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The amounts of large-tonnage mineral waste that are generated raise serious misgivings at environmental protection agencies. Most mineral waste is a valuable secondary raw material, but the lack of integrated technologies for their processing substantially slows down their processing. An assessment was made of the possibility of joint processing of quartz-leucoxene concentrate (waste from oil extraction) and brucite-containing waste from the production of refractories. Joint pyrometallurgical processing of two wastes made it possible to obtain magnesium titanate, a valuable product for different industries. In hydrometallurgical processing of magnesium titanate, a complex magnesium-titanium containing coagulant was obtained, which showed high efficiency in the process of treating high-pH wastewater (concrete mixing unit). In addition to increasing the purification efficiency (reducing the residual concentrations of pollutants), the use of a complex reagent made it possible to reduce reagent costs and intensify the sedimentation and filtration of coagulation sludge (simplification of the instrumentation). [ABSTRACT FROM AUTHOR]

• Concentrated solar energy offers a great potential in high temperature applications. • The synthesis of ceramic materials is energy intensive, thus contributing to climate change. • One of the methods to synthesize titanates is the solid-reaction route, which can be conducted with the utilization of solar energy. • Magnesium and calcium titanates were synthesize using concentrated solar energy. Solar energy is an adequate technology for different processes in metallurgy, materials processing, recycling, or ceramic-refractory materials, because of the high temperatures attained which are reached when the solar radiation is concentrated. This growing interest has also emerged from the obtaining of such temperatures without releasing pollutants such as carbon dioxide, SO x , NO x , or dioxins. Other benefits associated with concentrated solar energy are that this energy source is virtually free and the possibility of operating in places isolated from the electrical grid. Therefore, this research proposes the integration of concentrated solar energy in the production of calcium and magnesium titanates, which are materials with increasing demand in the field of electric components. Experimental work was carried out in the Odeillo solar furnace located in Font-Romeu-Odeillo-Via (France) using a 1.5-meter parabolic concentrator and mixtures of CaO and TiO 2 and MgO and TiO 2 in 1:1 molar ratio. Mixtures were subjected to values of incident radiation exceeding 900 W/m2 without using any special atmosphere and in very short times, which did not surpass 10 min. X-ray diffraction technique was employed to confirm the formation of the CaTiO 3 and MgTiO 3 perovskites. Therefore, concentrated solar energy might be a novel, fast, and environmentally sustainable manner of producing calcium and magnesium titanates. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, a mixture of magnesium oxide and titanium dioxide was mechanically activated in order to investigate the possibility of mechanochemical synthesis of magnesium titanate. Mechanical activation was performed for 1000 min in a high-energy vibro mill (type MH954/3, KHD Humboldt Wedag AG, Germany). The mill is equipped with housing having a horizontally placed shutter. The cylindrical stainless steel working vessel, with inner dimensions of 40 mm in height and 170 mm in diameter, has working elements consisting of two free concentric stainless steel rings with a total weight of 3 kg. The engine power is 0.8 kW. Respecting the optimal amount of powder to be activated of 50-150 g and the stoichiometric ratio of the reactants in the equation presenting the chemical reaction of magnesium titanate synthesis, the starting amounts were 20.2 g (0.5 mol) of MgO and 39.9 g (0.5 mol) TiO2. During the experiments, X-ray diffraction analysis of the samples taken from the reaction system after 60, 180, 330, and 1000 min of mechanical activation was performed. Atomic absorption spectrophotometry was used for chemical composition analysis of samples taken at different activation times. Based on the X-ray diffraction analysis results, it can be concluded that the greatest changes in the system took place at the very beginning of the mechanical activation due to the disturbance of the crystal structure of the initial components. X-ray diffraction analysis of the sample after 1000 min of activation showed complete amorphization of the mixture, but diffraction maxima characteristic for magnesium titanate were not identified. Therefore, the mechanical activation experiments were stopped. Evidently, the energy input was not sufficient to overcome the energy barrier to form a new chemical compound - magnesium titanate. The failure to synthesize magnesium titanate is explained by the low negative Gibbs energy value of -25.8 kJ/mol (despite the theoretical possibility that the reaction will happen), as well as by the amount of mechanical energy entered into the system during activation which was insufficient to obtain the reaction product. Although the synthesis of MgTiO3 was not achieved, significant results were obtained which identify models for further investigations of the possibility of mechanochemical reactions of alkaline earth metals and titanium dioxide.

