Pseudobrookite Structure Research Articles

Fabrication of flexible (Mg0.2Al0.2Fe0.2Ni0.2Co0.2)2Ti2.8O8 ceramics via compositionally complex ceramics method

A novel compositionally-complex flexible (Mg0.2Al0.2Fe0.2Ni0.2Co0.2)2Ti2.8O8 (abbreviated as CCC) ceramic with pseudobrookite structure was synthesized by solid-state reaction method. As compared to the fabrication process of flexible aluminum titanate ceramic (C. Babelot, 2011), the sintering temperature was significantly reduced from 1600 °C to 1200 °C by co-doping. And, the combinations of displacement (0.11–0.25 mm) and bending strength (10–40 MPa) were achieved by controlling the sintering condition. Among these, the specimen sintered at 1200 °C for 2 h (abbreviated as CCC-1200-2) presents a single-phase crystal structure and uniform elemental distribution. After that, its near-zero thermal expansion coefficient of 0.47 × 10−6 K−1 at low temperature was obtained and the nonlinear thermal expansion behavior was observed. Lastly, the thermal stability of sample CCC-1200-2 was checked out by annealing the samples between 900 °C and 1600 °C for various times up to 100 h. As a result, this study successfully fabricated the flexible CCC ceramics with improved mechanical properties, high thermal stability, and low sintering requirements, providing a new technology strategy for pseudobrookite-type ceramics and compositionally-complex ceramics fabrication.

Facile synthesis and physical properties of magnesium dititanate nanoparticles for antibacterial applications

AbstractThe modified aqueous co-precipitation approach was used to successfully manufacture magnesium dititanate (MgTi2O5) nanoparticles. Thermogravimetric analysis/differential scanning calorimetry (TG/DSC) was used to clearly reveal the thermal stability. Moreover, pseudobrookite structure, and surface morphology of MgTi2O5 nanoparticles were determined using X-ray diffraction (XRD), transmission electron microscope (TEM), and Fourier-transform infrared (FT-IR), and scanning electron microscope (SEM) techniques, respectively. The average size of the crystallites calculated by Scherer approach was compared to Williamson-Hall and TEM images results. The optical band gap of MgTi2O5 nanoparticles was found to be 3.81 eV for direct transitions. The effect of temperature on the conductivity of DC electricity was tested between the rages 303–503 K. The data on antibacterial activity showed that MgTi2O5 nanoparticles were antimicrobial and stopped the test microorganisms from growing. These findings revealed that MgTi2O5 will be extensively promising in environmental pollution control and antibacterial research.

Pseudobrookite Fe2-2xCoxTi1-½xO5: Structural, magnetic phase transformation and reflection loss characteristic

Single-phase pseudobrookite Fe2-2xCoxTi1-½xO5 (x = 0, 0.1, 0.2, and 0.4) with an orthorhombic structure has been successfully synthesized using a solid reaction and sintering at 1000 °C. Pseudobrookite Fe2-2xCoxTi1-½xO5 is an element that is abundant on earth and is attracting rapidly growing interest as a very promising candidate for the application of microwave absorbing materials. This paper studies the performance of exchange coupling in addition to the structural properties and microwave absorption characteristics of pseudobrookite Fe2-2xCoxTi1-½xO5. Qualitative and quantitative analysis of the X-ray diffraction (XRD) pattern show that all samples were single-phase pseudobrookite Fe2TiO5 with a space group of C m c m. The presence of Co causes the expansion of the lattice parameter with an indicator of an increase in the value of the unit cell volume as the composition of Co in the structure increases. Particle morphology and elemental composition were also observed using a scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS). The presence of Co2+ dopant ions does not affect the shape and size of the particles, while the crystallite size increased with the increase in the content of Co2+ dopant ions in the structure and Co elements of 1.82, 2.81, and 5.69 at% have been detected, which are contained in the composition x = 0.1, 0.2, and 0.4, respectively. The presence of the Co2+ dopant ion it stimulates the rearrangement of the cationic distribution in both tetrahedral and octahedral sites which will have an impact on changes in the magnetic properties of this pseudobrookite. Magnetic properties were analyzed by measuring magnetization (M) against a magnetic field (H) at 300 K (RT). The spontaneous magnetization at room temperature in pseudobrookite Fe2-xCoxTi1-½xO5 is ∼2.55, 7.41 and 8.67 emu/g for compositions of x = 0.1, 0.2 and 0.4, respectively. The coercive field is ∼424, 356 and 284 Oe for compositions of x = 0.1, 0.2 and 0.4, respectively. The presence of Co in the structure causes a magnetic phase transformation from paramagnetic to ferromagnetic behavior at room temperature. This ferromagnetic behavior can be explained due to the strengthening of indirect exchange interactions of Ti/Co – O – Fe/Co in addition to the interactions of Fe/Co – O – Fe/Co and Ti/Co – O – Ti/Co, as well as changes in the degree of inversion of this pseudobrookite structure, due to the presence of magnetic ion dopants. Magnetic parameters both Ms, Mr, and Hc show an increase with increasing Co2+ ion content at room temperature. This magnetic parameter is very important at room temperature to determine the absorption characteristics of microwaves through the resonant frequency. Microwave absorption characteristics are measured in the 8–12 GHz frequency range. The best reflection loss (RL) peaks were obtained at composition x = 0.1 of -24 dB at 10.6 GHz frequency. The presence of Co2+ dopant ions can produce a very significant increase in RL almost 3 times at the same absorption frequency. This increase in reflection loss can be attributed to the effect of the magnetic phase transformation of this material which has been described accordance of the magnetic coupling exchange interaction, which in turn changes the magnitude of the relative permeability value of this material complex.

