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An attempt was made to sinter relatively pure 3&Oa.2Si02 and 2Alz08 .SiOn compositions to low porosities at 1710' and 1650°C., respectively, using an addition of 1% MgO to each body to facilitate the reaction. The 3 & 0~. 2 S i O~ body sintered to a porosity of 7.1% and was practically all mullite. The 2AlZOs.SiOz body sintered to a porosity of 10.9% and was composed of m a t e and corundum. Strength and elastic modulus measurements were made at several temperatures up to 120O0C., and some observations of the load-bearing properties were made.

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A recent study1 the transverse strength and elastic modulus were determined in the range room temperature to 1200°C.for two relatively pure mullite bodies with AlrOa:Si02 ratios of 3:2 and 2:l. The bodies were fired to 1710" and 1650°C., respectively.Thirteen specimens of the 2:l composition were tested for strength (S) and elastic modulus (E) at room temperature and the results were plotted to yield Fig. 1. A straight line was fitted to the data by the method of least squares, giving the equationThe numerical data are shown in Table I, along with moduli of rupture computed from the empirical equation. Computed values are in reasonable agreement with observed strengths.Figure 1 indicates that the elastic modulus of the 2: 1 composition may not be regarded as a material constant at room temperature. When the elastic modulus is regarded as a variable quantity, the unit strains at fracture are approximately the same for all specimens. The elastic modulus is the ratio of stress to strain or E = u/e. Assuming the elastic modulus to be constant to failure, one can write E = S / e f , where S represents the modulus of rupture and e f the unit strain at failure. Substituting S/rf for E in equation (1) and solving for ef yields (2) (6.987 X l O -' ) S S -6588 €f = I I I 1 15.0 17.5 x)-0 22.5 ELASTIC MODULUS(psi. x Fig. 1. Modulus of rupture vs. elastic modulus for