Interface characteristics of Al_2O_3－13%TiO_2 ceramic coatings prepared by laser cladding

Al2O3-13%TiO2 （mass fraction） coatings, prepared by laser cladding on nickel-based alloy, were heated using high frequency induction sources. The coating microstructure and the interface between bond coating and ceramic coating were characterized by SEM, XRD and EDS. The results show that two-layer substructure exists in the ceramic coating： one layer evolving from fully melted region where the sintered grains grow fully; another layer resembling the liquid-phase-sintered structure consisting of three-dimensional net where the melted Al2O3 particles are embedded in the TiO2-rich matrix. The mechanism of the two-layer substructure formation is also explained in terms of the melting and flattening behavior of the powders during laser cladding processing. The spinel compounds NiAl2O4 and acicular compounds Cr2O3 are discovered in the interface between bond coating and ceramic coating. It proves that the chemical reactions in the laser cladding process will significantly enhance the coating adhesion.

Preparation of Crack-free 3Y-TZP/Al_2O_3 Composite Ceramic Fiber by Electrolysis-sol-gel Method

Polycrystalline 3Y-TZP/Al2O3 tetragonal zirconia fiber was obtained by the pyrolysis of gel fibers using zirconium oxychloride octahydrate（ZOC） as the raw material. The spinnable zirconia sol was prepared by electrolyzing the zirco-nium oxychloride octahydrate（ZOC） solution in the presence of acetic acid and sugar（ sucrose, glucrose or fructose） , in which the molar ratios of CH3 COOH/ZOC and sugar/ZOC were 1.0-4.0 and 0.2-0.4, respectively. The pre- pared tetragonal zireonia fibers sintered at different temperatures showed smooth and crack-free surfaces with diame, ters of 5-10 μm. The addition of Al2O3 enhanced the sintering process and prevented the crystals from growing. Thermogravimetric analysis（TG）, X-ray diffraction （ XRD ）, Fourier transform infrared spectroscopy（FTIR）, and scanning electron microscope（SEM） techniques were used to characterize the prepared fibers.

THE STRUCTURE AND PROPERTIES OF Li_2O-Al_2O_3-SiO_2LOW EXPANSION GLASS CERAMICS CONTAINING B_2O_3

Through measuring the coefficient of linear expansion, the structure and properties of the Li2O-Al2O3-SiO2 low expansion glass ceramics containing B2O3 are studied by JR and XRD. It is shoutn that the IR method is efficient in the study of the glass-ceramics structure. There is a " Boron abnormality" in the system which has an important influence on the properties of the glass-ceramics.

Mechanical properties and plasma erosion resistance of BN_p/Al_2O_3-SiO_2 composite ceramics

BNp/Al2O3-SiO2 system ceramic matrix composites with different volume fractions （10%-60%） of hexagonal BN particulates （BNp） were prepared by hot-press sintering technique. Phase components, microstructure, mechanical properties and plasma erosion resistance were also investigated. With the increase of h-BNp content, relative density and Vickers＇ hardness of the composite ceramics decrease, while the flexural strength, elastic modulus and fracture toughness increase and then decrease. The plasma erosion resistance linearly deteriorated with the increase of BNp content which is mainly determined by the density, crystal structure and atomic number of the elements.

Sintering,crystallization and dielectric properties of CaO-B_2O_3-SiO_2 system glass ceramics

CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is found that there are SiO2 and some unknown phases in CBS glass melting liquid from 1 300 ℃ to 1 500 ℃ and the amount of these phases decreases with the increase of the melting temperature. The CBS glass melted at 1 450 ℃ could be sintered from 830 ℃ to 930 ℃ and the bulk densities of the samples are all higher than 2.4 g/cm^3. From the points of the properties and energy conservation, the melting temperature of 1 450 ℃ is the optimal melting temperature. The glass ceramic sintered at 850 ℃ exhibits better dielectric properties： er=6.33, tan6=2.2×10^-3 at 10 GHz, and the major phases of the samples are CaSiO3, CaB2O4 and SiO2.

