Estimated Activation Energy Research Articles

Physicochemical Characterization and Thermodynamic Analysis of Avocado Oil Enhanced with Haematococcus pluvialis Extract

The consumption of fatty acids offers significant health benefits; however, they are prone to degradation by environmental factors. One method to preserve these fatty acids is the addition of synthetic antioxidants. This study focuses on the determination of peroxide and MDA formation rates at temperatures of 25 °C, 45 °C, and 65 °C. The oxidative stability of cold-pressed avocado oil was evaluated using pure astaxanthin, TBHQ, and H. pluvialis extract at concentrations of 100, 500, and 1000 ppm. Kinetic models and thermodynamic analysis were applied to determine the oxidation rate and compare the antioxidant effects of H. pluvialis extract with astaxanthin and TBHQ. The Arrhenius model was used to estimate activation energy (Ea), enthalpy, entropy, and free energy. Avocado oil with 500 ppm of H. pluvialis extract showed antioxidant effects comparable to TBHQ and pure astaxanthin. The activation energy of plain avocado oil was 40.47 kJ mol−1, while with H. pluvialis extract, it was 54.35 kJ mol−1. These findings suggest that H. pluvialis extract offers effective antioxidant properties and could serve as a natural alternative to synthetic antioxidants in food applications, despite the limitations of unprotected astaxanthin.

Enrichment of a Nigerian plagioclase-rich feldspar ore by methanesulfonic acid solution for improved industrial application: kinetic and statistical analysis

ABSTRACT To date, feldspar is a pivotal mineral, with projections indicating a substantial gap between supply and demand in the near future. This surge can be attributed to the increasing need for ceramic tiles, the growing demand for electronic devices, and advancements in glass manufacturing, which have led to the development of a specialised hydrometallurgical process capable of producing iron-free feldspar materials tailored for the ceramics and glass industries. Consequently, the enrichment of a locally sourced plagioclase-rich feldspar ore containing admixtures of albite (Na2.00Al2.00Si6.00O16.00:96-900-1633), anorthite (Ca8.00Si16.00Al16.00O64.0:96-900-0362), and quartz (Si3.00O6.00:96-901-2601) by the hydrometallurgical process was examined in methanesulfonic acid media. The experimental parameters during leaching including leachant concentration, pH, reaction temperature, and particle size on the ore dissolution were investigated and correlated with SPSS statistics version 25 using a mixed-effect model. At established conditions (4.0 mol/L MSA, 75 °C, pH = 2, – 75 + 56 µm), 94.50% iron removal efficiency within 120 minutes. The estimated activation energy of 18.65 kJmol−1 supported the proposed mixed control reaction mechanism as the rate-determining step for the ore enrichment.

Rietveld refined structural, optical and temperature dependent impedance spectroscopy of NiO–ZnO heterostructure composite: Synthesized through solid state method for high-frequency devices

Multifunctional NiO–ZnO heterostructure composite powder is economically synthesized through a solid-state route having a crystallite size of 23 (±2) nm. Chemical composition is identified through FTIR, the peak associated with Zn–O is detected at 1049 cm−1. However, the peaks detected at 870 cm−1 and 590 cm−1 show Ni–O stretching vibrations. UV-DRS technique is employed to estimate the energy band gap (Eg) around 3.18 eV. The impedance studies confirmed the presence of a non-Debye-type relaxation mechanism, electrical parameters confirm the contribution of electroactive regions i.e. grains and interfaces. An equivalent circuit model (R-CPE) is employed to measure various electrical parameters. Adiabatic small polaron hopping model is applied to estimate activation energies for Ni+2 (0.30 eV), Zn+2 (0.35 eV), and bulk (0.32 eV) respectively. The hopping length at the interface is estimated at around 0.8 Å by employing Mott's variable range hopping model. Jonscher's power law (JPL) is used to fit ac conductivity data, and conclude activation energy around 0.3 eV. The conduction mechanism through the whole frequency range (1–107 Hz) is governed by correlated barrier hopping. Various physical parameters i.e. binding energy (Wm), hopping length, and barrier height compared throughout the whole temperature range (313–393 K). The rate of increase in real permittivity at low frequency is related to the disorder of the cation at sublattices. These results deduced potential for NiO–ZnO heterostructure composite for high dielectric permittivity with low tangent loss for high energy storage applications.

