Ceramics

Abstract

HIS report deals eseentially with the developments during T the past year in a number of different types of ceramics, enamel and glass products, whitewares, refractories, and structural claywares. ENAMELED PRODUCTSDuring the past 3 or 4 years titanium enamels have gained general acceptance in the industry due to high opacity and good acid redstance (49). The chief advantage of these enamels is that they may be applied as thinner coatings than the sirconia-or tin oxide-opacified enamels, and hence, are more resistant to ohipping aa well aa being smoother and of greater reflectance.Twenty yeara ago ceramic enamels-on-steel were about 0.030 inch thick. Manufacturera could normally expect an 18% lom of their products in handling due to the chipping of such a heavy application. Ten yeara ago this loas had been reduced to 1% by the development of improved techniques and materials resulting in coatings about 0.016 inch thick. Ence World War 11, coating thickn-have been reduced to 0.010 inch with the advent of titaniwpacified covemoat enamels applied over the conventional cobalt-blue ground coats (8).The recent development of a special enameling steel has made possible the complete elimination of the ground coat, and consequently a further reduction in enamel thickness to 0.0066 inch. This steel is a completely deoxidized--"killed"--steel containing from 0.20 to 0.60% titanium. Although a nickel flash on the base metal is still neceaaary to promote optimum adherence, the complete deoxidation of the metal prior to enameling has eliminated surface defects such as reboiling which can often be traced to the evolution of gas by the metal at temper3tures necessary for maturing the enamel coating (10).In addition to the greater durability of titania-opacified enamels, they serve also to satisfy the demands of the enameling industry to cut costa by producing a superior enamel with a loiver maturing temperature. Thew enamels fire a t 1460" F. compared with the rirconia-opacified enamels which require 1620' F. The new titania enamels have a reflectance of about 85%, which repre-&nts an improvement over the older types for the same thickness of coating. They are also less critical to control from the standpoint of weight of application or firing temperature, and have a greater color stability, acid resistance, scratch resistance, and thermal shock resistance (61).The opacity and color of porcelain enamels are of primary importance to the consumer of these products. While other properties might be of greater functional importance, it is the color and opacity which largely determine his choice. The enamel industry must continually improve the color, color stability, and opacity of its products. Factors affecting these properties have been studied for titania-opacified enamels (61,W). Anatase is the crystalline phase responsible for opacity and it produces better spectrophotometric properties in titania enamels than does rutile. Any factor that inhibits the rate of crystal growth and/or rate of inversion of anatase to rutile will tend...