| 摘要 |
<p>Moulded silicate articles are produced from pulverulent lamellar structure silicic acids of formula H2SiyO2y+1 (y = 1.7-24) or their salts in which H+ is (partially) replaced by one or more of Li+, Na+, K+, NH4+, Ca2+, Cu2+, Co2+, Ni2+ and Mg2+ by. - (a) mixing the powder with water or organic solvent, extruding and/or pelletising to cylindrical or tubular mouldings, drying and then heat treating to convert most of the starting material into cristobalite and/or tridymite; or (b) pressing the powder in a mould under pressure and, during or after pressing, heat treating to convert most of the starting material into cristobalite and/or tridymite. Also claimed are (i) a moulded article consisting mainly of cristobalite and having a Shore hardness of at least 70 and a free or combined SiO2 content of at least 99 wt.% (measured after firing at 1000 deg.C); (ii) a moulded article consisting mainly of tridymite and having a Shore hardness of at least 70 and a free or combined SiO2 content of at least 94 wt.% (measured after firing at 1000 deg.C); (iii) a moulded article consisting of a mixt. of tridymite and cristobalite and having a Shore hardness of over 70 and a free or combined SiO2 content of at least 97 wt.%; (iv) a granulate consisting mainly of cristobalite and having a hardness of at least 20 bar and a free or combined SiO2 content of at least 99 wt.% (measured after firing at 1000 deg.C); and (v) a granulate consisting mainly of tridymite and having a pfizer hardness of at least 20 bar and a free or combined SiO2 content of at least 94 wt.% (measured after firing at 1000 deg.C).</p> |
