Thermodynamic properties of the NdBr3–MBr binary systems (M = Na,K)

Thixoforming involves heating different types of alloys to the semisolid state at high heating rates and forming in die-casting machines or conventional presses. At temperatures higher than the solidus and lower than the liquidus, the mush metal behaves like a high-viscosity thixotropic material. Therefore, determining the thermodynamic behavior of the solid-to-liquid transition is paramount to control thixoforming processes. This article describes a simple, novel experimental setup based on differential thermal analysis (DTA) for analyzing the phase transitions in an alloy heated using high heating rates typical of industrial applications. A365 alloy was chosen to demonstrate the effectiveness of the method as the phase transformations for this alloy in semisolid materials (SSM) processing are well understood. Samples were heated to 750 °C using constant linear heating rates of 5, 10, 15, 20, 25, 50, 75, 100 and 125 °C min in a Norax 25 kW 8 kHz induction furnace with an Omron E5CK temperature controller. AISI 316 austenitic stainless steel was used as the inert reference. Comparison of the results of DTA using the proposed method and the results of simulation with Thermo-Calc^® indicates that the proposed in situ DTA device and its method is suitable for analyzing phase transitions when high heating rates are used.     

Development of a high temperature treatment device for spent nuclear fuel

Novel reprocessing schemes and techniques are the focus of the Euratom FP7 project “Actinide Recycling for Separation and Transmutation” (ACSEPT), where the Paul Scherrer Institute (PSI) is represented in the pyrochemical domain. The subject of investigation is the selective separation of fission products (FPs) from spent nuclear fuel as a head-end step to either classical hydro based or pyro processes which are not yet applied on a large scale. The selective removal of FPs that are major contributors to the overall radiation dose or bear great potentials in terms of radiotoxicity (i.e. cesium or iodine), is advantageous for further processes. At PSI a device was developed to release volatile FPs by means of inductive heating. The heating up to 2,300 °C promotes the release of material that is further transported by a carrier gas stream into an inductively coupled plasma mass spectrometer for online detection. The carrier gas can be either inert (Ar) or can contain reducing or oxidizing components like hydrogen or oxygen, respectively. The development of the device by computer aided engineering approaches, the commissioning and evaluation of the device and data from first release experiments on a simulated fuel matrix are discussed.     

Dilatometry as a tool to study a new synthesis for calcium hexaluminate

By using a wet chemical route, pure calcium hexaluminate (CA₆) was yielded, significantly lowering the reaction temperature and shortening the synthesis time if compared to usual industrial procedures. owever, dilatometric studies performed on compacts made of the as-prepared powder, just after pre-heating at 450°C, has shown a superposition between sintering shrinkage and expansion related to CA₂ formation, an intermediate phase formed during calcination and phase evolution to CA₆. oupling of such opposite phenomena led to microcracking of the material, mainly if the heating rates (10°C min^-1) were high. However, lower heating rates (1-5°C min^-1) could quite avoid microcracking but also limit densification. This revised version was published online in July 2006 with corrections to the Cover Date.     

Laser experiments in a scanning electron microscope

In order to increase the information content of electron microscopic investigations a scanning electron microscope was combined with a pulsed Nd-glass laser in both the free running and the Q-switch mode. The equipment allows an in situ observation of melting, sintering and evaporation processes as well as of crack generation and growth at target surfaces. This article describes evaporation experiments for laser PVD of HTSC layers, Langmuir probe measurements in the corresponding plasma and crack processes by thermal shock loading in the SEM.     

Application of a fast X-ray diffraction method for studies of high temperature corrosion of steel surfaces

Summary A fast X-ray diffraction method was applied in order to study in situ high temperature corrosion of steel surfaces. The measuring system for high temperature corrosion testing consists of an X-ray diffractometer, a high temperature device with programmable temperature controller and a Si(Li)-detector for measurements of energy dispersive diffraction spectra at temperatures from 20 to 1500°C. With a measuring time of 100 s per diffraction pattern a series of 300 measurements can be performed during one day. The atmosphere in the high temperature device can be controlled. The samples were heated in air at ambient pressure, recording X-ray diffraction spectra every 20°C. In addition, isothermal experiments were carried out at different temperatures. From the diffraction spectra the peak intensities, lattice plane distances and lattice parameters of the base material and the oxides were calculated as a function of temperature or time. The method allows an in situ identification of the corrosion products and a direct observation of phase transitions.     