Unveiling the recrystallization mechanism and kinetics parameters in cold-rolled dual-phase stainless steel using differential scanning calorimetry

The present work aims to assess the Recrystallization mechanism and Kinetics parameters in Cold-Rolled Dual-Phase stainless steel. For this purpose, Differential Scanning Calorimetry was used over a range of 5–20 K/mn of heating rate, to identify the classical kinetic parameters such as recrystallization temperature, activation energy, and growth mechanism following 90 % reduction in thickness. The findings revealed that the recrystallization temperature increased with rising heating rates within the range [706.8–732] for the ferrite phase, as well as [1282.0–1360.3] K for the austenite phase. The estimated activation energies for ferrite and austenite recrystallization fell within the range of [207.2 ± 1.4–220.1 ± 2.5] kJ/mol and [220.2 ± 2.0–241.1 ± 4.0] kJ/mol, respectively. The Avrami parameter approached half-unity for both ferrite and austenite recrystallized phases for which results can be interpreted to be chiefly responsible for a general mechanism involving the growth of new grains with appreciable initial volume through a diffusion-controlled process.

Hot deformation characteristics and processing map analysis of Al-Zn/stainless steel particles-based composite

The hot deformation behavior of Al-Zn/martensitic stainless steel particles-based composite (Al-Zn/6 %SSp), was examined in this study. The composite was tested using isothermal compression at 200–350 °C/0.01–10 s−1 and a global strain of 0.5. From the results, it was noticed that the composite’s flow stress increased with strain rate increase and drop in temperature. The constitutive equation from the hot-worked composites resulted in an estimated activation energy of 226.27 kJ/mol, which was 58 % more than that for the self-diffusion of aluminum alloy (142 kJ/mol). These findings suggest dynamic recrystallization (DRX) as the dominant deformation mechanism, as confirmed from the microstructures of the hot worked samples mostly at high temperatures and strain rates. Work hardening was predicted to dominate the deformation process by the stress exponent (n) value of 10.36 (which exceeded 5), but this was inconsistent with the microstructural observations. Comparing the linear fitting of calculated flow stress data with the estimated flow stress yielded a correlation coefficient (R2) of approximately 0.97. This observation demonstrates an effective relationship involving the calculated stress with the computed stress value for the composite material that was fabricated. Based on the processing map analysis, the instability regime occurs at 200270 °C/0.01–10 s−1. The stable domain established was at 280–340◦C/0.01–10 s−1 which is most suitable for achieving the best microstructural conditions for enhanced service performance.

Fast Field-Cycling Nuclear Magnetic Resonance Relaxometry of Perfluorosulfonic Acid Ionomers and Their Perfluorosulfonyl Fluoride Precursors Membranes.

The spin-lattice relaxation rates (R1) of fluorine nuclei in perfluorosulfonic acid (PFSA) ionomer membranes and their precursor solid perfluorosulfonyl fluoride (PFSF) were measured by fast field-cycling (FFC) NMR relaxometry. The XRD profiles of PFSA and PFSF are similar and show a characteristic peak, indicating the alignment of main chains. While the SAXS profiles of the PFSA membranes show two peaks, those of the solid PFSF lack the ionomer peak which is characteristic of hydrophilic side chains in the PFSA ionomer membranes. The Larmor frequency dependence of R1 obeys power law and the indices are dependent on the sample and temperature. The indices of the PFSA membranes change from -1/2 to -1 along with the Larmor frequency and temperature dependence decrease, which is consistent with the generalized defect diffusion model. Estimated activation energies are in good agreement with those obtained from dynamical mechanical analysis and dielectric spectroscopy, indicating the segmental motion of the backbones as the common origin of these observations. On the other hand, the index changes to -3/4 in the case of the PFSFs, which has been predicted by the reptation model.

