Effect of Y2O3, CeO2 on Sintering Properties of Si3N4 Ceramics

The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride.     

Low-Temperature Densification Sintering and Properties of Monoclinic-SrAl2Si2O8 Ceramics

The dense monoclinic-SrAl₂Si₂O₈ ceramics have been prepared by a two-step sintering process at a sintering temperature of 1173 K (900 °C). Firstly, the pre-sintered monoclinic-SrAl₂Si₂O₈ powders containing small SiO₂·Al₂O₃ crystal phases were obtained by continuously sintering a powder mixture of SrCO₃ and kaolin at 1223 K (950 °C) for 6 hours and 1673 K (1400 °C) for 4 hours, respectively. Subsequently, by the combination of the pre-sintered ceramic powders with the composite flux agents, which are composed of a SrO·3B₂O₃ flux agent and α-Al₂O₃, the low-temperature densification sintering of the monoclinic-SrAl₂Si₂O₈ ceramics was accomplished at 1173 K (900 °C). The low-temperature sintering behavior and microstructure evolvement of the monoclinic-SrAl₂Si₂O₈ ceramics have been investigated in terms of Al₂O₃ in addition to the composite flux agents. It shows that due to the low-meting characteristics, the SrO·3B₂O₃ flux agent can urge the dense microstructure formation of the monoclinic-SrAl₂Si₂O₈ ceramics and the re-crystallization of the grains via a liquid-phase sintering. The introduction of α-Al₂O₃ to the SrO·3B₂O₃ flux agent can apparently lead to more dense microstructures for the monoclinic-SrAl₂Si₂O₈ ceramics but also cause the re-precipitation of SiO₂·Al₂O₃ compounds because of an excessive Al₂O₃ content in the SrO·3B₂O₃ flux agent.     

Si3N4—ZrO2陶瓷在高应力条件下的抗氧化性能

研究了Ｓｉ３Ｎ４－ＺｒＯ２复合材料在主同温主同应力条件下的抗氧化能力。结果表明：（１）Ｓｉ３Ｎ４－ＺｒＯ２复合材料的抗氧化性主要取产愉于表面状态和ＺｒＮ的生成量；当表面有较多的ＺｒＯ２或者无ＺｒＮ时，其氧化程度很轻。（２）Ｓｉ３Ｎ４－ＺｒＯ２材料具有国产强的抗热冲击能力和抗高温压应力能力。     

Synthesis of Long Afterglow Phosphor CaAl2Si2O8:Eu2+, Dy3+ via Sol-Gel Technique and Its Optical Properties

The long afterglow phosphor CaAl2Si2O8:Eu2 , Dy3 was prepared by a sol-gel method. The sol-gel process and the structure of the phosphor were investigated by means of X-ray diffraction analysis (XRD). It is found that the single anorthite phase formed at about 1000 ℃, which is 300 ℃ lower than that required for the conventional solid state reaction. The obtained phosphor powders are easier to grind than those of solid state method and the partical size of phosphor has a relative narrow distribution of 200 to 500 nm. The photoluminescence and afterglow properties of the phosphor were also characterized. An obvious blue shift occurs in the excitation and emission spectra of phosphors obtained by sol-gel and solid state reaction methods. The change of the fluorescence spectra can be attributed to the sharp decrease of the crystalline grain size of the phosphor resulted from the sol-gel technique.     

Effect of Rare Earths on Mechanical Properties and Microstructures of Si3N4-based Ceramics

Si3N4-hased ceramics exhibit excellentproperties such as high strength, high corro..sion resistance, high fire resisting property andhigh thermal shock resistance. However, up tonow, the application of St3N4-based ceramicsis still limited by their poor ductility, lowtoughness and stability. Adding fiber or whisher into ceramic matrix is a useful tougheningmethod, but fiber and whisker are costly and itis difficult to homogenize them in ceramic matrix. Furthermore, ceramic powders can not fill…     

Effects of MgO on Properties of La2O3-TiO2 Ceramics

The influence of MgO on sintering and dielectric properties of La2O3-TiO2 ceramics was investigated, and the mechanism also discussed. The results show that La2O3-TiO2 ceramics with MgO can be sintered between 1200 and 1280 ℃. With the increasing of the MgO, the dielectric constant of the material decreases, but the temperature coefficient of dielectric constant increases. Between 1 and 40 MHz,     

Adhesion of liquid nickel to materials of the Si3N4-ZrO2 and Si3N4-Cr2O3 systems

Conclusions Refractory silicon nitride materials containing up to 50 wt.% of chromic and zirconium oxides (stabilized with CaO) are suitable for applications involving contact with liquid nickel.Translated from Poroshkovaya Metallurgiya, No. 5(173), pp. 91–93, May, 1977.     

