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)     

Phillipsite-type synthetic zeolite with high silica contents and accompanying phases

A zeolite of P type with a molar ratio SiO₂ : Al₂O₃ of about 6 was obtained on laboratory and on enlarged scale, by synthesis carried out at 100°C in Na₂O K₂O SiO₂ Al₂O₃ H₂O system, without complexing agents. It was found that the products depend not only on the chemical composition of hydrogel but also on the kinetic factors such as: the material of the reactor wall, the amount of substrates taken for crystallization and stiring. It was found that the stability of zeolites increases in the order: L < T < Ch < P. The factors accelerating crystallization led to the more stable zeolites as products. The paper shows difficulties in implementing the laboratory results into an industrial production.     

X-ray quantitative determination of the phases in a batch for the synthesis of poly- and monocrystal yttriumaluminium garnet

For the synthesis of ceramics and single crystals of yttriumaluminium garnet, a batch consisting of Y₂O₃ and Al₂O₃ is first treated thermally in order to obtain the garnet phase Y₃Al₅O₁₂. It is possible to make a choice of the optimum technological parameters of the batch if the amounts of all oxide phases, present during the synthesis, are well known. A combined X-ray quantitative method is suggested for this purpose. The initial oxides and a garnet phase are determined by the method with external standard. The rest two impurity oxide phases are determined as binary system. The specific diffraction characteristics of the present compounds were taken into account. The amounts of all phases in the batch, treated thermally from 1373 to 2075 K at every 100 K are shown.     

Aluminum lactate – An attractive precursor for sol–gel synthesis of alumina-based glasses

A novel aluminum precursor, aluminum lactate (Al(lact)₃), was used in the sol–gel synthesis of alumina-based systems. The peculiar chelation properties of aluminum lactate in aqueous solution make this precursor quite attractive for the sol–gel synthesis of alumina-containing materials. Based on the reaction of aluminum lactate with different precursors such as phosphorus, boron, fluorine and others, (Na₂O–)Al₂O₃–P₂O₅, (Na₂O–)Al₂O₃–B₂O₃, (Na₂O–)Al₂O₃–B₂O₃–P₂O₅, (Na–)Al–P–O–F, amorphous gels and glasses were prepared. The local structures of glasses prepared by both sol–gel and melt-cooling methods were compared by using solid state NMR.     

Infrared transmission of (R2O OR R’O)–(TiO2, Nb2O5 OR Ta2O5)-Al2O3 glasses

The new families of aluminate glasses obtained by the present authors from their melts in the systems K₂O–Ta₂O₅–Al₂O₃, Na₂O–K₂O–Ta₂O₅–Al₂O₃, K₂O –Cs₂O– Ta₂O₅–Al₂O₃, K₂O–Nb₂O₅–Al₂O₃, Na₂Oz.sbnd;K₂O–TiO₂–Al₂O₃, BaO–TiO₂–Al₂O₃, BaO–ZrO₂–TiO₂–Al₂O₃ and Na₂O–K₂O–BaO–ZrO₂–Ta₂O₅–TiO₂ –Al₂O₃ showed high transmissions of visible and infrared (IR) radiation ranging from 0.4 to about 6 μm, as well as high refractive indices up to 2.0. Their physical and chemical properties such as glass-forming ability, softening temperature, hardness and hygroscopicity were comparable to conventional silicate glasses. These properties are useful for IR applications. The cause of the high IR transmission of the aluminate glasses was interpreted in terms of the masses of the constituent cations and the single bond strengths of the cations with oxygen ions.     

NMR studies on rapidly solidified SiO2Al2O3 and SiO2Al2O3Na2O-glasses

²⁷Al and ²⁹Si MAS NMR studies were performed on roller-quenched SiO₂Al₂O₃-glasses with Al₂O₃ contents ranging from 10 to 60 mol% and on SiO₂Al₂O₃Na₂O glasses containing 10 mol% Al₂O₃ and 2.5 to 10 mol% Na₂O. Pure aluminium silicate glasses show NMR peaks at 0, 30 and 60 ppm. The frequency distribution of the different Al-sites is not affected by the glass composition. In glasses of the system SiO₂Al₂O₃Na₂O the 30 ppm peak decreases to zero as the Na₂O content increases. The 30 ppm peak is assigned to distorted triclustered AlO-tetrahedra, rather than to fivefold coordinated Al. Triclustering of tetrahedra may provide for charge neutrality in glasses with molar excess of Al₂O₃ over Na₂O. As charge balance is increasingly achieved by addition of alkali ions, the tendency of tetrahedral triclustering is reduced, reflected by the disappearance of the 30 ppm peak in glasses containing ≥ 7.5 mol% Na₂O.     