Preparation of Al_2O_3-SiO_2-TiO_2-ZrO_2 Composite Ceramic Membranes by Sol-Gel Method

Al 2O 3-SiO 2-TiO 2-ZrO 2 supported membranes were prepar ed by Sol-Gel method. These composite ceramic membranes are level, even and no macro crack. There exist several crystalline phases such as Al 2O 3, TiO 2(a natase), Al 2SiO 5, and ZrO 2 in these membranes. Changing the molar ratio of Al∶Si∶Ti∶Zr,the kinds and content of crystal phases of composite membranes could be different, which may lead to a variety of microstructure of membranes. The surface nanoscale topography and microstructure of membranes were investiga ted by XRD,SEM,AFM,EPMA. The effects of additives and heat treatments on the sur face nanoscale topography and microstructure of composite ceramic membranes were also analyzed.

Preliminary Study on Combining K2O-Al2O3-SiO2 System Dental Glass Ceramic with Al2O3 Ceramic

Relationship between K2O-Al2O3-SiO2 system dental glass ceramics and Al2O3 ceramics was investigated. 4 groups of glass ceramic with the same components but different thickness（0.8, 1.2, 1.6, and 2.0 mm） were sintered on Al2O3 base ceramics according to the same thermal treatment system of leucite micro-crystallization reported in previous literatures. The products of each group were analyzed by polarizing microscope, X-ray diffractometer, and an INSTRON material testing machine. Under the thermal treatment system, leucite crystals were formed in samples of each group, and dispersed evenly. Meanwhile, the compressive strengths of group 3 and group 4 were higher than those of group 1 and group 2. Samples of group 3 showed better mechanical properties than others. The conclusions are drawn that Leucite crystals can be controlled in K2O-Al2O3-SiO2 system glass ceramic-Al2O3 ceramic composite material, and the thickness of glass ceramic has a notable influence on the compressive strength of this ceramic composite material.

Microstructure and microwave dielectric properties of lead borosilicate glass ceramics with Al_2O_3

The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B203-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope （FTIR）, differential thermal analysis （DTA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that with the increase of Al2O3 content the bands assigned to [SiO4] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings. The increase of the transition temperature Tg and softening temperature Tf of PbO-B2O3-SiO2 glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase with the increase of Al2O3 content, but the dielectric loss is worsened. By contrast, the 3% （mass fraction） Al2O3-doped glass ceramics sintered at 725℃ have better properties of density p=2.72 g/cm3, dielectric constant Er=6.78, dielectric loss tan8=2.6×10^-3 （measured at 9.8 GHz）, which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low sintering temperatures.

Thermal shock fatigue behavior of TiC/Al_2O_3 composite ceramics

The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference （ΔT） and number of thermal cycles （Ⅳ） on fatigue crack growth （Δa）. The mechanical properties and thermal fatigue resistance of TiC/Al203 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a ＂true＂ cycling effect （thermal fatigue）. Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.

Al_2O_3-SiO_2复合膜的制备与结构表征

以异丙醇铝和正硅酸乙酯为主要原料,用溶胶-凝胶法制备无支撑体Al2O3-SiO2复合膜.应用XRD、DTA-TGA、IR、BET等测试手段对复合膜的物相组成、热稳定性、孔结构进行表征.并且讨论了化学组成和煅烧温度对复合膜孔结构的影响.研究结果表明:550℃煅烧10h的复合膜物相组成为无定形的SiO2和γ-Al2O3晶体,粒度大小在2-4nm之间,化学组成为Al2O3/SiO2=3:2的复合膜在不同煅烧温度时,400℃煅烧的物相为γ-AlOOH和,γ-Al2O3,550-1150℃煅烧的物相为γ-Al2O3,1220℃煅烧的物相为γ-Al2O3和α-Al2O3,1300℃煅烧的物相为莫来石相和α-Al2O3;化学组成不同的复合膜主要是由Al-O网络和Si-O网络构成,没有形成Al-O-Si网络结构;复合膜具有良好的热稳定性;化学组成和煅烧温度对复合膜的孔结构有一定的影响.

溶胶-凝胶法制备Al_2O_3-ZrO_2-SiO_2复合薄膜

本文采用溶胶-凝胶法以异丙醇铝、正硅酸乙酯和氧氯化锆为原料,HNO3为催化剂,PVA为成膜助剂,在多孔陶瓷管上制得了Al2O3-ZrO2-SiO2复合薄膜。研究了组分配比对溶胶性质的影响,结果表明Al2O3∶ZrO2∶SiO2在8∶1∶2～12∶1∶2之间时可得到性能符合要求的溶胶。通过扫描电镜可观察到膜的孔径为2～5μm,且膜与基底结合良好。

Synergistically Toughening Effect of SiC Whiskers and Nanoparticles in Al_2O_3-based Composite Ceramic Cutting Tool Material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.

