High-temperature studies systems

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. 

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. 

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. 

Figure 8. The longitudinal dispersion for tracers from colunrn experiments and groundwater tracer studies is proportional to the length of the flow system studied. A typical value for the dispersion is roughly one tenth of the length of the system. While not much is known about dispersion in high temperature flow systems, it is nevertheless likely that a similar correlation exists. Hence dispersion will be important for a system of any size where mass transport occurs by fluid infdtration. Data from Gelhar et al. (1985).

Significant hydrothermal sites are known from a number of on- and off-axis seamounts. These include the Axial Volcano site on the JFR, a large sulfide deposit on a near-axis volcano at 13°N EPR, Loihi seamount in the Hawaiian-Emperor chain, the Lucky Strike hot-spot-related seamount site on the MAR, and a number of other localities. Axial Volcano and Lucky Strike have been studied most thoroughly, and have high-temperature hydrothermal systems. The Ashes vent field on the summit of Axial Volcano was the first to show effects of boiling at the reduced pressures encountered on the seamount relative to a normal ridge crest (Massoth et al. 1989). Many ridge-crest vent fields have been discovered in the last decade that show the effects of phase-separation into low-salinity vapor and more saline fluid (Butterfield 2000). 

Studies into the first of these types, the norbomene imides, have resulted in a high-temperature adhesive system known as LARC-13, which demonstrated improved process-ability over condensation polyimides. Some typical results obtained from this adhesive are shown in Table 4, demonstrating its high-temperature capabilities. 

Figure 4.4.41. Disaetized form of the transmission line model. e and e, are the potentials in the magnetite and solution phases, respectively. Here i and i, are the currents in the magnetite and solution phases, respectively I and / are the total current and the current flowing across the metal-solution interface and base of the pore, respectively RE and M designate the reference electrode and metal (working electrode) locations, respectively. (Reprinted with permission from J. R. Park and D. D. Macdonald, Impedance Studies of the Growth of Porous Magnetite Films on Carbon Steel in High Temperature Aqueous Systems, Corros. Sci. 23, 295 [1983]. Copyright 1983, Pergamon Journals Ltd.)...

J. R. Park and D. D. Macdonald [1983] Impedance Studies of the Growth of Porous Magnetite Films on Carbon Steel in High Temperature Aqueous systems, Corros. Sci. 23, 295. 

Thermodynamics of the Si-O-N system I, high-temperature study of the vaporization behavior of sihcon nitride by mass spectrometry. Journal of the American Ceramic Society, 79,1351-1360. 

Raghtmathan K, Ghosh-Dastidar A, Fan LS. High temperature reactor system for study ultrafast gas olid reactions. Rev Sci Instrum 64(7) 1989 1993, 1993. 

Pol] Polishchuk, V.E., Selissky, YA.R, High-Temperature Study of the Stracture and Electrical Properties of the Fe-Si-Al System (in Russian), Ukrain. Fiz. Zhur., 14, 1722-1724 (1969) (Phase Diagram, Experimental,, , 9)... 

Par] Parras, M., Gonzalez-Calbet, J.M., Vallet-Regi, M., Grenier, J.C., A High Temperature Study ofthe BaFe03 j, System , Solid State Ionics, 63-65, 714-718 (1993) (Crys. Structure, Experimental, 14)... 

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