Mn Ti Research Articles

Nanosized hexagonal Mn- and Ga-doped BaTiO3 with reduced structural phase transition temperature

Nanosized hexagonal BaTiO3 particles were synthesized at 1373 K, grain growth was prevented by reducing the temperature of the cubic–hexagonal phase transition. Crystal structures of nanosized hexagonal Mn- and Ga-doped BaTiO3 were studied by high-energy synchrotron radiation powder diffraction at BL02B2 of SPring-8. Substituting the trivalent cations of Mn and Ga for Ti weakened the Mn–O and Ga–O bonding forces and stabilized the hexagonal phase, which reduced the phase transition temperature. These nanoparticles can be used in the manufacture of electronic components, owing to the properties of hexagonal BaTiO3.

Enhanced High-Temperature Piezoelectric Coefficients and Thermal Stability of Fe- and Mn-Substituted Na0.5Bi0.5TiO3 Ceramics

Bismuth-based ferroelectric ceramics are currently under intense investigation for their potential as Pb-free alternatives to lead zirconate titanate-based piezoelectrics. The present work evaluated the thermal depoling behavior of various compositions of Na0.5Bi0.5TiO3 (NBT), one of the Bi-based materials of broad interest, through in situ and ex situ measurements of the piezoelectric constant (d33). A range of ceramics was prepared by substituting 0.5–2 at.% of Fe or Mn for Ti. It was found that a low dopant concentration (0.5 at.%) increases the depolarization temperature (Td) with a minimal loss in room temperature d33, allowing for high piezoelectric coefficients at elevated temperatures. For example, 0.5 at.% Fe substitution leads to an enhanced piezoelectric coefficient of d33 of 133 pm/V at an elevated temperature of 180°C. However, with further increase of dopant concentration, Td decreases in both Mn- and Fe-doped NBT. The in situ depoling measurements of 0.5 at.% Fe- and Mn-doped NBT in the present work exhibit the potential for higher temperature applications.

Casting defects induced fatigue damage in aircraft frames of ZL205A aluminum alloy – A failure analysis

Two different types of aircraft frame components, which had collapsed respectively in their former vibration-fatigue performance tests, were submitted for failure analysis. The two failed frames were both made of aerial material ZL205A, a high-strength cast Al–Cu–Mn–Ti alloy. According to a series of experimental procedures including visual observations, X-ray detections, fractography inspections, microstructure examinations, mechanical tensile tests, hardness measurements and fluorescent penetrating inspections, it was indicated that the fracture was attributed to fatigue cracks which were induced by casting porosity defects at the external surfaces of frames. Numerous fine fatigue striations presented in the vicinity of casting porosities. Especially, it was observed of a special appearance of latitude–longitude crossed fatigue striations on the fracture surface due to the coupled stresses supplied by the former multi-directional vibration tests. The overload fast-rupture regions on fracture surfaces suggested the typical cleavage fracture mode, which was characterized by a number of river patterns and cleavage steps. The intergranular spatial dendrite-shaped casting porosities largely contributed to the local stress-concentrations in matrix materials. Triangular grain boundaries induced by the former casting burnt implied that the intergranular melting phenomenon had occurred. Furthermore, the effect of groove-shaped structure at roots of spatial convex-bodies on the edge of casting porosity was especially analyzed. And the influence of the casting porosity size on fatigue cracks was briefly discussed.

The tunnel manganese oxide Na4.32Mn9O18: a new Na+site discovered by single-crystal X-ray diffraction

The title compound, tetrasodium nonamanganese octadecaoxide, Na(4.32)Mn(9)O(18), was synthesized by reacting Mn(2)O(3) with NaCl. One Mn atom occupies a site of 2/m symmetry, while all other atoms sit on mirror planes. The compound is isostructural with Na(4)Ti(4)Mn(5)O(18) and suggestive of Mn(3+)/Mn(4+) charge ordering. It has a double-tunnel structure built up from double and triple chains of MnO(6) octahedra and single chains of MnO(5) square pyramids by corner sharing. Disordered Na(+) cations occupy four crystallographic sites within the tunnels, including an unexpected new Na(+) site discovered inside the large S-shaped tunnel. A local-ordering model is used to show the possible Na(+) distribution, and the unit-cell evolution during charging/discharging is explained on the basis of this local-ordering model.

