Abstract: The annular gap-type ball mill for the continuous pulverization in particular of hard mineral substances comprises a closed grinding container (12) driven rotatingly and accommodating a rotor (13) driven in opposite direction. The outer surface of the rotor defines with the inner face of the grinding container (12) a grinding gap (20) which may contain grinding pellets.

Abstract: The invention relates to an annular gap-type ball mill for continuously pulverizing in particular mineral hard materials comprising an upright grinding container closed by a cover, and housing a rotor whose cone-shaped outer surface limits with the cone-shaped inner surface of the grinding container a grinding gap communicating with a feed aperture and containing grinding pellets, the rotor having a top portion being adapted in its shape to the inner surface of the cover, and including within its range a discharge opening. The annular gap-type ball mill is characterized in that the top portion of the rotor is conical to limit with the cone-shaped cover an annular discharge gap whose lower end of maximum diameter ends in an annular chamber at the open upper end of the grinding gap. The grinding pellets are prevented from sinking down in the grinding gap of which 100% are utilized for the grinding operation so that the residence time required for the pulverization of the mineral hard materials is reduced.

Abstract: A frit of the following approximate analysis in percent by weight______________________________________ Alumina Al.sub.2 O.sub.3 8 to 12 Boron trioxide B.sub.2 O.sub.3 40 to 60 Sodium monoxide Na.sub.2 O 6 to 14 Lead monoxide PbO 0 to 7 Calcium oxide CaO 6 to 11 Barium oxide BaO 7 to 12 Manganese oxide MnO 2 to 6 Cobalt oxide CoO 0 to 2 Silica SiO.sub.2 Under 1 ______________________________________when admixed with other materials, in parts by weight as follows ______________________________________ frit 30 to 60 aluminum powder 5 to 60 silicon powder 0 to 8 chromium trioxide 0 to 10 zirconium silicate 0 to 10 copper oxide 0 to 3 bentonite 0.5 to 3 water 70 to 80 ______________________________________applied to an iron-based part, and then fired at 800.degree. to 950.degree. C. results in a heat-resistant weldable enamel. It is especially suited for automobile engine mufflers.

Abstract: Substantially pure, synthetic crystalline .beta.-wollastonite having a specific BET surface of 1-30 m.sup.2 /g made by first producing calcium silicate hydrates having a molar ratio of SiO.sub.2 :CaO = about 0.7 to about 1.3 by hydrothermal treatment of an aqueous mixture of a source of CaO and SiO.sub.2 and then annealing the calcium silicate hydrates at about 800.degree.C to about 1150.degree.C to convert them to the .beta.-wollastonite. The invention also encompasses the use of the calcium silicate hydrates and the .beta.-wollastonite in the manufacture of ceramic materials and glazings.