Crystallization Behavior of Amorphous Si2BC3N Ceramic Monolith Subjected to High Pressure

The crystallization behavior of amorphous Si₂BC₃N monoliths by heating at 1000°C–1400°C and 5 GPa was investigated with the special attention to the nucleation mechanisms of β‐SiC and BN(C) phases. Nanoscale puckered structures arising in particle bridging areas were found and its evolution behavior well reflected the nucleation process of nanocrystallites. The temperature‐dependent crystallization of amorphous Si₂BC₃N monoliths at 5 GPa passes through four stages: The material remains amorphous below 1100°C. It undergoes partial phase segregation (1100°C–1200°C), followed by initiation of nucleation (1200°C–1250°C), and then nucleation and growth of β‐SiC and turbostratic BN(C) crystallites (>1250°C). The first principles calculation indicates the nucleation precedence of BN(C) phase over β‐SiC. BN(C) nucleates preferentially at bridges between ceramic particles causing SiC to concentrate in particle interiors thus forming capsule‐like structures.     

常压烧结制备多孔氮化硅陶瓷研究

选用Al2O3、Y2O3、Lu2O3三种氧化物作为烧结助剂,采用凝胶注模成型和气氛保护常压烧结工艺,成功制备了具有高强度和高气孔率的多孔氮化硅陶瓷材料.本文研究了三种烧结助剂对多孔氮化硅的力学性能、介电性能和微观结构的影响,以及对氮化硅陶瓷的烧结促进作用,结果表明Y2O3具有最佳的烧结活性促进作用,其微观结构表明β-Si3N4棒状晶粒搭接结构是使多孔氮化硅陶瓷材料具有较好力学性能的重要原因.     

Si3N4-MgO-Al2O3的SPS制备及其力学性能

利用氧化镁(MgO)和氧化铝(Al2O3)作为烧结助剂,采用放电等离子烧结(SPS)方法制备α-Si3N4陶瓷材料。讨论了SPS方法制备氮化硅材料的烧结行为和烧结机理,分析了烧结助剂添加量和烧结温度等影响因素与材料致密度的关系,利用XRD分析了样品的物相组成,SEM观察了样品断口的显微结构,并且测试了样品的力学抗弯强度。结果表明当烧结温度为1300~1500℃,烧结助剂含量为6%~10%时,可以制备出致密度变化范围为64%~96%的α-Si3N4陶瓷材料;当烧结助剂含量为10%时,材料在1400℃即可烧结致密,致密度可达到95%以上。烧结机理为SPS低温液相烧结。材料的力学强度为50~403MPa,并且与密度关系密切。     

烧结工艺对β-氮化硅陶瓷的影响

以β-Si3N4粉末为原料,以YAG（钇铝石榴石）为烧结助剂,通过气氛压力烧结（GPS）制备出致密的β-氮化硅陶瓷材料,形成大小均匀的柱状颗粒和小球状颗粒复合显微结构,研究了烧结助剂质量分数、烧结温度以及保温时间对β-氮化硅陶瓷致密化程度及力学性能的影响.     

放电等离子烧结Cu/Ti3AlC2的电性能及力学性能

以Ti3AlC2和Cu粉作为原料,使用放电等离子烧结制备Cu/Ti3AlC2复合材料,研究了不同烧结温度对复合材料的影响。结果表明,在750~800℃之间,Cu与Ti3AlC2之间会发生反应生成TiC相。同时随着温度在650~850℃不断增加,密度和抗弯强度不断增加在850℃达到最大值分别为8.33 g·cm^-3和531.4 MPa,而电阻率先减小在750℃达到最小值1.98×10^-7Ω·m后增加在850℃达到最大值6.47×10^-7Ω·m。Cu/Ti3AlC2复合材料性能随着温度的变化与其致密度和反应生成TiC有着密切的联系。     

放电等离子烧结Si3N4陶瓷

本文用放电等离子烧结法制备Si3N4陶瓷,通过排水法测定密度,X射线衍射法测定物相变化,透射电镜进行微观形貌的观察。发现在烧结过程中,当高于1450℃时MgO—CeO2与氮化硅粉末表面的SiO2反应形成硅酸盐液相,促进烧结致密化,冷却后形成玻璃相留在品界,氮化硅的致密化在1500℃接近完成,但高于1550℃时,出现MgO自析晶,微观形貌为相互交织的等轴状的α—Si3N4和柱状的β—Si3N4晶粒。     

