Effect of additions of TiO2, SnO2, and Al2O3 on electrical properties of tetragonal zirconia

Abstract

The effect of additions of TiO₂ and SnO₂ on the tetragonal phase of the ZrO₂–Y₂O₃ system has been investigated using complex impedance, X-ray, and transmission electron microscopy measurements. Neither addition acts to stabilize the tetragonal phase and SnO₂ increases the specific grain boundary resistance by a factor of 3. Additions of Al₂O₃ improve the specific grain boundary conductivity of GPR (general purpose reagent) grade material to a level comparable to that of commercially available grades of tetragonal zirconia.

MST/558     

Effect of zirconia additions on the reaction sintering of aluminium titanate

Yttria-stabilized zirconia was added to a chemically prepared mixture of alumina and titania. The effect of the zirconia on the microstructure and resultant properties was studied following reaction sintering to form aluminium titanate. An increase in mechanical strength was observed with little effect on the excellent thermal properties of the aluminium titanate. This was attributed to generation of extra microcracks by the transformation of the zirconia phase and the unusual microstructure produced by the presence of zirconia.     

烧结温度对TiO2压敏陶瓷非线性和介电性质的影响

基于一次烧结工艺,通过改变烧结温度,制备5种组分相同、(Sr,Bi,Si,Ta)掺杂的TiO2陶瓷试样.借助于伏安特性、介电频率特性、损耗频率特性及非线性系数的测定,研究烧结温度对TiO2基压敏陶瓷压敏和介电性质的影响.结果表明,在1200～1400℃范围内,随着烧结温度的降低,陶瓷的压敏电压降低、介电常数增大,同时非线性系数有所减小.兼顾陶瓷压敏和介电特性,烧结温度选择1350℃为宜.     

Effect of B2O3 and CuO additions on the sintering temperature and microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics

The effects of B₂O₃–CuO (BCu, the weight ratio of B₂O₃ to CuO is 1:1) addition on the sintering behavior, microstructure, and the microwave dielectric properties of 3Li₂O–Nb₂O₅–3TiO₂ (LNT) ceramics have been investigated. The low-amount addition of BCu can effectively lower the sintering temperature of LNT ceramics from 1125 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 2 wt% BCu-added ceramic sintered at 900 °C has better microwave dielectric properties of ε _r  = 50.1, Q × f = 8300 GHz, τ _f  = 35 ppm/°C. Silver powders were cofired with the dielectric under air atmosphere at 900 °C. The SEM and EDS analysis showed no reaction between the dielectric ceramic and silver powders. This result shows that the LNT dielectric materials are good candidates for LTCC applications with silver electrode.     

MgO对(Ba,Pb)TiO3系PTC热敏材料性能的影响

研究了MgO对(Ba,Pb)TiO<,3>基高温PTC陶瓷材料性能的影响.结果表明,添加摩尔分数为0.059%MgO后,降低了烧结温度,促进Ba、Pb的固溶,材料居里温度提高30℃;电阻温度系数提高6%,PTC效应明显增强;并且此时室温阻值降低3倍.     

ZrB2对浸入式水口用ZrO2-C材料性能的影响

浸入式水口渣线材料性能的优劣决定着连铸安全和效率的高低,为提高浸入式水口渣线的性能,本研究在ZrO2-C材料中加入ZrB2,探讨ZrB2对ZrO2-C材料性能尤其是抗侵蚀性的影响.结果表明:ZrB2添加到ZrO2-C材料中后,会显著提高材料的抗氧化性,其机理是高温下ZrB2生成B2O3,B2O3在高温下为液相,堵塞气孔,大幅度减缓氧化.适量ZrB2添加到ZrO2-C材料中后,可以提高材料的抗侵蚀性.但ZrB2容易在CO气氛下生成B2O3,B2O3易使氧化锆脱溶、分解,加速ZrO2-C材料的侵蚀.     

Effect of glass additions on the sintering behaviors and electrical microwave properties of BaO–Nd2O3–Sm2O3–TiO2 ceramics

The effect of Al₂O₃-doped silica glass (AS-glass) addition on the structure and dielectric properties of the BaO–Nd₂O₃–Sm₂O₃–TiO₂ (BNST) microwave materials was investigated. This BNST material has a dielectric constant (k) of 80 and a quality factor (Q×f) of 6000 GHz when sintered at 1350 °C for 2 h. Both the microstructure and the microwave dielectric characteristics were determined as a function of the sintering temperature and glass content. A Q×f as high as 8700 GHz was achieved in ceramics added with 20 wt % glass, however, the k value drops to 30. The high Q×f value is attributed to the improved densification of the dielectric when glass is added. Results of X-ray diffraction experiments indicate that glass addition enhances the growth in the longitudinal direction of the columnar crystal and a preferred (0 0 2) orientation. The presence of columnar structure plays an important role in the improvement of the microwave dielectric properties.     

Effect of sintering on TiO2-impregnated alumina foams

The effect of sintering on the bulk properties, morphology and phase composition of ultralight Al₂O₃ foams impregnated with TiO₂ was investigated in comparison with pure alumina foam in the temperature range of 900–1600°C in air. Impregnation was carried out by immersion of pre-sintered alumina foam in a sol of titanium isopropoxide-acetylacetone complex. The changes of the foam linear shrinkage, effective density and porosity were studied along with morphological evolution and relationship between these properties was demonstrated. Titania impregnation increased the linear shrinkage (LS) during sintering by a maximum of 5% relative to pure alumina foams. The change of LS and weight loss of TiO₂/Al₂O₃ foams lead to a final density of 0.19 g/cm³ and porosity of 95%. The initial coating was found to develop a mosaic structure due to early shrinkage of the coating. After sintering at 1600°C the coating reacted with the underlying Al₂O₃ surface and became uniformly distributed. Finally, it was shown that the reacting TiO₂ layer formed the tialite (Al₂TiO₅) phase below 1400°C. This Tialite coating remained intact under 1200°C without stabilizers.     

