Gelatin Molecular Weight And Its Decomposition Rule, In The Copper Electrolyte

It is well-known that to add some additives in the electrolyte of copper can make cathodic crystal more compact and promote the formation of new crystal by increasing the cathodic overpotential.While the amount of the additive gelatine in the electrolyte must be accurate, especially in high current density, the quanlity of cathodic surface will get worse and worse if we can not control the amount of the additive gelatine accurately.There are several reasons for controlling the concentration of the gelatine in copper electrolyte inaccurately:1. gelatin's molecular weight is uncertain;2. the complicated molecular formula of gelatine;3. gelatine can decompose at high temperature and acidity;This text does some theoretic studies about the decomposition law of the gelatine by using SDS—PAGE electrophoresis in the copper electrolyte, under a variety of test conditions such as different viscosity,different current density,different temperature,different acidity and so on.That is to determine the molecular weight and its distribution of the gelatine in the above mentioned test conditions. On the basis of the molecular weight and its distribution of the gelatine,we get the law of gelatine decomposition in different test conditions.The test results show that:1. There are three major factors in the decomposition of gelatine,that is temperature, concentration of sulfuric acid and electrolysis time. And the effect of its viscosity and the current density in the electrolyte of copper is very little, even negligible.2. The decomposition of gelatine is very sensitive temperature. The influence curve equation of gelatine decomposition on temperature is: M (t=2h)= 47875-416T+1.21 T~2-0.001 T~3, r~2= 0.9998 M (t=3h)= 69785-622T+1.85 T~2-0.002 T~3, r~2= 0.9934 M is the maximum molecular weight,T is temperature, r2 is correlation coefficient 3. The decomposition of gelatin is not so sensitive to the concentration of sulfuric acid as to temperature. Especially,at high temperature, concentration of sulfuric acid will propel the temperature to the decomposition of gelatin. Under 333K and 0.5 hour or 1.0 hour, The influence curve equation of gelatine decomposition on concentration of sulfuric acid is: M(t=o.5)= 809-8.4S+0.022S~2, r2=0.9724 M(t=1.0)= 257-2.4S+0.006S~2, r2=0.9943 M is the maximum molecular weight,S is the concentration of sulfuric acid, r2 is correlation coefficient4. In the actual copper electrolyte(45g/L Cu2+,180g/L sulfate and 333K) the molecular weight of the gelatine is below 10kDa after 2 hours, it is almost impossible to determine for it is below 2kDa after 3 hours.