Phase transition and microstructure evolution during the carbothermal preparation of Ti(C,N) powders in an open system

Phase transition and microstructure evolution during carbothermal reduction–nitridation of TiO₂ in an open system were investigated using XRD, TGA, SEM and laser particle analysis device. The results show that, the phase evolution sequences are: TiO₂ (anatase) → TiO₂(rutile) → Ti_nO_2n-1(n ? 4) → Ti₃O₅ → Ti(N,O) → Ti(C,N,O) → Ti(C,N). In the reaction process, the predominant reaction mechanism is TiO₂/C solid–solid reaction in the beginning and subsequent the gas–solid reactions mainly between oxides and CO, C and CO₂. The synthesizing powders gradually become finer in form of uniform spherical particles with the formation of cubic phase.     

Magnetisation studies of phase co-existence in Gd1 − xCaxBaCo2O5.5

Magnetic properties of hole doped, oxygen deficient double perovskite compounds, Gd_1 ? xCa_xBaCo₂O_5.5, have been investigated. Ferromagnetic transition temperatures increase and the anti-ferromagnetic transition temperatures decrease with Ca substitution leading to stabilisation of ferromagnetisim for x ≥ 0.05. A detailed study of the ferromagnetic phase indicates the presence of double hysterisis loops for Ca fractions, 0.05 ≤ x ≤ 0.2 in the 50–200 K temperature range, suggestive of the co-existence of two ferromagnetic phases with different co-ercivities. Based on the magnetisation and transport measurements a phase diagram is proposed for Ca doped GdBaCo₂O_5.5.     

Influence of W5+ ions on the optical properties of doped Bi12TiO20

There have been studied single crystals of undoped and doped Bi₁₂TiO₂₀ with two concentrations of W⁵⁺ (2.62 × 10¹⁷ cm⁻³ and 2.62 × 10¹⁸ cm⁻³). There have been obtained absorption spectra in the energy range of 10,482–15,408 cm⁻¹ by classical measurements. There have been determined the cross-section (σ_a) of the impurity absorption and the oscillator strength of d–d transitions. There have been calculated the refractive index of doped crystals and the concentration of Ti³⁺ ions in an undoped sample through an experiment.     

Synthesis of conducting ferromagnetic nanocomposite with improved microwave absorption properties

The present paper reports the synthesis of polyaromatic amine–ferromagnetic composite with nanosize TiO₂ (～70–90 nm) and γ-Fe₂O₃ (～10–15 nm) particles via in situ emulsion polymerization. Magnetic and conductivity studies demonstrate that the conducting ferromagnetic composite possesses saturation magnetization (M_S) value of 26.9 emu g^?1 and conductivity of the order of 0.46 S cm^?1, which are measured by vibrating sample magnetometer and four-probe technique, respectively. It is observed that the presence of the nanosized γ-Fe₂O₃ in the polyaniline–TiO₂ matrix affects the electromagnetic shielding property of the composite. Polyaniline–TiO₂–γ-Fe₂O₃ nanocomposite has shown better shielding effectiveness due to absorption (SE_A ～ 45 dB) than the polyaniline-γ-Fe₂O₃ (SE_A ～ 8.8 dB) and polyaniline–TiO₂ (SE_A ～ 22.4 dB) nanocomposite. The polymer composites were further characterized by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) technique.     

Preparation and characterization of novel magnetic ZrO2/TiO2/Fe3O4 solid superacid

Novel magnetic solid superacids were prepared by introducing TiO₂ and magnetic substrates by chemical co-precipitation method. The prepared materials were characterized by means of XRD, FT-IR, DSC and TEM techniques. The results indicated that the introduction of TiO₂ and magnetic substrates markedly hindered the phase transformation from tetragonal phase (t-ZrO₂) to monoclinic phase (m-ZrO₂) even calcined at 1200 °C. Furthermore, the solid superacids doped with magnetic substrates presented the superparamagnetic property. The morphology of the samples showed lamellar crystals with high purity and uniform size distribution, and the (101) lattice plane (d = 0.29 nm) could be clearly seen in the HRTEM image.     

Room temperature ferromagnetism in Co doped ZnO within an optimal doping level of 5%

We report on the structural, micro-structural and magnetic properties of Zn_1?xCo_xO (0 ≤ x ≤ 0.1) system. Electron probe micro-structural analysis on 5% Co doped ZnO indicates the presence of segregated cobalt oxide which is also confirmed from the Co 2p core level X-ray photoelectron spectrum. The presence of oxygen defects in lower percentage of Co doped ZnO (≤5%) enhances the carrier mediated exchange interaction and thereby enhancing the room-temperature ferromagnetic behaviour. Higher doping percentage of cobalt (>5%) creates weak link between the grains and suppresses the carrier mediated exchange interaction. This is the reason why room temperature ferromagnetism is not observed in 7% and 10% Co doped ZnO.     

