DC—PCVD法快速制备Si3N4薄膜

采用ＤＣ－ＰＣＶＤ方法，控制工艺参数，在ＧＣｒ１５钢试样上获得４０μｍ厚的，以Ｓｉ３Ｎ４为主要成分的非晶态绝缘薄膜，沉积速率约为３７Ａ／ｓ，讨论了沉积速率高的原因。     

用DC—PCVD法沉积非晶态Si3N4薄膜的研究

硅的氮化物薄膜用DC-PCVD装置沉积,这种装置在沉积过程中仅用直流电源。涂覆用的基体材料是单晶硅、2Cr13不锈钢等。用扫描电镜研究了薄膜的形态,用红外光谱、X射线衍射仪、透射电镜确认了薄膜的成分、结构。这些结果表明:涂覆试样由表面的超硬层,过渡层、基体三部分组成;超硬层主要含非晶态的Si_2N_4;薄膜由许多致密堆积的小球组成。涂覆试样的表面硬度(H_(V0.02))大约是43000～47000 MPa。涂层与基体之间结合力为15N左右。     

Si3N4超微粒的RF—CVD合成及其介电性质

利用自制的ＲＦ－ＣＶＤ装置合成了Ｓｉ３Ｎ４超微粒。着重考察了反应气混合方式对反应机理、化学含量、粒子形态及凝聚结构的影响。得到的Ｓｉ３Ｎ４粒子的典型尺寸为１０－５０ｎｍ，并且凝聚形成分形结构，其对应不同的反应温度合成的粒子的分形维数约为２．１５到１．７４之间。     

铟掺杂氧化锌纳米线的制备及光致发光特性

采用化学气相沉积法合成了高质量的铟(In)掺杂的氧化锌单晶纳米线。利用扫描电子显微镜、透射电子显微镜和粉末X射线衍射对其形貌与结构进行了表征。结果表明:纳米线的直径约为30nm,粗细均匀,具有六角纤锌矿结构。在纳米线的变温光致发光光谱中,由于In的掺杂,只观察到紫外发射峰,未见可见光发射峰;低温下的紫外发射来自于施主-受主对(donor-acceptor pair,DAP)的跃迁。随着温度的升高,DAP的跃迁逐渐减弱,在高于140K时,紫外发射来自于自由电子到中性受主(free-electron-to-neutral-acceptor,eA0)的跃迁。     

Si3N4/SiC/环氧树脂纳米导热复合材料的制备

以硅烷偶联剂KH-560改性的微米氮化硅/纳米碳化硅晶须(Si3N4/SiCw)为导热填料,浇注制备Si3N4/SiC/环氧树脂纳米导热复合材料.研究了环氧树脂种类、Si3N4/SiCw用量、复配比及表面改性对环氧树脂导热、力学和介电性能的影响.结果表明,环氧树脂的热导率随Si3N4/SiCw用量的增加而增大,当改性Si3N4/SiCw用量为50％[m(Si3N4) /m(SiCw)]=3/1时,环氧树脂的热导率为0.98 W/(m· K);复合材料的介电常数随Si3N4/SiCw用量的增加而增大,而力学性能则先增加后降低.     

聚苯硫醚/纳米Si3N4复合材料的制备及性能研究

表面改性处理的纳米Si3N4粉体与聚苯硫醚（PPS）熔融共混挤出制成PPS/纳米Si3N4复合材料,通过拉伸、冲击实验及动态力学性能测试考察了纳米粉体加入量对复合体系各项性能的影响。结果表明,纳米Si3N4填充PPS基复合材料的力学性能明显优于纯PPS。随粉体添加量的增加,复合材料的拉伸强度增大,当添加量为0.8 %时,拉伸强度提高了22 %。随粉体添加量的增加,复合体系冲击强度增大,当粉体添加量为1.2 %时,冲击强度和缺口冲击强度出现最大值,分别比纯PPS增加了33 %和41 %。动态力学性能测试表明,随粉体添加量的增加,PPS分子链段松弛所需能量增加,松弛过程增长,体系储能模量降低,损耗模量增加。     

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%.     

