X-ray Amorphous Material Research Articles

X-ray Diffraction Results from Mars Science Laboratory: Mineralogy of Rocknest at Gale Crater

The Mars Science Laboratory rover Curiosity scooped samples of soil from the Rocknest aeolian bedform in Gale crater. Analysis of the soil with the Chemistry and Mineralogy (CheMin) x-ray diffraction (XRD) instrument revealed plagioclase (~An57), forsteritic olivine (~Fo62), augite, and pigeonite, with minor K-feldspar, magnetite, quartz, anhydrite, hematite, and ilmenite. The minor phases are present at, or near, detection limits. The soil also contains 27 ± 14 weight percent x-ray amorphous material, likely containing multiple Fe(3+)- and volatile-bearing phases, including possibly a substance resembling hisingerite. The crystalline component is similar to the normative mineralogy of certain basaltic rocks from Gusev crater on Mars and of martian basaltic meteorites. The amorphous component is similar to that found on Earth in places such as soils on the Mauna Kea volcano, Hawaii.

Influence of the activating solution composition on the stability and thermo-mechanical properties of inorganic polymers (geopolymers) from volcanic ash

The influence of the activating solution composition on the stability and thermo-mechanical properties of geopolymers made from a Cameroonian volcanic ash is investigated. NaOH, KOH solutions and silicate solutions with low modulus were tested.The samples are cured at 90°C and the mechanical strength increases up to 21days. With NaOH the strength development is faster, with a dry and wet compressive strength respectively around 40MPa and 20MPa at 21days. The largest particles only act as reactive filler while smaller particles dissolve in the activating solution as seen by SEM. Pure volcanic ash and synthesized materials consisted of mostly X-ray amorphous material with some newly formed crystalline phases. KOH specimens were found to be thermally more stable, shrinking less than 3% after heating till 1000°C.The obtained results suggest the possible use of the synthesized materials for building applications and low temperature refractories up to 700–800°C.

Recrystallization of Amorphized α-TCP

Phase-pure α-TCP powder was milled using a high-energy planetary mill to obtain a partially X-ray amorphous material. Calcination at temperatures between 350 and 600 °C was employed to recrystallize the powder. The phase composition as a function of calcination time and temperature was determinedin-situusing high-temperature XRD equipment. It was found that the amorphous fraction recrystallized mainly to α-TCP, with only small amounts of β-TCP formed. At low temperatures (≤ 450 °C), a stable composition with approximately 85 wt-% α-TCP was found once 100% crystallinity was reached. The time required to reach full crystallinity depended on the calcination temperature. For temperatures > 450 °C a slow transformation to β-TCP was observed. The transformation rate depended on the calcination temperature and on the milling intensity. A moderately milled powder recrystallized to α-TCP, followed by a slow transformation to β-TCP at 600 °C, whereas an intensely milled powder also recrystallized to α-TCP, followed by a fast transformation to β-TCP at the same temperature.

Mechanochemical synthesis of γ-LiAlO2 studied by 6Li and 27Al NMR and synchrotron X-Ray diffraction

The structural transformations accompanying the mechanochemical synthesis of fine-particle γ-LiAlO2 have been studied by 6Li and 27Al NMR and in situ X-ray diffraction. Mechanical activation of a mixture of aluminum hydroxide and lithium carbonate in an AGO-2 planetary mill results not only in size reduction, intermixing, and partial amorphization of the starting materials but also in the mechanochemical synthesis of a carbonate form of aluminum lithium hydroxide. Subsequent heat treatment of the mechanically activated mixture leads to the release of water and carbon dioxide molecules and the formation of an X-ray amorphous phase containing aluminum in octahedral and tetrahedral oxygen coordination. The X-ray amorphous material converts to gamma lithium aluminate through an intermediate phase.

