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The introduction of the two-stage method of producing polished glass has resulted in a keen demand for large formed quartz refractories for the molten-glass hatchets because it was found that none of the known refractory types meet the requirements of the new production sector.Tentative industrial-scale tests demonstrated the inadequate spalling resistance of large quartz refractories produced from a monolithic glass block, and of slip-cast refractories. The latter, moreover, were found to emit small bubbles (seeds) into the glass melt. Cast quartz ceramic with a coarse-grain filler possesses good technical properties but cannot be produced in the form of thin-walled refractories because it separates into layers and forms cracks.Tests with specimens produced from quartz glass powder with organosilicon resin F-9 as binder showed that this material is highly spalling-resistant and does not emit bubbles into the glass melt. The present authors therefore carried out experiments with the aim of developing a technology for the manufacture of highly spalling-resistant quartz refractory products of unrestricted dimensions.The starting material was waste from the production of opaque quartz glass purified of admixtures and crystal phase. The binder was resin F-9 [i, p. 29] and polymethylphenyl siloxane lacquers of the following grades: modified (KO-915, KO-916), nonmodified (KO-08), polyaluminoorganosiloxane (KO-816), and polyphenyl siloxane (K0-815).The glass was crushed on a UD~G-4 type electrodischarge crusher, Screened, and purified of iron by a wash in hydrochloric acid and by electromagnetic separation. Part of the material was dry-ground in a ball mill with 0.2-0.3% GKZh-94 added to accelerate grinding. The ground material contained not more than 0.5% grains larger than 0.063 mm.The chemical composition of the pulverized quartz glass was as follows:99.6% SiO2, 0.09% A1203, 0.025% Fe203, 0.08% CaO, 0.06% MgO, 0.025% R20, and 0.11% other admixtures. The grain-size distribution of the molding batch was 10% fraction 1.0-0.5 mm, 55-35% 0.5-0.315 mm, 5-20% 0.315-0,09 mm, and 40-55% finer than 0.063 mm.Preliminary experiments showed that dense specimens (porosity 25-33%, apparent density 1.4-1.5 g/cm ~) cannot be produced by slip casting or plastic molding when using organosilicon substances as binder so that subsequently the test specimens were prepared by pneumatic rsmming and vibromolding (on equipment designed at the All-Union Institute of Refractories [2]).Tests were carried out to determine the optimal amount of organosilicon binder in the molding batch which would give products of high density and strength after firing. It was found that the optimal proportion of lacquers K0-915 or KO-916 in Khe batch for the vibromolding of the specimens is 7-9% and that of lacquers K0-08, K0-815, and K0-816 8-ii%. The variation of the properties of the pneumorammed quartz ceramics with the amount of resin F-9 in the molding batch is shown in Table i. A batch containing up to 13.5% binder can be soured, which will preserve its goo...

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Die optimalen Bedingungen zur Züchtung von CaLn4(SiO4)3O‐Einkristallen (Ln: La, Nd, Sm, Gd, Dy, Ho, Er, Yb, Y) werden ermittelt.