High-temperature measurements

Cells used for high-temperature measurements in furnaces often consist of silica sample tubes, supported by thin vanadium sleeves. The key to the analysis is whether it is possible to have a container that scatters in a sufficiently predictable way, so that its background contribution can be subtracted. With the current neutron flux available from both pulsed and reactor sources, sample volumes of... 

The temperature T of the system in equilibrium. This is measured in the usual way when T is not large. The measurement of high temperatures has attracted a considerable amount of attention on account of its great importance. A detailed description of the methods used in the measurement of high temperatures will be found in Le Chatelier and Bouduard s High Temperature Measurements, trans. Burgess (Wiley, New York). The chief methods are ... 

For PUF3 only high temperature measurements of magnetiam are available (27). The magnetic moment between 90 and 300 K is about lJgff = 1.6 ilg and decreases at higher temperature. 

The heat capacity function for the solid phase Is from Fink (4. Fink points out that although (U,Pu)02 UO2, and ThC>2 have solid-solid phase transitions, the available data (4) make It impossible to determine the existence of a similar phase transition for Pu02 If additional high-temperature measurements indicate the presence of a solid-solid phase transition, the heat capacity of Pu02 between the phase transition and 2701 K may be significantly higher. 

Figure 6. Area of the first peak In difference curve of the Pt Ljjj edge versus absolute temperature for 1% Pt on Cabosll in H2. The high temperature measurement (773 K) was subtracted from each of the other spectra.

High temperature measurements were carried out using a Bruker B-ST 100/700 variable temperature unit. 

Besides the advantage of the high-temperature measurements for quantitative interpretation of NOESY spectra, fig. 6 also indicates a special role of the high temperature maximum (note that positive cross-relaxation rates increase downward) of u". If the NOESY spectrum can be recorded at several temperatures around the cr" maximum, than calculated cross-relaxation rates can be used to obtain simultaneously the correlation time and the interproton distances without the necessity of any other knowledge. A typical problem in the cross-relaxation experiments is that cross-relaxation rate depends on two parameters, Tc and r (eq. (la)), and to calculate one of them the other must be independently known. However, the position of the maximum uniquely determines correlation time, and its height uniquely determines interproton distances. 

Over the years there has been a lot of interest in the decrease in melting temperature of small metal particles, relative to the bulk, theoretically [104,105,106] as well as experimentally [107,108,109,110]. Extrapolations from high temperature measurements have suggested that, for gold particles... 

High Temperature Measurements of the Rates of Uptake of Molybdenum Oxide, Tellurium Oxide, and Rubidium Oxide Vapors by Selected Oxide Substrates... 

In applying equation 33, Cpsl (the constant-pressure molar heat capacity of the stoichiometric liquid) is usually extrapolated from high-temperature measurements or assumed to be equal to Cpij of the compound, whereas the activity product, afXTjafXT), is estimated by interjection of a solution model with the parameters estimated from phase-equilibrium data involving the liquid phase (e.g., solid-liquid or vapor-liquid equilibrium systems). To relate equation 33 to an available data base, the activity product is expressed... 

Raman spectroscopy can be used in qualitative and quantitative measurements of both organic and inorganic materials, and it is successfully employed to solve complex analytical problems such as determining chemical structures. Gases, vapors, aerosols, liquids, and solids can be analyzed by spectroscopy. As well as room temperature observations, cryogenic and high-temperature measurements can be made, including in situ identification and quantification of combustion products in flames and plasmas (Laserna, 1996). 

In order to distinguish which expression for k2, if either, is correct, high temperature measurements and/or ab initio calculations of the rate coefficient for reaction (2) are required. Alternately, the computed differences in the values for atomic oxygen and for the temperature in the burned region at an initial ozone mole fraction of unity appear to be large enough that profile measurements above such a flame may be sufficient to distinguish between the two expressions. 

The author wishes to express his thanks to Dr. H. Weyten (VITO) for performing the high temperature measurements, Dr. R. Bredesen (SINTEF) for performing SASRA treatments, XRD-measurements and specific surface area measurements, Dr. J.A. Dalmon (IRC) for performing permeance and permselectivity measurements on the tubular membranes and Dr. A. Vredenburg (University of Utrecht) for performing the RBS measurements. These people are also kindly thanked for fruitful discussions on their respective measurments. 

Types-B, R, and S Thermocouples (Pt vs. Pt/Rh Alloy). Type-B, -R, and -S thermocouples are expensive, because they use either Pt or a Pt-Rh alloy for each conductor. These are among the most stable thermocouples, but have low sensitivity (10pV/°C) and are used only for high-temperature measurements. 

For high temperature measurements Hincke used a silica U-tube sealed at both ends at one end was a bulb A containing the substance (Fig. 5.VIII J). The manometric liquid was fused bismuth. The tube was supported at the bulb end by a fused-on hook, engaging with a hook on the wall of the heatr ing chamber, and a fused-on hook on the other side was connected by a wire with a balance-pan outside the furnace. The pressure of the vapour drove the liquid into the right-hand -side of the tube, and from the increase in weight the displacement of liquid, and hence the vapour pressure, could be calculated. Jenkins used a fused metal (Cd, Zn) as the manometric. liquid in one arm of a V-tube, and compensated, the vapour pressure by nitrogen gas. 

The various results for k 2 are tabulated in Table 6. The room temperature measurements are in good agreement, suggesting a value of (3.6 1.0)x 10 P.mole . sec for M = Ar, O2, and N2. Kaufman s early value, obtained by a somewhat indirect procedure, must be too large. Two measurements for M = SOj indicate k 2 = (12 2) x 10 l. mole". sec" for this third body. The high-temperature measurements, all made in complicated systems and obtained indirectly, show little consistency, and must all be regarded with reservations at the present time. 

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