Magnesium Particles Research Articles

The effects of admixtures of inorganic hydrates on the hydration hardening of magnesium potassium phosphate cement

Admixtures of Na2B4O7·10H2O (NB), Ca(NO3)2·4H2O (CN) and Na2SO4·10H2O (NS) are studied to discover how they affect the work performance, hydration-induced increases in temperature and mechanical performance of magnesium potassium phosphate cements (MKPCs). Analytical methods such as X-ray diffraction spectroscopy, eight-channel microcalorimetry and thermogravimetric-differential scanning calorimetry are used to investigate the underlying mechanisms of these changes. Incorporation of a single retarder (NB) results in short MKPC hardening times and low early strengths. Admixture with 1·5% or more NB and CN effectively lengthens the hardening time of MKPC, but greatly decreases its fluidity. Incorporation of NB, CN and NS in the ratios 1·5%:1·5%:5% results in an initial hardening time of 37·02 min and the appearance of two temperature peaks in the hydration temperature curve. The resulting cement mix has fluidity of 115 mm and strength of 52·56 MPa after 12 h of hydration. Reaction between NB and CN creates a calcium borate film that envelopes magnesium oxide particles, preventing dissolution of magnesium oxide and generation of the hydrated product MgKPO4·6H2O (MKP), thus slowing down the hydration process. Incorporation of an appropriate quantity of NS endows fluidity of MKPC that can reach 125 mm, owing to crystal waters released during solvation and changes in phase.

Enhanced thermal conductivity of ternary carbonate salt phase change material with Mg particles for solar thermal energy storage

Molten salts with high thermal conductivity play a key role to achieve a high thermal energy transfer efficiency during heat charging and discharging processes in a high-temperature concentrating solar energy system. In this work, a novel highly thermal conductive composite phase change material (CPCM) was designed by blending magnesium (Mg) particles with eutectic ternary carbonate salt (Li2CO3-Na2CO3-K2CO3) and used as heat transfer fluid (HTF) and/or thermal energy storage medium in advanced high-temperature concentrating solar power (CSP) plants. The thermo-physical properties of the composite systems were measured. Experimental results indicated that Mg particles dispersed in the molten salts with dendritic structure. The melting temperature of the CPCM had negligible change compared to pure carbonate salt, and the phase change enthalpy reached up to 160J/g. The effective thermal conductivity was 1.93W/(mK) for 2wt% of Mg, which was enhanced by 45.11% compared to pure ternary carbonate salts. The upper limit working temperature of the CPCM was measured to be 725°C in argon atmosphere. The wide working temperature range (ΔT=325°C) indicated its great thermal stability and high capacity of energy storage.

Facile Synthesis of MgO-Modified Carbon Adsorbents with Microwave- Assisted Methods: Effect of MgO Particles and Porosities on CO2 Capture

In this study, magnesium oxide (MgO)-modified carbon adsorbents were fabricated using a nitrogen-enriched carbon precursor by microwave-assisted irradiation for CO2 capture. The X-ray diffraction (XRD) patterns showed the characteristic diffraction peaks of MgO at 43° and 62.5°, and no impurities were apparent. By changing the microwave reaction time, the spherical structure of the parent material was transformed to a hybrid structure with MgO crystalline particles in a carbon matrix. The morphology evolution and properties of the prepared materials were also investigated using transmission electron microscopy and N2 adsorption, respectively. On optimising the conditions, the prepared sample attained a high CO2 uptake of 1.22 mmol/g (5.3 wt.%) under flue gas conditions (15% CO2 in N2). It was found that MgO affected the CO2 capture behaviour by enhancing the fundamental characteristics of the carbon surfaces.

Synthesis of pillar and microsphere-like magnesium oxide particles and their fluoride adsorption performance in aqueous solutions

We synthesized pillar and microsphere-like MgO particles and their fluoride removal performance. Samples of MgO were synthesized by calcination of precursors derived from MgCO3·3H2O and characterized using field emission scanning electron microscopy, X-ray diffraction, and N2 adsorption-desorption isotherms. The fluoride removal performance of the MgO samples was investigated in terms of adsorption kinetics and adsorption equilibrium. The effects of pH and the presence of other anions on the fluoride adsorption were also considered. The adsorption capacities of pillar and microsphere-like MgO particles were 151.51 and 166.66 mg/g, respectively. The pH of the aqueous solutions did not significantly affect the fluoride adsorption at pH 9 or lower. Except for phosphate, the effect of co-existing anions on fluoride adsorption was not considerable. Fluoride removal occurred through the substitution of hydroxyl groups on the surface of MgO with fluorides.

