Design,preparation, and structure of particle preforms for Si3N4（p）/Si3N4 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 conglomerations are of almost sphericity after conglomerated. There are large pores among the conglomerations and small pores within themselves 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 Si3N4 matrix. The conglomerations, however, are very compact. The CVI Si3N4 looks like cauliflowershaped structure. 2008 University of Science and Technology Beijing. All rights reserved.     

Microstructure and Dielectric Property of 3D BN_f/Si_3N_4 Fabricated by CVI Process

As potential wave-transparent materials applied at high temperatures, 3D BN_f/Si_3N_4 ceramic matrix composites were prepared by low pressure chemical vapor infiltration or deposition(LPCVI/CVD) process from SiCl_4-NH_3-H_2-Ar gas precursor at 800 oC. The densification process, microstructure and dielectric properties of 3D BN_f/Si_3N_4 composites were investigated. The results indicated that 3D BN_f/Si_3N_4 was successfully fabricated by LPCVI/CVD, with final open porosity of 2.37% and density of 1.89 g/cm~3. Densification kinetics of 3D BN_f/Si_3N_4 is a typical exponential pattern. The Si_3N_4 matrix was uniformly infiltrated into porous BN_f preform. The deposited Si_3N_4 matrix was amorphous by XRD analysis. Introduction of BN fiber into Si_3N_4 ceramic lowered the permittivity of Si_3N_4. The fabricated BN_f/Si_3N_4 composites possess low permittivity of 3.68 and low dielectric loss of lower than 0.01, which are independent of temperature below400 oC. Transmission coefficient of BN_f/Si_3N_4 composite is 0.57 and keeps stable below 400 oC. BN_f/Si_3N_4 can be fabricated at low temperature and may be candidates for the microwave transparent materials.     

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     

IC制造中氮化硅薄膜的制备方法

氮化硅薄膜是芯片制造中广泛运用的一种绝缘薄膜,其可用作芯片表面的掩蔽膜及钝化膜。简要介绍IC制造中几种主要的氮化硅薄膜的制备技术,并探讨新型的制备技术。     

Si3N4超微粉体及其制备

Si3N4陶瓷因其优异的力学性能和化学稳定性而在工业生产中广泛使用。Si3N4粉体的合成是制备Si3N4陶瓷的基础。本文在介绍Si3N4陶瓷性能、用途的基础上,详细论述了硅粉直接氮化法、SiO2还原氮化法、热分解法、气相法等Si3N4超微粉体制备技术,并对这4种工艺的优缺点进行对比。     

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.     

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.     

Facile Fabrication of Fe_2O_3/Nitrogen Deficient g-C_3N_(4-x) Composite Catalysts with Enhanced Photocatalytic Performances

The modification of graphitic carbon nitride can significantly improve the photocatalytic performance of graphitic carbon nitride(g-C_3N_4). Fe_2O_3/nitrogen-deficient g-C_3N_(4-x) composite catalysts were prepared with dicyandiamide as the precursor and Fe~(3+) doped in this study. The composite catalysts were characterized by XRD, SEM, FT-IR, XPS and photocurrent measurements. Close interaction occurred between Fe_2O_3 and nitrogen deficient g-C_3N_(4-x), more photogenerated electrons were created and effectively separated from the holes, resulting in a decrease of photocarrier recombination, and thus enhancing the photocurrent. Photocatalytic performance experiments showed that Fe_2O_3/nitrogen deficient g-C_3N_(4-x) could utilize lowenergy visible light more efficiently than pure g-C_3N_4, and the removal rate was 92% in 60 minutes.     

高性能Si3N4基可加工复合陶瓷的快速制备

采用SPS在1600～1650℃烧结5min可以获得致密的Si_3N_4-BN复相陶瓷,实验结果表明,随着BN体积分数的增加,BN聚集生长导致Si_3N_4-BN复相陶瓷强度总体均呈缓慢下降趋势,但仍然维持在很高的强度水平,BN体积分数为30%时三点弯曲强度接近900 MPa,而且拥有优异的可加工性能,SEM分析表明,借助SPS可以在实现Si_3N_4-BN复相陶瓷快速致密化基础上进行相组成及显微组织的调控和优化,从而改善材料的性能。     

Fabrication and characterization of SiO2（f）/Si3N4 composites

A silicon dioxide fiber-reinforced silicon nitride matrix (SiO2/Si3N4) composite used for radomes was prepared by chemi- cal vapor infiltration (CVI) process using the SiCl4-NH3-H2 system. The effects of the process conditions, including infiltration tem- perature, infiltration time, and gas flux were investigated. The energy dispersion spectra (EDS) result showed that the main elements of this composite contained Si, N, and O. The X-ray diffraction (XRD) results indicated that phases of the composite before and after treatment at 1350°C were all amorphous. A little fiber pull-out was observed on the cross section of the composite by scan electron microscope (SEM). As a result, the composite exhibited good thermal stability, but an appropriate interface was necessary between the fiber and the matrix.     

国家行业标准Si3N4结合SiC板的制定及应用

简介了Si3N4结合SiC制品的发展过程和应用范围,较为详细地介绍了该项标准制订情况,叙述了标准中产品的形状及代号、规格尺寸、技术要求、产品检验等内容,并对标准的应用情况进行了说明,以期标准的使用者能正确理解.     

