THE CHARACTERISTICS OF THE PRESSURELESS SINTERED Si_3N_4-MgO-Ce0_2 CERAMICS

An investigation of the pressureless sintering of Si3N4 with MgO-CeO2 revealed that MgO-CeO2 is a most effective sintering aid for silicon nitride. The amount of MgO-CeO2 and sintering conditions have a strong influence on the densification behaviour and mechanical properties of the sintered materials. The effect of the additive and sintering conditions are discussed. The silicon nitride pressureless sintered with MgO-CeO2 retained a relative density of 98. 5% and a bending strength of 950 MPa. The Si Mg-Ce-O-N system is of great value for application and theoretical study.     

OBSERVATION ON THE MICROSTRUCTURE OF SINTERED Si_3N_MgO-CeO_2 CERAMICS

The microstructure of the pressureless sin- tered Si_3N_4 ceramics with MgO-CeO_2 has been studied by TEM.The glassy phase is observed and confirmed directlyby microdiffraction.EDAX analysis results show that themain function of the CeO_2 lies in the glass phase which hard-ly contains any MgO.The cerium silicate galssy phase isgood to wet Si_3N_4 and MgO-CeO_2 is a most effective sinter-ing aid for Si_3N_4.Excessivee grain growth occurs at above1850℃,which is harmful to the mechanical properties.Mi-crocracks and dislocations are observed in the excessive largegarains     

ZrO2对热压Si3N4陶瓷材料断裂韧性及显微结构的影响

研究了ＺｒＯ２对热压Ｓｉ３Ｎ４陶瓷材料的断裂韧性Ｋｉｃ、显微结构及结构组成的影响。结果表明，Ｚｒｏ２的含量对Ｓｉ３Ｎ４陶瓷的断裂韧性有显著影响，在１０ｗｔ％时出现峰值ＫＩＣ为７．８３ＭＰａ．ｍ＾１／２，提高约２１．４％，热压Ｓｉ３Ｎ４－ＺｒＯ２系统中能有效地撸制ＺｒＮ的生成。     

无压烧结Si_3N_4－MgAl_2O_4－Al_2O_3系复合材料

本文对ｓｉ＿３Ｎ＿４－ＭｇＡｌ＿２Ｏ＿４－Ａｌ＿２Ｏ＿３系复合材料的无压烧结进行了研究。讨论了Ａ１＿２Ｏ＿３含量对材料性能的影响及烧结工艺对材料性能和显微结构的相互关系。实验表明：两段法烧结可以得到性能良好的Ｓｉ＿３Ｎ＿４－ＭｇＡｌ＿２Ｏ＿４－Ａｌ＿２Ｏ＿３复合材料     

THE ROLE OF MgO-CeO_2 IN THE DENSIFICATION OF Si_3N_4

An investigation of the pressureless sinteringof Si_3N_4 with MgO-CeO_2 reveals that Mgo-CeO_2 is a muchmore effective sintering aid for silicon nitride than eitherMgO or CeO_2.The amount of MgO-CeO_2 and MgO/CeO_2weight ratio has a strong influence on the densification be-haviour and mechanical properties of the sintered materials.The Silicon nitride pressureless sintered with MgO-CeO_2 re-tains a relative density of 98.5%,a bending strength of 950MPa.The Si-Mg-Ce-O-N system is of great value for appli-cation and theoretical study.     

Design,preparation,and structure of particle preforms for Si_3N_(4(P))/Si_3N_4 radome composites prepared using chemical vapor infiltration process

A particle preform was designed and prepared by conglomerating and cold-pressed process,which was condensed by chemical vapor infiltration(CVI)process to fabricate silicon nitride particles reinforced silicon nitride composites.The conglomera- tions are of almost sphericity after conglomerated.There are large pores among the conglomerations and small pores within them- selves in the preform according to the design and the test of pore size distribution.The pore size of the preform is characterized by a double-peak distribution.The pore size distribution is influenced by conglomeration size.Large pores among the conglomerations still exist after infiltrated Si_3N_4 matrix.The conglomerations,however,are very compact.The CVI Si_3N_4 looks like cauliflower- shaped structure.     