Dynamics of phase formation during the synthesis of magnesium diboride from elements in thermal explosion mode

The influence of the heating rate of the Mg + 2B mixture on the dynamics of the phase formation during the thermal explosion in the helium medium is investigated by the time-resolved X-ray diffraction method. It is shown that the MgB2 phase appears without the formation of intermediate compounds. The presence of impurity oxygen is a substantial factor affecting the formation kinetics of MgB2. The oxide film on the surface of magnesium particles has no time to form with the heating rate of the charge mixture of 150–200°C/min. A result of this circumstance is the reaction diffusion mechanism of the Mg + 2B = MgB2 reaction immediately after the melting of magnesium. Synthesis products mainly consist of MgB2 and MgO traces at a level of 5%. The thermal explosion temperature is 1100°C. A comparatively thick oxide film which retards melt spreading and shifts the onset of the formation reaction of MgB2 by 8–9 s grows on the magnesium surface at a heating rate of 30–50°C/min. Synthesis products contain MgB2 and up to 15% MgO. The thermal explosion temperature is 1020°C in this case.

Increasing of the Mechanical Properties of Friction Stir Welded Joints of 6061 Aluminum Alloy by Introducing Alumina Particles

Abstract The main aim of this investigation is to produce a welding joint of higher strength than that of base metals. Composite welded joints were produced by friction stir welding process. 6061 aluminum alloy was used as a base metal and alumina particles added to welding zone to form metal matrix composites. The volume fraction of alumina particles incorporated in this study were 2, 4, 6, 8 and 10 vol% were added on both sides of welding line. Also, the alumina particles were pre-mixed with magnesium particles prior being added to the welding zone. Magnesium particles were used to enhance the bonding between the alumina particles and the matrix of 6061 aluminum alloy. Friction stir welded joints containing alumina particles were successfully obtained and it was observed that the strength of these joints was better than that of base metal. Experimental results showed that incorporating volume fraction of alumina particles up to 6 vol% into the welding zone led to higher strength of the composite welded joints as compared to plain welded joints.

Combustion of Foamed Emulsions in the Quenching/Reignition Regime

In this paper, we consider the problems of combustion of a foamed emulsion consisting of oxygen bubbles dispersed in the emulsion, which represents a water solution of surfactant with oil drops distributed in it. The interest to study such problems is caused by the perspective of obtaining a new type of fuel based on a water–oil blend as well as by the need to solve ecological issues related to oil spilled on the water surface. At a significant content of water in the combustible foam, an irregular regime of flame propagation can be established that is related to sequential quenching and reignition of the foam. On the basis of experimental research, we study the influence of the magnesium oxide particle fraction, fuel concentration, and tube diameter on the speed of flame propagation in the foamed emulsion in the quenching/reignition regime. It is found that the presence of magnesium oxide particles in the foam leads to an increase in the total burning rate of the foam. A reduction in the tube diameter and the use of a leaner foam favor the onset of the quenching/reignition regime.

Experimental study of foamed emulsion combustion: Influence of solid microparticles, glycerol and surfactant

The use of water as a part of hydrocarbon fuel represents one of the perspective directions in elaborating new types of combustible systems. This paper considers issues of foamed emulsion combustion on the basis of experimental research. Combustible foamed emulsion is a mixture of oxygen bubbles and heptane drops dispersed in a water solution of stabilizer. Such foamed emulsions possess a set of unique properties and represent a vivid example of multiphase combustible system which could contain a significant amount of water. Thus a foam containing 83wt% of water is still combustible. Here we consider issues of foamed emulsion stability and combustion depending on the influence of magnesium oxide particles, stabilizer and glycerol concentrations. In this paper for the first time we are presenting that by addition of magnesium oxide particles the total burning rate of the foam can be changed for more than an order of magnitude. The dependence of total burning rate of the foam on the stabilizer concentration is not monotonic with a maximum at certain stabilizer content. The use of glycerol favors the shrinkage of the foamed emulsion and as a result the flame quenching.

