Process for the manufacture of a silica fiber based heat insulating material

A process for the manufacture of a silica fiber based heat insulating material comprising:

• (i) forming an aqueous suspension containing a fibrous ingredient, a binder, a substance containing boron as a sintering adjuvant and a surface-active agent;
• (ii) molding, from said suspension, a green billet with partial removal of water;
• and
• (iii) drying and firing the billet at high temperature, wherein:
• the fibrous ingredient consists of quartz fiber formed by quartz spraying;
• the fiber is pre-dispersed in water until there is formed a homogenous flowing slurry from which is molded a green fibrous block, with simultaneous partial removal of water;
• the green fibrous block is dispersed in water and mixed with an aqueous emulsion containing an organosilicon binder, a boron containing sintering adjuvant and a surface-active agent;
• a green billet is molded from the suspension thus obtained, a portion of the water being removed by suction;
• the green billet is compressed until a desired height is obtained and then it is dried, in the compressed state, at a temperature of up to 300.degree. C.;
• and wherein
• the billet is released from the pressure of compression and is fired at high temperature.