Investigation of compaction and sintering behavior of SiC powder after ultra-fine treatment

INTRODUCTION In powder compaction, the characteristics ofthe powder affect the compaction behavior and thequality of the pressed green body and its relativedensity, porosity, pore size distribution, sinteringand the consequent microstructure of the final sin-tered body. Superfine powder is prerequisite forpreparing high performance ceramic materials (Liu,1996; Lange et al., 1983; Lange, 1989). At present,most of the chemosynthesis methods are not suit-able for preparing industrial …     

液相烧结SiC基复合材料的组织与力学性能研究

以α-SiC和BaAl2Si2O8（BAS）为原料,采用热压烧结工艺制备了SiC基复合材料．研究了添加剂对液相烧结SiC基复合材料的致密化、显微组织、抗弯强度及断裂行为的影响．测试结果表明,添加剂BAS有效促进了SiC基复合材料的致密化．40wt％BAS／SiC复合材料的抗弯强度和断裂韧性分别高达454MPa和5．1MPa·m^1/2．复合材料的主要增韧机制为SiC晶粒的拔出、裂纹偏转和裂纹桥连．     

C纤维和SiC纤维增强SiC基复合材料微观结构分析

为减缓由于碳纤维与碳化硅基体热膨胀系数差异导致的微裂纹的产生,同时采用了C、SiC纤维作为增强体,通过有机前驱体浸渍裂解法(PIP)制备了(C-SiC)f/SiC复合材料,并通过扫描电子显微镜对复合材料的显微结构进行了分析,研究了复合材料中纤维排布方式以及基体相组成。研究发现,采用扫描电子显微镜的方法能够清晰地分辨出复合材料中各相的存在形式。从复合材料抛光面分析可以发现,在纤维束交错处存在束间基体聚集区域。复合材料基体主要由具有不同衬度的两相组成,分别是由含纳米SiC粉体浆料裂解产物和有机聚合物前驱体(PCS)裂解产物。PCS裂解产物主要呈带状,分布在浆料裂解过程中形成的裂纹和微孔中。     

Microstructure and mechanical properties of liquid phase sintered silicon carbide composites

Silicon carbide (SiC) composites were prepared by hot-press sintering from α-SiC starting powders with BaAl2Si2O8 (BAS). The effects of additives on densification, microstructure, flexural strength, and fracture behavior of the liquid phase sintered (LPS) SiC composites were investigated. The results show that the served BAS effectively promotes the densification of SiC composites. The flexural strength and fracture toughness of the SiC composites can reach a maximum value of 454 MPa and 5.1 MPa·m1/2, respectively, for 40% (w/w) BAS/SiC composites. SiC grain pullout, crack deflection, and crack bridging were main toughening mechanisms for the sintered composites.     

Sintering and microstructure of silicon carbide ceramic with Y3Al5O12 added by sol-gel method

Silicon carbide (SIC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 ℃ with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging‘.     

用原位拉伸研究复合材料的机械性能

用扫描电镜原位拉伸的方法研究了碳化硅纤维增强镁铝复合材料的机械性能. 通过对材料中裂纹的起源、扩展、断裂过程的观察研究, 发现在拉伸状态下, 裂纹最初起源于碳化硅纤维; 在碳化硅纤维与基体结合较强时, 裂纹首先在碳化硅纤维中扩展, 同时裂纹附近的碳化硅纤维亦开始产生微观裂纹、镁铝金属基体发生塑性变形, 最终断裂; 而在碳化硅纤维与基体结合较弱的状态下, 材料的韧性较高.     

