Investigation of the nitrogen-nickel-titanium system: The isothermal section at 900 °C

Phase relations in the ternary system N-Ni-Ti have been established experimentally for the 900 °C isothermal section assisted by thermodynamic modeling. Phase equilibria are characterized by an appreciable amount of up to ≅11 at. % N dissolved in the octahedral interstices of the crystal structure of Ti₂Ni. Two-phase equilibria are formed at 900 °C among the pairs Ti₂N + Ti₂NiN_x, TiN_1-x + Ti₂NiN_x, TiN_1-x + TiNi_1-x, and TiN_1-x + Ni(Ti)_x. The investigation is based on X-ray powder diffraction, metallography, scanning electron microscopy, and electron probe microanalysis techniques on about 50 alloys, which were prepared by arc melting or high-frequency levitation melting of appropriate blends of Ti,Ni-powders with TiN used to introduce nitrogen. Key experiments related to the N solubility in the Ti₂Ni phase have been triggered by an interactively performed thermodynamic modeling. The experimental results are in fine agreement with the thermodynamic calculation.     

Solid-state phase equilibria in the Titanium-Aluminum-Nitrogen system

The 1273K isothermal section of the Ti-Al-N phase diagram was studied using modern methods of physical and chemical analyses. The data obtained by various techniques are in good agreement and in harmony with the results of thermodynamic calculations. It has been reliably established that AIN can coexist with TiN_1−x , Ti₂AIN, and TiAl₃; the ternary nitride Ti₂AIN can be in equilibrium with TiAl₃, AIN, TiAl₂, TiAl, TiN_1−x , and Ti₃AIN; the solid solution based on α(Ti) coexists with Ti₃Al, Ti₃AIN, TiN_1−x , and Ti₂N. Literature data on phase equilibria in the Ti-Al-N system were analyzed, and a 1273 K isothermal section of the phase diagram has been suggested.     

质子酸处理二维碳化钛/碳纳米管复合材料的电磁屏蔽性能与机械性能

通过质子酸胶体处理,实现了碳化钛Ti₃C₂T_x的制备。此外,使用单壁碳纳米管(SWCNT)作为增强成分,提升了质子酸处理碳化钛(H-MXene)的机械性能——不仅保持了电磁屏蔽性能,而且将拉伸性能提升了近400%。结果表明,H-MXene和碳纳米管具有作为高机械性能电磁(EMI)屏蔽复合材料的潜力。     

X-ray diffraction study of Ba0.985Na0.015Ti0.985Nb0.015O3, Ba0.6Na0.4Ti0.6Nb0.4O3 and Ba0.3Na0.7Ti0.3Nb0.7O3 compositions

The Ba_0.985Na_0.015Ti_0.985Nb_0.015O₃, Ba_0.6Na_0.4Ti_0.6Nb_0.4O₃ and Ba_0.3Na_0.7Ti_0.3Nb_0.7O₃ compositions of the (1 − x) BaTiO₃–xNaNbO₃ (BTNNx) system have been studied by X-ray diffraction and by measurements of dielectric properties. The specimens with composition BTNN (x = 0.015, 0.40 and 0.70) have been refined by the JANA program from X-ray powder diffraction data. Ceramic samples with composition (1 − x) BaTiO₃ + xNaNbO₃ (where x = 0.015, 0.40 and 0.70) were prepared by calcinations from appropriate mixture of BaCO₃, TiO₂, Na₂CO₃ and Nb₂O₅. The calcined powder was sintered at temperature range 1200–1400 °C. As the composition x increased from 0.015 (and 0.70), the ferroelectric ceramics (x = 0.015, FE) with tetragonal phase changed to the ferroelectric relaxors (RFE, x = 0.40). RFE ceramics showed a peculiar diffuse phase transition and dielectric relaxation at the low temperature (down to 180 K) due to a frustration between RFE and FE state. These ceramics present the classical ferroelectric character when 0 ≤ x < 0.075 and 0.55 < x ≤ 1 and relaxor character when 0.075 ≤ x ≤ 0.55.     