Optical observation of real materials using laser scanning confocal microscopy Part 2 – direct observation of ferrite nucleation sites in weld metal and heat affected zone

High temperature laser scanning confocal microscopy (LSCM) allows in situ observation of microstructure changes that occur during welding thermal cycles in the weld metal and the heat affected zone (HAZ). To assess the effect of the inclusion type on the nucleation of intragranular acicular ferrite, direct verification of the nucleation site of the ferrite phase in the phase transformation of Si–Mn–Ti–B–Al weld metal was carried out by LSCM. Furthermore, it was observed that acicular ferrite can be formed in the HAZ by controlling the deoxidisation elements during the steel making process. The effect of the inclusion type on acicular ferrite formation in the HAZ was also assessed by tracking the ferrite formation behaviour during phase transformations by LSCM.

Single-Source Materials for Metal-Doped Titanium Oxide: Syntheses, Structures, and Properties of a Series of Heterometallic Transition-Metal Titanium Oxo Cages

Titanium dioxide (TiO(2)) doped with transition-metal ions (M) has potentially broad applications in photocatalysis, photovoltaics, and photosensors. One approach to these materials is through controlled hydrolysis of well-defined transition-metal titanium oxo cage compounds. However, to date very few such cages have been unequivocally characterized, a situation which we have sought to address here with the development of a simple synthetic approach which allows the incorporation of a range of metal ions into titanium oxo cage arrangements. The solvothermal reactions of Ti(OEt)(4) with transition-metal dichlorides (M(II)Cl(2), M = Co, Zn, Fe, Cu) give the heterometallic transition-metal titanium oxo cages [Ti(4)O(OEt)(15)(MCl)] [M = Co (2), Zn (3), Fe (4), Cu (5)], having similar MTi(4)(μ(4)-O) structural arrangements involving ion pairing of [Ti(4)O(OEt)(15)](-) anion units with MCl(+) fragments. In the case of the reaction of MnCl(2), however, two Mn(II) ions are incorporated into this framework, giving the hexanuclear Mn(2)Ti(4)(μ(4)-O) cage [Ti(4)O(OEt)(15)(Mn(2)Cl(3))] (6) in which the MCl(+) fragments in 2-5 are replaced by a [ClMn(μ-Cl)MnCl](+) unit. Emphasizing that the nature of the heterometallic cage is dependent on the metal ion (M) present, the reaction of Ti(OEt)(4) with NiCl(2) gives [Ti(2)(OEt)(9)(NiCl)](2) (7), which has a dimeric Ni(μ-Cl)(2)Ni bridged arrangement arising from the association of [Ti(2)(OEt)(9)](-) ions with NiCl(+) units. The syntheses, solid-state structures, spectroscopic and magnetic properties of 2-7 are presented, a first step toward their applications as precursor materials.

Amethyst and morion quartz gemstone raw materials from Turkey: color saturation and enhancement by gamma, neutron and beta irradiation

Color-enhancement investigations without using heating treatment from dull or pale to ideal saturation and/or changes to the formation of the rarer attractive colors are widely conducted to revalue abandoned gem material sources in the world. Such an investigation is carried out on pale or dull purple-colored amethyst and smoky-colored morion samples, which are two important gem species of the crystalline quartz (SiO2) mineral that are currently abandoned in natural deposits in Turkey because of their unattractive coloration. The results of color enhancements observed on these samples, after irradiation with artificial gamma, neutron and beta beams, were examined by comparing with samples with the ideal color saturation and also with colorless samples, using optical absorption (OA) and radioluminescence (RL) spectroscopy. The ICP-AES analyses reveal that the main impurity elements of over 100 ppm in abundance in these quartz species are aluminum, iron and titanium for amethyst, and aluminum, iron, titanium and manganese for morion. The OA spectra indicate that vivid purple coloration of amethyst is due to the transmittance at about 395–420 nm band gap as a result of absorbance peaks at 375, 480 and 530 nm. These absorbances may be related to the unusual oxidized small proportions of certain impurity ions, after being exposed mainly to gamma irradiation, such as Al(IV) from the total aluminum, Ti(V) from the total titanium and Fe(IV) from the total iron, respectively. However, the RL spectroscopy of amethyst samples before and after they were exposed to artificial gamma, neutron and beta radiation beams demonstrates that the ions most affected by irradiation are Fe(IV) first and Al(IV) and Ti(V) second, and these ions represent the RL peaks at 600, 720 and 495 nm, respectively. The OA spectra indicate that dark smoky coloration in morion is due to a lack of transmittance at the visible region as a result of the absorbance peaks at 375, 450–490, 620 and 730 nm. These absorbances also may be related to the unusual oxidized small proportions of certain impurity ions by irradiation, such as Al(IV) from the total aluminum, Ti(V) from the total titanium and Mn(III) from the total manganese, respectively. In addition, the buoyancies of these absorbance peaks in the visible region produce the color hues between light smoky and dark smoky colorations in morion samples. These oxidized ion states are more resistant and stable against environmental destructive conditions in comparison with amethyst. Thus, the dark smoky coloration of morion becomes dull or pale after relatively longer periods. But, the RL spectroscopy of morion before and after being exposed to gamma, neutron and beta irradiation beams demonstrates that the most induced ions from the irradiation are Mn(III) and Al(IV) first and Ti(V) second. These ions represent the RL peaks at about 400, 720 and about 500 nm, respectively.