New class of high-entropy pseudobrookite titanate with excellent thermal stability, low thermal expansion coefficient, and low thermal conductivity

As a type of titanate, the pseudobrookite (MTi2O5/M2TiO5) exhibits a low thermal expansion coefficient and thermal conductivity, as well as excellent dielectric and solar spectrum absorption properties. However, the pseudobrookite is unstable and prone to decomposing below 1200 °C, which limits the practical application of the pseudobrookite. In this paper, the high-entropy pseudobrookite ceramic is synthesized for the first time. The pure high-entropy (Mg,Co,Ni,Zn)Ti2O5 with the pseudobrookite structure and the biphasic high-entropy ceramic composed of the high-entropy pseudobrookite (Cr,Mn,Fe,Al,Ga)2TiO5 and the high-entropy spinel (Cr,Mn,Fe,Al,Ga,Ti)3O4 are successfully prepared by the in-situ solid-phase reaction method. The comparison between the theoretical crystal structure of the pseudobrookite and the aberration-corrected scanning transmission electron microscopy (AC-STEM) images of high-entropy (Mg,Co,Ni,Zn)Ti2O5 shows that the metal ions (M and Ti ions) are disorderly distributed at the A site and the B site in high-entropy (Mg,Co,Ni,Zn)Ti2O5, leading to an unprecedentedly high configurational entropy of high-entropy (Mg,Co,Ni,Zn)Ti2O5. The bulk high-entropy (Mg,Co,Ni,Zn)Ti2O5 ceramics exhibit a low thermal expansion coefficient of 6.35×10−6 K−1 in the temperature range of 25–1400 °C and thermal conductivity of 1.840 W·m−1·K−1 at room temperature, as well as the excellent thermal stability at 200, 600, and 1400 °C. Owing to these outstanding properties, high-entropy (Mg,Co,Ni,Zn)Ti2O5 is expected to be the promising candidate for high-temperature thermal insulation. This work has further extended the family of different crystal structures of high-entropy ceramics reported to date.

Effect of microstructure on thermal and mechanical properties of solid solutions Al2TiO5 - MgTi2O5

Aluminium titanate - tialite belongs to the compounds with pseudobrookite structure. The polycrystals made of tialite show valuable useful thermal properties: low thermal expansion, very low thermal conductivity and high resistance to thermal shock. These properties result from the cracks present in the microstructure, resulting from significant differences in the lattice coefficients of aluminium titanate. The basic disadvantage of tialite consist in a thermal decomposition occurring at the temperatures of about 750–1280 °C. This decomposition can be limited by structural and microstructural stabilization. The addition of cations, e.g. magnesium or iron, leads to the formation of stable solid solutions, while the addition of SiO2 or ZrO2 leads to the formation of secondary phases - diffusion barriers occurring at intergranular boundaries. Most often these additives are introduced simultaneously and at the reaction sintering stage. Stable solid solutions are usually produced by a classical solid phase reaction between the initial oxides: Al2O3, TiO2 and MgO. In this work, an innovative synthesis was applied to produce solid solutions, involving a heterogeneous isostructural nucleation with magnesium titanate. The polycrystals obtained in this way, at a much lower temperature, with a high content of solid solutions (95–96 %), high density, homogeneous microstructure with necessary microcracks were obtained. As a result, the obtained polycrystals exhibit the typical pseudobrookite structure behaviour as a function of temperature.

