硅溶胶添加对氧化铝多孔陶瓷烧结性能的影响

以煅烧α-Al2 O3粉末为原料,硅溶胶为高温结合剂,羧甲基纤维素钠为成型黏结剂,通过混料、困料、模压成型、高温烧结等工序制备氧化铝多孔陶瓷,利用SEM和XRD对多孔陶瓷微观形貌和晶体结构进行测试,并对多孔陶瓷的线收缩率、体积密度、显气孔率和抗弯强度进行表征,系统地研究硅溶胶添加对氧化铝多孔陶瓷高温烧结特性的影响.结果表明:低温下硅溶胶的热解产物石英型SiO2将氧化铝颗粒黏结起来,形成物理黏结,能提高多孔陶瓷的力学性能;烧结温度达1500℃时,SiO2开始与氧化铝反应形成莫来石,莫来石结合相的生成使得氧化铝多孔陶瓷趋于致密,力学性能优异,抗弯强度可达(105.5±8.0)MPa;随烧结温度的升高莫来石生成量增多,导致氧化铝多孔陶瓷的体积膨胀,进而使得孔隙率增大,力学性能降低.烧结温度介于1400～1500℃之间时,可以得到微观结构合理、力学性能优异、孔隙率适中的氧化铝多孔陶瓷.     

建筑回收物制备多孔陶瓷材料及其性能表征

以建筑垃圾为主要原料,Al_2O_3为铝源,AlF_3为晶须催化剂,MoO_3为烧结助剂,成功制备了钙长石-莫来石-刚玉多孔陶瓷。采用XRD和SEM分析了多孔陶瓷材料的物相组成及形貌,研究了在烧结温度1 350℃条件下,不同保温时间对多孔陶瓷材料开口孔隙率、孔径分布的影响,以及钙长石-莫来石-刚玉多孔陶瓷的双轴弯曲强度和油水分离性能。结果表明,当AlF_3含量为12%(质量分数)、MoO_3含量为4%(质量分数)时,在烧结温度1 350℃下,保温2 h,制备的钙长石-莫来石-刚玉多孔陶瓷性能最优。孔隙率分析可知,保温时间为2 h时,有利于原料中氧化铝相和玻璃相莫来石化,增加莫来石相的含量;此时多孔陶瓷材料具有46%的开口孔隙率,且样品中莫来石晶须的大量生长造成晶须之间的尺寸较为一致,使得样品的开孔孔隙孔径大小比较集中,比较适合进行油水分离。力学性能分析表明,保温时间为2 h时,样品的双轴弯曲强度为68 MPa,机械性能良好。油水分离性能研究表明,在不同的膜压差下,样品的油乳拦截率均能达到97%～99%,多孔陶瓷膜具有较好的油乳分离性能。     

样板晶生长法制备Y-TZP/板状氧化铝复相陶瓷的力学性能和可靠性

以带有玻璃涂层的氧化铝微粉、小尺寸板晶(样板晶)和Y-TZP微粉为原料,在常压、不同温度下,通过样板晶生长制备了Y-TZP/板状氧化铝复相陶瓷。对该复相陶瓷的室温力学性能的研究表明,在适当烧结温度下制备的复相陶瓷该材料具有较高的强度(800~900 MPa)和断裂韧性(11.8~15.2MPa·m1/2)。用扫描电子显微镜观察复相陶瓷的显微结构特点,表明该材料的增韧机制为氧化锆相变增韧和板晶对裂纹偏转和桥连机制共同起作用。用二参数Weibull分布来量化强度波动,表明该复相陶瓷具有很高的Weibull模量。      

含焦宝石的陶瓷支撑剂的制备及性能

以铝矾土和焦宝石为原料,以锰粉为烧结助剂,制备高强度低密度支撑剂,并对相关性能进行研究。结果表明:随着铝矾土和焦宝石制备的陶瓷支撑剂配方中铝含量的不同,其最佳烧结温度范围略有不同,最佳的烧结时间也存在差异。在微观结构上,陶粒的强度主要由刚玉骨架提供,当铝含量降低时,陶粒中虽然会出现部分莫来石相,但并不会影响其性能,说明低铝含量铝矾土可用于制备刚玉-莫来石质陶粒支撑剂。     

硅源对莫来石结合刚玉耐火材料性能的影响

以板状刚玉为骨料,莫来石为结合相,并以高岭土和无定型SiO2微粉作为合成莫来石的硅源,采用反应烧结工艺制备莫来石结合刚玉耐火材料,旨在降低莫来石的烧结成本及获得理想的显微结构.研究表明：以高岭土为硅源,莫来石生成量低于理论量,但生成温度较低,1550℃前已完成莫来石化反应,显微结构较均匀,烧结程度较好,莫来石呈长柱状;...     