Corrosion analysis of Al–Zn–In–Mg–Ti–Mn sacrificial anode alloy

The corrosion behaviour of Al–5Zn–0.02In–1Mg–0.05Ti–0.5Mn (wt%) alloy was investigated by SEM, EDX and TEM. The results show that there exist different corrosion types of the alloy in 3.5% NaCl solution with immersion time. At the initial stage of immersion, pitting predominate the corrosion around precipitates. The major precipitates of the alloy are MgZn 2 and Al 6Mn particles. The corrosion potential of the bulk MgZn 2 alloy is negative with respect to that of the α-Al and the bulk Al 6Mn alloy, so the MgZn 2 precipitate can act as activation centre, make the aluminum oxide film breakdown and cause the pitting corrosion. In the late stage, it turns out to be a uniform corrosion due to the control of dissolution precipitation of In and Zn ions.

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.

Modified composition of barium ferrite to act as a microwave absorber in X-band frequencies

The magnetic and electromagnetic wave absorbing properties of the Co–Mn–Ti substituted barium ferrites, BaCo x Mn x Ti 2 x Fe 12−4 x O 4 (0≤ x≥0.5), prepared by a solid-state technique, were investigated. The grain size uniformity and densification improved with increasing concentration of Co–Mn–Ti, while the permeability increased and the coercivity decreased remarkably. The reflection coefficients ( S 11 , S 12 ) of the ferrite samples were measured in the X-band frequency range (8–12 GHz) and their absorbing properties were calculated according to transmission line theory. The maximum reflection loss (−14.7 dB) is observed for the x = 0.4 sample. A ferromagnetic resonance frequency shift has been observed to depend on the Co–Mn–Ti concentration, which is an important phenomenon of barium ferrite for absorbing microwaves at high frequencies. Based on the magnetic and microwave measurements, BaCo x Mn x Ti 2 x Fe 12−4 x O 4 may be a good potential candidate for electromagnetic compatibility and for other practical applications at high frequencies.

CCNR type high field instability in Ti4+-substituted Mn–Zn ferrites

Polycrystalline samples of the spinel ferrite system Zn0.3Mn0.7+xTixAl0.1Fe1.9−2xO4 (x = 0.0–0.3) have been studied for electrical switching in the temperature range from 300 to 700 K and applied voltage range from 0 to 400 V. High electric field induced resistance switching of nearly 200% has been observed for all the compositions. The dependence of temperature and applied electric field strength on switching has been examined. The electric field and temperature required for switching increase with increase in Mn–Ti concentration. The results have been interpreted considering previous models and have been ascribed to the existence of space charge limiting current in the system. The switching observed, is of current-controlled negative resistance (CCNR)-type.

Identification of Mn Site in BaTiO3 by Synchrotron X-Ray Absorption Spectroscopy Measurements

In this work, an X-ray Absorption Spectroscopy (XAS) measurement was employed to determine the local structure of Mn in BaTiO 3 . A combination of Synchrotron X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) experiments was performed on Mn-doped BaTiO 3 samples. The BaTi 1 − x Mn x O 3 powder samples (where x = 0.01–0.2) were used for the XAS experiment. XAS spectra at the Mn K-edge were recorded in transmission mode. The spectra were collected at ambient temperature with a Ge(111) double crystal monochromator and recorded after performing an energy calibration. The features of the measured Mn K-edge XANES and EXAFS were both consistent with Mn on the Ti site and inconsistent with Mn on other sites. In addition, the dielectric and ferroelectric properties results also supported the possible Mn Ti substitution in BaTiO 3 material. The clear agreement between the two measured synchrotron XAS spectra, as well as supporting electrical results, was by far the strongest evidence of Mn substituting for Ti in BaTiO 3 structure.

