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25.18 ‑ Dolomite, whether or not calcined or sintered, including dolomite roughly trimmed or merely cut, by sawing or otherwise, into blocks or slabs of a rectangular (including square) shape; dolomite ramming mix.
Dolomite is a natural double carbonate of calcium and magnesium.
The heading covers crude dolomite as well as calcined and sintered dolomite. Dolomite is calcined at a temperature range of 700 °C - 1000 °C to convert it into magnesium and calcium oxides by releasing carbon dioxide. On the other hand, sintered dolomite is obtained by heating dolomite to a temperature range of 1700 °C - 1900 °C when it becomes a refractory material. The heading also includes dolomite which has been roughly trimmed or merely cut, by sawing or otherwise, into blocks or slabs of a rectangular (including square) shape.
This heading further includes dolomite ramming mixes which are used as refractory materials (e.g., for furnace lining). These products are traded in powder or granular form consisting predominantly of crushed sintered dolomite. Depending on the field of application or temperature at which the mix will be used, different non-hydraulic binding agents (e.g., tar, pitch, resins) are used.
However, the heading does not cover crushed dolomite for concrete aggregates, road metalling or railway ballast (heading 25.17).
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