纳米氮化硅粉体材料的ICP制备技术及TEM分析

用硅烷和氮气为反应气体,采用ICP等离子体化学气相沉积技术合成氮化硅纳米粉体。用朗缪尔探针诊断了反应室内等离子体参数,得到不同位置、不同功率下等离子体密度的变化规律,等离子体密度随着功率的增大而增大,由于离子鞘层的存在,提供了局部等离子体密度稳定的区域。利用TEM分析了纳米氮化硅的显微形貌,结果表明：纳米氮化硅粉体颗粒为球形,分布于20～40nm。     

Si3N4/Si3N4扩散连接的力学性能研究

采用热压法进行氮化硅陶瓷材料的扩散连接.结果表明:在1520℃,15MPa,60min条件下,氮化硅连接体的最高强度为448.6MPa,超过母材强度;平均连接强度为401.5MPa,为母材强度的96%.     

无压烧结Al2O3/Si3N4纳米复合陶瓷的力学性能

通过对Al2O3／Si3N4体系进行无压烧结,获得的试样相对密度大于98％,物相分析烧结体中没有Si3N4颗粒存在,而是形成β-SiAlON相。Si3N4和Al2O3反应生成的β-SiAlON相颗粒不仅分布在Al2O3晶粒晶界处,也存在于Al2O3晶粒内部,形成独特的“内晶型”结构。当受到外力时既能诱发穿晶断裂,又能引起裂纹偏转,起增强作用,但由于产生晶界滑移,材料韧性有所下降。     

无压烧结硼化锆基ZrB2-SiC复相陶瓷的结构与性能

以钇铝石榴石-YAG为烧结助剂,通过无压烧结制备了ZrB2-SiC复相陶瓷。研究了烧结助剂含量对烧结材料力学性能和显微结构的影响,材料的显微结构由扫描电镜SEM及其能谱分析EDS测定。研究结果表明,烧结助剂(YAG)和原料中的杂质形成玻璃相填充在晶界上,显著促进了硼化锆基ZrB2-SiC复相陶瓷的致密化。     

烧结工艺对Si3N4泡沫陶瓷性能的影响

本文在有机泡沫浸渍法制备多孔氮化硅陶瓷的过程中,讨论了升温速度、烧结助剂的添加量和烧结温度对氮化硅网眼多孔陶瓷显微组织、物相和力学性能的影响.研究结果表明,随Y2O3和Al2O3的含量的增加,烧结体的强度明显增加,且含量为20%时较优.通过分析聚氨酯海绵的DSC-TDA曲线,得出在150～475 ℃温度区间,要缓慢升温.烧结温度在1700 ℃左右较优,且相变较完全.     

无压烧结Al2O3/Si3N4纳米复合陶瓷的力学性能

对Al2O3／Si3N4体系进行无压烧结。获得试样相对密度大于98％,物相分析烧结体中并没有Si3N4颗粒存在而是形成SIALON相。Si3N4和Al2O3反应生成的β-SIALON相颗粒不仅分布在Al2O3晶粒晶界处也存在于Al2O3晶粒内部,形成独特的“内晶型”结构。当受到外力时既能诱发穿晶断裂,又能引起裂纹偏转,从而起到增强的作用。由于产生晶界滑移,韧性有所下降。     

Processing and Mechanical Properties of Zirconium Diboride-Based Ceramics Prepared by Spark Plasma Sintering

Zirconium diboride (ZrB₂) reinforced by nano-SiC whiskers has been prepared by spark plasma sintering (SPS). Of most interest is the densification of ZrB₂–SiCw composites accomplished by SPS at a temperature as low as 1550°C. The relative density of ZrB₂–SiCw composites could reach to 97% with an average grain size of 2–3 μm. Both flexural strength and fracture toughness of the composites were improved with increasing amount of SiCw. Flexural strengths ranged from 416 MPa for monolithic ZrB₂ to over 545 MPa for ZrB₂–15 vol% SiCw composites. Similarly, fracture toughness also increased from 5.46 MPa·m^1/2 to more than 6.81 MPa·m^1/2 in the same composition range. The relative density of ZrB₂–SiCw composites could be further improved to near 100% by adding some sintering aids such as AlN and Si₃N₄; however, the effects of different sintering additives on the mechanical properties of the composites were different.     

