Activation Energy Of Decomposition Research Articles

Theory-driven design of graphene-nickel gallate nanocomplex as functional catalyst for composite modified double base propellant

New graphene-nickel gallate nanocomplex (G-M-Ni) was designed, synthesized and characterized to deal with the requirement of functional combustion catalyst based on investigations of combustion mechanisms of propellant, structural analysis of catalyst and simulation results of quantum mechanics. The positive effect of G-M-Ni is not only reflected in the significantly increased burning rate, but also reflected in the reduction of friction sensitivity of composite modified double base (CMDB) propellant. The G-M-Ni nanocomplex exhibited significantly enhanced catalytic performances, and the burning rate of propellant at 20 MPa enhanced from 23.15 to 29.07 mm·s-1. Besides, the friction sensitivity of propellant reduced from 64 % to 36 % after addition of 0.5% G-M-Ni. The positive effect of G-M-Ni on CMDB propellant combustion is mainly attributed to its promotion impact on nitroglycerin (NG) pyrolysis, which significantly increased the differential charge density and decreased the decomposition activation energy (from 1.89 eV to 1.38 eV). The gas products produced by the rapid pyrolysis of NG are conducive to the heat feedback between the gas phase and the combustion surface, which makes the propellant have higher burning rate, bright flame, thin dark zone and flocculated quenching surface morphology. The findings in this study confirm the potential of G-M-Ni as a functional combustion catalyst for CMDB propellants, which has guiding significance and inspiration for the development of new combustion catalysts from the view of molecular-level insights. Novelty and significance statementRecently, graphene based functional combustion catalysts have attracted much attention in the field of solid propellants due to their excellent catalytic combustion performance, reduced sensitivity, and improved mechanical properties. Herein, novel graphene-nickel gallate nanocomplex (G-M-Ni) were designed, synthesized and characterized to deal with the to deal with the requirement of functional combustion catalyst based on investigations of combustion mechanisms of CMDB propellant, structural analysis of new material and simulation results of quantum mechanics. By taking graphene as the benchmark, the G-M-Ni nanocomplex exhibited significantly enhanced catalytic performances, and excellent effect on the reduction of friction sensitivity. The relationship between molecular structure of G-M-Ni and combustion characteristics of CMDB propellant were disclosed. The theory-driven design mode of this work may provide new pathways to tune combustion behaviors of CMDB propellants from the view of molecular-level insights.

NiCoCr2O4 as a potential catalyst for the thermal decomposition of ammonium nitrate: a kinetic investigation

The thermal decomposition of high energetic materials plays an important role in their thermal performance. Use of the catalyst is one of the efficient ways improve the thermal performance of the high energetic materials. Therefore, in this work nickel cobalt chromite (NiCoCr2O4) prepared using precipitation approach was utilized as a catalyst for decreasing the thermal decomposition temperature and activation energy of high energetic material ammonium nitrate (AN). The results suggest that AN/NiCoCr2O4 decomposes at lower temperature (240 °C) within a short temperature range (Thermo gravimetry decomposition curve = 180–250 °C). The kinetic study was investigated using Kissinger-Akahira-Sunose (KAS) and Kissinger method (5, 10, and 15 °C min−1 heating rates). The activation energy of AN was reduced from 158.0 to 141.5 kJ mol−1 and decrease in the pre-exponential factor was observed upon addition of NiCoCr2O4. The outcome of the present work can be used to design AN based high energetic formulations containing NiCoCr2O4 catalyst with better thermal decomposition performance.

