A Study On Pore Characteristics Difference Between Natural And Electrochemical Treated Turquoises From Maanshan,Anhui Province

Turquoise is a porous material,the main purpose of electrochemical treatment is to reduce the pores of turquoise.After electrochemical treatment,the color and texture of turquoise has been greatly improved.How to distinguish natural turquoise from electrochemically treated turquoise is one of the most difficult technical problems in gemological detection and identification academia.In this paper,the gemological characteristics of turquoise before and after electrochemical treatment were compared by means of gemological routine test,electron probe and XRD.The microstructures of turquoise before and after electrochemical treatment were compared and analyzed by using the method of the automatic surface analyzer,X-ray microscopy(CT)and scanning electron microscopy(SEM).The main findings and achievements of this study are as follows:Turquoise is a kind of aqueous copper-aluminum phosphate with the formula of Cu Al6 [PO4]4(OH)8 · 5H2 O.The surface color of natural turquoise after electrochemical treatment becomes darker,luster enhanced,density and hardness increases,pores and holes significantly reduced.The results of electron probe show that the content and distribution of Cu and Fe in the turquoise are not significantly different from those of natural turquoise.The contents of K,Na and P are higher than those of natural turquoise.XRD data show that the turquoise after electrochemical treatment,the line characteristics and natural turquoise have no significant difference,but the d value which means the interplanar spacing decreased after the treatment,indicating that the crystal arrangement of treated turquoise is more closely.Scanning electron microscopy observation shows that natural turquoise microcrystalline particles have integrite crystal,clear boundary,high degree of crystallization,and electrochemical treated turquoise crystal particles are small,closing,rounding and less crystallinity,microcrystalline aggregates were gel state.The main purpose of electrochemical treatment is to make turquoise pores less.The total porosity characteristics,adsorption-desorption curves and pore size distribution curves can be obtained by by using the surface analyzer.The results show that:(1)The total porosity,total pore volume,average pore size and specific surface area of turquoise after electrochemical treatment are reduced obviously.(2)There are obvious differences in the adsorption-desorption curves of turquoise between natural and treated turquoise.In the high pressure region,the slope of natural turquoise adsorption curve becomes larger,while the slope of adsorption curve of treated turquoise becomes smaller.The pore size distribution of natural turquoise is shown as parabolic,the curve is smooth.After the electrochemical treatment,the pore size of 50 nm or more is drastically reduced and concave.The pore size distribution curve below 50 nm is consistent with natural turquoise,indicating that the electrochemical treatment mainly improves and reduces the pores above 50 nm.In addition,the use of X-ray microscopy CT(Micro-CT)on the turquoise above the micron level of the pores were observed and analyzed:(1)natural turquoise in the surface through the internal through the large holes,after processing holes are not fully filled.(2)The natural turquoise has a "rhyolite" structure,and the pores are distributed along the "rhyolite",while the "rhyolite" structure of the electrochemically treated turquoise is not obvious and the pore distribution is disordered,indicating that the electrochemical treatment Turquoise internal structure has changed.This is the first time that the pore characteristics of natural turquoise and electrochemical treated turquoise have been researched.And treated turquoise in high pressure region,pore characteristics of pore size distribution above 50 nm pore size,pore filling and internal structure characteristics were found to be different from natural turquoise.By detecting the K content of turquoise and combining the difference of pore characteristics,it can effectively determine whether turquoise has been subjected to electrochemical treatment.