Effect of Environmental Conditions on Tin (Sn) Whisker Growth

This research focuses on tin whisker growth under two different environmental conditions namely hygrothermal and a salt solution. Tin coated brass coupons were used for this study to analyze the growth of tin whiskers over time. Their growth rates were examined periodically using optical and scanning electron microscopy. The physical characteristics of the tin whiskers were identified for each environmental condition. It was discovered that submersion of tin coated brass substrates in 5% salt solution considerably increased the density (number of whiskers per unit area), and the length of the whiskers. In addition, it was found that the geometry and aspect ratio of tin whiskers were different for each environment.

Mg_(2)Sn-induced whisker growth on the surfaces of Mg/Sn/Mg ultrasonic-assisted soldering joints

In this paper,the phenomena of Mg_(2)Sn-induced Sn whisker growth were explored on the surfaces of Mg/Sn/Mg ultrasonic-assisted soldering joints after aging treatment.The in-situ observation and thermal analysis confirmed that the formation and the corrosion of Mg_(2)Sn nanoparticles were the dominant reason of Sn whisker growth.The Mg_(2)Sn accumulation at the grain boundaries would pin the dislocation slip and affect the continuity of whisker growth,and the boundary angle would thus play a decisive role in the growth shape of Sn whiskers due to the pining effect of Mg_(2)Sn.This study might be conducive to elucidating the growth behavior of Sn whiskers and provide the exploration strategy to further improve the bonding strength of Mg/Sn/Mg ultrasonic-assisted soldering joints.

Mechanism and mitigation of spontaneous Ga whisker growth on Cr2GaC

Spontaneous growth of A-element whiskers on Mn+1AXn(MAX for short) phase materials poses a barrier to their practical applications, since it casts doubts on their stability. In this study, Ga whisker growth on sintered Cr2GaC samples was investigated. The elemental source for spontaneous growth of Ga whiskers is identified as the free Ga contained in the Cr2GaC material, not the lattice atoms from Cr2GaC grains, which removes the doubts on the stability of Cr2GaC material. The growth behavior and morphologies of the Ga whiskers follow a new catalysis-based model, with cleavage planes of Cr2GaC grains involved as nucleation sites. This model explains and predicts well the growth behavior of the whiskers. The mitigation strategy based on this model is in principle simple: to prevent free Ga in Cr2GaC material or limit it to a certain level;to avoid cleavage plane of Cr2GaC grains;to achieve high density of the Cr2GaC material.

Growth Habit of the Basic Oxysulfate Magnesium Whisker

The growth habit of the basic magnesium oxysulfate whisker was investigated based on the theoreticalmodelof anion coordination polyhedron growth units.It is found that typicalbasic magnesium oxysulfate whisker growth is consistent with anion tetrahedralcoordination incorporation rules.The growth units of basic magnesium oxysulfate whiskers are [Mg-（OH）_4]^（2-） and HSO_4^-.[Mg-（OH）_4]^（2-） is the favorable growth unit and whisker growth is in the direction of the [Mg-（OH）_4]^（2-） combination.A plurality of [Mg-（OH）_4]^（2-） s combine and become a larger dimensionalgrowth unit in a one-dimensionaldirection.Then HSO_4^- and larger dimensionalgrowth units connect as basic magnesium sulfate whiskers,according to the structuralcharacteristics of the basic magnesium sulfate whisker,which can guide the synthesis of magnesium hydroxide whisker.

GROWTH MECHANISM OF TiC WHISKERS PREMRED BY A MODIFIED CHEMICAL VAPOR DEPOSITION METHOD

High quality TiC whiskers have been prepared by a modified chemical vapor deposition (CVD) method using TiCl4 and CH4 as reactant gases and Ni as substrate. The deposition temperature and gas flow mies have ampreciable effect on the whisker growth.The whisker orientations and morphology are determined by X-my diffraction (XRD),scanning electron micmpmph (SEM) and transmission electron microgmph (TEM).In addition to the spherical tips, spiral growth microsteps and obvious terraces are observed at the tips and side faces of whiskers in the present eoperiment. The whiskers grow mostly along (100) direction. The whisker growth mechanism is discussed in detail.

CHEMICAL VAPOUR GROWTH OF CARBON WHISKERS ON CARBON FIBERS

The secondary reinforcement,crbon whiskers,may grow on the surface of parent rein- forcement,carbon fibres,by chemical vapour growth from acetylene using Fe salt as catalyzer.The optimal growing temperature is about 1000℃,and while the concentra- tion of catalytic solution is appropriate,the carbon whiskers may deposite uniformly and link each other on the parent carbon fibre surface.If the temperature or concentration is too high,the coarse clusters of carbon may deposite on the fibre surface.The mechanism of carbon whisker growth is believed that the carbon atoms in vapour phase dissolve in the Fe salt drops over fibres,then the solid carbon grains precipitate on the fibre surface.