A Study toward the Model Independence of Various Heating Rates Method in Thermoluminescence Glow Curve Analysis

This study analyzes thermoluminescence (TL) glow curves simulated in general order kinetics (GOK), one trap one recombination center (OTOR), and non‐interactive multi‐trap system (NMTS) models using various heating rates (VHR) method in linear heating scheme to extract the activation energy. A theoretical analysis to determine activation energy from TL curves using OTOR and NMTS models in an iterative manner, where the TL intensity is determined by using the Lambert‐W function, is proposed with its limitations. It is established that the activation energies in OTOR and NMTS models consist of the relevant GOK term and a respective correction term. Systematic analysis is carried out to study the improvement of the accuracy of activation energy derived from OTOR and NMTS model TL curves over the GOK model calculation. A quantitative analysis of the quasi‐equilibrium (QE) approximations is carried out for choosing appropriate system parameters. The validity of QE conditions are determined by studying variations of full width at half maximum as well as area under the curve as a function of heating rate. The present method is applied on some experimental data to estimate activation energies. This investigation reveals that the activation energy derived in VHR method has negligible dependence on the underlying theoretical models, i.e., the activation energy derived from GOK model calculation is significantly accurate for experimental scenario.

Improved hydrogen generation via NaBH4 hydrolysis: Synergistic role of sulfur and C4+-Doping unveils (440) high-index facets and modulates Co2+/Co3+ ratios in the Co3O4 lattice

Sodium borohydride (NaBH4) is crucial for eco-friendly “green” hydrogen (H2) storage, employing controlled release through catalyzed NaBH4 hydrolysis, mitigating its inherent sluggish self-hydrolysis. Precious metal catalysts enhance this process, but face scarcity and cost issues hindering widespread use, prompting interest in Co3O4, specifically with (311) orientation for abundant Co2+ sites. However, excess Co2+ on dominant (311) facets limits catalytic efficacy. This study presents a nuanced synthesis of sulfur (S)- and carbon (C4+)-doped Co3O4 that expose high-index (440) facets and optimize Co2+/Co3+ distribution. The catalytic performance of CoSC-0.1-700 on (440) facets demonstrates remarkable hydrogen generation rate of 4.1 L g−1. min−1 within 10.5 min, 1.81×, 2.42×, and 3.83× higher than control samples, and undoped Co3O4 with (311) dominance, and 1.24× higher than (220). An estimated activation energy (Ea) of 33.63 kJ mol−1, comparable to noble metals, indicates high performance and stability over ten (10) cycles. This approach promises sustainable future in "green" H2 production.

Leaching kinetics of waste pharmaceutical blister package aluminium in phosphoric acid media

This study investigated the process of treating secondary aluminium recovered from waste pharmaceutical blister packages (WPBs) using phosphoric acid solutions as a potential strategy for recycling this currently non-recycled waste material. The findings indicate that, when recycling via the hydrometallurgical process, the aluminium passivated during leaching can be effectively counteracted by employing moderately concentrated phosphoric acid solutions (1.0 M), elevated temperatures (60–80 °C) and specifically the addition of H2O2 (1.25–2.5 vol.%). Under these conditions, complete extraction of aluminium was achieved within four hours. The estimated activation energy (∼82 kJ/mol) indicates that the leaching reaction is primarily limited by the chemical reaction rate rather than film diffusion. An aluminium phosphate solution could be obtained by leaching WPBs in a way that is suitable for subsequent aluminium phosphate crystallisation. This approach could provide a promising pathway for valorising aluminium from the currently under-utilised waste fraction of pharmaceutical blister packages.

