bluuebunny/crossref_metadata_2025 huggingface dataset:
Tripartite mass transfer model: development, implementation in DYVRO, verification and validation
Authors: Neuhaus T. , Schaffrath A.
Published: December 2013

For the realistic simulation of condensation induced water hammer (CIWH) in horizontal pipes resulting from the contact of steam at sub-cooled water, an appropriate model for the mass and energy transfer due to phase change is needed. For this purpose the tripartite mass transfer (TMT) model has been developed that is introduced in the present paper. The TMT model is based on the assumption of isentropic processes and accounts for vaporization due to flashing, condensation due to isentropic decompression (homogenous condensation) and direct contact condensation at the phase interface. The TMT model shall be considered as a frame for sub-models which may be arranged for the three above-mentioned phase change phenomena. The TMT model has been implemented in the one-dimensional two-phase pressure surge code DYVRO mod 3. A verification and validation procedure was performed based on experiments at test facilities in Oberhausen (PPP), Rossendorf (CWHTF) and Budapest (PMK-2).
Pressure surge in Wendelstein 7-X experimental stellarator facility
Authors: Kaliatka A. , Uspuras E. , Kaliatka T.
Published: December 2013

Fusion is the energy production technology, which could potentially solve problems with growing energy demand of population in the future. Wendelstein 7-X (W7-X) is an experimental stellarator facility currently being built in Greifswald, Germany, which shall demonstrate that in the future energy could be produced in such type of fusion reactors. Lithuanian energy institute (LEI) in the frames of European Fusion Development Agreement (EFDA) program is cooperating with Max Planck Institute for Plasma Physics (IPP, Germany) by performing safety analysis of fusion device W7-X. In this paper the consequences of potential water hammer effects were analysed only for the case, when the plasma vessel is operating in the “baking” mode. “Baking” is the mode of facility operation during which the plasma vessel structures are heated up to 150°C in order to release absorbed gases from the surfaces and to pump them out of the plasma vessel before plasma operation. For the analysis the thermal-hydraulic model of target (torus) modules cooling / heating systems in W7-X facility was developed using RELAP5/Mod3.3 code. The performed analyses showed that the pressure pulsations in pipelines of cooling / heating systems are possible only in case of very fast closure of automatic valves in torus modules inlets and check valves in torus modules outlets. The maximum dynamic loading to cooling / heating systems pipelines due to such valves activations is in the range 0.12–0.28 MPa. Such dynamic load is insignificant and integrity of pipelines remains not violated. The pressure surge in pipeline connecting torus module in case of erroneous closure of automatic valve is eliminated due to operation of check valve on pipeline in torus module outlet.
Development of multi-group spectral code TVS-M
Authors: Lazarenko A. P. , Pryanichnikov A. V. , Kalugin M. A. , Gurevich M. I.
Published: December 2013

This paper is dedicated to the latest version of TVS-M code – TVS-M 2007, which allows the neutron flux distribution inside fuel assemblies to be calculated without using the diffusion approximation. The new spatial calculation module PERST introduced in TVS-M code is based on the first collisions probability method and allows the scattering anisotropy to be accounted for. This paper presents some preliminary results calculated with the use of the new version of TVS-M code.
Assessment of spectral history influence on PWR and WWER core
Authors: Bilodid Y. , Ovdiienko I. , Mittag S. , Kuchin A. , Khalimonchuk V. , Ieremenko M.
Published: December 2013

The few-group cross section libraries, used by reactor dynamics codes, are affected by the spectral history effect – a dependence of fuel cross sections not only on burnup, but also on local spectral conditions during burnup. Neglecting this effect leads to an additional component of error in neutron-physical characteristics. Two solution approaches to this problem implemented in the reactor dynamic code DYN3D are described and compared in this paper: a cross section correction method based on239Pu concentration and separate cross sections treatment for each axial layer of reactor core. Steady-state and burnup characteristics of a PWR and a WWER-1000 cores, calculated by DYN3D with and without cross section corrections, are compared. An impact of the correction on transient calculations is studied for a control rod ejection example. Studies have shown a significant influence of spectral history on axial power and burnup distributions as well as on calculated cycle length. Two different correction methods have shown similar major effects.
The European map of indoor radon concentrations: status and questions of quality assurance
Authors: Bossew P. , Gruber V. , Tollefsen T. , De Cort M.
Published: December 2013

As a first part of the long-term project “European Atlas of Natural Radiation”, a European map of indoor radon concentrations is currently under development. By mid-2011, 21 countries participate in the project, yielding a more or less complete coverage of the European territory. In this article we shortly present the current status before concentrating on questions of quality assurance. Such questions inevitably emerge in a project which attempts to integrate and harmonize large amounts of data of methodically different origin; aggregating them into a common map raises by itself questions of statistical significance.
Application of the tracer gas technology to investigate convective radon transport processes between mine workings and houses
Authors: Löbner W. , Schramm C. , Regner J. , Geringswald K. , Leichsenring F. , Schmidt P.
Published: December 2013

