Initial Mixture Research Articles

Laminar burning velocity of hydrogen, methane, ethane, ethylene, and propane flames at near-cryogenic temperatures

The primary objective of this study is to measure the laminar burning velocity of perfectly premixed hydrogen-air, methane-air, ethane-air, ethylene-air, and propane-air flames, at near-cryogenic temperatures and atmospheric pressure. Initial fuel-air mixture temperatures as low as 160 K were investigated. The experimental methodology was validated by comparing the results obtained with those from previous studies available in the literature and with numerical simulations using five different chemical mechanisms. First, for all fuels, the laminar burning velocity evolution as a function of the equivalence ratio followed the same trend at 295 K and 240 K. Regardless of the equivalence ratio and mixture composition, the laminar burning velocity decreased by 22 to 44% for hydrogen, methane, ethane, ethylene, and propane flames when the temperature was decreased from 295 K to 240 K. Second, for stoichiometric conditions, the laminar burning velocity decreased by about 50% for all fuels, when the temperature was decreased by 100 K, from 295 to 195 K. These experimental results were in excellent agreement with laminar burning velocities calculated by a power law of the ratio of unburned gas temperature to ambient temperature, with exponent values from the literature, obtained for temperatures above the ambient. All five chemical mechanisms provided a very good agreement, within or near experimental uncertainties, for most of the fuels and conditions investigated, even at low temperatures. Overall, this study provides valuable information on the laminar burning velocities of various hydrocarbon and hydrogen fuels at near-cryogenic temperatures, which can be useful for the design of cryogenic storage systems and the validation of chemical kinetic models for conditions below ambient temperatures.

Composition, structure, and magnetic properties of SiCxNyFez films produced by the PECVD method from a gas mixture of 1,1,1,3,3,3-hexamethyldisilazane, ferrocene, and helium

Composite SiCxNy:Fez films with magnetic properties were obtained by plasma-enhanced chemical vapor deposition from gas mixtures of hexamethyldisilazane, ferrocene, and helium. In the work, the ratio of elements of the initial gas phase was varied at a constant synthesis temperature of 873 K, which made it possible to obtain films that differ significantly in the content of elements, but are similar in structure. Using a complex of modern research methods: infrared spectroscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy, the relationship between changes in the concentration of elements of the initial gas mixture and changes in the composition of SiCxNy:Fez films was established. The structure of the obtained samples was studied by X-ray photoelectron spectroscopy, extended X-ray absorption fine structure, and X-ray phase analysis. Based on the data obtained, it is assumed that, in the studied range of conditions, the obtained films can be attributed to two different materials. Films containing less than 13% iron consist of an amorphous SiCxNy matrix with inclusions of disordered carbon and iron silicides. Films containing more than 27% iron are composite. The composite includes disordered carbon, iron silicides, and iron carbides. As well as inclusions of silicon nitride, silicon oxide and carbon nitride. It is assumed that the magnetic properties of the films are due to the content of iron silicides and iron carbides in them. Films containing more than 27 at% iron have ferromagnetic properties with a Curie temperature above room temperature.

Molecular Simulation of Biobutanol Recovery Using LTA and CHA Zeolite Nanosheets with an External Surface

LTA and CHA zeolites with silica and silico-alumino-phosphate (SAPO) composition have been recently proposed by Van der Perre et al. (ChemSusChem2017,10, 2968) to recover butanol from a mixture of butanol, ethanol, acetone, and water. Such a mixture is obtained from biomass fermentation, which is a sustainable alternative for butanol production. Here, we establish a computational methodology to simulate the three-step process, consisting of selective adsorption of butanol, with some ethanol and water, from the initial mixture, using a silica LTA nanosheet; desorption of the adsorbed mixture by increasing the temperature; and adsorption of the desorbed products in a CHA (silica or SAPO) nanosheet. A combination of Monte Carlo simulations, allowing to reproduce or predict single- or multiple-component gas adsorption isotherms, and molecular dynamics, giving the time evolution of the selective adsorption and desorption processes, have been used to model the experimental setup. A recently parameterized force field of general use for zeolites, AlPOs, and SAPOs has been tuned up in order to describe all interactions arising from this model, allowing to capture the thermodynamics of the system, the flexibility of the frameworks, and the effects of surface and bulk in the permeability of the nanosheets.

