"Use of organosilicon compounds in the reduction of the hydration tendency of magnesia (MgO) powders was studied. The powders used in this study were refractory grade basic raw materials. The hydration tendency of the grains before and after coating was assessed using an autoclave at 123 °C and/or 152 °C for 3 hours. Two families of organosilicon compounds were evaluated. Six organosilane compounds were employed using a solution treatment procedure. The compounds used were methyltrimethoxy silane, ethyltrimethoxysilane, n-butyltrimethoxysilane, octyltriethoxysilane, dodecyltriethoxysilane and phenyltriethoxysilane. Variables associated with the coating process and considered in this investigation included: type of organosilane, concentration of organosilane, solvent/water ratio, pH of the water, and the purity of the powder. The best results were achieved with methyltrimethoxysilane using an alcohol-water solution. After coating, no heat treatment was necessary to develop the protective coating. The hydration tendency of magnesia powders showed a reduction from 35% (neat) to 0.2% (coated) when tested at 152 °C for 3 hours.
The second organosilicon family used in the test was the reactive polysiloxanes, or more specifically, the silanol-terminated polysiloxanes. A low molecular weight compound and a high molecular weight compound were considered. The variables studied included concentration, type of solvent, and heat treatment condition after coating. Similar to the organosilane compounds, very low values for weight gain were obtained at 152 °C for 3 hours.
Preliminary studies with doloma (MgO·CaO) were also conducted with organosilanes and polysiloxanes. Unfortunately doloma did not respond satisfactorily to the treatments with organosilane or with silanol-terminated polysiloxanes, most likely due to the large amount of CaO present in this material (~ 60 wt%).
Magnesium oxide grains with a natural coating of hydromagnesite on the surface showed a fairly large increase in the hydration resistance compared to the same material without this layer, even when tested at 152 °C for 3 hours"--Abstract, page iii.
Moore, Robert E., 1930-2003
Anderson, H. U. (Harlan U.)
Smith, Jeffrey D.
Kohser, Ronald A.
Samaranayake, V. A.
Materials Science and Engineering
Ph. D. in Ceramic Engineering
University of Missouri--Rolla
xx, 210 pages
© 2000 Sergio Luiz Cabral da Silva, All rights reserved.
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da Silva, Sergio Luiz Cabral, "Improvement of the hydration resistance of magnesia and doloma using organosilicon compounds" (2000). Doctoral Dissertations. 1352.
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