vibrational and electronic states in defect complex materials (L. Konstantinov, B. Mihailova, E. Dinolova, M. Gospodinov, G. Bogachev)
1) Raman spectra of Bi12(Bi0.53Mn0.47)O 20 with sillenite structure are measured for the first time and the observed peaks are specified on the basis of calculated vibrational modes of a cluster of 33 atoms, generating the crystal structure through translation-symmetry operators. 2) Single crystals of Bi12TiO20 doped with Al, P, V, Cr, Mn, Cu, Cd, Co, W, Mo, Nd, Ag are grown and studied by Raman spectroscopy for the first time. It is shown that the doping changes the intensity ratio of transversal and longitudinal components of the anti-symmetric Ti-O stretching mode, generates an additional peak at 792 cm-1 (which results from a local symmetric stretching mode of XO4 tetrahedra and depends strongly on the interactions in the Bi-O network), and shifts the peaks sensitive to the geometry of BiOn polyhedra. 3) Structural properties of metal-containing boron carbide-based ceramics are studied by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. A method is proposed for high-temperature sintering of materials of very high micro-hardness and interesting properties controlled by the process parameters. The results obtained show that metal cations replace a part of boron atoms in icosahedral positions, thus stiffening the lattice and improving the mechanical properties of the material. 4) Raman spectra of Pb5MoO8 are measured [10] and interpreted in the framework of two structural models: one based on electron-diffraction data and the other on X-ray diffraction data, the latter being much more realistic. 5) For the first time polarized Raman spectra of single crystals of Bi2(MoO4)3 are measured and interpreted in the framework of small clusters which account for the crystal symmetry and the local atomic environment [39]. 6) Programs for calculating the energy of electron states in arbitrary model clusters are compiled for PC and through adding new modules to the program a method is developed for interpretation of optical spectra in both the ultraviolet and the visible range.
28. Crystal growth and characterization of lead molybdates (D. Nihtianova, B. Mihailova, L. Konstantinov)
Results on the crystal growth of PbMoO4, Pb2MoO5, Pb5MoO8 are reviewed [10,18,43]. Typical crystal defects are considered in connection with the growth conditions, special attention being paid to the phase inhomogeneity of the crystals. An actualized part of the PbO-MoO3 phase diagram is given. Pb5MoO8 is an incongruently melting compound. PbMoO4 is a compound with variable composition. These crystals are important for acousto-optical applications.
VI. STRUCTURE AND PROPERTIES OF DISORDERED SYSTEMS:
29. Raman spectra and vibrational states of silicate glasses (N. Zotov, H. Keppler, I. Ebbsjo, D. Timpel)
Realistic VDOS and Raman intensity calculation of Na2Si4O9 glass (NS4) using a Kirkwood-type potential is presented and the character of the vibrational modes in depolymerized alkali silicate glasses is discussed [22,23,24,77,78]. The NS4 glass was chosen due to its serving as a simple model for more complicated multi-component high-silica glasses and its structure and vibrational spectra have been intensively studied by neutron diffraction, reverse Monte Carlo simulations, Raman and nuclear magnetic resonance (NMR) spectroscopy.
Computer models with periodic boundary conditions were generated by molecular dynamics and reverse Monte Carlo simultions. Division of the VDOS of a-SiO2 and NS4 glasses into bands with different stretching character, participation ratio, bridging-oxygen motion and phase quotient is proposed. The band edges are shown to correspond to strongly localized modes. With increasing the degree of depolymerization the general character of the vibrational modes qualitatively remains the same which implies that the vibrational properties of silicate glasses are a completely local phenomenon reflecting the rigidity of the SiO4 tetrahedra.
The VV polarized Raman spectra arise mainly from bond-stretching scattering mechanism which depends on the derivative of the parallel bond polarizability, while the depolarized VH spectra from mixed bond-stretching and bond-bending scattering mechanism. The calculations show that the perpendicular polarizability of the silicon - bridging oxygen bonds is an order of magnitude smaller than that of the parallel bond polarizability and that their ratio is not affected by the presence of short-range disorder and depolymerization.
30. Mass transport in natural silicate melts in constant electrical fields (N. Zidarov, I. Mouchovski, M. Tarasov, M. Marinov)
The mass transport in basaltic melts in constant external electrical fields ranging from 0.1 to 1.25 V/cm is investigated. The melt was annealed for 24 to 96 hours and the electrical field was switched off after the melts quenching. The dependence of the electrical current on temperature and time is measured during the annealing. The concentration profiles of melt compositions are obtained by microprobe analysis after the quenching.
The mass transport in the melt is described by a system of differential equations for multicomponent unsteady-state diffusion, affected by ion migration. The system is solved and analytical solutions are derived using simplifying assumptions.
The viscosity; specific electrical conductivity; transference numbers and mobility of ions, as well as their effective binary diffusion coefficients; energies of activation of viscous flow and electrical conductivity are obtained from experimental data and analytical solutions.
