In the paper, a research on effects of baking temperature on chromite sand base of moulding sands bonded with sodium silicate is presented. Pure chromite sand and its chromite-based moulding sand prepared with use of sodium silicate were subjected to heating within 100 to 1200 °C. After cooling-down, changes of base grains under thermal action were determined. Chromite moulding sand was prepared with use of 0.5 wt% of domestic made, unmodified sodium silicate (water-glass) grade 145. After baking at elevated temperatures, creation of rough layer was observed on grain surfaces, of both pure chromite sand and that used as base of a moulding sand. Changes of sand grains were evaluated by scanning microscopy and EDS analyses. It was found that changes on grain surfaces are of laminar nature. The observed layer is composed of iron oxide (II) that is one of main structural components of chromite sand. In order to identify changes in internal structure of chromite sand grains, polished sections were prepared of moulding sand hardened with microwaves and baked at elevated temperatures. Microscopic observations revealed changes in grains structure in form of characteristically crystallised acicular particles with limited magnesium content, intersecting at various angles. EDS analysis showed that these particles are composed mostly of chromium oxide (III) and iron oxide (II). The temperature above that the a.m. changes are observed in both chromite-based moulding sand and in pure chromite sand. The observed phenomena were linked with hardness values and mass of this sand.
 Lewandowski, J.L. (1997). Materials for foundry moulds. Publisher Akapit. (in Polish).
 Sakwa, W., Wachelko, T. (1981). Materials for foundry moulds and cores. Publisher Śląsk. (in Polish).
 Janicki, E., Sakwa, W. (1965). Moulding materials – properties and application. Publisher Wydawnictwo Naukowo-Techniczne. (in Polish).
 Małachowska, A., Stachowicz, M. & Granat, K. (2012). Innovative microwave hardening of water-glass containing sandmixes in technical-economic approach. Archives of Foundry Engineering. 12(1), 75-80.
 Stachowicz, M., Granat, K. & Małachowska, A. (2014). Comparison of traditional method and modern microwave method of manufacturing cores of sandmixes with water-glass. Archives of Foundry Engineering. 14(spec.2), 83-88. (in Polish).
 Stachowicz, M., Mażulis, J., Granat, K. & Janus, A. (2014). Influence of molding and core sands matrix on the effectiveness of the microwaves absorption. Metalurgija. 53(3), 317-319.
 Stachowicz, M. & Granat, K. (2014). Possibilities of reclamation microwave-hardened molding sands with water glass. Archives of Metallurgy and Materials. 59(2), 757-760.