Deuterium permeation of low-activation vanadium alloys possible for reuse in a short time in fusion reactors

Low-activation vanadium (V) alloys are alternative to reduced-activation ferritic/martensitic steels for the blanket structural material. To make the reusage of the alloys possible in a short time, new-design concepts of V alloy have been suggested in National Institute for Fusion Science. In the present study, the deuterium permeation properties of the new-designed V alloys were investigated.The new-designed V-4Cr-4Ti alloy samples with high and low purity, named H44 and L44, respectively, were used. For comparison, the NIFS-HEAT-2 V alloy samples, named NH2 were also used.It was found from the permeation experiments that deuterium permeability coefficient of L44 was smaller than that of NH2, while the permeability coefficient of H44 was comparable with NH2. These results suggest the permeation coefficient of D of the new-designed V alloy was similar to those of the conventional V alloy, if Ti and O content was the same. Estimated activation energies of diffusion and permeation indicated that the permeation behaviors significantly depended on titanium oxides at the surface and in the bulk. Data obtained by a microscope with Auger electron spectroscopy indicated that the concentration and the composition of the oxide must change with air exposure during the maintenance and with hydrogen isotope exposure during the reactor operation. The obtained results suggest these changes of the concentration and the composition result in the change in the permeation characteristics of hydrogen isotopes.

Industrial waste-based Ni-catalysts for ammonia decomposition to produce clean hydrogen

The high mineral containing solid waste materials generated during aluminum production currently lacks any practical application. In this work, the potential of solid waste with/without additional nickel loading (10 to 20 wt%) was investigated as an active catalyst for low temperature ammonia decomposition to produce high purity hydrogen. The X-ray diffraction (XRD) analysis of the samples reveals that iron oxide was the primary component of solid waste with the ability to catalyze the ammonia decomposition reaction. The reducibility, metal support interaction and catalytic activity of the solid waste supported Ni-based catalysts were correlated by the reduction kinetics of the catalysts using temperature-programmed reduction (H2-TPR) data and nucleation/nuclei growth models. Based on the statistical indicators, it was concluded that the random nucleation model describes catalyst reduction adequately. The estimated activation energy for the reduction of the solid waste itself was significantly higher (108.5 kJ/mol) than that of solid waste supported catalyst containing 10 wt% Ni (86.6 kJ/mol). The increase in nickel loading also slightly decreased the activation energy of catalyst reduction, indicating an improvement in the reducibility of the nickel-containing catalysts. These reduction behaviors were also reflected in the ammonia decomposition reaction in a flow reactor. The addition of nickel onto the solid waste resulted in the creation of additional active nickel sites. Consequently, the nickel loaded solid waste supported catalysts exhibited significant improvements in ammonia decomposition activity. Among the three solid waste supported Ni-based catalysts, the catalyst containing 15 wt% Ni displayed the highest activity, that also remained unchanged over extended period, indicating the catalyst stability.

MoO3/MeMoO4 (Me = Cu, Ni, Co, Fe, Mn, and Cr) composites as materials for prospective optical and electrical applications

The composite MoO3/MeMoO4 (Me = Cu, Ni, Co, Fe, and Mn) ceramics were obtained by standard high-temperature sintering. Their structure was tested using XRD, SEM, EDS, and XPS. The occurrence of two phases was determined. The main MoO3 phase exhibited an orthorhombic Pnma space group related to the ceramic grain of micrometre size. The second phase was induced by doping with the Me atom. It showed various monoclinic structures and a smaller grain size. The XPS test confirmed the coexistence of the phases, which was reflected in several lines in the patterns. The valence band of the undoped MoO3 was located ∼3.3 eV below the Fermi level. An additional subband attributed to the Me 3d state was detected within the energy gap. The MoO3/MeMoO4 composites showed a valence band shifted toward the Fermi level and overlapped with the subband, originating from hybridized Mo 4d – Me 3d states. Magnetic susceptibility showed an antiferromagnetic state below ∼20 K for the Ni- and Fe-doped composites. The estimated magnetic moment magnitudes indicated the contribution from Me2+ and Me3+ ions that marked the occurrence of oxygen vacancies. Diffuse reflectance spectra exhibited anomalies in the Vis (∼500–650 nm) and the NIR (∼700–850 nm) ranges and tails in the ∼900–1000 nm range. The estimated magnitudes of energy gaps were attributed to defect-induced states. They corresponded to deduced oxygen vacancies (2.05–2.38 eV) and states or subbands induced by the introduced Me atoms (1.34–1.89 eV). Electric dc resistivity temperature dependence showed thermally activated dependence. The estimated activation energy varied from 0.27 eV to 0.58 eV, depending on the doping of the Me atom. The electric features were consistent with the electronic structure determined using XRD and XPS tests.

