Study On Process And Mechanism Of Melting Of Copper-based Master Alloy And Preparation Of Pure Copper Standard Sample

At present,there are few reports about the standard sample of pure copper at home and abroad.The pure copper standard sample,whether covering the element or content range,can not fully meet the chemical composition analysis of high purity cathode copper and standard cathode copper.This thesis focuses on the technology difficulties of preparation of copper standard samples at home and abroad,the low melting and high melting copper based master alloy and Cu-P alloy were prepared and aging treated,and the melting and aging mechanisms were explained.A standard sample of pure copper covering 18 kinds of impurity was then prepared based on the"six steps" method and the related performance testing were performed.The results have the vital significance to the development of China's nonferrous metal standard sample.The preparation experiments of low melting copper based master alloy show that with the increase of melting temperature,melting time,stirring rate and stirring time,the standard deviation value of Sb,Bi,Te,Se,Fe,Co,Cr,Si,Ag,Cd decreased firstly and then tended to be stable.With the melting temperature increases,the standard deviation of S elements decreased first and then increased;the standard deviation of Se and S elements was drastically reduced in the first 5 min,and then increased with time and tended to be stable;with the stirring rate increases,standard deviation of elements Cr,Cd first decreased and then increased.With the increase of melting temperature,melting time,stirring rate and stirring time,the standard deviation of Pb decreased first and then tended to be stable.Sb,Te,Se is different from Cu on the microscopic lattice structure,electronegativity,atomic radius,which leads to very low melting in Cu base.On the macro level,when the content of impurity elements is 1.0%,the melting region is narrow region near the melting point of copper at 1083?,resulting in the low solubility of copper alloys.Fe,Cr,Si and other elements,the melting region is slightly larger than that of the very low melting elements due to the differences in microstructure.Pb is different from above different elements,the crystal structure is different at different temperatures and the density difference with Cu is larger,the segregation phenomenon occurs at high temperature,so the addition of calcium carbonate is necessary because the melting point of Pb-Ca is similar to copper atoms,but the excessive amount of calcium carbonate will lead to the increase of Pb the loss.The preparation experiments of high melting copper based master alloy show that with the increase of melting temperature,melting time,mixing rate and mixting time,the standard deviation of elements Zn,Sn,Ni and Mn decreased first and then tended to be stable.With the increase of melting temperature,stirring rate and stirring time,the standard deviation of As decreased sharply and then increased gradually.The atomic radius of Zn and Sn is similar to Cu,and therefore the melting degreed is high.At the same time,the Cu-Zn alloy exists order transformation of a melting phase,the melting region of Cu-Sn alloys at 1083? is large,which is also the cause of high melting degree.With the increase of temperature and melting time,the standard deviation of impurity elements gradually decreased and finally reached a low value.However for non metal of As,too long melting time and high temperature will lead to loss of As.Ni has a same face centered cubic structure with copper,the electronegativity difference is small,and therefore it can melt fully in Cu base at high temperature.In view of the shortcomings of the traditional "charcoal covering method" in preparation of Cu-P alloy,the "multi layer covering method" was used in this work.With the increases of melting temperature,melting time,stirring rate and stirring time,the standard deviation of P elements decreased first and then increased,the suitable melting conditions are melting temperature 1300?,time 5 min,stirring speed 150 rpm,time 5 min.Under these conditions,the standard deviation of P reached the minimum value of 0.0021%,which is lower than the value of 0.0046%of the traditional method.The melting region of Cu-P is very wide at 1083?,but the melting performance is poor because of the characteristics of P of easy to burn and volatile.In this experiment,the charcoal was used to isolate from the air,when the reaction reached a certain temperature,the borax dehydration decomposed into four sodium borate with sticky glass form to isolate air,which preventing the oxidation of volatile phosphorus.As the experiment proceeds,the mixture of dry sand,borax and coke powder will sinter together and the wet sand will sinter into blocks,which furthermore prevents phosphorus volatilization.The aging experiments of Cu based master alloy show that with the aging time and aging temperature increasing,the tensile strength of Cu-Sb,Cu-Fe,Cu-Si,Cu-Cr and Cu-Zn alloy first increased,then decreased gradually to be smooth tendcy.With the aging temperature and aging time increasing,the tensile strength of Cu-Pb and Cu-P master alloy increased first and then decreased.The XRD results show that the alloy phases and copper phases occured after the aging treatment.The results of metallographic examination show that a melting alloy phase occurred,the defect of porosity and shrinkage was not observed and the alloy matrix is even and compact.After the solid solution(melting)treatment of alloy elements,the unstable supersaturated solid solution formed.After the aging treatment,the solid solution decomposed to the second phase at room temperature or high temperature.The precipitates in the form of mobile.dispersion can effectively prevent the dislocations and grain boundaries,so as to improve the performance of the alloy.The lattice defects produced by solid solution strengthening provided favorable conditions for precipitates nucleation and growth in early aging period,which produced the the peak hardness of the alloy in a very short period of time;after the particle gradually grew up and began to gather,leading to the results that the mechanical properties of the alloy increased firstly and then decreased with the increase of aging time.The development process of pure copper standard sample produced by "six step melting method" conforms to the requirements of standard sample technical specification for nonferrous metal product analysis(YS/T409).This method fully uses the difference in density,melting point and boiling point between alloy elements and abandons the traditional alloy preparation in which the elements easy to release is added in the end and difficult to smelt is added in the first.There are 18 kinds of impurity elements in the standard sample prepared,each element is divided into five standard values,and the content of the element rises in a gradient.The standard range of all the elements is 0.00002%? 0.0082%,the standard deviation ranges from 0.00001%to 0.0003%,the uncertainty range is 0.00001%to 0.0003%,the correlation coefficient of all elements in the standard curve are greater than 0.99,which show that the standard sample results of the standard samples are accurate,and the composition distribution is uniform.It can be used as a physical standard for calibration,analysis and quality measurement of pure copper.At present,it has been applied to more than 30 enterprises at home and abroad.