In areas featuring air-filled mine workings the convective radon transport through the disturbed bedrock is a frequent cause of high radon concentrations in dwellings. The vertical transport distance of the radon propagation can be more than one hundred meters. The application of tracer gases that can be detected by gas chromatography at extreme low concentrations allows the clear detection of mine-originated radon in dwellings and provides knowledge on the complex processes of radon transport. The successful application of the method is demonstrated on the basis of investigations of the impact of former uranium mine sites on the radon situation in dwellings.
Measurement of radionuclides within the Global Atmosphere Watch Programme of WMO
Authors: Steinkopff T. , Frank G. , Salvamoser J.
Published: December 2013

Within the framework of the Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization (WMO), the Deutscher Wetterdienst (DWD) is taking measurements of naturally occurring radionuclides at both the environmental research platform Schneefernerhaus (2650 m a.s.l.) and the summit of Germany's highest mountain Zugspitze (2962 m a.s.l). The radionuclides measured there include 7Be, 210Pb, 212Pb, 214Pb, 214Bi, and 222Rn. This paper especially presents the direct measurement of gaseous 222Rn with a limit of detection of < 0.05 Bq/m3. When combined with meteorological data, these measurements provide a valuable database for characterising air masses and a useful supplementary tool evaluating air transport models and identifying global atmospheric conditions.
Remarks on boiling water reactor stability analysis – part 2: stability monitoring
Authors: Lange C. , Hennig D. , Hurtado A. , Schuster R. , Lukas B. , Aguirre C.
Published: December 2013

In part 1 of this article we explained the partly relative complex solution manifold of the differential equations describing the stability behaviour of a BWR, in particular the coexistence of different types of solutions, such as the coexistence of unstable limit cycles and stable fixed points are of interest from the operational safety point of view. The part 2 is devoted to the surveillance of the stability behaviour. We summarize some stability monitoring methods and suggest to support stability tests by RAM-ROM analyses in order to reveal in advance the stability “landscape” of the BWR in a parameter region high sensitive for appearing of linear unstable states. The analysis of an especial stability test, performed at NPP Leibstadt (KKL), makes it clear that the measurement results can only be interpreted by application of bifurcation analysis.
Nuclear aspects and cyclotron production of the positron emitter 55Co
Authors: Talebi M. , Kakavand T. , Mirzaii M.
Published: December 2013

The radionuclide 55Co (T1/2 = 17.5 h, Eβ+ = 1.5 MeV, 76% β+ decay) is an important β+ emitting radioisotope. For production of 55Co via natFe(p, xn) 55Co reaction, an iron layer was deposited on a copper substrate by means of electro-deposition method which could be irradiated by 29.5 MeV protons at 100 μA. No-carrier-added (n.c.a.) 55Co was separated from the iron target via an anion exchange column (Dowex 1 · 8). The achieved production yield was 31.25 MBq/μAh. Also, excitation functions for the 55Co radionuclide via natFe(p, xn)55Co, 56Fe(p, 2n)55Co and 54Fe(d, n)55Co reactions were calculated by TALYS-1.4 code and TENDL-2011 database and compared with previous published data.
CFD analysis of a void distribution benchmark in a rod bundle
Authors: Krepper E. , Rzehak R.
Published: December 2013

The NUPEC “PWR Subchannel and Bundle Tests” (PSBT) were designed to investigate critical heat flux phenomena in rod bundles and yield data to validate hot channel codes. Some of the tests are suitable for validating a CFD wall boiling model. The paper presents CFD calculations of the void distribution tests of the PSBT benchmark using ANSYS CFX-12.1. First, relevant aspects of the implemented wall boiling model are reviewed highlighting the uncertainties in several model parameters. It is then shown that the measured cross sectionally averaged values can be reproduced well with a single set of calibrated model parameters for different tests cases. For the reproduction of patterns of void distribution cross sections attention has to be focussed on the modelling of turbulence in the narrow channel. Only a turbulence model with the capability to resolve turbulent secondary flows is able to reproduce at least qualitatively the observed void distribution patterns.
On the pair correlation function in a bubble swarm
Authors: Santarelli C. , Fröhlich J.
Published: December 2013

The paper presents results on the dynamics of bubbles in a mono- and in a bi-disperse bubble swarm. The radial pair correlation function provides insight into the characteristic bubble clustering length. The angular pair correlation function shows that for small distances the most probable alignment of a bubble pair is horizontal.
Experimental investigations of single and two-phase flow in a heated rod bundle
Authors: Barthel F. , Franz R. , Hampel U.
Published: December 2013

An experimental facility for the study of boiling flows in a 3 × 3 rod bundle geometry was setup. The bundle resembles in essential geometrical parts the geometry in a pressurized water reactor fuel element. The facility is operated with a refrigerant fluid. Beside standard instrumentation for temperature, pressure and flow rate we employed particle image velocimetry for single phase flow studies, gamma ray densitometry for integral gas fraction measurement sand ultrafast X-ray tomography for the study of the void dynamics in the cross-section. Moreover extensive thermo-instrumentation allows axial rod surface temperature measurements for the central heated rod. First results will be discussed in this article.
About the change in boiling behaviour of water with coolant additives in PWR
Authors: Nakath R. , Schuster C. , Hurtado A.
Published: December 2013

