Insulating lightweight refractory materials

Abstract

Insulating lightweight refractory materials which are resistant to attack by molten metals, particularly molten aluminum and its alloys and compositions used to form such materials. The materials are settable compositions which comprise a mixture of ceramic fibres, wollastonite powder, milled and/or screened vermiculite (optional), aqueous colloidal silica having a solids content of about 5-25% and preferably 12-15% by weight, and unmilled vermiculite. The weight ratio of the ceramic fibers to the wollastonite powder to the milled and/or screened vermiculite (when present) is 0.8-1.2:1.5-2.5:0.25-0.75, respectively. The amount of the unmilled vermiculite is up to 50% by weight of the total weight of the other solid ingredients. The composition optionally contains carbon fibres, metal fibres or inorganic fibres as reinforcements. The composition can be cast to form shaped products or used as a joining material or as a 'face-off' material to protect an underlying article. When dried, the composition forms a material which is insulating, light-weight and resistant to high temperatures and chemical attack by metals. The material can be made even more resistant to attack by a silicate coating and a fluoride solution surface treatment. The material is useful for forming items used in metal foundries and the like.