Abstract: A method for making mullite whiskers includes the steps of:preparing a mullite-intensive sol by mixing an alumina sol with a silica sol at a molar Al.sub.2 O.sub.3 /SiO.sub.2 ratio of 1.37-1.76,gelating said mullite-intensive sol by adding HF thereto at a molar HF/3Al.sub.2 O.sub.3 .multidot.2SiO.sub.2 ratio of 0.01-0.1,drying the gel at a temperature lower than 120.degree. C.; andcalcining the dried product in an open system at a temperature up to 1000.degree. C. and in a closed system at a temperature from 1200.degree.-1600.degree. C.

Abstract: A method for making composite mullite/cordierite ceramics comprises the steps of:preparing a mullite-intensive sol by mixing alumina and silica sols together at an Al.sub.2 O.sub.3 /SiO.sub.2 molar ratio of 1.37-1.76,preparing a cordierite-intensive sol by mixing alumina, silica and magnesia sols together,gelating a mixture of the mullite- and cordierite-intensive sols obtained at a weight ratio of 80:20-20:80calcinating the thus obtained gel at 1200.degree.-1400.degree. C., andcompacting and sintering the thus calcinated material at 1300.degree.-1450.degree. C.