Synthesis and thermal properties of inorganic polymers (geopolymers) for structural and refractory applications from volcanic ash

The volcanic ash occurring as an abundant and readily accessible natural resource in the Central African country of Cameroon was used to synthesize aluminosilicate geopolymers using sodium hydroxide as the sole alkaline activator. Both the curing conditions and the Na 2O/SiO 2 molar ratio were found to influence the development of compressive strength of the geopolymer cement paste, which achieved a maximum strength of 55 MPa at Na 2O/SiO 2 = 0.3. The formation of a mortar by the addition of 40 wt% sand to the optimized geopolymer cement composition reduced the compressive strength to 30 MPa, still within the useful range for construction applications. The geopolymers consist largely of X-ray amorphous material with a small content of crystalline phases. Scanning electron microscopy showed a homogenously distributed mixture of lath-shaped and agglomerated morphologies, with a homogeneous distribution of Si, Al and O in the geopolymer matrix. The geopolymers are relatively stable to heat, shrinking only slowly and retaining about 60% of their as synthesized compressive strength on heating to 900 °C. The FTIR spectra of both the as synthesized and heated geopolymers show two broad absorbance bands, between 820–1250 cm −1 and 450–730 cm −1 assigned to the internal vibrations of Si–O–Si, and Si–O–Al respectively. The compressive strengths and the thermal stability of these materials suggest their suitability for building applications and low-grade refractories.

Clay Mineralogy Along the Laterite Profile in Hubei, South China: Mineral Evolution and Evidence for Eolian Origin

AbstractIn spite of many studies of laterite origins in various parts of the world, the origin of laterite in the middle to lower reaches of the Yangtze River is still a topic of debate, thus leaving doubts about the prevailing environmental and climatic conditions at the time. The purpose of this study was to provide greater understanding of this subject by examining in more detail the associated mineralogical evolution, i.e. clay mineral composition, structural characteristics of clays in various beds with different degrees of weathering along the laterite profile, and the alteration mechanisms during the pedogenic process in tropical to semitropical climate conditions. High-resolution transmission electron microscopy (HTEM), X-ray diffraction, and wavelength dispersive X-ray fluorescence spectrometry were used to characterize the samples in order to link clay mineralogy in various beds with different degrees of weathering along the laterite profile to the formation and origin of laterites in the region. The laterite profile displayed a distinct layered structure and was divided into a saprolite (B4), a light colored net-like clay bed (B3), a brown-red gravelly clay bed (B2), and a dark-brown topsoil (B1), respectively, from bottom to top. The clay mineral assemblage of beds B1 and B2 was illite, kaolinite, and chlorite, while that of beds B3 and B4 was mainly kaolinite with minor illite. The bimodal particle-size distribution of clay minerals in the laterite profile indicated that fine-grained particles could have been produced by partial dissolution and decomposition of coarse-grained ones. Examination by HRTEM revealed that fine-grained particles usually occurred as X-ray amorphous materials in the upper soil beds, but with euhedral morphology in the lower portions, suggesting that the fine-grained particles in the lower soil beds might be partially neoformed during the weathering process. Amorphous spots occurred frequently in kaolinite crystals in the upper soil beds, while the structure of kaolinite was well preserved, with a well defined lattice-fringe image. The illite crystallinity index exhibited a trend of downward decrease, while the values of the chemical index of alteration (CIA = Al2O3/(Al2O3+ CaO+ K2O+ Na2O) × 100%) of the soil profile showed a trend of downward increase. Samples of the upper soil beds, B1 and B2, had comparable SiO2/Al2O3 ratios of 5.37–6.22, while those of the lower beds, B3 and B4, had significantly smaller SiO2/Al2O3 ratios of 1.92–3.98, suggesting that the latter had a greater degree of weathering than the former, in reasonable agreement with the results of the illite crystallinity and CIA index. In addition, samples from B1 and B2 had similar TiO2/Al2O3 ratios of 0.042–0.053, while those from B3 and B4 had comparable TiO2/Al2O3 ratios of 0.021–0.033, comparable to the value 0.020 of the bedrock, and were notably smaller than the upper soil beds, indicating that materials of the upper soil beds, B1 and B2, had a different origin from the lower soil beds. The upper bed was probably derived from eolian accumulation due to intensification of the winter monsoon and aridity in central Asia and was modified by intense chemical weathering since the late Pleistocene, while the lower bed originated from an in situ weathering of the underlying argillaceous limestone.

