PCB焊点焊接缺陷原因分析

PCB焊点焊接缺陷产生的原因可能很多,如果你从扩散焊接的特点考虑就会变得明了起来！熔化的焊料原子沿着被焊接金属的结晶晶界的扩散,扩散所需要的激活能也可称为“表面自由能”比体扩散小。一般锡料的活性能约为380达因/厘米,鲜活的铜面在助焊剂的辅助下约为1265达因/厘米,所以焊接可以良好进行。     

水溶性有机去膜液的主要成分及其作用原理概述

文章在大量的文献基础上总结了水溶性有机去膜液的主要成分,包括有机胺、有机溶剂、加速剂、缓蚀剂和消泡剂,并介绍了各种成分在去膜过程中的作用原理。重点介绍应用于去膜液中的各类缓蚀剂及其缓蚀机理,缓蚀剂包括含氮化合物、含硫化合物、有机酸、芳香族羟基化合物等。     

Sulfonylation from sodium dithionite or thiourea dioxide

The cheap and easily available sodium dithionite and thiourea dioxide have been used as the source of sulfonyl group in the synthesis of sulfones and sulfonamides recently.Compared with other methods for the sulfonylation reactions,the strategies using sodium dithionite or thiourea dioxide provide an alternative and complementary route to diverse sulfonyl compounds.During the reaction process,sulfur dioxide anion radical is the key intermediate,which is usually generated from a single electron transfer under suitable conditions.The advantages using sodium dithionite or thiourea dioxide in the sulfonylation reactions include mild conditions and broad substrate scope with excellent functional group compatibility.Further applications by using sodium dithionite and thiourea dioxide in organic transformations will be anticipated.     

疏水型纳米TiO_2膜的制备、表征及耐蚀性能研究

以乙酰乙酸乙酯(EAcAc)作稳定剂和阻聚剂制备超微TiO2溶胶,用提拉法在AISI316L不锈钢上构筑一层纳米TiO2膜,经水热后处理有效消除膜中的龟裂现象,经氟硅烷基化制备成疏水型纳米TiO2膜.用胶粒分布仪测定溶胶颗粒分布,接触角测试仪测定表面疏水性、XRD、SEM表征膜的形貌、结构,电化学线性极化法测定疏水型纳米TiO2膜在模拟体液(Ringer溶液)中的电化学行为.结果表明:TiO2膜呈多孔有序纳米膜,颗粒分布均匀,粒径约为15～18nm,厚度约375nm,TiO2为锐钛矿型,疏水型纳米膜可使不锈钢腐蚀电流降低3个数量级,其耐腐蚀性大幅度提高.     

铁基SiN表面陶瓷的结构及耐酸性腐蚀行为

研究了铁基表面镀硅（～５０ｎｍ 厚）经氮离子束处理（能量为 ４０ｋｅ Ｖ,剂量分别为５×１０１６,１×１０１７,５×１０１７ｃｍ － ２）后的表面结构和在 １ Ｎ Ｈ２ Ｓ Ｏ４ 水溶液中的腐蚀行为。 Ｔ Ｅ Ｍ 证明,各试样表面均存在一完整的非晶层;电化学测量和失重实验表明,试样的失重量与浸泡时间满足幂函数规律;经表面处理过的试样,腐蚀电位提高了 ３０～４０ｍ Ｖ,腐蚀电流密度下降了 ４～６ 倍;耐腐蚀性随氮离子剂量的增大而不断提高。文章还结合腐蚀表面的粗糙度（分形维数）讨论了离子注入对表面结构和耐蚀性的影响。     

紫外光固化自修复剂的微胶囊化及智能防腐蚀涂层的制备

利用在水相中原位生成的聚脲甲醛沉淀吸附在可见紫外光固化组份构成的油相表面,制备了包覆自修复剂的脲醛树脂（PUF）微胶囊. 光学显微镜及SEM表明,PUF微胶囊尺寸为118-663 μm,与PUF 形成过程中的搅拌速度有关. 在中等搅拌速度（600 r/min）时,可以得到最高的包覆率（97.52wt%）和产率（65.23wt%）. 将此微胶囊掺入水性聚氨酯乳胶中制成的涂层表面受损后,在紫外光照射下可以进行自修复,具有优异的金属防腐蚀性能.     

