had a similar trend, but the aver- age and maximum values mainly depended on the phase of starting materials and the thermal pro- cessing’s reactions and transfor- mations, which were not readily predicable. The investment casting shells, where colloidal silica was used


as a binder in most cases and a significant amount of fused silica was utilized as flour and stucco, more often showed increasing thermal conductivity at higher temperatures. Porosity had a significant influence on thermal conductivity. Between the two aluminosilicate


shells (4 and 6), 6 had the higher total porosity (37.65%) and exhib- ited lower thermal conductivity values throughout the measured temperature range. Another good example is the


weak temperature dependence of conductivity in the alumina-based shell (5). Since the photon radia- tion in alumina is not significant until 1,832F (1,000C), this radia- tion compensates phonon scatter- ing in alumina and the porosity effects, and consequently the


Fig. 5. The graphs show the comparison of values determined by the inverse and improved laser flash methods for shells 3 (a), 4 (b); 5 (c) and 6 (d).


42 | MODERN CASTING January 2015


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68