溶胶-凝胶-喷雾干燥法制备超细Al_2O_3-SiO_2二元粉体材料

以硝酸铝(Al(NO3)3·9H2O)和正硅酸乙酯(TEOS)为原料,采用溶胶-凝胶(Sol-Gel)技术并结合喷雾干燥(SPD)技术制得超细Al2O3-SiO2二元复合粉体材料,并分别于400℃、800℃、1000℃、1150℃和1200℃煅烧2 h;采用全自动比表面积与孔隙率分析仪、TEM、TG-DSC及XRD等仪器研究了热处理温度、pH值(分别为5.5、7和8)以及干燥方法对粉体材料的表面性能、显微形貌、物相组成及Al2O3-SiO2二元系晶体转变过程的影响.结果表明:由Sol-Gel-SPD制备的超细Al2O3-SiO2二元粉体材料的比表面积＞448 m2·g-1,而经1200℃煅烧2 h后所得的超细莫来石的比表面积34.05m2·g-1;TG-DSC分析表明:采用Sol-Gel-SPD制得的Al2O3-SiO2二元粉体材料的质量损失主要发生在500℃之前;XRD分析表明:粉体试样的开始莫来石化温度为1000℃,铝硅尖晶石(6Al2O3·SiO2)与非晶态SiO2在1150～1200℃完全转化为莫来石;比较不同pH值试样经1200℃煅烧后的TEM照片发现,当pH=7时,得到的超细莫来石粉体粒径最小,为50 nm.

Studies on the Structure and Properties of Multiphase Al_2O_3 Abrasion-resistant Ceramics

The Al2O3 abrasion-resistant ceramics is successfully prepared by using waste aluminum sludge as the main raw material with the addition of a little clay, talc and barium carbonate. The crystal structure and microstructure of ceramic are characterized by means of XRD, SEM, etc., and the physical and mechanical properties are also tested. The results show that besides the phase of corundum, a little mullite, Mg-Al spinel and hyalophane phases also exist in the product. These phases are produced via reaction in-situ, which can inhibit the overgrowth of Al2O3 grain in grain boundary, and improve the integral property of the material.

Al2O3-SiO2／AZ91D镁基复合材料的制备及其性能研究

采用硅酸铝纤维和镁合金制备出结构紧密的Al2O3-SiO2／AZ91D镁基复合材料。介绍了复合材料的制备工艺，适宜的挤压铸造工艺为：基体温度650℃、模具温度550℃、浇注温度760℃和压力30～50MPa。XRD、SEM、EDS和光学金相显微镜OM等分析结果表明：复合材料主要由Mg、β-Mg17Al12、MgO、AlPO4、3Al2O3·2SiO2和Mg2Si等结晶相组成；镁与硅酸铝纤维反应生成MgO和汉字状Mg2Si等产物；基体镁与硅酸铝纤维的界面形成比较紧密的结合层。与镁合金相比，复合材料的硬度和油摩擦性能有较大提高。

Al_2O_3-SiO_2气凝胶的制备及性能研究

以正硅酸乙酯(TEOS)和仲丁醇铝(ASB)为硅源和铝源,采用溶胶-凝胶和超临界干燥工艺制备出了高比表面积的Al_2O_3-SiO_2块状气凝胶,研究了不同溶胶配比及热处理温度对气凝胶结构的影响,利用红外光谱、氮气吸附、X射线衍射和扫描电子显微镜等手段对气凝胶的性能和结构进行了分析。结果表明,随Al/Si摩尔比增大,Al_2O_3-SiO_2气凝胶凝胶时间逐渐缩短,比表面积(1000℃)先增后减,当Al/Si摩尔比为4:1时,比表面积最高,为444.5 m^2/g;1200℃,Al/Si为8:1时比表面积最高,为115m^2/g,具有较好的高温热稳定性。红外分析表明Al_2O_3SiO_2气凝胶存在Al-O-Si键;在1000℃热处理后,Al_2O_3-SiO_2气凝胶中Si含量减少到一定程度才会出现γ-Al_2O_3。通过SEM观察表明Al_2O_3-SiO_2气凝胶粒子较Al_2O_3气凝胶小。

