19 research outputs found
Two-Component Rare-Earth Fluoride Materials with Negative Thermal Expansion Based on a Phase Transition-Type Mechanism in 50 <i>R</i>F<sub>3</sub>-<i>R</i>âF<sub>3</sub> (<i>R</i> = La-Lu) Systems
The formation of materials with negative thermal expansion (NTE) based on a phase transition-type mechanism (NTE-II) in 50 Tâx (temperatureâcomposition) RF3-RâF3 (R = La-Lu) systems out of 105 possible is predicted. The components of these systems are âmotherâ RF3 compounds (R = Pm, Sm, Eu, and Gd) with polymorphic transformations (PolTrs), which occur during heating between the main structural types of RF3: ÎČ-(ÎČ-YF3) â t-(mineral tysonite LaF3). The PolTr is characterized by a density anomaly: the formula volume (Vform) of the low-temperature modification (VÎČ-) is higher than that of the high-temperature modification (Vt-) by a giant value (up to 4.7%). In RF3-RâF3 systems, isomorphic substitutions chemically modify RF3 by forming R1âxRâxF3 solid solutions (ss) based on both modifications. A two-phase composite (ÎČ-ss + t-ss) is a two-component NTE-II material with adjustable parameters. The prospects of using the material are estimated using the parameter of the average volume change (ÎV/Vav). The Vav at a fixed gross composition of a system is determined by the ÎČ-ss and t-ss decay (synthesis) curves and the temperature T. The regulation of ÎV/Vav is achieved by changing T within a âwindow ÎTâ. The available ÎT values are determined using phase diagrams. A chemical classification (ChCl) translates the search for NTE-II materials from 15 RF3 into an array of 105 RF3-RâF3 systems. Phase diagrams are divided into 10 types of systems (TypeSs), in four of which NTE-II materials are formed. The tables of the systems that comprise these TypeSs are presented. The position of Ttrans of the PolTr on the T scale for a short quasi-system (QS) âfrom PmF3 to TbF3â determines the interval of the ÎTtrans offset achievable in the RF3-RâF3 systems: from â148 to 1186 ± 10 °C. NTE-II fluoride materials exceed known NTE-II materials by almost three times in this parameter. Equilibrium in RF3-RâF3 systems is established quickly. The number of qualitatively different two-component fluoride materials with the giant NTE-II can be increased by more than ten times compared to RF3 with NTE-II
Refinement of the Congruently Melting Composition of Nonstoichiometric Fluorite Crystals Ca1-xYxF2x (x = 0.01â0.14)
The concentration series of nonstoichiometric crystals Ca1âxYxF2+x (x = 0.01â0.14) was obtained from a melt by directional crystallization to refine the composition of the temperature maximum on the melting curves. A precision (±9 Ă 10â5 Ă
) determination of lattice parameters of the Ca1âxYxF2+x crystals with the structure of fluorite (sp. gr. Fm-3m) was performed, and a linear equation of their concentration dependence was calculated: a(x) = 5.46385(5) + 0.1999(4) x. The distribution of yttrium along the crystals Ca1âxYxF2+x, the content of which is determined by the precision lattice parameters, is studied. The congruently melting composition x = 0.105(5) of the Ca1âxYxF2+x phase is refined by the method of directional crystallization
Development of a population-based microsimulation model of osteoarthritis in Canada
Medicine, Faculty ofPopulation and Public Health (SPPH), School ofOther UBCNon UBCReviewedFacultyResearcherOthe
Six Layers P1 Cathode Strip Chamber Prototype (construction and first results)
A full scale six layer Trapezoidal Cathode Strip Chamber Prototype of 0.8m x 1.2m x 3.3m was constructed and tested at Fermilab. The chamber construction and the first results on the chamber characteristics are presented in this paper