A series of NIR-reflective brownish orange pigments comprising various amounts of Fe2O3 have been synthesized by a conventional solid-state reaction at 1100 °C. Magnesium titanate base pigment was synthesized from MgO and leucoxene mineral which was employed as TiO2 source. The resultant pigment had brownish gray appearance (L*a*b* = 68.67, 7.83, 18.68, respectively) and NIR reflectance of 81.0%. Incorporating the magnesium titanate pigment with various amounts of Fe2O3 (molar ratio (x) = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) resulted in a change of color hue to brownish orange, and a change of NIR reflectance from 81.0 to 41.1% upon the increase of Fe2O3 content. Optical bang-gap energies derived from diffused reflectance spectra reduced from 2.75 eV for the magnesium titanate to 2.25, 2.20, 2.10, 1.90, 1.70 and 1.60 eV for pigments incorporated with 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0 mole Fe2O3, respectively. At the optimum synthesis condition (x = 0.3), the pigment exhibited light brownish orange color hue (L*a*b* = 52.02, 23.94, 39.37) and NIR reflectance of 80.1%. An accelerated QUV weathering test according to the ASTM G154-16 standard revealed color fading (ΔE*) of only 0.95 indicating excellent weathering stability. [ABSTRACT FROM AUTHOR]

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In this study, magnesium titanate was prepared through the high-temperature reaction of ilmenite and MgO in a reducing atmosphere, and its formation process and mechanism under different conditions were investigated. The results showed that a reducing atmosphere is necessary to prepare magnesium titanate. Although Mg could replace Fe and form magnesium titanate without reductant, the generated magnesium titanate contained large amounts of iron. While a reducing atmosphere promoted the formation of magnesium titanate and accelerated the reaction rate, this is because iron oxide in the reaction system is reduced to metal Fe under a reducing atmosphere. The effect of iron reduction improved, the content of iron in the magnesium titanate decreased with increasing temperature, and pure particles of magnesium titanate were generated at 1450°C. Magnesium titanate was transformed along MgTi2O5→MgTiO3→Mg2TiO4 path with increasing MgO dosage. The magnesium titanate product, contains above 90% Mg2TiO4, was obtained by grinding and magnetic separation as non-magnetic product. [ABSTRACT FROM AUTHOR]

Magnesium titanate was prepared directly through external coal reduction of seashore titanomagnetite concentrate and magnesium oxide (MgO). The effects of roasting temperature and the type and dosage of reductants on the purity of generated magnesium titanate particles were systematically investigated. Scanning electron microscopy and energy-dispersive spectroscopy analyses were performed to characterize the magnesium titanate particles and observe their purity under different conditions. Results showed that the roasting temperature remarkably influenced the purity of magnesium titanate. At 1200, 1300, and 1400°C, some magnesium ferrite and magnesium aluminate spinel were dissolved in magnesium titanate. However, as the roasting temperature increased to 1500°C, relatively pure magnesium titanate particles were generated because no magnesium ferrite was dissolved in them. The type and dosage of the reductants also remarkably affected the purity of magnesium titanate. The amount of fine metallic iron disseminated in the magnesium titanate particles obviously decreased when lignite was used as a reductant at a dosage of 70wt%. Thus, high-purity magnesium titanate particles formed. At a roasting temperature of 1500°C and with 70wt% lignite, the magnesium titanate product with a yield of 30.63% and an iron content of 3.01wt% was obtained through magnetic separation. [ABSTRACT FROM AUTHOR]