Non-metallic electrical transport properties of a metastable λ -Ti3O5 thin film epitaxially stabilized on a pseudobrookite seed layer

A metastable phase of Ti3O5, λ-Ti3O5, has been studied as a promising optoelectronic material applicable to optical memories and switching devices because it undergoes structural phase transitions, accompanied by changes in optical and electrical properties, under a variety of external stimuli such as heat, visible light, pressure, and electrical current. Theoretical calculations and optical and magnetic measurements have suggested that λ-Ti3O5 is a metal. However, its electrical transport properties have not been directly measured to date because λ-Ti3O5 has so far been synthesized only as nanocrystals or aggregates thereof. In this study, we synthesized (100)-oriented λ-Ti3O5 epitaxial thin films on perovskite LaAlO3 (110) substrates by pulsed laser deposition. Precise control of oxygen supply during the growth and introduction of a MgTi2O5 seed layer with a pseudobrookite structure enabled epitaxial growth of λ-Ti3O5. These λ-Ti3O5 epitaxial thin films showed a lower electrical resistivity ρ (∼7.9 × 10−2 Ω cm) than bulk single crystals of β-Ti3O5 (high resistance phase) at 300 K. On the other hand, the ρ value of the λ-Ti3O5 thin films exhibited a semiconducting temperature dependence with negative dρ/dT.

Oxygen Transfer Capacity of Pseudobrookite Particles Derived from Ilmenite Mineral (x wt.%CuO/y wt.%red Mud-z wt.%ilmenite).

The minerals have a somewhat slower than other transition metals at critical reduction rates in their ability to deliver oxygen. Thus, single minerals alone do not exhibit a higher oxygen transfer capacity than metal oxide oxygen carriers. In this study, we try to solve the problem of single mineral ilmenite (FeTiO₃) by combining it with Fe-based red mud and Cu oxide. When the ilmenite was used without calcination, the CH₄-CO/air redox cycle showed rapid decayed. However, when ilmenite was calcined, the CH4-CO/air redox cycle became stable, and the oxygen transfer rate increased to 4.2%. This is because the FeTiO₃ structure was converted to the pseudobrookite (Fe₂TiO5) structure through the calcination process. That is, the Fe2+ ion in the ilmenite structure was converted into an Fe3+ ion. When 30 wt.% of red mud was added to the Fe ion, it reacted with the rutile-type titania mixed with pseudobrookite-typed Fe₂TiO5, producing an almost perfect pseudobrookite crystal. This resulted in a slight increase in the capacity of oxygen transfer to 4.9%. When 15 wt.% of Cu oxide was added, the oxygen transfer capacity increased to 6.0%. This performance was indicated by the cyclic voltammetry curve that remained constant even after 200 cycles. Here, we argue that if low-cost minerals as a base material are used in appropriate amounts, the production of a lowest-cost oxygen carrier can be achieved.

A wide visible light active photocatalyst Mg5Ta4O15-xNy for water oxidation and reduction

More than 1.6 eV band gap reductions have been realized on Mg5Ta4O15 by nitrogen doping with its pseudobrookite structure maintained. The nitrogen doped Mg5Ta4O15, i.e. Mg5Ta4O15-xNy, shows broad absorption in the visible light region and promising photocatalytic activity for both water reduction and oxidation reactions under visible light illumination (λ ≥ 400 nm). Apparent quantum efficiency as high as ~0.90% has been achieved at 420 ± 20 nm on Mg5Ta4O15-xNy which is comparable to a number of active metal oxynitrides photocatalysts. Apart from visible light absorption, Nitrogen doping on Mg5Ta4O15 is also accompanied by improved surface hydrophilicity and a negative shift of flat band potential. This simple strategy for band gap engineering can be extended to other metal oxides which may open new playgrounds in the design and development of efficient visible light active photocatalysts.

