Influence of grinding methods on infrared spectra of quartz powders

Studies of state analysis with instrumental method. IV

Abstract

In the analysis of inorganic powders by means of infrared spectroscopy, it is known that the shape and the intensity of spectrum change due to the particle size of powdered sample. Lejeune (Ref. 9), Duyckaerts (Fig. 9, 10), and Bonhomme (Ref. 11) investigated in detail the relationship between the particle size and spectrum of CaCO₃, and clarified that the effect was remarkable. Sato et al. recently showed that the absorption bands of α-SiO₂, Si₃N₄ etc. became stronger and sharper and adjacent bands were finely separated when the particle size decreased.
In the present paper, the shapes and intensities of infrared spectra were investigated for each α-SiO₂ ground with or without graphite powder (as asolid lubricant) in an agate mortar or a vibrating mill, in order to grasp quantitatively the relation of spectrum with the effect of particle size by grinding the powdered sample.
The results are as follows;
(1) α-SiO₂ can be ground into minute particles after 30 seconds in a vibrating mill, so the adjacent bands are well separated, the absorbances become constant, and their variations are hardly recognized even if the powder is ground further (Fig. 1, 2, and 5).
(2) On the other hand, in the case of grinding using an agate mortar, the particles of large size remain, so the absorbances tend to increase with the progress of grinding (see Fig. 4).
(3) The reproducibility of absorbance at 782 cm ^-1 band was investigated for 10 samples of each ground powder. As the result, it was found that the reproducibility became smaller with the progress of grinding, and the coefficients of variation became about 2% by the grinding of 2 minutes in a vibrating mill or of 22 hours in an agate mortar (see Table I).
(4) The addition of graphite powder has little effect in grinding by an agate mortar, whereas it has a remarkable effect in the case of a vibrating mill with which powder can easily be ground into particles of uniform size less than 1 μm. It makes clear that graphite adding effect reveals in the intensity and the sharpness of absorption band.