表面接触角的测量及表面张力在宝玉石鉴定中的应用

表面张力是固体表面重要的物理化学参数之一,其大小与温度和界面两相物质的性质有关。基于Young方程的推导,使用接触角测量法计算固体表面张力已被广泛应用于表面科学和工程领域。宝玉石材料大多具有光洁的表面,在接触角测量的准确性方面较其他表面不均一的固体材料具有明显的技术优势。本文运用现代仪器(FTA200动态接触角测量仪)测量了15个天然和合成宝玉石品种(钻石、合成碳硅石、合成立方氧化锆、碧玺、托帕石、翡翠、琥珀等),以及经覆膜和充填2种处理方法的宝玉石样品(镀膜钻石、覆膜托帕石、覆膜翡翠、覆膜琥珀、充填碧玺)的表面接触角,并运用公式计算其表面张力。测试数据表明,不同品种宝玉石的接触角数值存在差异,如钻石的接触角值为56.68°,其仿制品立方氧化锆的接触角值为37.79°;覆膜处理与未经覆膜处理的天然宝玉石的接触角数值差异明显,如琥珀的接触角值为92.49°,覆膜琥珀的接触角值为66.49°;充填处理宝玉石接触角的测试由于控制液滴的大小受条件限制操作难度较大,测试结果不能准确表达为裂隙中充填物的接触角数值,故充填处理的宝石不宜采用此方法进行区分。研究表明,对于部分宝玉石品种和覆膜处理宝玉石,其表面接触角及表面张力数值差异显著,可以作为宝玉石品种的辅助鉴定依据;尤其是运用接触角的差异对于宝玉石鉴定具有较好的判别性,能够对不同品种的天然宝玉石与表面覆膜的宝玉石样品进行有效区分。与常规宝石检测方法(如红外光谱、折射率测量方法)对比,接触角测量方法具有测量准确、操作简便,不破坏样品的特点,符合宝玉石无损鉴定的基本原则,且能够安全快速地测量高折射率宝石,可以解决宝玉石表面覆膜等与表面物性相关的检测疑难问题。

Application of Surface Contact Angle and Surface Tension Measurements in the Identification of Gem Materials

Surface tension is one of the important physical and chemical parameters of the solid surface, which is closely related to temperature and properties of the phases between the boundaries. Based on the Young function, the contact angle measurement method to calculate the solid surface tension has been widely used in surface science and engineering Comparing to other solid materials with inhomogeneous surface, most gemstones have a smooth surface, making it easy to measure the contact angle. In this study, the contact angle of 15 different types of natural and synthetic gemstones including diamond, moissanite, CZ, tourmaline, topaz, jade, amber. And some coated gemstones and fissure filled gemstones have been measured and compared using a dynamic contact angle testing device (FTA200). It was found that the differences in the contact angle for different types of natural and synthetic gemstones are suitable to be used in gemstone identification. For example, contact angle value of diamond and CZ is 56.68° and 37.79°, respectively. Furthermore, the contact angle values between the gemstone and gems with coating process have significant differences, such as the contact angle value of amber is 92.49°, while coated amber is 66.49°. Due to the limitations of the droplet size control restricted by experimental conditions, the contact angle of the fissure-filled gemstones cannot be measured accurately. Herein, this method is not suitable to identify gemstones with artificial fillings. Research shows that contact angle and surface tension values can be used as the basis of supplementary identification of gem species, especially for coated gems. Compared with the conventional gem identification methods (e.g. Infrared Spectrum, the refractive index measurement), contact angle measurement method has higher measuring accuracy, simple operation without destroying the sample, and conforms to the basic principles of gemstone nondestructive identification, especially for high refractive index gem. Contact angle measurement can solve the detection problems for surface-coated gems and related surface property.