Magnesium Titanium Research Articles

Characteristics of friction welded AZ31B magnesium–commercial pure titanium dissimilar joints

Abstract It is essential to understand the weld interface characteristics and mechanical properties of dissimilar joints to improve its quality. This study is aimed at exploring the properties of friction welded magnesium–titanium dissimilar joint using tensile testing coupled with digital image correlation, optical and scanning electron microscopy, x-ray diffraction and microhardness measurements. Microstructurally different regions such as contact zone, dynamic recrystallized zone, thermo-mechanically affected zone, and partially deformed zone in the magnesium side were observed. No discernible regions were observed in the titanium side, as it had not undergone any significant plastic deformation. Phase analysis indicated that the aluminium from the magnesium side diffused toward the weld interface and formed a thin continuous intermetallic layer by reacting with the titanium. Microhardness mapping showed a steep hardness gradient from the titanium to magnesium side. Critical analysis is done on the tensile characteristics of the specimen and the response of the local regions to the deformation process is mapped.

Cytotoxic effect of galvanically coupled magnesium–titanium particles

Recent work has shown that reduction reactions at metallic biomaterial surfaces can induce significant killing of cells in proximity to the surface. To exploit this phenomenon for therapeutic purposes, for example, for cancer tumor killing or antibacterial effects (amongst other applications), magnesium metal particles, galvanically coupled to titanium by sputtering, have been evaluated for their cell-killing capability (i.e. cytotoxicity). Magnesium (Mg) particles large enough to prevent particle phagocytosis were investigated, so that only electrochemical reactions, and not particle toxicity per se, caused cytotoxic effects. Titanium (Ti) coated magnesium particles, as well as magnesium-only particles were introduced into MC3T3-E1 mouse pre-osteoblast cell cultures over a range of particle concentrations, and cells were observed to die in a dosage-dependent manner. Ti-coated magnesium particles killed more cells at lower particle concentration than magnesium alone (P<0.05), although the pH measured for magnesium and magnesium–titanium had no significant difference at similar particle concentrations. Complete cell killing occurred at 750μg/ml and 1500μg/ml for Mg–Ti and Mg, respectively. Thus, this work demonstrates that galvanically coupled Mg–Ti particles have a significant cell killing capability greater than Mg alone. In addition, when the pH associated with complete killing with particles was created using NaOH only (no particles), then the percentage of cells killed was significantly less (P<0.05). Together, these findings show that pH is not the sole factor associated with cell killing and that the electrochemical reactions, including the reduction reactions, play an important role. Reduction reactions on galvanically coupled Mg–Ti and Mg particles may generate reactive oxygen intermediates that are able to kill cells in close proximity to the particles and this approach may lead to potential therapies for infection and cancer. Statement of SignificanceThis paper demonstrates that during active corrosion of both Mg and Mg–Ti particles cells cultured with the particles are killed in a dose-dependent particle concentration fashion. Additionally, galvanically-coupled magnesium–titanium microparticles kill cells more effectively than magnesium particles alone. The killing effect was shown to not be due to pH shifts since no differences were seen for different particle types and pH adjusted medium without particles did not exhibit the same level of killing. The significance of this work is the recognition of this killing effect with Mg particles and the potential therapeutic applications in infection control and cancer treatment that this process may provide.

Influence of the synthesis conditions on the structure and composition of the titanium–magnesium nanocatalyst and on its activity in isoprene polymerization

Synthesis of titanium–magnesium nanocatalyst in a high-pressure reactor under the conditions modeling the industrial conditions was studied. A laboratory scale plant including the units for the product synthesis, washing, and filtration was developed. The effect of elevated pressure (10–90 atm) on the process course, on the properties of the catalyst formed, and on the isoprene polymerization was studied for the first time. An increase in pressure leads to an increase in titanium incorporation into the catalyst from 1.52 to 2–2.3 wt % and simultaneously to an increase in the trivalent titanium content to 81 wt %. The titanium–magnesium nanocatalyst with such properties exhibits enhanced performance in isoprene polymerization without deteriorating the polymer microstructure. The development of the catalyst synthesis procedure on the laboratory scale plant will allow pilot-scale modeling of this process in the future.

