Carbide-Derived Carbons: WAXS and Raman Spectra for Detailed Structural Analysis

Quick characterization methods to determine the structure of carbon materials are sought after for a wide array of technical applications. In this study we present the combined analysis of the structure of carbide-derived carbons (CDCs) with Raman spectroscopy and wide-angle X-ray scattering (WAXS) methods. We present the optimal deconvolution method to be used for the detailed analysis of Raman spectroscopy data of CDCs and comparison to corresponding WAXS results is made. For a broad set of CDCs both WAXS and Raman spectroscopy data showed that the average graphene layer extent increases with synthesis temperature of CDC, while the coherent domain lengths obtained from Raman spectroscopy higher by an average of 4.4 nm. In addition, the presence of correlations between the parameters (D-band width and the parameter A∑D/A∑G) from Raman spectroscopy and the synthesis temperature are established. Based on the WAXS and Raman spectra data analysis the strong influence of the precursor carbide structure on the graphitization pathway is shown.

POTTERY FIRING PARAMETERS ACCORDING TO THE RAMAN SPECTROSCOPY DATA

Образцы круговой керамики XIII – начала XV в. из раскопок древнекарельских городищ Северо-Западного Приладожья исследованы методом рамановской спектроскопии с целью определения параметров обжига изделий (температура, длительность, атмосфера). Для анализа результатов применялись два подхода. Первый основан на идентификации в образце минералов-маркеров (атмосферные – гематит/магнетит, температурные – анатаз/рутил, хлорит), присутствие которых коррелирует с определенными условиями термообработки. Второй, инновационный подход, заключается в использовании рамановского палеотермометра, разработанного коллективом исследователей из Парижа (Deldicque et al., 2016) для вычисления температуры обжига древесины. Палеотермометр отражает зависимость структурной упорядоченности углеродистого вещества, рассчитанной по параметрам рамановского спектра угля, от температуры. Применение данного подхода стало возможным благодаря включению в выборку для анализа образца керамики редкой формы с древнекарельского городища Хямеенлахти и пробы формовочной массы сосуда из коллекции средневекового Новгорода, в составе которых ранее были идентифицированы частицы древесного угля. Ceramics dated to the XIII‑th – early XV‑th century from the excavations of ancient Karelian hill forts in North-Western Ladoga area were studied using Raman spectroscopy to characterize firing parameters (temperature, duration and atmosphere). Obtained data were analyzed by the means of two approaches. The former is based on the identification of minerals serving as markers (e.g. hematite/magnetite – for atmosphere, or anatase/rutile, chlorite – for temperature), which presence depends on the certain conditions of firing. The latter, innovative, consists in the use of the Raman paleothermometer, which has been recently elaborated by the research group from Paris (Deldicque et al., 2016) for estimation of firing temperature. The paleothermometer reflects the dependence between the structural ordering of carbonaceous matter, counted using Raman parameters of charcoal, and temperature. The possibility of the latter approach appliance appeared due to the presence of charcoal inclusions in two ceramic samples of the studied assemblage. One specimen arises from the rare shape vessel of Karelian hill fort Khyameenlahti and the second – from experimentally added sample of medieval pot from Novgorod the Great.

The Raman Estimation of the Composition of Clinopyroxene Inclusions in Natural Diamonds

<p>Clinopyroxenes (Na,Mn,Ca,Fe<sup>2+</sup>)<sub>1-2</sub>(Mg,Al,Cr,Fe<sup>3+</sup>)<sub>1-2</sub>[(Al,Si)<sub>2</sub>O<sub>6</sub>] are common inclusions in natural diamonds of either peridotitic or eclogitic paragenesis. The variety of the composition of pyroxene inclusions in diamonds records the chemical and the physical conditions of the mantle. New approach based on Raman spectroscopy data on 43 pyroxene inclusions in diamonds from Yakutian province (the Siberian craton) and their chemical analyses are provided in this study.</p><p>Raman spectroscopy is a high-resolution and non-destructive method used to detect the compositional and the structural characteristics of materials and minerals including high-pressure crystal inclusions in diamonds. Raman spectra of clinopyroxene inclusions in diamonds were collected by Horiba LabRAM HR800 Raman spectrometer with 532-nm laser. In addition, the compositional analyses were obtained by EPMA (JEOL JXA-8100) to correlate chemical variations with specific spectral features and Raman shifts.</p><p>Clinopyroxene inclusions show variations of chemical content in the wide ranges: SiO<sub>2</sub> 54.1-55.9 wt.%, Al<sub>2</sub>O<sub>3</sub> 0.31-4.11 wt.%,  Cr<sub>2</sub>O<sub>3</sub> 0.32-5.73 wt.%, FeO 1.81-3.49 wt.%, MgO 13.4-18.3 wt.%, CaO 16.1-22.9 wt.%, Na<sub>2</sub>O 0.28-3.82 wt.% for peridotitic type and SiO<sub>2</sub> 52.4-56.8 wt.%, Al<sub>2</sub>O<sub>3</sub> 4.46-17.8 wt.%,  Cr<sub>2</sub>O<sub>3</sub> <0.29 wt.%, FeO 2.22-11.4 wt.%, MgO 5.65-15.1 wt.%, CaO 9.81-17.1 wt.%, Na<sub>2</sub>O 3.118-8.121 wt.% for eclogitic type.</p><p>Generally, the inclusions yield Raman spectra with four high-intense modes (ν<sub>3</sub>, ν<sub>3’</sub>, ν<sub>4</sub>, ν<sub>11</sub>, ν<sub>17</sub>). Observed relative intense of most of these modes (except ν<sub>11</sub>) depend on changing of crystal orientation. The ν<sub>11</sub>-mode belongs to the Si-O stretching vibrations of bridging oxygen atoms (Si-O<sub>br</sub>). The recorded position of this mode varies in the ranges 665.6-675.1 cm<sup>-1</sup> for peridotitic type inclusions and 673.7-688.2 cm<sup>-1</sup> for eclogitic type inclusions. One of the factors controlling the shifts of position frequencies of n11-mode is composition.</p><p>Peridotitic clinopyroxenes display strong linear correlations between the shifts of position of the ν<sub>11</sub>-mode and contents of Al<sub>2</sub>O<sub>3</sub> (correlation coefficient r = 0.94), FeO (correlation coefficient r = 0.68), MgO (correlation coefficient r = -0.52), CaO (correlation coefficient r = -0.69), Na<sub>2</sub>O (correlation coefficient r = 0.92). Eclogitic clinopyroxenes show linear correlations between the shifts of position of the n<sub>11</sub>-mode and contents of Al<sub>2</sub>O<sub>3</sub> (correlation coefficient r = 0.95), FeO (correlation coefficient r = -0.64), MgO (correlation coefficient r = -0.85), CaO (correlation coefficient r = -0.59), Na<sub>2</sub>O (correlation coefficient r = 0.84). The most expressed correlations can be used for estimation of composition of inclusions in diamonds only by Raman spectroscopy data without destruction of diamond-host and for identification of clinopyroxenes from potentially diamondiferous mantle rocks.</p><p>Acknowledgments: Russian Science Foundation (16-17-10067) supported this work.</p>