TG, DSC, XRD, and SEM studies of the substituted lithium ferrite formation from milled Sm2O3/Fe2O3/Li2CO3 precursors

Formation of substituted lithium ferrite Li0.5SmxFe2.5–xO4 (where x = 0.06 and 0.2) from Sm2O3/Fe2O3/Li2CO2 precursors was studied by X-ray diffraction analysis, thermogravimetry, differential scanning calorimetry, and scanning electron microscopy. The mixture of powders was subjected to preliminary mechanical activation in a planetary mill. We analyzed samples based on the precursors and synthesized at 900 °C for 4 h in a laboratory furnace. It was found that ball milling of the precursors mixture in a planetary mill increases the powder reactivity. In spite of this, no substituted lithium ferrites were formed. It was shown that a two-phase composite that consists of pure lithium ferrite Li0.5Fe2.5O4 and SmFeO3 is formed during synthesis. An increase in the Sm2O3 content in the initial mixture provides an increase in the amount of the formed SmFeO3 phase. The synthesis of Li0.5Fe2.5O4 ferrite was confirmed by XRD analysis data, the Curie temperature (627–630 °C) measured using TG analysis in a magnetic field, and by the presence of an endothermic peak on the DSC curve corresponding to the order–disorder transition in the Li0.5Fe2.5O4 phase.

Mg-Ni-Nb2O5 Composite Produced by High-Pressure Torsion

A Mg-based composite material has been produced by the consolidation at room temperature of a Mg-5wt.% Ni-2wt.% Nb2O5 powder mixture subjected to high-pressure torsion (HPT), one of the processing methods to induce severe plastic deformations. The microstructure, density, and microhardness of the consolidated disks were characterized after the application of up to 30 revolutions in torsion under compression stresses of 3 and 5 GPa. According to the density measurements, the composite was consolidated in full after the application of five revolutions, although disks subjected to only one revolution exhibited densities close to the maximum measured value. On the other hand, grain size and microhardness measurements showed that differences existed at locations near the center and the periphery of the HPT-processed disks. Under the stress of 5 GPa, the grain size in the central regions stabilized at about 0.35 μm after five revolutions, while at the peripherical regions it gradually decreased with an increasing number of revolutions down to about 0.15 μm after 30 revolutions. In turn, the microhardness measured along a diametral cross section steadily increased with the number of revolutions between 1 and 10 revolutions, maintaining a gradient from the center to the periphery in all cases. With the application of 20 and 30 revolutions, only the peripheral regions increased considerably in hardness. It was discovered that the magnesium particles in the initial powder mixture had formed an oxide—hydroxide surface layer, which changed the expected final density of the consolidated material by about 2 to 4.5%. This superficial contamination of the Mg powders did not prevent the material from achieving full consolidation.

Laminar burning velocities of cyclopropane flames

Cyclopropane, c-C3H6, the simplest cycloalkane, is seldom included in detailed kinetic mechanisms for hydrocarbons, though it may exhibit unusual kinetic features yet to be analysed due to a lack of studies of its combustion characteristics. In this work, laminar burning velocities of cyclopropane flames have been determined using the heat flux method at atmospheric pressure and an initial gas mixture temperature of 298 K. The fuel consisting of 50% c-C3H6 + 50% N2 was burnt with air covering the range of equivalence ratios 0.6 – 1.5. The detailed kinetic model of the authors was extended by the reactions of cyclopropane and cyclopropyl radical, c-C3H5, with the rate constants selected from the literature. This mechanism, as well as the most recent mechanisms for c-C3H6 of Wang et al. (2022) and of Lei et al. (2022), have been compared with the burning velocities of propylene + air flames and with the new experimental results for cyclopropane flames. The model of Lei et al. (2022) significantly underpredicts the burning velocities for both fuels, on the other hand, good agreement with predictions of the present model and of Wang et al. (2022) was observed at 1 atm. However, further sensitivity and rate-of-production analyses revealed important differences in the pathways of c-C3H6 oxidation predicted by the two mechanisms. The present kinetic model was also tested using all available measurements of cyclopropane ignition delays in shock tubes, which combined cover the range of equivalence ratios from 0.33 to 3, at pressures 1 - 10 atm, and temperatures 1100 – 2100 K. Overall good performance of the model was demonstrated across these ranges of conditions and compositions of the mixture. A direct comparison of the experimental data shows that ignition delays of propylene are slightly longer than those of cyclopropane, yet in most cases within the overlapping uncertainties or scattering between different experimental facilities. The laminar burning velocities of c-C3H6 + air are slightly higher than those of C3H6 + air at least according to the predictions of the present mechanism and the model of Wang et al. (2022).