The analysis of the concentration profiles of the oxide components across the basaltic samples and the values of their physical-chemical, energetic, mass transport and structural characteristics shows:
1. If the applied external electric field is below 0.4 V/cm, the ionic current does not initiate noticeable polarization on the electrodes up to 100K above the melt temperature,
2. The mass transport in the melt is dominated by ionic migration of the metal cations, non-bonded with the polymeric melt structure.
3. Noticeable concentration gradients along the samples are observed only for Fe and Mg.
4. The mass transport of Fe and Mg is consistent with the Fick's law and the model of effective binary diffusion coefficients. The average values of these coefficients, obtained for FeO and MgO by two independent methods are in accordance with the reference data for basaltic melts.
5. The value of the diffusion coefficients and the mobility of Fe and Mg in the basaltic melt studied indicates that both diffusion and migration very likely play a role in processes of homogenous differentiation of basaltic melts in magmatic chambers.
Angular and power characteristics of a noncollinear acousto-optic tunable filter based on TeO2 were investigated both experimentally and theoretically [30]. The dependencies of the acoustic wave frequency bandpass width and the filter diffraction efficiency are studied as functions of the angle of incidence of the optical wave and of the acoustic signal power density.These dependencies are illustrated and tested on a prototype of a filter realized on TeO2. A good agreement of theory and experiment is demonstrated, which indicates that the approach used can be effective in designing such devices serving as dispersive elements of electrically tunable spectrometers.
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6. Georgiev G. 1998. Characteristicsofnoncollinearacousto-optictunablefilters. (Ph.D. thesis).
7. Grigorova M., H. Blyte, V. Blaskov, V. Rusanov, V. Petkov, V. Masheva, D. Nihtianova, L. Matinez, J. Muñoz and M. Mikhov. 1998. Magnetic properties and Moessbauer spectra of nanosized CoFe2O4 powders. - Journal of Magnetism and Magnetic Materials (JMMM), 183, 163-172.
8. Ignatova K., L. Nikolova, V. Dimov. 1997. Structure of Electrolytically Deposited Pd-Ag Powders. - J. Phys. Chem., 101, 6891-6894.
9. 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.
10. Mihailova B., D. Nihtianova, L. Konstantinov. 1998. Raman Spectroscopy Study of Pb5MoO8. - J. Raman Spectroscopy, 29, 405-410.
11. Mintova S., J. Hedland, V. Valtchev, B.J. Schoeman and J. Sterte. 1998. ZSM-5 films prepared from template-free precursors. - J. Mater. Chem., 8 (10), 2217.
12. Mintova S., D. Radev and V.Valtchev. 1998. Influence of the metal substrate properties on zeolite film formation. - Metal, 52, 447-450.
13. Moliner R., C. Braekman-Danheux, A. Fontana, I. Suelves, T. Thiemann and S. Vassilev. 1998. Low-cost catalytic sorbents for NOx reduction based on coal chars doped with transition metals. - In: D. McCaffrey (Ed.), Proceedings of the 3 rd Intern. Conf. on Coal Utilization Sc. and Techn. (CUSTNET), May 6-7, 1998, Bucharest, Romania, Session 3, 41-1 - 41-6.
14. Podolesheva I., V. Platikanova, I. Konstantinov, V. Dimov, M. Tarassov, 1998. Thermally Induced Processes in Thin Layers, Obtained by Coevaporation of TeO2 and Sn. - J. of Vac. Scl. and Tech., A 16(4), 2608-2611.
15. Tarassova E., M.Tarassov. 1998. Acessory Fe-Ti oxides from the Malkoturnovo pluton, Eastern Srednogorie. - Geochem., Mineral. and Petrol., 34, 43-50.
16. Todorov T., R. Petrova, K.Kossev, J. Matcicek, O. Angelova. 1998. Hexakis (urea-O) magnezium Dichlorate. - Acta Cryst., C54, 927-929.
17. Todorov T., R. Petrova, K. Kossev, J. Matcicek, O. Angelova. 1998. Magnezium Sulphate Tetraurea Monohydrate. - Acta Cryst., C54, 456-458.
18. Vassilev, P. and D. Nihtianova. 1998. Pb5O4MoO4. - Acta Cryst., 54, Part 8, 1062-1064.
19. Vassilev S. and C.Vassileva. 1998. Comparative chemical and mineral characterization of some Bulgarian coals. - Fuel Processing Technology, 55, 55-69.
20. Vitov O., I. Marinova. 1998. A thermotransfusion model for migration of gold, based on data from secondary dispersion aureoles. - Geol. and Miner. Res., 10, 15-22.
21. Vitov O., I. Marinova. 1998. Statistical model for gold distribution in secondary dispersion aureoles. - Geol. and Miner. Res., 4, 35-38.
22. Zotov N., H. Keppler. 1998.The influence of water on the structure of hydrous sodium tetrasilicate glasses. - American Mineralogist, 83, 823-834.
