Material Temperature Research Articles

Stoichiometric lanthanum chromite based ceramic interconnects with low sintering temperature

Ceramic interconnects for use in solid oxide fuel cells are expected to operate between 800∼1000 °C, sinter between 1400∼1500 °C to allow co-firing and meet a number thermal mechanical requirements. The perovskite type (ABO 3) lanthanum chromite based materials have emerged as a leading candidate that will meet these criteria by varying the composition on the A and B sites. A need therefore exists to determine this material's temperature dependent electrical and mechanical properties with respect to these site substitutions. In this investigation, oxide powders were prepared by the glycine-nitrate process. Ionic substitutions were carried out on A sites with calcium or strontium, and B sites with cobalt and aluminum, respectively. Only stoichiometric compositions were considered for the sake of stability. The powders and their sinterability were investigated by XRD, SEM, dilatometry and density measurements. The sintered materials were further examined by SEM, thermal expansion and electric conductivity measurements in order to elucidate the resulting microstructure, electrical and mechanical properties.

Characterization of YVO 4:Eu 3+ phosphors synthesized by microwave heating method

YVO 4:Eu 3+ phosphors were prepared using a domestic microwave oven operated at 2.45 GHz with 500 W. The temperature of raw materials with mixtures of Y 2O 3, V 2O 5 and Eu 2O 3 that were irradiated with the microwave increased to about 840 °C within 150 s. Subsequently, the temperature dropped sharply in spite of the continuing microwave irradiation. Measurement of the dielectric loss factor of the raw materials and products at 2.45 GHz at temperatures from 25 °C to 800 °C revealed a high absorption efficiency of microwave energy by V 2O 5, which provided a rapid increase in the raw material's temperature. A low dielectric loss factor observed for YVO 4:Eu engendered a sharp temperature drop after completion of the reaction of Y 2O 3 with V 2O 5.

Evaluation of the magnetocaloric effect from magnetization and heat capacity data

AbstractMagnetic refrigeration is based on the magnetocaloric effect (MCE) – the ability of some materials to heat up when magnetized and cool down when removed from the magnetic field. The available techniques for studying the MCE are: (i) direct measurements by monitoring the change in material's temperature during the application or removal of the magnetic field; and (ii) indirect calculations from experimental data of magnetization and/or heat capacity as functions of temperature and magnetic field. In this paper the procedure to evaluate the MCE from magnetization and zero‐field heat capacity data is described. The MCE – isothermal magnetic entropy change (ΔSM) and adiabatic temperature change (ΔTad) – of gadolinium (Gd) obtained by this procedure is presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A consistent cure kinetic model for AS4/3502 graphite/epoxy

Accurate cure kinetic model is crucial for correctly identifying the amount of heat generated for composite process simulation. This paper presents a new technique for identifying cure kinetics parameters for Hercules AS4/3502 prepreg by normalizing the DSC data. The cure kinetics is based on an autocatalytic model for the proposed method, which uses dynamic and isothermal DSC data to determine its parameters. Existing models are also used to determine kinetic parameters but rendered inadequate because of the material's temperature dependent final degree of cure. The model predictions determined from the new technique showed good agreement to both isothermal and dynamic DSC data. The final degree of cure was also in good agreement with experimental data.

Coupled heat and mass transport phenomena in siliceous aggregate concrete slabs subjected to fire

A mathematical and computational model simulating the coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures has been developed. Taking into account the conservation of mass, momentum and energy, and including the effects of evaporation and dehydration processes on the transport phenomena, a set of three coupled nonlinear differential equations is obtained. Siliceous aggregate concrete slabs subjected to the ASTM E119 standard fire exposure are modeled and validated against test data. Output depicts the coupled relationships between the material's temperature, moisture content, and pore pressure histories and distributions.