In this work, the effect of MgTiO 3 on silver diffusion in alumina/borosilicate low temperature co-fired ceramics was investigated. The added MgTiO 3 reacts with the glass to produce a new crystalline phase, which together with MgTiO 3 , acts as a barrier to block the diffusion of silver. The diffusion coefficient of the sample sintered at 900 °C for 30 min was reduced from 6.07 × 10−13 cm2/s to 3.50 × 10−13 cm2/s, and the diffusion activation energy was increased from 89.4 kJ/mol to 117.2 kJ/mol. In addition, MgTiO 3 promoted the compaction of sintering. The dielectric properties of the samples sintered at 900 °C for 30 min with 25% MgTiO 3 added were determined to be ε r = 7.8 and tanδ = 0.0005 (1 MHz), which are similar to the properties obtained for a sample with only alumina added (ε r = 6.9, tanδ = 0.0005 at 1 MHz). [ABSTRACT FROM AUTHOR]

Effect of temperature and Mg:Ti ratio on phase composition and microstructure of reduced pellets was investigated to verify the feasibility of preparation of magnesium titanate by adding MgO in carbonthermic reduction of the vanadium titanomagnetite concentrates (VTC). Thermodynamic analysis results showed that magnesium titanate is more easily generated than FeTi2O5 or TiO2 by the reaction of FeTiO3 and MgO under the reductive atmosphere, which was confirmed by the discovery of magnesium titanate at roast experiment. It was found that the optimum conditions for reduction of VTC pellets were temperature of 1250 ºC and Mg:Ti ratio of 2, and the main phases of reduction product were metallic Fe and magnesium titanate (Mg2TiO4). However, trace iron impurities in Mg2TiO4 particles were found by energy-dispersive spectroscopy (EDS), so further purification is required. [ABSTRACT FROM AUTHOR]

Post-sintering of magnesium titanate ceramics by hot isostatic pressing (HIP) in an oxygen-free atmosphere significantly alters various electrical properties of the product. In particular, the sintered material becomes a semiconductor. The aims of this paper are: to extend our investigations of the electrical properties of this material by expanding the frequency range of measurements, to design interpolation formulas for the frequency dependence of the complex relative permittivity, and to propose HIP-sintered magnesium titanate as a material for thermistors that have a negative-temperature-coefficient resistance (NTCR), as well as for varistors. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR 32005 and Grant no. ON 172057]

High-resistance state (HRS) current has significant effect on the reliability and power consumption of resistive switching memories. Low HRS current is helpful for obtaining ultra-low power and for high ON/OFF ratio nonvolatile memory application. The reduced HRS current of a sol-gel magnesium titanate nickelate-based resistive random access memory by using nickel (II) acetylacetone as substitute for acetylacetone in magnesium titanate (MTO) was presented. Forming-free, high ON/OFF ratio of over 106, excellent current distribution and good retention at 85 °C were achieved. Moreover, the effect of nickel (Ni) on the surface roughness, operation voltage, switching cycles, HRS current, ON/OFF ratio, current distribution, and switching behavior was explored. These results indicate that the incorporation of Ni in sol-gel MTO is an effective way to achieve high-performance memory devices.

Using a polyacrylamide gel method, phase pure and well-dispersed MgTiO 3 nanopowders were prepared at 800 °C for 2 h. It was found that a high mole ratio of monomers to precursors resulted in low formation temperature of MgTiO 3 , due to the highly mixing homogeneity and smaller particle sizes of precursors. Sintering behaviors of MgTiO 3 nanopowders under DC electric field from 500 to 800 V/cm were investigated. Nearly full dense MgTiO 3 ceramics can be prepared in 30 s. An abrupt and simultaneous increase in current density and power dissipation were observed in sintering process, which are characteristics of flash sintering. The power dissipation for the flash sintering was found to be 82 mW/mm 3 . The densities and average grain sizes of samples increase with the increase of the electrical field strength. It was suggested that Joule heating was the main mechanism of flash sintering of MgTiO 3 ceramics. Our work provides a useful route for the fabrication of dense MgTiO 3 ceramics at low temperature in short time. [ABSTRACT FROM AUTHOR]