钛酸铝陶瓷水基注凝成型工艺

本文采用水基凝胶注模成型工艺,通过控制技术参数,制备了固相含量为62%,粘度达到280mpa·s的钛酸铝陶瓷浆料.研究了抽真空时间对致密度以及固化时间的影响.随着有机单体和交联剂含量的增加,坯体的弯曲强度逐渐增大.通过分析影响因素,并改善制备条件,能够制备出强度为33.4MPa、可进行机加工的陶瓷坯体.     

TiO2- and Nb2O5-based photocatalytic composites

We have studied the influence of Nb content (0.35–60 wt %) and heat treatment on the phase composition, texture, and photocatalytic activity (PCA) of composites based on titanium(IV) and niobium(V) oxides and obtained materials that possess PCA under illumination at λ ≥ 900 nm.     

The effect of MgO additions on the kinetics of hot pressing in Al2O3

The kinetics of hot pressing of Al₂O₃ with and without MgO additives have been measured at 1475 and 1630° C and at 5 to 20 MPa using Al₂O₃ powders of different grain size and using different additive levels. Data obtained within the solid solution regime are interpreted in terms of diffusional creep processes. MgO additions accelerate densification within this regime; the consequent reduction in pore size, and hence in pore drag, can explain the function of MgO as sintering additive for Al₂O₃.     

Preparation of Al2TiO5 from alkoxides and the effects of additives on its properties

Al2TiO5 was prepared by the sol-gel method from alkoxides and its mechanical and thermal properties measured. The prepared Al2TiO5 powder was very fine and had a narrow particle-size distribution. The addition of mullite and Al2O3 to the prepared Al2TiO5 inhibited the grain growth during sintering, resulting in a decrease of microcracking and an increase of fracture strength. Al2TiO5/mullite composite exhibited a higher fracture strength than Al2TiO5/alumina composite. The thermal expansion coefficient of Al2TiO5 increased with the addition of mullite and alumina, and also increased with temperature up to 1000°C; however, it decreased in the temperature range between 1000 and 1200°C during heating, due to decomposition of Al2TiO5. The addition of mullite inhibited the decomposition of Al2TiO5, but the addition of Al2O3 accelerated it. Al2TiO5 prepared from metal alkoxides was also more stable than that prepared from the commercial alumina and titania powders. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of non-stoichiometry on the sintering of doped TiO2

The sintering of TiO₂ has been studied with respect to oxygen partial pressure ( ) and doping content. From the microstructural evolution, it is obvious that a decrease of the oxygen pressure promotes the densification with a comparatively smaller grain growth than in air sintering. This fact has been related with the influence of defects on the sintering. Both effects of and tantalum doping have been studied. They are interpreted on the basis of a model involving interstitial titanium, electron holes, titanium vacancies and complexes associating titanium vacancies with tantalum substituted titanium. This latter complex is probable according to previous microscopic studies of defects in TiO_2–x and may be important in highly doped compounds. The formation of such associates reduces the mobile defect concentration, however a decrease of the favour their dissociation. The titanium vacancies which are thus released allow the titanium ions to migrate, a necessary condition for the sintering.     

Low-temperature sintering and microwave dielectric properties of TiO<Subscript>2</Subscript>-based LTCC materials

Temperature stable high-K LTCC material was prepared. The influence of fabrication process on the crystalline phases, microstructures and microwave dielectric properties of TiO₂-Bi₂O₃-CuO ceramics were investigated. The crystalline phases and microstructures of TiO₂-Bi₂O₃-CuO ceramics were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. It was found that rutile TiO₂ phase and Bi₂Ti₄O₁₁ phase co-existed in the TiO₂-Bi₂O₃-CuO ceramics. Separate TiO₂ grains and Bi₂Ti₄O₁₁ grains distributed uniformly in the ceramic matrix. The composition 0.92TiO₂-0.08Bi₂Ti₄O₁₁ with 2 wt% CuO addition that was sintered at 900 °C for 2 h showed high dielectric constant (ε_r ~ 81), high quality factor (Q × f ~ 3,500 GHz) and near zero temperature coefficient of resonant frequency (τ_f ~ −5.1 ppm/°C), meanwhile the compatibility test showed that it could co-fire with silver electrode. The processing-microstructure-property interrelationship was also studied.     

Photocatalytic properties of nanocrystalline TiO2 thin film with Ag additions

In the present study, nanocrystalline TiO₂/Ag composite thin films were prepared by a sol–gel spin coating technique. While, by introducing polystyrene (PS) microspheres, porous TiO₂/Ag films were obtained after calcining at a temperature of 500 °C. The as-prepared TiO₂ and TiO₂/Ag thin films were characterized by X-ray diffractometry, and scanning electron microscopy to reveal the structural and morphological differences. In addition, the photocatalytic properties of these films were investigated by degrading methylene blue under UV irradiation.After 500 °C calcination, the microstructure of PS-TiO₂ film without Ag addition exhibited a sponge-like microstructure while significant sintering effect was noticed with Ag additions and the films exhibited a porous microstructure. Meanwhile, coalescence of nanocrystalline anatase-phase TiO₂ can be observed with respect to the sharpening of XRD diffraction peaks. The photodegradation of porous TiO₂ doped with 1 mol% Ag exhibited the best photocatalytic efficiency where 72% methylene blue can be decomposed after UV exposure for 12 h.