Theoretical Analysis of Chroming Electrolytes and Properties of Chrome Coatings

Abstract

According to the dynamic characteristics of the electrochemical system, according to V.F. Molchanov, it is possible to optimize the composition of chroming electrolyte and predict the properties of chromium deposits depending on the mode of deposition and the transition time. The possibility of using the transition time for the formation of the cathode surface colloid-dispersion film to study the chemical composition of the chroming solution is considered. The chemical composition can be optimized by the position of the maxima and minima on the polarization curves. An electrochemical cell can be described as a system by a differential equation, the form of which is determined by its internal structure, which varies with electrolysis conditions. The properties of the system are evaluated by a number of factors: the time of the transition process, forcing, attenuation, and the quality factor. This approach is used to develop a low-concentration chroming electrolyte with organic additives. Analytical dependences of chromium yield on current, micro hardness, roughness and deposition rate on deposition conditions are obtained. Chroming on non-stationary modes allows the most effective influence on the structure and physical-mechanical properties of coatings. When changing electrolysis parameters, it is possible to influence the structure and physical-mechanical properties of coatings, to obtain various functional chromium coatings with specified characteristics (adjustable micro hardness in thickness, porosity, internal stresses, corrosion resistance, wear resistance, roughness) from a single electrolyte. The use of a low-concentration electrolyte together with non-stationary deposition modes makes possible to increase the chromium current yield, covering and dissipative ability of the electrolyte, deposition rate, producibility and environmental friendliness of the process, and to reduce hydrogenation. The electrolyte with crystal violet additives has an increased current output (up to 28 %), an extended range of obtaining wear-resistant coatings up to 240 A / dm2, a high deposition rate of up to 2.5 μm / min, an increased micro hardness by 100-300 kg / mm2, reduced toxicity, a decreased absorbed hydrogen level at 500-700 cm3 per 100 grams of chrome coating and internal stresses at 600-950 kg / mm2.