Melting curve and fluid equation of state of carbon dioxide at high pressure and high temperature

Accepted by Journal of Chemical Physics; in pressThe melting curve and fluid equation of state of carbon dioxide have been determined under high pressure in a resistively-heated diamond anvil cell. The melting line was determined from room temperature up to $11.1\pm0.1$~GPa and $800\pm5$~K by visual observation of the solid-fluid equilibrium and in-situ measurements of pressure and temperature. Raman spectroscopy was used to identify the solid phase in equilibrium with the melt, showing that solid I is the stable phase along the melting curve in the probed range. Interferometric and Brillouin scattering experiments were conducted to determine the refractive index and sound velocity of the fluid phase. A dispersion of the sound velocity between ultrasonic and Brillouin frequencies is evidenced and could be reproduced by postulating the presence of a thermal relaxation process. The Brillouin sound velocities were then transformed to thermodynamic values in order to calculate the equation of state of fluid CO$_2$. An analytic formulation of the density with respect to pressure and temperature is proposed, suitable in the $P-T$ range 0.1-8~GPa and 300-700~K and accurate within 2\%. Our results show that the fluid above 500 K is less compressible than predicted from various phenomenological models

Melting curve of black phosphorus: evidence for a solid-liquid-liquid triple point

Black phosphorus (bP) is a crystalline material that can be seen as ordered stackings of two-dimensional layers, which lead to outstanding anisotropic physical properties. The knowledge of its pressure-temperature (P-T) phase diagram, and in particular, the slope and location of its melting curve is fundamental for better understanding the synthesis and stability conditions of this important material. Despite several experimental studies, important uncertainties remain in the determination of this melting curve. Here we report accurate melting points measurements, using in situ high-temperature and high-pressure high-resolution synchrotron x-ray diffraction. In particular, we have employed an original and accurate pressure and temperature metrology based on the unique anisotropic P-T response of bP, that we used as sensor for the simultaneous determination of pressure and temperature up to 5 GPa and 1700 K. We confirmed the existence of and located a solid-liquid-liquid triple point at the intersection of the low- and high-pressure melting curves. Finally, we have characterized the irreversibility of the transformation in the low-pressure regime below 1 GPa, as the low-density liquid does not crystallize back to bP but into red phosphorus on temperature quenching

X-ray crystallography of simple molecular solids up to megabar pressures: application to solid oxygen and carbon dioxide

International audienceA review of recently developed methods to study the structural properties of simple molecular solids under pressures up to the megabar range using synchrotron X-ray diffraction techniques is presented. This includes the growth of single-crystals at high pressure and temperature conditions and the use of He as pressuretransmitting medium. The application of these methods to solid O2 and CO2 is then presented as illustrative examples, showing how they enabled to solve long-standing debates on the structure of the high-pressure crystalline phases of these compounds

Proton Disorder and Superionicity in Hot Dense Ammonia Ice

International audienceWe report the experimental discovery of a new phase of ammonia ice, stable at pressures above 57 GPa and temperatures above 700 K. The combination of our experimental results and ab initio molecular dynamics simulations reveal that this new phase is a superionic conductor, characterized by a large proton diffusion coefficient (1:0 Â 10 À4 cm 2 =s at 70 GPa, 850 K). Proton diffusion occurs via a Grotthuss-like mechanism, at a surprisingly lower temperature than in water ice. This may have implications for the onset of superionicity in the molecular ice mixtures present in Jovian planets. Our simulations further suggest that the anisotropic proton hopping along different H bonds in the molecular solid may explain the formation of the recently predicted ionic phase at low temperatures

Extended and accurate determination of the melting curves of argon, helium, ice (H2O), and hydrogen (H2)