The present study investigates the effect of boric acid and lithium hydroxide on flow boiling phenomena in pressurized water reactors. The experiments were conducted in a boiling loop with up to 40 bar and 250 °C. The bubble size distribution was determined with a wire-mesh sensor. The results showed no indication that reactor-typical concentrations of boric acid or lithium hydroxide have a safety-relevant influence on the boiling behavior in pressurized water reactors.
Application of the Henyey-Greenstein and Anlı-Güngör phase functions for the solution of the neutron transport equation with Legendre polynomials: Reflected critical slab problem
Authors: Öztürk H.
Published: December 2013

The criticality problem for one-speed neutrons in a uniform homogeneous slab with reflecting boundary conditions is studied using Henyey-Greenstein (HG) and Anlı-Güngör (AG) phase functions. The critical half-thicknesses of the slab are performed with traditional spherical harmonics (PN) method for various values of the cross-section parameter, reflection coefficient and the scattering parameters of HG and AG phase functions. The numerical results obtained in case of using both HG and AG phase functions are tabulated in the tables and they are compared with each other.
Reassessment of external events in view of the Fukushima accident
Authors: Knochenhauer M. , Olofsson F. , Öhlin T.
Published: December 2013

As a consequence of the EU stress tests following the Fukushima NPP accident, the Nordic BWR Owners Group (NOG) initiated an analysis related to the capability of Swedish and Finnish BWR plants to withstand potential effects from external flooding and other extreme natural events. A review of existing analyses was performed with the intention to identify and reassess assumptions and simplifications made, and to judge whether all significant aspects of external events had been identified and considered. A previous NOG project dealing with methodologies for analyzing certain external events was used as a reference. Additional analyses were performed within three sub-projects addressing extreme water levels in the Baltic Sea and Skagerrak, methodology for the analysis of multiple external events, and main heat sink accessibility. It was concluded that the outcome from the previous NOG project can still be used as a basis, but some issues requiring further analysis were also identified.
Seismic fragility of a reinforced concrete structure
Authors: Kurmann D. , Proske D. , Cervenka J.
Published: December 2013

Structures can be exposed to seismic loading. For structures of major importance, extreme seismic loadings have to be considered. The proof of safety for such loadings requires sophisticated analysis. This paper introduces an analysis method which of course still includes simplifications, but yields to a far more realistic estimation of the seismic load bearing capacity of reinforced concrete structures compared to common methods. It is based on the development of pushover curves and the application of time-histories for the dynamic model to a representative harmonic oscillator. Dynamic parameters of the oscillator, such as modal mass and damping are computed using a soil-structure-interaction analysis. Based on the pushover-curve nonlinear force-deformation-capacities are applied to the oscillator including hysteresis behaviour characteristics. The oscillator is then exposed to time-histories of several earthquakes. Based on this computation the ductility is computed. The ductility can be scaled based upon the scaling of the time-histories. Since both, the uncertainty of the earthquake by using different time-histories and the uncertainty of the structure by using characteristic and mean material values, are considered, the uncertainty of the structure under seismic loading can be explicitly represented by a fragility.
Evaluation of radioactive emissions of lignite-fired power plants in Turkey using the Analytic Hierarchy Process
Authors: Büke T.
Published: December 2013

Radioactive emissions of 13 lignite-fired power plants in Turkey are of great concern to the public and to scientists alike. The purpose of this study is to evaluate these power plants, according to their radioactive emissions by using the Analytic Hierarchy Process. Control criteria are in particular 226Ra, 232Th, 40K and 238U emissions from the power plants. These control criteria are weighted according to the objective assessment. The calculations are repeated for three different objective assessments of control criteria namely the mortality risk coefficients for inhalation, ingestion, external exposure of 226Ra, 232Th, 40K and 238U. It has been calculated that the Çan lignite-fired power plant is ranking first while the Soma-B plant is ranking last according to the radioactive emissions of the power plants when the average of three different objective control criteria are used in the calculations.
Computational modeling of monoenergetic neutral particle inverse transport problems in slab geometry
Authors: Gomes R. R. , Barros R. C.
Published: December 2013

An analytical numerical method applied to three different types of monoenergetic neutral particle inverse transport problems in the discrete ordinates (SN) formulation is presented: (a) boundary condition estimation; (b) interior source estimation; and (c) effective slab length estimation. These three types of inverse problems governed by the linear integrodifferential transport equation in SN formulation are related respectively to medical physics; nuclear waste storage; and non-destructive testing in industry. Numerical results and a brief discussion are given to conclude the paper.
Thermal analysis of VWSB-IP1 at Tarapur
Authors: Verma V. , Singh R. K. , Vaze K. K.
Published: December 2013

High Level Liquid Radioactive Waste (HLLRW) produced during reprocessing of spent fuel from nuclear reactors is encased in the canisters after vitrification. The vitrified waste has high heat generation rate due to decay heat and needs interim storage under surveillance. The waste needs to be cooled continuously until major portion of the decay heat is dissipated. Natural circulation air cooling has been considered to cool the canisters. Canisters are placed in a storage vault and cooled by induced axial flow of air with the help of stack. The capacity of storage vault for Vitrified Waste Storage Block (VWSB) Facility proposed at Integrated Plant-1, Tarapur is designed for interim storage of waste generated of 30 yrs of IP1 plant operation. Canister and concrete temperature should be within the prescribed limit. Parametric studies have been carried out for the relevant parameters such as stack and duct dimensions, plenum height etc. Details canister temperature have been obtained using CFD code CFD-ACE+. Axial and radial temperature variation in the canisters, thimble and ventilation pipe have been evaluated in a location. Effect of natural convection (in air) within the canister and between thimble and canister is also studied. It was found that canister centerline temperature reduces by 20°C.
Fuel cycles of WWER-440: results of basic design modification
Authors: Saprykin V. V. , Yasnopolskaya I. I. , Novikov A. N. , Adeev V. A.
Published: December 2013

