升华再结晶法制备AIN晶须及其生长特性

以AIN粉体为原料，加入适量的CaO-B2O3矿化剂，采用升华再结晶法制备AIN晶须．初步探讨了反应器及其合成温度对产物种类的影响，研究了晶须的结构特征及其生长机理．结果表明，初期的合成产物包括AIN晶柱、晶须和非晶AIN纤维，以VLS机制生长：后期产物为AIN晶须，表现为VS生长机制：XRD及TEM分析表明，晶须大多呈现沿｛2110｝、｛101l｝和｛0001｝，l＝0、1、2、3的晶面生长．多数晶须宏观生长轴向平行于这些晶面的法线，而部分晶须由于发生斜生长，导致宏观生长轴向与这些晶面的法线斜交．     

碳热还原法合成AIN晶须及其生长机理

以Al2O3和石墨为原料，采用碳热还原法制备AIN晶须.研究了矿化剂的种类及温度等工艺对AIN晶须合成的影响结果表明，以CaF2和B2O3为矿化剂的AIN品须是以VLS机制生长的，高温下VLS机制可以转变为VS机制，同时存在两维成核及螺位错生长过程，晶须生长方向大多呈{101n}，（n=0，1，2，3）及{121m}，（m=0，1；2）的晶面生长     

不同形貌TaCx晶须的制备及生长机理

通过不同的原料体系在合适的工艺条件下成功制备出碳化钽晶须（TaCx）。由Ta2O5-NaCl-C-Ni和Ta2O5-NaF-C-C12H22O11（蔗糖）体委制备的晶须呈平直的纤维形态，其生长机理为气-液-固（VLS）机制。由Ta2O5-KCl-C-Ni体系制备的晶须一部分通过VLS机理生长，而另一部分则通过LS机理生长，前者呈四方柱状，后者呈具有锥状柱体和之字形端部的特殊形貌。所有的原料体系均是在相近的工艺条件下进行，即反应温度1150-1350℃，氮气气氛保护。本工作对晶须的化学成分、形貌、晶体结构和生长机理进行了较详细的研究。     

高温熔剂法制备氧化镁晶须的研究

采用MgCl₂·6H₂O为原料、KCl为助熔剂, 分段灼烧制备出直径1～50μm、长50～2000μm的MgO晶须. 通过对水氯镁石热解的理论分析、以及对灼烧各阶段产物的化学分析, 确定生成晶须的中间产物为无水氯化镁, 然后直接从无水氯化镁制备出MgO晶须. 并探讨了MgCl₂、HCl和H₂O浓度的变化对晶须形貌的影响. 提出了MgO晶须生长的机制: 即MgO分子在容器壁上非均相成核, 晶须生长的初期是以VLS机制进行, 在合成的后期, VLS机制变成VS机制.     

活性炭块诱发SiC晶须生长的研究

以含氢硅油为前驱体,选用3种不同的活性炭块(1cm×1cm×1cm)为基体,经交联、制粉、包埋,氩气保护下烧结制备SiC晶须(SiCw)。对含氢硅油的交联工艺进行了研究,以正交试验法研究交联温度、保温时间、催化剂含量、交联剂含量对含氢硅油交联程度的影响。结果表明,交联温度是影响含氢硅油交联度的主要因素;其次依次是保温时间、催化剂含量、交联剂含量。在不同基体的诱导研究中,石墨基体表面生成的晶须较平直,另外两种基体未见均匀分布且长直的SiC晶须生成。SiC晶须的产生是由基体的表面缺陷引发,较低温度下晶须头部液滴的存在说明其生长机制符合VLS机制。     

四脚状氧化锌晶须的研究现状及展望

四脚状氧化锌晶须(T-ZnOw)是目前发现的具有独特空间三维结构的晶须,并且其针部具有单晶性,由于其独特的晶体结构使得它在耐磨、减震、吸波等各个方面有着广阔的应用前景.阐述了T-ZnOw的晶体结构,介绍了氧化锌晶须的气-固(VS)和气液-固(VLS)生长机理,总结了其主要制备方法,如预处理氧化法、蒸气氧化法、平衡气量法、真空制备法和电化学沉积法等,并介绍了它的性能及其在增强复合材料、抗静电、抗菌和吸波方面的应用,总结展望了今后的研究方向.     

Ag(TCNQ)纳米晶须的生长机理

本文采用真空饱和蒸汽反应法在相对较低的温度下制备了一系列一维纳米结构的金属有机配合物Ag(TCNQ).用多晶XRD谱表征了样品的成份和晶体结构,通过SEM观察到了不同生长阶段的形貌.纳米晶须的生长分别经历了溶解、结晶和单向生长三个阶段.在此基础上,利用VLS模型初步解释了其生长机理.     

