Transient rates of gas sorption. I. Measurement of rapid gas uptake by Oxide Catalysts

1953 ◽  
Vol 6 (3) ◽  
pp. 221 ◽  
Author(s):  
ME Winfield
Keyword(s):  
Temperature Coefficient ◽  
High Temperatures ◽  
Negative Temperature Coefficient ◽  
Initial Pressure ◽  
Negative Temperature ◽  
Gas Uptake ◽  
First Order ◽  
Rapid Changes ◽  
Low Pressures ◽  
Glass Diaphragm

The rate of gas uptake by a porous solid in a constant volume system was deter- mined by measuring the decrease in pressure, using a capacitance-type glass diaphragm manometer. Techniques are described for admitting gas to adsorbent quickly, and for measuring rapid changes at low pressures and high temperatures. For water and alcohols the rates of uptake by thoria and alumina at 110-200 �C were found to have a negative temperature coefficient. Rates were first order with respect to initial pressure. Three types of rate dependence on mass of adsorbent were found - first, zero, and second order or exponential.

Aging of iron manganite negative temperature coefficient thermistors

1998 ◽  
Vol 13 (5) ◽  
pp. 1238-1242 ◽  
Author(s):  
T. Battault ◽  
R. Legros ◽  
A. Rousset
Keyword(s):  
Temperature Coefficient ◽  
Spinel Structure ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Octahedral Sites ◽  
Before And After ◽  
Structural Equilibrium ◽  
Electrical Data

“Aging,” defined as the drift of resistance with temperature after 1000 h, was investigated for iron manganite temperature coefficient thermistors. For these devices, aging is relatively large, about 10%. The cationic distributions before and after aging were determined by Mössbauer spectroscopy. These distributions explain all the x-ray diffraction and correlated electrical data. The origin of the aging observed on iron manganites thermistors has been identified. It is due to the migration of Fe3+ ions from tetrahedral to octahedral sites of the spinel structure in order to reach a structural equilibrium.

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