氧化对添加Al_2O_3的Si_3N_4陶瓷材料强度的影响

实验表明,Si_3N_4陶瓷在1200℃的空气中氧化后,其室温强度随着氧化时间的增加呈现出先增加后下降的趋势,其中在1200℃的空气中氧化75小时后宣温强度提高了16%。当在1300℃的空气中氧化100小时后,高温强度提高了22%。     

HIGH-TEMPERATURE CHARACTERIZATION OF SELF- REINFORCED Si_3N_4 WITH ADDITIVES Y_2O_3 AND La_2O_3

High-temperature strength and fracturetoughness,oxidation behavior,and thermal shock of the SRSi_3N_4 with Y_2O_3 and La_2O_3 as complex additives are inves-tigated.The research results show that the strength does notdecrease until 1400℃;the fracture toughness,while,in-creases with temperature rising and presents peak value at1350℃.The oxidation behavior obeys parabolic law,andthe oxidation procedure is mainly controlled by diffusion of additive ions.The high oxidation resistance of this mate-rial is primary due to the presence of refractory Y~(3 )andLa~(3 )at intergrnular glass phase.The thermal shock exper-iments show that the damage of strength is far larger thanthat of fracture toughness.     

HIGH TEMPERATURE STRENGTH OF AIN CERAMICS WITH Y_2O_3

The AIN ceramics with Y_2O_3 is prepared byhot-pressing.The phase compositions andtheir distributions are determined by X-ray,SEM and EPA.Both the relation betweenbend strength and temperature and the relationbetween bend strength and oxidation time in1300℃ air ore investigated.It is found thatthe bend strength decreases slightly with theincreasing of temperature below 1300℃ anddecreases violently within 1300～1500℃.The samples are oxidized in 1300℃ air andtheir strength decreases with the increasing ofoxidation time.The fracture mechanisms ofAIN ceramics with Y_2O_3 at differenttemperature and after being oxidized in1300℃ air are discussed.     

Processing and performance of 2D fused-silica fiber reinforced porous Si_3N_4 matrix composites

Two-dimension(2D)fused-silica fiber reinforced porous silicon nitride matrix composites were fabricated using slurry impregnation and cyclic infiltration with colloidal silica sol.The microstructure and fracture surface were characterized by SEM,the mechanical behavior was investigated by three-point bending test,and the dielectric constant was also measured by impedance analy- sis.The microstructure showed that the fiber and the matrix had a physical bonding,forming a clearance interface.The mechanical behavior suggested that the porous matrix acted as crack deflection,and the fracture surface had a lot of fiber pull-out.However,the interlaminar shear strength was not so good.The dielectric constant of the composites at room temperature was about 2.8-3.1.The relatively low dielectric constant and non-catastrophic failure indicated the potential application in the radome materials field.     

Si3N4／SiO2辅助介质剥离膜的研究

提出了利用Ｓｉ３Ｎ４／ＳｉＯ２双层介持膜作为ＧａＡｓＭＥＳＦＥＴ（Ｍｅｔａｌ Ｓｅｍｉｃｏｎ－ｄｕｃｔｏｒ Ｆｉｅｌｄ Ｅｆｆｅｃｔ Ｔｒａｎｓｉｓｔｏｒ）剥离工艺中的辅助剥离膜，研究结果表明，采用Ｓｉ３Ｎ４／ＳｉＯ２双层介质剥离膜，易于形成倒剪口剖面，金属剥离效果良好，是一种非常有效的辅助剥离膜。     

Si3N4-SiO2复合材料的制备及介电性能研究

以国产氮化硅、二氧化硅粉为原料，以氧化镁、氧化铝为烧结助荆，经干压成型后，在流动的高纯N2作为控制气氛的条件下，常压烧结出结构均匀，具有良好介电性能的Si3N4-SiO2复合材料。研究了原料、烧结温度、烧结助剂对材料介电性能的影响。结果表明：SiO2、MgO、Al2O3可促进坯体的烧结及致密，同时时材料的介电性能有较大的影响。当烧结温度低于1550℃时，随着烧结温度的升高，材料的介电常数趋于增大。当烧结温度高于1550℃时，随着温度的升高，材料中缺陷增加，相对密度降低，因此材料的介电常数趋于减小。     