Synthesis of HCP, FCC and BCC structure alloys in the Mg–Ti binary system by means of ball milling

Mg_xTi_100−x (35 ≤ x ≤ 80) alloys with hexagonal close packed (HCP), face centered cubic (FCC) and body centered cubic (BCC) structures were successfully synthesized by means of ball milling. Mg_xTi_100−x alloys with a BCC structure at x = 35 and 50 and with a HCP structure at x = 80 were synthesized by milling of Mg and Ti powder using stainless steel milling balls and pots. At x = 65, the BCC and HCP phases were synthesized. Mg_xTi_100−x alloys with a FCC structure were synthesized at x = 35 and 50 by milling using zirconia milling balls and pots. The FCC and HCP phases were synthesized at x = 65 and 80 using zirconia milling balls and pots. The crystal structure of Mg_xTi_100−x alloys synthesized by the ball milling method depended on the materials of milling balls and pots. That indicates that milling products are determined by the dynamic energy given by the milling setup. The lattice parameters of Mg_xTi_100−x in the HCP, FCC and BCC phases increased with increase of the Mg content, x.     

Structure and magnetic properties of Gd3(Fe1−xTix)29 (x=0.011–0.034)

Single-phase compounds Gd₃(Fe_1−xTi_x)₂₉ (x=0.0110.034) have been synthesized. Gd₃(Fe_1−xTi_x)₂₉ crystallises in a monoclinic lattice with space group P2₁/c, and the crystal structure is refined by the Rietveld technique based on X-ray powder diffraction data. Thermomagnetic analysis indicates that the Curie temperature of the compounds ranges from 517 K to 538 K. The saturation magnetizations of the Gd₃(Fe_1−xTi_x)₂₉ (x=0.011, 0.022, 0.034) at 1.5 K are 103.6, 102.0 and 94.3 Am²/kg, and the anisotropy fields at 1.5 K are 6.0, 6.2 and 6.4T, respectively.     

On Synthesis and Magnetic Properties of Nd(Fe, Mo, Ti)12Zx (Z=N, H)

NdFe_10+xMo_2−2xTi_x compounds with 0≤x≤1.0 have been prepared by using the reduction–diffusion process with superfine precursors as starting materials. With increasing Ti-content, the intrinsic magnetic properties, such as the Curie temperature, saturation magnetization and magnetocrystalline field, are improved. The interstitial compounds NdFe_10+xMo_2−2xTi_xZ_y (Z=N, H) were obtained and exhibit significant enhancement of the intrinsic magnetic properties upon nitrogenation.     

Thermodynamics of titanium,nitrogen, and oxygen in liquid alloy steels

The thermodynamics of Ti, N, and O in liquid iron was studied in order to establish a database to predict the TiN and TiO_x formation in liquid steels as a function of temperature. The interaction parameters between Ti, N, and O in liquid iron and the equilibrium constants for the formation of TiN, Ti₂O₃, and Ti₃O₅ in liquid iron were determined as a function of temperature. Formerly Graduate Student, Department of Metallurgical and Materials Engineering, Hanyang University, Gyeonggi, 426–791, Korea.     

Combustion synthesis of Ti(C, N)–TiB2 from a Ti–C–BN system

In this paper, a simple way of fabricating TiC_xN_y–TiB₂ ceramics through the combustion reaction of Ti, C and BN powder mixtures in an argon atmosphere is reported with an emphasis on the effects of the C/(C + N) ratio on the SHS reaction behaviors and mechanism. With the increase in the C/(C + N) ratio, the combustion temperature shows a zigzag variation behavior; the combustion wave velocity displays a similar variation tendency as did in the combustion temperature while the ignition delay time increases progressively. XRD results confirmed that TiC_xN_y–TiB₂ could form in all the samples. Microstructural observations revealed that both TiC_xN_y and TiB₂ grains had fine sizes of less than 1 μm in the products when the C/(C + N) ratio was lower than 0.5. Based on the characterization of quenched samples, the formation mechanism of the titanium carbonitride is proposed. Namely, the formations of TiN_0.3 and TiN are followed by the incorporation of C in TiN_x to form the titanium carbonitride solid solution.     

