Minerals, absorption coefficients

Benzoic acid derivatives also altered the electrical potential across the cell membrane in neurons of the marine mollusk Navanax lnermls (46). Salicylic acid (1-30 mM) caused a depolarization very rapidly (1-2 min) and decreased the ionic resistance across the membrane. As pH was decreased, more salicylic acid was required to reverse the effect of pH on the membrane potential (47). This result is contradictory to the influence of pH on the amount of salicylic acid required to affect mineral absorption in roots (32). The ability of a series of salicylic and benzoic acid derivatives to increase PD correlated with their octanol/water partition coefficients and pKa values (48). The authors proposed that the organic acid anions bound directly to membranes to produce the observed results. 

Opaque minerals like iron oxides are frequently examined in the reflectance mode - and usually give diffuse reflectance spectra. Reflectance spectra provide information about the scattering and absorption coefficients of the samples and hence their optical properties. The parameters of reflectance spectra may be described in four different ways (1) by the tristimulus values of the CIE system (see 7.3.3) (2) by the Kubelka-Munk theory and (3) by using the derivative of the reflectance or remission function (Kosmas et al., 1984 Malengreau et ak, 1994 1996 Scheinost et al. 1998) and, (4) more precisely, by band fitting (Scheinost et al. 1999). 

The ratio /spectrophotometric measurement, and the value of a is then calculated from eq. (3.5) to yield the desired absorption constant. The numerous absorption constants found in the literature arise from the choice of quantities incorporated in the constant b. Some of the terms most commonly used to express absorption in minerals are summarized in table 3.2. Note that optical densities (O.D.), representing the direct output from many spectrophotometers, lack specificity about sample thickness and element concentrations. Absorption coefficients (a) indicate that sample thicknesses have been measured or estimated. Molar extinction coefficients (e) require chemical analytical data as well as knowledge of sample thicknesses. 

We calculated the specific surfaces shown in Table 1 by an improvement of the procedure described in Reference 7. In our more recent studies of coals, rather than using the mass absorption coefficient of carbon, we have computed the mass absorption coefficient of each coal from the elemental composition given by the ultimate analysis. These mass absorption coefficients, which depend quite strongly on the composition and concentration of minerals in the coals, varied from about 7 to 12 cm /gm. We also have taken the values of the coal densities from Fig. 2 of Reference (17). This plot shows the coal density as a function of fixed carbon content and thus provides more reliable densities than the approximation we used in Reference (7). The quantity I A was calculated from the scattering data for colloidal silica samples by the procedure outlined in Reference 7. The proximate and ultimate analyses of... 

Maldener J., Rauch F., Gavranic M., and Beran A. (2001) OH absorption coefficients of rutile and cassiterite deduced from nuclear reaction analysis and ETIR spectroscopy. Mineral. Petrol. 71, 21-29. 

It can be seen from Figure 2 that a increases with increasing temperature d similar behaviour has een observed in rocks and minerals - By contrast, the absorption coefficients (a ) of amber glass have been found to decrease with increasing temperatfure. 

Rocks and Minerals. Absorption and extinction coefficients for several rocks and minerals- - — were found to increase apprecijably at high temperatures, eg a (peridot) increases from 0.5 cm at 25 °C to 4.3 cm at. 1240 °C. Values.of k. . (or a ) have been recorded by Kingery by Kawada (comparative linear flow... 

Frequently, these qualitative results are summarized in publications with semi-quantitative qualifiers, such as abundant , minor , and trace on the basis of the relative intensities of the peaks. Intuitively, one would expect the intensity of the diffraction peak from a particular mineral to be simply related to that mineral s abundance. However, it has long been recognized that this relationship is not straightforward. In a mixture of minerals, the peak geometry is affected by not only the relative and absolute abundance of the particular mineral and its crystallinity, but also by the X-ray absorption characteristics (termed the mass absorption coefficient) and particle size of the other minerals, and the amount of amorphous material in the sample. The end result is that the intensity relations among peaks for a multicomponent mixture can be very complicated. 

Transmitted IR spectra for rocks and minerals are generally measured by making thin sections of samples with thicknesses of from 20 to 200 pm, which depend on concentrations and absorption coefficients based on Beer-Lambert law. A Fourier Transform IR microsjjectrometer totally used in this study is equipped with a silicon carbide (globar) IR source and a Ge-coated KBr beamsplitter. IR light through a sample is measured using a mercury-cadmium-telluride detector. 

Calibration can be achieved by the use of synthetically prepared cement minerals, although these may be difficult to obtain. Since the composition of the sample is variable, and therefore so is its mass absorption coefficient, it is advisable to introduce an internal standard to both the calibration samples and samples for analysis. The elimination of the effect of variable absorption is achieved simply by taking all measured lines as a proportion of a line from the internal standard. 

The sound reduction, attenuation or insertion loss is defined as the difference in sound pressure level or sound power level before and after the enclosure (or any other form of noise control) is installed. The performance of the enclosure will be largely dependent on the sound reduction index (SRI) of the outer wall , assuming approximately 50% of the internal surface is covered with mineral wool or other absorption materials °. Typical values of sound reduction index for materials used for enclosures are shown in Table 20.3. Absorption coefficients are shown in Table 20.4. 

Absorption Spectra, of Aqueous Ions. The absorption spectra of Pu(III) [22541-70 ] Pu(IV) [22541 4-2] Pu(V) [22541-69-1] and Pu(VI) [22541-41-9] in mineral acids, ie, HCIO and HNO, have been measured (78—81). The Pu(VII) [39611-88-61] spectmm, which can be measured only in strong alkaU hydroxide solution, also has been reported (82). As for rare-earth ion spectra, the spectra of plutonium ions exhibit sharp lines, but have larger extinction coefficients than those of most lanthanide ions (see Lanthanides). The visible spectra in dilute acid solution are shown in Figure 4 and the spectmm of Pu(VII) in base is shown in Figure 5. The spectra of ions of plutonium have been interpreted in relation to all of the ions of the bf elements (83). 

Methods for calculating molar extinction coefficients of minerals are outlined in chapter 4 ( 4.3). The importance of the Beer-Lambert law, eq. (3.7), is that the molar extinction coefficient of an absorption band should be independent of the concentration of the absorbing species. Deviations from this law originating from cation ordering are discussed in chapter 4. 

Variations of extinction coefficients and spectrum profiles with changes in chemical composition of a mineral provide information on cation ordering in the structure. Examples involving Al3+-Mn3+ ordering in epidotes and andalusites are discussed in 4.4.2 and 4.5, and Mn2+-Fe2+ ordering in olivine is illustrated in fig. 4.8. Compositional variations of intensities of absorption bands in polarized spectra of orthopyroxenes described in 5.5.4. (fig. 5.15) have yielded Fe2+/M2 site populations (Goldman and Rossman, 1979), while similar trends in the crystal field spectra of synthetic Mg-Ni olivines described in 5.4.2.4 (fig. 5.12) have yielded site occupancy ratios of Ni2+ ions in the olivineMl and M2 sites (Hu etal., 1990). 

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