Flame retardant polyurethane foam prepared from compatible blends of ammonium ligninsulfonate-based and zinc alginate

Abstract Zinc alginate (ZnAlg) was prepared and subsequently employed to modify ammonium ligninsulfonate-based polyurethane foams (PUFs). A range of analytical techniques, including thermogravimetry, integral programmed decomposition temperature, activation energy, smoke density, cone calorimetry and scanning electron microscopy, were employed to characterise the modified PUFs. The results demonstrated that the PUFA15Z5 (15 % ammonium lignin sulfonate and 5 g ZnAlg) with the lowest mass loss exhibited the second-highest sample decomposition temperature (T50 %), second-highest peak temperature (TMAX2), IPDT and activation energy. Furthermore, the PUFA15Z5 sample exhibited the smallest smoke density (23.11) and the highest light transmittance (67.11 %). The peak heat release rate, total heat release, smoke production rate, total smoke release and four fire risk assessment indicators of the PUFA15Z5 were the lowest, while its carbon residue was the densest. The results demonstrated that the PUFA15Z5 exhibited the most favourable thermal stability, flame retardant properties and the lowest smoke toxicity. These findings provided a valuable reference for subsequent biomass-based flame retardant modified polyurethane foams (PUFs).

High-performance ammonium perchlorate propellants enabled by ferrocene-functionalized carbon nanotube catalysts

Ferrocene-based burning rate catalysts (BRCs) are essential for controlling the combustion of ammonium perchlorate (AP)-based composite solid propellants. However, their efficacy is often limited by migration during storage, leading to performance degradation. This work reports a novel class of covalently grafted ferrocene-functionalized multi-walled carbon nanotubes (CNT-Fc-n, n = 1, 2, 3) exhibiting enhanced catalytic activity and anti-migration properties. Structural characterization confirmed successful functionalization, while electrochemical analysis revealed facilitated electron transfer during AP decomposition due to π-π conjugation within the CNT-Fc-n structure. Consequently, CNT-Fc-n catalysts significantly reduced the AP decomposition activation energy, with CNT-Fc-3 (highest ferrocene loading) demonstrating the most pronounced catalytic effect. Specifically, CNT-Fc-3 lowered the AP decomposition temperature by 103 °C and 39 °C compared to pure AP and Catocene-catalyzed AP, respectively. Kinetic analysis revealed a 28-fold increase in the rate constant for CNT-Fc-3 catalyzed AP decomposition compared to pure AP. Moreover, the unique architecture of CNT-Fc-3 significantly reduced migration during a 50 °C simulation. This work presents a promising strategy for developing high-performance, migration-resistant BRCs for next-generation solid propellants.

Synergetic control of multi‐level interface structure of basalt fibers by plasma and chemical functionalization to enhance the mechanical, thermal and interfacial performances of PBZ composites

AbstractThe composites of polybenzoxazine (PBZ) containing functionalized plasma treatment basalt fibers (fP‐BFs) were fabricated through in‐situ polymerization‐mixing technique. fP‐BFs is an effective reinforcement material that can improve the mechanical, thermal, and interfacial properties of composites. Surface activation of fP‐BFs can be enhanced through plasma modification, which improves the interaction between fP‐BFs and 3‐aminopropyltriethoxysilane. A systematic study on fP‐BFs/PBZ composite showed that a processing power of 300 W, a processing time of 5 min, and a fiber content of 9% can achieve good comprehensive mechanical properties. Thermogravimetric analysis results showed that fP‐BFs‐7/PBZ has the highest thermal stability, and its carbon residue rate, decomposition temperature and thermal decomposition activation energy are 36.80%, 452.2 °C and 133.56 kJ/mol, respectively. The dynamic mechanical analysis experiment showed that the addition of fP‐BFs improved the Tg of the composites. Among them, fP‐BFs‐5/PBZ showed the highest Tg, reaching 233.2 °C.Highlights Plasma treatment produced multi‐level structure of basalt fibers (fP‐BFs). Polybenzoxazine (PBZ)/fP‐BFs composites showed excellent performance. Interfacial bonding mechanism between fP‐BFs and PBZ was elucidated. Interfacial interactions between BFs and PBZ contributed to property enhancement. This work provided a green fabrication strategy of PBZ composites.

