The crystallization mechanism in high strength glass-ceramics

The addition of NiO to a MgO Al₂ Al₂O₃ SiO₂ basic glass has an influence on the phase separation and crystallization mechanism. The differentiation of the components already detectable in the amorphous state continues in the crystallization process of the nickel-rich glasses. The formation of Ni Al-spinel in the bulk restricts the precipitation of high quartz crystals to the skin. The result is a high strength glass-ceramic with clearly distinguishable bulk and surface regions.     

Hydrothermal Synthesis of Zeolite Crystals Using Natural Scolecite

Natural scolecite is converted into analcime type zeolite by hydrothemal method at 180 °C at autogeneous pressure for 24 to 160 hours growth runs. Mordenite is detected in the final product. Cube and spheroid crystals of the products are illustrated and described. Crystals synthesized are characterized by X-ray diffraction, infrared spectroscopy EDAX and scanning electron microscopy. Particle size is estimated as 20–60 microns, induction period for nucleation as 12 hrs, and lattice parameter of cube crystals as 13.70 Å. Mechanism of growth, influence of anions and duration of growth etc. are discussed. It is established that the crystals grow in the system Na₂O Al₂O₃ SiO₂ H₂O.     

Infrared reflection spectra of selected modifications of SiO2 and Al2O3

Infrared reflection spectra were measured within the wave number range of 1400 – −400 cm⁻¹ for following SiO₂ and Al₂O₃ modifications: quartz, opal, quartz glass, cristobalite, tridymite, corundum, sapphire, ruby, gibbsite, boehmite, and diaspore. The spectral bands were attributed, according to literature quotations, to individual vibrations of bonds Si O, O Si O, Si O Si, Al O, O Al O, and Al O Al. The evaluation of infrared reflection spectra has shown that they are very sensitive to internal vibrations of Si O, Al O, which are affected by the symmetry of the surrounding crystal field. They are therefore selective for individual minerals and thus suitable for quick identifying purposes.     

Crystallization field study for the formation of single phase sodium clinoptilolite: Batch composition,seed and temperature effects

Although clinoptilolite is the most abundant zeolite mineral in nature, its synthesis under laboratory conditions has been difficult. A partial crystallization field study was done for the synthesis of clinoptilolite based on a nominal batch composition of 2.1Na₂O:Al₂O₃:10Si₂O:110H₂O to delineate the limits of composition and temperature within which sodium clinoptilolite can be produced as a single phase in high yields. Effects of temperature, SiO₂/Al₂O₃ molar ratio in the batch composition, and the use of different raw materials in batch preparation were studied. The need for the use of seed crystals for reproducible synthesis of clinoptilolite was established. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The crystallisation of alkaline-earth metal phosphates from alkaline-metal halide and alkali metal phosphate melts: Some preliminary solubility-temperature phase diagram studies

The solubility v temperature phase diagrams, for magnesium and calcium meta-, pyroand orthophosphate solutions in the alkalineearth metal halide melts and in different alkali metal phosphate melts, have been analysed: these are the pseudo-binary sections of the ternary P₂O₅ MO MX₂ and P₂O₅ MO Na(K)₂O systems at MO/P₂O₅= 1, 2, and 3, respectively. The temperature ranges and yields for crystallisations of alkalineearth, metal phosphates from these melt solutions are discussed.     

Hydrothermal synthesis of (Zr0.33 Ti0.67) O2–srilankite in the system ZrO2?TiO2?H2O?MF; (M = Na,K)

The hydrothermal synthesis in the system ZrO₂ TiO₂ H₂O MF; (M = Na, K) is discussed for the temperature range 573 K–773 K and the pressure of 100 MPa to 150 MPa. Starting with Zr- and Ti- butoxides their co-precipitated hydrolysates which had been annealed in different ways were used as initial products. The formation of mixed crystals (Zr, Ti)O₂ analogous to the rare mineral srilankite was dependent on the crystallinity and homogeneity of the initial products. 573 K and 100 MPa proved to be the most favourable conditions for synthesis. Higher temperatures (773 K) produced multiphase crystallizates of (Zr, Ti)O₂, baddeleyite, anatas, and rutile.     

Melting and crystallization of silicon layers on insulator with millisecond lamp heating

Melting and crystallization of silicon layers in a SOI structure (Si SiO₂ Si) at millisecond lamp heating have been studied by model calculations using the solution of conduction equation. Pulse heating conditions that do not lead to silicon substrate melting under SiO₂ have been determined. For pulses of 1 and 4.4 ms duration the silicon melt lifetime on the SiO₂ surface has been estimated. The lengths of the crystal oriented growth from windows in the SiO₂ layer that open the single-crystalline silicon substrate have been measured (25 and 64 μm).     

