Dynamics of non-equilibrium phase boundaries in a heat conducting non-linearly elastic medium

The phase transformation of the first kind in a non-linearly elastic heat conducting medium is simulated by the relationships on a strong discontinuity. A generalization of the Stefan formulation is given. An existence condition for stationary flow, analogous to the Gibbs phase equilibrium condition, is obtained for non-equilibrium phase boundaries. A pure dilatational phase transition in a compressible fluid and pure shear transformation of the twinning type in non-linearly elastic crystals are considered as model examples. The problem of the structure is solved for closure of the system of relationships on the shock.

A phase transformation ordinarily turns out to be localized in a narrow domain of space and it can be simulated in terms of the conditions on a strong discontinuity /1/. Formulation of the problem of the static equilibrium of liquid phases as well as of liquid and (non-linearly elastic) solid phases was given by Gibbs, who proposed a phase equilibrium criterion and formulated appropriate conditions on the shock; the extension of the Gibbs conditions to the case of the equilibrium of two solid phases is known in both the linear /2/ and non-linear /3/ theories of elasticity. The dynamic problem of the propagation of the equilibrium phase boundary is considered in the Stefan formulation as a rule, including the assumption about the continuity of the density (the strain tensor component) on the shock; the thermal problem is here separated from the mechanical one. Simulating the interphasal surface on the shock the temperature fields are merged by using the well-known Stefan conditions as well as the phase equilibrium condition that reduces to giving the temperature on the front.

The purpose of this paper is to extend the Stefan-Gibbs formulation to the case of the motion of a coherent isothermal phase boundary in a non-linearly elastic heat conducting medium and to derive the dynamic analogue of the phase equilibrium condition (and the Stefan conditions) with possible dissipation at the transformation front. Two dissipative mechanisms are examined, viscous and kinetic. The case of equilibrium phase boundaries was investigated in /4–6/.     

The thermodynamic properties of Ln2BaO4 (Ln = Sm, Dy, Ho)

The thermodynamic properties of the Ln₂BaO₄ phases (Ln = Dy, Ho, Sm) were studied by the electromotive force method with a fluoride electrolyte (890–1180 K), solution calorimetry in 1.07 N hydrochloric acid at 298.15 K, and differential scanning calorimetry (298–860 K). The experimental data were jointly processed, and the thermodynamic functions of the compounds over the temperature range 298–1200 K were calculated.     

Form I of desloratadine,a tricyclic anti­histamine

The title compound [systematic name: 8‐chloro‐11‐(piperidin‐4‐yl­idene)‐6,11‐dihydro‐5H‐benzo[4,5]cyclo­hepta­[2,1‐b]pyridine], C₁₉H₁₉ClN₂, was crystallized from ethyl acetate. The inter­esting feature of the reported structure is that it does not contain any strong hydrogen bonds, although the mol­ecule contains a secondary NH group, which is a good hydrogen‐bond donor.     

A WKB analysis of the buckling condition for a cylindrical shell of arbitrary thickness subjected to an external pressure

We consider the plane-strain buckling of a cylindrical shellof arbitrary thickness which is made of a Varga material andis subjected to an external hydrostatic pressure on its outersurface. The WKB method is used to solve the eigenvalue problemthat results from the linear bifurcation analysis. We show thatthe circular cross-section buckles into a non-circular shapeat a value of µ₁ which depends on A₁/A₂ and a mode number,where A₁ and A₂ are the undeformed inner and outer radii, andµ₁ is the ratio of the deformed inner radius to A₁. Inthe large mode number limit, we find that the dependence ofµ₁ on A₁/A₂ has a boundary layer structure: it is constantover almost the entire region of 0 < A₁/A₂ < 1 and decreasessharply from this constant value to unity as A₁/A₂ tends tounity. Our asymptotic results for A₁ – 1 = O(1) and A₁– 1 = O(1/n) are shown to agree with the numerical resultsobtained by using the compound matrix method.     

Reciprocating sliding wear behavior of laser-clad small amplitude Mo2Ni3Si/NiSi metal silicide composite coatings

Mo₂Ni₃Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo₂Ni₃Si primary dendrites and the interdendritic Mo₂Ni₃Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo₂Ni₃Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance.     

226Ra in milk of the dairy cattle from the rural region of Pernambuco, Brazil

Summary Studies performed by the Brazilian Nuclear Corporation (NUCLEBRAS), in collaboration with the Geological Survey Company of Brazil (CPRM), identified high levels of natural uranium in the districts of Pedra and Venturosa, in the rural region of the state of Pernambuco (PE) - Brazil, where the maximum value found in rocks was 22,000 mg.     

T-x-y diagram of the Ni-Bi-Se system

Some polythermal sections of the Ni-Bi-Se system have been investigated by DTA, X-ray powder diffraction, microstructural analysis, and microhardness measurements. The liquidus surface has been constructed for this system. The compounds NiBi₂Se₄ and Ni₃Bi₂Se₂ are formed by dystectic reactions and melt at 1088 and 980 K, respectively. The regions of primary and joint phase crystallization have been determined. A commutation of Bi₂Se₃-based thermoelements with a metal nickel bus-bar has been proposed.     

Mechanical mixtures of Me (Ni, Pd) Ce oxides and silica-supported heteropolyacids: Role and optimal concentration of each active species in n-hexane isomerization

Catalytic properties of silica-supported heteropolyacids (HPA) in a mechanical mixture with reduced Me-Ce oxides (Me = Ni, Pd) in n-hexane isomerization are studied. The role of each component of the mixed oxides (Ce and, typically, Ni and Pd) and their optimum content has been illuminated: cerium is not only beneficial for eliminating or preventing coke deposition but is also effective for maintaining the Keggin structure of the highly-organized HPA during the reaction and probably allows a better dispersion of the second metal species. Nickel and palladium, present as Ni⁰ and Pd⁰, reinforce the activation of the alkane, which is difficult to obtain by means of a direct attack by an acid, and, thus, enhance noticeably the activity of the catalyst. The best mechanical mixtures are obtained with 30–70 wt % NiCeO-HPW/SiO₂ and 50–50 wt % Pd_0.1CeO-HPW/SiO₂. These mixtures have the highest efficiency for a Ni/(Ni + W) atomic ratio of 0.66 and a Pd/(Pd + W) ratio of 0.40, respectively. Finally, the conversion of n-hexane is in the order HPW > HSiW > HBW, which seems to be consistent with the order of their acid strength as per the literature, but the isomerization selectivity appears to be slightly higher on HSiW. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 24–28. The text was submitted by the authors in English.