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

doi:10.13745/j.esf.yx.2020.5.51

Abstract

Abstract:

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.

Key words: turquoise, gas adsorption, pore characteristics, electrochemical treatment, X-ray micro-CT

CLC Number:

LU Taijin, DAI Hui, TIAN Gengfan, LI Ke, ZHANG Jian, CHEN Hua, KE Jie. Quantitative analysis of pore characteristics of natural and electrochemically treated turquoises based on gas adsorption method and X-ray micro-CT 3D imaging technique[J]. Earth Science Frontiers, 2020, 27(5): 247-253.

Figures/Tables 11

Fig.1 Natural (a) and electrochemically treated (b) turquoises

Table 1 Pore properties comparison of natural turquoise and electrochemically treated turquoise

样品	孔容/ (cm³·g^-1)	平均孔径/ nm	80 nm以下总孔隙度/%	比表面积/ (m²·g^-1)
天然绿松石	0.03	10	0.969	10.70
电化学处理绿松石	0.01	7	0.978	5.45

Fig.2 Gas adsorption-desorption curve of natural turquoise

Fig.3 Gas adsorption-desorption curve of electrochemically treated turquoise

Fig.4 Natural turquoise pore size distribution characteristic curve

Fig.5 Pore size distribution characteristic curve of electrochemically treated turquoise

Table 2 Pore characteristics comparison of natural turquoise and electrochemically treated turquoise by X-ray Micro-CT observation

样品	样品体积/ mm³	孔隙体积/ mm³	孔隙度/ %	孔隙特征
天然绿松石	787.22	15.41	1.9	含有表面贯穿至内部孔洞
电化学处理绿松石	812.53	13.00	1.6	孔隙被不完全充填

Fig.6 Micro-CT image of a natural turquoise specimen

Fig.7 Micro-CT image of an electrochemically treated turquoise specimen

Fig.8 Ripple structure in natural samples

Fig.9 Ripple structure is not obvious in electrochemically treated samples

References 24

[1]	张蓓莉. 系统宝石学[M]. 2版. 北京: 地质出版社, 2006: 390.
[2]	王濮, 潘兆橹, 翁玲宝, 等. 系统矿物学(下册)[M]. 北京: 地质出版社, 1987: 147-148.
[3]	李延祥, 先怡衡. 美国古代绿松石示踪研究[J]. 文物保护与考古科学, 2015(2):104-111.
[4]	薛鸿庆, 陈沛然, 李清华. 含铁绿松石的电子顺磁共振和电子探针研究[J]. 硅酸盐学报, 1985, 13(2):234-238.
[5]	陈全莉, 袁心强, 陈敬中, 等. 磷酸铝结合剂改性绿松石的结构特征[J]. 地球科学: 中国地质大学学报, 2010, 35(6):1023-1028.
[6]	KWON K R, BANG S Y, PARK J W, et al. Structural characteristics of Zachery treated turquoise[J]. Journal of the Korean Crystal Grousth & Grystal Technology, 2009, 19(2):95-101.
[7]	陈全莉, 亓利剑, 张琰. 绿松石及其处理品与仿制品的红外吸收光谱表征[J]. 宝石和宝石学杂志, 2006, 8(1):9-12.
[8]	YANG X Y, ZHENG Y F, YANG X M, et al. Mineralogical and geochemical studies on the different types of turquoise from Maanshan area, East China[J]. Neues Jahrbuchfür Mineralogie-Monatshefte, 2003(3):97-112.
[9]	HAN Y F, YE X H, HONG Z, et al. New oxygen-deficient cationic-ordered perovskites containing turquoise-coloring Mn⁵+O₄ tetrahedral layers[J]. Journal of Solid State Chemist, 2017, 247:20-23.
[10]	周彦, 亓利剑, 戴慧, 等. 安徽殿庵山绿松石的宝石学特征研究[J]. 宝石和宝石学杂志, 2013, 15(4):37-45.
[11]	张胜男. 湖北竹山天然绿松石与优化处理绿松石的对比研究[D]. 北京: 中国地质大学(北京), 2012.
[12]	陈全莉, 亓利剑, 袁心强, 等. 具磷灰石假象绿松石的热性能[J]. 地球科学: 中国地质大学学报, 2008(3):416-422.
[13]	陈全莉, 亓利剑. 马鞍山绿松石中水的振动光谱表征及其意义[J]. 矿物岩石, 2007(1):32-37.
[14]	陈全莉, 袁心强, 陈敬中, 等. 拉曼光谱在优化处理绿松石中的应用研究[J]. 光谱学与光谱分析, 2010, 30(7):1789-1792.
[15]	EMMANUEL F. The identification of Zachery-treated turquoise[J]. Gems & Gemology, 1999, 35(1):4-16.
[16]	陈全莉, 艾苏洁, 王谦翔, 等. 一类绿松石仿制品的宝石学特征研究[J]. 光谱学与光谱分析, 2016, 36(8):2629-2633.
[17]	OSUGI M E, CARNEIRO P A, ZANONI M V B. Determination of the phthalocyanine textile dye, reactive turquoise blue, by electrochemical techniques[J]. Journal of the Brazilian Chemical Society, 2003, 14(4):660-665.
[18]	陈全莉, 袁心强. 利用磷酸二氢铝结合剂再造绿松石的矿物学研究[J]. 宝石和宝石学杂志, 2010, 12(2):1-6.
[19]	陈全莉. 绿松石的再生利用工艺和机理研究[D]. 武汉: 中国地质大学(武汉), 2009.
[20]	INA R, COLETTE V, BERNARD C, et al. The origin of turquoise color in odontolite[J]. American Mineralogist, 2015, 86(11/12):1519-1524. DOI URL
[21]	李建军, 杨晓丹, 李桂华, 等. 未处理绿松石与扎克瑞(Zachery)绿松石孔隙度差异的某些表现[C]. 北京: 自然资源部珠宝玉石首饰管理中心, 2015: 259-266.
[22]	压泵法和气体吸附法测定固体材料孔径分布和孔隙度: GB/T 21650GB/T 21650.3—2011[S]. 北京: 中国标准出版社, 2011.
[23]	杨峰, 宁正福, 孔海涛, 等. 高压压泵法和氮气吸附法分析页岩孔隙结构[J]. 天然气地球科学, 2013(3):450-455.
[24]	林修煅. Micro-CT成像系统及其应用研究[D]. 西安: 西安电子科技大学, 2012.