Measurement at High Temperatures

Zhao Y, Barvosa-Carter W, Theiss S D, Mitha S, Aziz M J and Schiferl D 1998 Pressure measurement at high temperature using ten Sm YAG fluorescence peaks J. Appi. Phys. 84 4049... 

Therefore, in most cases, pH values measured at high temperatures in dilute solution should be considered approximate values only. In cases where the investigators address this problem and are careful to select a suitable electrode (namely, one that manufacturers claim to have almost hysteresis-free pH measurement and a stable isopotential point over the temperature range), the error associated with electrode performance will be small, and differences in reported pH values will correspond to differences in actual pH. In cases where pH is measured in concentrated sucrose solutions, the reported pH value should be considered as a nominal value only, and the differences in nominal pH values might not correspond to actual differences in hydrogen ion activity. 

Are the equilibrium constants for the important reactions in the thermodynamic dataset sufficiently accurate The collection of thermodynamic data is subject to error in the experiment, chemical analysis, and interpretation of the experimental results. Error margins, however, are seldom reported and never seem to appear in data compilations. Compiled data, furthermore, have generally been extrapolated from the temperature of measurement to that of interest (e.g., Helgeson, 1969). The stabilities of many aqueous species have been determined only at room temperature, for example, and mineral solubilities many times are measured at high temperatures where reactions approach equilibrium most rapidly. Evaluating the stabilities and sometimes even the stoichiometries of complex species is especially difficult and prone to inaccuracy. 

Long-term use of a sensor at higher temperatures damages or reduces the life of the sensor by reducing its precision and accuracy. Thus, a large number of measurements at high temperature should be avoided, to increase the life of the sensor. It is difficult to find a sensor that will operate at both very low and very high tempera-... 

The total spectrum should then appear as nine lines of equal width and relative intensities 1 2 4 6 6 6 4 2 1. It is noteworthy that lines 1, 3, 5, 7, and 9 have the correct intensity ratios for the so-called five-line set, and lines 2, 4, 6, and 8 are in accord with experiment for the four-line set. All that is wrong is that the intensity of the four-line set relative to the five-line set is too great except for the barium salt of methacrylic acid at room temperature (Bamford and Ward, 1961). However, the predicted intensities are approached when the spectrum is measured at high temperature, and the deviation at lower temperature arises because of the greater width of the even lines relative to the odd ones. 

The rubbery modulus may change during the measurement at high temperatures, because the polymer may participate in both postpolymerization and degradation reactions. 

The paramagnetism of 0 can also be measured by means of a Faraday balance (2fL). This technique has the advantage of being applicable to in situ measurments at high temperatures and is sensitive enough to detect 0" in synthetic MgO (2 ). We are currently pursuing this work with a Faraday balance and hope shortly to be able to report on new data. 

Problems of Precise Measurements at High Temperatures Constitution and Structure of Ultramarine, by F. M. Jaeger, Professor of Physical and Inorganic Chemistry, University of Groningen, Holland. Pp. 450, octavo, cloth, 137 figures. 2.25. 

For all these equipments, attachments permit measurements at high temperatures and in controlled atmospheres. 

A fine example of tliis type of work is the determination of Z)q(I2) from vapour density measurements at high temperatures by Perlman and Rollefson 8 8 These workers were interested in obtaining very accurate values of the equilibrium constant to see whether they exhibited any trend which would indicate the presence of 13 and incidentally in obtaining an accurate value of Dq(12) for comparison with the spectroscopically derived result. They introduced highly purified iodine into a silica bulb of known volume contained in a furnace controlled at temperatures between 723° K and 1,274° K, measured the pressure, and then removed the iodine and weighed it. Gas imperfection for molecular iodine was taken into account, but atomic iodine was assumed to be a perfect gas. 

Yashima M, Kakihana M, Shimidzu R, Fujimori H, Yoshimura M (1997) Ultraviolet 363.8-nm Raman spectroscopic system for in situ measurements at high temperatures. Appl Spectrosc 51 1224... 

Results with DCM on ground ZERONOX are shown in Figure 5, Even taken into account the error in these measurements, at high temperature (above 300° C) the smallest particle diameter (0.20-0.32 mm) gives the highest conversions, indicating some internal diflusion control at high ten erature. 

Likewise, the heat capacity values tabulated in the present compilation may appear different from those of other compilations, even when the original data are the same. This is due to the fact that the original measurements are usually heat content measurements at high temperatures and the accuracy of the heat content measurements is not sufficient to allow the temperature dependence to be fixed explicitly. Different people assume different functions to represent the temperature variation of the heat content or heat capacity. For example, some prefer to take an average constant heat capacity to represent data for a limited liquid range. Others will assume a linear variation with temperature with some relationship between the two coefficients of the heat capacity equation. 

Extending the current state of knowledge could involve measurements at high temperature with shock experiments to access transition pressures closer to the thermodynamic limit. Progress is currently being made to study the transition in individual nanocrystal particles, to both eliminate the ensemble statistics and allow for individual transitions to be observed on -femtosecond time scales. The study of nanocrystal solid-solid phase transitions to oxide nanosystems should also prove to be useful in understanding the microscopic process of solid-solid transitions relevant to geophysically important systems. 

Stress measurements at high temperature were performed with a similar equipment as used in drying experiments. The clamped strip-top layer combination is placed in a small tubular furnace positioned horizontally by a suitable sliding arrangement [28]. A small hole is provided at the bottom of the furnace for the laser beam. The exit at the bottom of the furnace must be placed close to the detector and so must be provided with a radiation screen and be cooled adequately. 

Sessile drop method is the most frequently used method (c.f. Section 6.2.4.1.). In the measurement at high temperatures the drop of the melt is lying on the solid base placed in a horizontal furnace tube. The contact angle is measured on photographs of the drop. 

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