Al2O3-ZrO2复相陶瓷研究进展

Al2O3-ZrO2复相陶瓷是高温结构陶瓷中最有前途的材料之一,近年来ZrO2增韧Al2O3（ZTA）受到广泛重视。本文对Al2O3-ZrO2复相陶瓷的结构、主要的制备方法及复合机理、发展趋势进行了叙述。     

(Y,Ce)-ZrO2增韧92Al2O3陶瓷的研究

采用自制均匀分散的(1.5Y,4Ce)-ZrO2微粉,通过适当工艺和92Al2O3复合,提高了92Al2O3陶瓷的韧性和强度.最后采用X-射线衍射分析、扫描电镜分析研究了该样品的机械性能与烧成制度、相组成及微观结构的关系.结果表明:92Al2O3陶瓷性能的提高归因于ZrO2的应力诱导相变增韧,并且当(1.5Y,4Ce)-ZrO2微粉的加入量为20%(质量分数)时,试样在1550℃烧成时,材料的抗弯强度、断裂韧性以及硬度得到了很好的改善.     

氧化铝基纳米复合陶瓷显微结构的研究

考察了Al2O3-SiC和Al2O3-ZrO2(3Y)-SiC纳米复合陶瓷的断裂方式。由于SiC的加入,材料以穿晶断裂为主。通过透射电镜观察,研究了纳米复合陶瓷中材料SiC颗粒的分布,证明所制备的材料为晶内型纳米复合陶瓷。在Al2O3-ZrO3(3Y)-SiC纳米复合陶瓷中,小的ZrO2颗粒分布于Al2O3晶粒内,大的ZrO2晶粒位于Al2O3晶粒间,ZrO2的分布影响Al2O3晶粒的形状。通过高分辨透射电镜,观察了Al2O3-SiC和Al2O3-ZrO2(3Y)-SiC纳米复合陶瓷中Al2O3/Al2O3,Al2O3/SiC,Al2O3/ZrO2的界面。在两颗晶粒间的晶界几乎没有玻璃相的存在,证明纳米复合材料中晶界得到了加强,有利于力学性能的提高。     

淀粉燃料对多孔Al_2O_3-ZrO_2(Y_2O_3)陶瓷性能的影响

为了提高多孔Al2O3-ZrO2(Y2O3)陶瓷的强度,以尿素和淀粉为燃料,用低温燃烧法合成活性较高的Al2O3-ZrO2(Y2O3)复合粉体,并用此粉体制备了多孔Al2O3-Zr O2(Y2O3)陶瓷,研究燃烧前驱体中淀粉的外加量(质量分数分别为0、15%、25%、35%、45%、55%)对多孔陶瓷显气孔率、抗折强度和显微结构的影响。结果表明:与尿素为燃料相比,以尿素和淀粉为燃料能提高复合粉体的烧结活性,有效改善多孔陶瓷的显微结构,提高多孔陶瓷的抗折强度。     

ZrO2基Al2O3-ZrO2-C质高温陶瓷材料抗渣性能研究

以板状刚玉、活性α—氧化铝、氧化锆(PSZ)、碳黑为主要原料,以金属硅和碳化硼作为添加剂,以热固性酚醛树脂作为结合剂,制备了ZrO2基Al2O3-ZrO2-C质材料。实验证明添加稳定氧化锆的Al2O3-ZrO2-C质高温陶瓷材料的抗渣性能优于添加单斜氧化锆、纳米氧化锆、金属铝的Al2O3-ZrO2-C质高温陶瓷材料。     

Y2O3改性Al2O3陶瓷微波介电损耗研究

本文以Al2O为模型材料研究了影响材料介电损耗的因素,发现Y2O3掺杂有利于陶瓷的致密化,并能对Al2O陶瓷的微结构与晶粒尺寸起到调控作用。由于离子半径的差别,Y^3＋离子难以进入刚玉结构的间隙或发生取代置换Al^3＋抖离子形成固溶体,而是与Al2O反应生成Al5Y3O12在Y2O3掺杂改性过程中,非本征因素成为影响Y2O3陶瓷微波介电性能的主要因素,使得Al2O陶瓷微波介电损耗从8．4×10^-5增加到2．2×10^-4。     

沉淀法制备Al2O3-ZrO2-Y2O3复合粉体的固相反应

采用化学沉淀法制备了不同配比的Al2O3-ZrO2-Y2O3复合粉体.通过X射线衍射研究了热处理过程中各物质之间的反应顺序及复合粉体的物相组成,结果表明升温过程中Y2O3优先与ZrO2反应生成固溶体,温度较高时,剩余Y2O3与Al2O3反应生成钇铝石榴石YAG;不同的制备工艺没有改变各物质之间的固相反应顺序,但影响了复合粉体中各物相的相对含量.     