Synthesis and heavy metal immobilization behaviors of fly ash based gepolymer

Two aspects of studies were carried out: 1) synthesis of geopolymer by using fly ash and metakaolin; 2) Immobilization behaviors of fly ash based geopolymer in a presence of Pb and Cu ions. As for the synthesis of fly ash based geopolymer, 4 different fly ash content (10%, 30%, 50%, 70%) and 3 types of curing regimes (standard curing, steam curing and autoclave curing) were investigated to obtain the optimum synthesis condition based on the compressive and flexural strength. The experimental results show that geopolymer, containing 30% fly ash and synthesized at steam curing (80° for 8 h), exhibits higher mechanical strengths. The compressive and flexural strengths of fly ash based geopolymer reach 32.2 MPa and 7.15 MPa, respectively. Additionally, Infrared (IR) and X-ray diffraction (XRD) techniques were used to characterize the microstructure of the fly ash geopolymer. IR spectra shows that the absorptive band at 1086 cm−1 shifts to lower wave number around 1033 cm−1, and the 6-coordinated Al transforms into 4-coordination during the synthesis of fly ash based geopolymer. The resulting geopolymeric products were X-ray amorphous materials. As for immobilization of heavy metals, the leaching tests were employed to investigate the immobilization behaviors of the fly ash based geopolymer synthesized under the above optimum condition. The leaching tests showed that fly ash based geopolymer can effectively immobilize Cu and Pb heavy metal ions, and the immobilization efficiency reached 90% greater when heavy metals were incorporated in the fly ash geopolymer in the range of 0.1% to 0.3%. The Pb exhibits better immobilization efficiency than the Cu, especially in the case of large dosages of heavy metals.

Thermal conductivity of high-porosity cellular-pore biocarbon prepared from sapele wood

This paper reports on measurements (in the temperature range T = 5–300 K) of the thermal conductivity κ(T) and electrical conductivity σ(T) of the high-porosity (∼63 vol %) amorphous biocarbon preform with cellular pores, prepared by pyrolysis of sapele wood at the carbonization temperature 1000°C. The preform at 300 K was characterized using X-ray diffraction analysis. Nanocrystallites 11–30 A in ize were shown to participate in the formation of the carbon network of sapele wood preforms. The dependences κ(T) and σ(T) were measured for the samples cut across and along empty cellular pore channels, which are aligned with the tree growth direction. Thermal conductivity measurements performed on the biocarbon sapele wood preform revealed a temperature dependence of the phonon thermal conductivity that is not typical of amorphous (and X-ray amorphous) materials. The electrical conductivity σ was found to increase with the temperature increasing from 5 to 300 K. The results obtained were analyzed.

Hydrothermal stability of NaBH 4 enclathrated sodalites with aluminosilicate and gallosilicate framework

The time dependent stability of tetrahydroborate sodalites with aluminosilicate- and gallosilicate framework was studied in water at room temperature and under hydrothermal conditions at 353 K. The experiments were carried out in different time intervals (4–48 h) using an excess of water according a solid:liquid mass ratio of 1:150. The kinetics of decomposition was followed by registration of weight loss, change of the pH-value and by X-ray powder diffraction as well as FT-IR spectroscopy. Both samples undergo remarkable time dependent decomposition. The decomposition rate is higher for the gallosilicate sodalite even though its crystal size is larger compare to the aluminosilicate sodalite. Besides formation of some X-ray amorphous material in both cases precipitation of crystalline aluminosilicate or gallosilicate was found, always connected with impurities of carbonate anions. FT-IR clearly showed that the remaining parts of sodalite structure of both samples were always pure tetrahydroborate sodalite. No borate species other than BH 4 − were detected. Thus, hydrolysis of the moisture sensitive BH 4 − anions by an entrance of water into intact cages can be excluded under the described experimental conditions.