This paper presents the current status of works performed to date to further upgrade fuel assemblies and fuel cycle of WWER-440 reactors, and also considers some innovations – both envisaged and implemented in practice – intended to improve their neutronic and operating parameters. Reactors were assumed to operate at 100% power in a steady-state refueling mode. Trial operation of third-generation fuel assemblies (FA-3), including a comparison between some calculated and measured results, is described as an example illustrating these new developments.
CFD analysis of temperature deviations in Gd assembly heads
Authors: Tóth S. , Aszódi A.
Published: December 2013

A CFD model for the head part of the VVER-440 fuel assemblies with Gd burnable poison has been developed. Using this model calculations are performed for some recent Gd assemblies of the Paks NPP with the code ANSYS CFX. The temperature distributions in the assembly heads are determined and the in-core thermocouple signals are evaluated. The computed signals are compared to the in-core measured data of Paks NPP. The study shows that the deviations between the in-core thermocouple signals and the cross-sectional average temperatures at the measurement level depend on the burn-ups of the fuel assemblies. These deviations are significant in the cases of low burn-ups and negligible in the cases of higher burn-ups. This behavior is caused by the depletion of Gd from the three fuel rods near the assembly center.
Uncertainties of the neutronic calculations at core level determined by the KARATE code system and the KIKO3D code
Authors: Panka I. , Keresztúri A.
Published: December 2013

In this paper the uncertainties of the neutronic calculations at core level – originating from the uncertainties of the basic nuclear data – are presented. The investigations have been made for a VVER-1000 core (Kozloduy-6) defined in the frame of the OECD NEA UAM benchmark. In the first part of the paper, the uncertainties of the effective multiplication factor, the assembly-wise radial power distribution, the axial power distribution and the rod worth are shown. After that the preliminary evaluation of the uncertainties of the neutron kinetic calculations are presented for a rod movement transient at HZP (Hot Zero Power) state, where the uncertainties of the time dependent core and assembly powers and the dynamic reactivity were evaluated. In both cases, we will see that the most important quantities –at core level and at HZP state – have a considerable uncertainty which is originating from the uncertainties of the basic cross section library in these investigations.
Comparison of sensitivity and uncertainty in Gd and Er containing fuels for VVER-1000 using TSUNAMI-2D
Authors: Frýbort J.
Published: December 2013

Computer calculations important for safe operation of nuclear reactors are inherently affected by uncertainties. These originate mostly in numerical method applied, the calculated system model developed by the user, and finally there are fundamental uncertainties in nuclear data. This analysis is aimed at comparison of uncertainties in nuclear data affecting model of VVER-1000 fuel assembly containing either gadolinium or erbium as a burnable absorber using TSUNAMI-2D. This tool for quantitative determination of nuclear data uncertainties is being developed in Oak Ridge National Laboratory (USA). This tool works with 1D and 2D deterministic calculations and 3D Monte-Carlo calculations and processes the results. Output of the calculation is a complete characterization of the solved system with an overall uncertainty of multiplication factor determination. Furthermore, different system responses can be defined (e.g. pin power peaking) and their sensitivity to nuclear data in dependence on neutron energy is determined.
The impact on the competence on severe accidents following the Fukushima event
Authors: Band S. , Schaffrath A. , Sonnenkalb M. , Weiß F.-P.
Published: December 2013

Fukushima related questions are currently being addressed at Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH within several research projects funded by the Federal Ministry for Environment, Nature Conservation and Nuclear Safety (BMU) and Federal Ministry of Economics (BMWi). In the following section first results of selected issues are presented.
On the creep resistance in cast Ni-base superalloys
Authors: Yuan C. , Guo J. T.
Published: December 2013

In this paper, we attempt to apply the modified hardening theory to estimate the creep resistance, which is considered as a key factor for controlling the creep deformation mechanism in cast nickel-base superalloys. It is suggested that, when the applied stress is high enough for the dislocations to cut into the γ′ particles, the creep resistance is almost a constant and independent of applied stress. At low applied stress, creep deformation is mainly controlled by dislocations climb, where the creep resistance has two components of a threshold stress and a friction stress. The model is verified for two cast nickel-base superalloys DZ17G and IN738. The results of detailed calculations are in good agreement with the experimental data.
Formation, stability, and presence of magnesium nitride in magnesium recycling processes
Authors: Bauer Christoph , Mogessie Aberra , Galovsky Ulrike
Published: December 2013

In this study an attempt has been made to identify analytical methods for detecting magnesium nitride, and document in which part of the magnesium recycling process this phase is concentrated. The samples were taken from a continuous fluxfree recycling session, where an AZ91D magnesium alloy was remelted and purified by blowing nitrogen through the melt. Exothermic reactions took place when magnesium nitride reacted to ammonia and Brucite and also when aluminium nitride reacted to ammonia and Gibbsite in a moisture-bearing environment. Because of this, it was essential to avoid any contact with moisture during the whole sampling and preparation process. The samples were exclusively handled in an argon atmosphere. Due to their crystallinity and Raman activity the nitrides were detected with X-ray diffraction and Raman spectroscopy, respectively. With the scanning electron microscope it was difficult to analyze small concentrations of nitrides since large, stable crystals were absent and the carbon coating absorbs the nitrogen Kα line.