Thermal kinetic, mechanical and wear properties of glass fiber reinforced polyamide 6 thermoplastic composites

AbstractPolyamide 6 (PA6) thermoplastic‐based composites are often used in automobile, aerospace, marine, and biomedical applications. Here, PA6 and its composites with varied chopped glass fiber (GF) concentrations of 5, 10, and 20 mass% were fabricated by injection molding. The specimens were characterized by structural, thermal kinetic, mechanical, as well as tribological analyses. Tribological performance was evaluated in dry pin‐on‐disc test apparatus with three different levels of time, speed, and load factors. The PA6/GF composites showed high decomposition activation energy compared to pure PA6. Thermal activation, Ea increased to 46.16% with increasing of GF content up to 10 mass% in the composites compared to PA6. PA6/5GF exhibited best mechanical properties (e.g., strength = 44.46 MPa and Hardness = 45.2). Addition of GF in PA6 significantly improved tribological properties, coefficient of friction (COF) and specific wear rate (WR) besides thermal stability and mechanical properties of the composites. Especially, COF and WR of PA6/5GF composite decreased by 17%–65% and 68%–92%, respectively, compared to PA6. ANOVA statistical results determined the significant contribution of the tribological factors to the performance metrics of the composites for COF and WR. Therefore, the PA6/5GF composite would highly be useful for tie‐rod gears and bearings as a crucial structural component in automotive bodywork.

Analysis of thermal stability for slow burning propellant based on isothermal testing: Self‐accelerating decomposition temperature (SADT) calculation and validation

AbstractBurning rate suppressants (BRSs) refer to a series of additives that reduce the burning rate of propellants, crucial for achieving sustained and stable thrust. This research focuses on assessing the impact of ammonium sulfate and ammonium oxalate on thermal stability and their potential as BRSs. Due to the stronger inhibitory effect of ammonium sulfate on the AP proton transfer process, the activation energy of propellant's first decomposition can be increased from 94.71 kJ mol−1 to 129.69 kJ mol−1 at a 3 % addition level. Based on Semenov model, the self‐accelerated decomposition temperatures (TSADT) were calculated and validated through 7‐day isothermal test. Introducing ammonium sulfate and ammonium oxalate raised the TSADT from 197.31 °C to 220.90 °C and 215.06 °C, respectively, deviating less than 4 % from experimental results. Among the propellants tested, those with ammonium sulfate showed prolonged response delay times (44.43–33.60 h), lower superheating temperatures (222.8–445.5 °C), and reduced mass loss rates (33.0–71.4 %) after 7 days of isothermal storage at 220–240 °C. The consistency between thermal analysis and isothermal test underscores the significant impact of activation energy on thermal stability.

Customized Green Energetic Tetra(Imidazole)Copper(II) Nitrate (Cu-Im) Complex/Ammonium Nitrate Co-crystal: A Novel Reactive Halogen-Free Oxidizer with Superior Stability and Decomposition Kinetics

AbstractAmmonium nitrate (AN) is the most promising affordable green oxidizer for solid propellants; however, its endothermic phase transitions and endothermic decomposition restrict its applications. This work shaded the light on multifunctional energetic complex tetra(imidazole)copper (II) nitrate (Cu-Im) with combustion enthalpy of 15.57 KJ/g as a high energy dense material, phase stabilizer, and catalyst for AN-based propellant. The Cu-Im complex was synthesized via a green simple solvent-free melt-assisting technique. As-synthesized Cu-Im complex demonstrated a highly pure crystalline structure with thermal stability up to 200 °C. Cu-Im complex was integrated into AN via an evaporative crystallization technique. The phase transitions and the thermal behavior of the developed Cu-Im complex/AN cocrystal were investigated via DSC and TGA. The Cu-Im complex stabilized the phase transition of AN up to 88.48 °C via an evolved strong hydrogen bonding system within the Cu-Im complex/AN cocrystal. Moreover, the energetic Cu-Im complex offered a significant decrease in the endothermic phase transition peaks associated with IV↔II, and II↔I by 38.81%, and 25.28% respectively. Additionally, AN strong endothermic melting was decreased by 45.32%. The Cu-Im complex converts the AN endothermic thermal decomposition peak with + 1400 J/g into an intensive exothermic peak with the release of -2241 J/g. The Cu-Im complex exhibited a superior catalytic effect via the decrease in AN decomposition temperature by 48.85 °C. Cu-Im complex offered a remarkable reduction in apparent activation energy of AN decomposition by 56.24% and 48.12% via Kissinger’s model and integral iso-conversional nonlinear Vyazovkin method (VYA) respectively. The superior catalytic performance of the Cu-Im complex was attributed to the evolution of CuO nanoparticles during its decomposition. The electron-deficient Lewis acid copper ions have a large affinity to electron lone pair of nitrogen; this effect could support the conversion of NH3 to N2 and H2. This catalytic action could boost the decomposition enthalpy of AN. Consequently, the developed Cu-Im/AN cocrystal could be considered a potential green substitute for perchlorate-based oxidizers.