The significance of X-ray investigations for the classification of multicomponent systems with mixed crystals in a solid phase

The X-ray investigations of solid phases in the multicomponent systems KCl KBr H₂O, K₂SO₄ (NH₄)₂SO₄ H₂O and KNO₃ NH₄NO₃ H₂O were conducted and the crystal lattice parameters of mixed crystals forming in these systems were determined. It was confirmed that in the KCl KBr H₂O system the continuous solid solutions were formed and in the K₂SO₄ (NH₄)₂SO₄ H₂O system the solid solutions with a miscibility gap were formed. In the KNO₃ NH₄NO₃ H₂O system the presence of two series of mixed crystals, namely the mixed crystals between ammonium nitrate and the double salt KNO₃ · 2 NH₄NO₃ and between potassium nitrate and the same double salt was confirmed. In this system a wide region of discontinuity (for x_NH4NO₃ = 0.083 – 0.67) also occurred. According to Roozeboom's classification, the KCl KBr H₂O system belongs to the 3^rd type, the K₂SO₄ (NH₄)₂SO₄ H₂O to the 5^th type (the discontinuous mixed crystals, the systems of peritonic type) and the KNO₃ NH₄NO₃ H₂O system is not comprised in this classification.     

Phase relations and crystal growth of YBa2Cu3O7−δ in the system YO1.5?BaO?CuO

The liquidus face of the system YBa₂Cu₃O_7−δ BaCuO₂ CuO was investigated by DTA. We found liquidus temperatures below 1000 °C only in a narrow region with small yttrium oxide content near the eutectic of the system BaCuO₂ CuO. The crystallization path of crystal growth experiments is discussed and the principle structure of the phase diagram is derived. Single crystals are grown being superconductive after thermal treatment in oxygen atmosphere.     

Sythesis and Characterization of Li3B5O8(OH)2 Crystals

Li₃B₅O₈(OH)₂ crystals were obtained in the system Li₂O B₂O₃ H₂O under hydrothermal conditions at fairly lower PT conditions. The crystals obtained were characterized through various techniques: XRD, wet chemical analysis and the measurement of ionic conductivity.     

Crystallization field and rate study for the formation of single phase sodium‐potassium and potassium clinoptilolite

Reproducible synthesis of clinoptilolite as the single crystalline phase was achieved in the narrow crystallization field at or around the nominal batch composition of 2.1(Na₂O+K₂O):Al₂O₃:10SiO₂:110H₂O at 140 °C. Clinoptilolites of high purity were crystallized in the pure sodium or mixed sodium‐potassium cation systems. Partial replacement of hydroxyl anions with the salts of carbonates or chlorides also yielded clinoptilolite as the single crystalline phase although at lower crystallization rates. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization and dielectric properties of low temperature dielectrics containing Li2O filler

Crystallization and dielectric properties of typical low temperature co-fired ceramics (LTCC) consisting of calcium zinc aluminoborosilicate glass and Al₂O₃ filler were investigated by substituting the Al₂O₃ filler partially with Li₂O at the levels of 2-10 wt%. Depending on the content of Li₂O, densification was found significantly affected by early crystallization that resulted from the formation of unexpected crystalline phases including LiAlSiO₄, Ca₂SiO₄, LiAlO₂, and LiAlSi₃O₈. The effect of hindering sintering via earlier crystallization became enormous regardless of firing temperature when >5 wt% Li₂O substitution occurred. It was observed that the substitution of 2 wt% Li₂O for Al₂O₃ was beneficial in producing promising performance at the low temperature of 750 °C, which can be highlighted with k ∼ 8.7 and tan δ ∼ 0.009 at 1 MHz.     

Growth of lanthanum heptamolybdate crystals by gel technique

The growth of single crystals of lanthanum heptamolybdate is achieved by allowing controlled diffusion of La ions through silica gel using the system La(NO₃)₃ MoO₃ NH₄OH HNO₃–Na₂SiO₃. The reaction mechanism leading to the growth is reported. Mechanism of crystallization of La heptamolybdate is discussed. Formation of Liesegang rings consisting of La heptamolybdate crystals in the system is reported. It is observed that concentration programming and seeded growth enhances the size of crystals. The crystals grown in the system are single crystal platelets exhibiting squarish or octagonal facets. Some crystals exhibit a spherulitic morphology.     

On the Synthesis and Characterization of Zeolite ZSM-20

ZSM-20 is a silicon-rich analog of the faujasite-structure, the synthesis of which is complicated. Starting from known synthesis recipes its crystallization in the system Na₂O · Al₂O₃ · SiO₂ · H₂O is investigated in the presence of tetraethylammoniumhydroxyde as templating agent. The aim was to find the critical conditions for its synthesis. The synthesis products obtained are investigated by X-ray diffraction, thermal analysis and i.r. spectroscopy.     