Improving the ammonium ion uptake onto natural zeolite by using an integrated modification process

Detailed investigation on the development of physical and chemical properties of a natural calcium-rich zeolite modified by an integrated process, as well as the relation between the development and ammonium ion uptake (AIU), was conducted. This process consisted of pretreatment (grinding and sieving), sodium salt modification and calcination. Both pretreatment and salt modification largely increased BET surface area, total pore volume and average pore diameter of the raw zeolite. Individual calcination at temperature above 150 °C caused framework collapse, losses of partial clinoptilolite and production of X-ray amorphous material, resulting in pore blockage and the decreases in pore volume and BET surface area. However, the introduction of sodium ion enhanced the heat resistance of the raw material from 150 to 400 °C, and Na + ion treatment followed by calcination could effectively improved pore and surface properties of zeolite, thus leading to the significant enhancement in ammonium ion exchange and adsorption capabilities.

Toward understanding the evolution of griseofulvin crystal structure to a mesophase after cryogenic milling

The purpose of this research is to investigate the response of crystalline griseofulvin to mechanically induced stress through cryogenic milling. Crystalline griseofulvin was subjected to cryogenic milling for two different lengths of time. Following cryo-milling, the samples were immediately analyzed by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD). The DSC thermograms of cryo-milled griseofulvin showed a complex exothermic event at around 65 °C for the 30 min cryo-milled sample and around 75 °C for the 60 min cryo-milled sample. A glass transition event was not observed for the cryo-milled samples. This is in direct contrast to the X-ray amorphous griseofulvin sample prepared through the quench melt method The XRPD patterns of cryo-milled griseofulvin show a loss of the crystalline Bragg peaks and a corresponding increase in diffuse scattering (halos). The disordered griseofulvin material produced through cryo-milling appears X-ray amorphous, yet different from the amorphous phase produced using the quench melt method. Both X-ray amorphous materials have distinctive DSC thermograms and X-ray powder patterns. These findings suggest that the evolution of the griseofulvin crystal structure during cryo-milling is not simply a crystal-to-amorphous transition but a transition to an intermediate mesophase.

Synthesis and heavy metal immobilization behaviors of slag based geopolymer

In this paper, two aspects of studies are carried out: (1) synthesis of geopolymer by using slag and metakaolin; (2) immobilization behaviors of slag based geopolymer in a presence of Pb and Cu ions. As for the synthesis of slag based geopolymer, four different slag content (10%, 30%, 50%, 70%) and three types of curing regimes (standard curing, steam curing and autoclave curing) are investigated to obtain the optimum synthesis condition based on the compressive and flexural strength. The testing results showed that geopolymer mortar containing 50% slag that is synthesized at steam curing (80 °C for 8 h), exhibits higher mechanical strengths. The compressive and flexural strengths of slag based geopolymer mortar are 75.2 MPa and 10.1 MPa, respectively. Additionally, Infrared (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are used to characterize the microstructure of the slag based geopolymer paste. IR spectra show that the absorptive band at 1086 cm −1 shifts to lower wave number around 1007 cm −1, and some six-coordinated Als transforms into four-coordination during the synthesis of slag based geopolymer paste. The resulting slag based geopolymeric products are X-ray amorphous materials. SEM observation shows that it is possible to have geopolymeric gel and calcium silicate hydrate (C–S–H) gel forming simultaneously within slag based geopolymer paste. As for immobilization of heavy metals, the leaching tests are employed to investigate the immobilization behaviors of the slag based geopolymer mortar synthesized under the above optimum condition. The leaching tests show that slag based geopolymer mortar can effectively immobilize Cu and Pb heavy metal ions, and the immobilization efficiency reach 98.5% greater when heavy metals are incorporated in the slag geopolymeric matrix in the range of 0.1–0.3%. The Pb exhibits better immobilization efficiency than the Cu in the case of large dosages of heavy metals.

