High-temperature studies

The rigidity of the y axis prevents the development of spherical surfaces for all but very small displacements. Morton suggests that the limit is reached when the displacement is equal to the metal thickness. This condition was satisfied in the high-temperature studies of Appleby and Tylecote and spherical doming of the disc specimen occurred. When the oxide is not very thin compared with the metal both the moduli for oxide and metal must be considered. Stringer" , in his excellent review of stress generation and relief in oxide layers, quotes a corrected formula, originally due to Brenner and Senderoff ... 

At the time of writing, in all papers published on adsorption studies on oxides surfaces, spectra have been reported of samples held at the ambient temperature of the sample compartment. It is obvious that when dealing with very volatile adsorbates, low temperature sample cells may be required to increase adsorption and also to prevent rapid desorption of the adsorbed species. In some instances, it is also desirable to record the spectra of species held at elevated temperatures for better correlation with industrial catalytic systems. It should be noted that there are only a few infrared spectra reported in the literature for high temperature studies of catalytic reactions. Sample emission at elevated temperature is a significant experimental complication in investigations of this type. 

The second high-temperature study reviewed in Section 2 (Ichimiya and Furuichi, 1968) employed the radioactivity of tritium (3H) as a tool for measuring its uptake and retention in silicon wafers. This study yielded... 

Henderson C.M.B., Knight K. S., Redfern S.A.T., and Wood B. J. (1996) High-temperature study of octahedral cation exchange in olivine by neutron powder diffraction. Science 271, 1713-1715. 

E.C. Cassidy et al, Investigations of the Exploding Wire Process as a Source for High Temperature Studies, (NBS Monograph 109),... 

In the 1960 s, interest turned to the oxidation of perfluorocarbons. In the United States, much work has been done at the Aerospace Corporation Photochemical, thermal, electric-discharge, and flame studies, as well as oxidation initiated by oxygen atoms and ozone, were performed in El Segundo, California. High-temperature studies were performed at the... 

In the paper by Rhodin in this volume a general discussion was given of microbalances. It is the purpose of this section to discuss the basis for our particular design and how it is applied to high-temperature studies. This will require, in addition, a rather detailed consideration of vacuum systems at high temperatures. 

All our studies were made at 30°C. Data in the literature suggest that as the temperature is lowered, these differences will become less because reaction with gegenion becomes much slower. On the other hand the differences will become even more pronounced as the temperature is raised above 30 °C. Thus, for high temperature studies the use of PF6 or SbF6 is clearly indicated. 

The newer technologies of photoelectron spectroscopy and photoionization mass spectrometry, when adapted to high temperature studies, have re-opened this topic for further investigation. In particular, photoelectron spectroscopy has provided information about the electronic structure of these species, a property largely Ignored in the earlier Investigations. 

Following the same principles as those which govern the designing of cells for absorption experiments, Raman cells for high-pressure, high- temperature studies have also been constructed by Lindner and Franck (see Tddheide, 1972). A Raman cell for use up to 7 kbar and 250 °C (Eckel et al., 1981) is shown in Fig. 6.7-8. 

Symmetrical ketones (R equals ethyl, propyl, isopropyl, w-butyl, isobutyl, and -heptyl) have been prepared in nearly "quantitative" yields by passing the acid vapors over thoria at high temperatures. Studies have been made of metallic oxide catalysts and temperature of reaction. In general, a thoria catalyst has been favored at temperatures of 400-500°. The apparatus and catalyst preparation have been described. ... 

The effect of organic ligands on dissolution of feldspar at ambient temperature has been observed by several groups to follow the same order as that observed by Furrer and Stumm (1986) for alumina citrate, oxalate > salicylate, tartrate > aspartate, acetate (Drever and Stillings, 1997). High-temperature studies of aluminosilicate dissolution in the presence of organic acids have also been completed, but are not reviewed here (see, however the review by Oelkers and Schott, 1998). 

T yg is from the high temperature studies of Dworkln and Bredig (8). enthalpy data. 

High temperature studies are summarized below along with the pertinent low temperatures studies. The selected heat capacities above 300 K are obtained from a Shomate plot of the adopted low temperature heat capacities and the enthalpies reported or derived from the work of Dennison (5), Kantor et al. (6), Olette (7), Serebrennikov and Gel d (8) and Magnus (9). 

These observations emphasise the conclusion that a simple dependence on an Arrhenius extrapolation from high-temperature studies can be unreliable. In the worst case, the derived rate constant for a 1% formulation in the absence of Carbopol is 9 orders of magnitude in error at 298 K. 

Each of the reported experiments took 12 h observation and the whole study was completed in significantly less time (around 2 weeks) than a conventional high-temperature study would require. Moreover, the studies were performed on the as is formulated medicines without the need to develop assay systems e.g. HPLC analyses). Further studies of this type on, for example, solid-state systems and solution-phase systems can be found in the literature. 

Fig. 2. Constant volume apparatus for the study of adsorption kinetics, equipped for high temperature studies and high speed pressure measurements. From ref. 82.

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