The axial thermal‐expansion coefficients of β‐eucryptite have been measured and correlated with the volume expansion of an aggregate measured dilatometrically. A mechanical analogy to the structure of β‐eucryptite is suggested which may explain the pronounced thermal contraction in the c direction.

High stresses arise in sintered B-eucryptite(Li20.Al2OI-2SiO2) during cooling from the 5ring temperature because of its extreme anisotropy of thermal expansion. These stresses cause extensive fracturing of the crystals, resulting in abnormally low mechanical property values at room temperature. During reheating, many fractures recombine, causing increase in strength and in elastic modulus with increasing temperature. Beta-eucryptite creeps under load at room temperature because of additional fracturing and the propagation of fractures. Equations are presented for calculating intend stresses in sintered singlephase aggregates of anisotropic crystah. lnhwluctionETA-EUCXYPTITE, L i d -Al&.2SiO,, is extremely anisotropic in thermal expansion, with coefficients of thermal expansion in the a and c crystallographic directions of 82 and -176 X lo-' per OC., respectively (Fig. 1).1 When a sintered aggregate of 8-eucryptite cools from the liring temperature, high tensile stresses arise in the a crystallographic direction. When these stresses exceed the strength of the crystals or the crystal interfaces, fractures occur.The influence of these internal fractures on the thermal expansion of 8-eucryptite aggregates has been previously described.' The object of this investigation was to determine what d e c t the fractures have upon mechanical properties. It was found that the mechanical properties are greatly influenced bN.the internal fractures, and are very similar to those of magnesium dititanate which is also highly anisotropic in thermal expansion.; II. Calculation of Internal StressThe magnitude and orientation of stresses in a crystal in a single-phase aggregate of anisotropic crystals depend on the orientation of the surrounding crystals, and an exact analysis of the state of stress would involve consideration of all possible crystal configurations. The problem is greatly simplified if it is assumed that the crystals in an aggregate must conform to the same strain as the bulk material during a temperature change.' When the elastic compliance constants are known, the stresses may be calculated using equations given by L L Z I~.~(~) If the elastic modulus, E, and Poisson's ratio, Y , are assumed to be the same in all crystallographic directions and constant with temperature and if shear stresses are assumed to be negligible, the following equations relate stress and strain for a temperature change TI-TI:1 Q = (a -a) AT = j j [a -~( u e + 0o)l where t . , us, and a . are the principal normal strains, stresses, and thermal-expansion coefiicients, respectively, in the indicated crystallographic directions and a is the thermalexpansion coefficient of the aggregate. The simultaneous solution of equations (1) gives the following equations for the principal normal stresses: When (3) a = '/a (a. + rq + a c ) which is not generally exact because of the internal stresses,' equations (2) become EAT ( a . -a ) l + v Ua = EAT (a -a ) 1 + v a = (4) EAT (ac -a ) l + r uc = In this case (5)i.e., the hydrostatic pressure on each crystal ...

An experiment to determine the nonstructural carbohydrate composition and nodal survival (LT50) of common carpetgrass was conducted between 1993 and 1994 at Baton Rouge, La. Nonstructural carbohydrates in stolons were primarily sucrose [70-130 mg·g-1 dry weight (DW)] and starch (8-33 mg·g-1 DW). Total nonstructural carbohydrate (TNC) composition of stolons ranged between 30 to 165 mg·g-1 DW. Node survival following exposure to 2 °C ranged from 0% in August-sampled grass to 48% in December. The LT50 following acclimation under field conditions was -2 to -4 °C. Environmental factors influenced nonstructural carbohydrate composition, partitioning, and node survival. No relationship between TNC concentration and low-temperature tolerance was found. This research confirms previous reports that low-temperature tolerance of carpetgrass is very poor, and its culture may be limited to geographical areas having moderate winter temperatures.

The thermal expansion, modulus of rupture, and modulus of elasticity of sintered magnesium dititanate were measured as functions of temperature and thermal history. The values increased with increasing temperature up to 1000°C., and hysteresis effects were found during cooling. Delayed strain effects were observed. These phenomena were attributed to the occurrence and recombination of internal fractures that result from stresses arising from the high anisotropy of thermal expansion of magnesium dititanate. J. P. Howe, "Properties of Graphite," J . Am. Ceram. SOC., 35 [ l l ] 275-82 (1952); discussions, ibid., pp. 282-83.

Priming or presoaking seed of common carpetgrass (Axonopus affinis Chase) and centipedegrass [Eremochloa ophiuroides Munro. (Kunz)] increased germination percentage and decreased mean time of germination (MTG) at 20, 25, and 30 °C. The effect of presoaking and priming was dependent on grass species and temperature. The optimum seed germination temperature for both of these warm-season species was 30 °C. Maximum effect on common carpetgrass or centipedegrass seeds was achieved by priming in 2% KNO3; higher concentrations did not improve germination percentage or MTG, and 4% was in some cases detrimental. Germination was higher and MTG lower at 20 and 30 °C than at 15 °C. Presoaking common carpetgrass and centipedegrass seeds was the most efficient seed enhancement treatment for germination at 30 °C.