Mictomagnetism in a new BaO.Fe2O3.B2O3 glass.

An homogeneous BaO ·Fe₂O₃ ·B₂O₃ glass containing 30% Fe₂O₃ is prepared by a splat-cooling technique. X-ray and electron diffraction reveal the product to be amorphous at room temperature. The crystallization, as shown by DTA studies, begins at 750 K, and up to 950 K, a temperature at which BaFe₁₂O₁₉ is shown to be present, the crystallizing products are mainly evolutive.The magnetic measurements show a probably mictomagnetic behaviour at low temperature with a maximum of magnetic susceptibility at 12 (±1) K. At higher temperature the susceptibility obeys a Curie-Weiss law with large negative Weiss constant and low Curie constant per Fe³⁺ ions. After crystallization the product is ferrimagnetic and could be used as a permanent magnet.Mössbauer study reveals that the glass mainly consists of Fe³⁺ ions in distorted sites and a hyperfine structure at low temperature; the magnetic ordering temperature is estimated to be about 44 (±1) K.     

Al2O3 and Al2O3--TiN wear resistance in a simulated biological environment

Alumina is widely used as a biomaterial because of its high biocompatibility and its good mechanical properties except toughness. In this study, a composite material Al₂O₃–TiN is considered as an alternative, the addition of TiN improving the mechanical properties of alumina. The wear behaviour of Al₂O₃ and Al₂O₃–TiN in aqueous solutions simulating living environments has been thus compared using a pin on disc wear-testing machine. The results show that the mechanisms of material removal during wear are different. For alumina, a mechanical wear mechanism is observed, reduced by the lubricating action of the wet media, and alumina–TiN is worn by a combination of tribochemical and abrasive effects.     

Plasma spraying of Al2O3 and Al2O3Y2O3

A microstructural study has been carried out of plasma-sprayed Al₂O₃ and mixed and sintered Al₂O₃Y₂O₃. In order to ascertain the degree of metastability achieved by plasma spraying, these results are compared with a similar experiment utilizing a CO₂ laser for melting and the hammer-and-anvil technique for quenching of the same materials. X-ray diffraction methods were used to determine the obtained phases and crystal structures. In addition, transmission electron microscopy was used to confirm the phases present and to study their morpology. The porosity was studied with both mercury intrusion porosimetry and small angle neutron scattering. The addition of Y₂O₃ is shown to decrease the porosity from 15% to 7.5%. Adhesion is likewise related to the addition of Y₂O₃ and it is seen that adhesion of the mixture is measurably improved over that of pure Al₂O₃. The implication of these results is discussed.     

The structure of Al2O3-Cr2O3 powders condensed from a plasma

The structure of Al₂O₃-Cr₂O₃ powders prepared by plasma oxidation of the mixed halides has been examined by X-ray diffraction, electron microscopy and electron spin resonance. The powders consisted predominantly of faceted spherical particles of a well crystallized solid solution of Cr₂O₃ in θ-Al₂O₃, with diameters of the order of 0.1 μm. Some larger particles of α-Cr₂O₃ were present in powders containing 17.8 and 24 wt% Cr₂O₃. The maximum solid solubility of Cr₂O₃ in θ-Al₂O₃ observed was 18 wt%. It is suggested that nucleation of crystallization of liquid Al₂O₃-Cr₂O₃ droplets occurs as a structure based on cubic close packing of oxygen ions and that the presence of chromium results in ordering to the θ-Al₂O₃ form rather than the δ-Al₂O₃ form usually observed in alumina powders prepared by plasma methods.     

Subsolidus,high temperature phase relations in the systems Al2O3-Cr2O3-ZrO2, MgO-Cr2O3-ZrO2 and MgO-Al2O3-ZrO2

In the temperature range 1600 to 1900° C, the system A₂O₃-Cr₂O₃-ZrO₂ is characterized by the coexistence of ZrO₂ (unstablilized) and an (Al, Cr)₂O₃ solid solution series. In the systems MgO-Cr₂O₃-ZrO₂ and MgO-Al₂O₃-ZrO₂ a nearly stoichiometric spinel coexists with both stabilized and unstabilized ZrO₂. At temperatures above 1600°C a new ternary Mg-Al-Zr oxide becomes stable in the MgO-rich part of the MgO-Al₂O₃-ZrO₂ system.     