Mechanical properties of anodized coatings over molten aluminum alloy

A method to measure interfacial mechanical properties at high temperatures and in a controlled atmosphere has been developed to study anodized aluminum surface coatings at temperatures where the interior aluminum alloy is molten. This is the first time that the coating strength has been studied under these conditions. We have investigated the effects of ambient atmosphere, temperature, and surface finish on coating strength for samples of aluminum alloy 7075. Surprisingly, the effective Young's modulus or strength of the coating when tested in air was twice as high as when samples were tested in an inert nitrogen or argon atmosphere. Additionally, the effective Young's modulus of the anodized coating increased with temperature in an air atmosphere but was independent of temperature in an inert atmosphere. The effect of surface finish was also examined. Sandblasting the surface prior to anodization was found to increase the strength of the anodized coating with the greatest enhancement noted for a nitrogen atmosphere. Machining marks were not found to significantly affect the strength.     

The effect of the sintering atmosphere on the densification of B4C ceramics

Densification of boron carbide during sintering may be improved by a two-stage process, namely heating to 2000°C under vacuum and sintering at 2190°C under argon. This sintering regime allows achieving a relative density of the ceramic bodies fabricated from a fine powder higher than 95%. The nitrogen treatment of the boron carbide phase at 1900°C leads to the formation of the BN phase and precipitation of graphite. Vacuum treatment of these samples at 2000°C leads to decomposition of the boron nitride phase. The liberated free boron may again react with graphite to form in situ boron carbide particles. The experimental investigations of the sintering behavior of the boron carbide phase under various atmospheres supported the thermodynamic predictions regarding the phase transformation. No evidence, however, was found for enhanced sintering under a nitrogen atmosphere.     

Preheating and heat addition by LASER beam in hybrid LASER-ultrasonic welding

Heating during welding in electronics is limited because of the high difference between the properties of the components that are in the close neighbourhood of the welding area. The temperature should not exceed 240 °C. In the classic processes of soldering, depending on the soldering alloy types, the heat is up to 300 °C. Such temperature is producing thermal degradation of the neighbouring polymers. New hybrid heating process is proposed within the paper. A double source laser-ultrasonic vibration could be used as thermal source. Because of the concentration of the heat source, the duration of the process is sensitively reduced in time (from minutes down to 5–10 s). More, applying the heat in two sequences, a preheating of the base material can be done and the result is a decreasing of the hardness with about 10–15 %, so a decreasing of the brittleness is happening. After the preheating, the processing heating is applied. The thermal field was analysed and specific mathematical models of the field were built. The temperature of the process was reduced down to about 130–150 °C. A comparison between laser heating and hybrid laser-ultrasonic heating, from the thermal field point of view, is presented within the paper.     

The study on microstructure and electrochemical properties of Al–Mg–Sn–Ga–Pb alloy anode material for Al/AgO battery

The microstructure of Al–Mg–Sn–Ga–Pb quinary aluminum alloy anode material and the influences of its electrochemical properties and self-corrosion rate in 4 mol/l NaOH +10 g/l Na₂SnO₃ medium were studied. The microstructure and morphology were characterized by metallographic microscope, transmission electron microscope, and scanning electron microscopy. The electrochemical properties were tested by electrochemical workstation, and the self-corrosion rate of Al alloy anode was studied by methods of recovery H₂ gas by discharge water. The results show that homogenization has not much impact on the electrochemical properties and the corrosion rate of the cast aluminum alloy anode material; besides, return annealing treatment of the cold-rolled Al–Mg–Sn–Ga–Pb quinary aluminum alloy anode material can reduce the rate of self-corrosion and make Al anodic potential shift negative steadily and improve the properties of the material.

     

Simulation of the densification of semicrystalline polymer powders during the selective laser sintering process: Application to Nylon 12

The processes of heating and densification of semicrystalline polymer powders during the selective laser sintering process are simulated using the finite element method. Based on a previously developed three-dimensional approach for the sintering of amorphous polymer powders, the modeling methodology is extended to semicrystalline polymers by taking into account the effects of latent heat during melting. In these simulations, the temperature-dependent thermal conductivity, the specific heat, the density, and the effect of latent heat are computed and then used as material constants for the integration of the heat equation. Results for the temperature and density distribution using Nylon-12 powder are presented and discussed. The effects of processing parameters on the density distribution are also presented. Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 6, pp. 1067–1073. This article was submitted by the authors in English.     

Effect of Microwave and Conventional Modes of Heating on Sintering Behavior,Microstructural Evolution and Mechanical Properties of Al-Cu-Mn Alloys

In this research, we intended to examine the effect of heating mode on the densification, microstructure, mechanical properties, and corrosion resistance of sintered aluminum alloys. The compacts were sintered in conventional (radiation-heated) and microwave (2.45 GHz, multimode) sintering furnaces followed by aging. Detailed analysis of the final sintered aluminum alloys was done using optical and scanning electron microscopes. The observations revealed that the microwave sintered sample has a relatively finer microstructure compared to its conventionally sintered counterparts. The experimental results also show that microwave sintered alloy has the best mechanical properties over conventionally sintered compacts. Similarly, the microwave sintered samples showed better corrosion resistance than conventionally sintered ones.     

