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Permeability of refractories to air
N O T E S FROM T H E U. S. B U R E A U OF MINES.* PERMEABILITY
OF REFRACTORIES
TO
AIR.
By H. W . Douda.
THE porosity of a refractory has generally been used as an indication of the suitability of the raw material for use in making refractories. Permeability to air has now been utilized as a measure of the same property. Fire clay, bauxite, silica, magnesite, zirkite, graphite, and insulating bricks were tested. A known volume of air was passed through a cylindrical section of brick, by displacement with water and the pressure and time were noted at each drop of 5o c.c. Permeability may be expressed as the number of cubic centimetres of air passing through a mass of refractory, one square centimetre in cross-section by one centimetre long, in one second under a pressure of one centimetre of water. Permeability is not directly proportional to porosity but is more dependent on pore structure, and to various degrees on temperature of burning, size of grain and method of manufacture. It has been more fully discussed in a paper recently presented by the author before the American Ceramic Society. THE
PROPERTIES OF SOME CLAY-LIKE THE "BENTONITE TYPE.
MINERALS
OF
By H. G. Schurecht and H. W . Douda.
BENTONITES are probably aggregates of alkaline hydrated silica and kaolinite in varying proportions. They, as is indicated in a more complete discussion of them by the authors, before the American Ceramic Society, are characterized by the following properties: Conchoidal fracture; an index of refraction between ~.48 and 1.54; high water of plasticity and high volume drying shrinkage, varying from those of highly plastic clays to II4.6I and I95.8 per cent., respectively; and a high content of alkali plus alkaline earth, usually more than 5 per cent. When added * Communicated by the Director. 559
OF REFRACTORIES
TO
AIR.
By H. W . Douda.
THE porosity of a refractory has generally been used as an indication of the suitability of the raw material for use in making refractories. Permeability to air has now been utilized as a measure of the same property. Fire clay, bauxite, silica, magnesite, zirkite, graphite, and insulating bricks were tested. A known volume of air was passed through a cylindrical section of brick, by displacement with water and the pressure and time were noted at each drop of 5o c.c. Permeability may be expressed as the number of cubic centimetres of air passing through a mass of refractory, one square centimetre in cross-section by one centimetre long, in one second under a pressure of one centimetre of water. Permeability is not directly proportional to porosity but is more dependent on pore structure, and to various degrees on temperature of burning, size of grain and method of manufacture. It has been more fully discussed in a paper recently presented by the author before the American Ceramic Society. THE
PROPERTIES OF SOME CLAY-LIKE THE "BENTONITE TYPE.
MINERALS
OF
By H. G. Schurecht and H. W . Douda.
BENTONITES are probably aggregates of alkaline hydrated silica and kaolinite in varying proportions. They, as is indicated in a more complete discussion of them by the authors, before the American Ceramic Society, are characterized by the following properties: Conchoidal fracture; an index of refraction between ~.48 and 1.54; high water of plasticity and high volume drying shrinkage, varying from those of highly plastic clays to II4.6I and I95.8 per cent., respectively; and a high content of alkali plus alkaline earth, usually more than 5 per cent. When added * Communicated by the Director. 559