The Mg-alloy was found to be free of impurities. Although nitrides were expected to be concentrated in the slag because of their greater density, they were found adhering at the nitrogen bubbles and accumulating in the dross. Large amounts of oxides were concentrated in the slag.
From waste to high strength alloy – recycling of magnesium chips
Authors: Lu L. , Lai M. O. , Lim S. H. , Chua B. W. , Yan C. , Ye L.
Published: December 2013

Ultrafine grained magnesium alloy was synthesized via mechanical milling of AZ91 chips. Mechanical property measurement revealed enhanced yield strength of 470 MPa after mechanical milling. The increase in yield strength is associated with reduction in grain size which restricts twining and dislocation gliding. The present investigation demonstrates that magnesium alloys can be cost-effectively recycled through the process of mechanical milling.
Liquid–liquid transition in elemental liquids investigated by sound velocity measurements: trends in the periodic table
Authors: Tsuchiya Y.
Published: December 2013

The velocity of sound has been measured as a function of temperature to investigate structural changes in the molten As–Sb alloy. The overall profile of temperature dependence of the sound velocity changes smoothly from Sb to As. The results indicate that a tendency to change structures in the supercooled state develops with increasing As fraction, and confirm the previous conclusion that molten As changes rapidly its structure in the undercooled state and is already in the high-temperature side of an assumed liquid–liquid transition at the melting point.
Bulk and surface properties of liquid Ga–Tl and Zn–Cd alloys
Authors: Akinlade O. , Awe O. E.
Published: December 2013

A simple thermodynamic model, based on the formation of self-associates, has been used to correlate the bulk and surface properties of mixing of liquid Ga–Tl and Zn–Cd alloys at temperatures of 973K and 900K, respectively. The model enables us to explain the positive deviation of the properties of mixing of the two liquid alloys from the ideal solution behavior. Our calculations indicate that the degree of phase separation in Zn–Cd, as measured using the Warren–Cowley short-range order parameter, is less than that in Ga–Tl. With regards to the surface, we show that the surface decomposition in Zn–Cd liquid alloys is greater than in Ga–Tl. We explain the contrast in the bulk and surface properties in terms of the possible roles of the entropic and enthalpic effects on the properties of mixing.
Fragility, kinetic stability and phase separations in the undercooled state of bulk glass formers – a case study on metallic model systems
Authors: Wilde Gerhard , Madge Shantanu V.
Published: December 2013

Several Pd-base alloys display a large tendency for glass formation that renders them especially suitable for investigations concerning (metastable) equilibrium properties of the deeply undercooled liquid including the glass transition, since the detrimental interference of premature crystallization can be avoided rather easily compared to other alloy systems. Here, thermodynamic, dynamic, and transport properties were analysed and compared to an Al-rich marginal glass former in the context of a possible relation between fragility, thermodynamic excess and kinetic stability against crystallization. Additionally, the possibility for liquid-phase separation occurring in the undercooled state of bulk glass-forming alloys is analysed as a function of thermal history, and critically discussed with respect of alternative mechanisms that are often summarized as ‘short-range ordering’.
Isothermal crystallization behavior of undercooled liquid Pd40Cu30Ni10P20 in terms of crystal growth, overall volume crystallization kinetics and their relation to the viscosity temperature dependence
Authors: Russew Krassimir , Stojanova Liljana , Kovacheva Rositza
Published: December 2013

The crystallization behavior of undercooled liquid Pd40Cu30Ni10P20 metallic alloy has been studied with the aid of differential scanning calorimetry, optical metallography, and electron microscopy methods. The crystallization occurs as a single-stage process starting preferably on the surface of casting voids in the sample volume and on the outer sample cutting planes. The linear crystal growth velocity of crystallizing cells was measured at several constant temperatures in the range 590–620 K. It is constant at constant temperatures and its temperature dependence is in good agreement with the theoretical concepts of Uhlmann using the temperature dependence of the viscosity of the alloy studied. A differential scanning calorimetry study of isothermal overall volume transformation kinetics of samples pre-annealed at 600K for 600s was carried out at several constant temperatures. The experimental data are interpreted on the basis of the equation of Kolmogorov-Avrami-Johnson-Mehl for the case of three-dimensional growth of a fixed number of pre-existing nuclei. The possibility to re-vitrify the crystallized samples by their melting in differential scanning calorimeter, followed by quick cooling with cooling rate of 5Ks−1 is shown. The volume transformation kinetics of revitrified samples has been also studied.
The magnesium-ytterbium system: A contribution to the thermodynamics of solid alloys
Authors: Borzone Gabriella , Parodi Nadia , Ferro Riccardo
Published: December 2013