Formation of metastable phases in magnesium–titanium system by high-pressure torsion and their hydrogen storage performance

No binary phases exist in the Mg–Ti binary equilibrium phase diagram and the two elements are totally immiscible even in liquid form. This study shows that four metastable phases (two with the bcc and fcc structures and two with the hcp structures) are formed in the Mg–Ti system by severe plastic deformation (SPD) through the process of high-pressure torsion (HPT). Investigation of hydrogenation properties reveals that these metastable phases are decomposed to pure Mg and Ti during heating before they can absorb the hydrogen in the form of ternary Mg–Ti hydrides. First-principles calculations show that the hydrogenation reaction should occur thermodynamically, and ternary Mg–Ti hydrides with the cubic structure should form at low temperature. However, the slow kinetics for this reaction appears to be the limiting step. Calculations show that the binding energy of hydrogen increases and the thermodynamic stability of hydrides undesirably increases by addition of Ti to Mg.

Kinetic evidences for reversible transformations of active centers in ethylene polymerization by titanium–magnesium catalyst: Effect of the polymerization temperature

The kinetics of ethylene polymerization at varied polymerization temperature over two modifications of titanium–magnesium catalysts that differ in their compositions and the molecular weight of the resulting polymers were studied by polymerization quenching by radioactive carbon monoxide. An increase in polymerization temperature in the range of 40–80 °C was found to significantly increase the number of active centers (CP), which contributes to the polymerization rate more significantly than an increase in the propagation rate constant (kP) does. The rise in the number of active centers with increasing polymerization temperature is shown to result in effective activation energy (Eeff) determined from the temperature dependence of polymerization rate being significantly higher than the activation energy of propagation reaction (EP) determined from the temperature dependence of the kP value. It was shown too the changes of the number of active centers and polymerization rate at variation of temperature in the single experiment have the reversible nature. The data on the number of active centers and the propagation rate constants at ethylene polymerization in the presence of hydrogen as a chain transfer agent are obtained. Introduction of hydrogen reduces the number of active centers at elevated polymerization temperatures (60–80 °C) and has virtually no effect on the CP value at lower temperatures; it also reduces the kP value at 40–80 °C. The findings on the effect of polymerization temperature on the number of active centers were used to propose a kinetic scheme including the reaction of reversible transformation of the precursors of active centers (alkyl derivatives of titanium) into an inactive state due to adsorption of a co-catalyst (triethylaluminum). The transformation of these complexes into active centers depends on polymerization temperature, presence of hydrogen, concentrations of monomer and organoaluminum activator.

Fabrication of polyamide membrane reached by MgTiO3 nanoparticles for ground water purification

Here, we report the fabrication of mixed matrix reverse osmosis membranes by interfacial polymerization (IP) of nanocomposite on porous polysulfone supports. Nanocomposites elaborated for this study comprise magnesium titanium oxide (MgTiO3) nanoparticles dispersed in polyamide host matrix synthesized by the in situ IP process on porous polysulfone commercial supports. Aqueous m-phenyl diamine and organic trimesoyl chloride nanoparticles mixture solutions were used in the IP process. Nanoparticles of MgTiO3 with a size of about 80nm were used as filler for the fabrication of the nanocomposite membranes with a concentrations varying from 0.0001 to 0.009 wt.%. The samples were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and contact angle setup. Their performances were evaluated based on the water permeability and salt rejection. Results indicated that the nanoparticles are well dispersed in the host matrix of polyamide layer and improved membrane performance under optimal nanoparticle content. By changing the concentration of the filler, hydrophilicity and roughness of the nanocomposite membranes were increased. Notably, the permeate water flux increased from 26 to 44.6 L/m2 h at the nanoparticles concentration of 0.001% with the maintaining of high salt rejection of 98%. These results were obtained with initial NaCl concentration of 2,000 ppm and under pressure of 225 psi. Also better hydrophilicity was obtained; the contact angle was decreased from 73 to 24°.

DFT modeling of the effect of magnesium dichloride on the catalytic activity of post-titanocene complexes in ethylene polymerization

The DFT study of magnesium dichloride effect on the catalytic activity of titanium complexes LTi(Y)Cl (where L is a saligenin-type ligand, and Y is Cl or Me) in olefin polymerization has demonstrated that heterobinuclear titanium–magnesium complex with –O– and –Cl– bridging bonds is the most stable product of the reaction between MgCl2 and LTi(Y)Cl and the most probable catalytic particle for ethylene polymerization.

