Structural and magnetic properties of C15 HoMn2 hydrides

Powder samples of cubic HoMn₂H_x hydrides, with 0 ≤ x ≤ 4.3, have been investigated by X-ray diffraction and AC/DC magnetometry as a function of temperature and external magnetic field. Hydrogen is demonstrated to strongly modify structural and magnetic properties. X-ray studies revealed many structural transformations placed at low temperatures. In particular, a transformation from the cubic to the monoclinic structure was detected, which so far has not been reported for other cubic RMn₂H_x (R - rare earth or Yttrium) compounds. The structural transformations are reflected in the magnetic behavior. The change in ordering temperatures implies a very strong relationship between the magnetic interactions and the Mn-Mn distance modified at hydrogen absorption. Tentative magnetic and structural phase diagrams are proposed. The presented results are compared with the properties of other cubic and hexagonal RMn₂H_x hydrides.     

Transamination Reactivity of Ti(NMe2)4 and Zr(NMe2)4 with 1,3,4,5,6-Pentamethyl-2-aminoborazine and Aryl Amines. Model Chemistry for the Formation of Metalloborazine Preceramic Polymers and MN/BN (M?=?Ti, Zr) Ceramic Composites

The transamination reactions between Ti(NMe₂)₄ and 1,3,4,5,6-pentamethyl-2-aminoborazine, (Me)₃N₃(Me)₂B₃(NH₂), and diphenylamine (Ph₂NH) and between [Zr(NMe₂)₄]₂ and 1,3,4,5,6-pentamethyl-2-aminoborazine, aniline (PhNH₂) and diphenylamine have been studied and the molecular product species have been isolated, spectroscopically characterized and single crystal X-ray structure analyses completed. The results of these studies have been used to interpret the outcome of reactions of Ti(NMe₂)₄ and Zr(NMe₂)₄ with borazinylamine preceramic polymers that, upon pyrolysis, produce TiN/BN, ZrN/BN and ZrH_0.6N/BN composite powders. The transamination reactivity of a two-point poly(borazinylamine) oligomer having terminal –NH₂ amino groups with Ti(NMe₂)₄ and Zr(NMe₂)₄ has been used to obtain metallated preceramic oligomers that, upon pyrolysis, give TiN/BN and ZrN/ZrH_0.6N/BN nanocomposites. Model reactions of 1,3,4,5,6-pentamethyl-2-amino borazine, aniline and Ph₂NH₂ with Ti(NMe₂)₄ and Zr(NMe₂)₄ are also described as models for the formation of the metallated oligomers. Molecular structure determinations for the metal amides are presented. We dedicate this paper to Professor Christopher W. Allen in recognition of his distinguished career and his accomplishments in inorganic ring and polymer chemistry.     

Relation between phase composition of compound zone and growth kinetics of diffusion zone during nitriding of steel

The present work is devoted to an investigation of the influence of the micro-structural evolution of the compound zone (iron (carbo)nitrides zone) upon the development of hardness profiles in the diffusion zone. A different phase structure of iron (carbo)nitrides zone on steel as compared to iron, further changing with the process, may result in upsetting of the quasi-equilibrium of nitrogen concentration in the iron (carbo)nitrides zone/diffusion zone interface. This, as a result, may have an impact on the kinetics of this layer's growth. The research carried out was aimed at solving this problem. It was to evaluate the influence of (carbo)nitrides zone, with an intentionally created diametrically different phase composition, on hardness profiles in the diffusion zone. The nitrided layers were characterised by a light optical microscopy, X-ray diffraction and measurements of hardness. It was observed that the evolution of the phase structure and phase composition of the compound zone contributes significantly, regardless of nitrogen potential and temperature, to the formation of the diffusion zone and in particular to its effective thickness. It makes this complex picture of nitrided case development on steel even more intricate.     

Effect of selected substances on the properties of frozen myofibril preparation obtained from mechanically recovered poultry meat

The experimental material was a myofibrillar preparation obtained from mechanically recovered poultry meat by the washing and separation of fat and connective tissues. Changes occurring during frozen storage were investigated in the preparation without and with the addition of the following substances: 2 g/kg carrageen, 2.5 g/kg sodium tripolyphosphate (TPP) mixture and 80 g/kg polydextrose, and 3 g/kg enzymatic preparation (ACTIVA WM) containing microbial transglutaminase (MTG). Samples with the addition of MTG were pre-incubated at the temperature of 7 ± 1 °C for 1, 3, 5, 24 h. All samples were stored at the temperature of approx. −23 °C for 2, 30, 60, 90 days. The smallest change in protein solubility was observed in samples with added TPP and polydextrose. Along with the extension of pre-incubation time of samples containing the enzyme a gradual decrease was found in the amount of soluble protein. Also the results of the investigations obtained using the DSC technique showed the most advantageous protective effect, i.e., causing the smallest decrease in enthalpy values of samples during freezer storage, in case of the addition of TPP and polydextrose mixture. Analysis of thermal drip volume from gels showed that carrageen was the most advantageous addition to the myofibrillar preparation. Moreover, a gradual increase was observed in the volume of thermal drip along with the extension of pre-incubation time of the protein isolate with enzymatic preparation. Results of gel texture testing indicated that the most advantageous effect on gel quality was found for ACTIVA applied in 3 and 5 h pre-incubation with the myofibrils. Assuming that among the analyzed properties the most important were thermal drip and gel texture, 3 g/kg MTG at pre-incubation time of 3 h was considered the most advantageous additive.     

