Physica B-Condensed Matter
The influence of preparation parameters on the particle size of nanosized silicon (n-Si) produced by laser-induced chemical vapour deposition (LICVD) was studied. The optimum parameters for synthesizing the right sized n-Si have been obtained, and they are as follows. The power density of CO2 laser is 1500 W/cm(2). The silane (SiH4) concentration is 10 vol%. The dilution gas is argon of high purity. The flow rate of reactant gases is 100 seem. And the pressure of the reaction chamber is 200 Torr. The particle size of n-Si prepared by LICVD can be varied in the range from 10 to 100 nm depending on the selection of preparation parameters.
关键词:
powders
Acta Materialia
The microstructure of TiNi(or Ni)/TiC composite prepared by mechanical alloying (MA) of elemental Ti, Ni and C powders has been investigated in detail. The result shows that large agglomerates with size 3-10 mm were abruptly formed for Ti50Ni20C30, Ti40Ni40C20 and Ti30Ni50C20 powders at the milling duration of 3 h 30 min-3 h 35 min, which suggests melting of the powders and subsequent quenching has occurred during MA. Transmission electron microscopy shows that spherical TiC grains, lath twin martensite (M) and B2 phase are directly formed after 3 h 35 min MA of Ti50Ni20C30 powders. It is also found that there exists definite orientation relationships between M and B2 phases which are very close to those obtained by Otsuka et al. in equiatomic TiNi martensite. The resultant phases are predominantly TiC and M phases with a small amount of B2 phase for Ti40NI40C20; and Ni and TiC phases for Ti30Ni50C20 after 3 h 35 min of MA. The microstructure characteristics of the as-milled materials are very similar to those of melted and solidified ones, which proves that melting of the powders and subsequent quenching has really occurred during the MA process. We concluded that MA in Ti50Ni20C30, Ti40Ni40C20 and Ti30Ni50C20 is not governed by a gradual diffusional reaction, but by a self-sustained high-temperature synthesis (SHS) one. The SHS reaction is believed to be triggered by the release of heat of formation of the TiC phase and ignited by the mechanical collisions. The thermodynamic and kinetic conditions for the SHS reaction is discussed, and it shows that MA is a versatile method in inducing SHS reaction in systems with large heat of formation.
关键词:
powders
Journal of Materials Research
The explosive reactions or self-propagating high temperature synthesis (SHS) take place during milling Ni20Ti50C30 and Ni50Ti30C20 elemental powder mixtures, The coexistence of agglomerates and powders in products indicates the occurrence of melting and solidification, TiC phase and NiTi compound were obtained during millingNi(20)Ti(50)C(30), while no compound of nickel and titanium was observed when milling Ni50Ti30C20, the final product of which is TiC and Ni. It is suggested that the explosive reaction is ignited by the heat releasing from initial formation of TiC through heavy collisions of milling balls, and the reaction between Ni and Ti, as well as the existence of Ni-Ti liquid, make the following reaction self-sustained. The variation of the addition of nickel did not affect the reaction time in both compositions, but made the reaction temperature different due to the difference of composition of Ni and Ti. It is estimated that the temperature during the reaction in Ni20Ti50C30 rises above 1112 degrees C, while in Ni50Ti30C20, it might rise above 1349 degrees C. However, no phenomenon suggests the melting of pure elemental Ti; the formation of TiC is mainly controlled by the diffusion mechanism in SHS.
关键词:
powders
刘会兴
,
卜景龙
,
魏恒勇
,
崔邁
,
魏颖娜
,
张利芳
耐火材料
doi:10.3969/j.issn.1001-1935.2015.05.001
以四氯化钛和异丙醚为主要原料，二氯甲烷为溶剂，采用非水解溶胶－凝胶法制备的 TiO2凝胶为钛源，按 n（C）n（Ti）为11．4引入相对分子质量为1300000的聚乙烯吡咯烷酮（PVP）作为碳源，采用碳热还原氮化法合成 TiN 粉体。通过 TG－DTA、XRD 和 FE－SEM研究了碳热还原氮化过程中 TiN 粉体的形成历程。结果发现，在800～1000℃碳热还原3 h，锐钛矿型 TiO2转变为金红石型 TiO2；在1000～1200℃碳热还原氮化3 h，金红石型 TiO2转变为 Ti3 O5，并逐渐氮化生成 TiOxNy；在1300℃碳热还原氮化3 h，TiOxNy 开始转变为 TiN，但其氮化并不完全，延长氮化时间至5 h，剩余的 TiOxNy 全部转化为 TiN。TEM和纳米粒度分析仪测试表明，合成的 TiN 颗粒发育良好，呈近似方形结构，约为250 nm，粒径分布在0．4～1．1μm。
关键词:
非水解溶胶-凝胶法
,
碳热还原氮化法
,
氮化钛
,
粉体
刘学建
,
李会利
,
黄政仁
,
王士维
,
江东亮
无机材料学报
doi:10.3724/SP.J.1077.2009.01159
以Al_2O_3和AlN为原料, 在氮气气氛下通过高温固相反应工艺合成氮氧化铝(AlON)粉体, 借助XRD分析系统研究了反应温度、保温时间及原料配比等工艺参数对反应产物相组成的影响并探讨了反应机理. 研究结果表明:该反应主要受热力学控制, 动力学因素也具有重要作用, 反应温度和保温时间对AlON粉体的合成均具有重要影响. 在相对较低的反应温度下, 通过AlN固溶进入Al_2O_3晶格形成富氧(O-rich)的AlON相;在相对较高的反应温度下, 产物中少量残余的AlN通过进一步扩散固溶进入O-rich-AlON晶格形成富氮(N-rich)的AlON相(N-rich-AlON);在1950℃时, 合成单相的AlON粉体.
关键词:
氮氧化铝(AlON)
,
粉体
,
固相反应
,
反应动力学
,
反应机理
龙文彪
,
罗瑞盈
合成材料老化与应用
以Vb(NO3)3·5H2O和TEOS为初始原料采用溶胶凝胶工艺制备Yb2Si2O7粉体,研究了乙醇的含量对溶胶凝胶过程和粉体粒径形貌的影响,并通过X射线衍射分析、热重差热分析及拉曼光谱分析对凝胶的相转变和热历程进行分析.研究表明,乙醇含量增加,粉体粒径减小,粒度均匀,溶胶凝胶时间延长;Yb(NO3)3与C2H5OH的摩尔比为1∶10,制备的凝胶经过1200℃煅烧2h后得到单相的β-Yb2Si2O7粉体,粉体粒径大小为130nm ～140nm,粉体可作为环境障涂层材料应用于碳化硅陶瓷基复合材料的腐蚀防护.
关键词:
Yb2Si2O7
,
溶胶凝胶工艺
,
粉体
,
制备
,
表征
