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Dicalcium silicate: An investigation into the dusting phenomenon and its control.

Deverill, Robert John. (1979) Dicalcium silicate: An investigation into the dusting phenomenon and its control. Doctoral thesis, University of Surrey (United Kingdom)..

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The detailed studies have shown that dicalcium silicate is a rather remarkable compound with one very interesting phase transformation. In the pure compound, on cooling heated material the s phase transforms at about 400°C to the gamma phase; this change involves a lattice expansion so great that it cannot be accommodated by the new phase which completely disintegrates to a fine powder. This transformation commonly known as "dusting" is however very easily inhibited and the aim of the work has been to understand a little better what affects this transition and how the phenomenon of disintegration may be controlled so that it may be used to advantage. One such example with which the project was linked involves the use of dicalcium silicate as a core material in the vacuum investment casting of nickel base alloys, where a stabilized core of the sintered material, after fulfilling its role at the casting temperature might self-disintegrate on cooling thereby eliminating the need to dissolve it from the casting. The work has shown that such an idea is quite feasible but that further development is necessary. The sensitive beta+gamma transformation is markedly influenced by the heat treatment given to powder compacts, and the degree of impurities within the sample. These facts led to the use of very pure powders which always seemed to give gamma at room temperature. Interest then grew around the use of particular chemical additives, homogenized within very pure dicalcium silicate in order to stabilize the beta phase during the sintering cycle, but which could be rendered ineffective on a second heat treatment (usually in vacuo), thereby allowing dusting to take place. Chromium trioxide is the most promising of the additives studied. The all-important question of whether cores of dicalcium silicate will disintegrate in a real casting situation when the core is under constraint, has not been finally answered but the work would suggest the use of porous cores to allow for the necessary volume expansion.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors :
Deverill, Robert John.
Date : 1979
Contributors :
Additional Information : Thesis (M.Phil.)--University of Surrey (United Kingdom), 1979.
Depositing User : EPrints Services
Date Deposited : 22 Jun 2018 13:00
Last Modified : 06 Nov 2018 16:52

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