M. V. Krishnaiah

Investigation of the thermal conductivity of selected compounds of gadolinium and lanthanum

Abstract As a part of the development of rare earth based ceramic materials for nuclear applications, the thermal conductivity of gadolinium zirconate, lanthanum zirconate and gadolinium aluminate was investigated employing the laser flash technique and covering a temperature range from 650 to 1400 K. Based on the temperature dependence of the thermal resistivity, the heat transport behaviour of these materials was briefly examined.

Investigation of the thermal conductivity of selected compounds of lanthanum, samarium and europium

Abstract As part of the development of rare earth based ceramic materials for a variety of applications, the thermal conductivities of lanthanum aluminate, samarium zirconate and europium zirconate were investigated, employing the laser flash technique and covering a temperature range from 650–1400 K. Based on the variation of the thermal resistivity as a function of temperature, the heat transport behaviour of these materials was briefly examined.

Thermal conductivity of rare earth–uranium ternary oxides of the type RE6UO12

The knowledge of thermophysical properties of the rare earth uranium ternary oxides of the type RE6UO12 (RE=La, Gd and Dy) is essential to understand the fuel performance during reactor operation and for modeling fuel behavior. Literature on the high temperature properties of this compound is not available and there is no report at all on the thermal conductivity of these compounds. Hence a study of thermal conductivity of this compound has been taken up. The compounds were synthesized by a solution combustion method using metal nitrates and urea. Thermal diffusivity of these compounds was measured by the laser flash method in the temperature range 673–1373 K. The specific heat data was computed using Neumann–Kopp’s law. Thermal conductivity was calculated using the measured thermal diffusivity value, density and specific heat data for different temperatures. The temperature dependence of thermal conductivity and the implication of structural aspects of these compounds on the data are discussed here.

Investigation of the thermal conductivity of calcium cerate and calcium zirconate

Abstract Thermal conductivity of calcium cerate and calcium zirconate was investigated employing the laser flash technique and covering a temperature range from 563 to 1453 K. Variation of the thermal resistivity of these materials as a function of temperature has been examined and the heat transport behaviour discussed.

Calorimetric study of selected NZP-type of ceramic materials

Sodium zirconium phosphate, NZP, ideally NaZr (PO ) , is a potential host matrix for nuclear waste. Thermophysical properties of 24 3 these materials are necessary to assess the thermal stability of these compounds. This paper presents the synthesis and calorimetric measurements of some NZP-type compounds containing alkaline earth elements. It also describes the indigenously developed room temperature drop calorimeter for low temperature calorimetric measurements. Calibration of the instrument is done with standard reference materials. Enthalpy increment of these materials is measured using this setup in the temperature range 373-873 K, and specific heat data are derived. Temperature dependence of enthalpy increment and specific heat of these materials, and the influence of the chemical composition on these properties are discussed.  2002 Elsevier Science B.V. All rights reserved.

Thermal conductivity of selected cermet materials

Cermets offer the benefits of both ceramics and metals. Due to the benefits associated with cermets, especially high temperature stability and thermal conductivity, there is renewed interest in their thermophysical properties. The present work describes thermal conductivity studies on selected cermets using laser flash technique in the temperature range 673-1373 K. This work describes the preparation and thermal conductivity measurement of urania-nickel cermets of composition 20 and 30 wt.% nickel by the solid-state reaction method. The thermal conductivity value is obtained as a product of the measured thermal diffusivity, estimated specific heat and room temperature density of these cermets. The theoretical value of the thermal conductivity is also computed for these cermets using different models for two-phase solid mixtures, such as parallel, series and Maxwell models. The calculated thermal conductivity, obtained using measured thermal diffusivity, of these cermets is compared with the theoretical values from the above models. Thermal conductivity integral values are also calculated and presented here.

Vaporization chemistry of hypo-stoichiometric (U,Pu)O2

Calculations were performed on hypo-stoichiometric uranium plutonium di-oxide to examine its vaporization behavior as a function of O/M (M = U + Pu) ratio and plutonium content. The phase U (1 Pu v O z was treated as an ideal solid solution of (1 - y) UO 2 + yPuO( 2-x) such that x = (2-z)/y. Oxygen potentials for different desired values of y, z, and temperature were used as the primary input to calculate the corresponding partial pressures of various O-, U-, and Pu-bearing gaseous species. Relevant thermodynamic data for the solid phases UO 2 and PuO (2-x) , and the gaseous species were taken from the literature. Total vapor pressure varies with O/M and goes through a minimum. This minimum does not indicate a congruently vaporizing composition. Vaporization behavior of this system can at best be quasi-congruent. Two quasi-congruently vaporizing compositions (QCVCs) exist, representing the equalities (O/M) vapor = (O/M) mixed exide and (U/Pu) vapor = (U/Pu) mixed oxide , respectively. The (O/M) corresponding to QCVC1 is lower than that corresponding to QCVC2, but very close to the value where vapor pressure minimum occurs. The O/ M values of both QCVCs increase with decrease in plutonium content. The vaporization chemistry of this system, on continuous vaporization under dynamic condition, is discussed.

Investigation of the Thermal Conductivity of Selected Rare Earth Aluminates

As a part of the thermophysical property studies on rare earth based oxide ceramics thermal conductivity of the aluminates of samarium and dysprosium was investigated employing laser flash technique and covering a temperature range from 673 to 1373 K. Heat transport behaviour was briefly examined by analysing the variation of thermal resistivity as a function of temperature.

Improved method of data acquisition and processing for the measurement of thermal diffusivity by the laser flash technique

Generally, in the laser flash technique, thermal diffusivity of any sample is calculated using the t1/2 value obtained by analyzing the transient signal. The t1/2 value, and thus the thermal diffusivity obtained in this way, will have a good amount of scatter in the data at low temperatures due to the weak signal and the pick up of external noise during the measurement. This necessitated suitable modifications in the data acquisition system to enhance the signal-to-noise ratio for the measurements carried out at low temperatures. This article presents the necessary modifications made in the existing data acquisition system. The measurements of thermal diffusivity of stainless-steel samples by the laser flash method and their results are discussed here.