Preparation of TiMn alloy by mechanical alloying and spark plasma sintering for biomedical applications

TiMn alloy was prepared by mechanical alloying and subsequently consolidated by spark plasma sintering (SPS) technique for exploration of biomedical applications. The microstructures, mechanical properties and cytotoxicity of the TiMn alloys were investigated in comparison with the pure Ti and Mn metals. Ti8Mn and Ti12Mn alloys with high relative density (99%) were prepared by mechanical alloying for 60 h and SPS at 700 °C for 5 min. The doping of Mn in Ti has decreased the transformation temperature from α to β phase, increased the relative density and enhanced the hardness of the Ti metal significantly. The Ti8Mn alloys showed 86% cell viability which was comparable to that of the pure Ti (93%). The Mn can be used as a good alloying element for biomedical Ti metal, and the Ti8Mn alloy could have a potential use as bone substitutes and dental implants.

Electrical conductivity–defect structure correlation of variable-valence and fixed-valence acceptor-doped BaTiO3 in quenched state

Insulation resistance degradation of dielectric BaTiO(3) is expected to be closely correlated to its defect structure frozen in from elevated processing temperatures. For BaTiO(3), respectively doped with variable-valence (Mn(Ti)) and fixed-valence acceptors (Al(Ti)), their defect structures were frozen in by quenching at different equilibrium oxygen activities in the range of -18 < log a(O(2))< or = 0 at 1000 and 900 degrees C, respectively, and their electrical conductivities were measured against temperature in the range of 200 < or =T/K < or = 494 by impedance spectroscopy. Frozen-in defect structures were calculated and compared with the conductivity as measured in the quenched state. A close correlation has been confirmed between the bulk conductivity as measured in the quenched state and the frozen-in defect structure as calculated. The effects of variable- and fixed-valence acceptor impurities on the defect structure and electrical conductivity in the quenched state are highlighted in the light of hole trapping, and the charge transport behavior in the quenched state is discussed.

Electrical and optical characterization of undoped BaTiO3 in the quenched state

On undoped polycrystalline BaTiO(3-delta) (99.9% nominal purity), that had been equilibrated and quenched at 1000 degrees C under different oxygen activities in the range of -19.4 < or = log a(O(2)) < 0.1, were measured optical reflectance spectra at 298 K and ac conductivity at 473, 523 and 573 K, respectively. It was observed that all specimens quenched at log a(O(2)) > -17 are electrically insulating and white in color, once powdered, and show optical absorption only at the absorption edge at approximately 3 eV. In contrast, those quenched at log a(O(2)) < -17 are electronically conducting and dark and exhibit a significant absorption in the IR region. This demarcating oxygen activity for the conductivity transition is ca. 13 orders of magnitude lower than that for the n-to-p type transition (delta = 0) in the equilibrium state, contrary to expectation. It is, thus, suggested that contrary to the textbook knowledge, the hole traps responsible for the conductivity transition in undoped BaTiO(3) may be variable-valent acceptor defects like Mn(Ti). The strong IR absorption in the semiconducting state is ascribed to small-polaron (Ti'(Ti)) hopping processes.

Hydrogen storage in Ti–Mn–(FeV) BCC alloys

Recently, the replacement of vanadium by the less expensive (FeV) commercial alloy has been investigated in Ti–Cr–V BCC solid solutions and promising results were reported. In the present work, this approach of using (FeV) alloys is adopted to synthesize alloys of the Ti–Mn–V system. Compared to the V-containing alloys, the alloys containing (FeV) have a smaller hydrogen storage capacity but a larger reversible hydrogen storage capacity, which is caused by the increase of the plateau pressure of desorption. Correlations between the structure and the hydrogen storage properties of the alloys are also discussed.

