341to 30" crack-front configuration, K is constant over ='I/eT and nearly equal to the strength-of-materials value. The strength-ofmaterials formula (Eq. (2)) is approximately correct for crack lengths >0.55W and ligament lengths >0.65W.
ReferencesI J. A. Kies and A. B. I. Clark; pp. 483-91 in Proceedings of the Second International Conferenceon Fracture, Brighton, April 1969.The melting, eutectic, peritectic, solidus, and liquidus temperatures in the system Zr-0 have been measured directly by a simple optical pyrometric technique requiring only a few hundred milligrams of sample. The saturation solubility of oxygen in a-Zr(s) between 1270" and 1980°C and the lower phase boundary of the ZrO,-, phase between 1900" and 2400°C have been measured by an isopiestic equilibration method. The oxygen solubility limit in a-Zr(s) agrees well with previous low-temperature studies and reaches a maximum solubility of 35*1 at.% 0 at the eutectic temperature, 2065"*5"C. The maximum melting temperature of a-Zr(ss) is 2130'2 10°C and corresponds to a composition of 25k1 at.% 0. Both of these temperatures are approximately 150" higher than previously reported. Liquidus compositions above the eutectic temperature were obtained via mass spectrometry from the kinetic behavior of the liquid solution-ZrO,-,(s) mixture as it approached equilibrium at 2125"*5"C. The lower phase boundary or solidus of the ZrOz-s phase departs appreciably from ideal stoichiometry above 1900°C and smoothly reaches its most reduced composition, 61 at.% (Zr0,.56), near 2300°C. The solidus is retrograde at higher temperatures. The melting temperature of the stoichiometric dioxide is 2710'2 15°C.
A technique has been developed for measurement of the contact angle of liquid metals with solid materials. The liquid metal, when contained in a small cup (inner diameter < 4 mm) forms a concave or convex mirror surface. For the present technique, an optical method was devised to measure the radius of curvature of this mirror surface, from which the contact angle can be determined. The surface of the liquid metal approaches sphericity as the diameter of its container is decreased. The optical system formed in this method is non-paraxial. An analytical formula, valid for a spherical non-paraxial mirror, for calculation of image size was deduced. The technique has been demonstrated using the mercury-graphite (15.9% total porosity) system at room temperature and the contact angle was determined to be 152.5 ± 2 • .
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