The Investigation on Enrichment of TiO2 from Ti-Bearing Slag

Titanium-bearing slag in this study was produced by subjecting titanium-bearing sea sand iron mineral to direct reduction smelting process. The enrichment and growth of titanium-rich phase in the titanium slag were investigated. The phases in slag were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. The results showed that Ti-rich phase had a pseudobrookite structure, and it was close to diffractogram of anosovite phase (M3O5 (M = Mg, Al, Ti)), in which the theoretical content of TiO2 is 73.2%. Line-scanning analysis was used to clarify the elements distribution trend in titanium slag. The results showed that Ti element was enriched in the anosovite phase, and Si and Ca assembled in the matrix phase. Mg and Fe elements were distributed in larger proportion in the anosovite phase, while the Al element was more enriched in the matrix phase. The experimental results showed that low cooling rate was in favor of titanium precipitate in anosovite phase. Moreover, the growth of anosovite crystal was characterized by kinetic model. These results provided further insights into the separation of anosovite from gangue by mineral processing.

Order of magnitude increase in photocatalytic rate for hierarchically porous anatase thin films synthesized from zinc titanate coatings.

In this paper we report on the use of aerosol assisted chemical vapour deposition (AACVD) to form thin films of the zinc titanate phases using zinc acetate and titanium isopropoxide as precursors in methanol solution. Analysis by XRD and XPS found that through variation in experimental conditions we have been able to synthesize films of zinc titanate with composition of Zn2TiO4 or Zn0.3Ti2.7O4.94, which adopt the spinel and pseudobrookite structure respectively. In addition, we have also formed hybrid films of Zn2TiO4 with either ZnTiO3 or ZnO. Using a technique previously reported with powders, the mixed ZnO and Zn2TiO4 films were treated with acid to produce porous Zn2TiO4 which, through reduction and vapour leaching of zinc, were converted to hierarchically porous thin films of anatase TiO2. This conversion was monitored by XRD. Analysis of photocatalytic activity of the hierarchically porous titania, using dye and stearic acid degradation tests, found a factor of 12 to 14 increase in rates of photocatalysis over conventional TiO2 thin films. Finally we are able to report a maximum formal quantum efficiency for stearic acid degradation of 1.76 × 10-3 molecules per photon.

Raman spectroscopy analysis of terra sigillata: the yellow pigment of marbled sigillata

Raman spectroscopy combined with synchrotron radiation‐based techniques and electron microprobe was used to study the yellow component of slips of marbled sigillata. Electron microprobe analysis emphasized on a significant corpus that the yellow component was well made from a titanium‐rich clay preparation while X‐ray absorption near edge structure investigation at Ti K‐edge confirmed the massive presence of pseudobrookite (Fe2TiO5) in good agreement with previous study. Raman spectroscopy was correlated with X‐ray absorption near edge structure results in order to extract the Raman spectra of pseudobrookite, which was compared with these ones of synthesized pseudobrookite powder reference. The investigation of a significant corpus (43 sherds) of marbled sigillata revealed that all samples exhibited similar Raman spectra in yellow zones attributable to the pseudobrookite structure. However, all spectra show the same features compared with the spectra of reference powder, that is, peak shifts and line broadenings, which could be related to Mg and/or Al substitutions in pseudobrookite crystals of marbled sigillata. The substitution plays a dual role in pseudobrookite structure: (1) stabilizes the structure through involving an increase of cationic disorder and (2) makes the color less dark and yellow, which could account for the nice yellow color of marbled sigillata. Copyright © 2016 John Wiley & Sons, Ltd.

Near the Ferric Pseudobrookite Composition (Fe2TiO5).

