scholarly journals Silver Precipitation Using Sodium Dithionite in Cyanide Media

2017 ◽  
Vol 56 (2) ◽  
Author(s):  
Isauro Rivera ◽  
Guillermo Juárez ◽  
Francisco Patiño ◽  
Iván A. Reyes ◽  
Antonio Roca ◽  
...  
Keyword(s):  
Activation Energy ◽  
Induction Period ◽  
Kinetic Parameters ◽  
Room Temperature ◽  
Chemical Precipitation ◽  
Sodium Dithionite ◽  
High Activation ◽  
Residual Content ◽  
Silver Precipitation ◽  
Reaction Orders

The nature of the reaction and the main parameters affecting Ag precipitation rate in the system Ag<sup>+</sup>-CN<sup>-</sup>-S<sub>2</sub>O<sub>4</sub><sup>2-</sup> are studied. From the results obtained, a process of chemical precipitation for Ag recovery is proposed, using an environmentally-friendly reducing reagent (sodium dithionite, Na<sub>2</sub>S<sub>2</sub>O<sub>4</sub>), leaving a residual content of Ag into the permitted environmental levels (-1 Ag). The levels of CN<sup>-</sup> in liquids wastes are of the order of 0.816 mol L<sup>-1</sup>, and they can be treated by ozonization processes for inerting cyanide. The results obtained indicate that Ag precipitation is achieved in less than 1 hour, with recoveries close to 99%, at room temperature. Silver precipitation is characterized by an induction period followed by a precipitation period, leaving a metal amount in solution less than 1 mg L<sup>-1</sup>. The main kinetic parameters studied lead to obtain the following apparent reaction orders: with respect to the initial [S<sub>2</sub>O<sub>4</sub><sup>2-</sup>] was <em>n</em> = 1.675, with respect to [CN<sup>-</sup>] was -1.24, with respect to [OH<sup>-</sup>] was ≈0 (between 10<sup>-4</sup> and 10<sup>-2</sup> mol L<sup>-1</sup>) and with respect to the initial [Ag<sup>+</sup>] was 0.524. An activation energy of 77 kJ mol<sup>-1</sup> was obtained. Under these conditions, Ag precipitation in the system Ag<sup>+</sup>-CN<sup>-</sup>-S<sub>2</sub>O<sub>4</sub><sup>2-</sup> is controlled by chemical reaction, characterized by high activation energy, and is independent of the hydrodynamic variables of the system.

Structural and Thermal Properties of Cu Doped Nanocrystalline Tin Selenide

2013 ◽  
Vol 665 ◽  
pp. 15-21
Author(s):  
N.N. Gosai ◽  
G.K. Solanki ◽  
K.D. Patel ◽  
Keyur S. Hingarajiya
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Room Temperature ◽  
Thermal Characteristics ◽  
Stable Operation ◽  
X Rays ◽  
Size Estimation ◽  
Prepared Compound ◽  
Thermoanalytical Techniques ◽  
Tin Selenide

Nanocrystalline Copper doped Tin Selenide have been prepared by aqueous solution method in double distilled water at room temperature. All the chemicals used for this were of Analytical Reagent grade and of 99.999 % purity. Structural confirmation of prepared compound and particle size estimation was done from X-ray diffractogram obtained by CuKαradiation of wavelength 1.540 nm. Compositional or elemental analysis of this compound was done using energy dispersive analysis of X-rays (EDAX) and it is found that prepared compound is nearly stoichiometric in nature. Thermal characteristics of SnSeCu nanocrystals were studied employing thermoanalytical techniques, viz. TGA and DTA. Thermogravimetric analysis (TGA) has been used for many years to evaluate thermal stability of material as it will determine the range of stable operation for a device made up out of these materials under investigation. Thermal analysis experiments were carried out with constant heating rate of 10 °C/ min in air from room temperature to 900 °C. The DTA pattern of SnSeCu nanocrystal shows a strong endothermic peak at 450 °C. The objective of this study is to determine activation energy and other kinetic parameters of prepared compound. Broido and Coats-Redfern (C-R) models are used to evaluate different kinetic parameters viz. activation energy, entropy, enthalpy, Gibbs mean free energy and they were found to have good correlation coefficient.

