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Alternative TitleResearch for Adjustment of Electrodeposition Process of Thick Coatings from Trivalent Chromium Baths
Thesis Advisor王志
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword三价铬电镀   三价铬活性络合物   铬电沉积速率   镀液配制
Abstract铬镀层因其优异的性能在工业、日常生活用品等领域都有广泛应用。但传统六价铬电镀工艺高毒、高污染,已经不能适应现在严苛的环保要求。而三价铬电镀工艺毒性低,且所获镀层组成和性能都与六价铬电镀工艺相近,得到了研究人员的普遍关注。然而,三价铬电镀厚铬技术一直未能应用到工业生产。分析其原因主要有两点:(1)在常规电镀条件下,铬镀层不能持续增厚;(2)镀液不稳定。本文针对以上问题,在前人研究基础上进行研究,并取得了如下进展:(1) 获得硫酸铬溶液在镀液配制及电镀条件下的组成。由电镀实验结果确认三价铬活性络合物的组成可能是 (三价铬离子络合物为六配体络合物,所有无机配体如不强调则省略),其中 活性最高。配制条件显著影响镀液中三价铬活性络合物浓度。当加热温度由60 °C增加到96 °C时,铬电沉积速率从0.40 升高到0.71 。随着三价铬活性络合物浓度增加,镀层中碳含量相应减少。(2) 研究了镀液组成对铬电沉积过程的影响。提高三价铬活性络合物浓度可以显著提高铬电沉积速率。当镀液中 的浓度达到0.5 M,脲浓度达到0.5 M时,电流效率可超过38%。硼酸、硫酸铝等缓冲剂的引入可以促进镀层在基体上的均匀分布。甲酸的引入可以大幅度提高光亮电流密度上限。(3) 研究了脉冲电流和镀液流动对铬电沉积的影响。脉冲电流和镀液流动都可以促进电镀过程中生成的副产物向镀液主体的传递。脉冲电镀会降低铬电沉积效率,镀液流动可以提高铬电沉积效率,并可促进厚铬的生成。在本文实验条件下,流动镀液电镀在60 min内获得了41 μm的镀层。综上,本文对三价铬活性络合物的存在形式得到了新的认识,所获镀液性能与文献报道数据相当,其最高电流效率超过文献报道平均值近一倍。并利用流动镀液的手段获得了厚铬镀层。
Other AbstractChromium coatings have been widely used in industry and everyday life. Conventional chromium coatings are electroplated from baths containing chromic acid, which are extremely toxic and restricted due to environmental pollution. Hence, owing to the low toxicity and similar coatings, trivalent chromium electrodeposition has attracted more attentions as an alternative to the traditional Cr(VI) plating. However, trivalent chromium plating arts are hardly used in industry to plate thick coatings. The reasons are twofold. One is chromium couldn’t deposit on the cathode steadily using the operation as other plating arts. The second is that baths of Cr(III) plating could not keep stable as plating. On the base of others, in this work, these problems were studied, and some progresses were achieved as followed:(1) The equilibrium composition of chromic sulfate was obtained under the concentration of preparing and plating. The forms of active Cr(III) complexes, (Cr(III) complexes are with 6 ligands, all the inorganic ligands are omitted here if not to emphasize), were identified by the electroplating experiments. Importantly, are more active than others. Conditions of preparation process of Cr(III) baths should be chosen carefully to produce active Cr(III) complexes. When the bath was heated at from 60 °C to 96 °C, the chromium deposition rate increased from 0.40 to 0.71 . With the concentration of active Cr(III) complexes increased, carbon content of coatings decreased.(2) The effect of the composition of Cr(III) baths on chromium deposition process was studied. Increasing the concentration of active Cr(III) complexes would enhance the deposition rate of chromium. When the concentration of both chromic sulfate and urea reached 0.5 M, the current efficiency would exceed 38%. Buffer, such as boric acid and aluminium sulfate, would make the thickness distribution of chromium coatings homogenization.(3) The effect of pulse plating and flowing baths on chromium deposition process was studied. They all enhanced the transmission of the subsidary products, which blocked the deposition of chromium, from cathode interface to the bulk solution. Pulse plating would decrease the deposition rate of chromium. However, flowing baths would increase the current efficiency of chromium deposition, and thick coatings were got as a result. Under the experiment condition of this work, thick coating of 41 was obtained in 60 min by flowing the bath.To sum up, a new knowledge about the form of active Cr(III) complexes was obtained in this work. The baths performance was similar with those reported by others. The highest current efficiency in this work is almost twice of the average. Thick coatings were deposited from this bath by flowing the bath.
Document Type学位论文
Recommended Citation
GB/T 7714
栗磊. 三价铬体系电镀厚铬过程调控的研究[D]. 中国科学院研究生院,2013.
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