Hydrophilicity and photocatalysis of Ti1−xVxO2 films prepared by sol-gel method

Ti_1−xV_xO₂ films were prepared by sol-gel dip-coating method. To study the effects of vanadium incorporation on the self-cleaning properties of TiO₂ film, the crystallization behavior and surface morphology of Ti_1−xV_xO₂ films were investigated by an X-ray diffraction (XRD) analysis and an Atomic force microscope (AFM) respectively. The band-gap E_g of Ti_1−xV_xO₂ was determined by optical transmission spectra. Hydrophilicity and photocatalysis of Ti_1−xV_xO₂ films were characterized. The results showed that Ti_1−xV_xO₂ films had super-hydrophilicity and greater photocatalysis under day light illumination when x = 0.1-0.2. An optimal photocatalytic activity was obtained when x = 0.15. Moreover, Ti_0.85V_0.15O₂ films were proven to have excellent photocatalysis and hydrophilicity in visible region simultaneously, which made the application of Ti_0.85V_0.15O₂ film as self-cleaning and anti-fogging material practical under everyday condition.     

Laser chemical vapor deposition of titanium nitride films with tetrakis (diethylamido) titanium and ammonia system

Wide-area and thick titanium nitride (TiN_x) films were prepared on Al₂O₃ substrate by laser chemical vapor deposition (LCVD) using tetrakis (diethylamido) titanium (TDEAT) and ammonia (NH₃) as source materials. Effects of laser power (P_L) and pre-heating temperature (T_pre) on the composition, microstructure and deposition rate of TiN_x films were investigated. (111) and (200) oriented TiN_x films in a single phase were obtained. The lattice parameter and N to Ti ratio of the TiN_x films slightly increased with increasing P_L and was close to stoichiometric at P_L > 150 W. TiN_x films had a cauliflower-like surface and columnar cross section. The deposition rate of TiN_x films increased from 42 to 90 µm/h at a depositing area of 10 mm by 10 mm substrate, decreasing with increasing P_L and T_pre. The highest volume deposition rate of TiN_x films was about 10² to 10⁵ times greater than those of previous LCVD using Nd:YAG laser, argon ion laser and excimer laser.     

Self-propagating high-temperature synthesis of TiCxNy–TiB2 ceramics from a Ti–B4C–BN system

An experimental study on direct formation of TiC_xN_y–TiB₂ ceramics by self-propagating high-temperature synthesis (SHS) was conducted using a Ti–B₄C–BN system. The effects of the C/(C + N) ratio on the combustion behavior and reaction products were investigated. Experimental characterizations of quenched samples show that the combustion reaction started with the formation of highly substoichiometric TiN_y and TiB due to the solid-state reaction between Ti and BN; and then the TiN_y precursor and TiB dissolved back into the titanium melt, forming the Ti–B–N liquid, which in turn transformed to the Ti–B–N–C liquid due to the dissolution of the carbon atoms diffused away from B₄C. Finally, the TiC_xN_y and TiB₂ particles are formed from the melt through the dissolution-precipitation mechanism.     

Combustion synthesis of Ti3Si1−xAlxC2 solid solutions from TiC-, SiC-, and Al4C3-containing powder compacts

Preparation of the Ti₃Si_1−xAl_xC₂ solid solution with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS) using TiC-, SiC-, and Al₄C₃-containing powder compacts. Due to the variation of reaction exothermicity with sample stoichiometry, the combustion temperature and reaction front velocity decreased with increasing Al content of Ti₃Si_1−xAl_xC₂ for the TiC- and Al₄C₃-added samples, but increased for the samples with SiC. In contrast to the formation of Ti₃(Si,Al)C₂ as the dominant phase for the TiC- and SiC-added samples, TiC was identified as the major constituent in the final products of samples adopting Al₄C₃. In addition, the evolution of Ti₃(Si,Al)C₂ was improved by increasing the Al content of the TiC- and SiC-added powder compacts, but deteriorated considerably upon the increase of Al₄C₃ in the Al₄C₃-containing sample.     

