The solubility of selenate-AFt (3CaO·Al2O3·3CaSeO4·37.5H2O) and selenate-AFm (3CaO·Al2O3·CaSeO4·xH2O)

The Se(VI)-analogues of ettringite and monosulfate, selenate-AFt (3CaO·Al₂O₃·3CaSeO₄·37.5H₂O), and selenate-AFm (3CaO·Al₂O₃·CaSeO₄·xH₂O) were synthesised and characterised by bulk chemical analysis and X-ray diffraction. Their solubility products were determined from a series of batch and resuspension experiments conducted at 25 °C. For selenate-AFt suspensions, the pH varied between 11.37 and 11.61, and a solubility product, log K_so=61.29±0.60 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·3CaSeO₄·37.5H₂O+12 H⁺⇔6Ca²⁺+2Al³⁺+3SeO₄²⁻+43.5H₂O. Selenate-AFm synthesis resulted in the uptake of Na, which was leached during equilibration and resuspension. For the pH range of 11.75 to 11.90, a solubility product, log K_so=73.40±0.22 (I=0 M), was determined for the reaction 3CaO·Al₂O₃·CaSeO₄·xH₂O+12 H⁺⇔4Ca²⁺+2Al³⁺+SeO₄²⁻+(x+6)H₂O. Thermodynamic modelling suggested that both selenate-AFt and selenate-AFm are stable in the cementitious matrix; and that in a cement limited in sulfate, selenate concentration may be limited by selenate-AFm to below the millimolar range above pH 12.     

Low-temperature sintering and microwave dielectric properties of 3Z2B glass–Al2O3 composites

A potential low temperature co-fired ceramics system based on zinc borate 3ZnO–2B₂O₃ (3Z2B) glass matrix and Al₂O₃ filler was investigated with regard to phase development and microwave dielectric properties as functions of the glass content and sintering temperature. The densification mechanism for 3Z2B–Al₂O₃ composites was reported. The linear shrinkage of 3Z2B glass–Al₂O₃ composites exhibited a typical one-stage densification behavior. XRD patterns showed that a new crystalline phase, ZnAl₂O₄ spinel, formed during densification, indicating that certain chemical reaction took place between the 3Z2B glass matrix and the alumina filler. Meanwhile, several zinc borate phases, including 4ZnO·3B₂O₃, crystallized from the glass matrix. Both of the reaction product phase and crystallization phases played an important role in improving the microwave dielectric properties of composites. The optimal composition sintered at 850–950 °C showed excellent microwave dielectric properties: ?_r = ∼5.0, Q·f₀ = ∼8000 GHz, and τ_f = ∼−32 ppm/°C at ∼7.0 GHz.     

Fabrication of Li2O-B2O3-P2O5 solid electrolyte by flame-assisted ultrasonic spray hydrolysis for thin film battery

Li₂O-B₂O₃-P₂O₅ glass soot was fabricated from aqueous precursor solution of a CH₃CO₂Li·2H₂O and BCl₃, POCl₃ by the flame-assisted ultrasonic spray hydrolysis. The aqueous precursor solution of the lithium acetates was first atomized with an ultrasonic vibrator (1.7 MHz). B₂O₃ and P₂O₅ were formed from BCl₃ and POCl₃ by oxy-hydrogen flame. Their properties were investigated by SEM, XRD, TGA-DSC and impedance analyzer. The formed particles in glass soot had spherical shape and the size of approximately 50-100 nm. XRD analysis revealed that the amorphous phase and crystalline phases were mixed in glass soot and the crystalline phases were B(OH)₃ and B₂O₃. The crystalline B(OH)₃ and B₂O₃ found in glass soot completely disappeared by heat treatment. Conductivity was measured by complex impedance method using impedance analyzer and the conductivity was 10⁻⁸ S/cm.     