拉曼光谱对新石器时期白石斧的研究

本文采用显微拉曼光谱技术 ,对云南省永仁县菜园子出土的新石器时期白石斧的表面和截面进行了测试研究 ,结合矿物拉曼谱确定了石斧白色和黑色物质的成分。通过对白石斧截面拉曼谱的分析 ,得出了石斧拉曼主峰 (46 2cm- 1 )的强度随深度变化情况的散点图 ,实验结果发现 ,石斧表面的腐蚀层厚约为 40 0 μm。石斧截面拉曼谱给出了与石斧埋葬年代和周围环境有关的信息     

Sulfur Composite Cathode Materials for Rechargeable Lithium Batteries

Conductive polymer/sulfur composite materials were prepared by heating the mixture of polyacrylonitrile (PAN) and sublimed sulfur. During the heating process, PAN was dehydrogenated by sulfur, forming a conductive main chain similar to polyacetylene. At the same time, the high‐polarity functional group –CN cyclized at the melt state, forming a thermally stable heterocyclic compound in which sulfur was embedded. The nanodispersed composites showed excellent electrochemical properties. Tested as cathode material in a non‐aqueous lithium cell based on poly(vinylidene fluoride) (PVDF) gel electrolyte at room temperature, the composite exhibited a specific capacity up to 850 mA h g^–1 in the initial cycle. Its specific capacity remained above 600 mA h g^–1 after 50 cycles, about five times that of LiCoO₂, and recovered partly after replacement of the anode with a fresh lithium sheet. The utilization of the electrochemically active sulfur was about 90 % assuming a complete reaction to the product, Li₂S.     

An Electrochemical Robotic System for Routine Cathodic Adsorptive Stripping Analysis of Ni2+ Ion Release from Corroding NiTi Shape Memory Alloys

Cathodic adsorptive stripping voltammetry (AdSV) as highly sensitive and selective method for quantifying trace amounts of dissolved Ni²⁺‐ions has been integrated into an electrochemical robotic device using the wells of microtiter plates as low‐volume electrochemical cells. A three‐electrode assembly integrating a Bismuth film‐modified glassy carbon electrode as working electrode and a glass capillary for delivering Ni²⁺ standard solution in conjunction with an adapted software allowed multiple AdSV measuring cycles to be performed one after the other in the individual compartments of a 24‐well microtiter plate. Of advantage for the automation was the possibility of an in‐well electrochemical removal of used and a replating of fresh Bi films in between distinct measuring cycles. With optimized parameters for the accumulation of the complex between Ni²⁺‐ions and dimethylglyoxime onto the surface of the Bi film electrode and the subsequent stripping procedure, automated adsorptive stripping voltammetry in the established system offered a linear dynamic range of up to 170 nM, a sensitivity of 12 nA/nM Ni²⁺ and a limit of of detection of 2.1 nM (N=16) for the detection of trace levels of Ni²⁺‐ions. Automated AdSV certainly is of convenience for studying larger number of samples due to the high‐throughput capability of the robotic apparatus. As example, the automatic quantification of Ni²⁺‐ion release from electropolished surfaces of NiTi shape memory alloys during corrosion in NaCl solutions is described.     

Corrosion resistance and lubricated sliding wear behaviour of novel Ni-P graded alloys as an alternative to hard Cr deposits

Alternative process to hexavalent chromium, substitute materials and new designs are urgently needed owing to the requirement of “clean” manufacture. This comparative study was conducted to systematically investigate the corrosion resistance and lubricated sliding wear behavior of graded Ni-P alloy deposits produced from a single plating bath by electrodeposition and hard Cr deposits, using potentiodynamic polarization and reciprocating ball-on-disc tribometer. Results showed that Ni-P deposits heat-treated at 400 °C with maximum hardness exhibited more than two orders of magnitude higher corrosion resistance than hard Cr deposits in 10 wt.% HCl solution. The Stribeck curves for the heat-treated Ni-P gradient deposits and hard Cr under lubrication conditions were obtained with accurate control of normal load and sliding speed during the wear process, three main different regimes corresponding to different lubrication mechanism were identified. Heat-treated Ni-P gradient deposits showed relatively poor wear resistance than hard Cr deposits under the lubrication conditions, which may be attributed to superior oil-retaining surface structure and the unique “nodular” effect of hard Cr in wear process.