In this article, the advantages of combined sintering in comparison with the conventional one, of mechanically activated magnesium titanate ceramic were investigated. The stoichiometric mixtures of MgO and TiO2 were mechano-chemically activated for 0, 10, 40, 80 and 160 minutes by ball milling and then isostatically pressed (CIP) to form green bodies. Conventional sintering was realized by heating up to 1400 oC and hold for 30 minutes in air atmosphere. Resulting ceramic samples with closed porosity were post-sintered by pressure assisted technique Hot Isostatic Pressing (HIP) at 1280 oC/3h in argon atmosphere with a pressure of 200 MPa. The best results were observed in the case of samples post-sintered by HIP, when single-phase MgTiO3 samples with relative density of 96% were prepared. [Projekat Ministarstva nauke Republike Srbije, br. OI 172057]

Silicon nitride-based composite ceramics with different contents of magnesium titanate have been fabricated via gas pressure sintering method. The phase compositions, microstructure, mechanical performances and dielectric properties of the composite ceramics were investigated. The density of the Si 3 N 4 -based composite ceramics firstly increased with additive of magnesium titanate powder up to 5 wt% and then gently decreased, and the mechanical properties firstly increased and then declined. Besides, the dielectric constant and dielectric loss increased with the increase of magnesium titanate contents. For the Si 3 N 4 -based composite ceramics with 5 wt% magnesium titanate powders, the flexural strength, elastic modulus, dielectric constant and dielectric loss reached 451 MPa, 274 GPa, 7.65, 0.0056, respectively. These results suggested that the magnesium titanate was beneficial for the improvement of mechanical performances and dielectric constant of Si 3 N 4 -based composite ceramics. [ABSTRACT FROM AUTHOR]

Nanoparticles with different morphology have been obtained by hydrothermal method in the system MgO-SiO-TiO-HO. It has been found that in the investigated temperature-time interval the formation of nanotubes of hydrosilicate with the structure of chrysotile with a small amount of impurity phases predominantly takes place. [ABSTRACT FROM AUTHOR]

The microwave dielectric properties of MgTiO 3 ceramics with isovalent substitutions of ( ( Li 1 / 4 1 + B 3 / 4 5 + ) 4 + , ( Mg 1 / 3 2 + B 2 / 3 5 + ) 4 + , and ( Al 1 / 2 3 + B 1 / 2 5 + ) 4 + (B=Nb 5+ or Ta 5+ )) at the Ti-site were investigated. All isovalent-substituted MgTiO 3 ceramics showed single phases of ilmenite structure with rhombohedral symmetry. Specimens with B=Ta 5+ showed higher quality factors ( Qf ) and lower dielectric constants ( K ) than those with B=Nb 5+ , because of the high degree of average covalency in the ceramics. The Qf values of specimens substituted with (Mg 1/3 B 2/3 ) 4+ at the Ti-site were higher than those of other isovalent-substituted MgTiO 3 ceramics, because of the high Ti-site bond strength of (Mg 1/3 B 2/3 ) 4+ . Because (Li 1/4 B 3/4 ) 4+ displayed the largest dielectric polarizability of the substituting species, MgTiO 3 ceramics substituted (Li 1/4 B 3/4 ) 4+ at the Ti-site showed the largest K value. The substituted specimens showed lower temperature coefficients of the resonant frequencies ( TCF ) than the pure MgTiO 3 ceramics, because of the increased Ti-site octahedral distortion. The relationships between the microstructures and microwave dielectric properties of MgTiO 3 ceramics were also discussed. [ABSTRACT FROM AUTHOR]