Phase relationships in the Ho–Mn–Ti ternary system at 773 K

The isothermal section of phase diagram of the Ho–Mn–Ti ternary system at 773 K has been investigated mainly by X-ray powder diffraction analysis with the aid of differential thermal analysis in this work. The existence of eight binary compounds HoMn 2, Ho 6Mn 23, HoMn 12, Mn 5Ti, Mn 2Ti, βMnTi, αMnTi and Mn 15Ti 85 has been confirmed in this system. At 773 K, the maximum solid solubility of Ti in αMn is about 8 at.%Ti. The homogeneity range of Mn 2Ti extends from about 31 at.% to 39 at.% Ti. The maximum solid solubility of Ho in Mn 2Ti phase is about less than 1 at.% Ho. The existence of solid solubility of other phases was not observed. No ternary compounds were found in this ternary system. At 773 K, the isothermal section of phase diagram of Ho–Mn–Ti ternary system consists of 11 single-phase regions, 19 two-phase regions and 9 three-phase regions.

Phase relationships in the Er–Mn–Ti ternary system at 773 K

The Phase relationship in the Er–Mn–Ti ternary system at 773 K has been investigated by X-ray powder diffraction analysis with the aid of differential thermal analysis and optical microanalysis techniques in this work. The existence of eight binary compounds Mn 15Ti 85, αMnTi, βMnTi, Mn 2Ti, Mn 5Ti, ErMn 12, Er 6Mn 23 and ErMn 2 has been confirmed at 773 K in this system. The maximum solid solubility of Ti in Mn is about 8 at%Ti. The homogeneity range of Mn 2Ti extends from about 31 at% to 39 at% Ti. The maximum solid solubility of Er in Mn 2Ti phase is about less than 1 at% Er. No ternary compounds were found in this ternary system at 773K. At 773 K, the isothermal section of phase diagram of Er–Mn–Ti ternary system consists of 11 single-phase regions, 19 two-phase regions and 9 three-phase regions.

Hydrogenation properties and microstructure of Ti–Mn-based alloys for hybrid hydrogen storage vessel

Abstract Ti–Mn-based AB2-type alloys which are suitable for a hybrid hydrogen storage vessel have been synthesized and evaluated hydrogenation properties. As the third element V was added to Ti–Mn binary alloys. All the alloys synthesized in this work mainly consist of the C14 Laves and BCC phase. In the case of Ti0.5V0.5Mn alloy, the amounts of hydrogen absorption was 1.8 wt.% at 243 K under the atmosphere of 7 MPa H2, and the hydrogen desorption pressure was in the range of 0.2–0.4 MPa at 243 K. The hydrogen capacity of this alloy did not saturate under 7 MPa H2 and seems to increase with hydrogen pressure up to 35 MPa that is estimated working pressure of the hybrid hydrogen storage vessel.

Spark plasma sintering synthesis of porous nanocrystalline titanium alloys for biomedical applications

The reason for the extended use of titanium and its alloys as implant biomaterials stems from their lower elastic modulus, their superior biocompatibility and improved corrosion resistance compared to the more conventional stainless steel and cobalt-based alloys [Niinomi, M., Hattori, T., Niwa, S., 2004. Material characteristics and biocompatibility of low rigidity titanium alloys for biomedical applications. In: Jaszemski, M.J., Trantolo, D.J., Lewandrowski, K.U., Hasirci, V., Altobelli, D.E., Wise, D.L. (Eds.), Biomaterials in Orthopedics. Marcel Dekker Inc., New York, pp. 41–62]. Nanostructured titanium-based biomaterials with tailored porosity are important for cell-adhesion, viability, differentiation and growth. Newer technologies like foaming or low-density core processing were recently used for the surface modification of titanium alloy implant bodies to stimulate bone in-growth and improve osseointegration and cell-adhesion, which in turn play a key role in the acceptance of the implants. We here report preliminary results concerning the synthesis of mesoporous titanium alloy bodies by spark plasma sintering. Nanocrystalline cp Ti, Ti–6Al–4V, Ti–Al–V–Cr and Ti–Mn–V–Cr–Al alloy powders were prepared by high-energy wet-milling and sintered to either full-density (cp Ti, Ti–Al–V) or uniform porous (Ti–Al–V–Cr, Ti–Mn–V–Cr–Al) bulk specimens by field-assisted spark plasma sintering (FAST/SPS). Cellular interactions with the porous titanium alloy surfaces were tested with osteoblast-like human MG-63 cells. Cell morphology was investigated by scanning electron microscopy (SEM). The SEM analysis results were correlated with the alloy chemistry and the topographic features of the surface, namely porosity and roughness.