Intercalation of uranium hexafluoride into graphite

1985 ◽  
Vol 50 (4) ◽  
pp. 947-955 ◽  
Author(s):  
Karel Klouda ◽  
Václav Rak ◽  
Josef Vachuška
Keyword(s):  
Carbon Atom ◽  
Surface Area ◽  
Gaseous Phase ◽  
Uranium Hexafluoride ◽  
Graphite Particles ◽  
Fluorination Agent ◽  
Increasing Temperature ◽  
Elementary Fluorine

Intercalation of UF6 into graphite, both from the gaseous phase and from the Ledon 113 solution, was studied. The amount of intercalated UF6 from the gaseous phase was found to be inversely proportional to the size of graphite particles. Intercalation increases with the increasing temperature and surface area of graphite. The contact of gaseous UF6 with graphite led to the formation of β-UF5 that is not intercalated. In the Ledon solution, β-UF5 is not formed. "Passivation" of graphite by elementary fluorine also prevents the formation of β-UF5 but the amount of intercalated UF6 decreases. The intercalation of UF6 into graphite from the gaseous phase is accompanied by the increase of the distance between the parallel carbon atom layers up to the values of about 884 pm. Ternary intercalates graphite-UF6-Ledon 113 are formed during the intercalation of UF6 from the Ledon 113 solutions and the distance between the parallel carbon atom layers is 848-875 pm. Thermogravimetry in the presence of air revealed that the binary intercalates graphite-UF6 decompose in a 3-step reaction while the ternary intercalates decompose in a 4-step reaction. In both cases uranium hexafluoride is not released but acts as a fluorination agent on the graphite carbon.

scholarly journals Oxidized BPL Carbons

1993 ◽  
Vol 10 (1-4) ◽  
pp. 75-84 ◽  
Author(s):  
S.S. Barton ◽  
M.J.B. Evans ◽  
J.A.F. Macdonald
Keyword(s):  
Nitric Acid ◽  
Surface Area ◽  
Water Adsorption ◽  
Adsorption Properties ◽  
Bet Surface Area ◽  
Adsorption Sites ◽  
A Value ◽  
Nitrogen Desorption ◽  
Oxidized Carbon ◽  
Increasing Temperature

A series of oxidized carbons has been prepared by treatment of the carbon with concentrated nitric acid at various temperatures, and the surface and adsorption properties of the prepared carbons studied. Water adsorption was modelled using a recently derived equation capable of predicting a value for the primary adsorption sites on the surface of a microporous carbon while fitting the experimentally determined isotherm at high relative pressures. The concentration of primary sites was seen to increase with increasing temperature of oxidation. The very highly oxidized carbon samples were found to have a significantly lower BET surface area determined from nitrogen desorption at 77 K and higher apparent density measured from mercury displacement.

scholarly journals Photoconductivity of activated carbon fibers

1991 ◽  
Vol 6 (5) ◽  
pp. 1040-1047 ◽  
Author(s):  
K. Kuriyama ◽  
M.S. Dresselhaus
Keyword(s):  
Activated Carbon ◽  
Surface Area ◽  
Carbon Fibers ◽  
Low Temperatures ◽  
Room Temperature ◽  
High Surface ◽  
Localized States ◽  
Activated Carbon Fibers ◽  
Disordered Carbon ◽  
Increasing Temperature

The conductivity and photoconductivity are measured on a high-surface-area disordered carbon material, i.e., activated carbon fibers, to investigate their electronic properties. This material is a highly disordered carbon derived from a phenolic precursor, having a huge specific surface area of 1000–2000 m2/g. Our preliminary thermopower measurements show that the dominant carriers are holes at room temperature. The x-ray diffraction pattern reveals that the microstructure is amorphous-like with Lc ≃ 10 Å. The intrinsic electrical conductivity, on the order of 20 S/cm at room temperature, increases by a factor of several with increasing temperature in the range 30–290 K. In contrast, the photoconductivity in vacuum decreases with increasing temperature. The magnitude of the photoconductive signal was reduced by a factor of ten when the sample was exposed to air. The recombination kinetics changes from a monomolecular process at room temperature to a bimolecular process at low temperatures, indicative of an increase in the photocarrier density at low temperatures. The high density of localized states, which limits the motion of carriers and results in a slow recombination process, is responsible for the observed photoconductivity.

