Measurement-phase relationships

Variables Measured Phase Relationship Equilibrium Constant (S°C.) Reference... 

Ratio measurement, polarity check and phase relationship ... 

This paper reviews data on certain thermodynamic aspects of the nonstoichiometric Pu-0 system, which may serve as a basis for use In reactor safety analysis. Emphasis Is placed on phase relationships, vaporization behavior, oxygen-potential measurements, and evaluation of pertinent thermodynamic quantities. Limited high temperature oxygen potential data obtained above the fluorite, diphasic, and sesquioxide phases In the Pu-0 system are presented. 

A detailed study of the phase relationships in the magnesium oxysulphate cement was carried out by Urwongse Sorrell (1980b). They used X-ray analysis to examine the phases present in the cement, and established the composition of the invariant liquids after equilibration by measuring specific gravity with the aid of a pycnometer. Specific gravities were related to concentration by means of a calibration exercise in which 30 stock solutions of sulphuric acid at concentrations between 0 and 79-5 wt % were prepared with distilled water. 

As discussed in previous sections the phase relationships in the lanthanide higher oxides of Ce, Pr, and Tb are quite complex and sensitive to environmental conditions, especially the oxygen partial pressures. Unless extreme care is taken, the property measurements will be on inadequately characterized materials. 

Each measurement, sensitive to the existence of ordering, agrees on the main features of the phase relationships suggested below for each system. Table I should be consulted for the lattice parameters for each sequence. 

The potential drops were measured across the sample rod and a standard resistor in series with a sensitive VTVM (vacuum tube volt meter) while the wave form was monitored with an oscilloscope. Two samples of composition Lal2.oo- o.oi were measured from 77° to 344° and 186° to 408°K., respectively, without irreversible temperature effects. One sample of composition Cel2.o7 was studied from 153° to 300 °K., but satisfactory Prl2 samples could not be obtained. Because of phase relationships and the relatively high resistivity found, Lal2.42 was studied as a pellet formed with a KBr press using a VTVM in the dry box. The results from one sample to another were somewhat erratic, partly because of extreme susceptibility to oxidation, but were sufficient to characterize the compound as salt-like as opposed to metallic. 

The quantum yields of fluorescence and phosphorescence, 4>f and d>p, may be determined experimentally by means of a fluorescent standard such as a rhodamine B solution whose independent of the exciting wavelength within a wide range. Lifetimes rp and rp are also experimentally accessible through time-resolved fluorescence measurements (phase method or single-photon counting) or by measuring the time dependence of phosphorescence. (Cf. Rabek, 1982.) In Table 5.2 the observable quantities and their relationship to rate constants are collected. 

Probably the most powerful tool for the exploration of phase relationships at interfaces is the use of synchrotron radiation to determine structures. This can be undertaken for a sequence of small volumes across the reaction zone [6]. The potential of the method is considerable, but, as yet, the number of applications has been small because there are few of these expensive facilities available. X-ray diffraction measurements are, however, widely used to confirm or identify the structure of both reactants and products, and can be extended to detect any topotactic relationship between them. Assumptions do have to be made concerning the absence of structural changes on cooling from the reaetion temperature to the temperature of strueture determination, if these temperatures are different. 

Cantilevers in AFM function as force transducers converting unknown force to measurable deflection. The value of the unknown force can then be expressed by Hookean mechanics following spring constant calibrations. In addition to static point loads, cantilevers can also be vibrated, e.g., by an oscillation piezo to which the fixed end of the beam is attached (or by other approaches). Excitation frequency, oscillation amplitude, and phase relationships are variables that govern dynamic tapping (intermittent contact) imaging. This problem will be discussed in the next section. 

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