TiN改性Al2O3纳米复相陶瓷的研究进展

Al2O3陶瓷具有高硬度、耐高温、耐腐蚀和耐磨损等优点．是应用最广泛的陶瓷之一．但脆性大．难以加工．严重限制了它的应用范围。主要介绍了TiN改性Al2O3纳米陶瓷的研究进展．与SiC、ZrO2改性Al2O3纳米陶瓷相比,TiN—Al2O3纳米复相陶瓷不仅力学性能优异,而且具有导电能力,可用于电火花加工．扩大了Al2O3陶瓷的应用范围。最后对Al2O3纳米复相陶瓷的发展前景作了展望。     

添加Al2O3-ZrO2(Y2O3)系易熔混合物的Al2O3质陶瓷

研制了添加Al2O3—ZrO2(Y2O3)系易熔混合物细粉碎颗粒的刚玉质陶瓷，并研究其结构和性能。指出利用这种易熔混合物对于制造陶瓷材料是很有前途的。     

络合沉淀法制备Al2 O3 -ZrO2复合粉

以工业纯ZrOCl2.8H2O,分析纯AlCl3.6H2O,分析纯Y2O3等为原料,将AlCl3.6H2O和ZrOCl2.8H2O分别配制成0.5mol.L-1和1mol.L-1的水溶液,按ZrO2和Al2O3的质量比为44:56配成混合溶液;将混合溶液与用盐酸溶解稳定剂Y2O3后配制成一定浓度的YCl3溶液混合并搅拌均匀,再向均匀溶液中加入2%PEG分散剂制成母液;然后向母液中滴加过量的0.5mol.L-1的草酸溶液形成络合母液,滴加氨水调节其pH值。研究了pH值在4~10之间,直接沉淀法和络合沉淀法对Al2O3-ZrO2复合粉前驱体溶胶团聚及粉体粒度分布的影响。利用透射电镜(TEM)和激光粒度分析仪对溶胶和复合粉粒度组成进行了分析。结果表明:采用草酸为络合剂,氨水为沉淀剂的络合沉淀法可以明显的改善Al2O3-ZrO2复合粉前驱体溶胶的团聚,干燥后得到的复合粉体没有明显的硬团聚;反应溶液的pH值为9时效果最佳;络合沉淀法制备的Al2O3-ZrO2复合粉的平均粒径为3.704μm,直接法制得的粉体的平均粒径为7.052μm。     

Air plasma-sprayed Y2O3 coatings for Al2O3/Al2O3 ceramic matrix composites

Al₂O₃/Al₂O₃ ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al₂O₃/Al₂O₃ CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y₂O₃ is considered a candidate EBC material for Al₂O₃/Al₂O₃ CMC. Up to 1 mm thick Y₂O₃ coatings were deposited by means of air plasma spraying (APS) on Al₂O₃/Al₂O₃ CMC with a reaction-bonded Al₂O₃ bond-coat (RBAO). APS Y₂O₃ coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y₂O₃/RBAO interface. The reaction zone between Y₂O₃ and Al₂O₃ comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.     

Al2O歧化法制备微细Al2O3/Al复合粉体

真空条件下,以Al2O3和Al为原料,通过Al2O歧化法制备微细Al2O3/Al复合粉体.XRD和SEM分析表明:在反应温度为1200～1400℃时,随着温度的升高,粉体中氧化铝含量升高;冷凝温度约为550～750℃时,复合粉体中的氧化铝包括稳定晶型和不稳定晶型;冷凝温度约为1100～1300℃时,复合粉体中的氧化铝全部为稳定晶型;冷凝温度约为550～650℃时,复合粉体的平均粒径小于0.5μm;冷凝温度约为750℃时,铝熔化、微粒团聚;冷凝温度约为1100～1200℃时,铝形成铝珠,氧化铝为不规则状、平均粒径小于2μm;冷凝温度约为1300℃时,氧化铝为片状.因此,通过选取合适的反应温度、冷凝温度,可以控制Al2O3/Al复合粉体中氧化铝的含量、晶型和粒径.     

Al2O3-based binders for corrosion resistance optimization of Al2O3–MgAl2O4 and Al2O3–MgO refractory castables

This work addresses the main aspects related to the use of alternative binders [hydratable (HA) or colloidal alumina (ColAlu)] in castables containing different spinel sources (pre-formed or in situ generated), in order to point out: (i) the features that control the corrosion behavior of these materials, and (ii) the key factors to better select a refractory composition. Thermodynamic calculations, corrosion cup-test and SEM analyses were carried out in order to evaluate the slag attack of the designed refractory compositions. According to the attained results, the alumina-based binders (HA or ColAlu) induced a more effective sintering process due to their high specific surface area, improving the physical properties and the binding level of the generated microstructure. The spinel grain size also played an important role in the corrosion behavior of these refractories, as the finer the particles, the greater their dissolution was into the molten liquid, leading to further precipitation of spinel in the solid–liquid interface as a continuous and thick layer. Among the evaluated compositions and considering the presence of silica fume, the most suitable formulation with optimized corrosion resistance was the one with in situ spinel generation and HA as a binder.     

