三价铬镀铬工艺初探

传统的镀铬是在含有六价铬的电镀液中进行的,六价铬对环境严重的危害,促进了三价铬镀铬工艺的发展.在铁基体上选取不同的三价铬镀铬配方进行试验,以铅板或石墨为阳极,20钢试片作阴极,对试片除油除锈后,直接进行三价铬镀铬,经过对镀层的外观、厚度及结合力的比较取舍,获得了外观及结合力较好的配方:52g/LCr3 ;40g/L KCl;10g/L KBr;46g/L HCOOH;53g/L NH4Cl;150g/L(NH2)2CO;10g/L H3BO3及少量的添加剂,以阳极石墨为基础,研究了不同种类及不同用量的润湿剂对镀层外观和孔隙率的影响,最终选定了对于三价铬镀铬配方较佳的润湿剂及其用量范围.对镀铬层用碳酸钠和磷酸钠进行中和浸渍,时间为3～5 min,可以减轻三价铬镀层发黄的问题.该工艺条件:DK=10～15 A/dm2,10～20℃带电下槽,pH值为0.5～1.0,电镀液的稳定性为12 A@h/L.镀层细致、光亮、孔隙率低,而且可以在常温下操作,节约能源.     

硫酸盐体系三价铬电镀黑铬的工艺

为了寻找更环保、更稳定的三价铬电镀黑铬工艺,采用Hull Cell和小槽试验优选了硫酸盐体系三价黑铬电镀液中发黑剂、辅助发黑剂的种类及用量,并对镀液和镀层性能进行了测试。结果表明:最优三价铬电镀黑铬工艺为35 g/L碱式硫酸铬,30 mL/L配位剂,150 g/L硫酸钠,80 g/L硫酸钾,70 g/L硼酸,3 mL/LBNW-1润湿剂,2～4 g/L半胱氨酸,1～2 g/L硫氰酸钾,pH值3.4～3.8,温度50～60℃,阴极电流密度5～10A/dm2;以该工艺进行三价铬电镀黑铬,镀液稳定性好、分散能力强,电流密度范围宽,可达2.5～15.0 A/dm2;该工艺制备的黑铬镀层主要成分为Cr,S以及少量有机物;镀层黑度好,耐蚀性好,与基体结合良好。     

镀铬液中三价铬离子和铁离子含量对镀液、镀层性能的影响

在电镀铬电镀液中,三价铬适用范围为装饰铬电镀2～8 g/L,工业铬电镀1～5 g/L.由于工业铬电镀时,因为混入的不纯物常包含有铁质成分,因此管理者大多将三价铬及铁离子含量合计在5～10 g/L的范围.     

海外文献速递

电镀20010101低铬镀铬——Nikolova S.Metalloberflarche,1999,53(12):37(德文) 研究了沉积条件对镀铬层性能的影响,温度和电流密度是两个主要沉积条件。使用低浓度的铬酸对环境有利,用曲线表明了铬的沉积速度与铬酸浓度的关系以及电流密度和槽液温度对电流效率,沉积速度,镀层光洁度、硬度的影响。20010102三价铬的硫酸盐镀铬层经热处理后形成的气体——Jedigarjan A A.Zasch Metall,1999,35(2):129(英文) 研究了电流密度、pH值、温度对用两种不同Cr(Ⅲ)电解液获得的镀铬层含H量的影响,镀液中表面活性剂起主要作用。当加热至400℃时,镀层中不仅有H2,而且有CO2气体放出,CO2的形成为槽液中草酸的分解所致。20010103 Cr3+、Fe3+对镀铬的影响——Krishnan R M.Bull Elec-trochem,1999,15(5):195(英文) 用Hull槽研究了不断提高Cr3+、Fe3+浓度对传统六价铬镀槽性能的影响,列出了在两种不同电流密度下沉积层的外观、电流效率、沉积速度、孔隙率、硬度(显微)与镀液中Cr(Ⅲ)浓度的关系,同时研究了镀液中Fe(Ⅲ)含量为1～20g/L的影响。适当的Cr(Ⅲ)浓度对镀铬有利,但过高的Cr(Ⅲ)会产生不良铬镀层;Fe(Ⅲ)始终对镀铬不利,大量的Fe(Ⅲ)会破坏镀铬层。20010104六价铬化合物镀铬的机理(第一部分)：基本电解液组成、文献资料和机理——Soeha J.Galvanotechnik,1999.90(11):2 976(德文) 提出了pH值对铬酸、重铬酸根离子、铬酸根离子化学性质的影响,列出了平衡常数。介绍了三价铬化合物的作用,新生氢使六价铬得以还原,解释了铬沉积过程中外来离子的作用,特别是硫酸的影响,研究了电流效率与硫酸浓度的关系。     

