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High-speeHigh-speed Chromium and Thick Chromium Platings from Environmental Trivalent Chromium Sulfate Solutions

Author: KangZhenHua
Tutor: ZengZhenOu
School: South China University of Technology
Course: Applied Chemistry
Keywords: Trivalent chromium Hexavalent Chromium Sulfate solution Plating Quick chrome Thick chrome plating
CLC: TQ153.11
Type: Master's thesis
Year: 2010
Downloads: 105
Quote: 1
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Abstract


Bright, hard chrome plating, wear and corrosion resistance, good performance, wide range of applications in industry. Traditional chrome plating process uses hexavalent chromium plating bath, have serious ecological environment and human health hazards in the electroplating industry by increasingly stringent restrictions on the use. The low toxicity of trivalent chromium plating, is the most promising alternative to hexavalent chromium plating bath chrome process. The present study the trivalent chromium plating chrome plating the main sulfate, chloride and sulfate - chloride three solution system, the most environmentally friendly chromium plating process which sulfate solution system. This paper studies the trivalent chromium sulfate solution system fast chrome with thick chrome plating. Trivalent chromium sulfate solution system by orthogonal experiments and single-factor experiments optimal bath composition and process conditions suitable for fast chrome plated thick chromium. The research results show that the optimal solution system of trivalent chromium sulfate bath composition: 0.5 mol / L the of Cr 3 , 0.7 mol / L HCOOH 60 0g / LH 3 BO 3 , 144g / L Na 2 SO 4 , 50g/LK 2 SO2 4 , 1.0 ml / L wetting agent, pH = 2.50. Using the above bath composition, the optimum current density of 10A/dm 2 and the bath temperature is 30 ~ 40 ℃ process conditions for rapid chrome plated surface can be obtained continuous and dense and uniform bright chromium plating, the current efficiency of up to 25.0% or more. This new process can be obtained on the copper substrate plating 10s average thickness of the chrome plating of more than 0.40μm, the average deposition rate can be achieved 2.50μm/min; chrome plating on low carbon steel substrate average thickness of 0.10μm, an average plating rate only 0.70μm/min. This new process for a long time in quick succession, chrome-plated, the plating bath consumption seriously, pH value decreased rapidly, need regular maintenance. Using the above bath composition 8-11A/dm 2 and the bath temperature at a current density of 30 ~ 40 ℃ under the process conditions can be plated to obtain a good performance of the thick chromium plating. For planar plating thickness greater than 30μm, obtained in the bath circulation flow conditions the white bright dense chromium coating, the average deposition rate can reach 25μm/hr. For cylindrical plating thickness greater than 50μm white light and dense chromium coating, available under the the plating rotation conditions (workpiece speed 20r/min) average plating rate greater than 20μm/hr. Cathodic protection, electroplating process available in the shock absorber thickness greater than 50 μm, uniform white bright chrome plating, the average deposition rate greater than 30μm/hr. Trivalent chromium sulfate solution system thick chromium plating, chrome plating thickness and the plating rate increases with current density and increase; reduced with increasing temperature. Thick chromium plating performance test results show that: trivalent chromium sulfate solution system electroplating chromium plating obtained by the average coefficient of friction of the chromium plating and the hexavalent chromium solution system plating is very close; the amount of wear in the same conditions than hexavalent chromium The less chrome plating solution system Plating, wear resistance better. System plating of trivalent chromium sulfate solution the chrome plating microscopic morphology nodulation-like hardness increases with increasing heat treatment temperature, the original plated chromium plating hardness of 730HV at a temperature of 500 ℃ conditions under heat treatment 1hr hardness increased to 1090HV. Characterized by XRD and DSC experiments with chrome plating: The results show that the trivalent chromium sulfate solution system plating the chromium plating (the original plated) is amorphous at room temperature, at a temperature of 293 ℃ from amorphous into crystalline states. A chromium plating layer (primary plating state) after heat treatment temperature higher than 293 ° C is a typical Cr polymorphs, the grain size of the nanoscale. Obtained in the high current density plating charred chrome plating is amorphous, and the difference is mainly charred chrome plating the higher carbon content and containing H, O and other impurity elements, the poor coating quality.

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CLC: > Industrial Technology > Chemical Industry > Electrochemical industries > Electroplating industry > A single metal plating > Chrome-plated
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