Flux growth of Fe2TiO4 from BaO-B2O3 in an iron crucible

Crystals of titanomagnetite have been grown from a barium borate flux in an iron crucible under an atmosphere of nitrogen following preliminary phase equilibrium and solubility studies. The crystals were octahedral, up to 4 mm in width, and their composition corresponded to the formula Fe_2.12 Ti_0.88 O₄. The Néel point was found to be 195 K.     

Wetting of gold by Bi2O3-B2O3 melts

The wetting of gold by Bi₂O₃-B₂O₃ melts has been studied by the sessile drop method, with the sample and substrate heated separately before being brought into contact. Only the melts containing 18.5 and 33.3 mol % B₂O₃ were found to have steady-state contact angles.     

Surface tension of PbO-B2O3 and Bi2O3-B2O3 glass melts

The surface tensions of xPbO-(100?x) B₂O₃ (x = 30–80 mol%) and xBi₂O₃-(100?x) B₂O₃ (x = 0–100 mol%) melts were measured using the ring method over the temperature range 973 to 1373 K. The compositional and temperature dependences of surface tension were investigated. Addition of PbO and Bi₂O₃ to B₂O₃ increased the surface tensions of their respective PbO-B₂O₃ and Bi₂O₃-B₂O₃ melts. The surface tension showed a maximum at 60 mol% PbO in the PbO-B₂O₃ melts and at 70–80 mol% Bi₂O₃ in the Bi₂O₃-B₂O₃ melts. The temperature coefficient of surface tension was examined on the basis of its relationship to the structure, and it was suggested that the temperature coefficient of surface tension decreases with an increasing content of four-coordinated boron.     

含钡玻璃粉体的表面修饰及其表征

为了降低BaO-B2O3-SiO2玻璃中钡离子在水中的析出，通过硫酸处理法对玻璃粉体进行了表面修饰，在玻璃粉体的表面形成一层不溶于水的BaSO4，从而阻断了钡离子与水的接触途径，使玻璃粉体更容易制备稳定的水基流延浆料，操作简便，且无毒副作用。研究发现生成的BaSO4层的厚度与硫酸的浓度和处理时间相关；硫酸钡层明显提高了玻璃粉的烧结温度。     

Phase equilibrium relations in the V2O3-La2O3 system

Phase equilibrium relations in the V₂O₃-La₂O₃ system were investigated by X-ray powder diffraction and metallographic techniques. Binary mixtures, prepared from high-purity V₂O₃ and La₂O₃ powders, were equilibrated at 1600° C and then arc-melted under a partial pressure of argon. The specimens were heat-treated at various predetermined temperatures for prolonged periods and the phases present were identified by reflected-light microscopy and X-ray powder diffraction. The system consists of only one binary compound LaVO₃. A eutectic between V₂O₃ and LaVO₃ was established at 1750° C and 19 mol % La₂O₃ and also between LaVO₃ and La₂O₃ at 1765° C and 75 moi % La₂O₃. No appreciable solid solubility was detected in the system.     

Effect of heat treatment and irradiation on electrical conductivity and crystallization in the BaO-B2O3-Fe2O3 glass system

A glass system was prepared according to the formula 75 mol % B₂O₃-(25 –x) mol % BaO –x mol % Fe₂O₃, wherex = 0, 1, 2.5, 5, 7.5 and 10. The glasses were subjected to heat treatment at 550° C for 2, 6, 12, 18 and 24 h. The glasses were also irradiated using-rays at a dose of 4.805 × 10⁴ rad h^–1 for 12, 18 and 24 h. An X-ray diffraction technique was used to identify the separated crystalline phases. The electrical conductivity and activation energy of untreated, heat-treated and irradiated samples were measured and calculated. The rate and the dimensions of crystallization were also calculated by using the Avrami equation. It was found that-Fe₂O₃ is the separated phase when a sample containing 7.5 mol% Fe₂O₃ is heat treated for 24h;-Fe₂O₃ and Fe₂O₃ are the separated phases when the sample containing 10 mol% Fe₂O₃ is heat treated for 6, 12 and 18 h, with the addition of BaO when the sample is heat treated for 24 h. A miminum value for the electrical conductivity of glass samples was found to occur around an Fe₂O₃/BaO ratio of 0.425. The rate of crystallization in the sample containing 10 mol% Fe₂O₃ is 1.30607 × 10^–3 and the geometry of crystallizationn is 1.2238, which indicates that the crystallization was in one dimension.     