Relationship between glass network structure and conductivity of Li2O-B2O3-P2O5 solid electrolyte

Solid state glass electrolyte, xLi₂O-(1 − x)(yB₂O₃-(1 − y)P₂O₅) glasses were prepared with wide range of composition, i.e. x = 0.35 - 0.5 and y = 0.17 - 0.67. This material system is one of the parent compositions for chemically and electrochemically stable solid-state electrolyte applicable to thin film battery. Lithium ion conductivity of Li₂O-B₂O₃-P₂O₅ glasses was studied in the correlation to the structural variation of glass network by using FTIR and Raman spectroscopy. The measured ionic conductivity of the electrolyte at room temperature increased with x and y. The maximum conductivity of this glass system was 1.6 × 10⁻⁷ Ω⁻¹ cm⁻¹ for 0.45Li₂O-0.275B₂O₃-0.275P₂O₅ at room temperature. It was shown that the addition of P₂O₅ reduces the tendency of devitrification and increases the maximum amount of Li₂O added into glass former without devitrification. As Li₂O and B₂O₃ contents increased, the conductivity of glass electrolyte increased due to the increase of three-coordinated [BO₃] with a non-bridging oxygen (NBO).     

Manifestation of the mixed-cation effect in dilatometric properties of RO (R2O) · 2B2O3 borate glasses upon replacement of Na2O by BaO, Na2O by MgO, and BaO by MgO

The dilatometric properties, such as the temperature coefficient of linear expansion in the range 20–300°C, the structural temperature coefficient of linear expansion, and the glass transition temperature T_g of RO(R₂O) · 2B₂O₃ glasses are investigated upon replacement of Na₂O by BaO, Na₂O by MgO, and BaO by MgO. It is revealed that, upon these replacements, the composition dependence of the temperature coefficient of linear expansion exhibits an additive behavior, whereas the composition dependences of the structural temperature coefficient of linear expansion and the glass transition temperature T_g deviate from an additive behavior. These regularities are associated with the difference in the energy of cation-oxygen bonds and a different effect of cations on the coordination state of boron.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Pevzner, Klyuev.     

Single crystal nanobelts of V3O7·H2O: A lithium intercalation host with a large capacity

In this study, single crystal V₃O₇·H₂O nanobelts were successfully synthesized using a simple hydrothermal route, in which templates or catalysts were absent. The synthesized V₃O₇·H₂O nanobelts are highly crystalline and have lengths up to several tens of micrometers. The width and thickness of the nanobelts are found to be about 30-50 and 30 nm, respectively. A lithium battery using V₃O₇·H₂O nanobelts as the positive electrode exhibits a high initial discharge capacity of 409 mAh g⁻¹, corresponding to the formation of Li_xV₃O₇·H₂O (x = 4.32). Such a high degree of electrochemical performance is attributed to the intrinsic properties of the single-crystalline V₃O₇·H₂O nanobelts.     

Fuel mixture approach for solution combustion synthesis of Ca3Al2O6 powders

Single-phase 3CaO·Al₂O₃ powders were prepared via solution combustion synthesis using a fuel mixture of urea and β-alanine. The concept of using this fuel mixture comes from the individual reactivity of calcium nitrate and aluminum nitrate with respect to urea and β-alanine. It was proved that urea is the optimum fuel for Al(NO₃)₃ whereas β-alanine is the most suitable fuel for Ca(NO₃)₂. X-ray diffraction and thermal analysis investigations revealed that heating at 300 °C the precursor mixture containing the desired metal nitrates, urea and β-alanine triggers a vigorous combustion reaction, which yields single-phase nanocrystalline 3CaO·Al₂O₃ powder (33.3 nm). In this case additional annealing was no longer required. The use of a single fuel failed to ensure the formation of 3CaO·Al₂O₃ directly from the combustion reaction. After annealing at 900 °C for 1 h, the powders obtained by using a single fuel (urea or β-alanine) developed a phase composition comprising of 3CaO·Al₂O₃, 12CaO·7Al₂O₃ and CaO.     

Hydrothermal synthesis and characterizations of 2D and 3D 4ZnO·B2O3·H2O nano/microstructures with different morphologies

2D and 3D nano/microstructures of 4ZnO·B₂O₃·H₂O with different morphologies have been successfully synthesized by a hydrothermal route in the presence of surfactant polyethylene glycol-300 (PEG-300). Lamellar-like nanoparticles and microsphere organizations of nano and microrods are fabricated by varying the reaction conditions. The products have been characterized by XRD, FT-IR, TG-DTA and SEM. The XRD data indicate the as-prepared samples present at pure phase 4ZnO·B₂O₃·H₂O with monoclinic symmetry. The SEM results reveal that the lamellar-like particles are about 30 nm in thickness and around several hundred nanometers in diameter. The microsphere organizations have different diameters, and the secondary structures are made from rod-like particles with different size and mode, respectively. The morphologies of products strongly depend on surfactant, hydrothermal temperature and time.     

