Y_2W_3O_(12)和Yb_2W_3O_(12)的制备及其负热膨胀性能

利用液相沉淀法制备了Y2W3O12和Yb2W3O12粉体。经室温XRD测定,Y2W3O12(空间群为Pnca)和Yb2W3O12(空间群为Pbcn)皆为单一的正交相。在50-800℃温度区间对两种粉体进行高温XRD测试,并利用软件TOPAS3.0对其在不同温度下的XRD图谱进行精修,发现Y2W3O12和Yb2W3O12都具有较大的负热膨胀特性,经计算两者的线热膨胀系数(αl)平均值分别为-6.38×10-6℃-1和-4.18×10-6℃-1。与高温固相反应法相比,液相沉淀法大大缩短了粉体的合成周期,降低了合成温度。     

负热膨胀材料的研究现状及展望

概述了负热膨胀材料的发展历程及国内外研究进展和发展方向,介绍目前所发现的负热膨胀材料的种类及结构特征,整理归纳国内外对负热膨胀的微观机理的认识,综述制备负热膨胀材料的传统工艺和新工艺方法,并主要介绍近年来对负热膨胀材料机理的新认识和主要研究成果,探讨负热膨胀材料研究所面临的问题和潜在的应用价值。     

稀土钨电极研究与应用

介绍了近年对TIG(钨极惰性气体保护焊)和PLASMA(等离子体)焊接、切割用钨电极材料的研究进展和应用情况 ,着重对稀土钨电极材料及稀土氧化物作用等有关研究问题进行了讨论。对W -La2O3、W -CeO2、W -Y2O3 电极材料的热电子发射能力和稳定性研究表明 :在中小电流时2.2-wt%La2O3-W电极具有较好的电子发射能力和稳定性 ,钇钨和铈钨次之 ;在大电流工作时 ,钇钨电极热电子发射能力和稳定性最好。对制备的二元复合稀土钨电极(W -La2O3-Y2O3、W -La2O3-CeO2、W -Y2O3-CeO2)和三元稀土钨电极(W -La2O3-Y2O3-CeO2)的性能与单元稀土钨电极材料(W -La2O3、W -CeO2、W -Y2O3)和钍钨电极材料进行了比较。结果表明 ,复合稀土钨电极材料的焊接电弧性能优于单元稀土钨电极和钍钨电极。但它们的性能又各不相同 ,可适应交流焊、薄板和中厚板不同焊接工作的需求。研究表明、电极的使用性能强烈依赖于稀土金属氧化物。燃弧过程中它们的行为是影响电极使用性能、电极温度、逸出功和电极稳定性的最重要的因素。     

高热导率低热膨胀系数Cu-ZrW_2O_8复合材料的制备与性能

以负热膨胀材料ZrW2O8与金属Cu为原料,分别采用常规烧结法和热压法制备具有高热导率低膨胀系数的新型Cu基复合材料Cu-ZrW2O8,研究ZrW2O8体积分数与烧结方法对该复合材料致密度、热导率及热膨胀系数的影响.结果表明:热压法制备的Cu-50%ZrW2O8复合材料的热导率达173.3 W/(m·K),致密度为91.6%,均明显高于常规烧结样品;热压样品的热膨胀系数为11.2×10-6K-1,稍高于常规烧结样品:在150～300℃温度范围内热处理后该样品的平均热膨胀系数降低到10.87×10 -6K-1,较纯Cu的平均热膨胀系数17×10-6K-1低很多,有望成为一种新型的电子封装材料.     

La2O3对ZrO2-Y2O3-Ta2O5陶瓷材料结构及性能的影响

采用固相合成法在氧化钇部分稳定氧化锆(YSZ)陶瓷材料的基础上引入氧化物Ta2O5以及稀土氧化物La2O3取代部分Y2O3,获得一种新型的La2O3-ZrO2-Y2O3-Ta2O5陶瓷材料。分别利用X射线衍射仪、扫描电子显微镜和STA-449C热膨胀仪对材料的物相组成、微观结构及热膨胀性能进行表征。结果表明,陶瓷材料的主晶相仍为四方相,晶粒尺寸减小,在RT～1200℃温度范围内热膨胀系数有所减小。     

