Growth mechanism of copper whiskers by the hydrogen reduction of cuprous iodide

A small quantity of cuprous iodide (less than 30 mg) was reduced by hydrogen at 650 or 700°C for various periods of time (15 sec to 4 min) and quenched to interrupt whisker growth. This was done in order to examine the nature of the growth of copper whiskers. Scanning electron microscopic observation and X-ray microanalysis revealed that almost all the whiskers quenched after the growth for 30 sec or less had cuprous iodide droplets at their tips and also the lateral surfaces were covered by thin cuprous iodide layers. The manner in which the copper crystals grow is similar to growth by the droplet mechanism or by the VLS mechanism in that the nutrient is supplied by a liquid drop on the tip of the whisker. Whiskers thicken during and after the growth in length. The whiskers quenched after the growth for 1 min or more had well-developed lateral surfaces and did not have the droplets at the tips. Preferential condensation and reduction were found to occur at the whisker edges. Based on the observed facts, a growth mechanism is presented. Secondary whisker growth on the whisker tips was also investigated.     

Sodium acetate tri-hydrate whiskers

A new kind of whisker, which has not been previously reported in the literature, was grown on membranes which were in contact with a saturated aqueous solution of sodium acetate, using several techniques. Cellulose acetate membranes were used in all the cases and growth was successful at 25 ± 2°C and 45–55% relative humidity. A dense colony of whiskers, sometimes stuck together in bundles, usually up to 5 cm in length and ranging in width from 0.3–100 μm, developed within 72 h of growth. The whiskers were identified as sodium acetate tri-hydrate by means of Debye-Scherrer X-ray powder method. Laue transmission photographs indicated the existence of twin crystals within the individual single crystal whiskers as proved by electron diffraction in TEM. Some whiskers included internal and external channels, and there were several secondary effects, such as thickening in the middle of a whisker, formation of arrow-heads or spirals at the tips and various modes of branching. The whisker morphology and the various growth phenomena may be explained as a whisker growth process from their bases, when we consider a continuous crystallization from material which is supplied through and over the membrane.     

Oriented growth of whiskers of AIIIBV compounds by VLS-mechanism

The oriented growth of GaAs, GaP, InAs and GaInAs whiskers on the same (GaAs, GaP) or different (InAs/GaAs, GaInAs/GaAs) substrates was studied. A detailed morphological study of GaAs whiskers on polar A(III), B(111 ) and non-polar (001), (011) substrates was performed. The growth conditions for ordered (perpendicular to substrate) growth on the A(111) and B(111 ) faces were determined. There were found discrete spectra of whisker systems on all substrates with the preferential growth of “arsenic” B{111 } faces. The dependence of the growth rate on the whisker diameter is typical for the vapour-liquid-solid (VLS) mechanism and is used for the determination of kinetic coefficients for polar faces. There was observed a periodic instability in growth of InAs and GaInAs whiskers.     

Über das Wachstum von Silberamalgamwhiskern

The growth of whiskers from silver amalgam is investigated; The whiskers grew in aqueous solution on mercury surface by means of one kind of internal electrolysis. They possess the shape of hexagonal capillary tubes filled with mercury. A potentiostatic method has been developed for measuring supersaturation, resp. overvoltage during the whisker growth. The same method permitted the experimentator lightly to rule the whisker growth process.     

Fundamental aspects of VLS growth

The kinetics and the mechanism of the vapor-liquid-solid (VLS) growth are discussed. Emphasis is placed on the dependence of the growth rate on the whisker diameter. It is found that the rate decreases abruptly for submicron diameters and vanishes at some critical diameter d_c ? 0,1 μm according to the Gibbs-Thomson effect. A new method for simultaneous determination of kinetic coefficients and of supersaturations has been developed. The method can be used to measure the coefficients of some materials as well as the temperature dependence of the coefficient for silicon and the activation energy of the process. From the dependence of supersaturation on the diameter we conclude that whiskers grow by a poly-nuclear mechanism. The periodic instability of the diameter is discussed and the rate-determining step is analysed. We conclude that phenomena on the liquid-solid interface are the decisive ones. In determining the role of liquid phase in vapor growth we measured the “liquid phase effectivity coefficient” as a function of crystallization condition; the coefficient typically was about 10²?10³. It is stressed that the liquid phase reduces the activation energy both on vapor-liquid interfaces (for chemical reactions) and on liquid-solid interfaces (for nucleation). The liquid phase ensures growth rates as high as 1 cm/sec, provided there are no barriers between the interfaces. The growth mechanism of the side faces was studied, and it was observed that the faces grow mainly by a chain mechanism rather than by two-dimensional nucleation. In work on surface diffusion in the VLS whiskers growth by CVD, we found that the whiskers grow mainly by direct deposition rather than by diffusion on the side faces. It is concluded that the VLS mechanism is important also for the vapor growth of platelets, films, and bulk crystals.     