草酸盐法制备硼酸镁晶须及其生长机理

以MgCl2·6H2O、H3BO3和H2C2O4·2H2O为原料,利用草酸盐法制备出长度为4.0～8.0μm,直径为0.6～1.5μm,长径比约为10,形貌良好的硼酸镁晶须。采用XRD、SEM及TG-DTA等分析手段,研究了烧结温度、烧结时间、n(B)/n(Mg)、n(H2C2O4)/n(Mg)对硼酸镁晶须的生长过程和质量的影响,探讨了其最佳制备条件。结果显示,硼酸镁晶须的最佳制备条件为:烧结温度为800℃,烧结时间为4.0h,n(B)/n(Mg)=1.2,n(H2C2O4)/n(Mg)=1.2。根据XRD和TG-DTA分析,MgC2O4前驱体对硼酸镁晶须的形成和生长有较大的促进作用,分解产物不引入其它杂质,使得制备的晶须纯度较高。晶须的生长机理为S-L-S机理。     

稻草制备SiC晶须

以废弃的稻草为原料,在1300～1400℃的氩气保护条件下制备SiC晶须。研究反应温度、反应时间、催化剂对SiC晶须制备的影响和反应机理。结果表明,SiC晶须在1350℃时生长最好;SiC晶须温度控制在1350℃左右为宜,采用先高温成核再低温保温的加热方式,反应时间控制在2h;碳化硅晶须主要以β型为主,同时含有少量α型SiC晶须。晶须以竹节状居多,晶须直径为10～200nm之间,长径比>10。用Fe粉和H3BO3作催化剂所生成的晶须较多,但其长径比较小。反应机理主要是VLS机理,以废弃稻草为原料制备SiC晶须为稻草应用提供了一种新的途径。     

纳米 KTi6O13w合成中的形态演化和生长机理

以纳米TiO2为原料，通过煅烧反应制备了纳米K2Ti6O13晶须，对晶须合成中温度和时间诱导的相变、形态演化和生长机理等进行了原位研究．结果表明;纳米TiO2作原料可显著降低晶须合成温度，适宜的煅烧温度为900-1100℃．形态演化观察和高温XRD分析表明；K2Ti6O13晶须的相变及生长对温度极为敏感，形态演化是基于初期爆发式的相变和随后串并联式的长大．K2Ti6O13晶须的生长遵守本研究提出的串并联机制，晶须轴向的生长台阶是串并联生长的直接结果．     

高长径比硼酸镁晶须的制备及生长机理研究

以六水氯化镁和硼砂为原料, 以氯化钠、氯化钾作为助熔剂, 通过熔盐法制备出长为200~800μm, 最大长径比为250, 品质均匀的硼酸镁晶须. 采用XRD分析、光学显微和SEM观察, 研究产物的结构和形貌, 并研究不同n(B)/n(Mg)、反应温度和时间对硼酸镁晶须生长过程及质量的影响, 结果表明, 反应的最佳条件是n(B)/n(Mg)=3:1、反应温度为900℃、恒温时间为6h. 根据XRD分析, 表明Mg₂B₂O₅晶须的生成经过中间产物方硼石Mg₃B₇O₁₃Cl的转化过程, 晶须生长需要一个富硼的环境. 晶须的生长机理符合L-S机理.     

Tin whiskers growth of SnAgIn solder on Kovar substrate with Au/Ni plating

In this research, the interactions of SnInAg solder on Kovar leadframes (Fe29Ni17Co) with Au/Ni UMB was studied, to reveal the whiskers growth mechanism. Samples were prepared by reflow process and aging, with SnInAg solder paste on the substrate. Scanning electron microscope was used to observe the morphology and the cross-sectioned structure of the whiskers. Focused ion-beam was used for the preparation of the transmission electron microscope (TEM) samples, and energy dispersive X-ray and TEM were then used to distinguish the different intermetallic compound (IMC) phases. It was found that, a special solder thickness range would be needed for the growth of whiskers. The root cause of this strip whiskers growth region was studied. It is worthy to mention that, the Sn–Cu reactions, which was reported by many former researches, was not the main source of the compressive stress here. It was found that the Au–Sn reactions, the IMCs transformation during the aging process, and the oxidation layer growth were dominating the whiskers growth. Effects of cracks on the whiskers growth were carefully observed and discussed, and it was found that cracks under a certain width could exempt the breaking of the oxidation layer at the solder surface, thus help the whiskers growth. On the other hand, wide cracks might accommodate the deformation of the solder layer and prohibit the whiskers from being erupted out.     

