共查询到19条相似文献,搜索用时 160 毫秒
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镍钨硼合金电沉积机理及镀层微晶尺寸 总被引:1,自引:0,他引:1
应用循环伏安、恒电位阶跃和X射线衍射 (XRD)等方法研究了Ni_W_B合金电沉积特点和镀层微晶尺寸 .结果表明 ,在以柠檬酸铵为络合剂的溶液中 ,Ni_W_B合金沉积层较Ni_W合金有较低的电化学活性 .电位阶跃i~t曲线分析表明 ,在玻碳电极上Ni_W_B合金电结晶过程遵循扩散控制瞬时成核三维成长模式 ,且随过电位的增加 ,电极表面晶核数增多 .XRD测试结果表明 ,随沉积电流密度提高 ,合金镀层微晶尺寸逐渐增大 ,说明电流密度提高将更加有利于Ni_W_B合金电结晶过程中的晶核生长 . 相似文献
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氯离子对铜在玻碳电极上电结晶的影响 总被引:7,自引:1,他引:6
采用线性扫描伏安法和计时安培法研究了硫酸铜溶液中铜在玻碳电极上电结晶 的初期行为。在含与不含氯离子的0.05mol·L~(-1) cUso_4-0.5 mol·L~(-1) H_2SO_4电解液中,循环伏安实验结果表明铜在玻碳基体上的沉积没有经过UPD过 程;氯离子明显使Cu的沉积和氧化峰变得尖锐,促进Cu的沉积速度。计时安培实验 结果表明,Cu的电结晶按瞬时成核和三维生长方式进行。氯离子不改变Cu的结晶机 理,但在I~t曲线中,导致电流达最大(I_m)所需的时间t_m减小、晶核数密度和生 长速度增大,从而明显改变Cu沉积层的质量。当Cl~-浓度在10~20mg·L~(-1)范围 内,成核的晶核数密度达较大,即氯离子的最适宜添加量。 相似文献
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采用循环伏安和计时安培法研究了羟基乙叉二膦酸(HEDPA)镀铜液中铜在玻碳电极上电结晶的初期行为。结果表明:羟基乙叉二膦酸(HEDPA)镀铜体系中,铜的电沉积过程经历了晶核形成过程;当溶液中不含CO32-时,其电结晶按连续三维成核方式进行,而CO32-的加入,使得铜电结晶按瞬时三维成核方式进行;成核数密度都随着电位的提高而增加。这可能是CO32- -以第二配体形式进入HEDPA和Cu2+构成的络合结构,从而形成更稳定的络合物吸附在电极表面所致。 相似文献
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锌在玻璃碳上的电化学成核机理 总被引:8,自引:0,他引:8
线性扫描伏安法和电位阶跃法被用来研究氯化钾镀锌溶液中锌在玻璃碳上电结晶的初期阶段。发现锌在该基体上的沉积没有经历UPD过程。在本实验条件下, 成熟晶核的生长受溶液中锌离子的扩散所控制, 而晶核形成的机理依有无添加剂存在而异。通过分析恒电位暂态, 求出锌离子的扩散系数D, 以及不同过电位η下的成核速度常数A和晶核数密度N_0。A和η的关系表明“原子模型”比经典的成核模型更适合于本研究体系。N_0与η的经验关系式由曲线拟合而得。本文着重讨论了过电位和添加剂对成核作用的影响。 相似文献
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The process of copper electrocrystallization on the Ag(111) face was studied in acidic perchlorate-sulfate electrolytes. Enhanced
rate of charge transfer in the course of nucleation and growth of epitaxial copper crystallites was observed in the solutions
with additives of sulfate ion as a result of local electrostatic effects under specific adsorption of anions. Copper nucleation
parameters were estimated in the framework of the diffusion models and atomistic theory of electrochemical nucleation. 相似文献
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应用循环伏安法和计时安培法研究了铋在玻碳电极上的电结晶行为.循环伏安曲线显示了铋在玻碳电极上成核的典型特征,并表明其于玻碳电极上的电结晶是一个扩散控制过程.根据计时安培法响应曲线分析阐明了铋的浓度和过电势对成核生长机理的影响.进一步的定量测试表明该成核速率常数A和活化点密度N0随过电势增加呈现指数增大规律;扩散系数D随过电势增加呈指数衰减.以上实验结果至今未见报道.同时表明:Scharifker公式和Heerman公式均可用于本实验的理论解释. 相似文献
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A predictive mathematical model to describe mass loss profiles of flame-retardant (FR) containing epoxy resin formulations is proposed. Mass loss is due to thermal degradation of the constituent components and can be described by a generic kinetic scheme with a given set of thermokinetic constants in the form of ordinary differential equations. The scope of this work is to determine the kinetic parameters of the thermal degradation of a known flame-retarded epoxy resin composition by using thermogravimetric analysis and using the acquired data to predict the degradation profiles for other formulations. The mass loss profiles of Visil and intumescent epoxy resin containing formulations were predicted by solving coupled systems of ordinary differential equations and then using Powell minimisation to find the optimal Arrhenius parameters, taking into account the mass ratio of the components in the mixture. The calculated kinetic constants for one formulation (85% resin-15% FR additives) are used to predict the mass loss profiles for other formulations (80% resin-20% FR additives and 90% resin-10% FR additives) with the assumption that the degradation mechanism does not change. The predicted thermal degradation profiles are compared with experimental data acquired using standard laboratory equipment in order to validate the proposed mechanisms. The kinetic parameters obtained adequately describe mass loss history of composite materials studied, even when extremely simplified kinetic schemes have been used. 相似文献
