Maximum Reaction Temperature Research Articles

An MD-study on changing the elemental distribution and composition by alloying to control front propagation in Al–Ni multilayers

To cover the wide range of applications of reactive multilayers, it is necessary to have the ability to vary and control their front propagation velocities as well as their maximum reaction temperatures. In this paper, Molecular Dynamics simulations are used to study the influence of Al alloying, Ni alloying, and Co alloying on Al–Ni multilayers. In the case of alloying with Al and Ni, the iso-stoichiometric case where both the Al and the Ni layers are alloyed is first studied. In the second step, the stoichiometry is varied by alloying only one of the two layers with the other element. This allows for achieving very small front propagation velocities. Furthermore, the Ni layer is alloyed with Co and the whole range from a binary Al–Ni to the binary Al–Co system is studied. The front propagation velocity does not change linearly with the alloying fraction and reaches a minimum where the Ni/Co alloy changes from a face centered cubic to a hexagonal close packed lattice.

Characterization and Biomechanical Study of a Novel Magnesium Potassium Phosphate Cement.

Magnesium potassium phosphate cement (MKPC) has attracted considerable attention as a bone regeneration material. However, there are only a few reports on its biomechanical properties. To evaluate the biomechanical properties of MKPC, we compared the mechanical parameters of pedicle screws enhanced with either MKPC or polymethyl methacrylate (PMMA) bone cement. The results show that the maximum pull-out force of the pedicle screws was 417.86 ± 55.57 and 444.43 ± 19.89 N after MKPC cement setting for 30 min and 12 h, respectively, which was better than that of the PMMA cement. In fatigue tests, the maximum pull-out force of the MKPC cement group was 435.20 ± 7.96 N, whereas that of the PMMA cement in the control group was 346.80 ± 7.66 N. Furthermore, the structural characterization analysis of the MKPC cement revealed that its microstructure after solidification was an irregular tightly packed crystal, which improved the mechanical strength of the cement. The maximum exothermic temperature of the MKPC reaction was 45.55 ± 1.35 °C, the coagulation time was 7.89 ± 0.37 min, and the compressive strength was 48.29 ± 4.76 MPa, all of which meet the requirements of clinical application. In addition, the MKPC cement did not significantly inhibit cell proliferation or increase apoptosis, thus indicating good biocompatibility. In summary, MKPC exhibited good biomechanical properties, high initial strength, good biocompatibility, and low exothermic reaction temperature, demonstrating an excellent application potential in the field of orthopedics.

Preparation and Performance Enhancements of Low-Heat-Releasing Polyurethane Grouting Materials with Epoxy Resin and Water Glass

Polyurethane (PU) grouting materials possess excellent fluidity and strong injectability. However, the high heat release during the reaction process restricts its application. In this study, with the addition of water glass (WG), a prepolymer was prepared by epoxy resin reacted with isocyanate to form modified polyurethane. The effects of epoxy resin and water glass on the compressive properties, expansion rate, structure of the cell, and maximum reaction temperature of the grouting materials were also investigated. The results showed that the cell size of modified PU was smaller and more regular, the maximum reaction temperature of the modified PU was reduced to 89 °C, and the compressive strength and expansion rate went up to 0.27 MPa and 57, respectively. This investigation will expand the application of PU grouting materials in underground engineering.

Global sensitivity analysis to identify influential model input on thermal risk parameters: To cottonseed oil epoxidation

Thermal runaway is still an important cause of accident in chemical industry. To evaluate the risk of such events, thermal risk assessment, which is a part of process safety, must be done. This assessment determines the safe operating conditions of a process by evaluating the thermal risk of an exothermic system. Nevertheless, based on thermal risk assessment, it is not possible to know which model inputs have the most influence on the thermal risk parameters. The knowledge of the most influential model inputs on thermal risk parameters is important to establish adequate safety barriers. Global sensitivity analysis was used to evaluate the influence of model inputs and their interaction on thermal risk parameters. It was performed on the exothermic system: epoxidation of cottonseed oil by performic acid in semibatch mode under isoperibolic conditions. The maximum reaction temperature and the time to reach this maximum reaction temperature were chosen as thermal risk parameters. We have also studied the influence of model inputs on the temperature rise. In the operating conditions of this study, it appeared that two parameters have the most influence on maximum reaction temperature and the temperature rise: the initial concentration of hydrogen peroxide and the jacket temperature, and one parameter for the time to reach this temperature: the jacket temperature.