Photocatalytic degradation of an azo dye using Bi3.25M0.75Ti3O12 nanowires (M = La,Sm, Nd,and Eu)

Bi_3.25M_0.75Ti₃O₁₂ (BMT, M = La, Sm, Nd, and Eu) nanowires were synthesized through simple hydrothermal route and their structural and photocatalytic properties were investigated. XRD results indicated that these compounds are of layered perovskites structure. In addition, the band gaps of Bi_3.25La_0.75Ti₃O₁₂ (BLT), Bi_3.25Sm_0.75Ti₃O₁₂ (BST), Bi_3.25Nd_0.75Ti₃O₁₂ (BNT), and Bi_3.25Eu_0.75Ti₃O₁₂ (BET) were estimated to be about 2.403, 2.594, 2.525, and 2.335 eV, respectively. Their photocatalytic activities were evaluated by photocatalytic degradation of methyl orange (MO) under visible light irradiation (λ > 420 nm). Bi_3.25M_0.75Ti₃O₁₂ (M = La, Sm, Nd, and Eu) showed markedly higher catalytic activity compared to traditional N doped TiO₂ (N-TiO₂) and pure bismuth titanate (Bi₄Ti₃O₁₂, BIT) for MO photocatalytic degradation under visible light irradiation. The high photocatalytic performance of Bi_3.25M_0.75Ti₃O₁₂ photocatalysts could be attributed to the strong visible light absorption and the recombination restraint of the e^?/h⁺ pairs resulting from doping of rare earth metal ions. Furthermore, BET nanowires exhibited the highest photocatalytic activity.     

Direct formation of new,phase-stable,and photoactive anatase-type Ti1−2XNbXScXO2 solid solution nanoparticles by hydrothermal method

A new anatase phase of photoactive Ti_1?2XNb_XSc_XO₂ (X = 0–0.2) solid solutions was directly formed as nanoparticles from precursor solutions of TiOSO₄, NbCl₅, and Sc(NO₃)₃ under mild hydrothermal conditions at 180 °C for 5 h using the hydrolysis of urea. With the increase of the content of niobium and scandium from X = 0 to 0.2, the lattice parameters a₀ and c₀, the crystallite size, and the optical band gap of anatase gradually increased. Their photocatalytic activity and adsorptivity were evaluated separately by the measurement of the concentration of methylene blue (MB) remained in the solution in the dark or under UV-light irradiation. The anatase-type Ti_1?2XNb_XSc_XO₂ (X = 0.05) showed approximately two times and three times as high photocatalytic activity as those of the hydrothermal anatase-type pure TiO₂ and commercially available reference pure TiO₂ (ST-01), respectively. The anatase phase of Ti_1?2XNb_XSc_XO₂ (X = 0–0.2) existed stably up to 900 °C during heat treatment in air. New rutile-type Ti_1?2XNb_XSc_XO₂ solid solutions are formed through the phase transformation. The starting temperature of anatase-to-rutile phase transformation for Ti_1?2XNb_XSc_XO₂ (X = 0–0.2) solid solutions was delayed but its completing temperature was accelerated.     

Evolution of different structural phases of TiO2 films with oxygen partial pressure and Fe doping and their electrical properties

We have studied the influence of oxygen partial pressure (OPP; 250 mTorr–1 × 10^?5 Torr) and Fe doping (2 and 4 at.%) on structural and electrical properties of TiO₂ thin films on LaAlO₃ substrates. X-ray photoelectron spectroscopy suggests that Fe is not in metal cluster form. It is found that the evolution of the three phases; anatase, rutile and brookite of TiO₂ as well as the magneli phase (Ti_nO_2n?1) strongly depends on the OPP and Fe doping concentration. All the films grown at 250 mTorr show insulating behavior, whereas films grown at 1 × 10^?2 and 1 × 10^?4 Torr reveal high temperature metallic to low temperature semiconducting transition. Interestingly, films deposited at 1 × 10^?5 Torr reveal charge ordering, which is contributed to the magneli phase of TiO₂. The present study suggests that functionality of TiO₂ thin film based devices can be tuned by properly selecting the OPP and dopant concentration.     

Preparation and properties of ce-doped TiO2 photocatalyst

TiO₂ nanoparticles doped with different content of Ce ion were prepared by sol–gel method. The samples were characterized by XRD, XPS, TEM, UV–Vis, and PL, the photocatalytic activity was evaluated by photocatalytic degradation of methylene blue (MB) under the irradiation of fluorescent lamp. The results indicate that Ce ion is incorporated into the lattice of TiO₂, which can restrain the increase of grain size, broaden the absorption region to visible light, and inhibit the recombination of the photo-generated electron and hole pairs. Moreover, the photocatalytic activity of Ce-TiO₂ in MB degradation is evidently enhanced. The MB degradation rate of the sample with Ce:Ti = 0.33% (molar ratio) in 8 h is 90.03%, which is much higher than that of P25 (68.19%).     