scholarly journals Transformation of Synthetic Allicin: The Influence of Ultrasound, Microwaves, Different Solvents and Temperatures, and the Products Isolation

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Dušica Ilić ◽  
Vesna Nikolić ◽  
Mihajlo Stanković ◽  
Ljubiša Nikolić ◽  
Ljiljana Stanojević ◽  
...  
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Conventional Method ◽  
Room Temperature ◽  
Transformation Products ◽  
Diallyl Disulfide ◽  
Optimal Method ◽  
Degradation Kinetic ◽  
Pharmacologically Active ◽  
Pharmacologically Active Compounds

The transformation of the synthesized allicin, using conventional method, the influence of ultrasound and microwaves, in different organic solvents (acetonitrile, acetone, methanol, and chloroform), at various temperatures (room temperature,45∘C, and55∘C) was investigated. Allicin degradation kinetic was monitored by HPLC. Allicin transformation under the effect of microwaves is faster than transformations performed under the influence of ultrasound or by conventional method. Increase of the temperature accelerates allicin transformation. Pharmacologically active compounds of (E)-ajoene, (Z)-ajoene, 3-vinyl-4H-1,2-dithiin, 2-vinyl-4H-1,3-dithiin, and diallyl disulfide were isolated from the mixture of transformation products of allicin under the influence of microwaves in methanol at55∘C, which is according to kinetic parameters (highest values of the order of reaction and the lowest activation energy) the optimal method.

On the use of Ozawa/Flynn/Wall method to determine aging activation energy for elastomers

2021 ◽  
pp. 009524432110203
Author(s):  
Sudhir Bafna
Keyword(s):  
Mechanical Properties ◽  
Activation Energy ◽  
Weight Loss ◽  
Oxygen Consumption ◽  
Dwell Time ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Kinetics Of ◽  
Wall Method

It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.

Application of Calculus Equation in Solving Thermal Decomposition Kinetics Parameters of Flame Retardant Wood

2014 ◽  
Vol 983 ◽  
pp. 190-193
Author(s):  
Cai Yun Sun ◽  
Yong Li Yang ◽  
Ming Gao
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Thermal Degradation ◽  
Phosphoric Acid ◽  
Flame Retardant ◽  
Kinetic Parameters ◽  
Flame Retardancy ◽  
Decomposition Kinetics ◽  
Thermal Decomposition Kinetics ◽  
Kinetics Parameters

Wood has been treated with amino resins and amino resins modified with phosphoric acid to impart flame retardancy. The thermal degradation of samples has been studied by thermogravimetry (TG) in air. From the resulting data, kinetic parameters for different stages of thermal degradation are obtained following the method of Broido. For the decomposition of wood and flame retardant wood, the activation energy is found to decrease from 122 to 72 kJmol-1.

Front instability in a condensed phase combustion model

2015 ◽  
Vol 4 (3) ◽  
pp. 153-176 ◽  
Author(s):  
Alexis Bonnet ◽  
Fathi Dkhil ◽  
Elisabeth Logak
Keyword(s):  
Activation Energy ◽  
Condensed Phase ◽  
Linear Instability ◽  
Combustion Model ◽  
Energy Limit ◽  
High Activation ◽  
Front Solution ◽  
High Activation Energy ◽  
Linearized Problem ◽  
Existence Of Zeros

AbstractWe consider a condensed phase (or solid) combustion model and its linearization around the travelling front solution. We construct an Evans function to characterize the eigenvalues of the linearized problem. We estimate this functional in the high activation energy limit. We deduce the existence of zeros with nonnegative real part for high activation energy, which proves the linear instability of the travelling front solution.