Zr1-xHfxW2O8的合成及负热膨胀特性的研究

采用固相化学反应的方法 ,成功合成了立方结构的Zr1 -xHfxW2 O8(x =0 ,0 3 ,0 5 ,0 7,1 0 )系列材料。X射线衍射结果表明 ,Hf4 +能替代Zr4 +形成二元固溶体 ,固溶体的晶胞参数与体积随着Hf4 +含量x的增加而降低。采用高、低温X射线衍射的方法测定晶胞参数和体积随温度的变化关系 ,结果表明 :Zr1 -xHfxW2 O8化合物在实验温度范围具有强烈的负热膨胀效应 ,但其负热膨胀系数不随Hf4 +含量x变化。在2 98～ 973K ,Zr1 -xHfxW2 O8线膨胀系数αl 约为 -6× 10 - 6 K- 1 ;在 83～ 2 98K ,Zr0 5Hf0 5W2 O8的αl=-9 6× 10 - 6 K- 1 。变温XRD研究还表明 ,Zr1 -xHfxW2 O8化合物从α ZrW2 O8相向 β ZrW2 O8相的转变温度随Hf4 +含量x的增加而略有升高 ,热重分析 (TGA )研究结果表明 ,Zr1 -xHfxW2 O8在室温大气条件下不吸水     

掺杂锆酸钐热障涂层材料的热物理性能

采用固相反应法制备Sm2Zr2O7、(La0.4Sm0.5Yb0.1)2Zr2O7和(La0.4Sm0.5Yb0.1)2(Zr0.75Hf0.25)2O7陶瓷材料.通过XRD、SEM分析了材料的物相组成和微结构形貌,采用激光闪烁法测定材料的导温系数,结合比热的计算结果推算出材料的热导率.利用热膨胀仪测定样品的热膨胀性能.XRD结果显示,通过固相反应法制备的陶瓷材料为单一的烧绿石相,在测试温度范围内,掺杂材料的热导率均低于Sm2Zr2O7材料,且(La0.4Sm0.5Yb0 1)2(Zr0.75Hf0.25)2O7的热导率最低(～0.7 Wm-1K-1),比Sm2Zr2O7的热导率(～1.3 Wm-1K-1)低～46%.热膨胀性能测试结果显示,三种材料为近似线性膨胀,掺杂材料的热膨胀系数低于Sm2Zr2O7.但元素掺杂消除了Sm2Zr2O7材料热膨胀系数在低温段的异常下降.     

热压法制备W-Mo-Cr-Al_2O_3复合材料的微观结构与力学性能

以亚微米级W、Mo、Al2O3粉末和微米级Cr粉为原料,在1 600℃下热压制备W-Mo-Cr-Al2O3复合材料,利用X射线衍射(XRD)、扫描电镜(SEM)和能谱分析(EDS)研究该复合材料的微观结构和断口形貌,测试复合材料的力学性能,对其断裂模式进行分析,并研究Al2O3含量对W-Mo-Cr-Al2O3复合材料性能的影响。结果表明:W-Mo-Cr-Al2O3复合材料中存在分布均匀的富W,Cr(W,Mo)金属相和Al2O3陶瓷相。W、Mo、Cr之间可以部分溶解,特别是Cr溶于Al2O3可增强金属相和陶瓷相的结合,使材料具有很高的强度和韧性。随Al2O3含量(体积分数)从10%提高到30%,材料的硬度提高17%,但抗弯强度和韧性分别降低8%和3%。复合材料的断裂模式为沿富W相/Al2O3相的界面、富W相/Cr(W,Mo)相界面及Cr(W,Mo)相/Al2O3相界面的沿晶断裂和Cr(W,Mo)相的穿晶断裂。     