Fabrication of graded porous titanium–magnesium composite for load-bearing biomedical applications

Abstract A kind of graded porous titanium–magnesium (Ti–Mg) composite, i.e., about 1–1.5 mm thick porous Ti layer is wrapped over the internal dense Ti–Mg composite, has been successfully fabricated by infiltration casting and acid etching. The outer porous Ti layer maintains its initial entangled structure, which can be easily adjusted to the ideal porosity and the porous structure. The thickness of the porous layer can be controlled by etching time. When the outer porous layer accounted for 41.6–42.4% of the total volume of the cylindrical sample, the compressive strength and the Young’s modulus of the as-prepared graded porous composite are 110 MPa and 5 GPa, respectively, being comparable to that of natural bone. The outer porous layer provides good osteoconduction ability, and the internal dense Ti–Mg composite contributes to the monolithic strength and stiffness. Such biomechanical properties suggest its potentials for load-bearing bio-applications.

Basicity of Stereoregulating Electron-Donor Compounds in Ziegler–Natta Catalysts: A Study by Infrared Spectroscopy and Chemical Exchange Reactions

The Lewis basicity of typical electron donor compounds used to modify heterogeneous Ziegler–Natta catalysts, such as diakyl ethers, silyl ethers, esters, and ketones, was characterized by determining their effects on the IR frequency of surface silanol groups of silica gel, which correlate with the heat of this specific interaction and with their “donicity”, i.e., with the heat of formation of their complexes with SbCl5. In this manner, ethers and silyl ethers are found to be more basic than ketones and esters. These differences in basicity are likely to affect the stereoregulating properties of such electron donor compounds in Ziegler–Natta polymerization catalysis. By consecutively adsorbing electron donors with various strengths on a MgCl2 support, it was shown that weakly basic donors, such as ethyl benzoate or dibutyl phthalate, are partially displaced by donors with higher basicity, such as valerophenone and propyltrimethoxysilane. This indicates that the displacement of inner donors of the ester type from a titanium–magnesium catalyst upon addition of typical external donors, such as silyl ethers, is controlled by the relative basicities of these donor molecules.

Production of nanocrystalline TiB2 powder through self-propagating high temperature synthesis (SHS) of TiO2–H3BO3–Mg mixture

Nanocrystalline TiB2 powders are produced through self-propagating high temperature synthesis (SHS) technique by igniting the stoichiometric mixture of titanium oxide (TiO2), boric acid (H3BO3) and magnesium (Mg) powder. Different percentages of NaCl are added to the mixture as SHS diluent in order to control the particle size of the TiB2. The synthesised and purified powder is characterised by X-ray diffraction and electron microscopes respectively. The SEM images show the presence of agglomeration of fine spherical particles. The TEM images reveal the formation of nanocrystalline TiB2 particles. The particle size is found to decrease with the addition of NaCl. The TEM images reveal the presence of crystallographic defects in the powder. In order to find out the reaction mechanism of TiO2–H3BO3–Mg system, the synthesis of TiO2–Mg and H3BO3–Mg mixtures is performed in inert atmosphere and phase analysis of TiO2–Mg and H3BO3–Mg mixtures reveal the reaction mechanism.

Microstructure and Mechanical Properties of Laminated Mg-Based Composites

A new design method to achieve the laminated Ti-Al-Mg composites by stack processing with magnesium alloy plate, aluminum powder, titanium mesh and vacuum hot-pressed sintered. Sintering laminated material in different sintering temperature. The microstructure, ingredient, structure of laminated material and the interface of Ti-Al, Mg-Al were analyzed by SEM and EDS. Test results show that the optimum sintering temperature is 550 oC, and after sintered the aluminum powder and magnesium alloy plate hang together relatively tight by slight interface reaction, and aluminum powder can able to better coating the titanium mesh within the matrix. Mechanical property test found that titanium mesh is role-playing the reinforcement in laminated material, and makes the mechanical properties of laminated material improving significantly.