ANALYSIS OF THE GROWTH MECHANISM OF TiAl_3 WHISKERS PREPARED BY IN SITU REACTION IN MOLTEN ALUMINUM

Some TiAl3 whiskers are found to be produced simultaneously during the formation process of TiB2 Particulates fabricated by in situ reaction in molten aluminum. The thec t of temperature of molten aluminum on the morphologies of the TiAl3 whiskers and the growth mechanism of the whiskers are studied in this paper. The results show that the aspect rutio of the TiAl3 whiskers decreases with the increase of the temperoture. The growth of the whiskers is proved to be controlled by a Vapor-LiquidSoltd (VLS) mechanism. The titanium and aluminum atoms in the catalytic droplet,however, have been coofrmed to react with each othen which is dtherent from other whlskcrs growing by a VLS mcchanism where the compostion in the catalytic droplet is a constant.

Study on the thermodynamics and the growth kinetics of synthesis of the β-SiC whiskers

The thermodynamics and the growth kinetics of synthesis of the SiC whiskers (SiC w ) from rice hulls are studied in this paper. The results show that the intimate contact of SiO 2 with C in the rice hulls resulted in the formation of SiC particle (SiC p ) at lower temperature, and the external ash of the hulls (w (SiO 2 )>98%) is the main silicon source for SiCw growth. The metallic composite catalyst increases the selectivity for SiCw growth and the reaction rate. The growth mechanism of the SiCw can be characterized as the VLS (vapour liquid solid) with the presence of the whisker forming catalyst: from SiC nucleation through enlargement and growing with the <1 1 1> crystallographic orientation in a certain diameter, then the SiC w is a complete single crystal of β SiC. The generation reaction of SiO is the rate determing step for synthesis of SiC w .

Mg_2(OH)_2CO_3·3H_2O Whiskers Growth Mechanism

From the perspective of growth units, the growth mechanism of Mg2（OH）2CO3.3H2O whisker is investigated in this paper. Results show that the growth morphology of Mg2（OH）2CO33H2O whisker is consistent with the model of anion coordination polyhedron growth units. The growth solution Raman shift of Mg2（OH）2CO;3H2O was monitored using Raman spectroscopy. The growth units are [Mg-（OH）4]2- and H2COv The growth process of Mg2（OH）2COf3H2O whisker is as follows： growth unit [Mg-（OH）4]2- first incorporates into the larger dimension [Mg-（OH）4]2-, then the [Mg-（OH）4]2-n combines with H2CO3 into a linear skeleton Mg2（OH）2CO3 in the same line. Mg2（OH）2CO3 combines with H2O by hydrogen bonds and ultimately transforms into Mg2（OH）2COf3H2O whisker. Magnesium carbonate whiskers have a layered structure, each of which is made of magnesium, carbon, oxygen, with H2O in between each layer. When skeletons are superimposed within the same plane as a parallelepiped one, they grow into solid cuboid-shaped whiskers. When the parallelepiped skeletons planes combine with each other through the cascading links, they grow into hollow cylindrical whiskers.

半水硫酸钙晶须生产制备的研究现状

简要介绍了半水硫酸钙晶须的生长机理及其制备方法的优缺点。综述了原料技术品质、工艺技术参数和外加剂等因素对半水硫酸钙晶须制备的影响。此外,还探讨了半水硫酸钙晶须的改性方法及其应用领域。最后,分析了当前工业生产与应用中面临的关键问题,并提出了相应的解决方案。

盐酸溶解磷石膏重结晶制备石膏晶须

以工业磷石膏为原料,使用盐酸对其进行溶解,探索了单因素试验条件(盐酸浓度、液固比、反应温度、反应时间)对磷石膏溶解率的影响,得到了磷石膏最佳溶解条件:盐酸浓度4 mol/L、液固比20 mL/g、反应温度80℃、反应时间20 min,在此条件下溶解率为86.12%;探究了控温速率对石膏晶须析出率、产物组分、结晶程度和微观显微形貌的影响规律,结果表明:降温速率差异对石膏晶须析出程度几乎没有影响;4种降温速率(0.40、0.30、0.27、0.20℃/min)下的产物均为二水硫酸钙;石膏晶须的特征衍射峰均较尖锐,形成的晶粒较大,结晶程度较高;随着降温速率的减小,石膏晶须的长径比不断增大、形貌更加均匀。研究成果为工业磷石膏的高值高效利用提供了新思路。

Synthesis of Mg_2B_2O_5 whiskers via coprecipitation and sintering process

Mg2B2O5 whiskers with high aspect ratio were synthesized by coprecipitation and sintering process using MgCl2-6H2O, H3BO3, and NaOH as raw materials and KCl as a flux. Their formation process was investigated by thermogravimetry and differential scanning calo- rimetry （TG-DSC）, X-ray diffraction （XRD）, and scanning electron microcopy （SEM）. It is found that the products synthesized at 832℃ are monoclinic Mg2B205 whiskers with a diameter of 200-400 nm and a length of 50-80 μm. Transmission electron microscopy （TEM） and selected area electron diffraction （SAED） analyses show that the whiskers obtained at 832℃ are single crystalline and grow along with the [010] direction. The growth mechanism of Mg2B2O5 whiskers was also presented.