原位制备细晶Si3N4-Si2N2O复相陶瓷

以Y2O3和Al2O3纳米陶瓷粉体作为烧结助剂，液相烧结非晶纳米Si3N4陶瓷粉体，制备Si3N4-Si2N2O复相陶瓷。Si2N2O相通过原位反应2Si3N4(s) 1．5O2(g)：3S12N2O(s) N2(g)生成。160012烧结，烧结体保温30min，Si2N2O体积分数达到52％，基本由细小均匀的球形晶粒构成。平均粒径尺寸210nm，相变过程中，个别颗粒异常长大，长径比达到1．5。保温时间对孔隙、密度和粒径产生重要影响：随着保温时间的延长，孔隙逐渐收缩减小，烧结体的致密度逐渐提高，晶粒逐渐长大，保温60min，孔隙几乎完全闭合，相对密度达到99．1％，平均粒径280nm。当保温时间达到90min时，相对密度增加并不明显，但平均粒径长大到360nm。     

La2O3, Ce2O3掺杂对原位合成Al2O3(p)/TiAl复合材料显微组织与性能的影响

借助XRD, SEM分析及力学性能测试, 分析了La2O3, Ce2O3掺杂对原位合成Al2O3颗粒强化钛铝基复合材料组织与性能的影响, 探讨了稀土氧化物（La2O3, Ce2O3）的细化机制. 研究结果表明： 掺杂稀土氧化物后产物由γ-TiAl/α2-Ti3Al双相、 Al2O3及Al4La或Al4Ce相组成;Al2O3颗粒分布于晶界处, 使基体晶粒得以细化;引入稀土元素后材料的密度明显增强, 氧化铝的团聚现象减弱. 力学性能测试表明, La2O3, Ce2O3的引入, 有效改善了复合材料的力学性能, 尤其是掺杂Ce2O3后, 材料的抗弯强度比未掺杂时提高了160%以上.     

Effect of Y2O3 on Dielectric Properties of BaTiO3 Ceramics

Tiny amount of rare earth Y2O3 can restrain the growth of grains and broaden the peak of BaTiO3 ceramics.Proper characteristics of capacitance change with temperature were obtained. Meanwhile, the insulation resistance increased with the increasing contents of Y2O3. In this system, the cooperation of Y2O3 with Ho2O3 was also discussed.It is concluded that the insulation resistivity reduces if the content of Y2 O3 is below 0.25 %. With the increasing content of additives, weak-binding electrons in grains will be compensated by V"8a so the insulation resistivity increased. The breakdown voltage is enhanced to 15 kV · mm-1.     

添加剂镍对原位合成TiB2-TiC复相陶瓷材料性能的影响

用TiH2，Ni和B4C作为原料，采用热等静压法制备了TiB2-TiC复相陶瓷材料，此方法工艺简单。成本较低。XRD研究表明在样品中只存在TiB2和TiC两相；TEM研究结果表明TiB2晶粒为规则的多边形和板条状，添加剂Ni位于TiB2/TiC交界处；显微硬度、断裂韧性和SEM断口形貌的研究结果表明添加剂Ni显著提高了TiB2-TiC复相陶瓷材料的综合性能。     

Study on Synthesis,Structure and Properties of Ba0.9 Sr0.1 TiO3: x Eu2 O3 Ceramics

A series of BaTiO₃ solid solutions were synthesized by sol-gel method during different aging time. The effect of aging time on the dielectric properties of BaTiO₃ ceramics was discussed. A series of BaTiO₃: x Eu₂O₃ and Ba_0.9Sr_0.1TiO₃: xEu₂O₃ solid solutions were synthesized by sol-gel method and their properties were investigated. The ceramics obtained were of high dielectric constants at room temperature. The results indicated that the dielectric properties of BaTiO₃ ceramics were improved by doping with Eu₂O₃. The doping of Sr²⁺ resulted in the decrease in T_c and the increase of dielectric constant. The dopant Eu³⁺ not only caused the decrease in T_c, but also caused the broadening of Curie peak.     

Cu/Al2O3复合材料的制备工艺、性能和组织研究

采用快速凝固离心雾化,原位反应和热挤压成形等工艺技术,制备了Cu/Al2O3复合材料,进行了Cu-Al系列合金粉末原位反应的热力学条件分析,确定了反应温度,研究了粉末成型压力与压坯密度,压坯烧结密度与电导率、硬度的关系,电导率、硬度随烧结时间的变化规律,以及材料显微组织随烧结时间的变化等,并与国内外有关行业制备的同类材料进行了综合性能比较.研究结果表明:Cu/Al2O3复合材料具有良好的物理、力学性能和较高的软化温度,为其生产应用提供了新途径.     

