激光清洗广泛用于去除风化石灰岩纪念碑上的黑色结壳。清洁效率通常使用常规分析技术进行测试,这不允许在处理之前和之后分析相同的样品。在本文中,首次使用微型计算机断层扫描(μ-CT)和微型X射线荧光光谱(μ-XRF)技术来评估从石灰岩纪念碑中收集的两种不同结壳的激光清洁效率。在处理前后对两种岩型的相同部分进行非破坏性分析。μ-XRF证实了黑皮中存在石膏,激光清洗两个样品后,S和其他典型元素均有明显下降。μ-CT清楚地显示了清洁前后石灰石的不同结构以及激光去除的地壳部分。这两种技术的结合可以评估,即使这两个样品的化学成分相似,它们对激光清洗的反应因其不同的织物/结构而不同。事实上,在一个样品中,硫酸钙在去除黑皮后仍然部分保留,而在其他样品中,硫酸盐层由于其更紧凑的结构而几乎完全烧蚀。在这两种情况下,显示激光清洁操作不会对原始石材造成任何结构修改或机械损坏。总之,使用这些新技术似乎非常有希望的研究激光烧蚀对岩石样品的影响,以便为其清洁设定最佳工作条件。
Laser cleaning is widely used to remove black crusts from weathered limestone monuments. The cleaning efficiency is commonly tested using conventional analytical techniques, which do not allow to analyze the same sample before and after the treatment. In this paper, micro computed tomography (μ-CT) and micro X-ray fluorescence spectroscopy (μ-XRF) techniques were used for the first time to evaluate the laser cleaning efficiency on two different encrusted quoins collected from a limestone monument. Analyses were carried out non-destructively on the same portion of the two lithotypes before and after the treatment. μ-XRF confirmed the presence of gypsum in the black crust, and showed a marked decrease of S and other typical elements after laser cleaning of both samples. μ-CT clearly showed the different structure of limestone before and after cleaning and the crust portion removed by the laser. The combination of the two techniques allowed to assess that, even if the two samples had a similar chemical composition, their response to laser cleaning was different on dependence of their different fabric/structure. In fact, in one sample calcium sulphate was still partially retained also after the black crust removal, whereas in the other sample the sulphate layer was almost completely ablated due to its more compact structure. In both cases, laser cleaning operation was shown not to cause any structural modification or mechanical damage of the original stone material. In conclusion, the use of these novel techniques appears very promising for studying the effects of laser ablation on rock samples in order to set the best working conditions for their cleaning.