Analysis of structural transformations during the synthesis of a MoVTeNb mixed oxide catalyst

This work presents a detailed investigation of the preparation routine for the multi-metal oxide Mo 1V 0.30Te 0.23Nb 0.125O x used as catalyst for the selective oxidation of propane to acrylic acid. In situ Raman spectroscopy on the initial aqueous polyoxometalate solution prepared from ammonium heptamolybdate, ammonium metavanadate and hexaoxotelluric acid reveals the coexistence of Anderson-type anions [TeM 6O 24] n− , M = Mo, V; n ≥ 6 and protonated decavanadate species [H x V 10O 28] (6− x)− . Raman analysis showed that the monomeric motif of the Anderson-type tellurate is preserved after addition of the Nb precursor and the subsequent spray-drying process. Calcination of the X-ray amorphous spray-dried material in air at 548 K seems to be the essential step, leading to a re-arrangement of the tellurate building blocks, generating nanocrystalline precursors of the phases finally established during treatment in helium at 873 K.

Comparative study of microstructural characteristics and stored energy of mechanically activated hematite in different grinding environments

Hematite concentrate was mechanically treated using different milling machines and experimental conditions in air atmosphere. The changes in phase constitution, particles size, specific surface area, lattice parameters and X-ray amorphous phase fraction of activated hematite were determined. It was found that the agglomeration of the particles take place during extended milling with accessible pores for Nitrogen gas. The higher media surface brought about the largest specific surface area whatever milling devices used. After 9 h of grinding with higher media surface, the maximum and minimum specific surface area resulted from the grinding in the tumbling and vibratory mills, accounting for 6.83 m 2/g and 18.42 m 2/g, respectively. For the same grinding condition, tumbling mill produced the lowest X-ray amorphous phase. The maximum X-ray amorphous material estimated around 85% from the grinding in the planetary mill with higher media surface for 9 h of milling. Structural changes were followed by XRD line broadening analysis (LPA) using the integral breadth method and Warren–Averbach approach. From the Williamson–Hall plots, it was understood that strain and size contributions exist simultaneously in the milled samples. Besides, the physical broadening increases as milling time and media surface increase regardless of milling types. Besides, it was found that hematite crystal is ‘soft’ between (024) and other crystallographic directions. From the Warren–Averbach approach, it was observed that the higher grinding media surface and prolonged milling favor the generation of small crystallite, higher microstrain, limited crystallite length and subsequently uniform activation of hematite. After 9 h of milling with higher media surface in tumbling, vibratory and planetary mills, the surface weighted crystallite size reached 17.3, 12.2 and 5.6 nm respectively. The maximum lattice strain, < ε L=10 nm 2> 1/2, in the grinding with tumbling, vibratory and planetary mills was found about 4.44 × 10 − 3 , 3.95 × 10 − 3 and 5.23 × 10 − 3 , respectively. The maximum dislocation density accounted for 46.3 × 10 14 m/m 3 in the planetary milling with higher media surface after 9 h of milling. The evaluation of energy contributions of structural defects suggested that the energy contribution of the amorphization was dominant and amounted to 92–98% of the overall stored energy in hematite, depending on milling conditions. Finally, for a given stress energy, the products of tumbling mill represent higher reactivity potential.