Effect of alumina on the structure and properties of Li2O–B2O3–P2O5 glasses

The structure of glasses within the system Li₂O–Al₂O₃–B₂O₃–P₂O₅ has been studied through ³¹P, ¹¹B and ²⁷Al Nuclear Magnetic Resonance, and the effect of Al₂O₃ substitution by B₂O₃ and P₂O₅ network formers on the structure and properties investigated for a constant Li₂O content. Multinuclear NMR results reveal that substitution of Al₂O₃ for B₂O₃ and P₂O₅ network formers in a glass with composition 50Li₂O·15B₂O₃·35P₂O₅ produces a change in boron environment from four-fold to three-fold coordination. Meanwhile aluminum can be present in four-, five- and six-fold coordinations a higher amount of Al(IV) groups is found for increasing alumina contents. The behavior of the glass transition temperature and electrical conductivity of the glasses has been interpreted as a function of the structural changes induced in the glass network when alumina is substituted for B₂O₃, P₂O₅ or both. Small additions of alumina produce a drastic increase in glass transition temperature, while it does not change for [Al₂O₃] greater than 3 mol.%. However, the electrical conductivity shows very different behavior depending on the type of substitution; it can remain constant when B₂O₃ content decreases or sharply decrease when P₂O₅ is substituted by Al₂O₃, which is attributed to a higher amount of BO₃ and phase separation.     

Solubility of Ag2O into the Na2O–B2O3–Al2O3 system

The solubility of Ag₂O was measured for the Na₂O–B₂O₃ and Na₂O–B₂O₃–Al₂O₃ system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag₂O for the Na₂O–B₂O₃ system above the melting point of Ag for the first time. It was found that the addition of Na₂O decreases the solubility of Ag₂O while the addition of Al₂O₃ had little effect on the solubility. The effect of Na₂O and Al₂O₃ on the solubility of Ag₂O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag₂O in Na₂O–B₂O₃–Al₂O₃ melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver.     

Self-diffusivity of iron in alkali–lime–alumosilicate glass melts

Self-diffusion coefficients of iron were measured in glass melts with the basic mol% composition of 16 R₂O, 10 CaO, x Al₂O₃ and (74 − x) SiO₂ with x=0, 5, 10, 15 and R=Li, Na, K and Cs in the temperature range of 900–1300°C using square-wave voltammetry. All diffusion coefficients had an Arrhenian dependence which depended on the type of alkali present and the Al₂O₃-concentration. Larger alkali cations, e.g. Cs⁺, as well as an increase in the Al₂O₃-content led to a decrease in the diffusion coefficients and also to an increase in viscosity. Within one glass composition, the Stokes–Einstein equation is fulfilled with respect to the dependence of the diffusivity upon viscosity. At constant viscosity, however, increasing size of the alkali cation and increasing Al₂O₃-content led to larger iron diffusion coefficients.     

Synthesis and characterization of ferrierite

Ferrierite, a medium-port molecular sieve zeolite, was synthesized as the only crystalline phase from an aqueous gel of composition 1.6 Na₂O · 1.6 K₂O · Al₂O₃ · 13.5 SiO₂ · 130 H₂O · 0.8 CO₂ · 2.4 (HCO₂)₂ at 250 °C in reaction periods ranging from 40 to 95 hours. The crystallization time was reduced with seeding. Ferrierite was a metastable phase in this system and it transformed into tridymite, high sanidine and orthoclase at longer reaction periods. At 200 °C, chabazite was crystallized from the same batch composition at a very slow rate. At temperatures higher than 250 °C and in the absence of carbonates and bicarbonates in the batch mixture, tridymite, high sanidine and orthoclase crystallized directly without the formation of ferrierite. The synthetic ferrierite sorbs benzene, toluene and cyclohexane and behaves as a medium port molecular sieve. The sorption capacity of ferrierite was improved by acid treatments with no deterioration of the crystal structure.     

The role of Al3+ ions in alumino borate glasses as revealed by molar volume,refractive index and microhardness

An attempt has been made determine the types of Al³⁺ structural units in potassium alumino borate glass. Therefore a number of investigations have been carried out on the relation between the composition of the glasses and their properties. The density, refractive index, and hardness of a number of compositions in which Al₂O₃ replaces B₂O₃ at constant K₂O were measured. It appears that the replacement of B₂O₃is not entirely without some consequencies.The concentration of non-bridging oxygen ions increases with the introduction of Al₂O₃.Non bridging oxygen ions start aappearing at alkali concentration of about 0.2 mol K₂O.     

Composition–structure–property relationships in boroaluminosilicate glasses

The complicated structural speciation in boroaluminosilicate glasses leads to a mixed network former effect yielding nonlinear variation in many macroscopic properties as a function of chemical composition. Here we study the composition–structure–property relationships in a series of sodium boroaluminosilicate glasses from peralkaline to peraluminous compositions by substituting Al₂O₃ for SiO₂. Our results reveal a pronounced change in all the measured physical properties (density, elastic moduli, hardness, glass transition temperature, and liquid fragility) around [Al₂O₃]–[Na₂O] = 0. The structural origin of this change is elucidated through nuclear magnetic resonance analyses and topological considerations. Furthermore, we find that addition of 1 mol% Fe₂O₃ exerts a complicated impact on the measured properties.     

