Young's modulus was measured over the temperature range 77°-850°K by an accurate resonance technique. Data are presented for single crystals of aluminum oxide with various orientations of the crystallographic axes and for polycrystalline aluminum oxide, thorium oxide, and magnesium oxide. The results show that the range of validity of a T 4 temperature dependence predicted by theory must be quite small. The temperature dependence is very well described over the whole temperature range by T exp(-T 0 /T), where To is an empirical parameter.

Young's modulus as a function of temperature was determined by a dynamic method for singlecrystal sapphire and ruby and for polycrystalline aluminum oxide, magnesium oxide, thorium oxide, mullite, spinel, stabilized zirconium oxide, silicon carbide, and nickel-bonded titanium carbide. For the single crystals, Young's modulus was found to decrease linearly with increasing temperature from 100OC. to the highest temperature of measurement. For all the polycrystalline materials, except silicon carbide, stabilized zirconium oxide, and spinel, Young's modulus was found to decrease approximately linearly with increasing temperature until some temperature range characteristic of the material was reached in which Young's modulus decreased very rapidly and in a nonlinear manner with increasing temperature. This rapid decrease at high temperature is attributed to grain-boundary slip. Stabilized zirconium oxide and spinel were found to have the same rapid decrease in Young's modulus at high temperature, but they also had a decidedly nonlinear temperature dependence at low temperature.

The linear thermal expansion of single-crystal and polycrystalline aluminum oxide and polycrystalline thorium oxide was measured from 100' to llOO'K with an interferometric technique. For each substance the results are well described by Gruneisen's equation using a Nernst-Lindemann energy function.

(J a nu a ry 21 , 1960) Th e six clastic co nstan ts (a nd six elast ic compli a nces) of co rundum were d etermin ed in t h e ki locycle p er second fr equ ency r a nge by a n acc uratc reso na nce mcth od. Th e res ul ts we re chec ked in t he m ega cycle p er seco nd ra nge wi t h a less acc urate, pulse velocity m et hod . Th e elast ic m oduli for polyc l"yst a llin e a lum ina calculated fr o m t he single crys tal co mpli a nces determ ined by t he reso nance m ethod a rc in good ag reem ent wi t h exp erim ental valu es o btai ned o n hi g h density p olycrystallin e alumin a. Th e va ri ation of Young' s m odulu s a nd of t h e s hear m odu lu wi t h o ri enta Uo n was calcul ated fro m t h e co mplia nces a nd t he res ults ar e show n g ra phi cally. Th e res ults of t he prese nt wo rk do not ag ree w ell wi t h pre vious wo rk on sin gle crystal sa pphire. Th e sp ecifi catio n of o rien tation an d t h e theor y used to calcul a te t he elast ic co ns ta nt a r e give n in de tail to s uppor t t h e co ntention t hat t he r es ults of t he prese nt wo r k a re correct.

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