Degradation of 2-chloroethyl ethyl sulfide (2-CEES), a stimulant of sulfur mustard, was investigated on the surface of polyacrylonitrile (PAN) nanofibres embedded with magnesium aluminate and magnesium titanate nanoparticles. The magnesium aluminate and magnesium titanate nanoparticles were prepared by the hydrothermal method and characterized by X-ray diffractometry, scanning electron microscopy and nitrogen adsorption BET. These metal oxide nanoparticles were mixed with PAN solution individually and then electrospun to produce nanofibres. Later, they were studied against the degradation of 2-CEES at room temperature (30±2 °C) using gas-chromatography coupled with flame ionization detector. The degradation and reaction kinetics data reveal that the 2-CEES degraded faster with higher amount of embedded metal oxide nanoparticles in PAN nanofibres. Moreover, the degradation yield of 2-CEES was higher in the case of PAN nanofibres embedded with magnesium aluminate nanoparticles relative to PAN nanofibres embedded with magnesium titanate nanoparticles. Fourier-transform infrared (FTIR) studies showed that the PAN nanofibres embedded with magnesium aluminate and magnesium titanate nanoparticles degrade 2-CEES by the formation of covalent/alkoxide bonds between the surface reactive oxide/hydroxyl group of metal oxide nanoparticles and 2-CEES. The result explores the role of modified PAN nanofibres with magnesium aluminate on the effective degradation of 2-CEES and possesses a suitable candidate for protective application. [ABSTRACT FROM AUTHOR]

The morphological manipulation and structural characterisation of TiO-MgO binary system by an aqueous particulate sol-gel route were reported. Different crystal structures including pure MgTiO, mixtures of MgTiO and TiO and mixtures of MgTiO and MgTiO were tailored by controlling Mg:Ti molar ratio and annealing temperatures as the processing parameters. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that all compounds crystallised at the low temperature of 500 °C. Furthermore, it was found that the average crystallite size of the compounds depends upon the Mg:Ti molar ratio as well as the annealing temperature, being in the range 3-5 nm at 500 °C and around 6 nm at 700 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanocrystalline structure with the average grain size of 25-30 nm at 500 °C depending upon the Mg:Ti molar ratio. Moreover, atomic force microscope (AFM) images presented that the thin films had a hill-valley like morphology made up of small grains. [ABSTRACT FROM AUTHOR]

Abstract: Thorough structural characterization of deep laying thin film, including the inference of interdiffusion profiles is frequently a complex problem. The use of RBS/PIXE holistic approaches, already shown to represent a powerful method, sometimes faces difficulties if standard experimental procedures are used. In this work, following a series of 4He Rutherford backscattering and 1H elastic backscattering experiments, carried out to study the influence of SrTiO3 as a possible cladding layer between Pt/TiO2/SiO2/(100)Si substrates and MgTiO3 films, a simple holistic RBS-PIXE is shown to be not enough for the solution of such a problem. Establishing of the Sr depth profile, was only possible after AFM, High-Resolution EDS PIXE and differential PIXE analysis were carried out. Results, problems faced and conclusions obtained are presented. [Copyright &y& Elsevier]

Abstract: Through the dielectric materials used for the making of type I multilayer ceramic capacitors, the ilmenite magnesium titanate MgTiO3 is of particular importance. Yet, it seems difficult to get pure MgTiO3 with a controlled stoichiometry. In order to be able to synthesize it by solid-state reaction, we therefore studied the mixing/grinding behavior of the precursors MgO+TiO2. The evolution versus pH of the zeta potential values of both MgO and TiO2 (anatase) powders shows that it is impossible to get correct pH values allowing a good dispersion state and thus an easy control of the mixing of these two species when considering only electrostatic repulsion. So, we considered to add dispersing agent in order to get a steric dispersion behavior. Rheological characterization of the slurries showed that we were able to get a good dispersion state during the process of mixing/grinding. XRD and SEM/EDX analysis shows the ability of obtaining “pure” MgTiO3 with a controlled stoichiometry after calcination by controlling the rheological behavior of slurries during mixing/grinding. [Copyright &y& Elsevier]

