Papers by Keyword: Magnesium

Abstract: Magnesium and strontium both play important roles in the growth of bone and so are desirable ions for substitution into hydroxyapatite (HA) intended for use as bioinstructive bone substitutes. A range of compositions were prepared by a solid state method based on the nominal composition of HA (Ca₁₀(PO₄)₆(OH)₂), with various levels of strontium and/or magnesium substitution: strontium-substituted HA (Ca₈Sr₂(PO₄)₆(OH)₂), magnesium-substituted HA (Ca_9.8Mg_0.2(PO₄)₆(OH)₂ and Ca₉Mg (PO₄)₆(OH)₂), and strontium and magnesium co-substituted HA (Ca_7.8Sr₂Mg_0.2(PO₄)₆(OH)₂ and Ca₇Sr₂Mg (PO₄)₆(OH)₂). Materials were characterised by powder X-ray diffraction, Fourier-transform infrared spectroscopy and Raman spectroscopy. These analyses indicated that the co-substituted materials were composed of mixtures of strontium-substituted hydroxyapatite and magnesium and strontium co-substituted β-tricalcium phosphate. In the magnesium-substituted materials, increased magnesium content was related to increased proportion of β-tricalcium phosphate phase, both with and without strontium co-substitution. The unsubstituted and strontium mono-substituted materials, however, were pure apatite phase, suggesting that magnesium was the destabilising factor in the phase compositions of the magnesium mono-substituted and magnesium and strontium co-substituted materials.

Abstract: In this study, the magnesium alloys AZ31, ZK10, and ZEK100 are investigated through microstructure, texture, and tensile test. The sheets were hot rolled, and different results were found for different chemical compositions. The contained elements affected the grain size, shear band, twins, and intensity of the basal texture of the magnesium alloy. Thus, if a magnesium sheet had finer grains and a weak (00.1) texture because of its chemical composition, it had the most favorable formability.

Abstract: Cavity defects of low-pressure lost foam casting (LP-LFC) for magnesium alloy were investigated by using ladder samples and claviform samples.The physical feature of typical cavity defects of LP-LFC for magnesium castings had been tested by optical microscopy and scanning electron microscopy. And the chemical constitution of cavity surface was also tseted by energy spectrometer. The result indicated that the cluster cavity defects were formed with the application of higher vacuum at the metal-mold interface, which caused the liquid-EPS residue in the castings. Some irregular shape cavity defects were caused by slag entrapment or coating slough. These cavity defects could be avoided through reducing pouring temperature, filling velocity and vacuum level, improving the permeability of coating.

Abstract: The RheoMetal process, previously also called the Rapid Slurry Forming process (“Rapid S”) or RSF process, is a novel method to produce high quality, cost effective, semi-solid magnesium slurries for component casting. The RheoMetal process uses an Enthalpy Exchange Material (EEM) as internal cooling to produce the slurry. Typical critical process parameters in the RheoMetal process are alloy content, stirring speed, superheat and EEM to melt ratio. In this study the effects of EEM to melt ratio and superheat on the slurry characteristics was examined for binary Mg-Al alloys in the range 5.8 - 11.2 wt % Al. Samples were quenched after slurry preparation and the microstructure was studied with respect to solid fraction and -Al grain diameter. The solid fraction increased with an increasing EEM to melt ratio for all three Al-contents investigated. Further, it was found that the solid fraction as well as the grain diameter decreased with increasing aluminium content (at constant EEM to weight ratio).

Abstract: The history of Thixomolding®, its technology and commercialization are reviewed along with recent evolution of new technology afforded by its metallurgical structure. Since Thixomolding was introduced in the early 1990’s, it has developed to more than 400 Thixomolding machines in the United States, Canada, Japan, China, Taiwan, Hong Kong, Malaysia, Korea, Germany, Belgium and France. Applications have been established in the electronics/communication, automobile, military, hand tool, medical and sporting goods markets. Thixomoldings principal advantages are in net-shaping, consolidation of parts, safety, environmental friendliness, mechanical properties and microstructure. The virtuous isotropic and fine-grained Thixomolded® microstructure has opened the door to derivative thermal mechanical processing for generating nanostructured Mg products of high strength/density along with improved ductility, fatigue strength, corrosion resistance and formability. This thermomechanical processing (TTMP) has been applied recently to the Thixomolded precursor to further refine the grain size and eutectic phases to nanometer sizes - providing yield strength above 300 MPa, fatigue strength of 150 MPa along with elongation of >10%. Alloys so processed include AZ50L, AZ60L, AM60, AZ61L, AZ70L-TH, AZ80, AZ91D, AXJ810-TH and Thixoblended® alloys of higher Zn content. Microstructure is related to processing and properties, as predestined by the Thixomolded microstructure. Fiber Metal Laminate composites based on this nanoMAG TTMP Mg product have demonstrated yield strength up to 900 MPa, with modulus of elasticity of 90 GPa.

