FUNDAMENTAL STUDY OF CLAY: PREPARATION OF A PURIFIED KAOLINITE SUSPENSION,I*

A method of preparing clean clay suspensions is described. Organic matter is removed by hydrogen peroxide and sodium hydroxide digestion, followed by an electro-dialysis treatment to remove other inorganic salts and to prepare a clay-water suspension. After NaOH is added, viscosity and titration values are given for (a) a regular water-washed Florida clay, (b) the same clay after electrodialysis, and (c) the same clay after a thorough cleaning according to the method described. If the sample contains lignite, a clean clay exhibits rheopexy at certain concentrations of NaOH.     

EFFECT OF COMPOSITION AND THERMAL HISTORY ON DIELECTRIC CONSTANTS OF SODA-BOROSILICATE GLASSES*

The dielectric constants, densities, and refractive indices of two series of soda-boro-silicate glasses were measured at 25° C. on some quenched specimens and on other specimens that were stabilized at different temperatures. The compositions of the two series were Na₂O-4.69 SiO₂-B₂O, (0 to 45%) and Na₂O B₂O₃-SiO₂ (30 to 100%), respectively. The structure of the glasses was found to depend on the ratio of oxygen atoms to the sum of the boron and silicon atoms and also on the concentration of the sodium ions. If the ratio of O to B + Si is greater than 2.0 or if the ratio of oxygen to sodium ions is less than 6.0, some of the oxygens are bonded only to one boron or to one silicon atom. The presence of “single-bonded” oxygen atoms in the glass structure leads to a lower density and a higher dielectric constant and refractive index. The dielectric constant decreases and the density increases continuously as the temperature of heat treatment is lowered. The effect of heat treatment is greater for the glasses which contain the larger number of “single-bonded” oxygen atoms and the higher concentration of sodium ions.     

PHOSPHATES IN CERAMIC WARE: IV,PHOSPHATE GLASSES*

Phosphorus pentoxide, which was used first to improve the color of heavy flint glasses, was later recognized as a valuable constituent of optical glasses, and the excellent ultraviolet transmission and low softening points of phosphate glasses have been found recently. Glasses that have a high content of P₂O₅ have poor chemical resistivity, but this drawback is largely overcome by the addition of alumina. A possible picture of the constitution of phosphate glasses is presented, and the effect of alumina is explained. Some of the properties of the phosphate glasses have been investigated and correlated with their chemical composition and structure.