Solar hydrothermal processing of agave bagasse: Insights on the effect of operational parameters

Hydrothermal processing of agave was performed using a batch solar reactor designed to operate with a coupling method where a concentrated solar system provides heat. This work analyzes the performance of a reactor and the main characteristics of the products at different operational parameters: temperature, biomass concentration and holding time under subcritical conditions. Experimental findings demonstrate that the solar heated reactor prototype allows reaching maximum reaction temperatures of 300 °C with stable pressures. Low heating rates reduced the propensity of the system to leak, which prevented variations in pressure throughout experiments. The most favorable conditions to improve the yields (up to 28%) and properties of the oil produced were 300 °C and no holding time at peak temperature (τ = 0 min), and an average constant direct normal irradiation of 745 ± 47 W/m2.

Effects of the feeding procedure on the thermal behaviors of autocatalytic esterifications in semibatch processes

Esterification reactions between anhydrides and alcohols catalyzed by sulfuric acid have broad applications in the food, cosmetic, and pharmaceutical industries. However, the exothermic behavior cannot be well explained, especially in semibatch reactors with different feeding procedures. In this study, a series of esterification processes in semibatch systems were conducted with a wide range of feeding rates with two different substrates. The structures of initial catalytic substrates were characterized using in situ Fourier Transform Infrared (FTIR) spectroscopy. A total of 11 reaction pathways, including those for the initial activation of substrates and the subsequent reactions of the feeding process, were calculated by the density functional theory (DFT) method. Three possible catalytic cycles of the esterification with specific acid catalysis, protonated intermediate, and protonated intermediate and H2O, were established for the semibatch esterification reaction based on calculated results and experimental evidence. Thermal safety parameters such as reaction enthalpy (ΔHr), adiabatic temperature rise (ΔTr,ad), and maximum temperature of the synthetic reaction (MTSR) were determined based on Wilson equation used to calibrate mixing heat. The results reveal that mixing heat was 2.5 kJ/mol with same mole ratio of n-butanol (nB) and propionic anhydride (PA). The reactions started by PA are dominant, no matter whether the substrate is nB or PA. The initial reaction rate is restricted by the low concentration of catalyst and active reactant when nB is used as substrate, which lead to significant reactant accumulation with high MTSR of approximately 160 °C. Furthermore, feeding nB into PA allows a controllable increase in the ΔTr,ad realized by changing the feeding rate and limiting the accumulation of reactant.

Accelerating Rate Calorimetry and Complementary Techniques to Characterize Battery Safety Hazards.

The hazards associated with lithium-based battery chemistries are well-documented due to their catastrophic nature. Risk is typically qualitatively assessed through an engineering risk matrix. Within the matrix, potentially hazardous events are categorized and ranked in terms of severity and probability to provide situational awareness to decision makers and stakeholders. The stochastic nature of battery failures, particularly the lithium-ion chemistry, makes the probability axis of a matrix difficult to properly assess. Fortunately, characterization tools exist, such as accelerated rate calorimetry (ARC), that characterize degrees of battery failure severity. ARC has been used extensively to characterize reactive chemicals but can provide a new application to induce battery failures under safe, controlled experimental conditions and quantify critical safety parameters. Due to the robust nature of the extended volume calorimeter, cells may be safely taken to failure due to a variety of abuses: thermal (simple heating of cell), electrochemical (overcharge), electrical (external short circuit), or physical (crush or nail penetration). This article describes the procedures to prepare and instrument a commercial lithium-ion battery cell for failure in an ARC to collect valuable safety data: onset of thermal runaway, endotherm associated with polymer separator melting, pressure release during thermal runaway, gaseous collection for analytical characterization, maximum temperature of complete reaction, and visual observation of decomposition processes using a high temperature borescope (venting and cell can breach). A thermal "heat-wait-seek" method is used to induce cell failure, in which the battery is heated incrementally to a set point, then the instrument identifies heat generation from the battery. As heat generates a temperature rise in the battery, the calorimeter temperature follows this temperature rise, maintaining an adiabatic condition. Therefore, the cell does not exchange heat with the external environment, so all heat generation from the battery under failure is captured.

