Microstructural Evolution and Densification Kinetics During Sintering of Oxide-Dispersed Tungsten Alloys

1993 ◽  
Vol 322 ◽  
Author(s):  
Li-Chyong Chen ◽  
Bernard P. Bewlay
Keyword(s):  
Microstructural Evolution ◽  
Electron Spectroscopy ◽  
Boundary Diffusion ◽  
Activation Energies ◽  
Sintering Behavior ◽  
Tungsten Alloys ◽  
Single Mechanism ◽  
Linear Heating Rate ◽  
Apparent Activation Energies

AbstractThe present paper discusses the role of ceria and hafnia dispersions in tungsten alloys on the microstructural evolution and densification kinetics during sintering. Densification kinetics were measured using dilatometry, and microstructural changes were examined using scanning electron microscopy and Auger electron spectroscopy. Activation energies for sintering were obtained by analyzing the shift of the iso-density points as a function of linear heating rate. Sintering of both tungsten and ceria-dispersed tungsten were found to be controlled by grain boundary diffusion, with apparent activation energies of 318±21 and 385±15 kJ/mole, respectively. However, densification of hafnia-dispersed tungsten is not controlled by a single mechanism. Under different conditions hafnia can enhance or retard densification; the mechanisms associated with this behavior are discussed. In particular, the relationships between sintering behavior and the tungsten-ceria and tungsten-hafnia interfaces are examined. Comparison with conventional oxide dispersoids, such as thoria, will also be made.

Sintering Behavior of Ba2CaWO6-Doped-Tungsten

1993 ◽  
Vol 322 ◽  
Author(s):  
J.A. Ruud ◽  
B.P. Bewlay
Keyword(s):  
Grain Boundary ◽  
Mass Loss ◽  
Boundary Diffusion ◽  
Activation Energies ◽  
Grain Boundary Diffusion ◽  
Sintering Behavior ◽  
Densification Mechanism ◽  
Early Stages ◽  
Kinetics Of

AbstractThe sintering behavior of Ba2CaWO6 co-sintered with W powder was investigated. Measurements of density and mass loss of sintered compacts showed that the Ba2CaWO6-doped-W had a lower density than undoped W and that there was little volatilization of Ba2CaWO6 at temperatures below 1750 °C. The activation energies for densification of Ba2CaWO6-doped-W and undoped W were both measured to be 389 kJ/mol, which indicates the same densification mechanism, grain boundary diffusion, operated for both materials. The reduced densification kinetics of the Ba2CaWO6-doped-W was probably due to increased coarsening in the early stages of sintering.

scholarly journals Effect of CaO on catalytic combustion of semi-coke

2021 ◽  
Vol 10 (1) ◽  
pp. 011-020
Author(s):  
Luyao Kou ◽  
Junjing Tang ◽  
Tu Hu ◽  
Baocheng Zhou ◽  
Li Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Combustion Rate ◽  
Activation Energies ◽  
Combustion Reaction ◽  
Tg Analysis ◽  
Conversion Rates ◽  
Apparent Activation Energies ◽  
Ozawa Integral Method ◽  
Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

Highly sinter-active nanocrystalline RE2O3 (RE = Gd, Eu, Dy) by a combustion process, and role of oxidant-to-fuel ratio in preparing their different crystallographic modifications

2007 ◽  
Vol 22 (3) ◽  
pp. 587-594 ◽  
Author(s):  
V. Bedekar ◽  
S.V. Chavan ◽  
A.K. Tyagi
Keyword(s):  
Combustion Process ◽  
Sintering Behavior ◽  
Stoichiometric Ratio ◽  
Monoclinic Modification ◽  
Fuel Ratio ◽  
Metal Nitrates ◽  
Powder Properties ◽  
Very High ◽  
Scanning Electron

Highly sinter-active powders of RE2O3 [rare earth (RE) = Gd, Eu, Dy] have been prepared using the corresponding metal nitrates as the oxidants, and glycine and citric acid as the fuels. Two different oxidant-to-fuel ratios, namely stoichiometric ratio and fuel-deficient ratio were used to explore the possibility of preparing different crystallographic modifications. By a careful control of oxidant-to-fuel ratio, nanocrystalline Eu2O3 and Gd2O3 could be prepared in cubic (C-type) as well as monoclinic (B-type) modifications. However, the high-temperature monoclinic modification could not be obtained for Dy2O3 due to a very high C-to-B-type phase transition temperature. The crystallite size, surface area, and sintering behavior were also studied for powders prepared using different oxidant-to-fuel ratios, and the results showed a remarkable correlation between different fuel contents and powder properties. Some of these powders resulted in pellets of nearly theoretical density. The sintered microstructure was studied by scanning electron microscopy.

Role of activation energies of individual phases in two-phase range on constitutive equation of Zr–2.5Nb–0.5Cu alloy

2017 ◽  
Vol 27 (1) ◽  
pp. 172-183 ◽  
Author(s):  
K.K. SAXENA ◽  
S.K. JHA ◽  
V. PANCHOLI ◽  
G.P. CHAUDHARI ◽  
D. SRIVASTAVA ◽  
...  
Keyword(s):  
Constitutive Equation ◽  
Activation Energies ◽  
Two Phase ◽  
Phase Range
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