Cellulose-g-poly(2-(dimethylamino)ethylmethacrylate) Hydrogels: Synthesis, Characterization, Antibacterial Testing and Polymer Electrolyte Application.

Hydrogels have been investigated due to their unique properties. These include high water content and biocompatibility. Here, hydrogels with different ratios of poly(2-(dimethylamino)ethylmethacrylate) (PDMAEMA) were grafted onto cellulose (Cel-g-PDMAEMA) by the free radical polymerization method and gamma-ray radiation was applied in order to increase crosslinking and content of PDMAEMA. Gamma irradiation enabled an increase of PDMAEMA content in hydrogels in case of higher ratio of 2-(dimethylamino)ethyl methacrylate in the initial reaction mixture. The swelling of synthesized hydrogels was monitored in dependence of pH (3, 5.5 and 10) during up to 60 days. The swelling increased from 270% to 900%. Testing of antimicrobial activity of selected hydrogel films showed weak inhibitory activity against Escherichia coli, Pseudomonas aeruginosa, and Bacillus subtilis. The results obtained by the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) indicate that chemically synthesized hydrogels have good characteristics for the supercapacitor application.

Effect of the Mass Fraction of NiTi-TiB2 SHS-Particles on the Phase Composition, Structure, and Mechanical Properties of Inconel 625-NiTi-TiB2 Composites Produced by Direct Laser Deposition.

This paper studies the impact of the mass fraction of NiTi–TiB2 particles obtained by the method of self-propagating high-temperature synthesis (SHS) on the phase composition, structure, and mechanical properties of composites made by direct laser deposition from an Inconel 625–NiTiz–TiB2 powder mixture. Composites were obtained from a powder mixture with the mass fraction of particles at 5–10 wt%, and they consisted of an Inconel 625 metal matrix wherein ceramic inclusions of titanium diboride TiB2 were distributed. Increasing the mass fraction of SHS-produced NiTi particles from 30 to 95 wt% led to the emergence of a NiTi intermetallide phase in the matrix material as well as an increase in the average TiB2 particle size and formation of their agglomerates. In addition, an increase in the microhardness of the materials was observed. The graph of tensile strength of Inconel 625–NiTi–TiB2 samples has a parabolic shape with a maximum at 1000 MPa (when the mass fraction of SHS-produced NiTi–TiB2 particles is at 30 wt%). A further increase in the mass fraction of NiTi–TiB2 led to a decrease in the tensile strength down to 400 MPa. Here the deformation of samples decreases linearly as the ratio of composite particles in the initial mixture increases. From a comparative analysis of the results obtained, the optimal mass fraction of composite NiTi–TiB2 particles in the Inconel 625-NiTi–TiB2 powder mixture was found to be 5 wt%.

The properties and health hazards from early nuclear weapon fallout: The Castle Bravo incident revisited