La_2O_3增强增韧(Mo_(0.7),W_(0.3))Si_2复合材料的作用机理

通过多组元自蔓延反应及热压烧结方法制备了(Mo0.7,W0.3)Si2材料及掺杂1.5.%(质量分数)La2O3的(Mo0.7,W0.3)Si2复合材料。采用X射线衍射(XRD)、扫描电镜(SEM)、电子探针(EPMA)、透射电镜(TEM)及物理机械性能测试方法对复合材料组织性能进行了表征,并深入探讨了其强韧化机理。结果表明:La2O3掺杂的(Mo0.7,W0.3)Si2复合材料由(Mo,W)Si2、(Mo,W)5Si3、硅酸镧构成。掺杂La2O3后,La2O3与脆性相Si O2形成硅酸镧化合物,与未掺杂La2O3的(Mo0.7,W0.3)Si2相比,复合材料的晶粒明显细化,强度和韧性均明显提高,其强化原因有细晶强化及颗粒弥散强化;韧化原因有晶粒细化、Si O2的减少、位错缠结、颗粒的拔出、裂纹偏转及微裂纹产生。     

Nd2O3掺杂对Y2O3-Ta2O5-ZrO2陶瓷相结构及热膨胀性能的影响

采用固相烧结法制备了Nd2O3掺杂Ta2O5-Y2O3-ZrO2体系热障涂层陶瓷材料。分别利用X-射线衍射仪、扫面电子显微镜和热膨胀仪对陶瓷材料的物相组成、显微结构以及热膨胀性进行了分析。结果表明,Nd2O3-Y2O3-Ta2O5-ZrO2陶瓷材料以四方相为主晶相,随着Nd2O3掺入量的增加,出现单斜相和少量其它杂相,且陶瓷材料的体积密度增大,热膨胀系数减小,晶粒也有所减小,表明稀土氧化物Nd2O3具有抑制晶粒长大和抗烧结的作用。     

Study on thermal expansion behavior of Dy2O3 - Al2O3 - SiO2 glass

Employing Dy2O3, Al2O3, and SiO2 as starting materials, several series of Dy2O3-Al2O3-SiO2 sealing glass were prepared. The relationship between their coefficients of thermal expansion and the contents of Dy2O3, Al2O3, and SiO2 were studied respectively. Experimental results showed that Dy2O3 and Al2O3 had a positive effect on the coefficient of thermal expansion of glass, whereas, SiO2 had a negative effect. The coefficient of thermal expansion of glass showed an apparent linear relation to the contents of these three raw materials, from which an estimation model was built, to calculate the coefficient of thermal expansion of sealing glass. Relative errors of the calculating results to testing results were no more than 2%, which suggested that the estimation model was reasonable. This study provides a good theory reference for the practical utilizing of this sealing material, through which a proper glass composition for good sealing could be easily found.     

Synthesis kinetics and thermophysical properties of La_2（Zr_（0.7）Ce_（0.3））_2O_7 ceramic for thermal barrier coatings

La2(Zr0.7Ce0.3)2O7 (LZ7C3) ceramic was synthesized by solid state reaction with La2O3, ZrO2 and CeO2 as starting materials. The synthesis kinetics, phase structure, mass loss and microstructure were studied by thermo gravimetric-different thermal analyzer (TG-DTA), X-ray difference (XRD) and scanning electron microscopy (SEM). The thermal conductivity and thermal expansion coefficient were measured by laser-flash method and pushing-rod method, respectively. XRD results showed that LZ7C3 was a mixture of La2Zr2O7 (LZ, pyro- chlore) and La2Ce2O7 (LC, fluorite). The lowest synthesis temperature and time of LZ7C3 were 1400 oC and 5 h. There were no peaks of La2O3 when the powder granularity was about 0.82 μm in the synthesis process. The atom ratio La:Zr:Ce of prepared LZ7C3 powder was very close to 10:7:3 which was the theory value of LZ7C3. The thermal conductivity of LZ7C3 decreased gradually with the temperature increased up to 1200 oC, and was located within 0.79 to 1.02 W/(m·K), which was almost 50% lower than that of LZ, whereas its thermal expansion coefficient was larger and the value was 11.6×10-6 K-1.     

Application of Glass Sealant for SOFC

Glass and glass-ceramic materials were investigated as SOFC seals at 800 ～ 850 ℃. The material was based on the glass and glass-ceramic in the BaO-CaO-Al2O3-SiO2-La2O3-B2O3 system. The sealant has a minimum thermal expansion mismatch with yttria-stabilized zirconia (YSZ)electrolyte and Ni/gYSZ for the anode. The sealant has a superior stability during the process of operation in SOFC and can withstand thermal shock during the process of thermal cycling. The results show that the BaO-CaO-Al2O3-SiO2-La2O3-B2O3 system sealant can be used as sealing materials for SOFC.     