Low-temperature synthesis of ZnNb2O6 powders via hydrothermal method

ZnNb₂O₆ powder was successfully synthesized via hydrothermal method with Nb₂O₅ and Zn(NO₃)₂·6H₂O as raw materials and cyclohexane as solvent. Phase composition, morphology, and chemical composition were determined via a combination of XRD, SEM, TEM and EDS techniques. The effects of synthesis temperature and reaction time on phase composition and particle morphology were investigated in this paper. The results showed that fine ZnNb₂O₆ powders could be obtained at a hydrothermal temperature of 190 °C or above under different reaction time.     

Precursor effects on ZrW2O8 formation kinetics

The synthesis of ZrW₂O₈ from different kinds of mixtures containing ZrO₂–WO₃, ZrO(NO₃)₂·2H₂O–WO₃, ZrCl₂O·8H₂O–WO₃, and ZrO₂–(NH₄)₁₀W₁₂O₄₁·5H₂O was investigated, and the kinetics was analyzed using JMA equation. It was found that ZrO(NO₃)₂·2H₂O, ZrCl₂O·8H₂O H₂O and (NH₄)₁₀W₁₂O₄₁·5H₂O that were used as inorganic precursors formed ZrO₂ and WO₃ after firing above 500 °C. The content of ZrW₂O₈ obtained by firing the mixtures is influenced by the kinds of precursors as well as mixing methods. The formation rate of ZrW₂O₈ depends on homogeneity related to mixing methods as well as the particle size of starting powders. Phase-pure ZrW₂O₈ is obtained from the ZrCl₂O·8H₂O–WO₃ mixtures at 1200 °C for 4 h, which is much shorter time than in the case of conventional ZrO₂–WO₃ mixtures. In the reaction kinetics of ZrO₂–WO₃ system, the Avrami exponent (n) is ∼0.5 above 1175 °C, indicating that the reaction is controlled by the diffusion-controlled reaction.     

Synthesis of an industrially important zinc borate, 2ZnO·3B2O3·3H2O, by a rheological phase reaction method

2ZnO·3B₂O₃·3H₂O is an industrially important zinc borate. Herein, 2ZnO·3B₂O₃·3H₂O has been prepared via a rheological phase reaction method using zinc oxide and boric acid as starting materials. This route is facile and acceptable for green chemical synthesis, producing no pollution and giving a yield of near 100% of theoretical value. And in this method, the complete conversion of the starting materials can be achieved in the presence of only 0.04 mL water (one drop of water). The products have been characterized by X-ray powder diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), scanning electron microscopy (SEM) and particle size distribution. The effects of experimental conditions on the products were investigated. The main factors that affect the formation of zinc borate are water volume, sealing state, reaction time and temperature.     

Controllable synthesis and flame retardant properties of bunch-, chrysanthemum-, and plumy-like 4ZnO·B2O3·H2O nanostructures

Three kinds of new 4ZnO·B₂O₃·H₂O nanostructures of bunch-, chrysanthemum-, and plumy-like morphologies have been synthesized under hydrothermal conditions at 140 °C in the presence of ethanol. The as-synthesized products were characterized by the chemical analysis, TG, XRD, FT-IR, SEM and TEM. All the synthesized 4ZnO·B₂O₃·H₂O nanostructures consist of nanoribbons. A series of control experiments confirmed that the morphologies of the products were influenced by the reaction time, temperature, and the presence of the surfactant of PEG-300. Furthermore, the flame retardant properties of the synthesized 4ZnO·B₂O₃·H₂O nanostructures were investigated by the thermal analysis method, demonstrating that they had the better behaviors than the non-nanostructure sample.     

Influence of CuO on the formation and coexistence of 3CaO·SiO2 and 3CaO·3Al2O3·CaSO4 minerals

The influence of CuO on the formation and coexistence of 3CaO·SiO₂ and 3CaO·3Al₂O₃·CaSO₄ minerals in Portland cement containing 3CaO·3Al₂O₃·CaSO₄ mineral is reported in this paper. The results show that a suitable amount of CuO can lower the clinkering temperature and improve the burn-ability of clinkers. It can also promote the formation of 3CaO·SiO₂ and 3CaO·3Al₂O₃·CaSO₄ minerals and facilitate the coexistence of the two minerals in the clinkers. But adding 1% CuO to the raw material can cause the decomposition of 3CaO·3Al₂O₃·CaSO₄.     