Effect of La2O3-Dopant on Microstructure and Microwave Dielectric Properties of CaO-MgO-Nb2O5-TiO2 System Ceramics

With the development of microwave integratedsystem for wireless communication, requirements ofthe microwave device are combined with high dielec tric constants (εr), low dielectric losses (Q = 1/tanδ) and near zero temperature coefficient for stabili ty and frequency selectivity[1,2]. But it is hard to findmaterials that satisfy all above mentioned requiredcharacteristics. In general, a ceramic with a high di electric constant has a larger positive temperature coef fi…     

原位反应合成致密Al2O3p-TiCp/Al复合材料

采用高能球磨细化晶粒、原位反应合成及热压技术制备了致密的Al2 O3 p TiCp/Al复合材料 ,并用XRD、SEM、以及EDAX等手段分析了复合材料的相组成、显微组织。结果表明 :Al TiO2 C三元体系在热压反应烧结后 ,可制得致密度较高的Al2 O3p TiCp/Al原位复合材料 ,其显微组织中Al2 O3 和TiC颗粒尺寸为 1μm左右 ,分布均匀。高能球磨有利于增强颗粒细化及弥散分布和反应。     

钛酸铅掺杂的Y_2Ti_2O_7基微波介质陶瓷的性能研究

以新型的具有中介电常数的Y2Ti2O7系微波介质陶瓷为研究基体,选用PbTiO3为改性添加剂,采用X射线衍射仪、扫描电子显微镜、网络分析仪和阻抗分析仪等现代测试仪器对材料的性能进行了表征,重点研究了PbTiO3掺杂后陶瓷材料的物相组成和介电性能。结果表明:PbTiO3掺杂没有改变材料的主晶相,仍为A2B2O7型烧绿石结构,由此推测PbTiO3可能固溶到Y2Ti2O7陶瓷晶格中。Pb2+占据Y3+所在的A位,且同时产生新的空位缺陷,破坏了材料的有序度,提高了晶格扩散速率,有效降低了陶瓷的烧结温度。少量Pb元素的加入使材料的晶胞常数增大,单位晶胞体积变大,Ti4+具有更大的运动空间,提高了材料本身的离子总极化率,从而提高材料的介电性能,尤其是介电常数值。当PbTiO3掺杂量为2%时,在1345℃下烧结,介电性能较好:εr=56.4,tanδ=1.21×10-3,Q×f=4776 GHz。     

掺钕氧化钪激光透明陶瓷纳米粉体的合成及研究

研究了化学共沉淀法合成Nd:Sc2O3纳米粉的工艺.以Sc2O3为基质材料,掺杂0.5％(原子分数)的Nd3+,添加适量聚乙二醇(PEG)和(NH4)2SO,作为分散剂,以氨水(NH3·H2O)和碳酸氢铵(NH4HCO3)混合溶液作复合沉淀剂,采用化学共沉淀法获得了碱式稀土碳酸盐前躯体,在1100℃下煅烧该前躯体4h,制备出性能良好的Nd:Sc2O3纳米粉.采用热重-差热分析仪(TG/DSC)、红外光谱分析仪(IR)、X射线衍射仪(XRD)、透射电子显微镜(TEM)等测试手段对Nd:Sc2O3前躯体和煅烧后的粉体进行表征.实验结果表明:在室温下,用氨水和碳酸氧铵混合溶液作为复合沉淀剂合成出的前躯体为碱式稀土碳酸盐.通过XRD和EDS能谱分析,Nd3+完全固溶于Sc2O3的立方晶格中,这将有利于制备激光透明陶瓷.在1100℃的温度下煅烧此前躯体得到的Nd:Sc2O3纳米粉具有颗粒粒度小(约50 nm)、分散性好、团聚程度轻、结晶良好的性能.因此,采用此工艺合成的粉体将有可能制备出的Nd:Sc2O3透明陶瓷.     

Structuring and Mechanical Properties of Composite Ceramics SiC(C) ― Si3N4, Sintered under High Pressure

We have studied the kinetics of high-pressure sintering of a composite SiC(C) ― Si₃N₄ powder of a certain phase composition. We consider structuring and mechanical properties of the ceramics obtained on the basis of this powder.     

Structuring and Mechanical Properties of Composite Ceramics SiC(C) ― Si3N4, Sintered under High Pressure

We have studied the kinetics of high-pressure sintering of a composite SiC(C) ― Si₃N₄ powder of a certain phase composition. We consider structuring and mechanical properties of the ceramics obtained on the basis of this powder.