LDH催化制备单晶a-Si3N4纳米线研究

提出了一种以LDH （水滑石类化合物）为催化剂,纳米硅粉为原料,在N₂-H₂混合气氛下制备单晶a-Si₃N₄纳米线的CVD （化学气相沉积）方法。研究结果表明：当H₂含量小于0.5%时,所制备的Fe/Mg/Al LDH催化剂具有优良的高温热稳定性,在1250℃下煅烧与还原后仍可保持自身结构完整与催化活性。通过降低还原温度与LDH中Fe含量、在LDH中引入Mo元素等手段,有效地降低金属Fe纳米晶粒直径、增大成核密度,所制备单晶a-Si₃N₄纳米线面密度可达5×10¹⁴～9×10¹⁴ m^-2,直径为30～50 nm,长度达20～80 μm （长径比>1000）。进一步研究表明本实验中纳米线为VLS （气液固）生长机制。     

纳米Si3N4粉体表面改性及其在橡胶中的应用研究

该文选择含羧基（-COOH）和腈基（-CN）的聚合物作为表面改性剂,研究了对纳米Si3N4粉体湿法改性工艺的影响因素,采用TGA对纳米Si3N4粉体改性效果进行了表征,确定了最佳改性时间（120min左右）、改性温度（60℃左右）和改性剂用量（5％左右）。把在此工艺条件下表面改性后的纳米Si3N4粉体加入橡胶中,当改性纳米Si3N4粉体的用量为生胶的0．5％（质量比）时,所制备的Si3N4／NBR复合材料的撕裂强度、拉伸强度、耐油性能均得到明显的提高。     

Si3N4／纳米SiC复相陶瓷的研究

采用纳米ＳｉＣ粉体制备了Ｓｉ３Ｎ４／纳米ＳｉＣｐ复相陶瓷。研究了制备工艺、纳米ＳｉＣ含量对材料性能及显微结构的影响,并对材料显微结构特点与强韧化机制进行了分析 。结果表明：添加２０ｖｏ％〈１００ｎｍ的ＳｉＣ粉体时,复相陶瓷的室温抗弯强度达８５６ＭＰａ,当添加１０ｖｏ％上述ＳｉＣ粉体时,复相陶瓷的增韧效果最佳,断裂韧性达８．２７ＭＰａｍ＾１／２,比基体材料提高了２３％。     

Effects of Thin Mullite Coating on the Environmental Stability of Sintered Si3N4

We investigated the effects of a chemically-vapor-deposited mullite coating (∼100 nm) on the oxidation resistance of sintered Si₃N₄ in air and steam environments. The coating was sacrificially incorporated into the thermally grown oxide (TGO) on Si₃N₄ during isothermal oxidation in air at 1400°C, leading to significantly reduced TGO growth as well as markedly improved TGO morphology. This improvement can be attributed to the refractory and viscous nature of the SiO₂-Al₂O₃ system, compared with SiO₂, when under the influence of alkali and/or alkaline-earth fluxing elements. However, the mullite coating had little effect on the stability of the ceramic in the steam environment at 1200°C, due likely to high activity of SiO₂ in mullite.     

硫化铋准纳米带阵列的可控合成及光学性质

以五水硝酸铋和硫脲为原料,采用籽晶技术和水热相结合的方法,在涂籽晶层的硅片上制备了大面积Bi2S3准纳米带阵列。利用X射线衍射、场发射扫描电子显微镜、透射电子显微镜、高分辨透射电子显微镜和电子衍射等对产物的结构和形貌进行表征。结果表明,合成产物为纯正交相的纯Bi2S3,纳米带阵列中的纳米带宽约为130 nm,长约2μm,并且沿[130]方向优先生长。使用涂有Bi2S3纳米籽晶的衬底是生长大规模准纳米带阵列的必要条件,衬底在高压釜中放置高度影响产物的形貌。Bi2S3准纳米带阵列的形成机理与自组装生长和Bi2S3的各向异性生长相关。产物的荧光光谱为从650nm到800nm的红光区域宽发光带,是由Bi2S3准纳米带阵列结构中的复杂缺陷导致的。     

氮化硅针状晶体的制备

采用Ｓｉ粉直接氮化的方法制备氮化硅针状晶体,通过热力不计算,选择了晶体 温度和压力范围,探讨了温度、压力、添加剂等对针状晶体晶相、形貌、产率的影响,并在１８５０℃、ＣａＯ质量分数为１０％条件下,制备了长径比为４￣１０的β－Ｓｉ３Ｎ４针状晶体,产率为６８％,采用ＸＲＤ,ＴＥＭ、ＳＥＭ对得到的氮化产物及针状晶体进行了表征。     

Synthesis of Si3N4 whiskers by rapid nitridation of silicon droplets

Belt-like β-Si₃N whiskers were successfully synthesized by nitriding of liquid silicon without catalysts at 1500°C by using micron-sized silicon powders within 10 minutes. Silicon droplets formed by the melting of silicon particles greatly facilitates the diffusion of nitrogen. Several whiskers cling together to form a whisker-cluster. The whisker-clustermorphology results from nitriding of separate silicon droplets. The growth of the belt-like β-Si₃N₄ whisker was controlled by vapor-liquid-solid mechanism. The synthesis of silicon nitride whiskers can be effectively improved by nitriding liquid phase silicon.     

