AIN陶瓷中的晶界第二相

晶界第二相是ＡＩＮ陶瓷显微结构的重要组成部分，对ＡＩＮ陶瓷的热导率有重大影响。本工作研究了以Ｙ２Ｏ３为烧结助剂的无压烧结ＡＩＮ陶瓷中，晶界第二相的组成、含量及其分布。结果表明：晶界第二相的组成主要决于配料中的Ｙ２Ｏ３／Ａｌ２Ｏ３比值，同时也受工艺因素影响；随着Ｙ２Ｏ３加入量增多，晶界第二相含量呈线性增加，其分布也变成从三个晶粒连接处延伸到所有晶界，还讨论了晶界第二相对热导率的影响，认为只要ＡＩＮ晶     

A1N陶瓷的晶界缺陷

本文研究以Ｙ２Ｏ３为烧结助剂的无压烧结Ａ１Ｎ陶瓷中，晶界第二相和气孔等晶界缺陷对热导率的影响。结果表明，Ａ１Ｎ陶瓷晶界第二相的组成主要取决于配料中的Ｙ２Ｏ３／Ａｌ２Ｏ３比值，同时也受工艺因素影响，随着Ｙ２Ｏ３加入量增多，晶界第二相含量线性增加，其分布也从三晶连接外延伸到所有晶界。     

A1N陶瓷的晶界缺陷

本文研究以Ｙ２Ｏ３为烧结助剂的无压烧结Ａ１Ｎ陶瓷中，晶界第二相和气孔等晶界缺陷对热导率的影响，结果表明Ａ１Ｎ陶瓷晶界第二相的组成主要取决于配料中的Ｙ２Ｏ３／Ａｌｋ２Ｏ３比值，同时也受工艺因素的影响。     

B_2O_3－Y_2O_3添加剂对AlN陶瓷显微结构及性能的影响

研究了以Ｂ_２Ｏ_３－Ｙ_２Ｏ_３作为助烧结剂的ＡｌＮ陶瓷的烧结特性及显微结构。结果表明，晶界处存在ＹＡｌＯ_３，Ｙ_４Ａｌ_２Ｏ_９及Ｙ_３Ａｌ_５Ｏ_（１２）等各种铝酸钇结晶物，Ｂ_２Ｏ_３可固溶到铝酸钇中形成固溶体。随烧结温度变化，第二相的种类、数量和分布不同，从而影响ＡｌＮ的热导率。在１８５０℃下，可获得热导率为１８９Ｗ／ｍ·Ｋ的ＡｌＮ陶瓷。     

SiC_w一AlN复合材料工艺因素的研究

本文研究了工艺因素（烧结温度、添加剂组成和含量）对ＳｉＣ＿ｗ一ＡＩＮ复合材料的影响。结果表明：１８５０℃是较合适的复合材料烧结温度，复合材料力学性能与添加剂组成和含量有密切关系。Ｙ＿２Ｏ＿３与ＳｉＯ＿２在烧结中起的作用不同，Ｙ＿２Ｏ＿３与ＡＩＮ表面的Ａｌ＿２Ｏ＿３形成液相，是一种良好的烧结添加剂，而ＳｉＯ＿２由于与ＡＩＮ形成２７ＲＳｉａｌｏｎ多形体，反而阻碍材料致密化。在添加８ｗｔ％左右Ｙ＿２Ｏ＿３时。复合材料力学性能最佳，抗折强度σ５２０ＭＰａ，断裂韧性Ｋ＿（ｌｃ）＝４．９８ＭＰａ·ｍ￣（１／２）     

添加剂对AIN陶瓷力学性能及抗氧化性能的影响

本文研究了Ａｌ２Ｏ３、Ｙ２Ｏ３、Ｌａ２Ｏ３、Ｙ２Ｏ３＋ＳｉＯ２几种类型的添加剂对ＡＩＮ陶瓷力学性能和高温抗氧化性能的影响。结果表明：Ｙ２Ｏ３＋ＳｉＯ２为一种较好的ＡＩＮ陶瓷添加剂，材料在烧结过程中由于２Ｈ＾５Ｓｉａｌｏｎ及８Ｈ－Ｓｉａｌｏｎ等纤维状的Ｓｉａｌｏｎ相形成，对材料起到一种自补强作用，ＳｉＯ２的存在使用ＡＩＮ陶瓷在氧化工程中形成Ｍｕｌｌｉｔｅ保护层，故使ＡＩＮ陶瓷肯有良好的力学性能及高温     