Thermal recombination strategy designed R-CN as active shell to improve catalyst activity

A new recombinant CN material (R-CN) was prepared with g-C3N4 as precursor by hydrothermal method combined with thermal recombination method, which has 2D ultra-thin structure, nanoscale folds, graphite-like texture and some pores, and has richer N and O elements than g-C3N4. R-CN can reduce high temperature decomposition peak of ammonium perchlorate (AP) to 356.06 oC, and its promoting effect is obviously better than that of g-C3N4. Based on specific structural composition and physicochemical properties of R-CN, a novel R-CN@MWO composite with core-shell was designed, which was applied to catalytic decomposition of AP and pressure enlarging effect during combustion process of cyclotrimethylenetrinitramine (RDX)+nitrocellulose (NC). With the introduction of R-CN@MWO, decomposition peak temperature and activation energy of AP are reduced by 104.67oC and 59.24 kJ mol−1, and peak pressure and pressurization rate of RDX+NC constant volume combustion test are increased by 11.33 and 118.54 times, respectively. Moreover, the combustion rate of R-CN@MWO-AP/HTPB propellant is 3.23 times that of AP/HTPB propellant. To sum up, R-CN as a coating layer can significantly enhance catalytic activity of MgWO4 for thermal decomposition of energetic materials.

Construction of rGH/NTO 3D-network composite with improved energy release efficiency and significantly reduced corrosiveness of 3-nitro-1,2,4-triazole-5-one

3-Nitro-1,2,4-triazole-5-one (NTO) is a high-energy insensitive explosive with broad application prospects. However, due to the slow energy release kinetics, high decomposition temperature and unsatisfactory safety performance, its effective application is affected. In this paper, a reduced graphene oxide hydrogel (rGH)/NTO composite material was prepared to improve both the physical and chemical properties of NTO. The morphology and structure of the samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that the rGH/NTO composites did not undergo polymorphic transformation during the preparation process. At the same time, the three-dimensional (3D) network structure formed by rGH can reduce the initial temperature and activation energy of NTO thermal decomposition, and significantly increase the energy release rate. In addition, combined with experiments and DFT theoretical calculations, it is verified that the synergistic effect of the composite material reduces the corrosivity of NTO and increases the insensitivity, thereby improving the effective safety performance. Therefore, the synergistic effect of 3D network structure composite strategy is expected to be extended to the multi-performance control of energetic materials.

Surface modification of nitrocellulose by interfacial self-assembly of metal-phenolic network for enhanced thermal stability and eco-friendly propulsion energy

Metal-phenolic networks (MPNs) have received widespread interest owing to their ability to incorporate metal ions and phenolic ligands in a modular manner. However, the effect of MPNs on nitrocellulose (NC), an energetic material for propulsion, has not been extensively investigated. Herein, we fabricated MPN-coated NC fibers (NC@MPN) and confirmed the successful coating and homogeneous distribution of MPN on the surface of NC through Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, scanning electron microscopy (SEM) and Energy Dispersive spectroscopy (EDS). The thermal stability of NC was enhanced as evidenced by differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC) and the ignition point test. The thermal decomposition activation energy of NC@MPN can reach 200.73 kJ•mol−1, 7.50 % higher than that of NC primitive fiber (186.72 kJ•mol−1). The ARC tests demonstrate that the implementation of MPN coating prolonged the time of entering the adiabatic section by 5.4 °C and the forecast temperatures for TD8 and TD24 have increased by 4.6 and 4.8 °C, respectively. Additionally, the ignition point was also raised by 2 °C. The aforementioned three experimental results provide evidence for the enhanced thermal stability conferred by MPNs. Besides, thermogravimetric analysis (TGA) results demonstrate a reduction in the residue from thermal decomposition. The present study presents a simple and robust coating strategy for the modular surface engineering of energetic materials, which significantly improves thermal stability and reduces the residues of thermal decomposition.