Carbon coating of magnesium particles

Magnesium when hydrided has low thermal and electrical conductivity and carbon coating would be useful to remedy this for a variety of purposes. In this study, carbon coating was achieved by co-feeding magnesium and methane into a thermal plasma reactor. This yielded carbonaceous material with magnesium particles 5–10 nm in size embedded in graphitic matrix. A further reduction down to 2–3 nm was possible but required reductions in the precursor feed rate. 2 wt% carbon was sufficient to fully protect magnesium particles of approx. 260 nm in size. Light milling, however, disrupts the continuity of graphitic envelop and the particles then react both with oxygen and hydrogen.

Allium cepa root tip assay in assessment of toxicity of magnesium oxide nanoparticles and microparticles

Allium cepa bioassay had been used from decades for the assessment of toxicants and their harmful effects on environment as well as human health. Magnesium oxide (MgO) particles are being utilized in different fields. However, reports on the adverse effects of MgO nanoparticles on the environment and mankind are scarce. Hence, the toxicity of MgO particles is of concern because of their increased utilization. In the current study, A. cepa was used as an indicator to assess the toxicological efficiency of MgO nano- and microparticles (NPs and MPs) at a range of exposure concentrations (12.5, 25, 50, and 100μg/mL). The toxicity was evaluated by using various bioassays on A. cepa root tip cells such as comet assay, oxidative stress and their uptake/internalization profile. Results indicated a dose dependent increase in chromosomal aberrations and decrease in mitotic index (MI) when compared to control cells and the effect was more significant for NPs than MPs (at p<0.05). Comet analysis revealed that the Deoxyribonucleic acid (DNA) damage in terms of percent tail DNA ranged from 6.8–30.1 over 12.5–100μg/mL concentrations of MgO NPs and was found to be significant at the exposed concentrations. A significant increase in generation of hydrogen peroxide and superoxide radicals was observed in accordance with the lipid peroxidation profile in both MgO NPs and MPs treated plants when compared with control. In conclusion, this investigation revealed that MgO NPs exposure exhibited greater toxicity on A. cepa than MPs.

Interactions between Exogenous Magnesia Inclusions with Endogenous Inclusions in a High Alloyed Steel Melt

Interactions between exogenous MgO particles and endogenous inclusions on the surface of a high alloyed steel melt have been investigated in situ in a high temperature confocal laser scanning microscope. Exogenous magnesia particle forms immediately a liquid Mg–Si–Al–Ti–Cr phase surrounding the solid particle. The real attraction forces between the liquid layer surrounding MgO particles and endogenous Al2O3 inclusions are determined in the range of 6 × 10−18 N to 1 × 10−16 N. In contrast to earlier investigations with exogenous Al2O3 particles, lower real attraction forces between exogenous and endogenous particle pairs have been observed in comparison to endogenous inclusions pairs.

Foamed emulsion – Fuel on the base of water-saturated oils

Combustible foamed emulsion is a mixture of oil drops and oxygen bubbles in an aqueous matrix. Such combustible foams represent a perspective type of fuel in whose production water-saturated hydrocarbons can be utilized directly. Experimental results show that even at water content of 90wt% there still is opportunity of flame propagation in the foam. The paper analyzes an influence of magnesium oxide particles and type of surfactant on the stability of foamed emulsion and the speed of flame propagation in it. The use of magnesium oxide micro-particles promotes the increase in flame speed especially at heightened volume fraction of oil in the initial emulsion. At the same time it causes destabilization of the foam. The use of anionic surfactant instead of surfactant of the mixed type leads to decrease in combustible foam stability and increase in flame speed.

Development of PLA/Mg composite for orthopedic implant: Tunable degradation and enhanced mineralization

Polylactic acid (PLA) orthopedic devices suffer from low degradation rate and inadequate osteoconductivity, and often lose efficacy in the late stage of implantation because of inflammatory response of acid products and inability integration to bone. In this work, 2 wt% and 5 wt% magnesium particles reinforced PLA were fabricated using solvent casting and investigated in terms of in vitro degradation and biomineralization. The uniformly distributed Mg particles slightly decreased the crystallinity of PLA. The pH value and variations in mass analysis during the in vitro degradation showed that the Mg incorporation could effectively neutralize the acidic products of PLA, as well as induce more apatite deposition. Great decrease in molecular weight of 2 wt% and 5 wt% Mg/PLA composites as compared to the neat PLA after 8 weeks' immersion made it possible to modulate the degradation rate of the PLA by controlling the proportion of Mg content and other key factors such as size and shape of the Mg reinforcements. In vitro cell culture revealed good biocompatibility of Mg/PLA, and the favorable characteristic for osteoblastic cells to adhere and spread. The cellular biomineralization results demonstrated significantly higher bone-like nodules deposition (both in number and area) achieved on the composite surfaces than that on PLA surface after 14 and 28 days culture. The promoting bone-forming ability derives from the degradation of Mg particles. The study elucidated the positive effects of Mg incorporated to PLA matrix on the degradation and osteogenesis, and provide an alternative for the currently used PLA implants.

