Li WANG
,
Xiaobu HU
,
Xiangang XU
材料科学技术（英文）
High purity silicon carbide (SiC) powder was synthesized in-situ by chemical reaction between silicon and carbon powder. In order to ensure that the impurity concentration of the resulting SiC powder is suitable for high-resistivity SiC single crystal growth, the preparation technology of SiC powder is different from that of SiC ceramic. The influence of the shape and size of carbon particles on the morphology and phase composition of the obtained SiC powder were discussed. The phase composition and morphology of the products were investigated by X-ray diffraction, Raman microspectroscopy and scanning electron microscopy. The results show that the composition of resulting SiC by in-situ synthesis from Si/C mixture strongly depends on the nature of the carbon source, which corresponds to the particle size and shape, as well as the preparation temperature. In the experimental conditions, flake graphite is more suitable for the synthesis of SiC powder than activated carbon because of its relatively smaller particle size and flake shape, which make the conversion more complete. The major phase composition of the full conversion products is β-SiC, with traces of α-SiC. Glow discharge mass spectroscopy measurements indicated that SiC powder synthesized with this chemical reaction method can meet the purity demand for the growth of high-resistivity SiC single crystals.
关键词:
Activated carbon
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null
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null
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null
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null
Haiping XU
,
Yanping SUN
,
Xinmou CHEN
材料科学技术（英文）
Nanocrystalline TiO2 was prepared by high frequency plasma chemical vapor deposition (HF-PCVD). The effects of additive AlCl3 on crystal phase, particle size and microstructural parameters of TiO2 nanocrystallites were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The nanocrystallites obtained experimentally are mixture of anatase and rutile, the uniform diameters of particles are about 30 nm. The phase transformation from anatase to rutile was accelerated by AlCl3, and rutile content is increased from 26.7 wt pct to 53.6 wt pct with increasing of addition of AlCl3 from 0.0 wt pct to 5.0 wt pct. The particle size is reduced and the size distribution becomes very narrow. The crystal lattice constants have the trend to decrease, and cell volumes appear as shrinkable.
关键词:
Additive AlCl¬
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null
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null
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null
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null
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null
吴友朋
,
刘祥萱
,
周友杰
,
莫斌
,
吴春
宇航材料工艺
doi:10.3969/j.issn.1007-2330.2010.01.011
对最佳的吸收剂颗粒粒度进行数值计算和分析.从趋肤效应和单个磁畴颗粒大小两个角度,以纯铁粉为例对最佳的粒度做了分析,结果表明,对于2～18 GHz的雷达波,铁粉颗粒在16 nm～1μm为好.还分析了利用纳米颗粒的量子尺寸效应来吸收电磁波时颗粒的尺寸范围,计算结果表明,此时颗粒尺寸至少应小于22 nm.
关键词:
吸波材料
,
颗粒尺寸
,
趋肤效应
,
单磁畴
,
量子尺寸效应
何健
,
徐中民
,
宋丽
,
王劼
,
王纳秀
材料科学与工程学报
doi:10.14136/j.cnki.issn 1673-2812.2015.05.014
为了研究不同尺寸的金刚石颗粒、不同切速比(进给速度与线速度之比值)、金刚线切割时间与不同往复切割次数对晶体色散元件表面粗糙度的影响,主要采用四种不同线径的电镀金刚石线在上述条件下做切割晶面(111)单晶硅分光晶体的实验,并实现在脆性材料单晶硅的塑性区域进行线切割加工.结果表明:在塑性区域加工单晶硅分光晶体的表面粗糙度与金刚石颗粒尺寸成正比、与切速比有密切关系,增加往复切割的次数可以有效降低分光晶体的表面粗糙度.此次研究能够给上海同步辐射光源晶体色散元件加工提供一定的参考价值.
关键词:
金刚石线
,
色散元件
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表面粗糙度
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颗粒度
,
切速比
伍颖斯
,
余皓
,
王红娟
,
彭峰
催化学报
doi:10.1016/S1872-2067(14)60114-5|
采用直接浸渍法、过氧化氢均相氧化沉积法和氨水催化水解法制备了石墨烯负载的铁、钴、镍金属氧化物纳米颗粒。研究了三种沉积方法对颗粒尺寸分布的影响；采用透射电子显微镜、傅里叶变换红外光谱、X射线衍射和X射线光电子能谱表征了催化剂的形貌与结构。用过氧化氢均相氧化沉淀法可制得粒径分布最均匀的纳米颗粒。过氧化氢的氧化作用可使石墨烯表面的氧化基团含量最大化，为纳米颗粒提供了足够的吸附与成核点。氨水加速了金属离子的水解与成核，导致纳米颗粒的粒径增大与不均。以苯甲醇氧化为探针反应考察了催化剂的性能。催化剂的活性按以下顺序逐渐下降：过氧化氢辅助沉积法>直接浸渍法>氨水催化水解法，与纳米颗粒尺寸增长趋势一致。纳米催化剂颗粒尺寸与其活性的良好关联性显示，发展石墨烯负载尺寸可控的纳米催化剂的方法具有重要意义。
关键词:
颗粒尺寸
,
石墨烯
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金属氧化物
,
过氧化氢
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苯甲醇氧化