Layered Double Hydroxide Modified Bone Cement Promoting Osseointegration via Multiple Osteogenic Signal Pathways.

Poly(methyl methacrylate) (PMMA) bone cement has been widely used in orthopedic surgeries including total hip/knee replacement, vertebral compression fracture treatment, and bone defect filling. However, aseptic loosening of the interface between PMMA bone cement and bone often leads to failure. Hence, the development of modified PMMA that facilitates the growth of bone into the modified PMMA bone cement is key to reducing the incidence of aseptic loosening. In this study, MgAl-layered double hydroxide (LDH) microsheets modified PMMA (PMMA&LDH) bone cement with superior osseointegration performance has been synthesized. The maximum polymerization reaction temperature of PMMA&LDH decreased by 7.0 and 11.8 °C, respectively, compared with that of PMMA and PMMA&COL-I (mineralized collagen I modified PMMA). The mechanical performance of PMMA&LDH decreased slightly in comparison with PMMA, which is beneficial to alleviate stress-shielding osteolysis, and indirectly promote osseointegration. The superior osteogenic ability of PMMA&LDH has been demonstrated in vivo, which boosts bone growth by 2.17- and 18.34-fold increments compared to the PMMA&COL-I and PMMA groups at 2 months, postoperatively. Moreover, transcriptome sequencing revealed four key osteogenic pathways: p38 MAPK, ERK/MAPK, FGF, and TGF-β, which were further confirmed by IPA, qPCR, and Western blot assays. Hence, LDH-modified PMMA bone cement is a promising biomaterial to enhance bone growth with potential applications in relevant orthopedic surgeries.

Simultaneously enhanced reaction temperature and velocity of self-propagating high-temperature synthesis via Joule-heat induced multi-channel heat flow

Simultaneous enhancement of reaction temperature and velocity of self-propagating high-temperature synthesis is still a challenge. Here, we propose a general method based on the Joule-heat induced multi-channel heat flow to simultaneously increase the reaction temperature and velocity of self-propagating high-temperature synthesis. A designed surface structure induces multi-channel Joule-heat accumulation at the surface of reaction components and subsequently multi-channel heat flow during the self-propagating processes. Multi-channel heat flow leads to the formation of two combustion stages: the self-propagating process and the Joule-heat induced grain growth, leading to an enhancement of the maximum reaction temperature up to 67%. Meanwhile, multi-channel heat flow will reduce the propagation distance of the reaction wave and the heat conduction between heat flow channels will increase the temperature of the reaction components, in turn, resulting in an increase in the reaction velocity that is five times higher. We expect that our findings will pave the way for the future application of self-propagating high-temperature synthesis in industries.

