Strength of Adhesion of Dried Clay Slurries to Window Glass as a Function of Slurry pH

Abstract

HE relative strengths of adhesion of dried clay-HzO slur-T ries to window glass were studied. The clays chosen were kaolinite, Dixie Bond (Ca montmorillonite), and Wyoming bentonite (Na montmorillonite) . Slurries of each clay (0.5% in distilled water) were applied to panels of window glass* and dried in a moving air stream at 50°C.Qualitative tests indicated that kaolinite was the easiest to remove and Wyoming bentonite the most difficult. The strength of adhesion appeared to increase as the particle size of the clay decreased, indicating that relative strength of adhesion depends on physical as well as chemical differences. X-ray diffraction patterns revealed that all the clays were oriented with their basal planes parallel to the glass surface.Because of surface silanol groups,' a glass surface is a weak Bronsted acid in neutral solutions. When the pH of the surrounding medium is increased, glass becomes a better H+ donor (more acid surface), and in an acid medium it tends to become an OH-donor ( a basic surface). Therefore, if the availability of H+ ions at the glass surface is important to the bonding of clays to glass, variation in strength of adhesion with slurry pH may be expected.Very fine particles of Dixie Bond clay were obtained by selective sedimentation. A slurry (0.5% in distilled water) prepared from this material was divided into four portions. The slurry, as prepared, had a pH of 4.7. The other portions were buffered to pH's of 4.0, 8.0, and 9.0. To study the effects of flocculation on strength of adhesion, each portion was subdivided into three fractions, two of which were treated with NaCl in concentrations of 200 and 750 mg per 500 ml of slurry. The latter concentration caused flocculation. Each fraction was applied to a separate plate of the glass and dried in a moving air stream at 50°C.The apparatus for measuring relative strengths of adhesion was a spring-loaded razor blade pressing down on the glass plate to be tested. The plates were mounted on a movable base which could be driven by a weight and pulley system. The mass (mg) necessary to move the plate under the blade, thus stripping off the clay, was recorded as the strength of adhesion. The values listed in Table I are the observed values minus a blank reading obtained with an untreated plate of glass.No consistent relation of strength of adhesion to NaCl concentration was observed. However, the average strengths of adhesion increased linearly with increasing pH, as shown in Fig. 1.

Influence of scrap glass powders and the maturing process in the unfired state on the body properties of a kaolinitic clay after firing

“…10a). 20,21 With increasing firing temperatures above the transformation point of the glasses the glass particles within the kaolinitic, carbonate-free clay A are melted while, due to the high kaolinite content, the surrounding clay matrix undergoes no phase reactions indicating the sintering process up to high temperatures (Fig. 10b).…”