23. Zotov N., H. Keppler. 1998.The structure of sodium tetrasilicate glass from neutron diffraction, reverse Monte Carlo simulations and Raman spectroscopy. - Phys. Chem. Minerals, 25, 259-267.
24. Zotov N., R.G. Delaplane, H. Kepler, 1998. Structural changes in sodium tetrasilicate glass around the liquid-glass transition: A neutron diffration study. - Phys. Chem. Minerals, 26, 107-110.
25. Breskovska V., V. Kostov- Kytin. Native elements - new finds for Bulgaria. - Compt. rend. Acad. bulg. Sci.
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27. Dontchev I. Hightemperature aluminium phases in metallothermic ferroalloy slags. - Compt. rend. Acad. bulg. Sci., 52, 2.
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29. Eskenazy G., S. Vassilev and E. Karaivanova. Chlorine and bromine in the Pirin coal deposit, Bulgaria. - Rev. Bulg. Geol. Soc.
30. Georgiev G. and L. Konstantinov. Angular and Power Characteristics of Non-Collinear Acousto-Optic Tunable Filters. - Optics & Lasers in Engineering.
31. Hedlund J., S. Mintova and J. Sterte. Controlling the Preferred Orientation in Silicalite-1 Films Synthesized by Seeding. - 12 IZC, Baltimore, Meryland, USA, July 5-10, 1998.
32. Hedlund J., S. Mintova and J. Sterte.Controlling the Preferred Orientation in Silicalite-1 Films Synthesized by Seeding. - Microporous and Mesoporous Mater.
33. Ivanov O. and L. Konstantinov. Temperature dependence of the surface photocharge effect in CdS. - Applied Surface Science.
34. Kamenov G., V. Kostov-Kytin, O. Petrov,. 1998. Sr-containing chabazite from the Kayryaka quarry, Bourgas region, Bulgaria. - Compt. rend. Acad. bulg.Sci, 51, 11.
35. Kolev Tz., Z. Glavcheva, R. Petrova, O. Angelova. 1998. Ammonium Hydrogensquarate Monohydrate. - Acta Cryst..
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39. Mihailova B., M. Gospodinov and L. Konstantinov. Raman Spectrum of Bi2(MoO4)3. - J. Raman Spectroscopy.
40. Mintova S., S. Mo and T. Bein. Nanoscale Films of AlPO4-5 Prepared by Microwave Synthesis. - 12 IZC, Baltimore, Meryland, USA, July 5-10, 1998.
41. Mintova S., S. Mo and T. Bein. Nanosized AlPO4-5 Molecular Sieves and Ultra Thin Films Prepared by Microwave Synthesis. - J. Mater. Chem.
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44. Paillaud J.-L., V. Valtchev, S.Mintova, and H. Kessler. Structure Analysis of Ion Exchanged Forms of a New Titanosiicate M2TiSiO3O9 x 2.5 H2O (M=NH4+, K+ and Li+). - 12 IZC, Baltimore, Meryland, USA, July 5-10, 1998.
45. Penev V., L. Konstantinov and M. Marinov. Geometrization of Chemistry: Formulation of the problem. - Compt. rend. Acad. bulg. Sci.
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51. Stanimirova Tz., N. Petrova. DTA and TG study of minerals from the hydrotalcite-takovite isomorphic series. Influence of Mg-Ni substitution. - Compt. rend. Acad. bulg. Sci.
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53. 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., 51.
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58. Tsintsov Z. Platinum-group minerals in sediments from Gotse Delchev graben, SW Bulgaria. - Compt. rend. Acad. bulg. Sci.
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66. Gergelchev V., V. Nikolov, E. Hristov, T. Petrov, E. Tarassova. 1998. New metallogenic assessment of the Chiprovtsi-Martinovo segment of the Western Bulgarian silver belt. - XVI Congr. CBGA, Vienna, Austria, Abstracts, 181.
67. Kostov-Kytin V. 1998. Lead-antimony chlorine sulphosalts, synthesis, crystal chemistry and prognoses for new structures. First competition for scientific work "The Earth known and unknown" to mark Earth day 22 of April. Category "Young Scientist" - I prize, summary, p. 5.
68. Landau M., D. Tavor, S. Verkey, M. Herskovitz, V. Valtcev and S. Mintova. 1998. Fundamental and Applied Aspects of Nanocrystalline-Zeolite and MCM-Supported Catalysts. - 2th Int. Symp. of Industrial and Fundamental Research in Catalysis, Beer Sheva, Israel, A 6.
69. Moliner R., C. Braekman-Danheux, I. Suelves, T. Thiemann, S. Vassilev. 1998. Catalytic sorbents for NOx reduction based on coal chars doped with transition metals from petroleum wastes. - Poster of the 6th FECS Conference, 22-29 August, 1998, Copenhagen, Denmark. In Env. Sci. and Poll. Research, 5 (3), p. 176.
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