Because of a very low thermodynamic stability, obtaining a pure monophasic compound of ferric pseudobrookite is quite difficult to achieve. Indeed, the low reticular energy of this phase leads easily to its decomposition and the occurrence of the secondary phases: hematite (Fe2O3) and/or rutile (TiO2). Samples with global composition Fe2-xTi1+xO5 (x = 0, 0.05, and 0.10) have been synthesized by the Pechini route and, thereafter, thermally treated at different temperatures. The concentrations of Fe2O3 and TiO2 secondary phases were accurately determined and correlated with the target compositions and the synthesis parameters, especially the thermal treatment temperature. As revealed by Mössbauer spectroscopy, all iron ions are at the III+ oxidation state. Thus, the formation of hematite or rutile as a secondary phase may be related to the occurrence of cationic vacancies within the pseudobrookite structure, with the amount of vacancies depending on the annealing temperature. In light of the presented results, it appears unreasonable to propose a "fixed" binary phase diagram for such a complex system. Furthermore, the occurrence of cationic vacancies induces a coloration change (darkening), preventing any industrial use of this reddish-brown pseudobrookite as a ceramic pigment.

Mineralogical anatomy and implications of a Ti–Sc-rich ultrarefractory inclusion from Sayh al Uhaymir 290 CH3 chondrite

Titanium-rich minerals are common in Ca–Al-rich inclusions from primitive chondrites. They are important not only for testing the condensation models for a gas with a solar composition, but also for constraining the redox conditions of the early solar nebula. In this study, we report the detailed mineralogical features and its oxygen isotope compositions of a Ti–Sc-rich ultrarefractory inclusion A0031 from a CH3 chondrite Sayh al Uhaymir 290. The A0031 inclusion has a compact and layered texture with the interior consisting of panguite, Sc-rich anosovite, Ti-rich davisite, and anorthite. A few hexaferrum, perovskite, and spinel crystals are present as inclusions in these minerals. Outside of Ti-rich davisite are a layer of Al–Ti-rich diopside and two grains of enstatite. This texture strongly suggests that A0031 has a condensation origin. Panguite is its third occurrence in nature and similar in composition to the type panguite from the Allende meteorite. Sc-rich anosovite in A0031 has a chemical formula of (Ti4+,Ti3+,Mg,Sc,Al)3O5 with the pseudobrookite structure. This is the second report of Ti3O5 in nature, but is the first description of anosovite formed in the solar nebula as an ultrarefractory phase. The discovery of Sc-rich anosovite in A0031 reveals the stability of Ti3O5 in the early solar nebula and supports the prediction of previous equilibrium condensation calculations. The panguite, Sc-rich anosovite, and Ti-rich davisite in A0031 show a large variation in Ti3+/Titot. The primitive nature of A0031 implies that the variations in Ti3+/Titot among different Ti-rich minerals are primary features. We propose that the distribution of Ti3+ and Ti4+ could be controlled mainly by their various competition abilities of incorporating into these Ti–Sc–Al-rich minerals. Similarity of Ti3+/Titot value between Ti-rich davisite from A0031 and those in other carbonaceous chondrites indicates that most refractory inclusions might have formed in highly reducing nebular settings. The 16O-depleted isotope compositions of A0031 confirm the existence of diverse oxygen reservoirs for CH Ca–Al-rich inclusions in the solar nebula.

Indentation Responses of Functionally-Graded Al<sub>2</sub>TiO<sub>5</sub>- Based Ceramics

Aluminium titanate, Al2TiO5 (AT) with the pseudobrookite structure is the only compound in the alumina-titania system. It is an excellent refractory and thermal shock resistant material due to its relatively low thermal expansion coefficient (1 ´10-6 °C –1) and high melting point (1860°C). However, its low mechanical strength, hardness and fracture resistance together with susceptibility to decomposition in the temperature range 900–1200°C has limited its wider application. In this paper, the innovative tailored design of functionally- graded Al2TiO5 – based ceramics system was presented. This involves the use of a vacuum heat-treatment or die-pressing to form hard graded layers of alumina on Al2TiO5. These hard outer layers will provide hardness and wear resistance to protect the softer but damage resistant underlayers. The results will also explore unresolved issues concerning the effect of graded interfaces on their physical and mechanical performance properties.