Thermal Risk Analysis Based on Reaction Mechanism: Application to the 2,6-Diaminopyrazine-1-oxide Synthesis Process

Thermal risk analysis is essential for the development of chemical reactions. This work should be carried out on the basis of a thorough comprehension of the reaction mechanism. In this article, the synthesis process for 2,6-diaminopyrazine-1-oxide (DAPO), an important intermediate in the synthesis of the famous explosive 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105), was employed to show the importance of understanding the reaction mechanism for thermal risk analysis. First, we investigated the reaction mechanism of DAPO synthesis. The reaction mechanism was divided into two stages on the basis of the amount of triethylamine dosed: the first half of triethylamine dosing and the second half of triethylamine dosing until the end of the reaction. Then the thermal properties of DAPO synthesis and the thermal stability of the materials involved were experimentally studied using a reaction calorimeter (RC1) and a differential scanning calorimeter (DSC), respectively. The results show that the temperature corresponding to the maximum reaction rate reached in a time of 24 h under adiabatic conditions (TD24) is higher than the maximum temperature of the synthesis reaction (MTSR) for both of these stages, indicating that once cooling failure occurs, immediately stopping addition of triethylamine could prevent the occurrence of secondary decomposition.

Study on the preparation and application of phenolic resin-based filling composite materials in coal mines

ABSTRACT An in situ modification method is used to synthesize a new type of phenolic resin-based composite material used to fill goafs and seal air leaks in roadways. This was followed by scanning electron microscopy, oxygen index, and compression tests. The results show that when the aluminium hydroxide, Sd-31 silicone oil and methylene chloride are added to the phenolic resin in a mass fraction ratio of 8%:5%:3%, the overall performance of the composite material is the best. Compared with unmodified phenolic resin, the oxygen index and compressive strength of thecomposite material are increased by 40.16% and 3.5 times, respectively. The maximum reaction temperature of foaming and curing is also reduced from 120.3 to 87.2°C. To verify the performance of the new material, field tests were carried out at Matigou coal mine in Gansu, China. The average air leakage rate of the working face was reduced from 12.8 to 2.1 %.

Infrared Spectra Patterns of Coconut Shell Charcoal as Result of Pyrolysis and Acid Activation Origin of Sulawesi, Indonesia

Coconut is one of the industrial plants that plays an important role in the Indonesian economy. The part of coconut that has a high economic value is the coconut shell. This study aims to see the maximum temperature of the coconut shell pyrolysis reactor and to examine the spectrum pattern of charcoal purified using the activation of hydrochloric acid (HCl), acetic acid (CH3COOH), nitric acid (HNO3) and hot water (H2O). The process steps are pyrolysis process carried out at a temperature of ± 310 °C for 2 hours and activation using 4 types of solvents with different acidity levels, soaking for 12 hours. Infrared spectra pattern testing using Fourier Transform Infrared (FTIR). The results of the pyrolysis process produce charcoal, liquid smoke, tar and condensed gases. The spectral pattern of each purified charcoal was analyzed using Fourier Transform Infrared (FTIR). The results of the analysis showed that the spectral pattern of activated charcoal showed a spectral pattern with a low level of impurity absorption, namely the spectral pattern of charcoal using HCl activator at a concentration of 2 M.

Synthesis and Infrared Performance of SiB6 Powder through “Chemical Oven” Self‐Propagating Combustion

SiB6 powders were prepared by the “chemical oven” method from Si and B powders. Here combustion with acid pickling “two‐step” mode replaces the traditional synthesis method which helps to avoid severe condition of high temperature and high pressure. It could realize maximum reaction temperature to about 2000°C, and the whole process just needs ∼30 s. The average diameter of products is ∼10 μm. And the raw material Si and B are ∼3 μm and ∼20 μm, respectively. The infrared emissivity of products was evaluated by UV‐vis spectrum with absorption band around 250∼2500 nm. All five samples show higher emissivity over UV‐visible light range with lower emissivity over near‐infrared range. Typically, the sample’s Si/B ratio of 1 : 1 shows highest integral intensity for about 0.85 compared with other molar ratios. It can be used as a more simple and effective method to obtain infrared ceramic SiB6 with high emissivity.