BaO-B2O3-SiO2玻璃助剂对ZST陶瓷烧结和性能的影响

研究了BaO-B2O3-SiO2玻璃助剂对TiO2/Zn2SiO4(ZST)复合陶瓷的烧结特性和微波介电性能的影响.BaO-B2O3-SiO2玻璃助剂在烧结过程中能形成液相,有效地将ZST复合陶瓷的烧结温度从1340℃降低至970℃.随助剂用量的增加,Zn2SiO4陶瓷的介电常数(εr)略有提高,品质因数与频率的乘积(Q×f)下降,频率温度系数(τf)无明显变化.添加8%(质量分数,下同)BaO-B2O3-SiO2玻璃助剂和一定质量比的TiO2(m(TiO2):m(Zn2SiO4)=11:89)的ZST复合陶瓷在970℃保温4h,具有较好的微波介电性能:εr=8.70,Q×f=21280GHz,τf=-9×10-6/℃.     

Phase equilibrium in the TeO2-B2O3-V2O5 system

Journal of Materials Science Letters -     

Thermodynamics of Cr3+-Cr6+ equilibrium in borate melts

The Cr³⁺-Cr⁶⁺ equilibrium was studied in lithium and sodium aluminoborate melts in an air atmosphere at different temperatures. A mechanism of the Cr³⁺-Cr⁶⁺ redox reaction in glass melts has been suggested. Enthalpy and entropy of the reaction in molten borates were calculated and the results thus obtained have been discussed thermodynamically.     

SiO2-Al2O3 metastable phase equilibrium diagram without mullite

A metastable binary phase diagram between SiO₂ (cristobalite) and-Al₂O₃ (corundum) in the absence of any mullite phase is presented. A eutectic is indicated at a temperature of 1260° C and a composition of 18 wt% ( 12 mol%) Al₂O₃. The liquidi of the proposed metastable system were positioned on the basis of the thermodynamic data calculated from the stable equilibrium diagram of Aksay and Pask [2]. Experimental evidence is also presented. A SiO₂-Al₂O₃ melt containing 80 wt% Al₂O₃ cooled at a slow rate in sealed molybdenum crucibles shows crystalline Al₂O₃ plus a glass phase whose composition followed the calculated extension of the stable Al₂O₃ liquidus to lower temperatures. Compacts of cristobalite—corundum mixtures were fired at subsolidus temperatures to estimate the eutectic temperature experimentally. The proposed metastable phase diagram effectively explains the formation of non-crystalline phases in subsolidus reactions, and microstructure obtained on solidification of high alumina melts.     

Oxidation-reduction equilibria of vanadium in CaO-SiO2, CaO-Al2O3-SiO2 and CaO-MgO-SiO2 melts

A series of redox studies of vanadium have been carried out in CaO-SiO₂, CaO-MgO-SiO₂ and CaO-Al₂O₃-SiO₂ melts/slags equilibrated over oxygen partial pressures (pO₂) range 10^–2–10^–9 atm at 1600°C. V₂O₅ level was varied from 1–5 mol%. Three different melt basicities and alumina contents were investigated. Magnesia content was varied between 3.5 and 4.9 wt%. A newly developed analytical technique based upon electron paramagnetic resonance (EPR) spectroscopy was successfully applied to these melts. Two redox equilibria corresponding to V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ pairs followed the O-type redox reaction over the oxygen partial pressure range investigated. Higher oxidation states of vanadium were stabilized with increasing basicity of slags. Two redox pairs coexisted within oxygen pressure region 10^–4–10^–6 atm. However, redox ratios did not indicate clear trends with increasing V₂O₅ content in CaO-SiO₂-V₂O₅ system. In CaO-SiO₂-Al₂O₃-V₂O₅ slags, a slight increase in redox ratios (V³⁺/V⁴⁺) was obvious when alumina quantity was changed from 3.22 to 5.44% at a basicity ratio 1.3, indicating an increase in slag acidity. CaO-MgO-SiO₂-V₂O₅ slags showed a sharp decrease in redox ratios (V⁴⁺/V⁵⁺) between 10^–2–10^–6 atm with addition of 3.5 wt% MgO, due to increasing free oxygen ions in slags.     