Magnesium-ytterbium alloys were investigated in order to determine the enthalpy of formation of YbMg2 and to check the phase diagram of the system. The system was investigated by using differential scanning calorimetry, electron microscopy, electron microprobe analysis, and X-ray diffraction analysis. The enthalpy of formation was measured by high temperature drop calorimetry. A value of −13.5 ± 0.5kJ/mol of atoms was obtained for the standard formation enthalpy of YbMg2.
Twinning in ultrathin silicon nanowires
Authors: Zhan Jinhua , Bando Yoshio , Hu Junqing , Golberg Dmitri
Published: December 2013

Galium nanodroplets induced the anisotropic growth of ultrathin (diameter (<5nm) silicon nanowires in accordance with the vapor-liquid-solid (VLS) mechanism. X-ray diffraction and dispersion spectroscopy, and scanning, and transmission electron microscopy (TEM) were used to characterize the product. High-resolution TEM analysis revealed the existence of twins in the nanowires. In contrast to the theoretically predicated 5-fold twinning in ultrathin Si nanowires (diameter (<6nm), no twinning on the {111} planes along the wire axial directions was observed. The possible reasons for the formation of novel nanostructures are discussed.
Enthalpies of formation measurements and thermodynamic description of the Ag–Cu–Zn system
Authors: Witusiewicz Victor T. , Fries Suzana G. , Hecht Ulrike , Drevermann Anne , Rex Stephan
Published: December 2013

The enthalpies of formation of β and γ alloys of the Ag–Cu–Zn system were determined by dissolution calorimetry. The melting and solid-state transformation temperatures as well as the enthalpies of the order/disorder and β/χ transformations were measured by differential scanning calorimetry. Thermodynamic descriptions are presented for the binary Ag–Zn system and for the ternary Ag–Cu–Zn system in the entire composition ranges. The thermodynamic model parameters of the constituent binaries Ag–Cu and Cu–Zn are taken from earlier assessments. Those for Ag–Zn and the Ag–Cu–Zn system are established based on relevant experimental data available in the literature completed with experimental data obtained in the present work. Several vertical and isothermal sections as well as the liquidus surface and thermodynamic properties are calculated using the evaluated parameters and show reasonably good agreement with experimental data available.
Subsolidus phase equilibria in the CeO2−x–SiO2–ZrO2 system: An experimental study
Authors: Zec Slavica , Bošković Snežvana , Popovic Nada , Bogdanov Žvarko
Published: December 2013

The phase equilibria in the CeO2–x–SiO2–ZrO2 system were studied in the subsolidus region in argon atmosphere, under isothermal heating and hot pressing, at 1400°C, different ceria, silica, and zirconia mixtures. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were performed to identify phases and to establish phase equilibria. Based on the results of many preliminarily investigated ternary compositions, possible tie lines are predicted. Compositions from the proposed tie lines were successively fired and ground until the changes of the phase compositions were not detected or were low enough to be neglected. Phases identified in these compositions confirmed the existence of five tie lines: Ce2Si2O7–ZrSiO4, Ce2Si2O7–ZrO2, Ce4.67(SiO4)3O–ZrO2, Ce4.67(SiO4)3O–Ce2Zr2O7 and Ce2SiO5–Ce2Zr2O7, which divide the CeO2–x–SiO2–ZrO2 composition triangle into six compatibility triangles. The formation of ternary compounds or ternary solid solutions in the CeO2–x–SiO2–ZrO2 system was not observed. The monoclinic high temperature polymorph of Ce2Si2O7 was detected. The cubic pyrochlore phases had different lattice parameters, caused by incomplete reduction of the tetravalent cerium ions also observed in the non-stoichiometric cerium oxide.
Thermal evolution of free volumes and of crystallization in amorphous Si–B–C–N ceramics
Authors: Reichle Klaus J. , Reimann Klaus , Sprengel Wolfgang , Rempel Andrej A. , Müller Anita , Schaefer Hans-Eckhardt
Published: December 2013

We report on the crystallization behavior of initially amorphous precursor-derived Si3B1C4.3N2 ceramics, making use of macroscopic and atomic scale investigation techniques. As derived from our kinetic studies upon heating, the following temperature sequence of solid state processes is observed with approximately the same kinetic time constants: after an initial densification in the amorphous state (1673K), crystallization occurs (1873K) with subsequent strain relaxation and disappearance of nanovoids (2073K). This behavior indicates an increasing activation enthalpy of the atomic mechanisms giving rise to these processes when the annealing temperature is increased. The nanovoids may be located in the turbostratic BNCx layers as derived from positron annihilation studies. For grain growth at high temperatures an activation energy of HG=3.9eV is derived.
Nanopowder dispersion and spray-drying process: the case of Cr2O3
Authors: Cellard Audrey , Zenati Rachid , Garnier Vincent , Fantozzi Gilbert , Baret Guy
Published: December 2013