Highly Transparent Mg0.27Al2.58O3.73N0.27 Ceramic Prepared by Pressureless Sintering

A novel aluminum magnesium oxynitride transparent ceramic with the chemical formula Mg_0.27Al_2.58O_3.73N_0.27 was firstly prepared by pressureless sintering of fine single‐phase powders at 1875°C for 24 h in nitrogen atmosphere. The ceramic was fully dense with the average grain size of 57.5 μm. The sample showed excellent in‐line transmission from the visible to middle‐infrared wavelengths with the maximum transmittance of 84%, which could be attributed to rare pores in the sintering body. The material also exhibited good mechanical properties of Vickers hardness (13.39 ± 0.18 GPa), fracture toughness (2.46 ± 0.3 MPa/m^1/2), and flexural strength (274 ± 6 MPa).     

Effect of Nano-Al2O3 on Mechanical Properties and Microstructure of Si3N4 Ceramics

Si3N4ceramics were prepared by pressureless sintering at 1 650 ℃ in nitrogen atmosphere using Si3N4powder as main starting material and adding nanoAl2O3powder( 3%,6%,9%,12%,and 15% in mass,the same hereinafter). The bending strength and fracture toughness( KIC) of the specimens were detected.The microstructure and phase compositions of the specimens were analyzed. The results show that Si3N4ceramics can be prepared by pressureless sintering when adding9%- 12% nano-Al2O3as active reactant,which dissolves in Si3N4,in-situ forming non-oxide SiAlON. The obtained Si3N4ceramics have the maximum bending strength of 710. 86 MPa and KICof 8. 61 MPa·m1 /2.The excellent properties come from many interwoven structures distributed uniformly in the ceramics matrix,which is composed of big and firm plate-like β-Si3N4,hexagonal SiAlON and sheet Si2N2O.     

氮气压力对氮化硅烧结行为的影响

本文在１４００－１７００℃温度范围内，分别在３０ａｔｍ和１ａｔｍ的Ｎ２中氮化硅陶瓷的烧结行为进行了比较研究，对比试验结果表明，在气压烧结过程吕其致密化和α－β相变速率滞后于常压烧结，晶界第二相组成也有所不同。为了避免高压气氮气被包陷和致密化滞后，在气压烧结过程的前期应避免使用高压氮气。     

常压烧结Si3N4-MgO-Y2O3-CeO2陶瓷的研究

本研究了Si3N4-MgO—Y2O3-CeO2陶瓷的烧结过程和微观结构,常压烧结氮化硅陶瓷的致密化主要通过液相烧结实现。微观分析结果表明,氮化硅烧结体的显微结构为等轴状的α—Si3N4和长柱状的β—Si3N4相互交织,这种结构有利于提高烧结体的强度和韧性。     

Si3N4-TiN纳米复相陶瓷的制备与性能研究

采用热压烧结方法制备了Si3N4-TiN纳米复相陶瓷,研究了纳米TiN颗粒的添加对Si3N4陶瓷组织、力学性能和抗热震性能的影响.研究结果表明:Si3N4-TiN纳米复相陶瓷的显微组织由粒径为100 nm左右的晶粒构成,TiN以独立颗粒的形式存在;纳米TiN颗粒的添加可以提高纳米Si3N4陶瓷的断裂韧性和抗弯强度,但对硬度影响不大;适量TiN颗粒的添加能改善纳米Si3N4陶瓷的抗热震性.     

工艺参数对气压烧结制备CaAlSiN3:Eu2+荧光粉性能的影响

采用气压烧结法制备了用于暖白光LED的红色氮化物CaAlSiN_3:Eu~(2+)荧光粉,利用X射线衍射仪(XRD)、扫描电镜(SEM)、荧光光谱仪(PL)对其物相组成、微观形貌、发光性能进行了表征。结果表明:在Eu~(2+)浓度为2mol%、反应温度为1700°C、反应压力为0.65MPa时,急冷温度为1200°C得到的荧光粉结晶最好,发光强度最强。通过改变急冷温度可以使发射峰波长从637nm红移到646nm,这是一种新的调控荧光粉发射峰的手段。经过酸洗后,荧光粉的发射峰强度可以提高约9.3%。     

Si3N4-MgO-CeO2陶瓷烧结中的致密化与自动析晶

用等离子放电烧结的方法制备了Si3N4-MgO-CeO2陶瓷，用排水法测定了密度，用X射线衍射的方法测定了物相变化。发现在烧结过程中，高于l450℃时,MgO-CeO2就会与氮化硅粉末表面的SiO2反应形成硅酸盐液相，促进烧结致密化，冷却后形成玻璃相留在晶界，氮化硅的致密化在l500℃接近完成。但高于l550℃烧结，MgO反而会析晶，提高氮化硅陶瓷的高温性能。