Search results for "Isothermal process"
showing 10 items of 114 documents
Gas phase chromatography of halides of elements 104 and 105
1992
On-line isothermal gas phase chromatography was used to study halides of261104 (T1/2=65 s) and262,263105 (T1/2=34 s and 27 s) produced an atom-at-a time via the reactions248Cm(18O, 5n) and249Bk(18O, 5n, 4n), respectively. Using HBr and HCl gas as halogenating agents, we were able to produce volatile bromides and chlorides of the above mentioned elements and study their behavior compared to their lighter homologs in Groups 4 or 5 of the periodic table. Element 104 formed more volatile bromide than its homolog Hf. In contrast, element 105 bromides were found to be less volatile than the bromides of the group 5 elements Nb and Ta. Both 104 and Hf chlorides were observed to be more volatile tha…
Gas-liquid chromatographic analyses
1984
A mixture of all nine chlorinated 4-hydroxybenzaldehydes and the parent homologue was separated on a non-polar SE-30 capillary column using various isothermal and temperature-programmed operating conditions. The relative retention data for the compounds are given and the retention indices together with the retention index increments for each position of chlorine substitution are examined. The retention order 3-Cl<parent<2,5-di-Cl<2,3-di-Cl<3,5-di-Cl<2-Cl<2,3,5-tri-Cl<2,3,6-tri-Cl<2,6-di-Cl<tetra-Cl isomer obtained indicates that the effect of the position of substitution on the retention behaviour is greater than that of the number of chlorine atoms. The retention is maximal with 2-Cl and 2…
Retention increments of isomeric chlorobenzenes
1983
The chlorobenzene isomers are used extensively as intermediates in a wide range of chemical products. More recently their determination in environmental situations has become of considerable importance and chromatographic procedures have been widely reported for their determination in both trace and major amounts. There are over 220 publications in which gas chromatography (GC) has been applied to the analysis of chlorobenzene. However, over 60 o/o of these works refer to the separation of only one isomer. Relatively few publications’-8 consider all the isomers, although the use of both capillary3’ and packedcolumns with polar and non-polar stationary phases has been reported. Temperature p…
Gas—liquid chromatographic analyses
1985
Abstract The gas chromatographic retention behaviour of methylethyl, 1-methylpropyl, 2-methylpropyl, 1,2-dimethylpropyl, 1-methylbutyl and 3-methylbutyl esters of benzoic and o-, m- and p-chlorobenzoic acids on low-polarity (SE-30) and polar (OV-351) capillary columns under several temperature-programmed and isothermal conditions is reported. The retention data and the Kovats retention indices for all 24 components are given and the separation of a complex mixture is discussed. The retention index increments have been used to examine the effects of chain branching and chlorine substitution. The results are compared with those for n-alkyl benzoates and monochlorobenzoates.
Molecular association in low-temperature and high-pressure polymorphs of 1,1,1,2-tetrachloroethane
2010
Interactions and aggregation of 1,1,1,2-tetrachloroethane molecules, Cl3CCH2Cl, have been investigated at low temperature and high pressure. Isobaric and isochoric crystallizations led to two polymorphs, characterized by single-crystal X-ray diffraction. The low-temperature polymorph α is monoclinic, space group C2/c, with molecules orientationally disordered in two sites at the temperature independent 70:30 rate. In isothermal conditions (295 K) 1,1,1,2-tetrachloroethane freezes at 0.73 GPa. The high-pressure polymorph β is monoclinic, space group P21/c, with the molecules fully ordered. The molecular aggregation at varied thermodynamic conditions results from the interplay of halogen inte…
Isothermal equation of state and phase stability of Fe 5 Si 3 up to 96 GPa and 3000 K
2017
The composition of Earth's core has first-order implications for understanding the thermal and chemical history of the deep Earth. The present work measures the pressure-volume equation of state of Fe5Si3 to 96 GPa in a diamond anvil cell using noble gas pressure media and demonstrates that Fe5Si3 is not stable at high temperature and pressure, but reappears during thermal quench. The isothermal equation of state at ambient temperature of Fe5Si3 is given by the bulk modulus KT,0 = 167 (8) and KT,0' = 5.1 (2)), with V0 = 56.29 cm3mol-1. At high temperatures and pressures we observed the disappearance of hexagonal Fe5Si3 diffraction peaks and the appearance of peaks corresponding to cubic FeS…
GdBO3 and YBO3 crystals under compression
2021
High-pressure X-ray diffraction studies on nanocrystals of the GdBO3 and YBO3 rare-earth orthoborates are herein reported up to 17.4(2) and 13.4(2) GPa respectively. The subsequent determination of the room-temperature pressure-volume equations of state is presented and discussed in the context of contemporary publications which contradict the findings of this work. In particular, the isothermal bulk moduli of GdBO3 and YBO3 are found to be 170(13) and 163(13) GPa respectively, almost 50% smaller than recent findings. Our experimental results provide an accurate revision of the high-pressure compressibility behaviour of GdBO3 and YBO3 which is consistent with the known systematics in isomor…
Synchrotron diffraction study of the isothermal oxidation of uranium dioxide at 250°C
2003
ABSTRACTThe structural evolution of UO2 during its oxidation to U3O8 at 250°C in air was studied by in-situ synchrotron X-ray diffraction on the D2AM-CRG beamline at ESRF. The aim of this study is to determine the phases that are likely to appear during the long-term storage of spent nuclear fuel. Our results are in disagreement with the literature in which the existence of an intermediate cubic phase is not reported. Instead, an α-U3O7 tetragonal phase (c/a < 1) was mentioned but not definitively observed. These previous interpretations may have been the result of poor instrumental resolution.
Colossal barocaloric effects in the complex hydride Li$_{2}$B$_{12}$H$_{12}$
2021
Traditional refrigeration technologies based on compression cycles of greenhouse gases pose serious threats to the environment and cannot be downscaled to electronic device dimensions. Solid-state cooling exploits the thermal response of caloric materials to external fields and represents a promising alternative to current refrigeration methods. However, most of the caloric materials known to date present relatively small adiabatic temperature changes ($|\Delta T| \sim 1$ K) and/or limiting irreversibility issues resulting from significant phase-transition hysteresis. Here, we predict the existence of colossal barocaloric effects (isothermal entropy changes of $|\Delta S| \sim 100$ JK$^{-1}…
Development of a combined solver to model transport and chemical reactions in catalytic wall-flow filters
2017
Abstract In this work, we develop a non-isothermal model for diesel particulate filters including exothermic and competing chemical reactions. We begin with an isothermal, single-reaction model and we gradually increase its complexity. By comparing various models, we aim at establishing the minimum degree of complexity required to effectively model the system under investigation. Based on the numerical simulations, we conclude that isothermal models are adequate only if the temperature of the catalyst is, at all times, completely below or completely above a critical temperature. However, if the goal is to predict the critical temperature, only non-isothermal models should be used. The resul…