The work reported in this paper was performed in order to develop and to optimize the dispersion of Cr2O3 nanopowders by a ball-milling method and to produce spherical micrometer-sized granules by spray-drying. The targeted application for such granules is the development of wear resistant nanostructured Cr2O3 coatings by plasma spraying. Cr2O3 nanopowders were dispersed in deionized water. The suitable dispersant (DarvanC) was determined by zeta potential measurements and the dispersant quantity was optimized by rheological tests. The influence of milling time, diameter of milling balls and weight ratio of milling balls to powder was studied by granulometric measurements. A well-dispersed and stable suspension was then obtained and spray-dried. Dense and spherical micrometer-sized granules, with a monodispersed distribution centered about 50μm, have been achieved and Cr2O3 plasma-sprayed coatings have been realized.
The role of chemisorbed anions in the aqueous processing of AlN powder
Authors: Krnel Kristoffer , Kosmačv Tomažv
Published: December 2013

In the production of ceramics containing AlN it is necessary to prevent the AlN powder from reacting with water. To do that, non-aqueous powder processing is required or water-resistant AlN powders must be used. Alternatively, as in the Hydrolysis Assisted Solidification process, which exploits the hydrolysis of AlN for the solidification of the ceramic suspensions, the hydrolysis has to be prevented at room temperature but initiated at elevated temperatures. In this study the role of the chemisorbed anions in the hydrolysis of the AlN was investigated in order to make the control of the hydrolysis reactions possible. The method for preparing water-resistant, hydrophilic AlN powder using the dispersion of the powder in a solution of aluminium dihydrogen phosphate is also presented. The mechanism leading to the formation of the protective surface layer is proposed and explained. The method was also successfully tested on nanosized AlN powder. This powder was processed in water and sintered to high density.
Development of high-temperature thermoelectric materials based on SrTiO3-layered perovskites
Authors: Wunderlich Wilfried , Koumoto Kunihito
Published: December 2013

For improving the performance of ceramic thermoelectric materials an increase in the effective mass is required because it is the main factor determining the Seebeck coefficient, in the case of a semiconductor with sufficiently high carrier concentration. The Ruddlesden–Popper phase Sr3Ti2O7, with its conducting perovskites layer in between the phonon absorbing SrO layers, is an example for advanced material design by nano-block integration. Using ab-initio simulations, the electronic bandstructure was calculated, and from the curvature of the bands the effective mass was deduced. While Sr3Ti2O7 has a smaller effective mass than the Nb-doped SrTiO3, the layered perovskites with substitution of Ta instead of Ti possess very large effective masses (m*/m0=9 in average) and a large thermopower is expected. In the experiments, however, the sufficient charge carrier concentration could not yet be reached.
The influence of the preparation method on the microstructure and properties of Al2O3/TiN nanocomposites
Authors: Gao Lian , Jin Xihai , Li Jingguo , Sun Jing
Published: December 2013

Al2O3/TiN nanocomposites were fabricated by hot pressing of powders prepared through ball milling (BM) and in-situ nitridation (PN) methods, respectively. And the mechanical and electrical properties as well as microstructure of the nanocomposites were studied. It was found that TiN showed a strong reinforcing effect in both materials. Due to the difference in the powder preparation method, the Al2O3/TiN nanocomposite from PN powder showed a finer TiN particle size and a more uniform microstructure than the nanocomposite from BM powder. As a result, the former material showed a superior electrical conducting behavior and better mechanical properties.
Quasi-equilibrium sintering of particle clusters containing Bernal holes
Authors: Wakai Fumihiro , Shinoda Yutaka , Akatsu Takashi
Published: December 2013

The transformation of spherical particle assemblies into dense materials by sintering is an idealized micromechanical model for studying the densification. The equilibrium configurations of particle clusters containing canonical Bernal holes, which are typical structural units in random packing of spheres, were calculated by using the Surface Evolver program. The quasi-equilibrium sintering of particle clusters, in which pores shrink keeping their equilibrium shapes, were analyzed as a response to the sintering stress and the macroscopic viscosity. Both sintering stress and macroscopic viscosity were determined as a function of the pore volume, the dihedral angle, and the pore coordination number. The densification curves in sintering simulation agreed with the predicted shrinkage rate.
Microstructure and mechanical behavior of Pt-modified NiAl diffusion coatings
Authors: Riethmueller J. , Dehm G. , Affeldt E. E. , Arzt E.
Published: December 2013

The performance of thermal barrier coatings (TBCs) in jet engines is strongly influenced by thermal and mechanical properties of the bond coat. In this investigation two different types of Pt-modified diffusion coatings developed for application as oxidation protection or as a bond coat in TBC systems were studied with respect to their microstructure and mechanical properties. The microstructural analyses based on different microscopy techniques and X-ray diffraction measurements revealed distinct differences between the two coatings: the coating aluminized by a gas phase process consisted solely of a (NiPt)Al phase, while the coating fabricated by pack-cementation consisted mainly of the two phases (NiPt)Al and Al2Pt, leading to a higher strength in comparison with the single-phase coating. In contrast, the ductility determined with 3-point bend tests between room temperature and 700°C was clearly better for the single-phase coating. Additionally, the substrate curvature of coated sheets was measured to gain some information about coating stresses.
Thermodynamic assessment of the Ce–O system in solid state from 60 to 67mol.% O
Authors: Seifert Hans Jürgen , Nerikar Pankaj , Lukas Hans Leo
Published: December 2013