The effect of composition on spinel crystals equilibrium in low-silica high-level waste glasses

The liquidus temperature (T_L) and the equilibrium mass fraction of spinel were measured in the regions of low-silica (less than 42 mass% SiO₂) high-level waste borosilicate glasses within the spinel primary phase field as functions of glass composition. The components that varied, one at a time, were Al₂O₃, B₂O₃, Cr₂O₃, Fe₂O₃, Li₂O, MnO, Na₂O, NiO, SiO₂, and ZrO₂. In the low-silica region, Cr₂O₃ increased the T_L substantially less, and Li₂O and Na₂O decreased the T_L significantly less than in the region with 42-56 mass% SiO₂. The temperature at which the equilibrium mass fraction of spinel was 1 mass% was 25-64 °C below the T_L.     

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.     

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.     

Preparation and properties of porous glass using fly ash as a raw material

The porous glasses were prepared by a conventional phase separation method using coal fly ash as a raw material, and the properties of these porous glasses were investigated. The composition of coal fly ash is basically composed of SiO₂–Al₂O₃–Fe₂O₃–CaO system and the SiO₂–B₂O₃–Al₂O₃–CaO–Na₂O system of glass was chosen as base glass composition. The pore diameter increases proportional to cube root of heating time (t^1/3), however, the early stage of phase separation is not clear. It is estimated that the rate determining step may be the diffusion process of structural units involving oxygen ions and the phase separation may take place by the nucleation and growth mechanism, and the relatively larger pores of above 1 μm can be obtained easily. The chemical composition of porous glasses is SiO₂–B₂O₃–Al₂O₃(–CaO–Na₂O). A relatively large amount of fly ash (>40%) can be used successfully for the preparation of porous glass.     

Effect of synthesis method on the structure and properties of AgPO3-based glasses

The relation between ionic conductivity, glass transition temperature and structure has been investigated in silver-metaphosphate, AgPO₃, glasses synthesized under varying conditions. The key finding of this work concerns the AgPO₃ doping with up to 3 mol.% Al₂O₃ when melting is done in alumina crucibles, a practice used widely for the synthesis of fast ion conducting glasses. Vibrational spectroscopy showed that Al₂O₃-doping increases the phosphate network connectivity by P-O-Al-O-P cross-links. This effect causes a drastic enhancement in ionic conductivity and glass transition temperature relative to Al₂O₃-free AgPO₃ glasses obtained by melting in Pt crucibles.     

Hydrothermal Synthesis and Morphology of Thomsonite and Edingtonite

The hydrothermal treatment of different glasses of the composition 2 Na₂O–8 CaO–10 Al₂O₃– 20 SiO₂ and 2 BaO–2 Al₂O₃–6 SiO₂ at one kilobar pressure in a temperature-range between 80 °C and 230 °C lead to the formation of the zeolite-minerals thomsonite (orthorhombic symmetry space-group Pbmn, a = 13.05 Å, b = 13.09 Å and c = 13.22 Å), and edingtonite (orthorhombic symmetry, space-group: P2,2,2, a = 9.55 Å, b = 9.67 Å and c = 6.52 Å). Under the chosen hydrothermal conditions both mineral phases are formed in the whole temperature interval.     

Nd3+:Y3Al5O12 laser ceramics: Influence of the size of yttrium oxide particles on sintering

The influence of the size of Y₂O₃ powder particles on the structure formation and densification of Nd³⁺:Y₃Al₅O₁₂ laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd³⁺:Y₃Al₅O₁₂ phase. Bulk swelling of pressed samples during sintering of 2.94Y₂O₃-0.06Nd₂O₃-5Al₂O₃ powders with the size ratio of the initial particles R(Al₂O₃/Y₂O₃) ～ 5 is observed. The application of different-sized powders (R ～ 2.5) provides quantitative ratios between phases in the 3Y₂O₃-5Al₂O₃ system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd³⁺:Y₃Al₅O₁₂ have been obtained by the solid-phase sintering of oxide powders (R ～ 2.5). The slope efficiency for 1 at % Nd³⁺:Y₃Al₅O₁₂ laser ceramics is found to be 33%.

     

Surface kinetics of nitrogen dissolution and its correlation to the slag structure in the CaO―SiO2, CaO―Al2O3, and CaO―SiO2―Al2O3 slag system

The kinetics of nitrogen dissolution into molten slag at 1873 K was investigated by an isotope exchange technique. Rate constants were correlated with the molten slag structure obtained from FT-IR spectra. The rate constant in the CaO―SiO₂ binary system showed a maximum value at a specific slag composition followed by a decrease in the rate due to excess O²⁻ blocking the surface sites for nitrogen adsorption. The rate constant in the CaO―Al₂O₃ binary system was comparatively constant within the experimental range of 45 mass% to 60 mass%. The rate constant in the CaO―SiO₂―Al₂O₃ ternary slag system was measured within the boundary of the liquidus line and showed a close correlation with the slag structure. Furthermore, the rate constant in the CaO―SiO₂―Al₂O₃ ternary system was found to be significantly higher compared to the binary system due to the correlated effect of lower binding energies of the Al―O bonds and the increased number of reaction sites available when smaller Si―O tetrahedral were simultaneously present with Al―O bonds.