Formation of Isolated Titanium(III) Ions as Active Sites of Supported Titanium–Magnesium Catalysts for Polymerization of Olefins

Electron spin resonance (ESR) studies reveal a high yield of isolated Ti3+ compounds (30–70% of the total titanium content) that form in superactive supported titanium–magnesium catalysts (TMCs) of composition TiCl4/MgCl2 with a low titanium content (≤0.1 wt%) after their interaction with different aluminum trialkyls (AlR3). These catalysts strongly differ from conventional TMCs with titanium contents of 1–3 wt%, which produce a set of isolated or associated Ti(II) and Ti(III) species after the interaction with the AlR3. A correlation is found between the content of the isolated Ti(III) ions and the activity in ethylene polymerization. According to temperature rising elution fractionation (TREF) data, the catalysts with a low titanium content (isolated Ti(III) ions) mainly produce polypropylene with a very high atactic‐fraction content. Organic products formed on the interaction of AlEt3 and AlMe3 with TMC are identified. The data obtained allow a scheme of Ti3+ and Ti2+ compounds formed in these catalysts to be proposed. image

Ternary compounds in the magnesium–titanium hydrogen storage system

Mg–Ti–H samples were mechano-chemically synthesized by ball milling in argon atmosphere or under elevated hydrogen pressure. The detailed reaction mechanism during hydrogen release and uptake during continuous cycling was investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) experiments. The thermal behaviour of the samples and hydrogen desorption properties were examined by simultaneous thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and mass spectrometry (MS) measurements. A ternary Ti–Mg–H compound with a fcc lattice form during mechano-chemical sample preparation in hydrogen atmosphere using metal powders, but not using metal hydrides as reactants. The amount of β-MgH2 increases during the first hydrogen absorption cycle at 300 °C at the expense of the high-pressure polymorph, γ-MgH2 and the amount of β-MgH2 remain constant during the following hydrogenations. This study reveals that the ternary compound tends to absorb increasing amounts of magnesium in the dehydrogenated state during cycling. A strong coupling between the amounts of magnesium in the ternary Ti–Mg–H phase and the formation of magnesium and magnesium hydride during hydrogen release and uptake at 300 °C is observed. The composition and the amount of the Ti–Mg–H phase appear to be similar in the hydrogenated state. Fast absorption–desorption kinetics at 300 °C and lower onset temperatures for hydrogen release is observed for all investigated samples (lowest onset temperature of desorption Ton = 217 °C).

A comparative study of ethylene and propylene polymerization over titanium–magnesium catalysts of different composition

ABSTRACTNew data on the molecular weight characteristics of polypropylene (PP) and polyethylene (PE) were obtained from the polymerization over supported titanium–magnesium catalysts differing in their compositions (presence and absence of internal and external donors). Internal and external donors were found to affect the molecular weight of polymers in a different manner for ethylene and propylene polymerization. The introduction of the internal donor increases the molecular weight of PP and does not affect the molecular weight of PE. The effect of external donor introduced to catalytic system on the polymer molecular weight depends on catalyst composition: for a catalyst without internal donor, the introduction of the external donor increases the molecular weight of PP and does not affect that of PE. In the case of catalyst with the internal donor, the introduction of the external donor increases the molecular weight of PP and substantially decreases that of PE. The data on polymerization degree of the polymers produced under conditions when chain transfer with hydrogen was the dominant reaction were used to calculate the values for ethylene polymerization over the catalysts of different composition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40658.

Effect of Syntesis and Frequency on Electrical Properties on Dielectric Ceramics MgCO&lt;sub&gt;3&lt;/sub&gt;-TiO&lt;sub&gt;2&lt;/sub&gt;

Magnesium titanate based dielectric materials are used for producing type-I capacitors. A common way of obtaining this material is a solid-state reaction. The process of sintering can be enhanced if mechanical activation preceedes. In this work starting powders of magnesium carbonate (MgCO3) and titanium dioxide (TiO2) with a rutile crystal modification were weighed to attain a 1:1 molar MgCO3:TiO2. Mechanical activation of the starting mixture was performed by high energy ball milling using ZrO balls and vessels with ball to powder mass ratio 40:1. The observed grinding times were 15, 30, 60 and 120 minutes. The isothermal sintering of compacted powders was conducted at 1100°C during 30, 60 and 180 minutes. For specimens synthesized in such a manner, microwave dielectric properties were measured, quality factor Q and the dielectric constant (εr) in function of frequency. The measurements of electrical resistivity, capacitance and loss tangent of samples were measured in the frequency range from 500 Hz to 5 MHz frequencies with a HIOKI 3532-50 LCR HiTESTER device at a constant voltage mode (amplitude 0.5 V of sinusoidal signal applied to the specimens).