Interfacial analysis of TiO2 coated carbon nanofibers and Mg-Al alloy matrix fabricated using a liquid pressing process

Novel structures of TiC/TiAl2/carbon nanofiber (CNF) hybrid reinforcements with attached magnesium oxide (MgO) particles were successfully fabricated in the matrix of the Mg alloy AZ91 (Mg 9wt%, Al 1wt%, Zn) composite. This was done using a novel liquid pressing process, coupled with in situ reactions between titanium dioxide (TiO2)-coated CNFs and the Mg alloy. Homogeneously dispersed hybrid reinforcement with strong interfacial bonding through TiC/TiAl2, led to dramatic improvement in the mechanical properties of AZ91 alloys, with the assistance of an anchoring effect by MgO particles chemically attached to the coating layer.

Thermal effects induced by laser ablation in non-homogeneous limestone covered by an impurity layer

Abstract This paper reports preliminary results concerning thermal effects induced by urban/industrial air pollutants deposited on a limestone rock when heated by pulsed laser in the cleaning process. The process of laser cleaning treatment of the crust is simulated using COMSOL Multiphysics 4.4, finite element analysis software. Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy and Laser Induced Breakdown Spectroscopy techniques have been used to analyze the chemical composition of the samples. Two elements found as being present into the dust and in the crust, such as iron and magnesium particles are used for simulation in COMSOL. Therefore, the profiles heat evolutions on the crust surface and inside limestone are obtained as thermal interactions between the three components (iron, magnesium and limestone), simulating the non-homogeneous materials. It has been observed that iron impurities caused by the dust deposition may damage the limestone through a process of overheating, as a consequence of a high thermal conduction phenomenon, recorded for the region with iron impurities and sizes of micrometric order are localized. The thermal contact between the three components results in plots that reflect their thermal interactions.

The effect of magnesium oxide morphology on adsorption of U(Ⅵ) from aqueous solution

Magnesium oxide particles with different morphologies have been synthesized by using different precursors of magnesium, and urea as precipitating agent. The as-prepared samples, and the magnesium oxide materials before and after adsorption of U(Ⅵ), which were characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX), TG and DSC thermal analysis and so on. The adsorption properties of Mg600-N, Mg600-S and Mg600-Cl adsorbents to U(Ⅵ) were estimated and compared. The treatment of uranium-containing wastewater with magnesium oxide was studied under static state in the laboratory, and also the effects of adsorption time, pH value of wastewater and temperature were discussed. Through the investigation of adsorption thermodynamics and adsorption kinetics, the adsorption capacity of the three types of MgO particles for uranium more than 1600mgg−1, the optimum pH was 3.0–4.0, and the thermodynamic parameter calculation results indicate that the adsorption process is a spontaneous endothermic process.

Copper-ore mining in Sweden since the pre-Roman Iron Age: lake-sediment evidence of human activities at the Garpenberg ore field since 375 BCE.

Historical documents, archaeological evidence and lake-sediment records indicate thus far that significant mining of iron and copper ores in the Berglsagen mining region in central Sweden did not begin until the late 12th century – first with iron in Norberg – and thereafter spreading rapidly throughout the region during the 13th century when also copper was included (e.g. Falun). Prior to this, iron was produced domestically from secondary sources such as bog iron, while geochemical analyses of bronze artefacts indicate copper was imported. The parish of Garpenberg was at the intersection between historical iron- and copper-mining districts, and consequently we expected our sediment record from the lake Gruvsjön (‘mine lake’) to follow the established 13th century development. However, a 2–3-fold enrichment in copper and lead occurred already during 375–175BCE (pre-Roman Iron Age), together with small increases in zinc, magnesium and charcoal particles, and changes in pollen. Together these indicate a clear pattern of human disturbance connected with the ore body bordering the lake. A second distinct phase occurred 115–275CE, but with an 8–9-fold increase in copper and lead along with other indicators. From 400CE a permanent increase in copper and lead occurred, which then accelerated from the 13th century as seen elsewhere in the region. Our results push back the evidence for early ore mining in Sweden from the Middle Ages to the pre-Roman Iron Age.