Mathematical Modeling of Biodiesel Production under Intense Agitation

2016 ◽  
Vol 14 (1) ◽  
pp. 445-451
Author(s):  
Aliakbar Roosta ◽  
Jafar Javanmardi ◽  
Elham Sadat Behineh
Keyword(s):  
Mass Transfer ◽  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Rapeseed Oil ◽  
Catalyst Concentration ◽  
Biodiesel Production ◽  
Transfer Coefficients ◽  
Increasing Temperature ◽  
Intense Agitation

AbstractIn this study, a new approach is proposed to investigate the kinetics of sunflower oil and rapeseed oil transesterification in the presence of potassium hydroxide. Transesterification is a heterogeneous process which affected by a number of parameters, that are not readily available in the literature, such as mass transfer coefficients, partition coefficients, and specific surface area of the dispersed phase. However, under intense agitation condition, mass transfer restrictions may be neglected, and the two phases are supposed to remain in thermodynamic equilibrium, during the process. Therefore, a model was developed independent of the mass transfer coefficient and specific surface area, which is reliable for the intense agitation condition. According to the results, the model is valid at least for mixing rates over 500 rpm. The results of the model were used to study the effects of temperature, methanol-to-oil ratio, and catalyst concentration on the biodiesel conversion. Biodiesel production rate increases with increasing temperature, although rapeseed oil transesterification is more temperature dependent. The results show that the maximum amount of catalyst concentration is less than 1% (by weight); however, the optimum value depends on the operating temperature. The optimum value of the methanol-to-oil-ratio decreases with increasing temperature. Thus, at higher temperatures, less amount of methanol and catalyst are required, which leads to easier purification of biodiesel.

scholarly journals Can water evaporation rates be enhanced by employing a different polar ambient?

2020 ◽  
Author(s):  
Ashish Karn ◽  
Jonathan Ambs ◽  
Shashank Singh Deo ◽  
Ayush Vyas ◽  
Ayush Dwivedi ◽  
...  
Keyword(s):  
Surface Area ◽  
Evaporation Rate ◽  
Practical Interest ◽  
Underlying Mechanism ◽  
Water Desalination ◽  
Water Evaporation ◽  
Great Practical Interest ◽  
Conventional Methods ◽  
Increasing Temperature ◽  
Temperature Surface

Enhancing evaporation rates are of great practical interest in many technological applications such as water desalination or drying in industry. Since the conventional methods of increasing evaporation viz. increasing temperature, surface area etc. may not be always practically feasible or economical, novel methods of evaporation enhancement are necessary. The current study explores the possibility of evaporation enhancement by introducing a Tetrafluoroethane gas ambient under different conditions of heating and circulation. Depending upon the temperature and circulation conditions, as enhancement of 58 to 375% in evaporation rate has been measured and physical explanations into the underlying mechanism have been suggested.

scholarly journals Effect of ultrasound on the dissolution of Mardin-Mazıdağı (Turkey) phosphate ore in dilute H3PO4 solutions

2019 ◽  
Vol 51 (2) ◽  
pp. 164-167
Author(s):  
M. Sinirkaya
Keyword(s):  
Reaction Time ◽  
Phosphoric Acid ◽  
Surface Area ◽  
Acid Concentration ◽  
Reaction Temperature ◽  
Acid Solutions ◽  
Liquid Interfaces ◽  
Phosphate Ore ◽  
Increasing Temperature ◽  
Solid Liquid

The dissolution of phosphate ore in dilute phosphoric acid solutions was investigated in both the absence and presence of ultrasound. Acid concentration, reaction temperature and reaction time were chosen as parameters. While the conversion fractions decreased with increasing temperature in dilute phosphoric acid in absence of ultrasound, these rates increased with increasing temperature in the presence of ultrasound. In the experiments, the expected effects of ultrasound were observed, such as decrease in the thickness of the diffusion layer on the solid–liquid interfaces in the suspension, leading to increased surface area.

scholarly journals Adsorption of carbon dioxide on MIL53(Al), CuBTC and K- NaX zeolite

2020 ◽  
Vol 4 (3) ◽  
pp. 30-42
Author(s):  
Fehime Cakicioglu-Ozkan
Keyword(s):  
Carbon Dioxide ◽  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Co2 Adsorption ◽  
Ultrasonic Method ◽  
Metal Organic Frameworks ◽  
Isosteric Heat ◽  
Metal Organic ◽  
Increasing Temperature

