TiN/SiNx submicronic multilayer coatings obtained by chemical vapor deposition in a fluidized bed reactor at atmospheric pressure (AP/FBR-CVD)

TiN/SiN_x multilayer coatings were deposited on stainless steel by Chemical Vapor Deposition in a Fluidized Bed Reactor at Atmospheric Pressure (AP/FBR-CVD) by reaction of TiCl₄ and SiCl₄ with NH₃ at 850 °C. Due to the immiscibility of crystalline TiN and amorphous SiN_x, interdiffusion between layers is avoided even at the high working temperature. The thickness of the individual layer was in the nanometer range. Coatings were characterized by means of SEM, TEM, GD-OES, SIMS, XRD and nanoindentation. A mechanism for the growth rate and diffusion of Ti and Si into the steel is discussed.     

等离子熔积直接成形形状特性的基础研究

系统分析了熔积成形技术中影响成形形状特性的原因,研究了转移弧电流、扫描速度和起弧高度对成形精度的影响机理.实验表明,以上参数对等离子熔积直接成形形状特性的影响显著,对改善零件的成形精度起决定性的作用;通过优化成形工艺参数,焊道表面质量得到显著好转.     

Reaction of Iradium with Metal Carbides in the Temperature Range of 1923 to 2400 K

The reactions of titanium carbide and hafnium carbide with iridium have been studied in thin film couples fabricated by vapor deposition processes. The reaction product layers after exposure in the temperature range of 1923 to 2400 K are dependent on the stoichiometry of the metal carbide layers and range from simple solid solutions to MIr_x compounds. The observed microstructures are predictable from available thermochemical data. The morphology of residual carbon in the reacted metal carbide-iridium product layer varies from interfacial deposits to uniform carbon dispersion and depends upon exposure temperature and metal carbide stoichiometry.     

常压CVD法制备氮氧化硅薄膜沉积特性的研究

采用常压化学气相沉积方法(atmospheric pressure chemical vapor deposition,APCVD)制备了氮氧化硅(Si—O—N)薄膜,研究了影响其沉积速率和生长模式的因素。在φ(NH_3):φ(SiH_4)=20:1,基板温度为650℃的条件下,当混合气体流量小于720ml/min时,薄膜的形成主要受气体扩散过程控制;当混合气体流量大于720 ml/min时,则主要受表面气相反应过程控制;混合气体流量为720 ml/min的条件下,氮氧化硅薄膜的沉积过程主要受基板表面的气相反应过程控制,薄膜沉积厚度与沉积时间成线性关系,反应速率为常数1640 nm/min,表面活化能为283 kJ/mol。通过SEM分析发现:氮氧化硅薄膜的形成方式符合三维成核模型,即反应初期Si,N,O等原子在基板表面相遇结合在一起形成原子团,一定数量的原子团构成临界核;反应中期临界核长大为岛状结构,岛不断长大,岛与岛之间相互接合形成通道网络结构;反应后期,原子不断填补网络空洞,最后成为连续薄膜。     

Surface Pretreatments of Silicon Nitride for CVD Diamond Deposition

The efficiency of different surface pretreatments (four standard chemical etchings and four diamond powder abrasive procedures) on silicon nitride (Si₃N₄) substrates for chemical vapor deposition (CVD) of diamond has been systematically investigated. Blank Si₃N₄ samples were polished with colloidal silica (∼0.25 μm). Diamond nucleation and growth runs were conducted in a microwave plasma chemical vapor deposition apparatus for 10 min and 6 h, respectively. Superior results concerning nucleation density ( N _d∼ 10¹⁰ cm⁻² after 10 min), film uniformity, and grain size (below 2 μm after 6 h) were obtained for the mechanically microflawed samples, revealing that chemical etchings (hot and cold strong acids, molten base or CF₄ plasma) are not crucial for good CVD diamond quality on Si₃N₄.     

Growth of sculptured polymer submicronwire assemblies by vapor deposition

We have grown helical nanowire assemblies of parylene C, thereby demonstrating that polymeric sculptured thin films (STFs) can be fabricated by a combination of physical and chemical vapor deposition processes. The deposition method is explained in detail and electron micrographs of 200-400 nm size sculptured thin film of parylene are given. The shapes of the submicron and nanowire assemblies can be engineered so that the polymeric STF acts as a template for preferential attachment of biomolecules.     

液相法制备纳米Fe_3O_4的研究进展

介绍沉淀法、微乳液法及水热法等纳米Fe3O4的制备方法,讨论了这些方法的优缺点。指出了沉淀法是目前制备纳米Fe3O4的最广泛应用的方法,而超声技术、交流电沉积与传统沉淀法的结合,是制备高纯度、小粒径、均匀分散的Fe3O4最有前途的方法。     

Low-temperature catalytic growth of carbon nanotubes under microwave plasma assistance

Various carbon nanotubes (CNTs) including aligned arrays, Y-branching and some other novel morphologies have been catalytically grown on anodic porous alumina template (APAT) and on the alumina-supported catalysts with methane (or benzene) as carbon source under microwave plasma assistance below 520 °C. The growth process could be simply operated since neither heating nor bias-voltage was applied to the catalysts or APAT. The results presented in this paper not only greatly richened the nanostructures of carbon family but also provided with a new technique path for synthesizing CNTs or some other nanostructures with the characteristics of low-temperature which has some special advantages or applications.     

化学气相沉积(CVD)炭/碳复合材料(C/C)研究现状

主要介绍了炭／炭复合材料（C／C）的化学气相沉积（CVD0制备方法及其影响因素，以及热解炭的组织与沉积机理。概括了VCD的基本方法，如等温法、压差法、热梯度法等。分析了温度、气流速率、气体浓度、预制体及孔隙的形状大小状况等对CVD过程的影响。列举了热解炭的组织，包括光滑层、粗糙层、各向同性体碳以及它们的变体，并对其生长特征及性能进行了较详细的描述。综述了热解炭的沉积机理，典型的有分子沉积、固态沉积、液滴沉积机理等。     

铬酸酐副产物硫酸氢钠的利用

对生产铬酸酐时副产的含铬硫酸氢钠的利用作了评论，介绍了8种方法，即，化学沉淀法、磷酸沉淀法、铬酸铬法、电解氧化法、过硫酸钠氧化法、制商品硫酸氢钠、酸泥制碱式硫酸铬、硫酸氢钠制碱式硫酸铬，其中以化学沉淀法、磷酸沉淀法和铬酸铬法应用最广。