Structure characteristics of AlN whiskers fabricated by the carbo-thermal reduction method

With Al2O3 and graphite as raw materials, CaF2 and B2O3 as additives, AlN whiskers were fabricated by a carbo-thermal reduction method. The fabrication mechanism and growth characteristics of AlN whiskers were investigated. At the beginning of the high-temperature fabrication, AlN whiskers grew by the vapour/liquid/solid (VLS) mechanism, and defects existed on the surfaces of the whiskers. In later stages, the VLS mechanism possibly changed to a vapour/solid (VS) mechanism, and the defects disappeared. The orientation of most AlN whiskers was normal to (n=0, 1, 2, 3), and normal to (n=0, 1, 2). The growth processes of both two-dimensional nucleation and screw dislocations existed at the same time. © 1998 Kluwer Academic Publishers     

Morphologies and growth mechanisms of aluminium nitride whiskers

Morphologies of AlN whiskers grown by the vapour–liquid–solid mechanism (VLS) were investigated. Several types of whisker structures, such as growth hill, wavy, crossed and stack structures, were found due to the variation of growth conditions. Growth mechanisms and orientations of AlN whiskers were also studied. Besides preferential crystallographic planes, several other planes were found to be growth layers due to the perturbation of the AlN lattice change caused by dissolution of oxygen. A screw dislocation growth mechanism was clearly confirmed. An oblique growth mechanism was found in this work, which may be the result of two processes: the vapour–liquid–solid process and dissolution of oxygen. This revised version was published online in November 2006 with corrections to the Cover Date.     

A study on in situ growth of TaC whiskers in Al2O3 matrix powder for ceramic cutting tools

In situ growth of tantalum carbide (TaC) whiskers was synthesized in an α-Al₂O₃ matrix powder via a carbothermal reduction technique within a temperature range of 1350–1500 °C in an argon atmosphere. The starting materials consisted of Ta₂O₅, C, Ni and NaCl powders. Different mixing methods and various reaction temperatures were employed. Most of the prepared whiskers were 0.2–0.5 μm in diameter and 5–15 μm in length. The reaction temperature of 1400–1450 °C was suitable for the growth of TaC whiskers and a wet mixing method was beneficial to increase the whisker yield. Some of the whiskers exhibited the needle shape while others exhibited the screw shape. The growth mechanism of the whiskers was a complex mechanism involving a helical screw dislocation mechanism and a vapor–liquid–solid process. No obvious influences of the Al₂O₃ matrix powder on the growth of TaC whiskers were found and the major impurities in the obtained powder were TaC particles, nickel and unreacted carbon.     

Vapor-solid-solid Si nano-whiskers growth using pure hydrogen as the source gas

This paper describes the growth mechanism and structure of Si whiskers grown on a Si substrate in a tungsten hot filament chemical vapor deposition reactor with pure hydrogen as source gas using a two step process. In the first step, atomic hydrogen etched the silicon surface, forming silicon hydrides that react with tungsten from the filament. The resulting silicide particles deposited on the silicon surface forming a mesh-like pattern. The particles work as an etching mask against hydrogen radical etching of the silicon surface and inverted-pyramids or V-groove-shaped surface texture were obtained. In the second step the filament current was reduced and whiskers grew onto the substrate due to the interaction of the silicon hydrides with the particles and subsequent precipitation of saturated Si. The whiskers were found to have tungsten silicide particles on their tip, suggesting the whisker growth was through the Vapor-Solid-Solid (VSS) mechanism. A balance between the hydrogen radical etching effect and the supply of silicon hydride from the etching reaction on the silicon surface is crucial for the growth of dense silicon whiskers.     

哑铃形碳化硅晶须生长的机理

研究了仿生哑铃形碳化硅晶须的生长机理，发现组成仿生晶须的念珠状小球与直杆状碳化硅晶须的生成过程是相对独立的，而且念珠状小球在直杆状晶须上的生长位置是一定的，首先，直杆状碳化硅晶须在反应空间中生成，然后由Si,SiO,SiO2等组成的非晶态物质的直杆状晶须上的缺陷位置沉积长大，形成包裹在晶须上的念珠涉球，念珠状小球不仅可以在制备碳化硅晶须的过程中生成，而且能够在已有的碳化硅和钛酸钾等晶须上生成。     

稻壳SiC晶须生长工艺和机理研究

在以稻壳为原料，氧化物类作催化剂反应生成ＳｉＣ晶须的过程中，催化剂的主要作用是形成液相，晶须生长方式以ＶＬＳ为主，同时料内有少量ＶＳ方式生长的晶须，料表面有少量ＣＶＤ方式生长的晶须。