Basalt Fibers: Alternative To Glass?
High-temperature performance and superior strength properties may make this late-comer a better choice in some applications.
By Anne Ross, Assistant Editor | August 2006
A hard, dense volcanic rock that can be found in most countries across the globe, basalt is an igneous rock, which means it began in a molten state. For many years, basalt has been used in casting processes to make tiles and slabs for architectural applications. Additionally, cast basalt liners for steel tubing exhibit very high abrasion resistance in industrial applications. In crushed form, basalt also finds use as aggregate in concrete.
Source: Bogen Imaging
Camera tripod specialist Gitzo SA has added a line of tripods and monopods that feature telescoping legs made from basalt fiber composites. The line joins tripod offerings in carbon composites and aluminum. At left is a fully extended basalt monopod; at right, a close up of a basalt tripod.
More recently, continuous fibers extruded from naturally fire-resistant basalt have been investigated as a replacement for asbestos fibers, in almost all of its applications. In the last decade, basalt has emerged as a contender in the fiber reinforcement of composites. Proponents of this late-comer claim their products offer performance similar to S-2 glass fibers at a price point between S-2 glass and E-glass, and may offer manufacturers a less-expensive alternative to carbon fiber for products in which the latter represents over-engineering.
IDEAS AND IDEOLOGIES
Paul Dhé from Paris, France, was the first with the idea to extrude fibers from basalt. He was granted a U.S. patent in 1923. Around 1960, both the U.S. and the former Soviet Union (USSR) began to investigate basalt fiber applications, particularly in military hardware, such as missiles.
In the northwestern U.S., where large basalt formations are concentrated, Prof. R.V. Subramanian of Washington State University (Pullman, Wash.) conducted research that correlated the chemical composition of basalt with the conditions for extrudability and physio-chemical characteristics of the resulting fiber. Owens Corning and several other glass companies conducted independent research programs, which resulted in several U.S. patents. Around 1970, however, U.S. glass companies abandoned basalt fiber research for strategies that favored their core product. The result was a better glass fiber including successful development of S-2 glass fiber by Owens Corning.
During the same period, research in Eastern Europe, which had been carried out in the 1950s by independent groups in Moscow, Prague and other locales, was nationalized by the USSR's Defense Ministry and concentrated in Kyiv, Ukraine, where technology was subsequently developed in closed institutes and factories. After the breakup of the Soviet Union in 1991, the results of Soviet research were declassified and made available for civilian applications.
Today, basalt fiber research, production and most marketing efforts are based in countries once aligned with the Soviet bloc. Companies currently involved in production and marketing include Kamenny Vek (Dubna, Russia), Technobasalt (Kyiv, Ukraine), Hengdian Group Shanghai Russia & Gold Basalt Fibre Co. (Shanghai, China), and OJSC Research Institute Glassplastics and Fiber (Bucha, Ukraine). Basaltex, a division of Masureel Holding (Wevelgem, Belgium), and Sudaglass Fiber Technology Inc. (Houston, Texas) convert basalt fiber into woven and nonwoven reinforcement forms for the European and North American markets, respectively.
LIKE, BUT UNLIKE
Basalt fiber is produced in a continuous process similar in many respects to that used to make glass fibers. Quarried basalt rock is first crushed, then washed and loaded into a bin attached to feeders that move the material into melting baths in gas-heated furnaces. Here, the process is actually simpler than glass fiber processing because the basalt fiber has a less complex composition. Glass is typically 50 percent silica sand in combination with oxides of boron, aluminum and/or several other minerals — materials that must be fed independently into a metering system before entering the furnace. Unlike glass, basalt fibers feature no secondary materials. The process requires only a single feed line to carry crushed basalt rock into the melt furnace. On the other hand, basalt fiber manufacturers have less direct control over the purity and consistency of the raw basalt stone. While basalt and glass are both silicates, molten glass, when cooled, forms a noncrystalline solid. Basalt, however, has a crystalline structure that varies based on the specific conditions during the lava flow at each geographical location. Basalt combines three silicate minerals — plagioclase, pyroxene and olivine. Plagioclase describes a number of triclinic feldspars that consist of sodium and calcium silicates. Pyroxenes are a group of crystalline silicates that contain any two of three metallic oxides, magnesium, iron or calcium. Olivine is a silicate that combines magnesium and iron — (Mg, Fe)2SiO4. This potential for compositional variety means that the mineral levels and chemical makeup of basalt formations can differ significantly from location to location. Moreover, the rate of cooling, when the original flow reached the earth's surface, also influenced the crystal structure. Basaltex R&D director Jean-Marie Nolf notes, therefore, that despite its ready availability from mines and open-air quarries around the world, only a few dozen locations contain basalt that has been analyzed and qualified as suitable for manufacture of continuous thin filaments. Ihor Markuts, sales and marketing director for Technobasalt, maintains that basalt formations in the Ukraine are particularly well suited to fiber processing. Dr. Boris Mislavsky, director of marketing and development for Kamenny Vek, agrees. His company currently gets all of its raw material from western Ukraine. While the company has a backup mine located in Russia, with a chemical composition close to its main source, it prefers to mine material from a single source. "All our materials come from the same quarry," he explains.