Early fallout is defined as the fallback to the earth’s surface of radioactive particles shortly after a nuclear detonation (often arbitrarily defined within 24 h). At the difference of wide spreading global fallout, early fallout mainly consists of larger particles that are often visible. The initial mixture is rich in short- and very short-lived radionuclides associated with a very high initial activity that decreases rapidly (in 7 h, the dose rate is reduced by 90%). The main danger of early fallout results from external irradiation by highly penetrating gamma-radiation that may cause acute radiation sickness. Only in the case of the thyroid, internal irradiation by the incorporation of radioiodine may prevail. The bombings of Hiroshima and Nagasaki are examples of airbursts with many fatalities by prompt effects (blast, burns, and initial ionizing radiations), but they produced little fallout. The nuclear test code-named Castle Bravo on the Marshall Islands (1954) did not have casualties by its blast, thermal or initial radiation effects, but the inhabitants of the nearby islands and the crew of a Japanese fisherboat (Lucky Dragon) were affected by large amounts of fallout. For the inhabitants of the Rongelap Atoll, the average dose from external irradiation was assessed at 1.6 Gy. From a clinical point of view, based on hematological data using the METREPOL classification system, the acute radiation syndrome can be categorized as mild (H1). Blood transfusions were not required, and antibiotics were not administered for prophylaxis or therapy of infections related to irradiation. The equivalent dose received by the thyroid resulted mainly from internal irradiation with 7.6 Gy. The major late effects were thyroid abnormalities, including thyroid failure, nodules, and malignant tumors. The 23 Japanese crewmen seem to have been irradiated by higher doses (2.9 Gy). Compared to the hematological data of the Rongelap victims, the evolution pattern over time is quite similar. Still, the absolute values of the cell counts are lower, and on average, the acute radiation syndrome can be categorized as rather moderate (H2). Considering the individual cases, data show a large interindividual variability, and the clinical severity category ranges from “no alterations” (H0) to severe (H3). Victims were treated with repeated blood transfusions and antibiotics. Several of them developed jaundice, and one of them died six months after the incident showing symptoms compatible with subacute liver failure. A radiochemical organ analysis revealed that only the bones were clearly contaminated with fission products. In the 1990s, many surviving crewmen were diagnosed with hepatitis C, incurred probably from blood transfusions that were often contaminated at the time, and died from hepatocellular carcinomas. Thyroid dysfunctions were not reported. The Castle Bravo case permits to study the health hazards resulting from early fallout independently from the prompt effects of a nuclear detonation. The prevailing external irradiation was confirmed, except for the thyroid with a higher dose resulting from radioiodine incorporation mainly caused by ingestion. As shown for the Japanese fishermen, the risks incurred by medical treatments must be carefully weighed against the benefits of the therapeutic intervention. The cause of death of the only short-term fatality is not fully elucidated, but is consistent with liver failure due to transfusion hepatitis rather than radiation effects.

Kinetic investigation of the ozone-assisted partial oxidation of fuel-rich natural gas mixtures at elevated pressure

The partial oxidation of natural gas in HCCI engines in terms of a polygeneration process could be a promising technology to flexibly produce useful chemicals, heat, and work, depending on demand. Because natural gas is relatively inert, high intake temperatures or compression ratios are required to initiate its conversion which can result in a lower lifetime of the engine. Alternatively, small amounts of more reactive species such as ozone can be added to the initial mixture to provide radicals at more moderate conditions and initiate the main ignition. In this study, plug-flow reactor experiments are performed to assess the influence of ozone on the fuel conversion and product formation during the partial oxidation of methane and natural gas. Experiments are performed in the temperature range of 373 K to 973 K at 4 bar and equivalence ratios of 2. Molecular-beam mass spectrometry coupled with electron ionization is used as analytical technique to detect the mixture composition at the outlet of the reactor. The results show that even very small amounts of ozone can help to shift the conversion onset to much lower temperatures and increase the yields of useful chemicals. The data can further be used to improve reaction mechanisms describing the conversion of hydrocarbons in the presence of ozone. A literature ozone reaction mechanism has been implemented in two recent hydrocarbon mechanisms and the results of simulations using these mechanisms are compared to the experimental data with respect to the low-temperature intermediates which influence ignition. Predictions differ substantially from the experimental results identifying starting points for further investigations. The speciation data provided in this work contribute to extending the reaction kinetics of ozone assisted fuel conversion to higher pressure.

