Aluminosilicate fibers (commonly called refractory ceramic fibers (RCFs) in the United States) are amorphous fibers belonging to a class of materials termed synthetic vitreous fibers (SVFs), also termed man-made mineral fibers or manmade vitreous fibers. This class of materials also includes glass wool, rock (stone) wool, slag wool, mineral wool, and specialpurpose glass fibers. Fibers can be classified in various ways, such as natural versus synthetic, organic versus inorganic, and crystalline versus amorphous. Several fiber taxonomies have been proposed.

Production

ASWs are SVFs produced by melting (at ～1925°C) alumina, silica, and other inorganic oxides, and then blowing or spinning these melts into fibers. These fibers can also be produced by melting blends of calcined kaolin, alumina, and silica. The bulk fibers produced by this process can be used directly for some applications, but are more commonly converted into other physical forms, including blanket, modules (folded blanket capable of being installed rapidly in industrial furnaces), paper, felt, board, vacuum formed parts, textiles, and putties or pastes. Conversion to various physical forms takes place at locations where aluminosilicate fibers are produced, facilities operated by converters (producers of intermediate goods) or end users. Primary manufacturing facilities for aluminosilicate fibers are located in North and South America, Europe, and Asia. Conversion facilities and end users are distributed throughout the industrialized world.

Use

ASWs have several desirable properties for use as hightemperature insulating materials, including low thermal conductivity, low heat storage (low volumetric heat capacity), thermal shock resistance, lightweight, good corrosion resistance, and ease of installation. Depending upon the fiber composition, the maximum end-use temperature for ASWs can be as high as 1430°C (2600°F). Because of this capability, these fibers are also included in the class of high-temperature insulating wools (HTIWs). Benefits of the use of ASW insulation include reduced energy costs and reduced greenhouse gas emissions. The energy savings can be substantial when compared to conventional high-temperature insulation such as insulating firebrick.

Applications

Applications and markets for ASWs are principally industrial and vary by product form and country including furnace linings and components in the cement, ceramic, chemical, fertilizer, forging, foundry, glass, heat treating, nonferrous metals, petrochemical, power generation (cogeneration), and steel industries. ASWs are used for passive fire protection applications where thin, lightweight materials are needed to prevent flame penetration. ASWs are also used to a minor degree in emission control applications such as heat shield insulation, catalytic converter support mat, and filtration media for air bag inflators. Though sometimes referred to in the literature as a substitute for asbestos, aluminosilicate fibers are not typically used in asbestos applications. Aluminosilicate fibers are priced substantially higher than various types of asbestos and have maximum end-use temperatures substantially greater than those for asbestos (which vary depending upon the product but are typically 850°C).

Safety information

Aluminosilicate fibers are white fibrous solids, soluble to a degree in human lung fluid (see below). The usual physicochemical parameters relevant to fate and transport (e.g., solubility, vapor pressure, octanol–water partition coefficient, and Henry’s law constant) are not applicable or relevant; vapor pressure, octanol–water partition coefficient, and Henry’s law constant are exceedingly low and not measurable. Fibers are capable of being transported in the air and are removed by gravitational settling. The Member State Support Document submitted to the European Chemicals Agency in favor of listing aluminosilicate fibers as a substance of very high concern (SVHC) notes that environmental fate and hazard data were not relevant.

Numerous in vitro and in vivo studies have been conducted on both natural and synthetic fibers to try to understand and measure cytotoxicity, mutagenicity, and genotoxicity. Many of these studies have proven inconclusive, so mechanism(s) of action are still unclear. Other studies have indicated that aluminosilicate fibers are less active biologically than various forms of asbestos.