Effect of temperature and time in the hydrothermal treatment of HY zeolite

Zeolite HY was steamed at 1 bar water pressure in steps of 100 K from 473 K to 1073 K in dependence of the time (0.5–20 h). Three routes of hydrothermal reactions can be outlined: At low temperature (473 K), a partly framework dissolution occurs accompanied by the formation of X-ray amorphous material. At intermediate temperatures (773–873 K), framework dealumination takes place with the occurrence of different non-framework species. Thereby, with increasing steaming time, saturation of the Si/Al ratio occurs on low levels (Si/Al ratios of about 4 and 5, respectively). At 973 K, a crossover from a low level saturation in Si/Al (6) towards higher values (11) is observed, which is accompanied by a partial amorphization of the zeolite with formation of aluminium oxide and silica gel and a significant decrease in crystal size as well. At high temperatures (1073 K), a fast thermal decomposition occurs. The IR spectra directly reveal an aluminosilicate phase as decomposition product of the framework. At 573 K, the zeolite framework remains unchanged.

Analytical evidence of amorphous microdomains within nitridosilicate and nitridoaluminosilicate single crystals

Single crystals of new nitridosilicates and nitridoaluminosilicates with excellent R values in X-ray investigations were analysed quantitatively using 30 to 60 microm single-spot LA-ICP-MS. Significant discrepancies between expected and measured chemical composition could not be explained by the crystallographic data. High spatial resolution analysis using electron probe microanalysis (EPMA, 10 microm) leads to the discovery of inhomogeneities in the crystalline material. The application of standard single-spot LA-ICP-MS with a spatial resolution of 30 to 60 microm is not suitable for the analysis of these crystals as the existing inhomogeneities dominate and alter the determined concentrations. However, owing to the better detection capabilities, a scanning LA-ICP-MS procedure enables a more representative analysis of single crystals of Ca(5)Si(2)Al(2)N(8) than single-spot LA-ICP-MS as a result of a larger sampling volume. It is highly likely that these impurities consist of amorphous, vitreous phases as powder diffraction X-ray data indicates the existence of a significant fraction of an X-ray amorphous material besides crystalline silicates. These microdomains contain less aluminium, silicon and calcium or are nearly free of aluminium, which explains the detected discrepancies in the chemical composition.

Pressure-induced amorphization, crystal-crystal transformations, and the memory glass effect in interacting particles in two dimensions

We study a model of interacting particles in two dimensions to address the relation between crystal-crystal transformations and pressure-induced amorphization. On increasing pressure at very low temperature, our model undergoes a martensitic crystal-crystal transformation. The characteristics of the resulting polycrystalline structure depend on defect density, compression rate, and nucleation and growth barriers. We find two different limiting cases. In one of them the martensite crystals, once nucleated, grow easily perpendicularly to the invariant interface, and the final structure contains large crystals of the different martensite variants. Upon decompression almost every atom returns to its original position, and the original crystal is fully recovered. In the second limiting case, after nucleation the growth of martensite crystals is inhibited by energetic barriers. The final morphology in this case is that of a polycrystal with a very small crystal size. This may be taken to be amorphous if we have only access (as experimentally may be the case) to the angularly averaged structure factor. However, this `X-ray amorphous' material is anisotropic, and this shows up upon decompression, when it recovers the original crystalline structure with an orientation correlated with the one it had prior to compression. The memory effect of this X-ray amorphous material is a natural consequence of the memory effect associated to the underlying martensitic transformation. We suggest that this kind of mechanism is present in many of the experimental observations of the memory glass effect, in which a crystal with the original orientation is recovered from an apparently amorphous sample when pressure is released.