Improving 1.54 μm emission by inducting Ti ion in Er3+/Yb3+ codoped phosphate glass ceramic

Er³⁺/Yb³⁺ doped phosphate glasses were prepared by high-temperature melting method. Under 975 nm excitation, the intensity of the visible light in the sample doped with TiO₂ is weaker compared to that of the sample un-doped with TiO₂ However, the intensity of the 1540 nm emission in the sample doped with TiO₂ is stronger than that in the sample un-doped with TiO₂ The sample can efficiently improve the 1540 nm emission by absorbing visible light.     

Effects of ZrO2 addition on phase stability and photocatalytic activity of ZrO2/TiO2 nanoparticles

ZrO₂/TiO₂ nanoparticles with various Zr/Ti ratios (0–0.9) were prepared by a polymer complex solution method (PCSM). The prepared samples were characterized using transmission electron microscopy (TEM), the Brunauer, Emmett & Teller (BET) method, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The ZrO₂/TiO₂ photocatalyst showed a high specific area and small crystal size. The XRD pattern for the Zr/Ti = 0.1 sample indicated that the addition of ZrO₂ stabilized the anatase phase of TiO₂ up to 800 °C. The photocatalytic activity of Zr/Ti = 0.1 sample was higher than that of the TiO₂ sample and commercially available Degussa P25. The high photocatalytic activity can be attributed to stronger adsorption in the visible light region, higher specific area, smaller crystal size and increased surface OH groups.     

Effect of the Ti/Na molar ratio on the acidity and the structure of TiO2 nanostructures: Nanotubes,nanofibers and nanowires

TiO₂ nanotubes were prepared by the hydrothermal treatment of TiO₂ particles with different NaOH concentrations (5, 7, 10 and 12 N) at 140 °C; afterwards, HCl was added until reaching pH 1. Both the crystalline phase and coordination of the TiO₂ nanotubes, composed principally of H₂Ti₃O₇ and H₂Ti₄O₉·2H₂O, were significantly affected by the NaOH rinsing treatment. Likewise, the surface area, pore volume and pore size of the TiO₂ nanotubes changed with the NaOH rinsing treatment. Finally, the NaOH rinsing treatment exerted a notable effect on the generation of Brönsted sites, which is shown by the following sequence: NT7 > NT10 > NT12 > NT5; meanwhile Lewis sites were only present on the NT5 sample.     

A study on the mechanochemical behavior of TiO2–Al–Si system to produce Ti5Si3–Al2O3 nanocomposite

In the present study Ti₅Si₃–Al₂O₃ nanocomposite was synthesized by a displacement reaction between Al and TiO₂ in ball milling of TiO₂, Al and Si powders. The effect of milling time and heat treatment temperatures were also investigated. The structural changes of powder particles during mechanical alloying were investigated by X-ray diffraction (XRD). Morphology and microstructure of powders were characterized by scanning electron microscopy (SEM). It was found that after 10 h of MA, the reaction between Al and TiO₂ initiated in a gradual mode and after about 45 h of milling, the reaction was successfully completed. The final product consisted of Ti₅Si₃ intermetallic compound with a crystallite size of 13 nm and amorphous Al₂O₃. Heat treatment of this structure at 1050 °C led to the crystallization of Al₂O₃ and ordering of Ti₅Si₃. The crystallite size of Ti₅Si₃ and Al₂O₃ after annealing at 1050 °C for 1 h remained in nanometer scale. So the final product appeared to be stable upon annealing.     

Zr doped anatase supported reticulated ceramic foams for photocatalytic water purification

Titanium dioxide films were deposited on macroporous reticulated Al₂O₃ and alumina–mullite foams with pore sizes of 15 ppi (pores per inch). Coatings were prepared from suspensions of precursor powders of Aeroxide^® P25 nanopowder and precipitated TiO₂ by using a dip coating process. The TiO₂ forms films with a thickness of ～2–20 μm. The photocatalytic activity was characterized as the mineralization rate of an aqueous phenol solution under UVA irradiation by the TOC technique. Precipitated TiO₂ films have nearly the same photocatalytic activity as a titania suspension, in which powder aggregates have a size comparable with the thickness of the films. Samples made of Aeroxide^® P25 nanopowder, in which the size of aggregates is ～0.1 μm show higher efficiency of photodecomposition in suspensions with films. The doping of precipitated anatase with Zr(IV) in the atomic ratio Zr/Ti = 0.008 significantly improves the photocatalytic activity of the foam supported titania. Zr doped anatase films show better performance as the films prepared only from Aeroxide^® P25 nanopowder.     