Synthesis of Calcium Chloroborate Whiskers Via Sedimentation and Sintering Process

Single crystalline calcium chloroborate（Ca2B5O9Cl） whiskers with uniform diameter have been fabricated by a two-step process. The precursor was firstly prepared by the sedimentation reaction between CaCl2, H3BO3 and Na OH aqueous solutions, and then sintered at different temperatures for 6 h with KCl as flux. The XRD indicates that the product synthesized at 600 °C is Orthorhombic Ca2B5O9Cl. SEM and TEM results show that the Ca2B5O9Cl is whisker with the diameter about 0.2-0.5 μm and the length up to 15 μm. SAED analysis shows that the whisker is single crystalline and grows along [001] direction. The possible formation process and growth mechanism were proposed.

Synthesis of tetrapod-shaped ZnO whiskers and microrods in one crucible by thermal evaporation of Zn/C mixtures

Tetrapod-shaped ZnO whiskers and microrods were synthesized in one crucible by thermal evaporation of Zn/C mixtures at 930 ℃ in air without any catalyst.The digital camera,optical microscopy,scanning electron microscopy,energy dispersive X-ray spectroscopy,and X-ray diffraction techniques were used to study the morphologies and crystal structures of these tetrapod-shaped ZnO microcrystals.The results show that these two types of ZnO tetrapods are grown at different heights within the same crucible.The legs of these tetrapod-shaped ZnO crystals are hexagonally faceted.Some tetrapod-shaped ZnO whiskers show hierarchical structures.A short button-like hexagonal ZnO microcrystal is observed at the triple junctions of some tetrapod-shaped ZnO whiskers.The tetrapod-shaped ZnO microrods are capped by two sets of hexagonal pyramids with two different groups of crystal planes for the surfaces.These two types of tetrapod-shaped ZnO microcrystals have different side faces and aspect ratio,which are believed to be the result of their different growth behaviors.The octa-twin model was used to discuss the different growth behaviors of these two types of ZnO tetrapods.The crystal planes of the legs and the pyramids were determined.

FORMATION OF AIN WHISKERS BY NITRIDATION OF AI/AIN POWDERS

The aluminum nitride whiskers were synthesized by the nitridation of Al/AlN powders in a flowing nitrogen atmosphere. The whiskers were about 0. 5祄 in diameter and 10~20祄 in length, and they were straight and had smooth surfaces. The morphology of the whiskers were studied by means of SEM and TEM. The AlN whiskers were grown via vapor-solid (VS) mechanism.

Synthesis of SiC Whiskers from Silicon Nitride in Argon Atmosphere

SiC whiskers were synthesized by carbothermal reduction of silicon nitride, α-Si3N4 and β-Si3N4 powders were used as silicon sources, and graphite, active carbon and black carbon as carbon sources, as well as boron oxide as catalyst. The synthesized SiC whiskers were characterized by XRD and SEM. The results showed that the synthesizing temperature should be above 1716 K; the decomposition of Si3N4 was the limited step in the synthesis of SiC whiskers; and catalyst not only offered the liquid condition, but also restricted the growth of SiC whiskers along one dimension. LS mechanism seems to explain well the growth of SiC whiskers.

莫来石晶须的制备、生长机制及应用研究进展

莫来石晶须具有耐高温、耐磨损、抗氧化、热膨胀系数小、抗热震性好等性能,是一种优异的复合材料补强剂。介绍了莫来石晶须的制备方法,包括固相法、熔盐法和溶胶-凝胶法,并对莫来石晶须的气-固生长机制和液-固生长机制进行了分析。概述了莫来石晶须在陶瓷增韧、隔热保温、分离及过滤和聚合物性能优化等方面的应用。结合目前莫来石晶须在制备和应用中存在的问题,对莫来石晶须未来的发展进行了展望。

碱式氯化镁晶须的制备及其生长机理研究

以六水氯化镁和氨水为原料,醇水溶液为溶剂,通过沉淀法制备碱式氯化镁晶须。采用X射线衍射、扫描电子显微镜、透射电子显微镜、拉曼光谱等手段对晶须结构进行表征,并探究其生长机理。结果表明:不同溶剂所制备的碱式氯化镁晶须化学式均为2Mg(OH)2·Mg(OH)Cl·4H2O。碱式氯化镁晶须的形成机制符合负离子配位多面体生长基元理论,晶须是沿着(201)晶面生长,乙醇或乙二醇的加入都能使晶须沿着一维方向生长且表面更光滑。当采用质量分数为20%乙二醇时所制备晶须的长径比为95,且具有更好的分散性和尺度均一性。

可焊性锡镀层失效机理分析与对策

锡具有良好的延展性、导电性、焊接性,常作为可焊性镀层广泛用于电子焊接行业。在应用过程中,镀层的变色、晶须生长及焊接性能的下降逐步成为人们关注并需要及时解决的技术问题。简要分析了可焊性锡镀层性能失效机理,从电镀工序角度对提高镀层性能稳定的解决策略进行了梳理,并对镀锡层的质量控制技术方向进行了展望。