International audienceThe melting curves of argon, helium 4, ice (H 2 O), and hydrogen (H 2) have been measured from room temperature up to a maximum temperature of 750 K. This extends the previous determination of the melting lines of H 2 and He by nearly a factor of 2 in pressure. The experiments were carried out with a resistively heated diamond anvil cell. Improved accuracy with respect to previous determinations, when existing, was achieved by the use of an optical metrology which gives an in situ measurement of both the pressure and temperature of the sample. The melting lines of argon and H 2 O are found to be well represented by the following Simon-Glatzel equations: Pϭ2.172ϫ10 Ϫ4 T 1.556 Ϫ0.21 ͑argon͒ and Pϭ2.17ϩ1.253͓(T/354.8) 3.0 Ϫ1͔ (H 2 O). But the Simon-Glatzel form was found inadequate to reproduce the melting data of 4 He and H 2 over the whole temperature range. In the case of 4 He, this deviation from a Simon law is explained by the softening of the pair interaction with density. A Kechin equation is proposed for H 2 : Tϭ14.025(1 ϩ P/0.0286) 0.589 exp(Ϫ4.6ϫ10 Ϫ3 P). This form is in excellent agreement with all published experimental data for H 2 and interestingly predicts a maximum on the melting curve at 128 GPa and 1100 K

Performances of a VIPA-based spectrometer for Brillouin scattering experiments in the diamond anvil cell under laser heating

International audienceVIPA-based Brillouin spectroscopy is implemented for in-situ measurements at high pressure and temperature in laser-heated diamond anvil cells. Its performances are compared to those of the widely used Tandem Fabry–Perot instrument. A significant reduction of the collection time is in particular enabled. The usefulness of VIPA-Brillouin spectroscopy for High Pressure studies is here illustrated by revisiting the nitrogen melting curve up to 45 GPa. VIPA-Brillouin spectroscopy has the potential to become an important platform to investigate the equation of state properties of warm dense molecular systems

Structure of Polymeric Carbon Dioxide CO2−V

International audienceThe structure of polymeric carbon dioxide (CO2-V) has been solved using synchrotron x-ray powder diffraction, and its evolution followed from 8 to 65 GPa. We compare the experimental results obtained for a 100% CO2 sample and a 1 mol % CO2/He sample. The latter allows us to produce the polymer in a pure form and study its compressibility under hydrostatic conditions. The high quality of the x-ray data enables us to solve the structure directly from experiments. The latter is isomorphic to the-cristobalite phase of SiO2 with the space group I-42d. Carbon and oxygen atoms are arranged in CO 4 tetrahedral units linked by oxygen atoms at the corners. The bulk modulus determined under hydrostatic conditions, B0=136 GPa, is much smaller than previously reported. The comparison of our experimental findings with theoretical calculations performed in the present and previous studies shows that density functional theory very well describes polymeric CO2

Polymeric phase V of carbon dioxide has not been recovered at ambient pressure and has a unique structure

TesisObjetivo: determinar el nivel de conocimientos, actitudes y prácticas frente al uso de métodos anticonceptivos en los estudiantes de la escuela de terapias de rehabilitación de la Facultad de Tecnología Médica de la UNFV. El agustino - Octubre 2017. Material y método: el presente estudio es de enfoque cuantitativo, prospectivo; de corte transversal y diseño transversal descriptivo. La muestra de la investigación fue probabilística. La técnica empleada será la encuesta y el instrumento fue el cuestionario. Resultados: se aplicó el cuestionario a una muestra de 122 estudiantes de 1er a 4to año de terapias de rehabilitación de 19 a 25 años, la aplicación duro de 10 a 20 minutos. En el análisis estadístico de resultados, en cuanto al conocimiento sobre métodos anticonceptivos, el 93% tiene buen conocimiento, en cuanto al lugar donde se informaron sobre los métodos anticonceptivos, se obtiene que el 70% de estudiantes se informaron por internet, el 25% se informaron en un centro de salud y el 5% se informó por la universidad. En relación a la actitud se obtiene que es favorable en un 87%, en cuanto a las prácticas sobre métodos anticonceptivos se obtiene que el 94% de los estudiantes que han tenido relaciones sexuales usaron método, el 39,62% usaron preservativos, el 52,17% indicó usarlo porque es más práctico. Conclusiones: se tiene como resultado que: el nivel de conocimiento encontrado en la escuela de terapias físicas de rehabilitación es bueno en un 93% teniendo como meta fortalecer los conocimientos en torno a este tema ya que al ser profesionales de la salud es necesario que cuenten con conocimientos básicos sobre métodos anticonceptivos. La relación entre la actitud y práctica de los estudiantes frente al uso de métodos anticonceptivos da como resultado que al tener una actitud favorable, la práctica será óptima en: 59,26%(64)

Polymeric phase V of carbon dioxide has not been recovered at ambient pressure and has a unique structure

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