热风炉长寿与低蠕变Al2O3-SiO2系耐火材料的探究

回顾了中国热风炉用低蠕变Al2O3-SiO2系耐火材料研发的历程。通过对比矾土基低蠕变Al2O3-SiO2系耐火材料与莫来石基低蠕变Al2O3-SiO2系耐火材料的实际使用结果认为,要实现热风炉长寿命,对于热风炉用耐火材料而言,除了要求其具有优异的抗蠕变性能外,还应具有优良的抗热震性、抗CO和碱蒸气侵蚀等综合性能。针对中国资源综合利用的现状和可持续发展战略要求,建议使用红柱石或莫来石基原料制备Al2O3-SiO2系低蠕变系列耐火材料;即通过对原料进行分级,实现天然Al2O3-SiO2系原料(主要是红柱石)和人工合成Al2O3-SiO2系原料资源的综合利用,优化材料的矿物组成,制备以莫来石为主晶相结构,Al2O3质量分数低于75%的莫来石基低蠕变系列制品,并结合性价比进行优化配置,真正实现热风炉的长寿化,应该是今后长寿型热风炉用Al2O3-SiO2系耐火材料研发的重点。

Al_2O_3含量及热处理温度对Al_2O_3-SiO_2系浇注料抗铝液侵蚀性的影响

采用坩埚法和浸泡法研究了不同Al2O3含量（质量分数分别为80%~85%、65%~70%、40%~45%、25%~30%）及不同温度（分别为110、800、1100和1 400℃）热处理后的Al2O3-SiO2系浇注料的抗铝液侵蚀性,借助电镜和能谱分析研究了被850℃铝液侵蚀后试样的显微结构。结果表明：（1）随着Al2O3含量的增加,Al2O3-SiO2系浇注料的抗铝液侵蚀性增强;（2）在1 100℃热处理后,浇注料的抗铝液侵蚀性最差;（3）铝液渗入浇注料内部后,铝液中的Al和Mg与浇注料中的石英和莫来石相发生反应,将SiO2还原成Si,Al和Mg则氧化成Al2O3和MgO,MgO进而与Al2O3反应生成尖晶石,破坏试样的结构;（4）对于Al2O3含量较高的Al2O3-SiO2浇注料,尖晶石富集层较致密,可阻止铝液继续向浇注料内部渗透。

Influence of pyrolytic carbon coatings on complex permittivity and microwave absorbing properties of Al_2O_3 fiber woven fabrics

The pyrolytic carbon （PyC） coatings were fabricated on A1203 fiber fabrics by the method of chemical vapor deposition （CVD）. The microstructures of A1203 fibers with and without PyC coatings were characterized by SEM and Raman spectroscopy. The influence of deposition time of PyC on the DC conductivity （ad） of A1203 filaments and complex permittivity of fabrics at X band （8.2-12.4 GHz） were investigated. The values of Crd and complex permittivity increase with increasing deposition time of PyC. The electron relaxation polarization and conductance loss were supposed to be contributed to the increase of ε＇ and ε＂, respectively. In addition, the reflection loss （RL） of fabrics was calculated. The results show that the microwave absorbing properties of Al2O3 fiber fabrics can be improved by PyC coatings. The best RL results are for 60 min-deposition sample, of which the minimum value is about -40.4 dB at about 9.5 GHz and the absorbing frequency band （AFB） is about 4 GHz.

Effect of Nano-ZrO_2 on Microstructure and Thermal Shock Behaviour of Al_2O_3/SiC Composite Ceramics Used in Solar Thermal Power

The Al2O3-ZrO2（3Y）-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength of samples with 10vol% nano-ZrO2 sintered at 1480℃ were 3.222 g/cm3 and 160.4MPa,respectively.The bending strength of samples after 7 times thermal shock tests （quenching from 1000℃ to 25℃ in air medium） is 132.0MPa,loss rate of bending strength is only 17%.The effect of nano-ZrO2 content on the microstructure and performance of Al2O3-ZrO2（3Y）-SiC composite ceramic was investigated.The experimental results show that the bending strength of samples with above 10vol% nano-ZrO2 content has decreased,because the volume expansion resulting from t-ZrO2 to m-ZrO2 phase transformation is excessive;Adding proper nano-ZrO2 would be contributed to improve the thermal shock resistance of the composite ceramics.The Al2O3-ZrO2（3Y）-SiC composite ceramic has promising potential application in solar thermal power.