Synthesis and characterization of carbonaceous replicas of multilayered vesicular siliceous materials

Synthesis of novel, carbon porous replicas of vesicular siliceous materials has been described. The original siliceous materials consist of small, spherical structures resembling onions, known in the literature as multilamellar vesicles (MLVs). They have been characterized with a number of analytical methods that allow one to determine its 3-D structure and basic parameters of the pore system. Carbonaceous materials, made similarly of onion-like porous structures, have been obtained using a standard procedure to form replicas. They have been characterized by the same methods as those applied to the parent materials.     

Non-isothermal micromixing in turbulent liquids: Theory and experiment

Partial segregation of reagents occurs when reaction rates exceed mixing rates and frequently causes product distributions to be mixing-dependent. A simultaneous temperature segregation, whereby the temperature in a reaction zone differs from that in its surroundings, has rarely been considered when mixing reagents in the liquid phase. The Prandtl number is usually sufficiently small that engulfment, not thermal conduction, determines the local temperature. The engulfment model of micromixing can then be extended by a heat balance to specify this temperature. To evaluate this model, a new pair of fast competitive reactions (neutralisation and acetal hydrolysis) has been characterised thermochemically and kinetically. A Mettler RC1 calorimeter was operated under isothermal and adiabatic conditions with various stirrer speeds and HCl was slowly added to a mixture of NaOH and 2,2-dimethoxypropane. Measured hydrolysis yields compared quite well with the extended engulfment model, although temperature segregation was of minor importance. It was also unimportant in other reaction systems (simultaneous neutralisation and ester hydrolysis; diazo coupling) employed earlier to study micromixing. Suggestions for further work are made.     

Alkali-metal promoted rhodium-on-alumina catalysts for nitrous oxide decomposition

Catalytic activity of γ-alumina supported rhodium catalysts in nitrous oxide decomposition into dinitrogen and dioxygen has been determined, the total conversion being reached at 450 °C. Rhodium is present at alumina surface in three forms: metal particles, Rh₂O₃ and rhodium zero valent atoms interacting with oxygen ions at the metal/support interface. Linear dependence of the catalytic activity on rhodium dispersion has been found. Deposition of alkali metal cations: Li, Na, K and Cs as promoters at the surface of alumina results in a considerable increase of rhodium dispersion and hence catalytic activity. The effect of promoters depends strongly on the speciation of alkali metals and rhodium used in the preparation of the catalyst. Both alkali metal cations and rhodium compete for the same OH groups at the alumina surface. The electronegativity of alkali metal oxides is much greater than that of alumina and their deposition increases the negative charge of surface oxide ions hindering the diffusion of rhodium and preventing the growth of its larger particles.     

Effects of support on hydrogen adsorption/desorption on nickel

The effects of alumina, silica and carbon on hydrogen adsorption on nickel were studied by the temperature-programmed desorption (TPD) method. The examinations were carried out in the flow system, starting TP measurement at 100 K, which resulted in the formation of complete characteristics of the interaction of hydrogen with supported nickel. The examinations have shown that each support modifies in its own way the state of hydrogen adsorbed on nickel. Alumina and silica insignificantly affect hydrogen strongly adsorbed on nickel, but significantly affect hydrogen weakly adsorbed; in particular, the effect of silica depends qualitatively on the way of preparation of the examined sample. Carbon affects significantly both strongly and weakly adsorbed hydrogen.     

Social reference points and accessibility of trait-related information in self-other similarity judgments.

Two experiments examined latencies of self-other similarity judgments. The judgments were obtained for traits for which self was prototypical, other was prototypical or neither was prototypical. Two question types used were as follows: self-as-referent questions ("How similar is X to you…?") and other-as-referent questions ("How similar are you to X…?"). Judgments were faster for self-prototypical traits than for neither-prototypical traits regardless of the question form. Judgments for other-prototypical traits were faster than judgments for neither-prototypical traits in the case of the other-as-referent questions, but not in the case of self-as-referent questions. Results support the notion that both self and representations of specific others serve as habitual reference points. However, they also suggest that, compared to other social prototypes, self is a more rigid reference point, which is not easily affected by linguistic factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)