STUDY OF RADICAL COPOLYMERIZATION REACTION OF UNSATURATED POLYESTERS WITH ACRYLIC ACID

One of the promising and inexpensive types of raw materials, taking into account the use of modern technologies for the production of sealing and adhesive materials, are unsaturated polyesters of various compositions.The aimof this work is to study the reaction of radical copolymerization of polyethylene(propylene)-glycolfumarate with acrylic acid in a dioxane solution at various molar ratios of the initial polymer-monomer mixture. Methodology.The composition of the copolymers was identifiedby HPLC spectroscopy by analyzing the mother liquors, the structure was confirmed by IR spectroscopy. The copolymerization kinetics was studied by the dilatometric method. The degree of swelling of the copolymers was determined by the gravimetric method, and their degree of unsaturation, by the bromid-bromate method. Radical copolymerization constants calculated by the Mayo-Lewis integral method.The results obtainedindicate thatfor any composition of the initial polymer-monomer mixture, the composition of the copolymer is enriched with acrylic acid links, and with an increase in its content in the initial polymer-monomer mixture, the reaction rate increases significantly.An increase in the content of unsaturated polyester in the initial polymer-monomer mixture leads to a decrease in the ability of the copolymer to absorb moisture, which makes it possible to assume their use as bases in the production of sealing and adhesive materials. Conclusion. An analysis of the numerical values of the copolymerization constants showed a higher activity of acrylic acid in comparison with unsaturated polyesters, thereby confirming the previously put forward assumption aboutthe relatively lower reactive ability of the latter.

Refinement of the eutectic composition in the LaB6–VB2 system

The LaB6–VB2 alloy with the eutectic structure was obtained by cold crucible induction melting followed by crystallization. The mole ratio of components in the initial powder mixture was 35 : 65. The structure and composition of the LaB6–VB2 material were studied by X-ray diffraction, scanning electron microscopy, and X-ray microanalysis. The composition of the alloy is represented by two boride phases — cubic LaB6 and hexagonal VB2. Two-phase eutectic regions up to 500 μm in size represent a LaB6 matrix filled with 0.8–2.0 μm thick VB2 fibers (filamentary, rod crystals). VB2 fibers are predominantly oriented along the direction of the temperature gradient that appeared when cooling the melt, i.e. from the outer surface of the sample to its center. The integrated phase area analysis was used to determine the eutectic composition: 42 Ѓ} 1 mol% LaB6 and 58 Ѓ} 1 mol% VB2.

A study on biological properties of titanium implants coated with multisubstituted hydroxyapatite

In this work, it was found that the composition of hydroxyapatite coatings deposited on a titanium substrate depends on the temperature of detonation products and on the composition of the initial explosive mixture. Depending on the detonation mode, it was possible to obtain a coating of oxyhydroxyapatite containing or not containing an admixture of other calcium orthophosphates. It was shown for the first time that the structure of multisubstituted Zn–Si-hydroxyapatite and Ag–Zn–Si-hydroxyapatite with substitution degree x(Zn) = x(Si) = 0.2 and x(Ag) = 0.1 has lower thermal stability as compared to unsubstituted hydroxyapatite. The formation of a small amount of the α-Ca3(PO4)2 phase upon detonation deposition of the multisubstituted hydroxyapatites was obviously due to structural transformations that occurred when the material was heated by the detonation products. In vivo biological testing of titanium implants coated or not coated with hydroxyapatite revealed that the coating significantly accelerates osteogenesis in the gap between native bone and the implant; this acceleration improved implant fixation. In animals with the uncoated plates, fibrogenesis processes significantly outstripped the osteogenesis. The presence of Zn and Si ions in the apatite coating had a potentiating influence on the osteoinduction caused by hydroxyapatite. Osteogenesis in this case was more complete and characterized by pronounced processes of mineralization of the bone plates. The addition of Ag ions to the Zn–Si-hydroxyapatite at a concentration of 1 at.% did not impair its osteogenic activity and did not have a toxic effect on bone tissue, while imparting antibacterial properties to the material.