Isothermal and non-isothermal decomposition mechanisms of bastnaesite during the hydrogen-based mineral phase transformation

The hydrogen-based mineral phase transformation-flotation process can realize the efficient development of iron-bearing rare earth ores. The isothermal and non-isothermal decomposition mechanisms of bastnasite in the hydrogen atmosphere were studied to optimize the hydrogen-based mineral phase transformation process. The thermal decomposition of bastnasite first produced REOF, which would react with oxygen to produce rare earth oxides and fluorides during the analysis process. The thermal decomposition was an endothermic reaction, and the generated gas were mainly CO2 and trace CO, with a mass loss of about 20%. Increasing the temperature can greatly promote the thermal decomposition. After thermal decomposition, the particles showed a layered structure, and many parallel slits run through the particles. The porosity and specific surface area of the particles were significantly improved. The apparent activation energy of isothermal decomposition was 71.80 ± 5.40 kJ/mol, and the kinetic mechanism was random nucleation and growth model (n = 2). The apparent activation energy of non-isothermal decomposition was 201.96 kJ/mol, and the kinetic mechanism was phase-boundary controlled reaction mechanism (n ≈ 2).

NO Dissociation on Platinum and Platinum-Rhodium Alloy: A Theoretical Investigation

In this computational study, the preferential adsorption and co-adsorption sites of various chemical species (N, O, and NO) on the Pt (111) and Rh3Pt (111) surfaces were identified. The preferential adsorption site for NO and co-adsorption sites for N and O on the Pt (111) surface are the hollow (fcc) sites; and these on the Rh3Pt (111) surface are the hollow (fcc1) site and hollow N(hcp2)-O(fcc1) sites, respectively. The activation energies of the NO dissociation reaction on the Pt (111) and Rh3Pt (111) catalytic surfaces are 2.35 and 2.02 eV, respectively. The lower activation energy of the NO decomposition on the Rh3Pt (111) surface is explained by the stronger back-donation from the 4d orbital of the Rh atoms to the 2π* anti-bonding orbital of the NO molecule. The activation energies of the N and O recombination reaction on the Pt (111) and Rh3Pt (111) catalytic surfaces are 1.51 and 2.30 eV, respectively. The study indicates that the Rh3Pt (111) surface not only facilitates the NO decomposition but also better prevents N and O from recombination. Copyright © 2024 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Experimental and theoretical study on the thermal stability and pyrolysis mechanism of octamethyltrisiloxane (MDM) with lubricating oil

In actual organic Rankine cycle systems (ORCs), the inclusion of lubricating oil in the working fluid is nearly unavoidable. Under the condition of high-temperature operation, the presence of lubricating oil can potentially exacerbate the thermal stability of the working fluid. The impact of polyol ester (POE) and mineral lubricant on the thermal stability of octadethyltrisiloxane (MDM) is studied. Results indicate that both POE and mineral lubricant contribute to the decomposition of MDM to a certain extent. Specifically, at a 5.0% mass fraction of POE and mineral lubricant, MDM remains its stable at 230 °C and 210 ℃, respectively. However, as the mass fraction of lubricant increases, the decomposition of MDM intensifies, with mineral lubricant exhibiting a more pronounced effect compared to POE lubricant. Regarding pyrolysis products, the presence of lubricants leads to an increase in CH4, C2H6 and C2H4 gases. Furthermore, the addition of lubricant promotes the formation of siloxane oligomers, particularly MD5M to MD9M, and enhances the production of unidentified products. Compared to MDM, both POE and mineral lubricant molecules exhibit lower bond dissociation Gibbs free energies. The free radicals generated from lubricant decomposition are prone to hydrogen abstraction reactions with MDM to promote MDM decomposition. Moreover, ReaxFF simulation results demonstrate that lubricant molecules also enhanced the activation of MDM and increased its susceptibility to Si-C bond cleavage. Following the removal of the methyl group, the Si-O bonds in the radicals are more likely to break, leading to the formation of additional siloxane oligomers through Si-O bond recombination. Kinetic analysis reveals that the apparent activation energy of MDM decomposition drops from 134.4 kJ∙mol−1 to 110.8 kJ∙mol−1 as the mass fraction of n-hexadecane (model compounds for mineral lubricant) rises from 0% to 10.30%.