Advanced sedex ( nsitive etector of othermic processes)

The instrument described is suitable for the investigation of the thermal behaviour of substances and reaction mixtures under production conformable conditions; this is made possible by the sophisticated design of the sample chamber: easy stirring of the samples, measuring under any gas atmosphere and while bubbling gas through the sample, choice of the sample container and visual observation during the measurement. The control device allows the choice of one of three operational modes: constant temperature, linear increase in temperature, and adiabatic control; this permits the application of the SEDEX apparatus for a variety of methods including dynamic scanning, isoperibolic measurements, and (quasi) adiabatic studies.     

Advanced sedex (sensitive detector of exothermic processes)

The instrument described is suitable for the investigation of the thermal behaviour of substances and reaction mixtures under production conformable conditions; this is made possible by the sophisticated design of the sample chamber: easy stirring of the samples, measuring under any gas atmosphere and while bubbling gas through the sample, choice of the sample container and visual observation during the measurement. The control device allows the choice of one of three operational modes: constant temperature, linear increase in temperature, and adiabatic control; this permits the application of the SEDEX apparatus for a variety of methods including dynamic scanning, isoperibolic measurements, and (quasi) adiabatic studies.     

Development of a voltage-applicable heating specimen holder for in situ observations of solid oxide fuel cells with an environmental transmission electron microscope

A voltage-applicable heating specimen holder is developed to observe solid oxide fuel cells (SOFCs) in an environmental transmission electron microscope. An SOFC specimen can be heated and has a voltage applied in an oxygen gas atmosphere using the holder. Oxygen ion migration and redox reactions in the specimen could also be realized. The heating unit, which consists of nickel–chromium alloy mounted on the tip of the developed specimen holder, can heat the specimen up to 1200 K in an oxygen gas atmosphere. A specimen preparation method for the SOFC structure is also established using a focused ion beam technique. The holder has high stability for high-resolution imaging and electron energy loss spectroscopy under the in situ condition. The mechanical and electrical stabilities are estimated from high-resolution images and electron energy loss spectra of the heated and voltage-applied specimen in an oxygen gas atmosphere. The developed holder is a powerful tool to reveal the microstructural and electronic structural changes that occur by electrochemical reactions at the interfaces of an SOFC.     

Corrosion fatigue on 2024T3 and 6056T4 aluminum alloys

Fatigue corrosion phenomenon is a form of degradation that is because of the combined occurrence of a mechanical cyclical stress and a corrosive environment. Fatigue corrosion can be an issue in commercial and military aircraft, and has the potential to affect the structural integrity and the useful life of an aerostructure. Although the distinct consequences of both fatigue and corrosion have been extensively documented for aluminum alloys, their synergistic action is not completely understood and continues to be an area of considerable scientific and industrial interest. In this paper, a novel approach is proposed and applied for monitoring the electrochemical behavior of different types of aluminum alloy samples while they are subjected to fatigue loading. Cyclic load experiments were conducted on bare 2024T3 and 6056T4 aluminum alloy samples in the presence of an aggressive aerated solution of 3.5% NaCl over a range of frequencies. The R‐ratio was 0. Two different aluminum alloys have been tested in both high‐ and low‐cycle fatigue. In the former case, the maximum stress experienced by the specimen is lower than the material yield strength, which means that the average expected number of cycles to failure is high; in the latter case, the maximum stress experienced by the specimen during the test is higher than the material yield strength, which means that the average expected number of cycles to failure is low. The open circuit potential(OCP) was monitored versus time during the tests described above. The observed OCP variations are interpreted as the occurrence of corrosion during crack initiation and propagation at the air formed oxide/solution interface film. As expected, there is a more pronounced influence of corrosion at lower fatigue frequencies. Crack propagation allows bulk material to be progressively more exposed to the aggressive environment, which stimulates accelerated crack propagation, resulting in a lower fatigue resistance. Copyright © 2010 John Wiley & Sons, Ltd.     

