基于气体吸附法和X射线Micro-CT三维成像技术定量解析天然和电化学处理绿松石孔隙特征

Quantitative analysis of pore characteristics of natural and electrochemically treated turquoises based on gas adsorption method and X-ray micro-CT 3D imaging technique

绿松石是一种多孔材料,其孔隙特征直接影响其颜色、光泽、硬度、耐久性等性质,进而影响其市场价值,电化学处理的主要目的是降低绿松石孔隙度从而使其耐久、保色。采用全自动比表面仪、X射线显微CT(Micro-CT)等测试分析手段,对电化学处理前后绿松石的孔隙特征进行了对比研究。比表面仪研究发现,电化学处理后的绿松石总孔隙度、总孔体积、平均孔径及比表面积均有一定程度的变化;吸附-脱附曲线高压区域天然绿松石吸附曲线斜率变大,而电化学处理绿松石吸附曲线斜率变小;天然绿松石孔径分布曲线为类抛物线,而电化学处理绿松石孔径分布曲线呈内凹曲线状。Micro-CT研究结果表明:天然绿松石中出现的由表面贯穿至内部的大孔洞,经电化学处理后孔洞被不完全充填;天然绿松石存在"流纹状"结构,孔隙沿"流纹"分布,而电化学处理绿松石的"流纹状"结构消失,孔隙分布杂乱无章。本研究首次从孔隙特征角度入手,发现天然绿松石与电化学处理绿松石在高压区域吸附曲线特征、50nm孔径以上孔隙分布曲线、孔隙充填情况和内部结构等方面存在明显差异。通过检测绿松石的钾(K)含量,并结合孔隙特征差异,可以有效地对绿松石是否经过电化学处理进行检验判定。

Turquoise is a porous material,its pore characteristics directly affect its color,luster,hardness,durability and other properties important for its market value.The main purpose of electrochemical treatment for the enhanced turquoise is to reduce pores and change the porous properties to make it durable and colorful.In this paper,we used a specialized fully automated surface analyzer and X-ray micro-CT(Micro-CT)imaging technique to analyze the pore characteristics of turquoise before and after electrochemical treatment.We found that the pore volume and total porosity,average pore size,and specific surface area of turquoise after electrochemical treatment were all reduced to a certain extend.The slope of the adsorption curve became larger for natural turquoise in the high-pressure region and smaller for turquoise under electrochemical treatment.The pore size distribution curve is parabolic for natural and concave for electrochemically treated turquoises.Micro-CT investigation reveals that some large pores that run through the rock are not completely filled by electrochemical treatment.Natural turquoise has a"ruffled"pore structure along the"ripple",while the"ruffled"structure disappears and pore distribution became disordered in the treated samples.Starting from the perspective of pore characteristics,we found in this study that natural and electrochemically treated turquoises have obvious different pore characteristics,including adsorption and pore distribution curve characteristics,pore filling conditions,and internal features in pore diameters above 50 nm.It is possible to effectively identify natural turquoise from those treated by electrochemical process based on potassium contents and pore characteristics.