热处理对3D C/C复合材料断裂行为的影响

采用3D炭纤维预制体,以丙烯作为碳源,氮气作为载气,利用自制的快速CVI炉制备了C/C复合材料。详细分析了不同CVI工艺下,热处理对C/C复合材料断裂强度、断裂方式以及材料均匀性的影响。力学性能测试结果表明,材料的弯曲断裂特征与制备过程中受到的高温热处理次数有关。与1次连续CVI工艺相比,多阶段连续CVI工艺下,C/C复合材料经过2次"CVI-热处理"循环工艺后,其密度达1.8 g/cm3,抗弯强度达196.69 MPa,断裂方式为假塑性断裂,材料在Weibull概率分布下强度分散性较小。     

Carbon quantum dots: An innovative additive for water lubrication

Water soluble carbon quantum dots(CQDs) were prepared and used as lubricant additives in deionized(DI) water. The impacts of CQDs on the tribological properties of water were evaluated for both Si_3N_4-on-steel and Si_3N_4-on-Si_3N_4 contacts. Experimental results show that the coefficient of friction(COF) reduced in the two types of tribopairs after the addition of CQDs.Maximum reductions in COF were found to be 30% and 14% for the Si_3N_4-steel and Si_3N_4-Si_3N_4 contacts, respectively. In terms of wear behaviors, the CQDs notably improved tribofilm formation on the Si_3N_4 disk surface for the Si_3N_4-Si_3N_4 contacts,confirming that the nanoparticles increase friction while providing better protection from wear. This research will help to expand the application of CQDs as promising additives in water-based lubricants.     

Preparation and Photocatalytic Performance of Double-Shelled Hollow W_(18)O_(49)@C_3N_4@Ti_3C_2 Microspheres

C_3N_4,C_3N_4@Ti_3C_2 and W_(18)O_(49)@C_3N_4@Ti_3C_2 hollow spheres were successfully prepared by using SiO_2 template followed by gradual deposition method.The degradation of phenol solution and photolysis ability were tested to characterize its photocatalytic activity.Compared with the single-shelled C_3N_4 and C_3N_4@Ti_3C_2 hollow spheres,double-shelled W_(18)O_(49)@C_3N_4@Ti_3C_2 hollow spheres possessed larger surface area and fast charge separation efficiency,exhibiting about 8.9 times and 4.0 times higher H_(2 )evolution than those of C_3N_4,C_3N_4@Ti_3C_2 hollow spheres,respectively.The photocatalytic mechanism of the W_(18)O_(49)@C_3N_4@Ti_3C_(2 )hollow spheres were carefully investigated according to the results of morphology design and photoelectric performance.A Z scheme mechanism based on the construction of heterojunctions was proposed to explain the improvement of photocatalytic performance.This new charge transfer mechanism appears to greatly inhibit the recombination of electrons/holes during the charge transfer process,while maintaining its strong hydrogen reduction ability,resulting in a higher photocatalytic performance.     

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.     

激光引发气相化学合成Si3N4超细粉末

利用CO_2激光引发在NH_3/Si_3H_4体系中化学合成超细、高纯Si_3N_4粉末。实验研究了反应参数和反应条件,在较好的实验条件下制备出近似球形、粒径约20mm、纯度98％的无定形Si_3N_4粉末。     

Pressureless infiltration of Si3N4 preforms with an Al-2wt%Mg alloy

The pressureless infiltration process to synthesize a silicon nitride composite was investigated. An Al-2wt%Mg alloy was infiltrated into silicon nitride preforms in the atmosphere of nitrogen. It is possible to infiltrate the Al-2wt%Mg alloy in silicon nitride preforms, The growth of the composite with useful thickness was facilitated by the presence of magnesium powder at the interface and by flowing nitrogen. The microstructure of the Si3N4-Al composite has been characterized using scanning electron microscope. During the infiltration of Si3N4 preforms, Si3N4 reacted with aluminium to form silicon and AIN. The silicon produced during the growth consumed in the formation of MgSiAIO, MgSiAlN and Al3.27Si0.47 type phases. The growth of the composite was found to proceed in two ways, depending on the oxide content in the initial preforms, First, less oxide content preforms gave rise to MgAlSiO and MgAlSiN type phases after infiltration. Second, more oxide content preforms gave rise to AlN-Al2O3 solid solution phase （AlON）, The AlON phase was only present in the composite, containing 10% aluminium in the silicon nitride preforms before infiltration.     

YBa＿2Cu＿3O＿（7－δ）高温超导薄膜的保护层研究

论述了钇钡铜氧高温超导薄膜在大气中的不稳定性，对比二氧化硅，阐明了氮化硅薄膜作为保护层的优点，并报导了做潮湿实验前后的对比实验结果．最后讨论了氮化硅作为高温超导薄膜保护层的可行性．     

合金元素对Si3N4陶瓷生成的影响

以合金元素为添加剂制备氮化硅陶瓷.比较了Ti、Mg、Fe和A l四种合金元素对氮化硅生成的效果,结果表明单一元素Fe的效果比较明显;探讨了Fe含量在0.25%~5%(质量百分数)之间对Si3N4生成的影响,为了避免Fe-Si化合物的生成,Fe的加入量不宜大于1%;对比了复合元素(Fe A l)添加与单一元素(Fe)添加的效果,在添加剂含量相同的条件下,复合元素(Fe A l)比单一元素(Fe)的氮化效果较理想.     

Si3N4/TiC纳米复合陶瓷材料显微结构

利用日立H-800透射电境、日立S-570型扫描电境及RAX-10A型X射线衍射仪对Si3N4/TiC纳米复合陶瓷材料的微观组织、结构和成分进行了研究.结果表明,TiC纳米颗粒弥散分布在基体β-Si3N4晶内和晶界,所制备的材料为晶内/晶间混合型纳米复合陶瓷.通过对Si3N4/TiC纳米复合陶瓷材料断裂方式的观察表明,材料断裂为沿晶断裂和穿晶断裂复合型,纳米粒子对裂纹扩展起到偏转和钉扎作用.纳米Si3N4颗粒的加入促进了基体长柱状β-Si3N4晶粒多峰分布的形成,类晶须晶粒在裂纹扩展过程中产生桥接和拔出.