| The consumption of gold accounts for a large proportion of total gold consumption in the jewelry industry,and gold electroforming process has great advantages in gold jewelry processing technology.The traditional gold electroforming process is a highly stable cyanide system,and this process will cause grant damage to the environment and physical damage to the operator.The application and popularization of cyanide-free electroforming process have certain necessity.At present,the mainstream cyanide-free electrodeposition system is the sulfite-thiosulfate system,which has high cost and is difficult to popularize.Some other cyanide-free gold electrodeposition systems disclosed are mainly laboratory research at this stage.Up to now,the research on gold electrodeposition systems is mainly based on industrial electroplating thin gold layer,and the research on thick gold layer used in jewelry industry is rare.This project has developed a new cyanide-free gold electroforming process,and carried out systematic research.The effects of different kinds of single additives and combination additives on the electrodeposition process were analyzed by electrochemical means.Four kinds of organic additives selected in the paper can increase the cathodic polarization to a certain extent,and the combined additives have the best effective.The use of additives facilitates the obtaining of electrodeposited layers with small grain size from the system.Based on the single-pulse power supply,the effects of the types of additives and process conditions on the surface morphology,microstructure characteristics and composition of the electrodeposited layer(the content of gold and the harmful elements according to the rules of jewelry industry)of the electrodeposited layer were studied systematically.The difference in the type and concentration of the additive will have a great influence on the microstructure,grain size and crystal texture of the electrodeposited layer,and ultimately affect the Vickers hardness value of the electrodeposited layer.On the basis of the base electrolyte,add the combined additives can obtain a gold electrodeposited sample with good glossiness and surface flatness,a grain size of 42.0 nm and a Vickers hardness of 115.8 HV.Under the ideal power supply parameters,the gold content can reach to 99.9%.And the use of additives will not introduce sensitizing elements harmful to the human body as ruled by the jewelry industry.Comparing the grain sizes of samples with different glossiness,it was found that samples with fine grain sizes had higher glossiness.Grain size is the major determinant of the hardness of the electrodeposited layer.On the premise of the grain size is not much different,the better the sample orientation,the higher the hardness value.The higher the microscopic flatness of the electrodeposited layer when there is a better crystal orientation.The cyanide-free gold electrodeposition system uses a complex formed by chloride ions and trivalent gold ions as a gold complex in this study.In this system,the gold plate can be used as the anode as a soluble anode.Based on the previous research,the parameters of the bidirectional pulse power supply were further optimized,and it was found that the pulse period had a great influence on the results of the electrodeposited layer.On the basis of the basic electrolyte,the bidirectional pulse power can be used to obtain gold electrodeposited samples with a grain size between 60 nm and 70 nm,whose Vickers hardness can reached to 117.0 HV,and have a preferred orientation based on the(111)crystal plane.Based on the cyanide-free gold electrodeposition process studied in this paper,the effects of DC power supply,single-pulse power supply and bidirectional pulse power supply on the electrodeposited layer were compared.Under the condition of pulsed power supply,especially under the condition of bidirectional pulse power supply,the glossiness of the sample is better,the Vickers hardness value is obviously increased,and good orientation under the condition of single pulse power supply.By using Bidirectional pulse power,the gold electrodeposition sample with a grain size of 37.97 nm can be get,whose Vickers hardness value can reach up to 122.8HV.The non-cyanide gold electrodeposition process studied in this study has good stability,and can maintain high stability even after continuous electrodeposition for about 18 hours,and obtain a gold electrodeposited layer with good macroscopic characteristics.The stable gold electroforming samples can be obtained in about 18 h by simulating the industrial production process under laboratory conditions,and the samples can meet market requirements after post-treatment.In order to improve production efficiency,the current density range can increased to 1.0A/dm2~1.5A/dm2 based on optimal current density.When the current density is further increased,the uniformity of the sample is degraded by the influence of the concentration polarization.When the current density is increased to 2.5 A/dm2,a large amount of decomposition of the organic additive is caused,co-deposition of C and Au occurs,and the the purity of gold will decrease.The gold electroforming samples obtained from the mainstream cyanide system on the market and the cyanide-free system of this subject were compared.The sample obtained in this subject has smaller grain size,a better crystal orientation,and a smaller microscopic particle size.The Vickers hardness value of the cyanide system on the market is about 70 HV.The Vickers hardness of the gold electroformed sample obtained by the cyanide-free gold electroforming process studied in this paper can reach up to about 105 HV.The study on trivalent gold-related complexes are few,this paper studies a new cyanide-free gold electrodeposition process take trivalent gold complexes as the research object.The gold electroforming in the jewelry industry is different from the industrial electrodeposition process,which is more stringent for gold content and trace elements.The electrodeposition of thick gold requires a long electrodeposition cycle and requires high stability to the system.Based on the new cyanide-free gold electrodeposition process,the ideal thick gold layer was obtained,and the related factors affecting the hardness of the electrodeposited layer were discussed.Finally,the gold electroforming samples are obtained by simulating the production conditions in the laboratory,which can meet the market requirements.The research of this subject has high theoretical research and application value. |
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