| In order to save gold,increase the microhardness,corrosion resistance of gold coating and decrease the toxicity of bath,the process of plating 22K gold is studied.The bath of 22K gold is completely cyanide free,and use sulfite as complexant.Use the orthogonal test to establish the optimal process.The gold component,gloss,thickness and morphology,microhardness of the coating are studied systematically by means of SEM,gloss tester,microscope and microhardness tester.The hall cell method and inner-pole method is used to test the throwing power and coveting power of the bath.The cyanide free process is studied,which uses Na3Au(SO3)2 as main salt,Cu as alloying metal,Na2SO3,tartrate Kalium-Natrium and citrate Potassium as complexant. Effects of concentration of CuCl2,cathode current density and operating temperature on the gold composition and coating appearance are also investigated.The results show that the optimal technological formulation of plating 22K gold is determined to be composed of 8g/L Na3Au(SO3)2 as metallic gold,3g/L CuCl2,100g/L Na2SO3,30 g/L tartrate Kalium-Natrium,50g/L citrate Potassium,and 30～40g/L K2HPO4,while the optimal operational conditions are suggested as operating temperature 50℃,cathode current density 0.2A/dm2,pH value 8.5～9.0 and swept cathode.The 22K gold coating obtained at the optimal conditions has properties of golden color,uniformity,nicety, between gradeⅡandⅢbrightness,high microhardness,good adhesion and corrosion resistance,it has 93.47%Au,according with 22K standard.The optimal cyanide free bath has better throwing power and covering power than that of low cyanide bath.The bath has no toxicity and it is easy to operate and treat waste residue.In order to improve the brightness of the coating,effects of brightener on the coating are investigated.The results show that coating brightness have been improved in some extent when brightener is added.22K gold coating obtained from cyanide free bath have brightly golden color and other excellent properties and can be applied to decorative coating.
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