Document 6R65zQywG6Np1KjgqROnqqwq6

198 Journal of The American Ceramic Society--Johnston Vol. 47, No. 4 Chrysotile asbestos can be dispersed essentially to the col loidal state when agitated at high speed in water in the presence of colloidal alumina. Presumably the coating of colloidal alumina, evidenced in Fig. 4, provides a strong positive repulsive charge which promotes separation of ulti mate fibrils. Such dilute (0.5 to 2%) viscous translucent sols can be dried to semitransparent asbestos sheets in which the alumina plays the additional role of binder. Kaolin and graphite, when coated with colloidal alumina, are adsorbed from dilute solution onto surfaces such as glass or cellulose and remain as a thin layer which is not easily rinsed off. An excess of colloidal alumina must be avoided in this case ; only enough must be added to coat the clay or graphite, since if more is present, the glass or cellulose will be covered preferentially with the free colloidal alumina to the exclusion of the larger alumina-coated particles. The foregoing phenomena suggest means for depositing very uniform layers of alumina-coated particles of the order of lp in thickness on a variety of surfaces. Effects on lubricity, electrical conductivity, light transmission, and other phe nomena might be expected, depending on the nature of the deposited material Acknowledgment The writer wishes to acknowledge the cooperation of Vernon Keirstead in preparing the electron micrographs. April 19 i Oxidation-Reduction Equilibria in Iron-Containing Glass PLAINTIFFS EXHIBIT \KW-009,4 7fe by W. D. JOHNSTON Research and Engineering Center, Pittsburgh Corning Corporation, Pittsburgh, Pennsylvania The oxidation-reduction equilibrium between tion state of iron in the melt was then determined by chemical ferrous and ferric iron in Na20 -2Si02 glass melts analysis. was studied by equilibrating melts with various The glass used had the nominal composition Na?0 2SiO; + oxygen partial pressures. Exceedingly long ~2.5 wt% Fe203. Several master melts were prepared from equilibration,times were required to obtain mean reagent-grade Na2C03, Si02, and Fe203 in a platinum crucible. ingful results. The reaction appears to be dif Small quantities of the master melts (2 or 3 g) were placed fusion-controlled and may be expressed as in 5- or 10-cm3 Morganite recrystallized alumina crucibles or 202- + 4Fes + 4Fe2+ + 02. Data are pre sented in' which the valence of iron varies from in some cases, as mentioned later, in platinum crucibles. The crucible was lowered by a platinum or molybdenum wire into predominantly +3 to predominantly +2. the hot zone of a vertical tube furnace under a controlled atmosphere. At the end of the experiment, the crucible was I. Introduction quenched by raising it out of the hot zone. Samples were repeatedly reground and refired for periods of at least 20 hours ery little-quantitative work has been done to elucidate Voxidation-reduction equilibria of variable valence ions in glass melts. The state of knowledge has been re until a constant chemical analysis indicated that equilibrium had been attained. The furnace tube was constructed of mullite. The temperature of the furnace was controlled to viewed by Tress,1 who was forced to relate thermodynamic within 1C as indicated by a Pt-PtlORh thermocouple en equilibria for pure oxide systems to what was presumed to be cased in a mullite sheath suspended inside the furnace tube an oxidation-reduction sequence in glass obtained from the beside the sample. The temperatures used were 1100, observation of glass colors. An attempt at a more quantita 1200, 1270, 1300, and 1450C. tive study has since been made by Baak and Homyak,2 who Atmospheres used included oxygen, air, oxygen-free C02, measured the iron oxidation state in air as a function of tem CO-C02 mixtures, CO in equilibrium with carbon (the cruci perature in glass melts containing small additions of iron ble in this case), and H2 saturated with H0 at 0C. The CO- oxide. In their work, the iron was almost completely tri- C02 mixtures were metered using constant-head-type capillary valent. A more extensive investigation of the iron-oxygen equilibria in low-viscosity, high-iron silicate slags of metal lurgical interest has been made by Turkdogan and Bills.5 In their work, the iron valence was varied from predominantly divalent to predominantly trivalent. A general review of the literature dealing with iron-containing glass has been made by Weyl.4 In no case has a systematic investigation of the iron oxida tion-reduction equilibria been made on a high-viscosity glass melt in which the oxidation state of the iron was varied over a wide range. The purpose of the present work was to deter mine the conditions for the formation of the various valence states of iron and to' permit an oxidation-reduction equation to be written describing this process. II. Experimental Procedure Glass melts containing small quantities of dissolved iron oxide were equilibrated in various atmospheres. The oxida Received July 19, 1963; revised copy received November S, 1963. The writer is research chemist, Research and Engineering Cen ter, Pittsburgh Coming Corporation. 1 H. J. Tress, "Thermodynamic Approach to Redox Equilibria in Glasses," Phys. Chem. Classes, 1 |6) 196-97 (1960); CeramAbstr., 1961, October, p. 238t. 2 T. Baak and E. J. Hornvak, Jr., "Iron-Oxygen Equilibrium in Glass: Effect of Platinum on Fe2+/Fes+ Equilibrium," JAm. Ceram. Soc., 44 [11] 541--44 (1961). 3 E. T. Turkdogan and P. M. Bills, "Thermodynamic Study of Fe0-Fe20j-Si02, Fe0-Fe203r-P20s, and FeO-Fe2Oj-SiOj-P2Os Molten Systems," J. Iron Steel Inst. {London), 186, 329-39 (1957). 4 W. A. Weyl, Coloured Glasses. Dawsons of Pall Mall, London, 1959. 541 pp. ,`Si 7 flowmel mixture 'jl Chen total ir( accord! was det ff sulfate. ' added j. 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