The structure of deposited coke on hydrocracking and reforming catalysts: Coke deactivation and kinetics

AbstractThis comprehensive study investigates the structural deposition of coke, particularly its association with sulphides, in spent hydrocracking and reforming catalysts, leveraging advanced kinetic modelling and characterization techniques. Its objective is to elucidate coke removal kinetics, offering insights into optimizing catalyst regeneration. Utilizing thermogravimetric analysis, spectroscopic methods, and modelling, the research outlines the characteristics and kinetic behaviour of coke during regeneration. The novelty aspect of this study is the use of a reaction‐based model for accurate kinetic analysis and identifying optimal conditions for coke removal. The study recognized both hydrogen‐deficient and hydrogen‐rich amorphous coke, alongside graphitic coke spent catalysts. Thermogravimetric analysis revealed that coke constitutes ~23.8% and 4.6% of the total weight in hydrocracking and reforming catalysts, respectively. The traditional model‐free method for deactivation was found inadequate in predicting coke in the spent reforming catalyst, likely due to the presence of low‐temperature hydrocarbons of soft coke within the catalyst pores. In contrast, a reaction model‐based deactivation approach yielded more consistent evaluations for soft and hard coke of spent catalyst. For the spent hydrocracking catalyst, the estimated activation energies for coke decomposition were 41.56 and 128.97 kJ/mol for soft and hard coke, respectively, during regeneration. Although the coke in the spent reforming catalyst displayed similar temperature trends for decomposition, the average activation energies were 52.61 and 128.62 kJ/mol for soft and hard coke, respectively. The theoretical results from the multi‐reaction model for coke decomposition are consistent with the experimental results for both catalysts.

Characterization of Li+ Transport through the Organic-Inorganic Interface by using Electrochemical Impedance Spectroscopy

Understanding Li+ transport at polymer||inorganic interfaces is crucial for developing composite electrolytes in solid-state batteries. In our investigation, we employed impedance spectroscopy and established a multilayer methodology for assessing Li+ transport at this interface. The inorganic phase chosen was Li6.25Al0.25La3Zr2O12 (Al−LLZO), and the organic phase comprised a Poly(ethylene oxide) (PEO) network with dangling chains. Li+ incorporation in the polymer, as a free either salt or associated with anion grafting onto the PEO network, was explored. Additionally, the PEO network was either pressure-adhered to the inorganic surface (ex-situ configuration) or synthesized onto the Al−LLZO surfaces (in situ configuration) to investigate processing effects on Li+ transport. Using a Transmission Line Model for impedance data analysis, our study identified two key elements governing Li+ transport at the interface: Ri, representing resistance along the ionic pathway, and Rt and Ct, describing distributed resistance and capacitance within the interface. We observed that Ri is influenced by the polymerization process in the presence of Al−LLZO ceramic, while Rt remains constant regardless of the synthesis method. This suggests varying Li+ concentrations at the interphase in the in situ configuration, while interface/interphase heterogeneity remains consistent across configurations. The estimated activation energy indicates more energetically favorable direct Li+ transport in the in−situ configuration.

Glycerol carbonate synthesis via Zn(OBu)2/AlCl2(OBu) initiated-glycerolysis of urea

Glycerol carbonate (4-hydroxymethyl-1,3-dioxolane-2-one) was efficiently synthesized from glycerolysis of urea initiated by Zn(OBu)2/Al(OBu)Cl2. The zinc-aluminum complex mixture was prepared from zinc chloride (ZnCl2) and aluminum tri-sec-butylate (Al(OBu)3. The complex successfully initiated the urea glycerolysis in 1 : 1 ​mol ratio of glycerol to urea to produce glycerol carbonate up to 85% and selectivity up to 97% at 150 ​°C and 1 ​atm of N2 for 4 ​h in the absence of solvents. Isocyanate was observed as a key intermediate in this reaction. A kinetic study showed the reaction likely followed pseudo first-order kinetics with estimated activation energy (Ea) of 38 ​kJ/mol. Density-functional theory calculations with MN15-L functional described the formation of glycerol carbonate as spontaneous with the Gibbs free energy of −28.41 ​kJ ​mol−1.