高体积分数铝基复合材料制备工艺的研究

阐述了压铸法制备SiC/Al铝基复合材料的工艺,测试了碳化硅的粒径特性,并对碳化硅颗粒微观形貌进行了观察,采用湿法制备了碳化硅体积分数为60%碳化硅预制件素坯,并用该素坯制备了SiC/Al铝基复合材料。     

Research on Gelcasting Formation of SiC-Al_2O_3-Y_2O_3-La_2O_3 Systems

Siliconcarbide (SiC)ceramicmaterialsareusefulad vancedmaterialsinmanyfields,suchasmedicalbiomateri als ,hightemperaturesemiconductors ,synchrotronopticalel ementsandhighstrength /lightweightstructuralmaterials[1] .However,theactualapplicationisstilllimitedduetoitslowreliability ,highmachiningcosts[2 ] .Gelcastingprovidesane conomicalandfeasiblenet shape forminghomogeneousandflawlessgreenbodieswithcomplexgreenshapes.　　Gelcastingconsistsofin situpolymerizationthroughwhichamacromolecularnetwor…     

超薄纳米SiC催化材料对氧还原反应催化性能研究

目的:开发高效廉价的氧还原反应催化剂。方法:采用超声剥离法,以商业SiC为原料,成功获得了超薄纳米SiC催化剂,对其形貌进行了表征,并对其催化氧还原(ORR)性能进行研究。结果:超声处理能有效地剥离商业SiC,获得超薄催化剂。超薄纳米SiC催化剂对氧还原反应的起始电位和电流密度均与商业Pt/C催化相近,氧还原反应以4电子路径为主,在较低电位下能获得较大的动力学电流。结论:本实验制备的超薄催化剂,有望作为高效低成本燃料电池的潜在材料。     

SiC/Si浓悬浮体的胶体特性及流变性研究

凝胶注模成型是一种制备均匀性好、强度高和形状复杂的陶瓷部件的成型技术 ,目前已在各种精密陶瓷材料的近净尺寸成型制备中得到了广泛应用 .但已有研究工作主要针对微米和亚微米尺寸的陶瓷粉末的成型 ,而大多数高级耐火材料制品都属毫米级粗颗粒的高温材料 .本文研究了粒径为毫米级粗颗粒体系SiC/Si粉末的Zeta电位、分散性以及SiC/Si浓悬浮体的流变性 ,制备了固相体积分数高达 72 %的SiC/Si浓悬浮体并浇注出形状复杂的均一致密的SiC/Si坯体     

碳化硅质量对微波加热的影响

本文主要研究了碳化硅的质量对微波加热升温速度的影响。结果表明,碳化硅试样的质量过大或过小,其平均升温速度均较小,只有当试样质量在某一适范围内,平均升温速度可达最大值;同时还表明,在低温阶段,碳化硅试样质量越小,升温越快,高温阶段,质量越小升温越慢。     

基于集群磁流变单晶碳化硅基片抛光加工的工艺研究简

基于集群磁流变效应超光滑平面抛光理论及试验装置对单晶碳化硅基片进行了平面抛光试验,结果表明,金刚石磨料对单晶Sic基片具有较高的材料去除率;加工间隙在1．5I砌左右具有较好的加工效果,随着加工时间的延长表面粗糙度越来越小,且30min内表面粗糙度变化率达到89％以上。通过优化工艺参数对单晶SiC进行集群磁流变平面抛光,发现经过30min加工,表面粗糙度Ra从42．1m下降到4．2nm,表明集群磁流变效应平面抛光用于加工单晶SiC基片可行且效果显著。     

反应烧结Cr/Si/C复相陶瓷的微观结构表征与力学性能

本文采用掺杂Cr2C3的方法探究增韧补强反应烧结SiC陶瓷的途径。通过凝胶注模成型及反应烧结工艺制备Cr/Si/C复相陶瓷由SiC、Si和CrSi2组成,CrSi2由Cr2C3与熔融Si反应生成;材料中SiC颗粒分布均匀,CrSi2存在明显偏析;Gr/Si/C复相陶瓷抗弯强度接近反应烧结SiC/Si陶瓷,平面应变断裂韧性KIC达到3.81MPa.m1/2;CrSi2分布不均和弱化界面结合是抗弯强度以及弹性模量降低的原因。     

AlC~+和SiC~+基态的分子结构和光谱属性

应用QCISD(T)/6-311++G(3df,3pd)和B3LYP/6-311++G(3df,3pd)方法,对AlC+和SiC+基态的分子结构和光谱属性进行了详细的理论计算.得到了AlC+和SiC+基态的能量,平衡结构,谐振频率.同时根据原子分子反应静力学原理,导出了AlC+和SiC+基态的合理离解极限和离解能.计算结果表明,AlC+和SiC+基态的光谱常数与现有的文献结果基本一致.部分光谱常数是第一次给出理论的报道.     

