Mapping of the structural perfection of vapor grown αHgI2 crystals by means of γray rocking curves Refractive index and elastic properties of singlecrystal corundum (αAl2O3) up to 2100 K Volume expansion and annealing compaction of ionbombarded singlecrystal and polycrystalline α Al2O3In previous work the thermoluminescence of golden sapphire (AhO. containing Ni and Mg), which was " irradiated under liquid nitrogen, was compared with glow curves of fused borax seeded with Ni and Mg. The emission intensity obeyed, reasonably well, the expression l=aNok'exp[ -1!(dT!dt) t: k'dT J-In the present paper it is shown that light-induced glow curves in ,,-irradiated sapphire have the form of a second-order decay process, namely I =lo [b!(b+t)]m. Gamma-ray induced thermoluminescence in ruby shows dominant emission bands with maxima at about 150 0 K and 240oK. Light-induced thermoluminescence in ')'-ray damaged ruby shows an afterglow long after the crystal has reached room temperature.
tures which could be systematically correlated with the conditions controlling the occurrence of either form. Hence, no account has been taken of this polymorphic behavior in drawing up the CaO-Nbz05 phase diagram. Where 3Ca0.-Nb& is indicated as being one of the crystalline phases present, i t can be either type I or type I1 or both. The X-ray data were used merely as a means of identifying the chemical nature of the phase(s) present.It is considered t o be probable that the liquidus curve of the high-lime end of the system will proceed in a n unbroken curve from the highest point observed, 1940OC (for a composition containing 55% CaO), up t o 2570°C, the published melting point for 100% Ca0.15 The equipment available did not permit this region of the system t o be studied conveniently, but it has been demonstrated that no further lime-rich compound can be expected t o occur. It must be pointed out that, in the course of this work, no attempt has been made to investigate possible low-temperature polymorphs or phases whose equilibrium regions do not reach the liquidus curve, other than t o point out the two modifications of the compound 3Ca0.Nb205. Hence, no such polymorphs or phases appear in Fig. 1. I6 E. E. Schumacher. "Meltinrr Points of Barium. Strontium. and Calcium Oxides," j. Am. Chuenz. Soc., 48-[2] 396-405 (1926); Ceram. Abstr., 5 [7] 233 (1926).Stress-strain curves and stress-relaxation curves were determined at various temperatures (lo to 7OOC) and concentrations (16 to 22 wt%) for attapulgite suspended in water. Stress-relaxation experiments were conducted under different conditions on samples which were relaxed for various durations of time between successive cyclic deformations. The flow properties are given in terms of rheopexy and thixotropy. The flow curve (for shear rates 0 to 700 per second versus shear stress) shows, first, a rheopectic hysteresis loop which changes on repeated shearing to a reversible and reproducible non-Newtonian flow curve. After resting the system for about 12 hours, the resulting flow curve shows a thixotropic loop. Viscosity as a function of pH shows an inversion at pH N 6.3. A model for explaining the observed facts is proposed. The script S type of looped-over flow curves showing both rheopectic and thixotropic characteristics is explained in terms of breakage of "logjammed" and crystalline bundles. A plot of the yieldpoint viscosities versus the reciprocal of temperature for the rheopectic and thixotropic curves shows activation energies of about 1 and 2 kcal respectively. An autographic rotational viscometer was designed and utilized to obtain the data reported so that the objectionable effects of frictional heating in the sample were minimized. The calibration response of the viscometer to a glycerol standard shows good agreement with published viscosity data.
The flow behavior of bentonite colloidal suspensions is given i n terms of the stress-strain relations with respect to variables of concentration, suspension medium, hydrogen-ion concentration, temperature, a n d the successive application of shear stress. Repeated cycling (successive reruns of upcurve a n d downcurve) caused thixotropic hysteresis loops which decreased in size to a final constant a n d reproducible flow curve. A hysteresis loop did not appear for a mixture of less than 20 wt% bentonite a n d glycerin. The flow curves are discussed i n terms of bondings in "cardhouse" a n d "blockhouse" models for dilute a n d concentrated suspensions respectively. Eyring's rate theory of viscosity is discussed briefly in terms of the well-known generalized viscosity equation which was applied successfully t o given flow curves. Physical and chemical characterizations are compared in terms of thixotropic flow models for aqueous, glycerol, a n d oil (Bentone grease) suspensions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.