New insights into the hydrothermal carbonization process of sewage sludge: A reactive molecular dynamics study

In this work, reactive molecular dynamics simulations using the ReaxFF force field were performed to investigate the hydrothermal carbonization (HTC) process of sewage sludge. The focus was on the reaction mechanism, the effect of water content and temperature on the formation of different products. The results showed that temperature was the most important factor controlling the HTC process, with higher temperatures leading to more rapid carbonization reactions and lower H/C and O/C ratios in the hydrochar product. The estimated activation energy of the HTC process was in the range of 126–169 kJ/mol, depending on the water content. The H/C and O/C ratios of the hydochar product obtained from the simulation were in excellent agreement with experimental data. Overall, this work provides valuable new insights into the reaction mechanism and key factors influencing the HTC process of sewage sludge.

Investigation of the Hot Deformation Behavior and Mechanism of a Medium-Entropy CoCr0.4NiSi0.3 Alloy

The CoCrNi-based medium-entropy alloys (MEA) have been extensively investigated due to their exceptional mechanical properties at both room and cryogenic temperatures. To investigate the hot deformation behavior and the recrystallization mechanism of the CoCr0.4NiSi0.3 medium-entropy alloy, a series of deformation tests was conducted using the MMS-100 thermal simulation tester, with deformation conditions of 0.001–1 s−1/850–1150 °C. During the hot deformation process, the flow stress initially increases up to its peak value before gradually decreasing towards a steady state level. Higher flow stress levels are observed with increasing strain rate and decreasing deformation temperature. The estimated activation energy for hot deformation of this alloy is approximately 423.6602 kJ/mol. The Arrhenius-type constitutive equation is utilized to establish a modified model while incorporating power dissipation theory and the instability criterion of a dynamic material model to construct power dissipation maps and instability maps. By superimposing these maps, hot processing maps with strains of 0.4, 0.5, and 0.7 are derived. In this investigation, it is observed that regions of instability exclusively occur when the true strain exceeds 0.4. These regions of instability on the hot processing map align well with experimental findings. The suitable range of parameters for hot-working decreases as the true strain increases. The microstructure was analyzed using electron backscatter diffraction and transmission electron microscopy (TEM) techniques. The volume fraction of dynamic recrystallization (DRX) decreases with increasing strain rate but diminishes with rising temperature. The TEM characterization elucidated the mechanism of DRX in this MEA. The presence of the long-period stacking ordered (LPSO) phase was observed in both the face-centered cubic matrix and hexagonal close-packed recrystallized grains under different deformation conditions. The LPSO phase originates from the matrix at a low strain rate, whereas it is generated during recrystallization at a high strain rate. The observed increase in flow stress of the as-cast MEA is primarily attributed to the synergistic effects arising from the interaction of the dislocation with twins and the second phase. The onset of instability is effectively suppressed within a limited range through the formation of coherent second phases such as L12, LPSO, and superlattice structures resulting from phase transitions. These second phases serve as nucleation sites for recrystallization and contribute to the strengthening of dispersion. Furthermore, their interaction with dislocations and twins significantly influences both flow stress behavior and recrystallization kinetics under hot deformation. These findings not only deepen our understanding of the underlying deformation mechanisms governing MEA but also offer valuable insights for designing CoCrNi-based alloys with improved mechanical properties at elevated temperatures.

Fish waste oil extraction using supercritical CO2 extraction for biodiesel production: Mathematical, and kinetic modeling