Room temperature synthesis of titanium dioxide nanoparticles of different phases in water in oil microemulsion

We report the synthesis of crystalline titanium dioxide nanoparticles of two different phases (rutile and anomalous pseudobrookite) at room temperature by a novel microemulsion technique. In this method, one of the reactants (titanium tetrachloride) is dissolved in the continuous organic phase, whereas the second reactant (ammonium hydroxide) is added as an aqueous solution. The site of the reaction has been controlled by using two different addition methods for the second reactant. The size and the crystalline phase of the titanium dioxide nanoparticles varied according to the site of the reaction between the two reactants. Reaction in the aqueous core gives rutile titanium dioxide nanoparticles having an average size of 4.2 nm verified by X-ray diffraction and FTIR. The reaction in the organic phase gives rise to crystalline anomalous pseudobrookite titanium dioxide nanoparticles of much larger size (10–40 nm). This anomalous pseudobrookite structure is thermally unstable and converts to rutile on high temperature treatment.

Role of entropy in the stability of cobalt titanates

The standard molar Gibbs free energy of formation of Co2TiO4, CoTiO3,and CoTi2O5 as a function of temperature over an extended range (900 to 1675) K was measured using solid-state electrochemical cells incorporating yttria-stabilized zirconia as the electrolyte, with CoO as reference electrode and appropriate working electrodes. For the formation of the three compounds from their component oxides CoO with rock-salt and TiO2 with rutile structure, the Gibbs free energy changes are given by:Delta(f)G degrees((ox))(Co2TiO4) +/- 104/(J . mol(-1)) = -18865 - 4.108 (T/K)Delta(f)G degrees((ox))(CoTiO3) +/- 56/(J . mol(-1)) = -19627 + 2.542 (T/K) Delta(f)G degrees((ox))(CoTi2O5) +/- 52/(J . mol(-1)) = -6223 - 6.933 (T/K) Accurate values for enthalpy and entropy of formation were derived. The compounds Co2TiO4 with spinel structure and CoTi2O5 with pseudo-brookite structure were found to be entropy stabilized. The relatively high entropy of these compounds arises from the mixing of cations on specific crystallographic sites. The stoichiometry of CoTiO3 was confirmed by inert gas fusion analysis for oxygen. Because of partial oxidation of cobalt in air, the composition corresponding to the compound Co2TiO4 falls inside a two-phase field containing the spinet solid solution Co2TiO4-Co3O4 and CoTiO3. The spinel solid solution becomes progressively enriched in Co3O4 with decreasing temperature. (c) 2010 Elsevier Ltd. All rights reserved.

Thermodynamic Analysis of Mn-depleted Zone Near Ti Oxide Inclusions for Intragranular Nucleation of Ferrite in Steel

A series of thermodynamic analyses have been performed to elucidate possible mechanism of Mn-depleted zone (MDZ) development near Ti oxide inclusions as nucleation sites of Intragranular Acicular Ferrite (IGF) transformation in steels, using a computational thermodynamic approach (CALPHAD). It is demonstrated that thermodynamic calculations are able to reproduce experimentally known inclusions evolution in the steels. The MDZ development near the Ti2O3 inclusions is shown to be a result of Mn absorption into the Ti2O3. Moreover, from thermodynamic analysis of phase equilibria in the Mn–Ti complex oxide system, it is proposed that a phase change of inclusion from (Ti3O5) s.s. (pseudobrookite structure solid solution dissolving Mn) to (Ti2O3) s.s. (ilmenite structure solid solution dissolving Mn) accelerate the Mn absorption into the Ti2O3 inclusion in steel. From a series of thermodynamic calculations, optimum thermal heating condition to enhance Mn absorption into Ti2O3 inclusions as well as IGF formation is discussed.

Microwave dielectric properties of Mg4Al2Ti9O25 ceramics

Phase-singular Mg4Al2Ti9O25 ceramics with the pseudobrookite structure suitable for microwave devices such as antenna substrate have been prepared by gel-carbonate method with the dielectric permittivity of 24.7 (at 2–8 GHz), Q-values>30,000 and temperature coefficients in permittivity (TCK) of less than +17 ppm K−1. The dielectric characteristics are accountable in terms of ordering in the cation sub-lattice.

Lithium Insertion into Nano Phase MgTi2O5 with Pseudo Brookite Structure

not Available.

Interactions in the Al2TiO5-Ti2O3 System

Interactions in the Al2TiO5-Ti2O3 system were studied and the regions of existence of Al2−2xTi2x3+Ti4+O5 solid solutions with a pseudobrookite structure were determined.