Cotton stalk decomposition with DBD low-temperature plasma: Characteristics and kinetics

DBD low-temperature plasma (DLTP) is recognized as one of the most efficient technologies for treating cotton stalks. This study investigates the impact of various conditions on the gas production characteristics of cotton stalks (CS) and delves into the DLTP decomposition kinetics of CS and CSC in oxygen-enriched (30 % O2/Ar) and CO2 atmospheres. The decomposition rates of CS followed the order CO2 > N2 > Ar. The decomposition behavior of CSC in oxygen-enriched DLTP (30 % O2/Ar) aligned well with the chemical reaction model. The activation energies for CSC decomposition at 900 °C and 1000 °C were determined to be 23.8 kJ/mol and 33.8 kJ/mol, respectively. Moreover, the reaction rate decreased at higher carbonization temperatures, which proved to be detrimental to the decomposition of CSC. The DLTP decomposition of CSC in CO2 exhibited consistency with the fitting results of the unreacted shrinking core model, revealing an observed activation energy of 19.4 kJ/mol.

Effects of graphene organic iron nanocomplex on the pyrolysis and laser ignition performance of TKX-50

Novel graphene iron tannate and graphene iron gallate nanocomplex (G-D-Fe and G-M-Fe) were designed, prepared and characterized by SEM, EDS, FTIR, RAMAN and XPS equipment. The catalytic property of the G-D-Fe and G-M-Fe for energetic TKX-50 was explored by DSC, kinetic calculation and laser ignition. The synthesized G-D-Fe and G-M-Fe present a positive impact on pyrolysis and ignition combustion of TKX-50, resulting in the significantly reduced decomposition temperature, activation energy (Ea) and ignition delay time. After adding G-D-Fe (G-M-Fe), the first and second decomposition peak temperatures (TFDP and TSDP) of TKX-50 were decreased by 42.3 °C (43.9 °C) and 45.0 °C (49.6 °C), respectively. At the conversion degree of 0.2–0.8, the nonlinear kinetic data showed that after adding G-D-Fe and G-M-Fe, the Ea of TKX-50 decreased from 163.5 to 141.3 and 145.4 kJ·mol−1 respectively. Additionally, after adding G-D-Ni and G-M-Ni, the laser ignition delay time of TKX-50 was reduced from 58 ms to 26 ms and 28 ms, respectively. The possible catalytic mechanism of preferred combustion catalyst G-D-Fe was disclosed by in-situ FTIR and gas-phase MS-FTIR analysis. The results are helpful to broaden the catalysts for pyrolysis and ignition combustion of TKX-50 and to disclose the catalytic mechanism.

Effect of internal phase particle size on properties of site mixed emulsion explosive at plateau environment

To study the effect of internal particle size on the microstructure properties and thermal decomposition characteristics of site mixed emulsion explosive at different altitudes. Site mixed emulsion explosive was prepared with different shear rate. The particle size, viscosity, sensitized bubbles, detonation velocity and peak pressure of the emulsion explosive were tested after stored at different simulated altitudes. The thermal decomposition characteristics of emulsion matrix prepared at three different rotational speeds were measured by thermogravimetric analyzer and kinetic analysis was performed by non-isothermal model Kissinger–Akah–Sunose (KAS) method. The results show that with the increase in altitude, the internal phase size showed a trend of first increasing and then decreasing, and the number of sensitized bubbles within the emulsion explosive decreases. At an altitude of 0 m, the detonation velocity and peak overpressure of the emulsion explosive prepared by 1600 r min−1 increased 4.78% and 29.09%, respectively compared with 1200 r min−1, and at an altitude of 4500 m, the detonation velocity increased 11.87%, the peak overpressure increased 43.98%. The thermal decomposition activation energy of the emulsion matrix at 1600 r min−1 increased 13.14% compared to 1200 r min−1. It shows that in the production of site mixed emulsion explosive at high altitude, reducing the particle size of the internal phase of emulsion explosives in a certain range can effectively improve the performance of emulsion explosives.

