The Surface Treatment of Fibrous Gypsum with Organic Acids and Bases

Abstract

The surface treatments of fibrous gypsum, i. e. needle-like crystal of αC_aSO₄4·1/2 H_2aO with various carboxylic acids and amines were studied. The reactions proceeded most effectively when acids or amines were added to gypsum immediately after the heat treatment (of gypsum) under vacuum (Table 1). The IR spectra (Figs. 3, 4) togather with the thermogravimetric analysis (Fig. 2) showed that the surface products with carboxylic acids and amines decomposed at 300-500°C and at 200-300°C, respectively. Adsorptions of water and hexane on gypsum before and after the treatment with butyric acid or butylamine, indicated that the surface reacted with acid was hydrophilic and organophobic in nature, while the surface reacted with amine was organophilic and hydrophobic (Figs. 5, 6). The configuration of the surface product is discussed on the basis of the IR spectra.