高强隔热刚玉-镁铝尖晶石-莫来石多孔陶瓷材料的制备

以氧化铝、石英粉和电熔镁砂为主要原料,以纸浆废液为结合剂,通过原位反应烧结制备复相高强隔热陶瓷,研究MgO添加量对所制备多孔陶瓷的显气孔率、抗折强度、耐压强度和抗热震性能的影响。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和电子万能试验机对材料的物相组成、显微结构和力学性能进行表征,并对多孔陶瓷的显气孔率和抗热震性能进行测试。结果表明:5%(质量分数)电熔镁砂与氧化铝、石英粉在1450℃下原位反应烧结3h可制备得到刚玉-镁铝尖晶石-莫来石多孔复相陶瓷,耐压强度达270.25MPa,抗折强度超过45MPa,同时显气孔率达26.46%,常温导热系数为1.469W·m^-1·K^-1,隔热性能良好,且3次热震后的残余抗折强度保持率超过27%,是极具应用前景的工业窑炉内衬材料。其中MgO含量变化会直接影响该多孔陶瓷三相组成、相形态、气孔孔径及分布,使得多孔陶瓷抗折强度、耐压强度和抗热震性能呈现非单调变化的规律。     

红柱石制备莫来石泡沫陶瓷

以红柱石和氧化铝为主要原料、聚苯乙烯粒子为造孔剂,通过烧结法制备莫来石泡沫陶瓷,借助XRD和SEM分析了烧成温度和骨料配比对获得莫来石相组成和结构的影响规律,并通过正交试验,探讨烧结温度、造孔剂加入量和骨料配比等工艺参数对制备莫来石泡沫陶瓷性能的影响.结果表明:造孔剂加入量对密度和强度的影响较大,烧结温度次之,骨料配比最小;最佳的因素水平为烧结温度1 450 ℃,EPS质量分数5%,骨料质量比m(红柱石)∶m(氧化铝)=80∶20,此时表观密度为0.52 g/cm³,抗折强度0.36 MPa.     

莫来石含量对钙长石/莫来石复相多孔陶瓷组织结构与性能的影响

以CaCO₃、SiO₂、α-Al₂O₃为原料, 采用泡沫注凝法制备了不同莫来石含量的钙长石/莫来石复相多孔陶瓷, 研究了莫来石含量对复相多孔陶瓷的体积密度、气孔率、抗压强度、热导率及微观组织和结构的影响. 结果表明, 莫来石含量对气孔率有很大的影响, 烧结过程中液相出现引起的收缩是气孔率下降的主要原因; 在气孔率相近的情况下, 莫来石含量较高试样的抗压强度和热导率也较高, 致密的孔壁、长柱状的莫来石晶粒使得复相多孔陶瓷的抗压强度提高. 所制备的钙长石/莫来石复相多孔陶瓷的开口气孔率介于60.8%~75.2%, 抗压强度为12.94~36.95 MPa, 热导率为0.30~1.33 W/(m·K).     

振动浇注成形的高强度碳化硅基耐火材料

以黑碳化硅、烧结白刚玉粉(WFA),二氧化硅微粉(MS),氧化铝微粉(RA),铝酸钙水泥(CAC)作为主原料,添加不同比例的金属硅粉,采用振动浇注+高温氮化的工艺制备了碳化硅基耐火材料.研究了金属硅含量分别为5％、7％、9％,氮化温度分别为1300℃、1420℃、1500℃对试样冷/热态抗折强度、物相组成和显微结构的影响.结果表明:试样的冷态和热态强度随氮化温度的增加和原料中金属硅含量的增加而增加.1420℃氮化后,原料中金属硅含量为7％和9％的试样,1200℃的热态强度都可超过50MPa.原位形成的大量氮化物将颗粒与基质结合,形成网络结构.氮化物的形成及其结构对提高冷态和热态强度起决定作用.     