Modeling the Thermal Behavior of Concrete Slabs Subjected To the Astm E119 Standard Fire Condition

A mathematical and computational model simulating the coupled heat and mass transfer and related processes in porous media exposed to elevated temperatures has been developed. Taking into account the conservation of mass, momentum, and energy, and the evaporation of free and chemically bound water released by dehydration and their effect on the transport phenomena, a set of three coupled nonlinear differential equations is obtained. Carbonate aggregate concrete slabs subjected to the ASTM E119 standard fire exposure are modeled and validated against test data. Output depicts the coupled relationships between the material's temperature, moisture content, and pore pressure histories and distributions. Language: en

Dielectric characteristics of neodymium heptamolybdate crystals grown by gel encapsulation technique

AbstractResults obtained from the dielectric studies of neodymium heptamolybdate crystals grown in the system Nd(NO3)3 –MoO3 –NH4OH– HNO3 —Na2SiO3 by gel encapsulation technique are presented. The variation of dielectric constant (ε′), dielectric loss (tanδ) and conductivity (σ) with frequency at different temperatures is studied. The dielectric constant of the material increases sharply, attains a peak value and then decreases rapidly, as material's temperature rises from room temperature to higher degrees. The temperature at which the peak value is attained is the transition temperature of the material. Dielectric loss (tan δ) follows almost a similar behaviour. The conductivity (σ) is also found to be temperature‐and frequency‐dependent. This sharp rise in ε′ is attributed to the contribution from space charge polarization. Theoretically obtained data using the expression ε′ = a0 + a1 T2 and —In σ = a + b(T — T0)2 for T < T0) fits very well with the experimentally obtained data indicating that space charge polarization increases as some power of temperature larger than one.

Solid state: Superfast annealing: Application of laser and electron-beam annealing portends three-dimensional ICs and economical photoelectric cells

Laser or electron beam annealing can be carried out with either pulsed or steady beams. The beams may be large or small, may persist for only nanoseconds or dwell on a spot for many milliseconds. However, in all cases, the power of the beam must be high enough to raise the material's temperature to the melting point, or at least to within a few hundred degrees of it. The range of applications for these clean, fast-heating methods has gone far beyond annealing of defects to a variety of other materials manipulation possibilities. For years, lasers have been used in the processing of metals and ceramics: to weld metals and flash-melt alloys, for surface hardening and drilling holes in metals and hard insulators, for example. They have also been used in the electronics industry for silicon wafer scribing and labelling, wire bonding, resistor trimming, and interconnection path selection by pulsed laser erosion. The new field addresses the manipulation of semiconductor material properties themselves.

The relationship between material properties and the economics of fusion power

Fusion power cost is Influenced by materials, fabrication costs and a large number of material properties that impact reactor performance and safety. Reactor performance parameters that are affected include thermal to electrical conversion efficiency, neutron wall loading (power density), availability, and plasma burn time. Chief among the material properties affecting the above reactor performance parameters are the material's temperature limit and the mechanical, thermal and radiation damage properties that determine life and reliability. Extensive materials testing will be required to satisfy a reliability goal of not more than one wall failure per year. Material properties may affect safety issues such as tritium inventory, waste disposal and coolant choice. Determination of the impact of material properties on the cost of fusion power is addressed. This determination is incomplete in some cases.

The efficiency of energy-utilization in chemical processes

Chemical processes may be regarded as a transfer of chemical energy from the starting material into the products. The work equivalent of any material is the maximum amount of shaft work or electrical energy which can possibly be obtained from it when heat and matter are exchanged with the environment. It depends on the material's temperature, pressure and chemical composition as well as on the respective properties of the environment. All contributions to the work equivalent of any substance can be expressed in the same consistent units and evaluated quantitatively, including the contribution due to chemical composition. A measure of the efficiency of energy utilization in a chemical process—based on the first and second laws of thermodynamics—can be obtained, if one compares the total output of work equivalent in all outgoing streams to the total input. This concept is developed in a formal way and applied to the analysis of two industrial processes.