Observation of Rheed Intensity Oscillations During PbSe/CaF2/Si(111) MBE

1996 ◽  
Vol 441 ◽  
Author(s):  
W. K. Liu ◽  
X. M. Fang ◽  
P. J. McCann ◽  
M. B. Santos
Keyword(s):  
Activation Energy ◽  
Melting Point ◽  
Substrate Temperature ◽  
High Melting ◽  
Arrhenius Behavior ◽  
High Activation ◽  
High Melting Point ◽  
Mbe Growth ◽  
Sublimation Energy ◽  
Initial Nucleation

AbstractRHEED intensity oscillations observed during MBE growth of CaF2 on Si(111) and PbSe on CaF2/Si(111) are presented. The effects of substrate temperature and initial nucleation procedure are investigated. Strong temporal oscillations of the specular beam intensity are found to be most readily observed at temperatures below 200°C for both CaF2 and PbSe. Growth rates measured as a function of cell temperatures exhibit Arrhenius behavior with activation energies of 5.0 eV and 1.93 eV for CaF2 and PbSe, respectively. The relatively high activation energy obtained for CaF2 is consistent with the high melting point and sublimation energy of ionic fluorides.

The slow oxidation of methane

1956 ◽  
Vol 235 (1201) ◽  
pp. 158-173 ◽  
Keyword(s):  
Activation Energy ◽  
Hydrogen Peroxide ◽  
Induction Period ◽  
Hydrofluoric Acid ◽  
Pressure Rise ◽  
Pressure Change ◽  
Kcal Mole ◽  
Gaseous Products ◽  
Oxidation Of Methane ◽  
Reproducible Manner

Mixtures of methane and oxygen behave in a reproducible manner at temperatures of 440 to 520°C and initial pressures of 100 to 350 mm when reacting in Pyrex vessels freshly cleaned with hydrofluoric acid. The apparent order of the reaction ranged from 2∙3 to 2∙6 and the overall activation energy from 29 to 41 kcal/mole. Analyses of the products formed have been made, together with measurements of pressure change. Formaldehyde is formed from the commencement of the reaction including the induction period, but its concentra­tion reaches a maximum near the stage where the pressure rise is a maximum, and then falls off. Hydrogen peroxide is also formed, less rapidly in the earliest stage, but its rate of formation overtakes that of formaldehyde and it reaches an even higher concentration. No other peroxides were detected, nor was methanol found. Hydrogen was present in the gaseous products. These observations are not in full accord with some of the conclusions derived from earlier investigations.

scholarly journals Synthesis and electrical characterization of Ca2Nd4Ti6O20 ceramics

2016 ◽  
Vol 34 (1) ◽  
pp. 164-168
Author(s):  
Raz Muhammad ◽  
Muhammad Uzair ◽  
M. Javid Iqbal ◽  
M. Jawad Khan ◽  
Yaseen Iqbal ◽  
...  
Keyword(s):  
Activation Energy ◽  
Dielectric Constant ◽  
Room Temperature ◽  
Sol Gel ◽  
Electrical Characterization ◽  
Sintered Sample ◽  
First Time ◽  
Alkoxide Precursors ◽  
Room Temperature Dielectric Constant

AbstractCa2Nd4Ti6O20, a layered perov skite structured material was synthesized via a chemical (citrate sol-gel) route for the first time using nitrates and alkoxide precursors. Phase analysis of a sample sintered at 1625 °C revealed the formation of an orthorhombic (Pbn21) symmetry. The microstructure of the sample after sintering comprised rod-shaped grains of a size of 1.5 to 6.5µm. The room temperature dielectric constant of the sintered sample was 38 at 100 kHz. The remnant polarization (Pr) and the coercive field (Ec) were about 400 μC/cm2 and 8.4 kV/cm, respectively. Impedance spectroscopy revealed that the capacitance (13.7 pF) and activation energy (1.39 eV) of the grain boundary was greater than the capacitance (5.7 pF) and activation energy (1.13 eV) of the grain.

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