Full width at half maximum of low-angle basal phyllosilicate X-ray diffraction reflections: fitted peaks vs. diffraction traces

ABSTRACTBernard Kübler measured illite ‘crystallinity’, the half-height width or full width at half maximum (FWHM) of the X-ray diffraction line of illite/mica at 10 Å, directly on the diffraction traces; this procedure has since been followed by the vast majority of workers. However, some workers have recently measured the FWHM of the fitted Pearson VII function rather than on the diffraction traces. The FWHM of this function for low-angle phyllosilicate diffraction peaks (FWHM*PVII) is almost consistently ‘broader’ than those measured directly on the diffraction trace profiles (FWHMtrace) by up to 0.08°Δ2θ for the broader peaks. The Pearson VII function shows gentle curvature (‘smoothing’) at its tops and fast fading of the tails relative to virtually all 10 Å diffraction traces. The broad FWHM*PVII results from the consequent lowering/’under-fitting’ of the peak tops and the upper tails and compensatory broadening/’over-fitting’ of the intermediate peak flanks. FWHM*PVII ‘contraction’ with respect to FWHMtrace and enhancement of the peak maximum is found on traces of muscovite strips. The fitting reliabilities of the Cauchy function are almost invariably better than those of the Pearson VII function. Their FWHM*Cauchy values are narrower for both the illite/mica 10 Å and the chlorite 7 Å reflections; although they still differ somewhat from the FWHMtrace, they are much closer, usually within 0.02°Δ2θ. This markedly lesser broadening of FWHM* of the Cauchy of the Pearson VII function is the result of its stronger top curvature and notably faster tail fading (less ‘smoothening’). For higher-angle mica peaks, the FWHM* values of the Pearson VII and Cauchy functions converge, usually differing only by 0.01–0.03°Δ2θ for the 5 Å peak, and even less for the 3.3 Å peak. It is therefore strongly recommended that FWHM values of the illite/mica 10 Å reflections be measured on the diffraction traces rather than on fitted functions. Where peak fitting is unavoidable (e.g. in order to separate the contributions of adjoining, partly resolved or unresolved reflections on broadened 10 Å reflections), Cauchy rather than Pearson VII functions should be used.

Nylon 66/nano CaCO3 composites

The nylon 66/nano-CaCO3 composites were prepared by melt blending on a twin-screw extruder. Scanning electron microscopy (SEM), polarized light microscopy (PLM), thermal loss (TGA) and differential scanning calorimetry (DSC) The effects of nanometer calcium carbonate on the polycrystalline behavior and thermal properties of nylon 66/nano CaCO3 composites were investigated. The results show that the nanometer calcium carbonate particles are dispersed in the nylon 66 matrix and exist in the form of aggregates. The nanometer calcium carbonate has the effect of heterogeneous nucleation, which can reduce the size of the spherules. The decomposition temperature of the nylon 66 is 400 ℃, the addition of nano-CaCO3 to reduce the decomposition temperature. At the same time, DSC test showed that the β-crystalline form in the material reduced the melting temperature of the material. The addition of nano-CaCO3 in the nylon 66 matrix resulted in the decrease of the crystallization temperature and the increase of the half-height width of the endothermic peak. The lower the crystallization temperature, the wider the crystallization temperature range.

Er3+/Yb3+/Ce3+ Co-Doped Fluoride Glass Ceramics Waveguides for Application in the 1.5µm Telecommunication Window

Er3+-doped fluoride glass ceramics planar waveguides containing LaF3 or binary LaF3- ZrF4 nanocrystals have been fabricated by Physical Vapour Deposition (PVD). A quantitative analysis of the photoluminescence for the 1.5μm emission band of Er3+ ions has demonstrated that erbium ions are partitioned in both crystals and vitreous phase; the solubility of Er3+ in the segregated LaF3 nanocrystals can reach 30 mol% and the emission bandwidth has been found to be greater than that of the precursor glass (71nm at the half-height width). In order to increase the luminescence of Er3+, codoping with Yb3+ and Ce3+ has been investigated. The high Er3+ concentration and spectral width could make this nanostructured fluoride material suitable for planar amplifier in the C telecommunication band.

Sulphur-33 nuclear magnetic resonance spectroscopy of sulphones

The sulphur-33 nmr spectra of 28 sulphones were measured in deuterochloroform solutions at 27.716172 MHz. The spectra were referenced with respect to an external aqueous ammonium sulphate solution and the chemical shifts lay in the range 0 ± 20 ppm, with many lines having a half-height width of less than 200 Hz. Instrumental parameters that affect the spectra were studied. Some of the sulphur-33 resonances can be correlated well with carbon-13 or oxygen-17 resonances in appropriate analogous compounds, and with the Taft σ* parameter.

The action spectrum of hemoprotein oxidase in Nitrobacter agilis

A photochemical action spectrum for the relief by light of the carbon monoxide inhibition of respiration in Nitrobacter agilis (ATCC No. 14123) has been determined by the method of Castor and Chance, the first such determination in a chemolithotrophic organism. The cells were grown at 30 °C in liquid culture, were used when consuming 2–4 mM/ml per day of nitrite, and were concentrated by centrifuging. They respired actively at room temperature for about 3 h in air but only 75 min in the CO:O2 (4:1) mixture. Consistent γ and α bands of a hemoprotein spectrum were obtained from the combined results of two cultures. The maxima are at 432 ± 2 and 592 ± 2 nm; the γ/α height ratio is 6.4 (±22%) and the half-height width of the γ band is 15 nm. Since cytochrome a1 but not a3 has been reported in several Nitrobacter studies, the conclusion is that an a1-type cytochrome is a terminal oxidase in Nitrobacter agilis. The great scatter in the points around the β peak presumably results from the many cultures used, and possibly from differing oxidase activities in different phases of growth. The breadth of the peak could result from the presence of cytochrome o in some cultures. The possibility of more than one terminal oxidase is not excluded.