Preparation and photocatalytic activity of nano-sized nickel molybdate (NiMoO4) doped bismuth titanate (Bi2Ti4O11) (NMBT) composite

Various compositions of nano-sized (NiMoO₄)_x-doped Bi₂Ti₄O₁₁ (x = 0.01, 0.05, 0.1) composites have been prepared by chemical solution decomposition (CSD) method using triethanolamine (TEA) as complexing agent. Ni(II) is one of reactive species on the catalyst surface and Mo(VI) ion helps to compensate the charge of the lattice. The photocatalysts based on the above compositions have been tested for photobleaching of methyl orange (MO) solution under Hg-lamp. The prepared nanopowders are characterized by XRD, EDAX, UV–vis spectra, specific surface area (BET), zeta potential, ESR and HRTEM analyses. The average particle size of nickel molybdate-doped bismuth titanate lies around 30 ± 2 nm measured from TEM. Result shows nickel molybdate-doped bismuth titanate (NiMoO₄)_x(Bi₂Ti₄O₁₁)_1−x (NM_xBT_1−x; x = 0.01) composite is found to be more photoactive compared all the compositions studied except degussa P25 titania.     

Oxidation of Ti3SiC2 between 900 and 1200 °C in Air

Ti₃SiC₂ materials were synthesized by hot pressing using a new starting-material system consisting of a TiC_x(x=0.6)/Si powder mixture. The oxidation of Ti₃SiC₂ at temperatures between 900 and 1200 °C in air for up to 100 h resulted in the formation of an outer TiO₂ layer, an intermediate SiO₂-rich layer and an inner (TiO₂ + SiO₂) mixed layer. During oxidation, Ti diffused outwards to form the outer TiO₂ layer, and oxygen transported inwards to form the inner (TiO₂ + SiO₂) mixed layer. At the same time, the carbon in Ti₃SiC₂ escaped into the air. Below the scale, there was a narrow oxygen-affected zone, The oxidation at the scale-matrix interface proceeded by the disintegration of the lamellar Ti₃SiC₂ grains to form crystallites with a size of a few tens of nanometers containing oxygen. The detailed scale characteristics and oxidation mechanism are described.     

The Heusler Phase Ti25(Fe50 − x Ni x )Al25 (0 ≤ x ≤ 50); Structure and Constitution

Alloys with composition Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50) were investigated employing electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). For TiFe₂Al, in situ neutron powder diffraction (ND) was used for the inspection of phase constitution covering the temperature range from 27 °C (300 K) to 1277 °C (1550 K). Combined Rietveld refinement of ND and XPD data for TiFe₂Al revealed that Fe atoms occupy the 8c site in space group Ti with a small amount of Al sharing the 4a site, and the remaining Ti and Al atoms adopting the 4b site. This structural model was successfully applied in the refinement of all alloys Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50). Partial atom order exists on the Fe-rich side while complete order is observed for the Ni-rich side. Profiles recorded by in situ neutron powder diffraction for TiFe₂Al in the range of investigated temperatures show two phases, namely Heusler phase and MgZn₂-type Laves phase. Diffraction peaks from the Heusler phase dominate the profiles at lower temperatures but at higher temperatures the MgZn₂-type Laves phase is the main phase. No CsCl-type phase was found in the alloy in the investigated temperature range. The thermal expansion coefficient of TiFe₂Al is 1.4552 × 10⁻⁵ K⁻¹.     

