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Formation Enthalpy (formation + enthalpy)

Distribution by Scientific Domains

Physics and Astronomy	60%
Polymers and Materials Science	40%

Selected Abstracts

MBE growth of InAsN on (100) InAs substrates

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2005
V. Sallet
Abstract The growth of InAsN on (100) InAs substrates by molecular beam epitaxy is investigated. The incorporation of nitrogen in the alloy is compared with the case of GaAsN grown on GaAs. Under the same conditions, lower nitrogen contents are systematically measured in InAsN. In both cases, nitrogen incorporation was found to be enhanced with the decrease of the arsenic flux supplied to the surface, whereas the nitrogen concentrations measured in InAsN and GaAsN as a function of the growth temperature follow opposite tendencies. For GaAsN, the N content slightly increases as the growth temperature raises from 360 °C to 460 °C. On the contrary, for InAsN alloys, no significant amount of N is observed over the range 420,460 °C and a decrease of the growth temperature down to 370 °C is required to incorporate 1% of nitrogen in InAsN. The comparison of formation enthalpies of binary constituents enables to understand these behaviours. A following discussion addresses the local environment of N atoms in GaInAsN materials. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Crystalline , -Alumina Deposited in an Industrial Coating Unit for Demanding Turning Operations,

ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010
Kirsten Bobzin
Crystalline PVD ,-Al2O3 - coatings offer great potential for their use in high-speed cutting operations. They promise high hot hardness and high oxidation resistance at elevated temperatures. This is important for coatings that are used for machining of materials with low thermal conductivity such as stainless steel or Inconel 718 because heat generated during cutting can barely be dissipated by the chip. Because of the prevailing bonding forces of alumina, adhesion-related sticking can be reduced even for dry cutting. Furthermore, the high formation enthalpy of alumina prevents chemical reactions with frictional partners. The present work gives an overview of the deposition of ,-Al2O3 thin films on WC/Co-cutting inserts by using pulsed MSIP (magnetron sputter ion plating) PVD technology. To improve adhesion, a (Ti,Al)N bond coat was employed. The samples were analyzed using common thin film test equipment. Cutting tests and pin-on-disk examinations were carried out to test the coating's performance. For turning operations, the difficult-to-machine austenitic steel 1.4301 (X5CrNi18-10) was used. In comparison to a state-of-the-art (Ti,Al)N coating, (Ti,Al)N/,-Al2O3 showed a longer tool life. [source]

Thermodynamic Reassessment of ZrO2,CaO System

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2009
Kun Wang
In this work, several thermodynamic assessments adopted widely for ZrO2,CaO system are reviewed and examined, the existing discrepancies are summarized, and a new assessment is carried out based on the formation enthalpy of two compounds (CaZr4O9 and Ca6Zr19O44) and experimental activity data concerning cubic solid solution. The thermodynamic parameters of all phases have been optimized by the least squares minimization procedure, a self consistent set of the optimized Gibbs energy parameters has been derived, which can be safely used to extrapolate into the multicomponent system. Compared with experimental data and the results in this work as well as the results reported previously, it is demonstrated that the present thermodynamic assessment is in better agreement with most of the experiments. [source]

Natural oxidation of InN quantum dots: the role of cubic InN

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2010
David González
Abstract The natural aging process occured in indium nitride quantum dots (QDs) heterostructures as a consequence of exposure to the atmosphere has been studied by means of transmission electron microscopy and electron beam related techniques. The comparison between GaN-capped and uncapped InN QDs kept at room conditions during 36 months indicates the structural changes that take place. While the capping layer seems to act in a protective way avoiding any change in the QDs, the uncapped structures suffer a series of phase transformations, where the original wurtzite structure is replaced by a layer of cubic phases. The main constituent of this layer is shown to be bcc-In2O3 formed by the substitution of the nitrogen atoms by oxygen from the atmosphere. This supposes a transformation from a hexagonal to a cubic structure, explained by the existence of an oxygen-rich cubic InN acting as an intermediate phase. The difference in the formation enthalpy between the original and the final product, together with the good match between the crystals would explain this transformation that shows the high instability of InN at environmental conditions. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Thermal vacancies and self-diffusion energy in 2024 Al-alloy by positron annihilation lifetime technique

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
Emad A. Badawi
Abstract Positron annihilation lifetime technique (PALT) is one of the most important nuclear non-destructive techniques. It was used to study the thermal vacancies in one of the most important engineering aluminum alloys , the 2024 Al-alloy. Quenching experiments were usually performed on thin specimens to ensure a uniform quenching rate throughout the specimen. The specimens were prepared with dimensions of 0.15 × 1.5 × 1.5 cm3. After grinding, polishing and etching, samples of 2024 were homogenized for 12 h at 673 K and annealed for 90-min., before being quenched in water (277 K). Positron lifetime measurements followed. From such measurements, it is possible to deduce the vacancy formation enthalpy, which in combination with the results of self-diffusion measurements, gives a value for migration enthalpy of the vacancy. These are very important quantities in the study of the annealing of irradiation induced defects. The use of the quenching technique in the positron annihilation study has the advantage that it allows a distinction between vacancy and dislocation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]