Quasi-nondestructive techniques

In the museum context, nondestructive (or quasi-nondestructive) techniques such as X-ray fluorescence (XRF) (Chapter 5) are often preferred for the analysis of inorganic objects, although microanalysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) (Chapter 9) is growing in importance, since the ablation craters are virtually invisible to the naked eye. Raman and infrared spectroscopy (Chapter 4) are now being used for structural information and the identification of corrosion products to complement X-ray diffraction (Section 5.4). 

Fully nondestractive techniques do not touch the membrane surface and may be used during operation. These requirements make it that such techniques are likely limited to in-line transport measurements and optical reflection measurements. The transport measurements are discussed under quasi nondestructive techniques. Spectroscopic ellipsometry provides the thickness and composition for layers with 0p < 50 nm and X < 5 p,m, mutually independent, for the optically smooth supports and membranes. The composition is in that case obtained from interpretation of the refractive index and may include information about 4>p and the amount of adsorbed molecules. The use of this method was demonstrated first in Benes et al. (2001) for the layer thickness and CO2 sorption in supported amorphous silica membranes, as shown in Figure 34.10, left. Spectroscopic ellipsometry is now used routinely in our laboratory for layer thickness of supported (-y-alumina) membranes. This analysis involves determination of the optical constants of uncoated macroporous AKP15 and AKP30 a-Al203 supports, described in Figure 34.11. As the -y-alumina membranes are optically transparent, the dispersion in refractive index n can be described as a Cauchy type material with the form... 

Instrumental (quasi nondestructive) bulk analysis technique... 

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