Basalt fiber is formed from melted, drawn, basalt rock, which is a ubiquitous natural resource covering nearly one-third of the earth’s surface, including much of the ocean floor. Many natural formations that have become popular tourist destinations are also made of basalt rock, including Ireland’s Giant’s Causeway and Devils Postpile National Monument in California.
To turn rock into fiber, basalt furnaces are heated to approximately 1,500 degrees Celsius, 200 degrees hotter than similar fiberglass furnaces, to melt the rock before it is drawn through platinum/rhodium bushings to form basalt fibers. As fibers leave the furnace, they are treated with sizing, which prepares them for use in downstream applications and for binding with resin systems. Sizing for basalt fiber is very similar to fiberglass in chemistry and purpose. Basalt fiber sizing helps protect the fiber and promote adhesion between fiber and polymer.
Basalt fiber is available as continuous material or can also be chopped, milled, twisted, woven, knitted or processed many other ways. It is typically 13 or 17 micrometers (μm) in diameter but can range from 9 to 21 μm. Standard linear densities for fiber range from 68 tex to 4800 tex. Basalt fiber is compatible with any standard resin system.
For use in FRP applications, basalt fiber is processed similarly to fiberglass. Nearly any process that currently uses fiberglass can use basalt as a substitute material with limited changes to key processing conditions.
Basalt fiber, which can easily replace fiberglass as a reinforcement, occupies the middle of the market for both price and performance when compared to fiberglass and carbon fiber. It provides significant mechanical performance advantages over fiberglass while being much less costly than carbon fiber for parts that require added performance. Basalt fiber is stiffer and stronger than fiberglass and has shown, in some circumstances, to provide additional impact performance.
Although basalt is slightly denser than fiberglass, at 2.63 g/cm3, its extra performance advantages mean composites with basalt fiber can be even more lightweight and unlock additional design creativity when compared to fiberglass. Basalt is also significantly higher performing and more insulative in high-temperature conditions. For example, basalt is used in heat shields and mufflers.