初始硅粉粒度对自蔓延高温合成氮化硅的影响

研究了平均粒度分别为２,７．８和１５．４μｍ的３种初始硅粉在氮气中的燃烧氮化规律。初始硅粉粒度越细,则在氮气中的燃烧温度高越高,燃烧滤蔓延速度越快,激活能也越低;较细的硅粉表面的硅蒸发通量大,ｐｓｉ高,易于形成延长方向与硅粉表面垂直的针状或柱状、纤维状晶体;而较粗的硅粉则易于形成氮化硅包覆层,且可以通过“包覆爆裂”机制继续进行二次氮化。较细的硅粉在氮气中的燃烧温度曲线上只出现一次燃烧峰,而较粗的硅     

Architectural design and cryogenic synthesis of Si3N4@(TiN–Si3N4) for high conductivity

Si₃N₄@(TiN–Si₃N₄) composites with heteroshelled structure were designed for enhanced conductivity and successfully synthesized through the simultaneous reduction and in‐situ cocoating process in liquid ammonia at around ?40°C. The heteroshells were composed of nanosized TiN and Si₃N₄ particles, which were amorphous with the size ranging from 10 to 40 nm. Using spark plasma sintering, dense bulk composite with >98.1% relative density of theoretical value were obtained and their electrical conductivity were increased to an adequate value (6.62 × 10² S·cm^?1) for electrical discharge machining by compositing 15 vol% TiN to Si₃N₄, which is superior to the previous reports. The excellent electric performance could be attributed to the heteroshelled structure which guarantees the conductive network can be formed and kept with minimal TiN content. The nanosized Si₃N₄ powders in the shells reduce the content of conductive powders and limit the growth of TiN particles.     

Enhanced thermal conductivity in Si3N4 ceramic with the addition of Y2Si4N6C

Si₃N₄ ceramic was densified at 1900°C for 12 hours under 1 MPa nitrogen pressure, using MgO and self‐synthesized Y₂Si₄N₆C as sintering aids. The microstructures and thermal conductivity of as‐sintered bulk were systematically investigated, in comparison to the counterpart doped with Y₂O₃‐MgO additives. Y₂Si₄N₆C addition induced a higher nitrogen/oxygen atomic ratio in the secondary phase by introducing nitrogen and promoting the elimination of SiO₂, resulting in enlarged grains, reduced lattice oxygen content, increased Si₃N₄‐Si₃N₄ contiguity and more crystallized intergranular phase in the densified Si₃N₄ specimen. Consequently, the substitution of Y₂O₃ by Y₂Si₄N₆C led to a great increase in ~30.4% in thermal conductivity from 92 to 120 W m^?1 K^?1 for Si₃N₄ ceramic.     

Preparation and mechanical properties of Si3N4 nanocomposites reinforced by Si3N4@rGO particles

A new type of reduced graphene oxide-encapsulated silicon nitride (Si₃N₄@rGO) particle was synthesized via an electrostatic interaction between amino-functionalized Si₃N₄ particles and graphene oxide (GO). Subsequently, the Si₃N₄@rGO particles were incorporated into a Si₃N₄ matrix as a reinforcing phase to prepare nanocomposites, and their influence on the microstructure and mechanical properties of the Si₃N₄ ceramics was investigated in detail. The microstructure analysis showed that the rGO sheets were uniformly distributed throughout the matrix and firmly bonded to the Si₃N₄ grains to form a three-dimensional carbon network structure. This unique structure effectively increased the contact area and load transfer efficiency between the rGO sheets and the matrix, which in turn had a significant impact on the mechanical properties of the nanocomposites. The results showed that the nanocomposites with 2.25 wt.% rGO sheets exhibited mechanical properties that were superior to monolithic Si₃N₄; the flexural strength increased by 83.5% and reached a maximum value of 1116.4 MPa, and the fracture toughness increased by 67.7% to 10.35 MPa·m^1/2.