Smart Sustainable Production Management for City Multifloor Manufacturing Clusters: An Energy-Efficient Approach to the Choice of Ceramic Filter Sintering Technology

The development of environmentally friendly technologies, including additive technologies, contributes to the formation of sustainable production in city multifloor manufacturing clusters (CMFMCs). This paper discusses an approach to the implementation of energy-intensive technological processes in such clusters using examples of the manufacturing of ceramic and metal–ceramic products. The manufacturing of ceramic and metal–ceramic products in high-temperature furnaces is associated with an increased electricity consumption. The use of modern ceramic micro- and nanopowders makes it possible to switch to more energy-saving technologies by reducing the sintering temperature and shortening the technological cycle. This requires the use of additional activating and inhibiting additives in the initial powder mixtures to obtain products with the necessary physical and mechanical properties. The purpose of this paper is to present a model and indicators to assess the energy efficiency of the choice of sintering technology of foam ceramic filters for smart sustainable production management within CMFMCs. The use of the proposed indicators for assessing the energy efficiency of sintering foam ceramic filters makes it possible to improve the technological process and reduce the completion time of its thermal cycle by 19%, and reduce the maximum heating temperature by 20% to 1350 °C. The adoption of a different oxide technological alternative and the use of the proposed model and indicators to assess the energy efficiency of the sintering technology of foam ceramic filters allows to choose less energy-intensive equipment and save up to 40% in electricity. The proposed model to assess the energy efficiency of the sintering technology of foam ceramic filters can be used to control their production under the power consumption limitations within the CMFMCs.

Liquid-Phase-Assisted Catalytic Nitridation of Silicon and In Situ Growth of α-Si3N4.

Si3N4 powders were synthesized with Fe, Co, or Ni as catalysts using Si powder at 1250 °C in a nitrogen atmosphere by liquid-phase-assisted catalytic nitridation synthesis (LPA–CNS). The catalytic effects of the metals on the nitridation of silicon powder were investigated by mixing the powder with 2 wt% by mass of Fe, Co, or Ni in a high-temperature liquid phase in flowing nitrogen. The α-Si3N4 micro-morphology could be effectively changed by adjusting the type of catalyst in the initial reaction mixtures. Fe, Co, and Ni promoted the formation of α-Si3N4 at 1250 °C and controlled the morphology of the α-Si3N4 particles. The hexagonal flakes of α-Si3N4 with a better defined morphology were obtained using Ni as the catalyst, compared to that obtained from the other two catalysts.

Development of a method and algorithm for calculating the equilibrium of methanol synthesis under medium pressure

The object of research is the synthesis of methanol under medium pressure, and the subject of research is the calculation of the equilibrium composition. A method and an algorithm for calculating the equilibrium composition of products are proposed. Calculations have been carried out using two mechanisms of methanol synthesis. First of all, the first approach to the mechanism of methanol synthesis was applied, which provides for the formation of methanol from a mixture of carbon oxides and hydrogen by the simultaneous reaction of methanol synthesis from carbon monoxide (IV) and steam reforming of carbon monoxide (II). The poor convergence of the system of two equations on the basis of this interaction mechanism is established, which complicates the selection of initial approximations and the choice of a real solution. At the second stage, the mechanism of the formation of methanol from carbon monoxide (II) with the simultaneous flow of steam reforming of CO in the opposite direction is considered. The degree of the equation describing the dependence of the equilibrium constant on the partial pressures of the reactants decreases in comparison with the first approach and causes much better convergence when solving the system of two equations. The use of a coefficient that takes into account the effect of pressure on the value of the equilibrium constant is proposed, and its dependence on temperature is approximated. The developed algorithm is implemented in MathCAD, while the relative maximum deviation for methanol is 8.53 %. The third approach is to use two coefficients that adjust the equilibrium constant depending on pressure. In this case, the relative maximum deviation of methanol is 16.25 %. The program according to the proposed algorithm takes into account the multiplicity of the initial data, namely the possibility of varying the composition of the initial mixture, pressure and temperature. The calculation was carried out according to the initial data of industrial implementation of methanol synthesis. Comparison of the equilibrium concentration of methanol with the real one at the outlet of the synthesis column established the degree of equilibrium reaching 39.4 %, which indicates the presence of a reserve of methanol synthesis and the possibility of increasing the practical yield of methanol.

