Powdered minerals spectra

Mineral standards were hand crushed to -1/4 inch, then ground to a fine powder in a ball mill (alumina elements) or Bleuler Model 526/LFS678 puck mill. The resultant powder was aerodynamically classified in a Bahco Model 6000 micro particle classifier and the finest fraction ( 18 throttle) was collected. A size criterion of 90% or more by weight of particles 5 micron and smaller in diameter was used for the mineral standards. Sizes were verified by Coulter Counter. Duplicate 13 mm KBr pellets were prepared and the spectra were weight-scaled by techniques similar to those reported by Painter (3) and Elliot (4). With one exception, all the mineral standard spectra were averages of spectra from duplicate pellets. The one exception was the iron sulfate spectrum, which was obtained as the difference spectrum by subtracting the spectrum of HCl-washed weathered pyrite from that of the weathered pyrite. A weight correction was applied to the difference spectrum. 

For infrared measurements, cells are commonly constructed of NaCI or KBr. For the 400 to 50 cm 1 far-infrared region, polyethylene is a transparent window. Solid samples are commonly ground to a fine powder, which can be added to mineral oil (a viscous hydrocarbon also called Nujol) to give a dispersion that is called a mull and is pressed between two KBr plates. The analyte spectrum is obscured in a few regions in which the mineral oil absorbs infrared radiation. Alternatively, a 1 wt% mixture of solid sample with KBr can be ground to a fine powder and pressed into a translucent pellet at a pressure of —60 MPa (600 bar). Solids and powders can also be examined by diffuse reflectance, in which reflected infrared radiation, instead of transmitted infrared radiation, is observed. Wavelengths absorbed by the sample are not reflected as well as other wavelengths. This technique is sensitive only to the surface of the sample. 

Crystallinity is a metric related to mineral maturity and is a measure of mineral crystallite size, mineral maturity, and the amount of substitution into the apatitic lattice. Crystallinity increases when crystals are larger and more perfect (i.e. less substitution). It is directly proportional to the inverse width of the 002 reflection (c-axis reflection) in the powder x-ray diffraction pattern of bone mineral. Several features in the infrared spectra of bone correlate with mineral crystallinity, most of which are components of the phosphate Vi,V3 envelope [8]. Any of these correlations should be usable in the Raman spectrum provided there are no other overlapping Raman peaks. However, there has been less emphasis on crystallinity in the bone Raman literature and only the inverse width of the phosphate Vi band has been used as a measure of crystallinity [9-12]. 

Figure 10.1 Comparisons of visible to near-infrared spectra of calcic pyroxene in transmitted and reflected light. Polarized absorption spectra of single crystals are correlated with the reflectance spectrum of a powdered sample of the same mineral (cf. fig. 5.14).

Light (or near-ir and uv radiation) that is incident on opaque minerals is partly absorbed and partly reflected by them. There are two kinds of reflection processes that occurring when light is reflected from a flat polished surface of the mineral (specular reflectance) and that occurring when the light is reflected from the mineral after it has been finely powdered (diffuse reflectance). The latter arises from radiation that has penetrated the crystals (as in an electronic absorption spectrum) and reappeared at the surface after multiple scatterings in this case there will also be a specular component to the reflectance from light that is reflected from the surfaces of the particles. The specular reflectance of a flat polished surface of an opaque mineral measured at normal incidence can be related to the n and k terms of the complex refractive index (N) in which ... 

The sodium salt is a white powder, little soluble in pure water, but solubilized in the presence of lithium ions. The solutions are unstable, and conversion to the [a2 P2Wi706,] ° anion is complete after several hours. In molar acetic acid-lithium acetate buffer the half-wave potentials (V vs SCE) are — 0.52 (4e) and —0,78 (2e). The PNMR spectrum of a freshly prepared solution in molar acetic acid-lithium acetate buffer exhibits two equal resonances at -l-O.l and —13.3 ppm (85% H3PO4 reference). In the IR spectrum the P—O bands are at 1130, 1075, and 1008 cm(KBr pellet). As occurs with hydrated compounds, some bands are shifted if the measurements are performed in mineral oil (1130, 1086, and 1009 cm " ). 

Near-IR photoacoustic spectra have been reported for talc and other minerals [38]. Samples were passed through a 240-mesh (64jim) sieve, and were ground first if necessary. The powder was oven-dried overnight at 105°C prior to analysis. Bands were observed at 1.4S (O-H band), 2.14, 2.18, 2.27, 2.36, 2.43, and 2.S0 /tm. The UV-visible photoacoustic spectrum was featureless. 

Glass Some workers prepare mulls by grinding the sample with mineral oil between the surfaces of a ground-glass joint. In a few instances we have observed in the resulting spectrum a broad band due to powdered glass. 

Qualitative spectrochemical analysis requires only a very small sample. Frequently a complete qualitative analysis can be obtained from a 1-5 mg sample and a single exposure. All readily detectable elements can be observed from one spectrum of the sample. Qualitative analysis also is possible with samples difficult to handle by more traditional chemical methods for example, glasses, refractory materials, slags, minerals, etc., can be handled by reducing the sample to a fine powder. No chemical treatment or chemical separation is required. 

This class of solids is an extension of the sample types already discussed, and many of the procedures already highlighted may be used here. If the material dissolves in a suitable solvent, then a cast film may be prepared on an IR transmitting window or on the surface of an ATR element. Moldable materials, such as polymer pellets, may be prepared as hot-pressed films, with care taken to ensure that material does not thermally degrade. Grind-able materials can be handled as previously discussed for powders using the compressed halide pellet, mineral oil mull, or diffuse reflectance methods to acquire the spectrum. 

Particles in gas streams vary so widely in terms of size, density, shape, stickiness, friability, erosiveness, surface charge, and other characteristics that no one method of separation, and not one type of separator, is suitable for processing the entire spectrum of materials. Thus the separation equipment must be capable of processing a very wide variety of material—from pellets to sub-micron powders, from hard minerals, like garnet sand, to soft food products like rolled oats. Some of these materials are very free-flowing, others tend to compact or cake. The products and types of particles shown in Figs. 1.2.1 and 1.2.2 are rather typical of the myriad of substances that can, and have been, successfully conveyed and subsequently classified or separated in modern separation equipment, including cyclones, bag filters and electrofilters. 

Rayalu et al. [12] have estimated the crystallinity of fly ash zeolites-A using XRD and infrared (IR) spectroscopy for identification, quantification and their framework structure. Zeolite A has been synthesized by fusion of mixtures of fly ash and sodium hydroxide in 1 1.2 ratios at temperatures from 550 to 600 °C for 1-1.5 h of heating time. It has been reported that powder XRD analysis was employed to monitor the formation of zeolite-A. The infrared, IR, technique has been proposed for monitoring crystaUinityof end product after synthesis. Based on the characterization results, it has been opined that the unreacted fly ash associated with the zeohte-A as impurities in the final yield, have negligible influence on its application as an adsorbent or cation exchanger. As such, the crystallinity of end product as per interpretation of XRD peaks of commercial zeolite-A have been reported to match closely with the crystallinity interpreted from IR spectrum of the mineral. 

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