Abstract: Mg-5wt.%Al alloy based composites reinforced with 0wt.%, 1wt.%, 2wt.% silicon carbon (SiC) particles (average particle size about 3.5µm) were prepared under flux protection conditions. The microstructures, textures, components and hardness of the above composites were investigated through optical microscope, scanning electron microscope, X-ray diffraction and sclerometer. The results indicate that SiC particles are distributed along grain boundaries, limiting grain growth and conducing to the refinement of the matrix. The hardness of composites increases with the increase of SiC particles addition amount. The presences of Mg2Si and the binary carbide Al4C3 were observed in the composites. The Al4C3 phase has a crystal structure closer to that of Mg than to that of SiC, which can be act as a potential nucleant for Mg-5wt.%Al alloy.

Abstract: Environmental performances of fluorite used as catalyzer for chemical reaction between MgO and Si were investigated by performing pilot scale experiments of Mg production. F amounts of 0.012-0.116 kg were added in the charged briquettes and Mg slag generated from the chemical reaction in most of the tests weighted 4.26-4.96 kg with F contents ranging 0.21-2.52%. Based on high recoveries of F, 83-100%, in the slag after the reaction, it is estimated that there are little or no F compounds leaving the retorts during the pilot tests. However, high amount of F, 72.9 mg/kg, was leached out from an Mg slag sample obtained from an Mg plant, making it necessary to decrease amount of fluorite used as catalyzer for the reaction or to improve operation conditions, thus, enhancing rate for chemical reaction between MgO and Si in Pidgeon process.

Abstract: Abstract: The present experiment was conducted to a steel, Fe-20%Cr-10%Mn-6%Ni, in a 25kg intermediate frequency vacuum induction furnace at 1873K under protection of 0.08 MPa nitrogen gas. The inclusions in the steel were studied both before and after Al, Mg was added. The results revealed that the inclusions were removed more efficiently after treated by Al, Mg and the cleanness of metal was promoted to a higher level. The Al treated inclusions had more Mn, Cr and Fe at the core and a significant amount of Al around periphery according to line scanning analysis. After Mg was introduced, it concentrated at the surface of inclusions. The remaining Al content was as low as 0.01% which was lower than expected. The reaction between the Al and MgO crucible should be responsible for it and trace amount of Mg was found in the Al treated inclusions.

Abstract: The element phosphorus plays key role in plants metabolism. It is widely used as fertilizer. This element is usually found in insoluble forms (Ca₁₀(PO₄)₆F₂). The solubilization in phosphoric acid (H₃PO₄) is a process widely used in fertilizer industry. The impurities in the phosphate exert significant influence on recovery and productivity phosphoric process, besides affecting the quality of products. The objective of this work is to analyze the influence of some of these main impurities (iron, aluminum and magnesium) in the production process of phosphoric acid. A referential methodology (induced crystallization) of phosphoric acid production was developed. Samples of igneous phosphate concentrate contaminated with iron, aluminum and magnesium were prepared for the experiments. The reaction control parameters were similar to an industrial operation of phosphoric acid dihydrate process. Reductions in conversions, increases in viscosity and density of phosphoric acid were observed with increasing presence of these impurities. In the filtration step was found increase in resistivity of the cake with the increase of the impurities content. The iron mineral element promoted an increase in induction time of crystals nucleation.

Abstract: In this study, a constant current density was used in magnesium microarc oxidation treatment. The microstructure, chemical composition, phase composition and corrosion resistance of the micro-arc oxidation film were characterized by XRD and EDS. The experimental results showed that the test pieces of magnesium would formed an silver-gray uniform densification oxide film on the surface, the film-formed materials was amorphous by XRD analysis, and on this basis we preliminary discused the film-forming mechanism.