B2O3—Y2O3添加剂对AlN陶瓷显微结构及性能的影响

研究了以Ｂ２Ｏ３－Ｙ２Ｏ３作为助烧结剂的ＡｌＮ陶瓷的烧结特性及显微结构。结果表明，晶界处存在ＹＡｌＯ３，Ｙ４Ａｌ２Ｏ３及Ｙ３Ａｌ５Ｏ１２等各种铝酸钇结晶物，Ｂ２Ｏ３可固溶到铝酸钇中形成固溶体。     

Al2O3添加量对Y—TZP陶瓷烧结及力学性能的影响

研究了Ａｌ２Ｏ３添加量对Ｙ－ＴＺＰ陶瓷烧结及力学性能的影响，结果表明，微量Ａｌ２Ｏ３可固溶于ＺｒＯ２中而提高材料致密度，使Ｙ－ＴＺＰ的强度、耐磨性等力学性能也同时得到提高，过量Ａｌ２Ｏ３处ＺｒＯ２晶界上阻碍致密化，２０ｗｔ％Ａｌ２Ｏ３，１５５０℃，４ｈ未能烧结，使各项力学性能明显下降。     

稀土氧化物在Al2O3透明陶瓷晶界浓度分布的非平衡态热力学分析

采用高纯Ａｌ２Ｏ３超细粉末,烧制成掺杂稀土氧化物的Ａｌ２Ｏ３透明陶瓷。以ＥＰＭＡ法观测透明陶瓷晶界处的化学组成及稀土氧化物的定态浓度分布,用非平衡态热力不理论分析晶界偏析行为,研究发现,添加物在Ａｌ２Ｏ３透明陶瓷晶界的浓度分布为非平衡态和学组成分布,ＭｇＯ,Ｌａ２Ｏ３,Ｙ２Ｏ３富集于晶界,符合定态耦合模型。     

液相烧结SiC陶瓷

采用Ｙ２Ｏ３,Ａｌ２Ｏ３为烧结助剂,研究了烧结助剂的含量及组成对ＳｉＣ陶瓷的烧结性和力学性能的影响。结果表明,Ｙ２Ｏ３,Ａｌ２Ｏ３原位形成了ＹＡＧ,材料以液相烧结机制致密化,与传统的固相烧结相比,液相烧结使ＳｉＣ陶瓷性能显著提高,在较佳条件下,材料强度和韧性分别达到７０７ＭＰａ,１０．７ＭＰａ·ｍ＾１／２,显微结构观察表明,裂纹偏转和微裂纹为主要的增韧机理,这与其弱的界面结合有关,而强度的提高则得     

晶界相对半透明氮化铝陶瓷透过率的影响

分别添加质量分数为3%的CaF2和Y2O3为烧结助剂,在相同烧结工艺制度下采用放电等离子烧结(spark plasma sintering,SPS),制备了两种半透明AlN陶瓷.两种样品有相近的密实度和晶粒尺寸,但是它们的透过率却相差很大.用扫描电镜,X射线衍射分析和透射电镜结合能量散射型X射线光谱分析仪对样品微观结构进行分析.结果表明:晶界相的存在及分布方式对样品透过率有重要影响.添加CaF2的样品表现出很高的纯度,晶界及三角晶界处观察不到第二相.添加Y2O3的样品中,由于生成的晶界相Y3Al5O12沿AlN晶界分布,阻隔AlN晶粒之间的连接,在晶界处造成光散射,导致样品透过率下降.     

