High-temperature density measurement

There are only a few suitable methods for high-temperature density measurement. The reason is the corrosive nature of molten salts and the thermal dilatation of the materials used for measurement. Most convenient for molten salts are the methods of hydrostatic weighing and the maximum bubble pressure method. For more viscous liquids, such as some silicate melts, the falling body method is suitable. These three methods will be described in detail here. For further study the reader is referred to an excellent book by Mackenzie (1959). 

For assessing the viability and accuracy of high-temperature potentiometric measurements, the reference systems should be used. If Pt(H2) or YSZ(Hg/HgO) electrodes are used as the indicator electrodes, an aqueous solution with well-known activity of H+ (aq) should be used as the reference systems. At temperatures below 250 °C, the dilute aqueous solutions of strong acids and bases, such as HCl(aq) or NaOH(aq), can be employed to precisely calculate the activity of H+ (aq) so that the measured potential can be compared with the calculated one within a few millivolts or less. If HCl(aq) or NaOH(aq) is to be used at temperatures above 250 °C, the association constants of the electrolytes should be taken into account. Furthermore, at these temperatures, the precision of the calculated activities of H+ (aq) can be decreased. However, even in the low-density, supercritical aqueous solution, a reference system, which consists of a couple of three-component aqueous solutions, can be found to test the accuracy of the Pt(H2) or YSZ(Hg/HgO) electrodes within about 3 mV. Each of the three-component aqueous solutions consists of NaCl and either HC1 or NaOH... 

The density dependence of the frequency of spectral maxima obtained in the MD simulations of BJH water is compared in Figure 21 with all available experimental data. One point from high-pressure, high-temperature Raman measurements of Walrafen et al. (1988) is also plotted in Figure 21 for comparison, although it corresponds to a somewhat lower temperature and higher pressure (443 K and 3300 MPa, respectively) than those used in the simulations. Except for one point, there is a remarkable agreement between simulated and measured values. 

Speoifie volume The speeifie volume of polymers varies with the solvent. Good solvents give higher values of the specific volume while poor solvents give lower values. A plot of the polymer specific volume as a function of solubility parameter gives a maximum value, which is taken to be the solubility parameter of the polymer. High precision density measurements at carefully controlled temperatures are needed for this method (168). The partial specific volume is defined as... 

X-ray diffraction and surface area measurements suggest that these W-atom surface densities correspond to saturation coverages, which markedly inhibit zirconia sintering and tetragonal to monoclinic transformations at high temperatures. Zr02 surface areas after 1073 K calcination are 4 m g" and increase to an asymptotic value of 51 m g for W surface densities above 5-6 W-atoms nm (Figure 4). Similarly,... 

By putting the system into a high pressure bomb (36) the magnetic system can be used to measure the densities of aqueous solutions over a wide pressure range with a precision of 11 ppm. We presently are developing a magnetic float system that can be used to measure the densities at low pressures to high temperatures (200°C). 

---