Microstructure and properties of Si3N4 ceramics obtained from addition of β-phase seeds and celsian

The silicon nitride based ceramics obtained by the addition of β-Si3N4 seeds was fabricated using celsian as the additive and by pressureless sintering. The microstructure of the material was observed and analyzed using XRD, SEM, and TEM and the mechanical response of this array microstructure was characterized for flexural strength and fracture behavior. The result shows that the growth of the larger aspect ratio grains initiate mainly from the seeds through the heterogeneous nucleation mechanism during the process of phase transformation, and the intergranular phase BaAl2Si20s services as good refractory materials. In contrast to conventional processing, a stable bimodal microstructure and complicated component with a lower cost can be achieved using the abovementioned process theoretically and practically.     

气门钢表面激光熔覆Si3N4陶瓷层的研究

利用激光在气门钢表面熔覆Si3N4陶瓷.对熔覆粉末成分、熔覆处理的工艺参数、熔覆层的组织、相组成及结合界面作了分析研究.     

Fabrication of Fine-Grained Si3N4-Si2N2O Composites by Sintering Amorphous Nano-sized Silicon Nitride Powders

1 IntroductionAs high-temperature structure materials ,nitride ce-ramics possess the excellent mechanical properties ,highmelting temperature ,low density, high elastic modulusand strength, and good resistance to creep, wear andoxidation[1-3]. The intrinsic brittleness and hardness ofsilicon nitride ceramics , however , make it difficult andcostly to machine into complex-shaped components[4 ,5].The fracture toughness of sintered silicon nitride ceramicsmust beimprovedif these ceramics areto be…     

EFFECTS OF In_2O_3 DOPING AND SINTERING TEMPERATURE ON THE ELECTRICAL PROPERTIES OF ZnO VARISTORS

ZnOvaristorshaveexcellentnon--linearcurrent--voltage(IV)characteristicsandenergyabsorptionability,makingthemvaluableasvoltagesuppressersinpowersystemsandelectroniccircuitsLlj.Thecurrentvoltagedependenceofvaristorsisdescribedbytherelation:I=C(V)"whereIisthecurrentdensity,Caconstant,Vthevoltage,andathecoefficientofnon--linearity.ThestudyresultsshowthatpureZnOgrainhasnottheelectricalconductivity.Intheprocessofitspreparation,thedefectisproducedinthegrain,andmakeitann--typesemiconductor.Thecer…     

THE STRUCTURE AND PROPERTIES OF Li2O-Al2O3-SiO2 LOW EXPANSION GLASS CERAMICS CONTAINING B2O3

Through measuring the coefficient of linear expansion, the structure and properties of the Li2O-Al2O3-SiO2 low expansion glass ceramics containing B2O3 are studied by JR and XRD. It is shoutn that the IR method is efficient in the study of the glass-ceramics structure. There is a " Boron abnormality" in the system which has an important influence on the properties of the glass-ceramics.     

Fabrication of high performance 3D SiO<Subscript>2</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite via perhydropolysilazane infiltration and pyrolysis

The continuous fiber reinforced ceramic matrix composites have received consider-able attention for structural applications because of their excellent thermal stability, light weight, and damage tolerance imparted by the reinforcing fibers. Silica fibers, with ex-cellent ablative resistance, thermal shock damage resistance, dielectric properties, chemical stability and flexibility, are suitable for fabricating high temperature antenna window materials to meet the requirements of communication, …     

2%Cl_2/20%O_2/Ar 环境中 Si_3N_4 陶瓷的高温腐蚀(英文)

使用ｔｈｅｒｍｏｇｒａｖｉｍｅｔｒｉｃ分析和表面分析法,对２％Ｃｌ２／２０％Ｏ２／Ａｒ环境中Ｓｉ３Ｎ４陶瓷在１１５０℃和１３５０℃时的化学反应进行了研究。在１１５０℃,ＳｉＯ２层Ｃｌ２有少的渗透趋向,氧扩散穿过ＳｉＯ２层而发生反应。但在１３５０℃,某些添加物和杂质,向表层和晶养扩散,且Ｃｌ２与Ｓｉ３Ｎ４的反应对腐蚀有较大影响。