Y2O3和B2O3对莫来石低温烧结的影响

由于Si4+和Al3+离子在莫来石晶界处扩散速率低,莫来石陶瓷难以烧结.为了降低莫来石陶瓷的烧结温度,在莫来石中添加Y203.B2O3为烧结助剂,研究了添加剂在单独和混合添加情况下对莫来石陶瓷体积密度、抗弯强度以及微观形貌等的影响.同时,研究了烧结温度及保温时间对莫来石陶瓷性能的影响.研究表明,添加剂显著地降低了莫来石的烧成温度,添加Y2O3充当烧结助剂比添加B2O3具有更好的效果,随着温度的提高,陶瓷强度由37.39MPa增至77.89MPa,体积密度由1.99g/cm3增至2.60g/cm3.     

Chemical bonding and interlocking between hydratable alumina and microsilica after drying at 110 °C and firing at 800 °C

Chemical bond changes between microsilica and hydratable alumina were studied by X-ray photoelectron spectroscopy and Fourier transformation infrared spectroscopy. The formation of Si–O–Al bond was detected by the decreased O 1s and Si 2p binding energy and the lowered vibration frequency of hydratable alumina with the addition of microsilica after drying at 110 °C and heating at 800 °C. Furthermore, it was observed by scanning electron microscope that the interlocking structure developed between the particles of hydratable alumina and microsilica after drying at 110 °C and the sintering took place among the particles after heating at 800 °C. Therefore, it is proposed that the increased strength of the castables after drying and heat treatment at intermediate temperatures was attributed to the presence of microsilica which resulted in the formation of Si–O–Al bond and interlocking structure between hydratable alumina and microsilica particles.     

热压缩过程中2205双相不锈钢的组织演变和软化机制

在不同变形温度和应变速率条件下对2205双相不锈钢进行高温压缩实验,研究了变形温度、应变速率和变形量对其显微组织中铁素体和奥氏体两相的影响,分析了高温变形软化机制。结果表明：随着变形温度的提高这种钢的峰值应力及其对应的应变逐渐减小。随着变形温度从850℃提高到950℃,2205双相不锈钢显微组织中的铁素体向奥氏体的转变占主导地位;变形温度高于950℃时,随着变形温度的提高铁素体与奥氏体之间的强度水平之差逐渐减小,显微组织中的奥氏体向铁素体的转变占主导地位。在本文的热变形条件下2205双相不锈钢的显微组织中铁素体呈现出与奥氏体不同的软化机制,铁素体的软化机制为动态回复和动态再结晶,而奥氏体因层错能较低其软化只能通过有限程度的动态回复进行。     

莰烯基冷冻浇注成型法制备定向通孔氧化铝陶瓷

由莰烯、氧化铝、Texaphor 963组成的陶瓷料浆,在温度梯度的诱导下,用冷冻浇注成型法制备了氧化铝陶瓷坯体,经干燥、烧结后,制备出了高孔隙率、高强度的定向通孔氧化铝陶瓷.通过扫描电镜观察其孔结构,并对其孔隙率、抗压强度和收缩率进行分析测试.结果表明:料浆的固体含量和烧结温度显著影响试样的气孔率、抗压强度和收缩率;...     

Pressureless sintering of AlN-SiC composites

SiC-AlN composites have been successfully pressureless sintered by using commercial SiC and AlN powders with the optimum amount of sintering aid. The important parameters during pressureless sintering, including the amount and type of sintering aids, sintering temperature, sintering period and packing powder have been studied. Yttria was found to be a better sintering aid than alumina or calcia. The yttria sintering aid reacts with AlN and SiC powders and forms a Y-Al-Si-O-N grain-boundary phase to assist densification during pressureless sintering. With 2 wt% yttria, SiC-AlN composites can be pressureless sintered to high density at 2050–2100 °C for 2 h under the firing conditions where alpha-pp packing powder is used during firing. The microstructure and phases of the composites were characterized by using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffractometry.     

