The impact of crystallite size of naturally occurring and synthetic wollastonite on its modifying effect in epoxy coatings

Abstract

The efficiency of application and finiteness of raw material supply base of naturally occurring wollastonite leads to the fact that the synthesis of this filler on the base of available renewable raw material, for example, rice husk, is of actual importance. Depending on the ratio of calcium carbonate : silicon oxide (received from rice husk), synthetic wollastonite could have different phase constitution. It consists mainly of pseudowollastonite and wollastonite. Other silicates of lime, for example, larnite, could be also present in its composition. The maximum content of wollastonite was registered in the sample with the ratio CaCO3:SiO2=1.2:1 and it is significantly lower than of naturally occurring mineral Miwoll 10-97. Naturally occurring wollastonite demonstrates the highest modifying effect, from the perspective of wear reduction and harshness enhancement of epoxy coatings. Synthetic wollastonite obtained at the ratio CaCO3:SiO2=1.2:1 is slightly less efficient. Along with that, there could be observed the regularity that the larger the crystallite size of wollastonite, the higher its abrasion resistance and harshness of filled epoxy coatings. When the content of silicon oxide in the composition of synthetic wollastonite grows, the size of its crystals has a tendency to decrease. Given this, the synthesis of wollastonite should be directed towards the enlargement of its crystals size, i.e. it is recommended to increase the content of calcium carbonate in its composition and to lower fusion temperature in order to reduce pseudowollastonite formation.