Synthesis of Magnesium Nanofibers by Electroless Reduction and their Hydrogen Interaction Properties

Magnesium (Mg) is successfully synthesized from the direct reduction of dibutylmagnesium (MgBu2) with calcium (Ca). By adding 1‐dodecanethiol, the morphology of the magnesium particles is controlled and magnesium nanofibers with a length of 0.4–4 µm and a width of 40 nm are obtained. Besides magnesium nanofibers, isolated irregular shaped calcium particles are also observed as a by‐product of the reaction. The nanofibers readily absorbed hydrogen at 300 °C and hydrogen release occurred at much lower temperatures (360 °C) compared to the equivalent bulk material. More remarkably, these nanofibers remain stable during hydrogen cycling, but they partially react with the remaining calcium to form the ternary hydride phase Ca19Mg8H54—a phase that is usually obtained at high temperatures &gt;500 °C and hydrogen pressure 2500 MPa. Hydrogen absorption within these magnesium nanofibers shows a slightly lower enthalpy as compared to bulk magnesium. However, the hydrogen desorption properties are influenced by the presence of calcium and its reaction with magnesium.

Degradation of fluoroelastomers in rapeseed biodiesel at different oxygen concentrations

The degradation of fluoroelastomers (FKM) based on different monomers, additives and curing systems was studied after exposure to rapeseed biodiesel at 100 °C and different oxygen partial pressures. The sorption of fuel in the carbon black-filled FKM terpolymer was promoted by the fuel-driven cavitation in the rubber. The bisphenol-cured rubbers swelled more in biodiesel than the peroxide-cured FKM, presumably due to the chain cleavage caused by the attack of biodiesel on the double bonds formed during the bisphenol curing. With any of the selected types of monomer, the FKM rubbers absorbed biodiesel faster and to a greater extent with increasing oxygen partial pressure due to the increase in concentration of the oxidation products of biodiesel. Water-assisted complexation of biodiesel on magnesium oxide and calcium hydroxide particles led to dehydrofluorination of FKM, resulting in an extensive fuel uptake and a decrease in the strain-at-break and the Young's modulus of the rubbers. An increase in the CH2-concentration determined by infrared spectroscopy, and the appearance of biodiesel flakes in scanning electron micrographs of the extracted rubbers, were explained as being due to the presence of insoluble biodiesel grafted onto FKM on the unsaturated sites resulting from dehydrofluorination. The extensibility of the GFLT-type FKM was the least affected on exposure to biodiesel because this rubber contained less unsaturation and metal oxide/hydroxide particles.

Electrodeposited Magnesium Nanoparticles Linking Particle Size to Activation Energy

The kinetics of hydrogen absorption/desorption can be improved by decreasing particle size down to a few nanometres. However, the associated evolution of activation energy remains unclear. In an attempt to clarify such an evolution with respect to particle size, we electrochemically deposited Mg nanoparticles on a catalytic nickel and noncatalytic titanium substrate. At a short deposition time of 1 h, magnesium particles with a size of 68 ± 11 nm could be formed on the nickel substrate, whereas longer deposition times led to much larger particles of 421 ± 70 nm. Evaluation of the hydrogen desorption properties of the deposited magnesium nanoparticles confirmed the effectiveness of the nickel substrate in facilitating the recombination of hydrogen, but also a significant decrease in activation energy from 56.1 to 37.8 kJ·mol−1 H2 as particle size decreased from 421 ± 70 to 68 ± 11 nm. Hence, the activation energy was found to be intrinsically linked to magnesium particle size. Such a reduction in activation energy was associated with the decrease of path lengths for hydrogen diffusion at the desorbing MgH2/Mg interface. Further reduction in particle size to a few nanometres to remove any barrier for hydrogen diffusion would then leave the single nucleation and growth of the magnesium phase as the only remaining rate-limiting step, assuming that the magnesium surface can effectively catalyse the dissociation/recombination of hydrogen.