The safe disposal of organic waste is a big environmental issue in landfills because of its huge generation volume. The main goal of this research is to determine the effect of supercritical carbon dioxide (scCO2) on the extraction of fish waste oil from discarded fish waste for producing biodiesel. Oil from fish waste was extracted using supercritical fluid extraction process using CO2 as a solvent. The supercritical carbon dioxide (scCO2) extraction was carried out with varying extraction pressure (10–40 MPa), temperature (32–80 °C), and treatment time (15–120 min). The maximum fish waste oil yield obtained was about 77.2 % at a temperature of 80 °C, a pressure of 30 MPa and a time of 60 min. The kinetics and thermodynamic behavior of the scCO2 extraction were calculated using Arrhenius law and Eyring theory, respectively. The estimated activation energy Ea value was 24.45 kJ/mol for the scCO2 extraction of discarded fish waste oil. Approximately 87 % of biodiesel was produced from scCO2 extracted oil via alkaline transesterification process with reaction temperature of 65 °C, NaOH loaded 1 wt%, fish oil to methanol molar ratio of 1:9, and treatment time of 3 h. The characterization of the produced biodiesel showed that its properties complied with the biodiesel standards (EN 14214 & ASTM D6751). The finding of this research revealed that the fish waste could be consumed as a biofuel feedstock.

Preparation of industrial ammonium diuranate from a boltwoodite ore as a mediator for nuclear fuel and catalytic utilizations

To date, uranium is one of the most crucial critical metals and a high supply-demand gap is forecasted in the coming years. However, the upsurging interest in uranium in nuclear fuel cycles prompted an engineered hydrometallurgical route capable of producing a high-grade ammonium diuranate [(NH4)2U2O7] capable of serving as an intermediate in nuclear base fuel and catalytic industries. Consequently, the processing of an indigenous boltwoodite ore containing admixtures of albite (Na2.00Al2.00Si6.00O16.00), boltwoodite (Na2.00K2.77U3.00Si6.00O9.00H4.00), thorite (Th4.00Si4.00O16.00), and quartz (Si6.00O6.00) by the hydrometallurgical process was examined in hydrochloric acid media. The experimental parameters during leaching including lixiviant concentration, reaction temperature, and particle size on the ore dissolution were investigated. At established conditions (2.5 mol/L HCl, 75 °C, 75 μm), 99.1% of the initial 10 g/L ore was dissolved within 120 min. The estimated activation energy of 17.30 kJ/mol indicated a mixed control reaction mechanism as the rate-determining step for the ore dissolution. The thermodynamic and kinetic tests were also examined to explore dissolution feasibility. The apparent change in enthalpy (ΔH = 73.95 kJ/mol) and negative values of Gibb's free energy change affirmed that the U(VI) extraction is endothermic and spontaneous for temperatures between 300 K and 348 K. Almost 99.3% U(VI) in the pregnant solution was quantitatively extracted using TBP in kerosene, and 97% of the total U(VI) was quantitatively precipitated using NH4OH solution. The precipitate was further crystallized to obtain industrial-grade ammonium diuranate comparable with the international standard specification of nuclear purity ASTM C 788–03; recommended to serve as a mediator in the nuclear fuel and catalytic industries.

Resolving an inconsistency in the estimation of the energy for excitation of cardiac muscle contraction.

In the excitation of muscle contraction, calcium ions interact with transmembrane transporters. This process is accompanied by energy consumption and heat liberation. To quantify this activation energy or heat in the heart or cardiac muscle, two non-pharmacological approaches can be used. In one approach using the "pressure-volume area" concept, the same estimate of activation energy is obtained regardless of the mode of contraction (either isovolumic/isometric or ejecting/shortening). In the other approach, an accurate estimate of activation energy is obtained only when the muscle contracts isometrically. If the contraction involves muscle shortening, then an additional component of heat associated with shortening is liberated, over and above that of activation. The present study thus examines the reconcilability of the two approaches by performing experiments on isolated muscles measuring contractile force and heat output. A framework was devised from the experimental data to allow us to replicate several mechanoenergetics results gleaned from the literature. From these replications, we conclude that the choice of initial muscle length (or ventricular volume) underlies the divergence of the two approaches in the estimation of activation energy when the mode of contraction involves shortening (ejection). At low initial muscle lengths, the heat of shortening is relatively small, which can lead to the misconception that activation energy is contraction mode independent. In fact, because cardiac muscle liberates heat of shortening when allowed to shorten, estimation of activation heat must be performed only under isometric (isovolumic) contractions. We thus recommend caution when estimating activation energy using the "pressure-volume area" concept.