Thermal conductivity of （Sm1-xLax）2Zr2O7 （x=0, 0.25, 0.5, 0.75 and 1） oxides for advanced thermal barrier coatings

Pyrochlore oxides of general compositions, A2Zr2O7, where A is a 3+ cation (La to Lu), are promising candidate materials for ap-plications as high temperature thermal barrier coatings because of their high melting points, high thermal expansion coefficients, and low thermal conductivities. In this study, oxides of Sm2Zr2O7, (Sm0.75La0.25)2Zr2O7, (Sm0.5 La0.5)2Zr2O7, (Sm0.25La0.75)2Zr2O7 and La2Zr2O7 were prepared by solid reactions at 1600 ℃ for 10 h using Sm2O3, La2O3 and ZrO2 as the reactants. The phase compositions of these ceramic ma-terials were analyzed by X-ray diffractometer (XRD) and fourier transform infrared spectroscopy (FT-IR) methods, respectively. The micro-structure was observed by scanning electronl microscope (SEM). The thermal conductivities of these ceramic materials were measured using laser-flash method. XRD and FT-IR results showed that pure ceramic materials with pyrochlore structure were prepared successfully. SEM results indicated that microstructures of these ceramic materials were dense and grain boundaries were very clean. The La2O3 doped Sm2Zr2O7 pyrochlores (Sm0.75 La0.25)2Zr2O7 and (Sm0.5 La0.5)2Zr2O7 had lower thermal conductivity than the undoped Sm2Zr2O7. The thermal conductivity of (Sm0.25La0.75)2Zr2O7 was found to be lower than that of La2Zr2O7. The results showed that these ceramic materials had the poten-tial to be used as candidate materials for TBCs.     

渗铜用钨骨架制备工艺的研究进展

钨铜复合材料结合了钨的高熔点、高硬度、低膨胀系数和铜的高导电、导热性能,是一种性能十分优良的复合材料。熔渗法是目前制备钨-铜材料中广泛应用的方法,而熔渗法制备钨铜材料的关键是怎样获得一定致密度的钨骨架。目前制备钨骨架常用的方法主要有以下4种：（1）高温烧结;（2）模压成形;（3）挤压成形;（4）注射成形。本文就目前这4种常用钨骨架的制备工艺进行了简要的介绍和评述。     

含钨新材料研究进展

评述了1997年以来我国在含钨新材料研究上的一些进展。用前驱物脱水法制备了ZrW2O8和ZrM o2O8化合物,并证明具有立方晶体结构的ZrW2-XM o2XO8当W:M o为一定范围时都有热伸缩性质,有望成为热伸缩性能优良的材料。用机械-物理固相反应法制得了W S2纳米晶体,并证明其S-W-S纳米簇团为中空球,且W S2纳米晶粒径越小摩擦性能优越,更适用于超真空等领域。用煅烧钨酸铵制成的纳米W O3掺杂ZnS气敏材料对H2S具有较高的选择性和灵敏度。用溶胶-凝胶法和旋转镀膜技术制出的气致变色W O3纳米薄膜,在节能、信息等领域应用前景良好。     

Study on Microstructure of Alumina Based Rare Earth Ceramic Composite

Analysis techniques such as SEM, TEM and EDAX were used to investigate the microstructure of rare earth reinforced Al2O3/(W, Ti)C ceramic composite. Chemical and physical compatibility of the composite was analyzed and interfacial microstructure was studied in detail. It is found that both Al2O3 and (W, Ti)C phases are interlaced with each other to form the skeleton structure in the composite. A small amount of pores and glass phases are observed inside the material which will inevitably influence the physical and mechanical property of the composite. Thermal residual stresses resulted from thermal expansion mismatch can then lead to the emergence of dislocations and microcracks. Interfaces and boundaries of different types are found to exist inside the Al2O3/(W, Ti)C rare earth ceramic composite, which is concerned with the addition of rare earth element and the extent of solid solution of ceramic phases.