Decolorization of beads-milled TiO2 nanoparticles suspension in an organic solvent

In this paper, a new method is proposed for the decolorization of a yellow-hued suspension of rutile TiO₂ nanoparticles in an organic solvent (diethylene glycol dimethylether). The presence of color has always been undesirable in a suspension of nanoparticles filler used for industrial needs, particularly for optical applications.A colorless suspension was achieved by irradiating well-dispersed TiO₂ nanoparticles in an organic solvent with UV-light (λ = 254 nm) for 5 h. TiO₂ nanoparticles of 1 and 5 wt.% were dispersed using a beads mill method. Trimethoxytrifluor(propyl) silane was used as a dispersant to achieve stability. The effect of the UV-light irradiation on the TiO₂ nanosuspension was investigated by means of a Fourier transform nuclear magnetic resonance analyzer (FT-NMR). The dispersant was partially desorbed due to the interaction of UV light and the TiO₂/dispersant complex. Thus, an enhanced transparency and the absence of color were obtained for well-dispersed TiO₂ nanoparticles in an organic solvent.     

Three-dimensionally ordered macroporous Ti1−xTaxO2+x/2 (x = 0.025, 0.05, and 0.075) nanoparticles: Preparation and enhanced photocatalytic activity

Anatase phase, three-dimensionally ordered macroporous (3 DOM) Ti_1−xTa_xO_{2 + x / 2} (x = 0.025, 0.05, and 0.075) nanoparticles with macropore diameter 290 to 310 nm, wall thickness 50 to 80 nm, and particle size 10 to 12 nm were prepared by combination of the sol–gel chemistry and polystyrene (PS) templating procedure. The products exhibited relatively narrower band gaps and larger BET surface areas than those of the starting solitary 3 DOM metal oxides, and their photocatalytic activities for the degradation of an aqueous 4-nitrophenol remarkably enhanced compared with 3 DOM anatase TiO₂, Ta₂O₅, and Degussa P-25.     

Influence of SrTiO3 modification on dielectric properties of Mg(Zr0.05Ti0.95)O3 ceramics at microwave frequency

The microwave dielectric properties and microstructures were investigated in the (1?x)Mg(Zr_0.05Ti_0.95)O₃–xSrTiO₃ (hereafter referred to as (1?x)MZT–xST) system. The compounds were prepared via the conventional solid-state reaction. Compositions in the (1?x)Mg(Zr_0.05Ti_0.95)O₃–xSrTiO₃ system were designed to compensate the negative temperature coefficient of the resonant frequency of Mg(Zr_0.05Ti_0.95)O₃. The values displayed nonmonotonic mixture-like behavior, because the TiO₂ phase was formed in the MZT composite ceramics with increasing x. A close zero τ_f of 0.2 ppm/°C could be achieved at 0.96MZT–0.04ST with ?_r = 20.8 and Q × f = 257,000 GHz.     

Phase formation and microwave dielectric properties of Pb2+ and Sr2+ doped La4Ti9O24 ceramics

Phase formation and microwave dielectric properties of the Pb²⁺ and Sr²⁺ doped La₄Ti₉O₂₄ ceramics were investigated. Using electron diffraction and Rietveld analysis of the X-ray powder diffraction patterns, we show that the increase in the concentration of Pb²⁺ and Sr²⁺ doping results in the structural transition from La₄Ti₉O₂₄ to a La_2/3TiO₃-type phase (Ibmm, No. 74). A change in the crystalline phase considerably affects the microwave dielectric properties, increasing the ɛ_r from 37 to 130, reducing Q × f from 25,000 to 5500, and increasing temperature coefficient of the resonant frequency (TCF) from 15 to 300 ppm/°C.     

Influence of Ti3SiC2 content on tribological properties of NiAl matrix self-lubricating composites

NiAl matrix self-lubricating composites (NMCs) with various contents of Ti₃SiC₂ were fabricated by in situ technique using spark plasma sintering. The effects of Ti₃SiC₂ content on tribological properties of NMC were investigated. The results showed that NMC were composed of the matrix phase of NiAl alloy, enhanced phase of TiC and lubricating phases of Ti₃SiC₂ and C. NMC with 10 wt.% Ti₃SiC₂ exhibited low friction coefficient of 0.60 and wear rate of 5.45 × 10⁻⁵ mm³ (N m)⁻¹ at the condition of 10 N–0.234 m/s at room temperature. The optimum content of Ti₃SiC₂ was 10 wt.%. The excellent tribological performance of NMC could be attributed to the balance between strength and lubricity, as well as synergetic effect of enhanced phase and lubricating phases. The wear mechanisms changed with the increasing of the doped content of Ti₃SiC₂.