Joint Application of Biological Techniques for the Remediation of Waste Contaminated with Hydrocarbons

Cleaning the oil industry's fuel storage and management facilities generates high levels of hazardous waste. This research aims to assess the use of biological bioremediation treatments, most commonly used for decontaminating soil, by applying them to hydrocarbon-contaminated waste. Turned pile composting using food-derived sludge as a co-substrate and the necessary proportion of bulking agent enabled the bioremediation of the initial mixture via the succession of microbial populations (PLFAs), with a 70% lower TPH concentration obtained 6 months after the start of the process. Subsequent bioassays using the composted material showed survival rates of over 80% with earthworms (Eisenia andrei) and a larger decrease in TPH in the joint treatment with earthworms and plants (Pennisetum clandestinum). The composting process reduces the concentration of hazardous organic compounds, allowing for the proper development of fauna and flora in the compost by improving the biodegradation rate.Graphical

Activated Sintering of Cr2O3-Based Composites by Hot Pressing

The paper presents and discusses questions on structure formation during the sintering process of Cr2O3-based composites using the hot pressing method, when a chemical reaction between the components takes place. The task was difficult because Cr2O3 decomposes when sintered at temperatures above 1300 °C. The proposed novel method allowed for interaction between aluminum and chromia, thus avoiding the decomposition of the latter. Here, ultrafine aluminum powder played the role of the active agent forming a liquid phase and reacting with Cr2O3. The appearance of the solid solutions of (Cr,Al)2O3 with different stoichiometry of Cr and Al depended on the aluminum content in the initial mixture. The solid solution significantly strengthened boundaries between composite phases, resulting in the composite material of high fracture toughness between 5 and 7 MPa m½ and bending strength of ca. 500 MPa. The best mechanical properties exhibited the cermet with 22 wt.% of the restored chromium.

Synthesis, characterizations, and magnetic behavior of novel (CuNiTiZnFe)3O4 high entropy spinel oxide

In this report, a modified solid-state synthesis technique is optimized to synthesize a single spinel phase for a novel (CuNiTiZnFe)3O4 High Entropy Oxide (HEO) and studied for magnetic behavior. Three different approaches were adopted for the synthesis of pure spinel HEO. In the first approach, The initial mixture of constituent oxides was admixed, and sintered at 1050 °C for 20 h. For the second and third approaches, the mixture of constituent oxides was ball-milled for 2 h, and 10 h separately, followed by sintering at 1050 °C for 20 h. A small amount of undiffused constituent oxide peaks are present in both the first and second approaches. However, the sample synthesis through 10 h milling followed by sintering has single spinel (CuNiTiZnFe)3O4 HEO phase. The single spinel HEO phase formation was confirmed through the le-Bail refinement. The lattice parameter for the well-fitted XRD pattern is 8.415161 A°. Further, the investigation was focused on the magnetic behavior of the single spinel HEO phase. The value of magnetization and coercivity is 16.11 emu/g and 10.66 Oe, respectively. The synthesized HESO has typical ferrimagnetic nature and has the second-highest value of Ms reported so far for HEOs. The ionic states of different cations present in the (CuNiTiZnFe)3O4 HESO were also investigated through X-ray photoelectron Spectroscopy. XPS analysis reveals that Fe and Ni are in the +3 and + 2 states, Cu and Zn are in the +2 states, and Ti is in the +4 states.

Lattice-Boltzmann modeling of lifted hydrogen jet flames: A new model for hazardous ignition prediction

This numerical study deals with the hazardous ignition of a jet flame in a vitiated co-flow. A novel formulation, based on a passive scalar variable, will be presented to predict hydrogen auto-ignition events. The model, derived from the theoretical analysis of the Jacobian, correctly describes the appearance and absence of auto-ignition in complex configurations based on initial thermodynamic and mixture conditions. No chemical reaction and species equations are required to perform the simulations. Results of Lattice Boltzmann Methods (LBM) simulations of a 3D H2/N2 Cabra flame will be presented using a detailed H2-Air mechanism. Validation against experimental and numerical results will be provided for the lift-off (distance to auto-ignition). The passive scalar predictions are successfully compared with the reactive simulations. The results show a potential extension of this model to an extensive spectrum of hydrogen safety and large-scale turbulent combustion applications.