Oxidation of UN/U2N3-UO2 composites: an evaluation of UO2 as an oxidation barrier for the nitride phases

Composite fuels such as UN-UO2 are being considered to address the lower oxidation resistance of the UN fuel from a safety perspective for use in light water reactors, whilst improving the in-reactor behaviour of the more ubiquitous UO2 fuel. An innovative UN-UO2 accident tolerant fuel has recently been fabricated and studied: UN microspheres embedded in UO2 matrix. In the present study, detailed oxidative thermogravimetric investigations (TGA/DSC) of high-density UN/U2N3-UO2 composite fuels (91-97 %TD), as well as post oxidised microstructures obtained by SEM, are reported and analysed. Triplicate TGA measurements of each specimen were carried out at 5 K/min up to 973 K in a synthetic air atmosphere to assess their oxidation kinetics. The mass variation due to the oxidation reactions (%), the oxidation onset temperatures (OOTs), and the maximum reaction temperatures (MRTs) are also presented and discussed. The results show that all composites have similar post oxidised microstructures with mostly intergranular cracking and spalling. The oxidation resistance of the pellet with initially 10 wt% of UN microspheres is surprisingly better than the UO2 reference. Moreover, there is no significant difference in the OOT (~557 K) and MRT (~615 K) when 30 wt% or 50 wt% of embedded UN microspheres are used. Therefore, the findings in this article demonstrate that the UO2 matrix acts as a barrier to improve the oxidation resistance of the nitride phases at the beginning of life conditions.

A chemical oxygen generator using seawater and a chemical oxygen generator using seawater and moderator to control the temperature

Oxygen is generated from adduct sodium percarbonate in granular form using seawater as the solvent. When the total seawater is increased from 100 ml to 250 ml, the instantaneous flow increases from 1000 ml/min to 3000 ml/min. In spite of the more lively reaction with the additional water, the maximum reaction temperature is reduced from 60 °C to 40 °C. This oxygen generation method without the additional weight of a moderator to control the temperature could be used as the oxygen side of a PEM fuel cell in oxygen-denied environments. Using a moderator, an unexpected effect is observed near the beginning of the reaction in seawater: a flat temperature line that is reproducible. The highly exothermic heat of formation of oxygen from peroxide is temporarily balanced by the endothermic heats of dissolution of the adduct and moderator. This phase transition-like temperature effect is evidence of a 2-step process in solution.

Synthesis of active electrocatalysts using glycine–nitrate chemistry

Due to sluggish oxygen reduction reactions, development in the solid oxide fuel cell (SOFC) field is stagnant. Two solutions, increasing the active surface or use of precious materials, can stimulate the oxygen reduction kinetics on electrodes. Thus, to gain both these benefits, the present article addressed the synthesis of high surface-area mixed oxide ionic–electronic conductor La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) using chemistry of the propellant glycine–nitrate reaction. In this study, different fuel to oxidant ratios (ψ), 2.0, 2.6, and 3.0 were used to control the exothermicity of reaction and powder properties. The maximum reaction temperature of 1337 K at ψ = 3.0 resulted in coarsened powder. In contrast, comparatively less exothermicity of reaction at ψ = 2.0 resulted in powder with substantial Brunauer–Emmett–Teller surface area of 10.97 m2 g−1, with maximum powder compaction achieved at sintering of 1273 K. With optimal direct current in-plane electrical conductivity of 341 S cm−1, H2-temperature-programmed reduction showed excellent catalytic activity for the sample obtained at ψ = 2.0. The electrochemical performance comparisons of electrodes in two different cell geometries – with and without a gold catalytic current collecting layer (Au–CCCL) – revealed the least polarization and cell resistance in the cell with Au–CCCL. The electrode area specific resistance and cell conductivity using Au–CCCL were 0.097 Ω cm−2 and 0.15 S cm−1, respectively.