Electronic Conduction in the Na2O ·nAl2O3–Y2O3 System

The electronic conductivity of Na₂O · nAl₂O₃–Y₂O₃ materials is found to vary from 10^–5 to 10^–1 S/m between room temperature and 800°C and to increase from 10^–5 to 10^–4 S/m as the frequency increases from 100 Hz to 200 kHz. The temperature variation of conductivity is interpreted in terms of the energy band structure.     

Microstructure and Strength of Al2O3/Al2O3 Joints Bonded with ZnO-Al2O3-B2O3-SiO2 Glass-Ceramic

ZnO-Al2O3-B2O3-SiO2 （ZABS） glass powder was used as interlayer to join alumina ceramics. The effect of joining temperature on the microstructure and strength of joints was investigated. The results showed that the ZABS glass can react with alumina substrate to form a layer of ZnAl2O4 at Al2O3/glass interface. Bending test exhibited that low joining temperature （1150℃） led to low joint strength due to the formation of pores in the interlayer, originated by high viscosity of the glass. High joining temperature （1250 ℃） also resulted in low joint strength, because of large CTE （coefficient of thermal expansion） mismatch between amorphous interlayer and alumina substrate. Therefore, only when the joining temperature was appropriate （1200℃）, defect-free interface and high joint strength can be obtained. The optimum joint strength reached 285 MPa, which was the same as the base material strength.     

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.     

La2O3在MgO-Al2O3-SiO2-TiO2微晶玻璃中的作用

在ＭｇＯ－Ａｌ_２Ｏ_３－ＳｉＯ_２－ＴｉＯ_２玻璃中添加不同数量的氧化镧,采用差热分析、Ｘ射线衍射及电子显微镜等技术研究了氧化镧对玻璃析晶过程与力学性能的影响．氧化镧的加入使玻璃中析出α－堇青石相的温度降低;同时避免了高膨胀方石英相的析出．随着氧化镧加入量的增加,玻璃整体析晶能力下降,微晶玻璃中晶相含量减少,晶粒尺寸增大,微晶玻璃的弹性模量与硬度减小,断裂韧性增加,体现出大尺寸长柱状金红石晶粒的增韧作用．     

Phase formation kinetics in SrO-Al2O3-SiO2-B2O3 glass

Phase formation in Sr-celsian glass, containing 3 wt% B₂O₃ (SA2SB), was investigated by using non-isothermal and isothermal kinetic analyses. While stoichiometric celsian (SA2S) glass showed two-stage crystallization of glass, from glassy state to hexacelsian and from hexacelsian to monocelsian, SA2SB glass showed direct crystallization of glass to monocelsian, resulting in considerable decrease in the temperature of monocelsian formation. The activation energy for monocelsian formation in SA2SB glass was 390 kJ/mol, which is lower than those for hexacelsian and monocelsian formation respectively in SA2S glass. The Avrami exponent of SA2SB glass was 2.0, indicating two-dimensional crystal growth with interface-controlled mechanism at a zero nucleation rate.     

Liquidus surface in the HfO2-Y2O3-La2O3 system

The liquidus surface in the HfO₂-Y₂O₃-La₂O₃ system was studied by differential thermal analysis in helium at temperatures of up to 2500°C, derivative thermal analysis in air at temperatures of up to 3000°C, x-ray diffraction, optical microscopy, and electron microscopy. The liquidus surface was found to comprise five primary crystallization fields-those of theH-Y₂O_3-,C-Y₂O_3-,F-HfO_2-, andX-La₂O₃-based solid solutions and the pyrochlore phase La₂Hf₂O₇. Three invariant equilibria were identified in the system studied-two peritectics and one eutectic.