Monte-Carlo model for the hydrogenation of alkenes on metal catalyst

A Monte-Carlo model for the simulation of alkene hydrogenation on metallic catalysts has been developed and implemented in Fortran language. We describe the model employed for ethylene hydrogenation on platinum and show the flow chart of the program. Computational characteristics such as number of necessary calculations to reach steady state, running times on different platforms, and effect of the size of the catalyst matrix, are presented. Good correlation between simulated and experimental data was observed. A subroutine allows for visual observation of the reaction. This approach is very useful for obtaining a personal impression of the important factors governing the reaction. By using this example the advantages of Monte-Carlo simulation to test the level of understanding of catalytic phenomena are discussed. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 396–403, 1998     

A Thermal Decomposition Study of Individual and Co-Precipitated Y, Ba and Cu Oxalates

Y-Ba-Cu oxalate powder with a presumed Y:Ba:Cu molar ratio of 1:2:4 was prepared by a modified co-precipitation method and its solid-phase thermal decomposition was studied from 25 to 1000°C, the major evolved gases being H₂O and CO₂. The air-dried powder contained residual moisture. It required isothermal heat treatment for elimination of the evolved gases. The melting point of the co-precipitation Y-Ba-Cu oxalate powder, determined by DSC at a heating rate of 10°C min⁻¹ was approximately 882°C in N₂, 949°C in air and about 979°C in O₂. The dependence of the sintering properties of this material upon the atmosphere and the temperature is considered. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of Gas Type on the Thermal Efficiency of Microwave Plasmas for the Sintering of Metal Powders

Microwave plasmas have enormous potential as a rapid and energy efficient sintering technology. This paper evaluates the influence of both plasma atmosphere and metal powder type on the sintering temperatures achieved and the properties of the sintered powder metal compacts. The sintering is carried out using a 2.45 GHz microwave-plasma process called rapid discharge sintering (RDS). The sintering of three types of metal powder are evaluated in this study: nickel (Ni), copper (Cu) and 316L stainless steel (SS). An in-depth study of the effects of the plasma processing parameters on the sintered powder compacts are investigated. These parameters are correlated with the mechanical performance of the sintered compacts to help understand the effect of the plasma heating process. The substrate materials are sintered in four different gas discharges, namely hydrogen, nitrogen oxygen and argon. Thermocouple, pyrometer and emission spectroscopy measurements were taken to determine the substrate and the discharge temperatures. The morphology and structure were examined using scanning electron microscopy and X-ray diffraction. The density and hardness of the sintered compacts were correlated with the plasma processing conditions. As expected higher densities were obtained with powders with lower sintering temperatures i.e. nickel and copper when compared with stainless steel. Under the power input and pressure conditions used, the highest substrate temperature attained was 1,100°C for Cu powder sintered in a nitrogen atmosphere. In contrast under the same processing conditions but in an argon plasma, the temperature achieved with SS was only 500°C. The effect of the plasma gas type on the sintered powder compact chemistry was also monitored, both hydrogen and nitrogen yielded a reducing effect for the metal in contrast with the oxidising effect observed in an oxygen plasma.     

Potential of thermal analysis in preparation and characterization of solid catalysis

Supported catalysts contain often only small amounts of active component(s) which renders their characterization difficult, particularly because they usually contain a substantial amount of water. Thermal analysis (TA) coupled with mass spectrometry (MS) offers an interesting potential for characterizing such material, various steps of catalyst preparation as well as crucial properties of fresh and used catalysts can be investigated. Some examples illustrating the versatility of TA-MS in catalysis research, such as solid-state reactions occurring upon exposure of the precursors or catalysts to reducing, oxidizing or inert atmosphere, are presented in this study. The combined use of TA and MS allows in many cases a much more detailed interpretation of the observed phenomena than could be achieved by one of these methods alone.     

Rapid concentration of deoxyribonucleic acid via Joule heating induced temperature gradient focusing in poly-dimethylsiloxane microfluidic channel

This paper reports rapid microfluidic electrokinetic concentration of deoxyribonucleic acid (DNA) with the Joule heating induced temperature gradient focusing (TGF) by using our proposed combined AC and DC electric field technique. A peak of 480-fold concentration enhancement of DNA sample is achieved within 40 s in a simple poly-dimethylsiloxane (PDMS) microfluidic channel of a sudden expansion in cross-section. Compared to a sole DC field, the introduction of an AC field can reduce DC field induced back-pressure and produce sufficient Joule heating effects, resulting in higher concentration enhancement. Within such microfluidic channel structure, negative charged DNA analytes can be concentrated at a location where the DNA electrophoretic motion is balanced with the bulk flow driven by DC electroosmosis under an appropriate temperature gradient field. A numerical model accounting for a combined AC and DC field and back-pressure driven flow effects is developed to describe the complex Joule heating induced TGF processes. The experimental observation of DNA concentration phenomena can be explained by the numerical model.