Optical absorption and selective thermal emission in directionally solidified Al2O3-Er3Al5O12 and Al2O3-Er3Al5O12-ZrO2 eutectics

Al₂O₃-Er₃Al₅O₁₂ and Al₂O₃-Er₃Al₅O₁₂-ZrO₂ eutectic ceramic rods were directionally solidified using the laser floating zone technique at several growth rates. Binary eutectic microstructure consisted in a three-dimensional interpenetrated network of the eutectic phases whereas the ternary eutectic showed a geometrical microstructure at low growth rates and a nanofibrillar pattern at high rates. The microstructure size was strongly dependent on the growth rate, decreasing when the processing rate increased. The optical absorption was measured in the samples at room temperature and Judd–Ofelt analysis was used to model the optical absorption of the Er³⁺ ions. Thermal emission of the eutectic rods was studied at temperatures up to 1600 °C. An intense narrow emission band at 1.55 μm matching with the sensitive region of the GaSb photoconverter was obtained. The intensity of the selective emission band is larger for the binary eutectic than for the ternary compound and increases as the microstructural size decreases.     

Al2O3/Al2O3扩散连接机理的研究

采用热压方式进行氧化铝陶瓷材料的扩散连接，并深入探讨了其连接机理，结果表明：采用适当的连接工艺，可使此种材料产生塑性形变，接触面积增加，空洞收缩和闭合，扩散进行充分，1420℃，15MPa热压60min条件下，获得的最高强度为357MPa，超过母材强度平均连接强度为250MPa，是母材平均强度的85％。     

Ruby micro-piezospectroscopy in GdAlO3/Al2O3(/ZrO2), Er3Al5O12/Al2O3(/ZrO2) and Y3Al5O12/Al2O3(/ZrO2) binary and ternary directionally solidified eutectics

The fluorescence from (naturally present) Cr³⁺ impurities was used to measure the residual stress in the alumina phase of six melt-grown ceramic eutectic composites associating gadolinum aluminum perovskite (GAP), erbium aluminum garnet (EAG) or yttrium aluminum garnet (YAG) with α-alumina and cubic zirconia. Such measurements are reported for the first time in the GAP containing eutectics.In the usual hydrostatic assumption, we conclude to a residual compression in the range of ～70–400 MPa depending on the sample composition. The validity of the hydrostatic assumption is questioned when a microscope is used for the measurements.     

Separation of Phases by Spinodal Decomposition in the Systems Al2O3−Cr2O3 and Al2O3−Cr2O3−Fe2O3

Separation of phases was investigated in the hexagonal (rhombohedral) systems Al₂O₃−Cr₂O₃ and Al₂O₃−Cr₂O₃−Fe₂O₃. The binary system shows a miscibility gap with a T_c of 950°C; the miscibility gap for the ternary system was determined for a constant Cr₂O₃ content of 16.6 mol%. Dark field transmission electron microscopy of solid solutions annealed within the miscibility gap showed dark and light lamellas ∼50 to 200 Å thick. X-ray diffraction results for the solid solutions in the ternary system indicated that, in the early stages of annealing, broadening occurred only on (hkl) reflections where l≠0. There was no major change in the X-ray diffraction patterns of the annealed solid solutions in the binary system. Electron diffraction results indicated, however, that phase separation in both systems proceeded in the [001] direction. Solid solutions in the binary system separated very slowly; the separation could be enhanced hydrothermally. The mechanism of the separation of phases in both systems is spinodal and proceeds as follows: solid solution→intermediate modulated phase→equilibrium phases.     

Erosion mechanism of the postmortem Al2O3-Ti2O3-Al sliding gate containing novel Al2O3-Ti2O3 raw materials

Al₂O₃-Ti₂O₃-Al sliding gates were prepared from Al₂O₃-Ti₂O₃ raw materials, sintered corundum and aluminum, and used in trials at steel works. The sliding gate with 30 wt% Al₂O₃-Ti₂O₃ added was used on an 80 t ladle for 4 cycles without macrocracks. The postmortem sliding gate can be divided into the permeation layer (0–0.1 mm), transition I layer (0.1–10 mm), transition II layer (10–20 mm) and unchanged layer from the hole working face outward. XRD, SEM and industrial CT were used to analyze the postmortem sliding gate. The results show that, in the Al₂O₃-Ti₂O₃-Al sliding gate, both Al and Ti₂O₃ are involved in reactions, Ti₂O₃ transforms into Ti₂O and TiO in the transition I layer, and part of the Ti₂O₃ in the transition II layer transforms into Ti₈O₁₅. Titanium compounds with different densities are dispersed in the matrix and form microcracks to improve the thermal shock resistance of the sliding gate, which improved the performance.