机械力活化对脱硫石膏制备硫酸钙晶须的影响

对脱硫石膏原料进行机械力活化,然后采用降温重结晶法制备出硫酸钙晶须.借助扫描电镜、图像粒度分析仪和相关软件进行表征,并初步讨论了机械力活化对晶须成核和生长过程的影响.结果表明:经过机械力活化的脱硫石膏可以制备有较大长径比的硫酸钙晶须.在水浴反应温度为75℃,硫酸浓度为2.5 mol/L,机械力活化时间为3.5 h,浆料浓度为2;的条件下,制备的硫酸钙晶须平均长径比为150,平均直径为2.1μm.     

Effect of added carbon black on iron whisker growth

As previously reported, mass-growth of iron whiskers can be achieved by reduction of halide admixed with carbon black. In order to investigate the role of added carbon black on iron whisker growth, the growth rates and morphology have been investigated. It was found that the effect is related to an adsorption process at the tip growth sites which are limiting the reaction. The heat of adsorption of the halide increases and markedly multi-nucleous growth and large growth rates appear on many whiskers. There is no effect of carbon black below 500°C since the vapor pressure of the adsorbed halide is small.     

改性羟基磷灰石晶须牙科复合树脂材料的制备及研究

采用硅胶对制备的HAP晶须进行表面改性形成SiO2颗粒附着,然后以硅胶改性的HAP晶须为填料混合甲基丙烯酸酯制备复合树脂材料.二氧化硅对晶须改性是通过形成凝胶颗粒与晶须结合并通过热处理形成牢固的结合.通过XRD、FT-IR光谱和SEM以表征微结构、键性质以及表面相组成.结果表明:经硅胶改性的HAP晶须表面有SiO2小颗粒附着,随着煅烧温度的增加,SiO2颗粒的数量明显增多,尺寸有变大的趋势.复合树脂材料的弯曲强度随改性晶须煅烧温度的增加而增加,以600 ℃煅烧的改性晶须为原料制备的树脂样品,其弯曲强度最高,达到89.46 MPa.     

Growth rate and morphology of silicon carbide whiskers from polycarbosilane

The growth rate of silicon carbide whiskers grown from polycarbosilane was measured and the growth morphology was investigated. The plot of whisker length vs. growth time was almost linear up to a certain growth time but tended to become time-saturated, independent of growth temperature. Cessation of whisker growth was caused by a change of the growth process from vapor–liquid–solid (VLS) to vapor–solid (VS). Decrease in whisker length with growth time was observed in the higher temperature range. Arrhenius plots of growth rate were almost linear in the lower temperature range, but deviated markedly from linearity in the higher temperature range. This deviation was caused by the coexistence of the VS process and the VLS process during whisker growth.     

Growth of hollow Se–Te whisker crystals

On the basis of micro- and macro-morphological studies the mechanism responsible for the growth of Se–Te whiskers has been suggested. It has been shown that Sc–Te whiskers grow by layer growth mechanism in which screw dislocation is not the source of step but the growth proceeds by two-dimensional nucleation. This has been supported by the supersaturation data. The plausible mechanism for the growth of hollow whiskers has also been suggested.     

Study of the evaporation mechanism in silicon carbide crystals growth from vapour phase

Investigation of the thermal etching (evaporation) of the source material in the process of silicon carbide crystal growth from the vapour phase by the sublimation method has been carried out. It has been established that silicon carbide etching in the temperature interval (2200–2600) °C takes place with the formation of whiskers of evaporation. The mechanism of their formation has been examined and the character of the whisker distribution in the charge of the source silicon carbide has been studied.     

Investigation of the formation and growth processes of silicon carbide monocrystals

The formation and growth processes of SiC monocrystals from vapour phase by sublimation method have been investigated. It is shown that the peaks of the evaporation and growth whiskers are the centres of SiC monocrystals formation. One of the mechanisms of development of the whisker into SiC platelet is established. It is shown that on the naturally mirror like crystal face either the edge of the crystal or the screw dislocation, situated on the crystal edge, is the source of the steps. On the stepped crystal face the root of the crystal is the source of the steps.     

煅烧和除碳温度对氮化硼晶须的影响

以三聚氰胺和硼酸为原料通过水浴加热合成晶须前驱体,然后经高温烧结成功制备出BN晶须.扫描电镜显示制备的BN晶须为针状结构,其直径和长径比分别为2～3 μm和40～100.通过X射线衍射分析,制备的BN晶须为六方晶相,晶格参数为a=0.2524 nm和c=0.6592 nm.红外光谱图谱表明在1383 cm-1和 812 cm-1处存在两个明显的B-N特征吸收带.晶须的烧成制度以及除碳温度对晶须形貌和性能的影响研究结果表明,当烧成温度为1700 ℃、除碳温度为600 ℃时可制备出形貌良好和结晶度高的氮化硼晶须.     

Catalytic epitaxy of ZnO whiskers via the vapor–crystal mechanism

A model of oriented growth of (0001) ZnO whiskers on sapphire substrates via the vapor–crystal mechanism using the catalytic properties of gold islands is proposed. The morphological transition from the primary pyramidal ZnO structures to hexagonal ZnO whiskers is described in terms of the minimization of the free energy density of three-dimensional heteroepitaxial islands.     

