Fibrous insulation and process for making the same

A process for making a light weight fibrous insulation having a density between approximately 10 lbs./ft..sup.3 and 38 lbs./ft..sup.3, said process comprising:

• forming a slurry containing by weight about 2.1% to about 7.5% ceramic fibers, about 18% to about 22% colloidal silica binder which is capable of forming a ceramic when fired, no more than about 5.4% ceramic filler of a granular nature, and about 60% to about 80% water;
• felting the slurry to form a soft felt in which some fibers cross over other fibers to create a network having interstices in which the granules of the filler generally locate and wherein the crossing fibers and the fillers form junction points;
• causing the binder to concentrate at the junction points and to gel at the junction points by introducing into the soft felt enough ammonia gas to elevate the pH of the liquid within the felt to at least about 6.5;
• and subjecting the felt to microwave energy to dry the felt such that the drying is substantially uniform throughout so as to prevent the binder from migrating to the surface of the felt.

An insulative material comprising:

• ceramic fibers disposed in a random network such that some of the fibers cross over other fibers, creating interstices in the network;
• a granular ceramic filler with the granules thereof being in the interstices of the network, whereby the crossing fibers and the fillers form junction points in the network;
• and a binder concentrated at the junction points of the fibrous network and holding the fibers and the granules of the filler in place, the binder being silica;
• the insulative material having a density between approximately 10 lbs./ft..sup.3 and 38 lbs./ft..sup.3 with the fibers constituting between approximately 20% and 80% of the weight of the material, the binder between approximately 10% and 40%, and the granular filler not more than approximately 50%.