Preparation and characterization of Cr2O3-TiO2-Al2O3-V2O5 green pigment

Green pigments with high near infrared reflectance based on a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition have been synthesized. Cr₂O₃ was used as the host component and mixtures of TiO₂, Al₂O₃ and V₂O₅ were used as the guest components. TiO₂, Al₂O₃, and V₂O₅ were mixed into 39 different compositions. The spectral reflectance and the distribution of pigment powder were determined using a spectrophotometer and a scanning electron microscope, respectively. It was found that a pigment powder sample S9 with a Cr₂O₃-TiO₂-Al₂O₃-V₂O₅ composition of 80, 4, 14 and 2 wt%, respectively, gives a maximum near infrared solar reflectance of 82.8% compared with 49.0% for pure Cr₂O₃. The dispersion of pigment powders in a ceramic glaze was also studied. The results show that the pigment powder sample S9 is suitable for use as a coating material for ceramic-based roofs.     

Glass transition and crystallization of ZnO-B2O3-SiO2 glass doped with Y2O3

The effect of Y₂O₃ on the glass transition kinetics, crystallization kinetics, phase separation and crystallization behavior of 60ZnO–30B₂O₃–10SiO₂ glass has been investigated by non-isothermal differential thermal analysis, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The glass transition activation energies E_g calculated by using both Kissinger and Moynihan model decrease from 668?kJ/mol to 573?kJ/mol for Kissinger model, and 682?kJ/mol to 587?kJ/mol for Moynihan model with the increase of yttrium oxide doping content from 0 to 6?mol%. And the glass crystallization kinetics parameters, crystallization activation energy E_c and Avrami exponent n stands for crystal growth, are also obtained on the basis of several well developed equations. Increase of about 58?kJ/mol in Ec values obtained by different theoretical equations is caused by addition of 6?mol% yttrium oxide into 60ZnO–30B₂O₃–10SiO₂ glass, and the Avrami exponent (n close to 2) suggests that crystal growth in 60ZnO–30B₂O₃–10SiO₂ glass doped with or without yttrium is mainly one-dimensional growth of crystals. The results on the phase separation and crystallization behavior occurred at 893?K and 993?K respectively for base and doped glass, are well consistent with the glass transition and crystallization kinetics results. Hence, addition of yttrium oxide into 60ZnO–30B₂O₃–10SiO₂ glass decrease the glass transition activation energy while increase the crystallization activation energy of glass, thereby the stability of glass structure is improved. Phase separation phenomenon and crystallization behavior occurred at glass surface provide some useful information for preparing glass ceramics with micro- or nano-crystals in surface.     

Study on non-isothermal crystallization kinetics of the BaO-CaO-Al2O3-B2O3-SiO2 glass for IT-SOFCs sealing

The crystallization ability plays a key role in effecting thermal ability of sealing glass for intermediate temperature-solid oxide fuel cells (IT-SOFCs) to prevent fuel leakage during operation and insulate the cell stack from the external atmosphere. Herein, using differential thermal analysis (DTA) techniques, the growth mode of crystals precipitated in BaO-CaO-Al₂O₃-B₂O₃-SiO₂ (BCABS) sealing glass through the heat treatment was calculated in terms of non-isothermal crystallization kinetics for the first time. The calculated results showed that the average kinetic exponent n of the glass was approximatively 1, indicating that the crystal nucleuses became to form and further grew with one-dimensional mode from the surface inwards. Scanning electron microscope (SEM) observations clearly revealed that a large number of one-dimensional filamentous crystals have been formed on the interface between the sealing glass and the electrolyte after the heat treatment at 973?K for 100?h, which perfectly coincided with the theoretical calculations, and the glass was well combined with the electrolyte without any visible cracks or peeling at the interface. The one-dimensional growth of hexagonal BaAl₂Si₂O₈ crystals verified by X-ray diffraction (XRD) could effectively decelerate the decrease of thermal expansion coefficient of glass to ensure enhance the thermo-stability of the BCABS sealing glass for IT-SOFC.     