热处理气氛对AIN／SiCw（Y2O3—SiO2）复合材料性能的影响

将ＡＩＮ／ＳｉＣｗ（Ｙ２Ｏ３－ＳｉＯ２）复合材料在氧气氛和氮气氛下进行热处理,研究热处理气氛对材料性能的影响,并利用ＸＲＤ、ＥＰＡ、ＳＥＭ和ＨＲＥＭ等技术分析了材料的相组成、显微结构和粒界相。结果表明：该材料在１３００℃空气中热处理,材料性能得到改善,材料的断裂强度和韧性增长幅度明显大于氮气气氛下的热处理。在空气中氧化处理对Ｙ２Ｏ３－ＳｉＯ２组成靠近其低共熔点组成的试样具有良好的增强增韧作用,可有     

Fabrication and Properties of Closed-pore Al_2O_3-based Refractory Aggregates

A novel Al_2O_3-based refractory aggregate with closed-pore structure was fabricated utilizing superplasticity with submicro-sized Al_2O_3 and MgO as raw materials,and SiC as a high temperature pore-forming agent.The effect of MgO on porosity,phase composition and microstructure of the refractory aggregate has been investigated. For comparison,the common Al_2O_3-based refractory aggregates and porous ones with open-pore structure were also prepared. The results indicate that the closed porosity of Al_2O_3-based refractory aggregate increases as the content of MgO increases. When the content of MgO is 15 mass%,the closed and apparent porosities are 14. 5% and 1. 1%,respectively. The main phase compositions are Al_2O_3 and MgAl_2O_4. The formation mechanism of closed pores is that the fine-crystallinegrain Al_2O_3 ceramic possesses superplastic deformation ability after adding MgO at high temperatures. When SiC powder is added to the Al_2O_3 ceramic,the generated gases by the reaction of SiC at the sintering temperature can provide a pressure to make grain boundaries slide. Then,the gases are enclosed by crystalline grains to form the closed pores. The slag corrosion resistance of the fabricated closed-pore Al_2O_3-based refractory aggregate is better than the common refractory aggregate and porous ones.     

液相烧结氧化铝和氧化钇稳定四方氧化锆复相材料的显微结构与力学性能

以TiO2，MnO2及CaO—Al2O3-SiO2玻璃为烧结助剂，利用液相烧结法制备了氧化铝和3％氧化钇稳定四方氧化锆复相材料。研究了烧结助荆对材料致密化、显微结构及力学性能的影响。结果表明：除TiO2可与ZrO2晶粒形成部分固溶外，烧结助剂主要以晶间玻璃相的形式存在，并影响了Y2P3在ZrO2晶粒中的分布。烧结助荆的引入显著促进材料的致密化，降低了烧结温度，使材料具有细晶结构，因而具有良好的力学性能。     

Effect of CaO on the Thermal Conductivity of Aluminum Nitride

The effect of CaO on the thermal conductivity of aluminum nitride pressureless sintered with 3 wt% Y₂O₃ as a sintering aid was investigated. Over the composition range of 0 to 2.0 wt% additions, CaO decreased the thermal conductivity of the sintered parts by 10%. CaO doping rendered the secondary oxide phases more wetting and thus with a greater tendency to penetrate along the grain boundaries. Furthermore, CaO segregation to the grain boundaries was observed even on those grain boundaries apparently free of secondary phases. These microstructural changes disrupted the connectivity of the high thermal conductivity AIN grains and were the main factors contributing to the decrease in the thermal conductivity of the ceramic parts. CaO additions to samples doped with SiO₂ had the opposite effect, increasing the thermal conductivity. CaO removed SiO₂ from the AIN grains and incorporated it into the oxide second phases, most likely through charge-compensating substitutions Ca²⁺+ Si⁴⁺ for Y³⁺ and/or Al³⁺. Thus, AIN samples containing both SiO₂ and CaO had higher thermal conductivity than those containing comparable amounts of SiO₂ alone.     