Thermal decomposition behavior of Mountain Pass rare earth concentrate in air/CO2 atmosphere

The Mountain Pass mine is recognized as one of the world’s primary sources of rare earth minerals. These rare earth minerals mainly consist of bastnaesite and a small amount of monazite phosphate, which cannot be decomposed and recovered through conventional oxidative roasting and hydrochloric acid leaching process. An efficient, clean, and economical process called the "combined method" was proposed for the utilization of the Mountain Pass mine to extract rare earths from Mountain Pass rare earth concentrate (MPREC). The main steps of this process include weak oxidation atmosphere roasting, step leaching of hydrochloric acid, solid-liquid separation, the monazite slag with sulfuric acid roasting water leaching, etc. In this paper, the roasting process of MPREC under a weak oxidation atmosphere was investigated. The study examines the thermal decomposition kinetics, phase transition process, and leaching behavior of MPREC in air/CO2 atmosphere. Results show that, the activation energy (Ea) for MPREC thermal decomposition in air and CO2 atmosphere are 146 and 320 kJ/mol, respectively. At temperature above 500 °C in air or above 700 °C in CO2 atmosphere, REOF are generated from bastnaesite through an in-situ reaction with CaO, which is decomposed from CaCO3, to form CaF2 and rare earth oxide (REO). Thus, F is regulated into solid phase. In an oxidizing atmosphere, the thermal decomposition of bastnaesite is accompanied by the rapid oxidation of Ce(Ⅲ). In contrast, the oxidation of Ce(Ⅲ) in a CO2 atmosphere is significantly inhibited. At 700 °C, the oxidation rate of Ce in air is 74.09%, while in a CO2 atmosphere, it is only 33.83%. The hydrochloric acid leaching experiment shows that, the leaching rate of rare earth after roasting at 600 °C under an air atmosphere reaches to 82.9%, and it reaches 87% after roasting at 800 °C under a CO2 atmosphere. The reduction of Ce oxidation in a weak oxidizing atmosphere significantly improves the leaching rate of Ce.

Isoconversional kinetic analysis of thermal decomposition of Bidirectionally stabilized amorphous formulation loading Vitamin D3 (Cholecalciferol) and Calcium Carbonate

Cholecalciferol, generally known as vitamin D3 (VD), and calcium (Ca2+) are very common dietary co-supplements in the pharmaceutical formulations, as they are symbiotically and pharmacologically dependent. Development of the VD/Ca2+ formulation is highly challenging due to stability and solubility issues, mainly for VD instability toward temperature, light, oxygen and pH. In this study, VD was loaded into carrier which consisted of amorphous calcium carbonate (ACC) and hydroxypropyl methylcellulose acetate succinate (HPMCAS), yielding amorphous VD/ACC/HPMCAS formulation with various composition ratios. The structural and thermal stability study of the formulations was conducted to find that VD was a promising molecule for the stabilization of ACC even with the trace amount (0.6 %). On the other hand, ACC stabilized the amorphous state of VD; thus, they had a bidirectional stabilizing effect. The amount of VD played a significant role in thermal stabilization of the VD/ACC/HPMCAS formulations, for which kinetic analysis was performed. Using isoconversional expanded Friedman's model (FRM) activation energies of decomposition of the organic part were determined as 190, 133, and 114 kJ mol−1 for VD/ACC/HPMCAS = 0.6/64.0/35.4, 2.3/56.8/40.9, and 4.9/52.6/42.5 formulations, respectively, revealing that the formulation with the highest amount of VD (4.9 %) was the least stable. The dissolution advantage for VD by amorphization was also demonstrated.

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.