A thermodynamic dataset was developed for the central part of the Ce–O system covering the range between CeO and CeO up to about 2000K. All literature data for the thermodynamic functions, the phase diagram and crystallography were critically assessed. The modeling of the phases takes into account their crystal chemistry including order–disorder behavior. From the dataset, diagrams were calculated for the (1) heat capacities of CeO and CeO, (2) enthalpy increment of CeO, (3) chemical potentials of oxygen in CeO, (4) partial enthalpies of oxygen in CeO, (5) the partial phase diagram of Ce–O and (6) chemical potentials of oxygen in the two-phase areas. These diagrams reproduce fairly well the experimental data from literature.
Phase transformations of iron nitrides at low temperatures (<700 K) – application of mechanical mixtures of powders of nitrides and iron
Authors: Leineweber Andreas , Aufrecht Jochen , Mittemeijer Eric Jan
Published: December 2013

Annealing at low temperatures (T<670K) of mixtures of iron nitride powders and iron powder is shown to induce phase transformations through nitrogen transfer between different powder particles. This nitrogen transfer occurs via loose mechanical contact points between different powder particles; nitrogen transport via the gas phase can be excluded. Unique scientific possibilities offered by this type of phase transformation studies are discussed.
Reconstruction and structural transition at metal/diamond interfaces
Authors: Zhang Wenqing
Published: December 2013

Based on density-functional calculations, interfacial reconstruction and structural transition at diamond(111)/M/copper (M = Ag, Cu, Ni, Co) interfaces are studied by analyzing the atomistic structures of the interfaces. Tuning the strength of chemical bonds across the interfacial plane (out-of-plane), we show that interfacial reconstruction happens as a result of competition between the out-of-plane chemical bonds and the in-plane bonds within the diamond substrate. A relatively weak out-of-plane bond may easily lead to reconstruction of interfacial structures. A structural transition from one-dangling-bond- to three-dangling-bond-terminated interface is also observed as the out-of-plane bond is sufficiently strong, which leads to a dramatic enhancement of the adhesion of the interface.
Aqueous solution deposition of indium hydroxide and indium oxide columnar type thin films
Authors: Qiu Yu , Gerstel Peter , Jiang Linqin , Lipowsky Peter , Bauermann Luciana Pitta , Bill Joachim
Published: December 2013

Crystalline In(OH)3 and UV-emitting In2O3 thin films with a unique columnar morphology have been successfully prepared for the first time via a simple aqueous solution deposition method. In the present study, sulfonate-terminated self-assembled monolayers on single-crystal Si wafers were used as substrates for the film deposition. Uniform In(OH)3 thin films formed on self-assembled monolayers in aqueous solutions of InCl3.4H2O at 60°C. These films, containing columnar In(OH)3 crystals, showed preferential growth orientation along the [100] direction. The current understanding of the film formation mechanism was discussed. After annealing in air at 400°C, these films were converted to nanocrystalline In2O3 films without modification of the morphology. Photoluminescence emission from In2O3 films was reported at approximately 3.4eV, which was ascribed to the near-band-edge emission.
On the mechanisms governing the texture and microstructure evolution during static recrystallization and grain growth of low alloyed zirconium sheets (Zr702)
Authors: Dewobroto N. , Bozzolo N. , Barberis P. , Wagner F.
Published: December 2013

Low alloyed zirconium sheets (Zr702) have been cold-rolled up to 80% thickness reduction and submitted to various isothermal treatments. The aim was to identify the mechanisms which produce microstructure and texture changes during recrystallization and grain growth. XRD and texture analysis, FEG–SEM with EBSD as well as TEM were used to analyze the various specimens. Three types of substructures were observed in the initial deformed material. Accordingly, the nucleation starts in the most deformed areas and continues in the somewhat less deformed areas, which corresponds to a non oriented nucleation and results in a set of new grains, the size of which is very rapidly stabilized. In the last stage of recrystallization, the grains which have resisted the recrystallization disappear progressively by several mechanisms including in situ recrystallization. Therefore, the texture at the end of the recrystallization resembles the one of the deformed state. Normal grain growth leads to a moderate grain size increase due to the precipitates which slow down the grain boundary motion. This is also the stage where the texture changes due to the size advantage, after recrystallization, of grains in some specific orientations.
Sintering of Si3N4 with Li-exchanged zeolite additive
Authors: Matovic B. , Rixecker G. , Boskovic S. , Aldinger F.
Published: December 2013

This paper deals with the densification and phase transformation of Si3N4 with additives of Li-exchanged zeolite during pressureless sintering at significantly reduced temperatures. Dilatometric shrinkage data show that the first liquid forms as low as 1080°C. Upon sintering at 1500°C the bulk density increases to more than 95% of the theoretical density without phase transformation from -S3N4 to -Si3N4, i.e. the phase transformation lags behind the densification process. Above 1500°C the secondary phase is completely converted into a glass and the -to- transformation takes place. Under these conditions the grain growth is anisotropic, leading to a microstructure which has potential for enhanced fracture toughness. The results show that a very effective low-temperature sintering additive for silicon nitride can be obtained from Li-exchanged zeolite.