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A novel zinc(II) hydroxide complex with a rare alkylthiolate donor in the coordination sphere is formed in aqueous solution from the dissolution of the zinc alkyl precursor complex (PATH)ZnCH(3) (PATH = 2-methyl-1-[methyl(2-pyridin-2-ylethyl)amino]propane-2-thiolate) in H(2)O and protonolysis of the Zn-C bond to give (PATH)ZnOH (1). The (PATH)ZnOH complex has been shown to promote the hydrolysis of 4-nitrophenyl acetate (4-NA) by a detailed kinetic study and is the first functional model for the zinc form of the enzyme peptide deformylase. From a fit of the sigmoidal pH-rate profile a kinetic pK(a) of 8.05(5) and a pH-independent second-order rate constant (k" max)) of 0.089(3) M(-1) s(-1) have been obtained. The kinetic pK(a) is similar to the pK(a) of 7.7(1) determined by a potentiometric study (25 degrees C, I = 0.1 (NaNO3)). Observation of both rate enhancement and turnover shows that 1 acts as a catalyst for the hydrolysis of 4-NA, although the turnovers are modest. Activation parameters have been obtained from a temperature-dependence study of the rate constants (E(a) = 54.8 kJ mol(-1), DeltaH++ = 52.4 kJ mol(-1), and DeltaS++ = -90.0 J mol(-1) K(-1)), and support a reaction mechanism which depends on nucleophilic attack of 1 in the rate-determining step. This is the first kinetic and thermodynamic study of a 4-coordinate zinc hydroxide complex containing a thiolate donor. In addition it is only the second time that a complete set of activation parameters have been obtained for the zinc-promoted hydrolysis of a carboxylic ester. This study puts the basicity and nucleophilicity of a (N(2)S)ZnOH complex in context with those of other L(n)()ZnOH complexes and enzymes. 相似文献
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Jingxian Yu Hanxi Yang Xinping Ai Yongyan Chen 《Russian Journal of Electrochemistry》2002,38(3):321-325
The zinc electrodeposition onto glassy-carbon electrode from the sulfate, chloride and acetate solutions is examined using cyclic voltammetry and chronoamperometry. The surface morphology of zinc deposited films is observed by scanning electron microscopy. The results show that all mechanisms of the zinc electrocrystallization on glassy-carbon electrode in the three solutions follow the same three-dimensional instantaneous nucleation and growth. The anions mainly affect the nucleation densities during zinc deposition, which results in different surface morphology. In the presence of acetate and chloride ions, the deposited zinc film tends to grow in a multi-layered pattern, while in sulfate solution the zinc deposition forms irregular grains. 相似文献
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棉秆催化热解特性及动力学建模研究 《燃料化学学报》2011,39(8):585-589
通过不同添加剂处理棉秆的热重实验,分析NaOH、Na2CO3、Na2SiO3、NaCl、TiO2、HZSM-5六种添加剂催化棉秆热解动力学特性,结合原料的组分分析,建立三组分独立平行一级反应热解动力学模型对试样热失重行为进行模拟,采用非线性最小平方算法求解热解动力学参数。研究发现,添加剂的加入改变了三组分动力学参数,在碱性添加剂作用下,纤维素和半纤维素热解活化能都有较大程度降低,且碱性越强,纤维素热解活化能越低,而半纤维素热解活化能越高;中性添加剂NaCl对纤维素和半纤维素热解活化能的影响不大;酸性添加剂使纤维素和半纤维素的热解活化能有所增大,但所有添加剂对木质素热解活化能的影响不明显。 相似文献
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在弱酸性柠檬酸盐体系铜锡合金镀液中,采用线性扫描伏安(LSV)、循环伏安(CV)和计时安培实验方法,运用Scharifker-Hills(SH)理论模型和Heerman-Tarallo(HT)理论模型分析拟合实验结果,研究铜锡合金在铜电极上的电沉积过程与电结晶机理.结果表明,铜锡合金在铜电极表面实现共沉积并遵循扩散控制下三维瞬时成核的电结晶过程.电位阶跃从-0.80 V负移至-0.85 V(vs SCE),HT理论分析得到铜锡合金的成核与生长的动力学参数分别为成核速率常数(A)值从20.19 s-1增加至177.67 s-1,成核活性位点密度数(N0)从6.10×105cm-2提高至1.42×106cm-2,扩散系数(D)为(6.13±0.62)×10-6cm2s-1. 相似文献