The comparison of alumina and zirconia fibres using simple thermal and mechanical techniques

The laboratory development of sol/gel ceramic fibres requires rapid objective means of assessing the mechanical and thermal properties of a product at the earliest stages of preparation. The merits of a simple tumbling test, leading to a fibre friability index, and the Bend Stress Relaxation test, which gives a high temperature creep rating, are demonstrated on commercial Saffil and Safimax alumina fibres and a development Saffil zirconia fibre, each in staple blanket form. Measurements on Altex continuous alumina/silica fibre and Nicalon are also presented.Standard and off specification alumina fibres are readily distinguished by their friability indices which correlate with the fibre strain to break.Saffil and Safimax alumina are comparable to Nicalonin terms of creep and superior to Altex. Saffil zirconia approaches alumina creep performance after post firing to 1250°C.     

Enhancing mechanical properties and permeability of ceramic shell in investment casting process

In the present investigation, the mechanical properties and hot permeability of the ceramic shell used in investment casting process were improved by modifying the ingredients of conventional slurry. The modifications were made by adding a varying content of nano alumina, camphor and a mixture nano alumina and camphor (hybrid mixture) individually into the conventional slurry. The properties, viz. green strength, fired strength, corner strength, load bearing capacity, self-load deformation and permeability of the modified shells were investigated and compared with conventional shell. The experimental results revealed that the green strength of all the shells increased with an increment of the additives into the slurry. The maximum green, fired and corner strengths were exhibited by the nano alumina modified shell with 1 wt% nano alumina addition. The lowest self-load deformation at elevated temperature was also attained by the nano alumina modified shell with 1 wt% nano alumina addition. The addition of camphor significantly improved the permeability of the shell among all the developed shells. But, addition of camphor decreased the strength of the shell. It was also found that addition of hybrid mixture into the slurry simultaneously increased the mechanical properties and permeability of the shell.     

Magnetoresistive properties of Ni-based thick films

Investigations have been carried out on the electrical properties of nickel-based films prepared from air-fireable pastes on alumina substrates. In particular, magnetoresistive effects have been studied as a function of temperature, strength and direction of the magnetic field. These properties were determined in films at different stages of formation, i.e. prepared at various peak firing temperatures and dwell times, and compared with those displayed by nickel foils. These results provide the basis for the development of magnetoresistive thick-film sensors.     

Fabrication,properties and structure of a high temperature light alloy composite

Paniculate alumina reinforced Al-4Cr-1 Fe alloys were fabricated from rapidly solidified aluminium alloy powder and commercially purchased alumina powder by traditional powder metallurgical techniques involving powder mixing and cold compaction followed by hot extrusion. The tensile tests at ambient temperature indicated a considerable improvement in the mechanical strength at the expense of ductility and modulus. Poor values of modulus were explained by the presence of porosity in the composites. The high temperature mechanical properties of the matrix, tested at 350 °C after prolonged exposure to the test temperature under static air conditions, were intrinsically poor. Additions of the filler material, alumina particles, up to a weight fraction of 15% did not improve the high temperature performance of the matrix substantially. Possible causes for this are discussed and alternatives proposed.     

The effects of processing conditions on the resistivity and microstructure of ruthenate-based thick film resistors

Elevated temperature processing parameters affect the microstructure and electrical behaviour of thick film resistors on alumina substrates. Blended resistors (DuPont QS87 series) with a nominal sheet resistivity of 56 kΩ/□ and temperature coefficient (TCR) less than ±100 p.p.m K-1 were fired in a laboratory process that simulated production ramp rates and atmosphere. Resistances were measured in situ during firing in a three-factor, replicated experiment with two levels and centrepoints for peak temperature, firing time and probe current. Room temperature resistance values after firing show a strong correlation to temperature and time, which both increase resistance and flatten the R(T) curve around room temperature. In situ resistance during firing shows a weaker correlation, inverse with temperature because the thermally activated glass conduction has a greater share of the composite conduction at firing temperature. X-ray diffration (XRD) shows lead ruthenate, alumina, and zirconium silicate present in the resistors. The ruthenate lattice parameters increase with increasing firing temperature and time. Qualitative particle coarsening is observed with increasing firing temperature and time by transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDX) shows lead ruthenate, CuBi ruthenate and zirconium silicate crystallites dispersed in a lead silicate glass matrix, without much particle chaining. Resistance changes are attributed to increased separation of ruthenate particles by coarsening. This revised version was published online in August 2006 with corrections to the Cover Date.