Crystal growth of Ca3−xYxMn2Ge3O12 and phase relations in the PbO?B2O3?GeO2 based melts

The bulk crystals of Ca_3−xY_xMn₂Ge₃O₁₂ garnets were grown on a seed from the PbO B₂O₃ GeO₂ based melts, where the primary crystallization field of garnets was found. The saturation temperatures of the melts were determined before each growth run. The dependence of Y incorporation into the crystals versus the melt composition was also evaluated.     

Some Physicochemical Parameters of Saturated Ternary Solutions of Systems with Mixed Crystals in their Solid Phase

The measurements of density (ϱ), viscosity (η) and hydration number (n_h) of saturated solutions of ternary systems KCl KBr H₂O, K₂SO₄ (NH₄)₂SO₄ H₂O and KNO₃ NH₄NO₃ H₂O with mixed crystals in the solid phase have been conducted. It has been confirmed, that the occurence of the extremes on the curves of dependence of the properties (ϱ, η, n_h) on the composition of saturated solution may be the base for the supposition that beside mixed crystals the double salts have also been formed in the solid phase of a given system.     

Single crystal preparation of MnxCr3–xO4 by flux method

Mn_xCr_{3 x}O₄ was prepared by the flux method. Melts of PbO PbF₂, Bi₂O₃ B₂O₃, B₂O₃, Na₂B₄O₇, and Na₂W₂O₇ Na₂WO₄ were used. The best results could be yielded with the PbO PbF₂ flux, from which crystals with 2–4 mm in thickness were grown. The Bi₂O₃ B₂O₃ flux produced crystals with 1–2 mm in thickness. The spinell structure of the chromite was proved by X-ray investigation.     

Crystallization behavior during cooling and glass-forming ability of Al2O3-poor Li2O–Al2O3–SiO2 melts

The influence of K₂O/(MgO + K₂O) on some melt properties, including crystallization during cooling of melts and glass-forming ability, was investigated in the Li₂O–Al₂O₃–SiO₂ system with low Al₂O₃ content. The dependence of viscosity on K₂O/(MgO + K₂O) above 1000 °C showed a monotonic decrease due to the reduction of [MgO₄] concentration and the conductivity also decreased due to the larger ion radius of K. The temperature dependence of conductivity for all melts showed an abrupt change at one temperature due to crystallization in which temperature of crystallization decreases with increase of K₂O. The crystallization behavior near liquidus temperature was studied quantitatively by calculating the crystal volume fraction from apparent viscosity value. The glass-forming ability of the melts was discussed by using data related with viscosity and crystallization. Finally, it was suggested that the melts with K₂O/(MgO + K₂O) ? 0.75 have a good glass-forming ability.     

Microstructure and spacings of directionally solidified metal-semiconductor eutectic alloys

Directionally solidified metal-semiconductor eutectic alloys, representing nonfacetted facetted eutectics, show a variety of microstructures caused by the great differences in semiconductor volume fraction (Zn Ge 7,8 %; Ge ZrGe₂ 98.6 %), the influence of growth rate and temperature gradient at the solid-liquid interface. The Al Si, Ag Si, Ag Ge, Zn Ge, Cu₃Si Si, NiGe Ge, CoGe₂ Ge, Mn₃Ge₂ Ge, FeGe₂ Ge, Mn₁₁Si₁₉ Si, Cu₃Ge Ge, Ge TiGe₂ and Ge ZrGe₂ eutectics habe been investigated. The following three models are applicable for the calculation of the spacings as a function of growth rate and temperature gradient at the solid-liquid interface to certain microstructures: diffusion-determined growth, branchinglimited growth and phase-lead-determined growth.     

On the Formation of the Garnet Phase in Oxidic High-Temperature Solutions

The paper informs on the formation of the garnets Y₃Fe₅O₁₂, Y₃Al₅O₁₂ and Gd₃Ga₅O₁₂ as primary phase in the ternary solvent mixtures PbO PbF₂ B₂O₃ and PbO MoO₃ B₂O₃. There are correlations with formerly measured oxygen ion concentrations (OIC) in the solvents:

• i each garnet grows in a special region of the OIC, the phase boundaries are parallel to the lines of constant OIC and
• ii the garnet solubility increases distinctly with decreasing OIC. This emphasizes the important role of the oxygen ions for the garnet formation.

Solubility models are discussed taking into consideration both previous and present results. We conclude that the garnet formation is described best by a model reaction of the type RE rare earth elements, Y; M Al, Fe, Ga.