Measurements on powder samples

Frequently, Tg detection is a requirement in pharmaceutical and food studies, but it is difficult to obtain solid bar samples. The greater sensitivity of DMA over DSC offers excellent Tg determination, especially where only small amounts of amorphous material are present. To use the Material Pocket, 10-50 mg of sample is poured into the V-shaped trough and the pocket is tightly closed with a pair of phers or a small vice. The absolute values of the storage modulus E ) and loss modulus E ) will not be quantitative, due to the stiffness of the metal Material Pocket. However, during a 7 process the change of each of these parameters is quantitative. 

A more comprehensive description of both the technique and the data can be found in 

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In the case of transuranimn compounds, measurements on powder samples in fields up to 100 kOe show spin rearrangement in NpAs and NpAs2 . ... 

Since the approximate charge on vanadium is +1 in the M.O. approximation, a value of the spin orbital coupling constant = 135 cm.-1 is taken for V+.30 The calculation then gives g = 1.983, gll — 1.940, with (g) — 1.969. This is in excellent agreement with the accurately known (g) = 1.962 value for aqueous solutions of VO2, 25-27 The measurements on powdered samples of the vanadyl sulfates also give (g) values in reasonable agreement with this calculation. 

In general however only measurements on powdered samples are performed, which yield the average magnetic susceptibility. In this case there is no way for obtaining the principal molecular values and directions. 

We report solid State C NMR measurements on powder samples of C o and of a mixture of and C70. The NMR results show that, at 296 K, Cm molecules rotate rapidly and isotropically in the solid state, while C70 molecules rotate somewhat more anisotropically. These results are consistent with the proposed spherical geometry of Cm and prolate spheroidal geometry of C70. The rotational correlation time of Cm molecules in the solid state becomes greater than 50 /ts at about 100 K. 

Interest in the structures and properties of fullerenes has received new impetus from the recent discovery that the molecules Cm and C70 can be prepared in large quantities by comparatively simple procedures. The ready availability of solid samples of Cm and C70 now permits their characterization by a variety of physical methods. In this paper, we report the results of solid-state C nuclear magnetic resonance (NMR) measurements on powder samples of Cm and of a mixture of Cm and C70. Our NMR results indicate that Cm rotates rapidly and nearly isotropically in the solid state at 296 K and that C70 also rotates at 296 K, although somewhat anisotropically. The rotation of Cm molecules becomes slow on the time scale of our measurements at about 100 K. 

At present, theoretical calculations are capable of reproducing and predicting NMR parameters with high accuracy. This is especially important in solution-state NMR for predicting the parameters of the individual components involved in dynamic processes. A theoretical approach is also used to calculate the solid-state parameters (e.g., the orientations of the principal components of the chemical shift), which are unavailable from measurements on powdered samples. 

YbCdCu4 have been measured on powdered samples prepared from single crystals. variable-amplitude cross-polarization (VACP) and... 

The catalytic activities of oxides and oxide-supported catalysts are affected by their electrical properties (21,181). When these properties are measured on powder samples, the experimentally determined values are strongly dependent upon interparticle spacing, particle size, etc., and so numerical results of different observers are not directly comparable. However, each individual group of investigators has followed its own uniform procedure, and the over-all results of various studies are comparable. 

For samples of polycrystalline or disordered solids the concentration of spins per unit weight is usually the quantity of interest. Errors due to different densities of the sample and the reference and of different samples can then occur. A procedure to normalize the signal intensity by the mass to length ratio of the sample has therefore been recommended for quantitative measurements on powder samples [14]. The procedure may be motivated for a sample contained in a normal ESR sample tube as follows ... 

The glass density (d) was measured on powdered samples by the pycnometry method with an accuracy of 0.005 g cm Young s modulus ( ) and Poisson s ratio (y) were measured by the pulse-echo technique on 4 mm thick rectangular specimen. Vickers indentations (load of 9.8 N apphed during 15 s), were performed to estimate both Meyer s hardness (H) and the indentation fracture toughness (Kc) by means of the following equations ... 

GdN, GdP, GdAs, GdSb, GdBi. In all these compounds Gd is trivalent and in an S state. In fig. 4 we have plotted the inverse susceptibilities of GdAs and GdSb versus temperature, measured on powdered samples or on small crystallites. 

Susceptibility measurements on powder samples (Troc and Lam 1974) and on monocrystalline samples (Busch and Vogt 1978) show very distinctly the transition at 66 K (see fig. 52). Up to 1000 K the Curie-Weiss law is strictly obeyed (Busch et al. 1979a). The anisotropy of the magnetic susceptibilities is very well marked. The transition at 66 K was further confirmed by neutron diffraction experiments (Lander et al. 1972b, Marples et al. 1975). There were various attempts to find distortions in UAs, Knott et al. (1980) and Lander and Mueller (1974) could not detect measurable distortions. Only recently a tetragonal distortion with c/a = 1.0002 was identified for the type lA structure (McWhan et al. 1990), an indication of strong orbital contributions. 

Maple et al. (1978) established the magnetic and superconducting transition temperatures T x, and T in the system (Luj HO <)Rh4B4 by means of low frequency ac-susceptibility measurements on powdered samples (fig. 71) as low as 0.07 K. T i, T,-2 and become identical at x = 0.92. Samples were synthesized by arc melting (Ar) and subsequent annealing in sealed Ta tubes at 1150 C for 2 weeks, then at 900°C for 1 week, finally at 800°C for 1 week. No structural details were given (CeCo4B4-type, P42/nmc). 

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