PPS复合导热材料的研究与有限元模型分析

通过有限元分析软件ABAQUS,模拟了三氧化二铝(Al2O3)填充聚苯硫醚(PPS)两相复合材料逾渗结构以及Al2O3填充PPS合金三相复合材料双逾渗结构,并将得到的理论导热率与实验结果进行对比验证,分析了填料分布情况对材料热导率的影响。模拟结果表明:只有当导热填料含量超过逾渗阈值,其导热性能才能有明显的提高,双重逾渗结构的形成,能有效降低逾渗阈值。SEM分析表明,选用不同的合金组分,由于相容性的差异和黏度的差异,填料在PPS合金中的分布情况也有不同,热导率也有较大的差异。在所述配方中PPS/UHMWPE/Al2O3(质量比为35:15:50)复合体系热导率最高,可达1.592W/(m.K),而同质量配比的PPS/PS/Al2O3复合体系的最低,只有0.639W/(m.K)。     

Al2O3-ZrO2陶瓷体系中晶粒生长模型的研究

研究了Al2O3-ZrO2陶瓷体系中两相晶粒生长，提出了双相体系的晶粒生长模型，并解释了“内晶型”结构是如何形成的。研究发现，两相结构的形成与温度、保温时间及ZrO2等二相的数量有关系，其中温度的影响最为显著。内晶型ZrO2结构的形成是基体晶粒急剧长大的结果，而不是以往研究的以纳米粒子为生长点，基体粒子的成核、长大。有利于基体晶粒急剧生长的条件也有利于内晶的形成；内晶的形成过程可概括为Ostwald生长与基体晶粒的快速长大。但值得注意的是，并不是ＺrO2的含量越多，形成的内晶型结构就越多。     

Effect of Al_2O_3-ZrO_2 Composite Powder on Thermal Shock Resistance of ZrO_2 Sizing Nozzles

ZrO_2 sizing nozzles with a basic formulation were prepared using 45%( by mass,the same hereinafter)( Mg,Y)- PSZ aggregate,55%( Mg,Y)- PSZ fines and 5% PVA binder. Al_2O_3-ZrO_2 composite powders( 3%,6%,9% and 12%) prepared by sol- gel method were added to replace the equal amount of( Mg,Y)- PSZ fines. Effects of Al_2O_3- ZrO_2 composite powders on physical properties,phase composition and microstructure of the ZrO_2 sizing nozzles were studied.The results show that: the performances of the modified sizing nozzles with 3% Al_2O_3-ZrO_2 composite powder are better than those of the nozzles without composite powder used in current production process,and the thermal shock resistance of the former nozzles is six times of that of the latter one.     

Thermodynamic and Kinetic Effects of Oxygen Removal on the Thermal Conductivity of Aluminum Nitride

High thermal conductivity, low dielectric constant, high electrical resistivity, low density, and a thermal expansion coefficient that matches well with that of silicon are the principal attributes of AIN that have attracted much attention over the past decade. It is also now well established that oxygen as an impurity lowers the thermal conductivity of AIN. Processing techniques have been developed which not only facilitate pressureless densification of AIN but also enhance its thermal conductivity. The present work explores the thermodynamics and the kinetics of oxygen removal and the resultant enhancement of thermal conductivity. Polycrystalline AIN ceramics were fabricated with Y₂O₃, Dy₂O₃, Yb₂O₃, CaO, BaO, or MgO as additives. Samples were sinter/annealed at 1850°C for up to 1000 min. The AIN grain size of sintered samples ranged between 2 and 9 μm. The samples typically contained two or three phases with the predominant phase being AIN. Secondary phases in Y₂O₃-doped AIN consisted of yttrium aluminates which were along three grain junctions and along grain facets. The presence of Y₃Al₅O₁₂, YAIO₃, and Y₄Al₂O₉, as well as Y₂O₃, depending upon the Y₂O₃/Al₂O₃ ratio, was revealed by X-ray diffraction. Thermal conductivity increased with the amount of additive and annealing time. Thermal conductivity also depended on the type of additive. Samples with thermal conductivity up to 200 W/(m · K) were fabricated. The variation in thermal conductivity with the type and the amount of the additive is explained on the basis of the thermodynamics of oxygen removal. In particular, the higher thermal conductivity of CaO-doped, in comparison with MgO-doped, samples is rationalized on the basis that the free energy of formation, ΔG°, of CaAl₂O₄ is less than that of MgAl₂O₄. It is proposed that the higher the |ΔG°|, with ΔG° < 0, the higher is the resultant thermal conductivity. An increase in the thermal conductivity with annealing time is attributed to the kinetics of oxygen removal from AIN grains.