Abstract: Calcium-doped MgTiO3–MgTi2O5 (MCT) ceramics prepared using a reaction-sintering process were investigated. Without any calcination involved, the mixture of MgO, CaCO3, and TiO2 was pressed and sintered directly. MCT ceramics were obtained after 2–6h sintering at 1150–1250°C. MCT containing high percentage of MgTi2O5 phase (45.6%) was observed at 1150°C/2h sintering and the percentage decreased to 37.2% at 1300°C/2h sintering. The maximum density 3.85g/cm3 could be obtained at 1250°C. Dielectric constant at 10MHz reaches 23.7–25.9 in MCT ceramics sintered at 1150 and 1200°C. ɛ r =22.4 and Q × f ∼40,400GHz (at 9.8GHz) and a τ f value of −9.6ppm/°C were obtained in MCT ceramic sintered at 1300°C/2h. The reaction-sintering process has been proven a simple and effective method to produce dense MCT ceramics with good dielectric properties even without the addition of sintering aid. [Copyright &y& Elsevier]

Abstract: Ceramic composites of barium strontium titanate (Ba0.3Sr0.7TiO3) mixed with magnesium titanate (MgTiO3, in a range of 5 to 40 mol%) were prepared and studied. At the low MgTiO3 content (5%), a solid solution of Ba0.3Sr0.7TiO3 with MgTiO3 is observed at 1250 °C and the solubility is extended to 40% MgTiO3 when the sintering temperature increases to 1350 °C. When sintered at 1250 °C, the dielectric constant and microwave property Qxf values of composites decrease with increasing MgTiO3 content due to the dilution effect of MgTiO3 phase. Sintering at 1350 °C results in an enhanced microwave property, attributed to the single phase of Ba0.3Sr0.7TiO3 and large grained structures. With 10% MgTiO3 sintered at 1350 °C, the dielectric constant is 365 and the Qxf value is 1467 GHz indicating their potential in microwave applications. [Copyright &y& Elsevier]

A series of AlMCM-41 molecular sieves were synthesized starting from a hydrogel keeping the following molar composition: 1CTMABr:4.58SiO2:(0.437+X)Na2O:XAl2O3:200H2O. Tetramethylammonium silicate (TMAS) was used as silicon source and cethyltrimethylammonium bromide (CTMABr) was used as structure template. The obtained materials were characterized by nitrogen adsorption, XRD and TG/DTG. Acid properties were determined by pyridine thermodesorption. Model-free and Flynn-Wall kinetic models were used in order to correlate the total acidity with the apparent activation energy of pyridine desorption. [ABSTRACT FROM AUTHOR]

We have studied the application of magnesium titanate thin films as buffer layer for the improvement of adhesion of Pt films to Si substrate. Magnesium titanate films were successfully prepared on Si(100) substrate by electron beam evaporation. The crystal phase of MgTi 2 O 5 and MgTiO 3 films on Si substrate were observed. These films had a very smooth and densely packed surface morphology and showed a good characteristic as the adhesion layer for Pt. Also, AES analysis showed the excellent properties as the reaction barrier layer between Pt and Si. [ABSTRACT FROM AUTHOR]

Wet milling by a multi-ring media mill was carried out for aqueous slurries of Mg(OH)[sub 2] and TiO[sub 2] powder mixtures in the concentration range from 6.9 to 50 wt%. Rings used as grinding media were made of partially stabilized zirconia or polyoxymethylene. Products were characterized by thermogravimetry-differential thermal analysis, X-ray diffractometry and EPMA. ZrO[sub 2] contamination in the product was determined by X-ray flurescence analysis. The temperature of endothermic peaks of dehydration remained almost unchanged regardless of slurry concentration but decreased with increasing compressive force exerted by grinding rings. The homogeneity of the product is correlated with the temperature of exothermic peaks above 1100 K due to the crystallization of MgTiO[sub 3], but not with the endothermic peaks around 650 K. The increase of the slurry concentration increases the homogeneity of the product, facilitating the formation of single-phase MgTiO[sub 3] on subsequent heating. The increase of the compressive force of grinding rings brings about not only the homogeneity but also the phase purity of MgTiO[sub 3]. [ABSTRACT FROM AUTHOR]