Determination of the marker for automation of torrefaction and slow pyrolysis processes – A case study of spherical wood particles

Abstract Torrefaction and slow pyrolysis are processes that can be used for improving the fuel properties of low-quality biomass, which could be effectively used for improving fuel logistics and making biomass a fully tradeable commodity. Automation of these processes could prove vital for their economic viability and carbon footprint, giving the possibility to reduce manpower requirement and raining time for operators. Automation based on online control of the quality of biocoal is not possible. However, finding a suitable marker in torgas could make automation possible. Results presented in the study show that formaldehyde can be considered as a viable marker. Obtained results are limited to torrefaction and slow pyrolysis of lignocellulosic biomass at a maximum reactor temperature of 430 °C. Temperature measurements show that endothermal evaporation of the bound moisture delays the time necessary to reach the point where exothermal reactions start taking a leading role in the thermal decomposition process, which is extremely important in the context of thermal run-away of such installation. Artificial neural network proved to be an effective tool for determining of correlation between the heating value of pyrolysis gas and its concentration of formaldehyde. This could be used in advanced control solutions for pyrolysis gas combustion systems.

Dynamic optimization of low-density polyethylene production in tubular reactor under thermal safety constraint

A commercial low-density polyethylene (LDPE) which is produced by the polymerization process of ethylene in the presence of initiators in a long tubular reactor is the most widely used in polymer industry. The highly exothermic nature of the LDPE polymerization process and the heating-cooling prerequisite in the tubular reactor can lead to various problems, particularly safety in terms of thermal runaway and productivity, i.e., decreasing monomer conversion. Therefore, model-based optimization of an industrial LDPE tubular reactor under thermal safety consideration is required to be implemented. A first principle model for this process is developed and validated using industrial data. Mass and energy balances have been derived from kinetics of LDPE polymerization. Thereafter, an expression of reactor temperature under critical condition is developed and incorporated in the reference model for the thermal safety study. In order to ensure the process is thermally safe and meets the desired product grade, the constrained dynamic optimization is proposed to maximize the conversion of the monomer using orthogonal collocation (OC). The dynamic optimization result shows that the maximum reaction temperature under critical condition constraint can be satisfied by optimizing the reactor jacket. Moreover, it is achieved without jeopardizing the monomer conversion and the product grade.

Hazard evaluation for chlorination and amination reactions of fluorocytosine production process

Reaction thermal runaway is one of the most important reasons leading to chemical accidents. With the rapid development of the chemical industry in the world, especially the fine chemical industry, various safety accidents also occur frequently. Therefore, it is necessary to study the exothermic behavior of the reaction process. In this study, reaction calorimeter was used to study the exothermic phenomena during the chlorination reaction and amination reaction. Differential scanning calorimetry was performed on the reactants, and thermogravimetric experiments were performed on the products. In addition, adiabatic experiment was performed to study the thermal runaway behavior of amination products under adiabatic conditions. The results showed that the target reactions generated a large amount of heat in the initial stage. The maximum temperature of amination reaction is higher than the initial decomposition temperature of the amination product under adiabatic condition. The pyrolysis of amination product was divided into three stages. The product had a high apparent activation energy at the beginning of decomposition, and the apparent activation energy decreased as the decomposition progressed.

Improved dimensional stability of water‐blown polyurethane foam with aluminum hydroxide and magnesium hydroxide

AbstractWater is eco‐friendly and safe; thus, it used as a blowing agent in the fabrication of water‐blown polyurethane (PU) foam. However, water‐blown PU foam may experience dimensional instability due to shrinkage of the cells inside the foam. In order to reduce cell shrinkage due to the loss of CO2 gas, vacuum formation is prevented in the closed‐cell foam and the maximum reaction temperature must be raised to increase the degree of curing of the PU foam. In this study, two flame retardants, aluminum trihydrate (ATH) and magnesium dihydrate (MDH), were selected as additives to partially open the cells and increase the maximum reaction temperature. ATH and MDH were both effective for increasing the maximum foam reaction temperature and decreasing dimensional change. Notably, PU foams with 7.5 wt% ATH were the most dimensionally stable at both room temperature and high temperature. Moreover, the compressive strength and flexural strength of such foams were also improved compared to those of the foams without any additive.