三价铬彩色钝化工艺的研究

三价铬钝化毒性小,将成为六价铬最有可能被接受的替代品.通过正交试验和单因素试验,得到了三价铬彩色钝化膜的最佳工艺条件为:3.0 mL/L Cr2(SO4)3·6H2O、5 g/L丙二酸、5 g/L NaNO3、1g/L Ni盐、0.6 mL/L有杌硅封闭剂,pH值1.6,钝化温度25℃,钝化时间80 s.探讨了pH值、钝化温度、钝化时间与封闭剂浓度和耐蚀性的关系.在最佳工艺条件下得到的钝化膜呈彩色,能通过79 h中性盐雾试验.     

Fe-Ni-Cr合金电沉积工艺参数对镀层铬含量的影响

为了在铁基上获得耐腐蚀性能好的、光亮致密的Fe-Ni-Cr合金镀层,在氯化物-硫酸盐混合体系中,研究了在铁基上电沉积Fe-Ni-Cr合金的工艺,确定出电沉积铁镍铬合金的最佳工艺条件:阴极电流密度14 A/dm2,镀液温度30℃,pH值2.0,镀液中CrCl3·6H2O浓度为25g/L.结果表明,合金镀层中Cr含量越高,镀层耐蚀性能越好,在最佳工艺条件下,镀层中Cr的含量接近6%,Fe的含量为54%,镀层光亮致密且耐蚀性好.     

羧酸盐-尿素体系脉冲电沉积纳米晶铬镀层的工艺优化

六价铬电沉积工艺毒性高、污染大,三价铬电沉积工艺低毒、低污染,应用前景广阔.运用正交设计法优化了镀铬液配方,确定了其工艺参数,研究了影响脉冲电沉积纳米铬镀层质量的主要工艺因素,分析了镀液组成对铬镀层厚度和电流效率的影响,得到了羧酸盐-尿素体系脉冲电沉积纳米晶铬镀层的最佳工艺.结果表明:影响镀层厚度的主次因素分别是配位剂A(柠檬酸钠)、配位剂B(碳原子数不少于8的一元羧酸盐)和CrCl3˙6H2O的浓度;影响电流效率的主次因素分别是配位剂A、CO(NH2)2和配位剂B的浓度.扫描电镜观察和电子能谱分析结果表明,铬镀层晶粒尺寸小于100nm,厚度均匀,表面光滑,结晶细致.该工艺能制备厚度为11.2um的铬镀层,其电流效率高达25.32%.     

镁合金铬磷化工艺的试验研究

利用正交试验法和对比实验法研究了一种镁合金铬磷化处理工艺,通过分析计算获得了AZ91D镁合金铬磷化处理液的最佳配方及工艺参数:铬酐12 g/L,次磷酸钠20～30 g/L,室温处理8min.用该工艺方法处理AZ91D镁合金,表面得到了一层致密均匀、附着力和耐蚀性良好、厚度为2.5～3.5 μm的铬磷化膜层,将其用于涂装前的打底层可以大大提高漆膜的附着力和耐蚀性能.该工艺对镁合金的涂装生产具有一定的参考价值.     

锌镍合金镀层三价铬钝化研究

镀锌层三价铬钝化在防腐蚀能力上无法满足一些工件高防腐蚀性能的要求,为此,采用锌镍合金进行三价铬钝化,通过盐雾试验考察了其防腐蚀能力.钝化液主要成分:77 g/L Cr(NO3)3·9H2O,13吕/L(COOH)2,15 g/L CH2(COOH)2,2g/L马来酸酐,8 g/L Co(NO3)2·6H2O,5 mL/L含硅化合物.结果表明,控制pH值在1.6～2.0,温度60～70℃,时间30 s以上,所得钝化膜防腐蚀能力超过常规镀锌六价铬钝化膜.锌镍镀层三价铬钝化既保护了环境,又能满足工件高防腐蚀性能的要求.     

镀铬槽中三价铬的控制办法

我厂有一镀铬槽容积为720 L,含CrO_3 200～250 g/L,H_2SO_4 2～2.5 g/L,三价铬2～7g/L,温度54～58℃,D_K30～50 A/dm~2。用于各种注射模、塑压模、橡胶模镀硬铬。由于模具大部分形状复杂,型腔和内孔都得装上各种象形阳极和辅助阳极,从而使三价铬容易增高。三价铬增高后影响铬层光亮度,光亮区范围缩小,降低溶液导电性,使槽电压升高。过去新配槽液用不到半年三价铬就达8 g/L以上,每     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。