CRYSTALLIZATION OF MERWINITE FROM MELILITE COMPOSITIONS.
BUILDING RESEARCH STATION WATFORD (ENGLAND)
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In the course of an investigation of the systems gehlenite-akermanite and akermanite-gehlenite-merwinite unexpected crystallization phenomena were observed involving crystallization of merwinite from melilite compositions. The melilites are major constituents of the basic alkaline rocks and of blast-furnace slag and the system gehlenite-akermanite is a principal member of the melilite group. The metastable formation of merwinite, which is reported, is discussed in the context of other recent observations on the stability of melilites. The second purpose of this report is to present, in outline, the diagram of the liquidus surface of the partial system akermanite-gehlenite-merwinite which is based on the examination, but high-temperature microscopy and X-ray analysis, of 120 compositions. Dicalcium silicate, a compound relevant to the stability of slag aggregates for concrete, has a large primary crystallization field in this partial system. The boundaries of this field have been delineated providing some new information towards the selection of slag aggregates for concrete. Author