Ti-Al-Nb2O5系原位合成Al2O3晶须的形成机理分析

本文研究了以粉埋法原位合成的Al2O3晶须的形态和反应过程以及晶须的生长机理.通过物相测试表明产物由Al2O3、TiAl3、NbAl3和少量的AlN相组成,SEM结合EDS分析表明原位合成了直径小于100nm的Al2O3晶须,晶须呈棉絮状分布于基体交界处.基于铝的过剩,TiAl3相是Ti-Al界面的唯一产物.Ti与O2以反应时间短的动力学势优先形成的TinOm中间产物是Al2O3晶须生成的控制步骤.Nb2O5与铝液的双效复合催化作用,提高了晶须的生成速率;同时Al的用量因AlN的生成而减小,导致生成晶须的催化活性点减小,而扩散到每个活性点周围的TinOm及Nb2O5浓度增加,导致晶须分布密而均匀.Al2O3晶核在催化剂的作用下以螺旋位错生长形成长径比较为理想的Al2O3晶须.     

陶瓷纤维/莫来石晶须原位增强堇青石-莫来石轻质隔热材料

以蓝晶石、粘土、氧化镁粉为原料,以淀粉为造孔剂和固化剂,引入适量的硅酸铝陶瓷纤维或多晶莫来石纤维和AlF3,通过莫来石晶须在陶瓷纤维表面的原位形成,制备了具有陶瓷纤维/莫来石晶须互锁结构的堇青石-莫来石轻质隔热材料.研究了陶瓷纤维在AlF3的作用下对材料显微结构观察、常温力学性能和导热系数的影响.研究表明:在AlF3的作用下,莫来石晶须在硅酸铝纤维表面垂直生长,部分穿插在发育良好的堇青石晶粒中;这种具有陶瓷纤维/莫来石晶须互锁结构的的陶瓷材料,其力学性能得以提高并降低了材料的导热系数.     

MOCVD法制备一维定向ZnO晶须阵列及掺杂研究

采用大气开放式MOCVD技术,以Zn(C5H7O2)2为前驱物,在玻璃和单晶硅基片上生长了沿c轴高度定向、规则排布的氧化锌晶须阵列.在此基础上,采用多气路输送不同金属有机源的方法,进行了ZnO晶须的掺杂,制备了掺铝元素的一维定向晶须阵列.XRD结果表明未掺杂ZnO晶须为六方纤锌矿结构,沿c轴高度取向;掺铝ZnO晶须晶体结构仍为六方纤锌矿结构,沿c轴择优取向.SEM结果显示,未掺杂的ZnO晶须阵列排布规则,长径比达到20;掺杂ZnO晶须随着铝掺杂浓度的增加,晶须的形貌及排布规则性变差.     

添加CaSO4·2H2O为晶种制备磷石膏半水硫酸钙晶须

以固体废弃物磷石膏为原料,在传统常压醇水热法的基础上添加CaSO₄·2H₂O为晶种制备半水硫酸钙晶须。采用单因素试验法探究了晶种含量、丙三醇含量和磷石膏质量分数对晶须结构和形貌的影响,确定晶须的最佳制备工艺条件。采用SEM和XRD对样品进行表征分析,实验结果表明:添加CaSO₄·2H₂O晶种制备晶须的长径比(49.29)比只添加丙三醇的样品的长径比(30.99)提高了近60%;当丙三醇与水的体积比(V)为1、晶种含量为1%、磷石膏质量分数为5%时制备的晶须的平均直径为0.65 μm,长径比达到了62.15,晶须的尺寸均匀。这说明添加1%CaSO₄·2H₂O晶种、V为1的丙三醇和质量分数为5%的磷石膏在常压下能制备出高长径比和尺寸均匀的半水硫酸钙晶须。     

六钛酸钾晶须的制备及生长机理的研究

通过KDC方法成功制备了六钛酸钾(K2Ti6O13)晶须,并进行了热重分析和差热分析,研究烧结时间和烧结温度对K2Ti6O13晶须结晶过程的影响,通过X射线衍射分析了K2Ti6O13晶须的相组成和晶体指数.此外,通过扫描电子显微镜和透射电子显微镜研究晶须的微观结构,揭示了K2Ti6O13晶须的生长机理.     

Porous silica alcogel matrix entrapped with liquid electrolyte: Ionic conductivity and growth of whiskers

Highly porous silica alcogel, with pores entrapped with liquid electrolyte solutions of KH₂PO₄, has been successfully prepared by hydrolysis and polycondensation of tetraethylorthosilicate (TEOS) giving interesting “solid-liquid electrolyte composites”. The entrapped liquid electrolyte solution gives high liquid-like ionic conductivity (10⁻⁵ S·cm⁻¹). Further, on storage the entrapped solution slowly reaches the surface pore-heads where it evaporates resulting in the growth of long crystalline whiskers. Higher relative humidity (>60%) slows down the evaporation and has been found to be favorable for whisker growth.