Strength improvements in clay-based ceramic reinforced with discontinuous basalt fiber

Clay-based ceramics are used in a wide variety of applications and could benefit from the addition of a reinforcing fiber. Basalt fibers are similar to glass fibers in regards to their relatively high strength and low cost, but they have an additional advantage of improved refractory properties. The clay used was based on a powder mixture of (by weight) 45% Kentucky ball clay, 40% talc, and 15% Georgia kaolin. This powder was mixed with 28% of its own weight of 0.1 M sodium carbonate solution (for formability) and up to 20% (cumulative weight) of discontinuous basalt fibers. The basalt fibers used had a 14 Πam diameter and were either chopped (6 mm long) or milled (~150 Πam long). The samples were hand-formed into 1x1x10 cm bars using plastic molds. Bars were fired to temperatures ranging from 850 to 1250 °C for 2 hours. The addition of the chopped basalt caused warping after firing, and so was not studied further. It was concluded that chopped fibers should only be used if their orientation can be controlled. The addition of milled basalt fibers improved strength at all temperatures (up to about 40% higher strength) except for the 1250 °C firing where the basalt-reinforced samples melted. After firing to 1050 °C, there was a clear distinction between fiber and matrix when viewed with electron microscopy/spectroscopy, but this was not seen for the 1150 °C fired samples. This work demonstrates that milled basalt fibers may be used as a cost-effective reinforcement for clay-based ceramics.