CO2 adsorption on K exchanged NaX zeolites, and metal organic frameworks (MOFs), namely Cu-BTC and MIL53 (Al) was studied at 5 °C and 25 °C.  Exchange via ultrasonic and traditional methods, was conducted at 50 °C and 70 °C. The maximum replacement of Na+ ion with K+ ion in the extra framework of zeolite was increased from 76% to 83% with increasing temperature from 50 °C to 70 °C in the ultrasonic method which is more effective than traditional one. Compared with the zeolites, the MOF adsorbents used in this work have higher Langmuir specific surface area values namely 1278, 1473 and about 1000 m2/g for MIL 53, Cu-BTC and zeolite adsorbents respectively. The resulting CO2 isotherms can be well represented by the Toth equation. Comparison of the isosteric heat of adsorption at zero loading shows that CO2 was adsorbed more weakly on MOFs than zeolites.

Moisture Sorption Characteristics of Ready-to-eat Chicken Wheat Crisps Prepared Using Resistant Starch and Chicken Powder with Wheat Flour

2017 ◽  
Vol 2 (2) ◽  
pp. 163 ◽  
Author(s):  
Shefali Bhardwaj ◽  
V. K. Shiby ◽  
M. C. Pandey ◽  
Natarajan Gopalan
Keyword(s):  
Surface Area ◽  
Water Activity ◽  
Goodness Of Fit ◽  
Moisture Sorption ◽  
Isosteric Heat ◽  
Coefficient Of Determination ◽  
Sorption Data ◽  
Temperature Equilibrium ◽  
Increasing Temperature ◽  
Parameter Values

Fibre and protein enriched chicken wheat crisps were evaluated for their adsorption behaviour at a temperature range of 5 °C - 40 °C and a water activity range of 0.1-0.9. Sigmoid type II isotherm was obtained for the product and the sorption data was fitted to 3 models namely BET, GAB, and Peleg model. Each model was statistically evaluated by means of root mean square (%) and coefficient of determination (R2). Peleg and GAB gave the best fits for the moisture sorption data evaluated on the basis of regression analyses and goodness of fit. Surface area of adsorption was evaluated using parameter values obtained from the BET model and the surface area decreased with increase in temperature. Equilibrium moisture content at a particular water activity and isosteric heat of sorption were seen to decrease with increasing temperature. We conclude that the chicken wheat crisps can be stored at 25 °C for a better shelf life.

scholarly journals Adsorption of phosphate ions from an aqueous solution by calcined nickel-cobalt binary hydroxide

2016 ◽  
Vol 75 (1) ◽  
pp. 94-105 ◽  
Author(s):  
Fumihiko Ogata ◽  
Erimi Ueta ◽  
Megumu Toda ◽  
Masashi Otani ◽  
Naohito Kawasaki
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
Correlation Coefficients ◽  
Hydroxyl Groups ◽  
Order Model ◽  
Molar Ratios ◽  
Phosphate Ions ◽  
Increasing Temperature ◽  
Adsorption Desorption

Different molar ratios of a Ni/Co binary hydroxide (NiCo82, NiCo91, and Ni100) were prepared and calcined at 270 °C (NiCo82-270, NiCo91-270, and Ni100-270). The properties of the adsorbents and the amount of adsorbed phosphate ions were evaluated. The adsorbents calcined at 270 °C had a nickel oxide structure. The amount of adsorbed phosphate ions, the amount of hydroxyl groups, and the specific surface area of the calcined adsorbents at 270 °C were greater than those of the uncalcined adsorbents. The amount of adsorbed phosphate ions was related to the amount of hydroxyl groups and the specific surface area; the correlation coefficients were 0.966 and 0.953, respectively. The adsorption isotherm data for NiCo91 and NiCo91-270 were fit to both the Freundlich and Langmuir equations. The amount of adsorbed phosphate ions increased with increasing temperature. The experimental data fit the pseudo-second-order model better than the pseudo-first-order model. A neutral pH was optimal for phosphate ion adsorption. In addition, the phosphate ions that were adsorbed onto NiCo91-270 could be recovered using sodium hydroxide, and the adsorbent was useful for the repetitive adsorption/desorption of phosphate ions. Collectively, these results suggest that NiCo91-270 is prospectively useful for the adsorption of phosphate ions from aqueous solutions.