Molten salt synthesis of α-Al2O3 platelets using NaAlO2 as raw material

α-Al₂O₃ platelets were prepared by a molten salt synthesis method when NaAlO₂ was used as raw material. The effects of the stirring rate during the gel preparation, heating temperature, type and addition amount of molten salts, addition of plate-like α-Al₂O₃ seeds, additives such as TiOSO₄ and Na₃PO₄·12H₂O on the morphology of α-Al₂O₃ were studied. High stirring rate during the gel preparation and high heating temperature not only help to restrain the overlapping of α-Al₂O₃ platelets, but also improve the size distribution. When the heating temperature increases to 1200 °C, most of α-Al₂O₃ platelets are hexagonal in its morphology, and the size of platelets becomes relatively uniform. When Na₂SO₄-K₂SO₄ flux is used instead of NaCl-KCl flux, it is easy to obtain α-Al₂O₃ platelets with a big size. When the molar ratio of salt to final Al₂O₃ powders increases to 4:1, most of α-Al₂O₃ platelets are hexagonal, and the overlapping of powders is inhibited. The addition of a small amount of plate-like seeds has a significant effect on the size of α-Al₂O₃ platelets. With the increase of seed amount, the diameter of α-Al₂O₃ platelets tends to decrease. The addition of 5.45 wt.% TiOSO₄ results in the formation of hexagonal α-Al₂O₃ platelets with an average diameter of 5.1 μm and an average thickness of 1.4 μm. Thin α-Al₂O₃ platelets with a discal shape are obtained owing to the co-addition of 0.51 wt.% Na₃PO₄·12H₂O and 3 wt.% TiOSO₄.     

Simple fabrication of polyhedral grain-like microparticle Cu0.5Zn0.5HPO4·H2O and porous structure CuZnP2O7

Polyhedral grain-like microparticle Cu_0.5Zn_0.5(HPO₄)·H₂O was simply synthesized by heterogeneous reaction using a mixture of CuCO₃, ZnO, phosphoric acid and water at room temperature for 30 min. The thermogravimetric study indicates that the synthesized compound is stable below 250 °C and its final decomposed product is CuZnP₂O₇. The pure monoclinic phases of the synthesized Cu_0.5Zn_0.5(HPO₄)·H₂O and its final decomposed product CuZnP₂O₇ are verified by XRD data. The presences of the HPO₄²⁻ ion and H₂O molecule in the Cu_0.5Zn_0.5(HPO₄)·H₂O structure and the P₂O₇⁴⁻ ion in the CuZnP₂O₇ structure are confirmed by FTIR data. The thermal stability, the morphology based on polyhedral grain-like microparticles and porous structure of the studied compounds are different from previously reported phosphates, and may affect their activities for potential applications (catalysis, electronics, etc.).     

Influence of glass phase on Al2O3 fiber-reinforced Al2O3 composites processed by slip casting

The present work describes the processing of alumina fiber reinforced alumina ceramic preforms consisting of chopped Al₂O₃ fibers (33 wt%) and Al₂O₃ (67 wt%) fine powders by slip casting. The preforms were pre-sintered in air at 1100 °C for 1 h. A lanthanum based glass was infiltrated into these preforms at 1250 °C for 90 min. Linear shrinkage (%) was studied before and after glass infiltration. Pre-sintered and infiltrated specimens were characterized by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, porosimetry and flexural strength. The alumina preforms showed a narrow pore size distribution with an average pore size of ∼50 nm. It was observed that introducing Al₂O₃ fibers into Al₂O₃ particulate matrix produced warp free preforms with minor shrinkage during pre-sintering and glass infiltration. It was observed that the infiltration process fills up the pores and considerably improves the strength and reliability of alumina preform.     

Structural, thermal and crystallization kinetics of ZnO–BaO–SiO2–B2O3–Mn2O3 based glass sealants for solid oxide fuel cells

Glass compositions in the system 40SiO₂–30BaO–20ZnO–(x)Mn₂O₃–(10 − x)B₂O₃ glasses have been synthesized and the thermal, structural and crystallization kinetic properties characterized. The lower concentration of Mn₂O₃ in place of B₂O₃ acts as a network former and suppressed the tendency of phase separation in glasses. On the other hand, concentration of Mn₂O₃ > 7.5 mol% induce phase separation in the glass matrix. The highest activation energy for crystallization is observed in the composition without B₂O₃ (INM4) (355 kJ/mol). The values of thermal expansion coefficient (TEC) and viscosity of this glass is 8 × 10⁻⁶ K⁻¹ and 10^4.2dPa s (850 °C), respectively. After long heat treatment (800 °C for 100 h), thermodynamically stable hexacelsian and monoclinic phases are formed. These phases are not detrimental to SOFC application.