The elastic properties of single-crystalline erbia (Er2O3) at room temperature have been investigated using resonant ultrasound spectroscopy. The three independent stiffness constants of anisotropic Er2O3 cubic type-C crystals have been measured. The values of the stiffness constants were c 11= 256.4 GPa, c 12= 146.8 GPa, and c 44= 75.2 GPa. From the stiffness constants, the estimated values for dense polycrystalline erbia for Young's modulus, the shear modulus, the bulk modulus, and Poisson's ratio at room temperature were 179 GPa, 67 GPa, 183.3 GPa, and 0.337, respectively. The value of Young's modulus is a minimum along [001] and a maximum along [111]. The value of the shear modulus is independent of the direction in the (001) and (111) planes, whereas it decreases in (11¯0) from 75 GPa along [001] to 55 GPa along [110]. 相似文献
Within the framework of Cahn’s pioneering theory of spinodal decomposition, the effect of the epitaxial stress on the stability of a binary alloy solid solution against infinitesimal compositional fluctuations is revisited. It is shown that the elastic energy term due to a coherent lattice mismatch with a substrate modifies the linearised diffusion equation. This term is particularly high when size effects between the two constituents are strong. It is then necessary to take into account anharmonic terms in the expression of the elastic energy. From the modified diffusion equation, a new spinodal curve, called the epitaxial coherent spinodal, may be calculated for different substrate lattice parameters. The results of the model are compared with recent experiments on coherently grown (001) Au–Ni alloys. A modulated structure has been evidenced upon annealing which is in good agreement with our calculations.
Résumé
Dans le cadre de la théorie de la décomposition spinodale développèe par Cahn, nous présentons l’effet des contraintes épitaxiales sur la stabilitéd’une solution solide d’alliage binaire soumise ádes fluctuations de compostion infinitésimales. Les contraintes induites par l’épitaxie cohérente sur un substrat ayant un paramètre de maille différent de celui de la solution solide considérée sont àl’origine d’un terme d’énergie élastique dont il faut tenir compte dans l’équation de diffusion. Ce terme devient particulièrement important lorsque les effets de taille entre les deux constituants sont grands. Nous montrons qu’il est alors nécessaire de considérer dans l’expression de l’énergie élastique les termes anharmoniques. Une nouvelle spinodale, appelée spinodale cohérente épitaxiale, peut être calculée pour différentes valeurs du paramètre de maille du substrat. Les calculs sont comparés avec les résulats expérimentaux obtenus sur des alliages Au–Ni (001) élaborés de manière cohérente. Une structure modulée a étémise en evidence au cours de recuits, ce qui est en accord avec les résultats du modèle. 相似文献
An effective method was proposed to determine the two organic-phase rate constants of the primary and secondary reactions which have differences in rates. The goal was achieved by employing the reaction of two mixed l-alcohols and dibromomethane in an alkaline solution of KOH/chlorobenzene two-phase medium under phase transfer catalysis. A new product of unsymmetric acetal was obtained in this work. The intermediate ROCH2Br (a-haloalkyl ether) was not detected during or after the reaction when using high reactive alcohols. This result indicated that ROCH2Br was more reactive than the organic reactant CH2Br2. This high reactive a-haloalkyl ether implied that the rate constants of secondary reactions are larger than those of the primary reactions. The resistance of mass transfer of the catalyst ((C4H9)4NBr, QBr) and the active catalyst, ((C4H9 )4NOR, QOR R: c4h9and C8h17) transferring from the aqueous phase to the organic-phase and vice versa were found to be negligible. The organic-phase reaction is a rate-determining step of the phase transfer catalytic reaction, A measured constant concentration of tetrabutylammonium alkoxide (QOR) during the reaction leads to the application of pseudo-first order rate law. The reaction rate constant of ROCh2Br acts 104 larger than that of CH2Br2. 相似文献
Soymilk, a colloidal dispersion obtained by wet milling of soya bean (Glycine max (L) Merill), was subjected to the foam-mat drying process at 65°C using two foam stabilizers namely, carboxy methyl cellulose (CMC) and glyceryl distearate (GDS) at 5, 10 and 15% levels. While CMC did not produce a stable foam at any of the levels used, it was however, found that a minimum of 10% GDS was required to produce a stable foam. The physical characteristics and reconstitution properties of 10% GDS foamed soymilk powder and 15% GDS foamed soymilk powder were found to be similar but better than those of unfoamed soymilk powder and inferior to those of a spray dried powder sample. 相似文献
In the present work, the vibration problems of rectangular plates modeled by Eringen’s microstretch theory are investigated for the identification of the upper bounds of the microstretch moduli of the plate material. The calculated frequencies of the plates are obtained by extending the Ritz method to the microstretch plates. The three dimensional (3D) vibration analysis of the plates shows that some additional frequencies occur among the classical frequencies as characterizing the microstretch effects. Then it is also observed that these additional frequencies disappear and only the classical frequencies remain with the increasing values of microstretch constants. The inverse problem is established for the identification of the upper bounds of the microstretch elastic constants as an optimization problem where an error function is minimized. 相似文献
Interference layer metallography was usedto identify the phases present in the aluminidecoating on superalloy IN738LC. They are: twointermetallic aluminides NiAl and Ni_3Al, y-solidsolution and a Cr-rich solid solution, twosulphides M_(23)C_6 and MC, and two sulphides(Al,Cr)_3S_4 and (Cr,Ti)_3S_4. ZnS and ZnSe areproposed to be vapor deposited onto the surfaceof the specimen to get good colour contrastand good light-dark contrast. The refractiveindex and absorption coefficient of all thesephases have been detemined. 相似文献
Apparent rate constants for the reactions of four selected pharmaceutical compounds (metoprolol, naproxen, amoxicillin, and phenacetin) with chlorine in ultra-pure (UP) water were determined as a function of the pH. It was found that amoxicillin (in the whole pH range 3-12), and naproxen (in the low pH range 2-4) presented high reaction rates, while naproxen (in the pH range 5-9), and phenacetin and metoprolol (in the pH range 2.5-12 for phenacetin, and 3-10 for metoprolol) followed intermediate and slow reaction rates. A mechanism is proposed for the chlorination reaction, which allowed the evaluation of the intrinsic rate constants for the elementary reactions of the ionized and un-ionized species of each selected pharmaceutical with chlorine. An excellent agreement is obtained between experimental and calculated rate constants by this mechanism.The elimination of these substances in several waters (a groundwater, a surface water from a public reservoir, and two effluents from municipal wastewater treatment plants) was also investigated at neutral pH. The efficiency of the chlorination process with respect to the pharmaceuticals elimination and the formation THMs was also established. It is generally observed that the increasing presence of organic and inorganic matter in the water matrices demand more oxidant agent (chlorine), and therefore, less chlorine is available for the oxidation of these compounds. Finally, half-life times and oxidant exposures (CT) required for the removal of 99% of the four pharmaceuticals are also evaluated. These parameters are useful for the establishment of safety chlorine doses in oxidation or disinfection stages of pharmaceuticals in treatment plants. 相似文献