Gas Phase Synthesis of Molybdenum and/or Iron Nitrides, Carbides and Sulfides

1994 ◽  
Vol 368 ◽  
Author(s):  
Michael R. Close ◽  
Jeffrey L. Petersen
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Lower Surface ◽  
Iron Nitrides ◽  
Ammonia Vapor ◽  
Surface Areas ◽  
Molybdenum Sulfides ◽  
Molybdenum Carbides ◽  
Increasing Temperature

ABSTRACTThe thermolytic decomposition of Mo(CO)6 with hydrogen sulfide or ammonia vapor (in a He carrier stream) at temperatures ranging from 300 to 1100 °C produces high surface area molybdenum sulfides (MoS2 or Mo2S3) or molybdenum carbides (hexagonal Mo2C) and carbonitrides, (hexagonal MoN(C) or cubic Mo2N(C)), respectively. The MoS2 surface areas range from 16.7 to 82.0 m2/g, while the surface areas of molybdenum carbides and carbonitrides vary from 14.9 to 21.1 m2/g. The maximum surface area for MoS2 is achieved at 500 °C and decreases with increasing or decreasing temperature. The surface area of the carbonitrides formed from 300 to 800 °C increases with increasing temperature up to 950 °C, where lower surface area Mo2C is formed. Crystallographically pure hexagonal MoN is prepared by decomposing Mo(CO) 6 in pure ammonia. Fe(CO) 5 decompositions in ammonia produce FexZ (where 5.8≥x≥1.6 and Z=C and N), and in some cases elemental Fe. Hexagonal Fe3 N(C) forms when Fe(CO) 5 is thermolyzed in ammonia from 300 to 600 °C, with surface areas ranging from 9.5 to 13.7 m2/g, whereas orthorhombic Fe3C and cubic Fe are produced at 700, 800, 900 and 1000 °C with surface areas of 6.7, 7.6, 2.2 and 2.0 m2/g, respectively. Within the same phase, the surface areas of the carbonitrides increase with increasing reaction temperature. These iron and molybdenum carbonitrides catalyze the conversion of CO/H2 to alkanes and methanol. Based on preliminary catalytic studies, the highest rate of methane (2850 g/kg/hr at 374 °C) and methanol (440 g/kg/hr at 284 °C) formation was accomplished with an FeMo carbonitride prepared by decomposing Mo(CO)6 and Fe(CO)5 in ammonia at 800 °C.

scholarly journals Fabrication of high surface area acid-treated activated carbon from pomegranate husk for 2,4-dichlorophenol adsorption

2021 ◽  
Author(s):  
Ensiyeh Taheri ◽  
Mohammad Mehdi Amin ◽  
Ali Fatehizadeh ◽  
Eder C. Lima
Keyword(s):  
Activated Carbon ◽  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Xrd Analysis ◽  
Absorption Capacity ◽  
Surface Areas ◽  
Adsorption Condition ◽  
Pomegranate Husk ◽  
Increasing Temperature

Abstract In the present study, zinc chloride followed by acid treating was employed for fabrication activated carbon with a high surface area from pomegranate husk (APHAC) for 2,4-dichlorophenol (2,4-DCP) adsorption. The APHAC was a well-developed pore and exhibiting specific surface areas of 1576 m2/g. Based on the XRD analysis, the diffraction peaks between 15 ° and 35 ° corresponded to amorphous carbon, and the pHpzc values of APHAC was 6.15 ± 0.15. According to batch experiments, the optimum adsorption condition of 2,4-DCP was pH of 3, contact time 60 min, and APHAC dose of 1.75. The absorption capacity of 2,4-DCP at the APHAC dose of 0.5 promptly decreased from 259.5 ± 12.9 mg/g at the initial concentration of 150 mg/L to 74.5 ± 3.7 mg/g dose of 2 g/L. With increasing temperature from 10°C to 50°C, the adsorption efficiency declined from 99.8 ± 0.5% to 75.6 ± 1.89%. The isotherm and kinetic of 2,4-DCP by APHAC revealed that Freundlich and Elovich satisfactorily fitted with experimental data.

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