Formation of isolated titanium(III) ions in superactive titanium–magnesium catalysts with a low titanium content as active sites in ethylene polymerization

Superactive supported titanium–magnesium catalysts (TMCs) with a low titanium content (≤0.1wt.%), in distinction to conventional TMCs (≥1wt.%), were shown to interact with AlR3 of different compositions to produce compounds with a high (30–70%) concentration of isolated (ESR visible) Ti3+ ions.For the first time a correlation between the content of isolated Ti3+ species in these catalysts and activity in ethylene polymerization was found.

Electrochemical Characteristics of the Magnesium Titanium Composite Oxide-Coated Spinel-Type Lithium Manganese Oxide

In this experiment, the spinel-type lithium manganese oxide (LiMn2O4) prepared via solid-phase sintering method was coated with magnesium titanium composite oxide (MgTiOx) in the presence of polyvinyl pyrrolidone (PVP) under the ultrasonic wave. The crystal structures, surface morphologies and electrochemical properties of the sample prepared were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical analysis. The X-ray diffractions indicated that the LiMn2O4 coated with MgTiOx were similar to that of the pure LiMn2O4, and they both showed sharp and high peaks. The particles of the samples prepared with PVP did not aggregate obviously, and the samples were coated completely and homogeneously. At charge-discharge rates of 0.2C, the first discharge capacity can reach more than 120 mAh / g. Compared with pure LiMn2O4, the capacity attenuation of MgTiOx-coated LiMn2O4 reduced after fifty cycles, and showed good electrochemical performance.

Influence of humidity on moving away of TiCl2 from salt fusion at the electrolysis of MgCl2

The results of the study of the effect of titanium chloride during the electrolysis of molten magnesium chloride after reduction of titanium chloride are given. It was found that the humidity of molten chlorides has a significant effect on the removal of titanium from the melt. The results of processing the results of experiments allowed the building of regression equation. It is shown that moisture in the salt has a significant effect on cleaning the electrolyte from titanium impurities. Analysis of the results of experiments of the content of magnesium oxide showed that it does not exceed 0.05% by weight that is an indirect proof of reactions between magnesium oxide and titanium compounds. To effectively remove the titanium compounds from the molten salt it is proposed to load the moistened salt in the head unit of production line or in a separate working electrolyzer during the filling of the next portion of magnesium chloride.

A study of the formation process of titanium–magnesium catalyst for propylene polymerization

The catalyst formation by reacting magnesium diethoxide with titanium tetrachloride in the presence of stereoregulating electron donor – di-n-butylphthalate (DBP) – is studied by sampling the intermediate products during catalyst synthesis. Chemical and phase composition, porous structure, activity and stereospecificity of these products are investigated. It is show that before DBP adding the X-ray amorphous product consisting of MgCl2 and TiCl3(OEt) is formed. This product has micro-mesoporous structure, very high surface area, but low activity and low stereospecificity. DBP has a significant effect on both the chemical composition of the catalyst due to removing inactive TiCl3(OEt), entering DBP and TiCl4 in solid product and formation of MgCl2 crystallites with mesoporous structure. At the same time the significant increase of the activity and stereospecificity is observed. Following TiCl4/chlorobenzene treatment of solid product completes these processes, provides some increasing the surface area at similar mesoporous structure and additionally increases activity and stereospecificity.

Synthesis of ultrafine magnesium oxide and titanium oxide powders

The formation of magnesium and titanium hydroxides (differing in the rate of primary particle formation) and conversion of the hydroxides to ultrafine oxide powders of controlled size have been studied using scanning electron microscopy, X-ray diffraction, differential thermal analysis, and analysis of the particle size distributions of solid materials from scattered laser light intensity. The particle size of the synthesis products has been shown to be influenced by the initial concentration and nature of precursors and precipitants, ultrasonic processing, additions of low-molecular-weight organic compounds, and dehydration temperature and time.