Arsenic speciation in synthetic jarosite

Iron sulfate minerals may incorporate arsenic released from oxidizing arsenian pyrite and other sulfide minerals. For example, in the southern Mother Lode gold district of California, As is concentrated in jarosite, ideally KFe 3(SO 4) 2(OH) 6, that formed by the oxidation of sulfides in mineralized outcrops and mine tailings containing ∼100 to ∼2000 ppm As. These weathering crusts, which are vulnerable to storm erosion, are of concern as a source for the transport of As into watersheds. Both arsenatian jarosite and scorodite [FeAsO 4·2H 2O] provide only temporary storage mechanisms for As in the environment because of the limited pH and redox conditions over which they are stable. To evaluate the extent of incorporation of As into jarosite, a series of jarosites in the system K 2O–Fe 2O 3–As 2O 5–H 2SO 4–H 2O was synthesized at 95 °C and 1 bar. Potassium arsenate was included at relative molar proportions of 1–50% As T,aq (defined as 100*As/(As+S)) in the starting solutions. Arsenic was incorporated into all samples at higher proportions relative to S than in the starting solutions. Synchrotron X-ray diffraction results indicated that jarosite was formed from starting solutions that contained up to 20% As T,aq. An X-ray amorphous phase also formed in samples containing As and, at 25% As T,aq in the starting fluid, only an amorphous phase was obtained. Starting fluids with 33% and 50% As T,aq produced poorly crystalline scorodite. Scanning electron microscope (SEM) images show textural differences among the jarosite samples, from relatively uniform anhedral to subhedral particles 0.5–1 μm across in low-As jarosite samples, to smaller grains (<0.2 μm) dispersed in a groundmass in the samples richer in As. Results from SEM, SXRD and Raman spectroscopy suggest that most As in the synthetic samples enters the amorphous phase, but quantitative analytical electron microprobe (AEM) analyses showed that the grains of jarosite contain up to ∼30% As T,s. Iron K-edge and As K-edge extended X-ray absorption fine-structure (EXAFS) spectra of the arsenatian jarosite showed As and Fe environments consistent with substitution of As for S. SXRD indicated unit-cell expansion with increased substitution of As in jarosite. The extent to which As is accommodated in the jarosite structure may be limited by the charge-balance mechanism and deficiency of Fe in octahedral sites. The X-ray amorphous material produced in the syntheses exhibits short-range order and is similar to scorodite over small domains, on the order of 10–14 Å. Raman spectroscopy showed several broad peaks in the 750–950-cm −1 Raman shift spectral region, associated with As–O vibrations. The relative intensities of bands related to As–OFe and As–O vibrations are also consistent with substitution of As for S in jarosite, and with small, scorodite-like domains in the amorphous material. Collectively, these data show that the strong association between Fe and arsenate during nucleation of the solid materials leads to As retention in the oxidized Fe minerals produced during weathering of arsenian pyrite and other As-rich sulfide minerals.

Technology of New Materials with Controlled Properties in Integrated Industrial Waste Treatment

A method of industrial waste treatment by melting in a reducing medium with the subsequent separation of the mixture was considered. This method produces x-ray amorphous raw material of constant chemical composition, which contains almost no compounds of iron and other transition metals. The raw material produced can be used to manufacture glass ceramics that are transparent in the visible region and have a low thermal expansion coefficient. Glass ceramics were synthesized that are promising for use as substrates for optical and magneto-optical data storage media, for manufacturing visible and near-IR bandpass filters, and also for producing optical fiber materials. The possibility of obtaining porous materials with different types of crystal structures, low density, and controlled pore size and type was demonstrated.

Thermal reactions of kaolinite with potassium carbonate

It was previously established that kaolinite reacts with K2CO3 on heating to form products of KSiAlO4 composition. In the present study we investigated the solid state reactions with K2CO3 of four kaolinites of different thermal stability. The mixtures were calcined at temperatures ranging from 400-700°C and washed before or after boiling with the remaining K2CO3. FTIR spectra indicated that the X-ray amorphous material formed after calcining the mixtures at 500-590°C had a SiAlO4 tetrahedral framework. Attempts to convert the products to zeolites gave promising results. After calcining at 700°C under atmospheric pressure synthetic kaliophilite (KSiAlO4) was obtained. These conditions are appreciably milder than previously reported for kaliophilite syntheses. Conversion to kalsilite increased with decreasing thermal stability of the original kaolinite. In similar reactions with KCl much less K was incorporated into the amorphous phase and kaliophilite was not obtained. The reactions of the four kaolinites with K2CO3 or with KCl were similar in trend, but differed in detail.