As is well known from literature, the grinding process, which is an unavoidable step in sample preparation, may strongly modify the physical properties of chrysotile through amorphisation. The aim of this work is to establish the proper milling time to apply to the samples before an accurate X-ray powder diffraction quantitative analysis. We have used the RIR (reference intensity ratio) analytical method, based on the measurement of the ratio I/Is between the intensity of the strongest line of an analyte and the intensity of the analytical peak of a standard material, when they are thoroughly mixed 50:50 by weight. We have studied how the RIR value changes as a function of the milling time of the sample and how the accuracy of this quantitative method is affected.

Quantitative determination of phase abundances using X-ray powder diffraction is a technique in wide use today. Of the various methods employed, the Chung, or RIR method, is one of the most common because it can provide reliable results for all sample types. However, improvements can be made to the Chung method of analysis for phases which exhibit large chemical or preferred orientation effects. These effects can often be accommodated by using intensity regions that encompass several reflections, by averaging intensities from nonparallel reflections, or by using RIR values that are allowed to vary based on a predetermined functional relationship. To accommodate the effects of preferred orientation and variable composition in feldspars, RIR values versus the intensity ratio between two peaks of feldspar standards mixed with corundum have been determined. Curves of RIR have been formulated for: (1) feldspar RIR13.0−14.0° versus the intensity ratio (13.0–14.0° 2θ intensity region/27.0–28.75° 2θ intensity region); (2) feldspar RIR23.6° peak versus the intensity ratio (23.6° 2θ peak/27.0–28.75° 2θ intensity region); and (3) clinoptilolite RIR020 versus (020 reflection/22.1–23.0° 2θ intensity region). For example, RIR values for the highly variable 13.0–14.0° 2θ region for feldspar can be improved such that the quantitative results produced has a standard deviation of only 15% instead of 53% using a fixed-average value. From these curves, improved RIR values can be obtained for the quantitative analysis of unknowns. Additionally, intensity ratios can be determined between two peaks of a phase so that given the intensity of one peak, the intensity of the other peak can be readily calculated. This allows for subtraction of the intensity of a peak from one phase overlapping a peak from a second phase which is to be used for quantitative analysis but which cannot be decomposed by profile fitting.

Because of their potential to induce a number of pathological diseases and their widespread industrial usage in the past, the fibrous minerals forming asbestos have been the subject of a number of studies in the past. Although quantification of asbestos minerals by optical and electron microscopy (SEM, TEM) is a routine technique in the case of dispersed airborn fibers, the detection and the quantification of small amount of fibrous minerals like chrysotile in bulk materials such as building materials is exceedingly difficult. A method for the detection and evaluation of asbestos minerals in massive samples is described, based on a combination of Rietveld and RIR (Reference Intensity Ratio) methods. Lower detection limits are about 0.5-1.0 wt % for chrysotile, depending on powder pattern, counting statistics, and matrix absorption. The chrysotile wt % determined on powder diffraction profiles collected on a conventional instrument is precise to about 1.0 wt % absolute (relative error in the range 0-10%). The technique is of straightforward application. If compared with the commonly used microscopic or spectroscopic techniques, it is of much advantage from the point of view of time, and the results are more accurate and statistically significant of the bulk material. A model for the cylindrically disordered structure of fibrous chrysotile is especially developed for the simulation of the X-ray powder patterns, and it is proposed here.