Corrosion of S3N4 and sialons in V2O5 melts

Si₃N₄ based ceramics such as hot isostatically pressed Si₃N₄, hot pressed Si₃N₄, hot pressed sialons containing 0, 30, 60 and 100% of phase were corroded by V₂O₅ melts at 700 to 1000C. These Si₃N₄-based ceramics were oxidized to SiO₂ and dissolved into V₂O₅ melts. The surface chemical reaction controlled shrinking core model adequately described the relationship between the weight loss of the specimen and time for the corrosion reactions in V₂O₅ melts, and the apparent activation energies were 69 to 112kJ mor^–1. phase Si₃N₄ and sialon showed higher corrosion resistance than phase sialons, but no clear relationship between the corrosion rate and the content of additives was found. The specimens corroded by V₂O₅ melts showed no significant degradation in the fracture strength up to 30wt% of weight loss.     

Phase equilibrium relations in the binary system Bi2O3-ZnO

Phase equilibria in the binary system Bi₂O₃-ZnO were studied by quenching technique. Heat-treated compositions were subjected to X-ray diffraction for phase identification, and differential thermal analysis, optical and scanning electron microscopy were used to determine the solid-liquid equilibria occurring in this system. The data thus obtained revealed that incorporation of a small amount of ZnO to the high-temperature face-centered cubic lattice of Bi₂O₃ leads to the formation of a body-centered cubic solid solution (-Bi₂O₃), which extends up to a composition of 2.2 mol% ZnO at a temperature near 750°C. On cooling, the -Bi₂O₃ solid solution undergoes a eutectoid transformation at a temperature of 710°C to yield the low-temperature monoclinic polymorph of Bi₂O₃ (-Bi₂O₃) and Bi₃₈ZnO₅₈. The eutectoid occurs at a composition of 1.8 mol% ZnO. The compound Bi₃₈ZnO₅₈ has a crystal structure analogous to the body-centered cubic -Bi₂O₃ solid solution and melts incongruently at a temperature near 753 ± 2°C to yield -Bi₂O₃ and liquid. A binary eutectic occurs between Bi₃₈ZnO₅₈ and ZnO at a composition near 25 ± 1.0 mol% ZnO with a melting temperature of 738 ±2°C. Based on the data obtained in this study, a revised phase diagram of the binary system Bi₂O₃-ZnO is proposed.     

The phase equilibrium diagram of the system CaO-Al2O3-CaF2

The phase equilibria of the system CaO-Al₂O₃-CaF₂ have been studied by quenching in sealed platinum capsules followed by microscopic and X-ray examination of quenched products. The established phase diagram contains five ternary eutectics, two ternary peritectics and two invariant points of four-phase monotectic transformations. The system Al₂O₃-CaF₂ has been established to be the stable diagonal of the reversible reciprocal system Al₂O₃ + 3CaF₂ = 3CaO + 2AlF₃. In the high-fluoride region a wide zone of liquid immiscibility has been found. The system also shows such rarely noticed but theoretically possible phenomena as the transformation of peritecticals into eutecticals and occurrence of three different primary fields under single continuous zone of liquid immiscibility.     

Formation of diffusionlessly transformed tetragonal phases in rapid quenching of ZrO2-Y2O3 melts

ZrO₂ polycrystals, partially stabilized by 2 to 7 mol% Y₂O₃, were arc-melted and rapidly quenched using an arc-imaging furnace with a hammer-anvil unit. Some of the specimens were further annealed at 1700° C for 3 h in air. The phases and the microstructures of these ZrO₂-Y₂O₃ polycrystals were examined through X-ray diffraction and transmission electron microscopy. Special emphasis was placed upon the examination of the microstructure of the metastable tetragonal phase (t phase) which was formed by a diffusionless transformation of the high-temperature cubic phase. It was found that the t phase exhibits a twinned and mosaic structure made of alternating layers of twin-related variants. A comparison of the present experimental results with other related works has also been made.     

Observation of CaO corrosion by K2O melts

A qualitative investigation of CaO single crystal and hot-pressed polycrystal behaviour in high K₂O melts is presented. Under carefully controlled anhydrous conditions, no intermediate crystalline compound was detected at temperatures up to 800° C. Calcium oxide dissolves preferentially along grain boundaries and/or along 1 0 0 directions on {1 0 0} faces. The melt viscosity gradually increases with its CaO content. The single crystal corrosion rate, therefore, decreases with time and a protective glassy layer may eventually develop on its surface.Supplied by Cristal-Tec, Grenoble, France.Prepared by calcination of CaCO₃, Prolabo, Paris, France.