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Thiourea in Electroplating and Chemical Plating

Thiourea is white and lustrous crystal, easily soluble in water, melting point between 176 ~ 178 ℃, in the process of heating can be dissolved in ethanol. Due to the existence of lone pair of electrons on the sulfur and nitrogen atoms in the molecule of thiourea, it can form complexes with a variety of metal ions, but the complexation constant is generally small. It is worth noting that because the sulfur atom in thiourea has a special affinity for precious metals, thiourea is often able to form stable complexes with precious metals, which is widely used in electroplating and chemical plating of precious metals. Moreover, thiourea is a small molecule with good coplanarity, so it is very easy to be firmly adsorbed on the metal surface, thus changing the electronic structure of the metal surface.


The Role of Thiourea in Electroplating and Chemical Plating

 

1, Used As a Coordination Agent

According to the composition of thiourea molecule, the sulfur atom is easy to form stable complexes with metal ions such as Au, Ag and Cu, for example, when thiourea is fused with Ag+, the coordination ion is [Ag(H2NCSNH2)3]+, which has a relatively high stability constant. In other words, in the use of thiourea, the stability can be enhanced by ligandisation with noble metals.
 

(1) Role in Electroplating

In silver electroplating, silver crystals show a gradual growth on the thiourea adsorption layer, that is, there is a close correlation between the size and number of silver crystals and the deposited layer of thiourea.
 

(2) Role in Chemical Plating

According to the characteristics of the use of thiourea and chemical plating, there are differences in different chemical plating. For example, in the chemical plating fusion of Cu and Cu alloy surfaces, adding thiourea to the plating solution will derive certain organisms, which will ultimately achieve the purpose of degrading the plating solution. Throughout the process, the concentration of thiourea must be controlled in the range of 0.3-2.0 mol/L to enhance the effectiveness of the coordination, to avoid the emergence of unreasonable problems in the use of technology; the use of thiourea in chemical plating, in the plating of Sn-Pb alloys on the Cu plating, the formation of stable coordination compounds can be effective in improving the equilibrium of the Cu and Sn, and to give full play to the advantages of the use of thiourea and chemical plating to improve the overall effect of the use of technology. The overall effect of the technology is improved.
 

2, Used As Chemical Stabiliser

Thiourea as a stabiliser in chemical plating, in the reaction with some metal ions, will play with the stability of the compound, change the concentration of thiourea in time to achieve the purpose of easing the plating rate. It is found that thiourea can stabilise the fusion of chemically plated copper and ensure the compactness and corrosion resistance of the plated layer. Thiourea is used in chemical plating solution, the stability of the use of the more obvious, such as in the printed circuit process, through the incorporation of two paperless, can enhance the joint ability of ions, always maintain the ionic electrical activity, so as to achieve the purpose of stabilising the solution.
 

3, Used As Electroplating Additives

According to the molecular structure of thiourea, in which the sulfur atom has a more obvious coordination effect, can achieve the purpose of blocking the solution metal ion discharge, and the formation of an adsorption layer on the surface to be blocked, but also can improve the role of cathodic plan, to achieve the purpose of the refinement of the plating layer, and to achieve the purpose of the process of production of flat and smooth regulation of the product. In the experimental process, the plating solution in thiourea will generate sol MeS in case of hydrolysis, and through selective adsorption, it can play the effect of active centre in the electrode and improve the flatness and brightness of the plating layer. Firstly, thiourea is used in the field of electroplating, through the use with electroplated zinc, thiourea as copper plating additives can improve the adsorption capacity of the plating layer, to meet the technical needs of the industrial industry. In the experimental study, adding a small amount of thiourea to the copper plating solution can enhance the flatness of the zinc plating layer, and it can also improve the corrosion resistance of the material to meet the current industrial industry's demand for the production of materials. It can also improve the appearance characteristics of the copper plating layer and optimise the use of thiourea in the electroplating process.
 

4、Used in Other Processes

In the process of industrial operation and sustainable development of the background, the industrial industry in improving product quality at the same time, in order to better improve the appearance of the process, need to combine the structural composition of thiourea, will be used in electroplating and chemical plating in the field, in order to enhance the overall effect of the process of production. In the use of thiourea, it can not only be used as a grain refiner in electroplating and chemical plating, but also has the role of accelerator.

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