# A Systematic Study of the Cryogenic Milling of Chrysotile Asbestos
## 2 Materials and Methods
### Characterisation Techniques  
Morphometric investigation of chrysotile fibres following various milling durations were performed, using a JSM-6010 PLUS/LA Scanning Electron Microscopy (SEM) equipped with and Energy Dispersive X-ray (EDX) spectrometer (Oxford INCA-350). EDX is an analytical method useful for identify and quantify (only semi-quantitative results) the elementary compositions of the materials observed with the SEM. EDX analyses were conducted to verify the changes in the elemental composition undergone by the chrysotile fibres after prolonged milling. Specimens for these analyses were prepared as follows: some milligrams of fibres were suspended in 5 mL of ethanol and a drop of the resulting suspension was placed on conductive, double-stick carbon tape attached to an aluminium stub [43]. After complete evaporation of the solvent, the specimen was coated with a thin film of carbon (10 nm thick), using a Carbon Coater-Balzers CED-010. The length of the chrysotile fibres was determined by processing SEM images obtained by secondary electron imaging and appropriate magnifications (500-20,000\(\times\)). A series of representative SEM images were analysed using ImageJ software, which provides accurate measurements of the lengths of both straight and curved fibres [44]. The fibre length distributions were constructed based on a statistically representative number of fibres (Table 2). As mentioned above, Russian chrysotile forms irregular, curvilinear aggregates of fibres and fibril bundles. Therefore, the length of the fibres was measured for each sample, considering both single fibres and fibril bundles. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **CHR** & **CHR5** & **CHR10** & **CHR20** & **CHR30** & **CHR40** \\ \hline Length classes (\(\upmu\)m) & & & & & & \\
0–5 & 7.00\% & 9.43\% & 12.5\% & 34.4\% & 65.3\% & 95.2\% \\
5–10 & 7.50\% & 21.7\% & 41.7\% & 32.8\% & 28.1\% & 1.08\% \\
10–15 & 10.5\% & 11.3\% & 16.7\% & 11.5\% & 2.04\% & 1.61\% \\
15–20 & 13.5\% & 8.49\% & 12.5\% & 6.56\% & 3.57\% & 0.54\% \\ \textgreater{}20 & 61.5\% & 49.1\% & 16.7\% & 14.8\% & 1.02\% & 1.61\% \\ \hline Average (\(\upmu\)m) & 33.9 & 29.80 & 14.32 & 10.7 & 4.89 & 1.91 \\ Maximum (\(\upmu\)m) & 188.1 & 159.8 & 79.9 & 53.6 & 22.1 & 22.1 \\ Minimum (\(\upmu\)m) & 1.36 & 1.45 & 2.02 & 1.29 & 0.43 & 0.25 \\ Standard error & 1.99 & 3.08 & 2.08 & 1.34 & 0.27 & 0.21 \\ N & 200 & 100 & 100 & 100 & 200 & 200 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Fraction of chrysotile fibres comprised in a given interval of fibre length after each milling treatment and main statistical parameters of fibre lengths. Raw chrysotile (CHR); chrysotile after 5 min of milling (CHR5); chrysotile after 10 min of milling (CHR10); chrysotile after 20 min milling (CHR20); chrysotile after 30 min of milling (CHR30); chrysotile after 40 min of milling (CHR40). Number of fibres (N). X-ray powder diffraction (XRPD) data were collected using an X'Pert PRO PANalytical \(\theta\)/\(\theta\) diffractometer (CuK\(\alpha\) radiation, 40 kV and 40 mA), equipped with a stripe detector (X'Celerator). Powders were mounted in aluminium sample holders, using a side-loading technique. A step scan of 0.0167\({}^{\circ}\)2\(\theta\) was used with a time of 1 s/step in the 5\({}^{\circ}\)-40\({}^{\circ}\) 2\(\theta\) range. The incident beam pathway included a 1/4\({}^{\circ}\) divergence slit and 1/4\({}^{\circ}\) anti-scattering slit. The pathway of the diffracted beam included a soller slit (0.04 rad), an antiscatter blade (5 mm) and a Ni filter. The XRPD patterns were analysed using the X-Pert High Score Plus software DATABASE [45]. Fourier Transform Infra-Red (FTIR) spectroscopy analyses of the chrysotile samples were performed in the spectral range 600-4000 cm\({}^{-1}\), using a Bruker Vertex 70 spectrometer (Ettlingen, Germany) equipped with a DTGS detector and a KBr beam splitter.