The effects of thermal treatment and irradiation on the chemical properties of natural diamonds.

The modification of nitrogen-contaminated diamonds into color-enhanced diamonds is usually achieved by irradiation and thermal treatment (annealing). These treatments affect nitrogen contamination chemical bonding, vacancy concentration, and atom orientation centers in the diamond lattice. In this study, natural diamonds were subjected to irradiation and thermal annealing color enhancement treatments to produce green, blue, and yellow fancy diamonds. The study followed the changes that occur during treatment relying on visual assessment, fluorescence, UV-vis, FTIR, and EPR spectroscopy to characterize paramagnetic centers. The results indicated that diamonds containing high levels of nitrogen contamination presented a relatively high carbon-centered radical concentration. Two paramagnetic groups with different g-values were found, namely, low g-value centers of 2.0017-2.0027 and high g-value centers of 2.0028-2.0035. It is suggested that the 2.0017-2.0022 centers correlate with blue centers, whereas the 2.0023-2.0027 centers correlate with yellow centers. It was also found that thermal treatment was required to produce blue and yellow fancy diamonds, whereas no such treatment was needed to produce green diamonds.

Effect of Diamond Polishing and Thermal Treatment on Carbon Paramagnetic Centers' Nature and Structure.

Diamonds contain carbon paramagnetic centers (stable carbon radicals) in small concentrations (at the level of ~1 × 1012 spins/mg) that can help in elucidating the structure of the nitrogen atoms' contaminants in the diamond crystal. All diamonds that undergo polishing are exposed to high temperatures, owing to the friction force during the polishing process, which may affect the carbon-centered radicals' concentration and structure. The temperature is increased appreciably; consequently, the black body radiation in the visible range turns orange. During polishing, diamonds emit an orange light (at a wavelength of about 600 nm) that is typical of a black body temperature of 900 °C or higher. Other processes in which color-enhanced diamonds are exposed to high temperatures are thermal treatments or the high-pressure, high-temperature (HPHT) process in which the brown color (resulting from plastic deformation) is bleached. The aim of the study was to examine how thermal treatment and polishing influence the paramagnetic centers in the diamond. For this purpose, four rough diamonds were studied: two underwent a polishing process, and the other two were thermally treated at 650 °C and 1000 °C. The diamonds were analyzed pre- and post-treatment by EPR (Electron Paramagnetic resonance), FTIR (Fourier transform infrared, fluorescence, and their visual appearance. The results indicate that the polishing process results in much more than just thermal heating the paramagnetic centers.

On-line in situ determination of deuterium content in water via FTIR spectroscopy.

Hydrogen stable isotope ratios are critical indicators in environmental geochemical studies for characterizing runoff, determination of groundwater groups and water uptake by plants etc. (generally used in combination with 18O analysis). While the common technique for this hydrogen isotope measurement is Mass Spectrometry, FTIR (Fourier transform infra-red) spectroscopy may be an alternative method, with the advantage of direct and simple operating measurements. The FTIR spectrometer has the advantage of performing in situ measurements, which can delineate continuous geochemical processes. In situ measurements decrease errors that may be a consequence of sample delivery to the laboratory and off-site analysis procedures. In this study, we have developed a new simple procedure for in situ hydrogen stable isotope ratio measurements. We discovered that the HDO (hydrogen, deuterium, and oxygen) absorbance peak at 2504 cm-1 is the most suitable for water sample direct analysis, with the FTIR device, using a circular sample cell for liquid samples. A case study analyzing water samples from a karstic cave (Sif cave, Israel) verified the following: (a) on-line determination of water D/H ratio can be carried out with the portable FTIR spectrometer (and thus can be used for field measurements such as in the Sif cave) and (b) the D concentration sensitivity achieved was at a 0.01‰ level, with a standard deviation of 0.006‰.