非晶碳化硅薄膜光学特性的热退火效应

通过Raman光谱、紫外-可见透射光谱技术及原子力显微镜对非晶碳化硅薄膜结构和光学特性的热退火效应进行了研究。结果表明,碳化硅拉曼谱带随退火温度的增加而逐渐红移和尖锐化,显示了薄膜中晶化有序度的提高。退火后薄膜包含大量紧凑的纳米团簇,膜面相对于未退火样品较为粗糙。根据紫外-可见透射光谱导出的光学带隙从原始样品的1．86eV连续增加到经1050℃退火样品的2．23eV。碳化硅薄膜中纳米团簇的形成及其晶化程度的增加导致了薄膜光学带隙的蓝移效应。     

Influence of surface roughness on the color of dental-resin composites

This study deals with the influence of surface roughness on the color of resin composites. Ten resin composites (microfilled, hybrid, and microhybrid) were each polished with 500-grit, 1 200-grit, 2 000-grit, and 4 000-grit SiC papers. The roughness parameter (R _a) was measured using a Plμ confocal microscope, and field-emission scanning electron microscope (Fe-SEM) images were used to investigate filler morphology. Color was measured using a spectroradiometer and a D65 standard illuminant (geometry diffuse/0° specular component excluded (SCE) mode). Surface roughness decreased with grit number and was not influenced by filler size or size distribution. A significant influence of R _a on lightness (L*) was found. Lightness increased with decreases in roughness, except for specimens that underwent polishing procedure 4 (PP4; 500-grit, 1 200-grit, 2 000-grit, and 4 000-grit SiC papers consecutively). Generally, it was found that surface roughness influenced the color of resin composites. The composites that underwent PP1 (500-grit SiC paper) exhibited significant differences in chroma (C*), hue (h°), and lightness (L*) compared to composites that underwent PP3 (500-grit, 1 200-grit, and 2 000-grit SiC papers consecutively) and PP4. Color difference (ΔE*) between the polishing procedures was within acceptability thresholds in dentistry.     

自蔓延高温合成层状Ti_3SiC_2陶瓷的相形成过程

采用自蔓延高温合成方法,以Ti、Si、C粉为原料合成了层状Ti3SiC2陶瓷材料,用X射线衍射分析了燃烧合成产物的相组成,并结合反应物体系的差热分析和X射线衍射分析探讨了自蔓延高温合成Ti3SiC2的相形成过程,进而建立Ti-C-Si体系在自蔓延燃烧合成反应过程的物理模型.     

^11B^35Cl和SiC的势能函数

采用从头计算的方法研究了^11B^35Cl和SiC的结构和势能函数。对基态的^11B^35Cl,采用的是CISD／6—311＋G＊的方法。对基态的SiC分子采用的是B3LYP／6—311＋＋G＊＊的方法。根据CISD方法（对^11B^35Cl）和B3LYP方法（对SiC）的计算结果,采用最小二乘法拟舍出了Murrell-Sorbie势能函数的参数。并得出了力常数和光谱数据。     

SiC颗粒对Al-Zn合金激光快凝晶粒组织的影响

Al-Zn合金和SiCp/Al-Zn复合材料的激光重熔晶粒组织的对比研究表明 ,SiC颗粒对凝固初生相的生长具有阻碍作用。在颗粒尺寸较大和颗粒含量较高的条件下 ,激光熔池中会形成非外延生长的晶粒     

SiC传感器信号采集与处理系统设计

本文设计制作了一个模拟／数字（A／D）转换卡，可将经过SiC传感器调理后的毫伏级的模拟信号转成数字信号，并进行相应的显示和存储，可广泛应用于各种中低频小信号采集处理系统中．