Effect of SI Content on the Oxidation Resistance of Ti3Al1-x Si x C2 (x⩽ 0.25) Solid Solutions at 1000–1400°C in Air

The oxidation behavior of Ti₃Al_1-x Si _x C₂ (x ⩽ 0.25) solid solutions was investigated in flowing air at 1000–1400°C for up to 20 hrs. Similar to Ti₃AlC₂, Ti₃Al_1-x Si _x C₂ (x⩽ 0.15) solid solutions display excellent oxidation resistance at all temperatures because of the formation of the continuous α-Al₂O₃ protective layers. However, Al₂(SiO₄)O formed during oxidation of Ti₃Al_1-x Si _x C₂ (x=0.2 and 0.25) solid solutions at and above 1100°C, which is believed to be responsible for the deterioration of oxidation resistance of Ti₃Al_0.75Si_0.25C₂ at 1300°C. Additionally, Ti₅Si₃ was also found in the oxidized samples. This implies that Ti₅Si₃ precipitated from Ti₃Al_1-x Si _x C₂ solid solutions during oxidation. But it has been proven that Ti₅Si₃ has little effect on the oxidation resistance of the material, which is attributed to an interstitial carbon effect.     

原位生成TiCx增强Ni合金复合材料的制备及力学性能研究

以Ti₃AlC₂和Ni合金粉为原料,采用原位热压烧结法制备了TiC_x/Ni合金复合材料。高温下Ni合金引起Ti₃AlC₂分解形成TiC_x,Al原子和少部分Ti原子从基体中脱离,并与Ni合金发生反应。添加20Vol%Ti₃AlC₂和40Vol%Ti₃AlC₂时,TiC_x中x的值分别为0.625和0.715。利用XRD、SEM和 EDS等表征方法对复合材料进行物相分析以及微观结构分析。研究表明,原位生成的TiC_x与Ni合金基体结合牢固,所制备的复合材料具有优异的力学性能,添加20%Ti₃AlC₂和40%Ti₃AlC₂时,复合材料的压缩强度分别达到了2.2 GPa和2.09 GPa,相应的压缩断裂应变分别为9.6%和8.5%。     

Preparation of low-oxygen Ti powder from TiO2 through combining self-propagating high temperature synthesis and electrodeoxidation

An effective method was reported to prepare low-oxygen Ti powder, which included two experimental steps: the fast conversion of TiO₂ to TiO_x<1 powder by self-propagating high-temperature synthesis (SHS) process and the generation of low-oxygen Ti powder by electrodeoxidizing TiO_x<1 powder at the cathode in molten CaCl₂. The key intermediate steps were analyzed by XRD, SEM and electrochemical testing techniques. The results demonstrated that TiO_x<1 powder (TiO_0.325 and TiO_0.97) was generated after acid leaching MgO in SHS products with TiO₂/Mg molar ratio of 1:2, and the TiO_x<1 powder with 16.3 wt.% oxygen could be transformed into pure titanium powder with 0.121 wt.% oxygen by electrodeoxidation at a constant potential of -3.3 V for 10 h. The electrodeoxidation of TiO_x<1 powder in CaCl₂ molten salt follows the step-by-step deoxidation mode, and the lattice of TiO_x<1 powder after electrodeoxidation shrinks.     

Influence of B site substituent Ti on the structure and thermophysical properties of A2B2O7-type pyrochlore Gd2Zr2O7

Since the structural integrity of A₂B₂O₇-type pyrochlores relies mostly on the interconnecting BO₆ octahedra, Ti⁴⁺ was selected to partially substitute Zr⁴⁺ in Gd₂Zr₂O₇ in order to distort the pyrochlore structure in order to improve the material’s thermophysical properties for potential use as high-temperature thermal insulation. As evidenced by X-ray diffraction and Raman spectroscopy studies, incorporation of Ti⁴⁺ simultaneously leads to long-range ordering of the pyrochlore structure as well as local lattice distortion. These two effects have been shown to be competitive in determining the crystal energy of the Gd₂(Zr_1−xTi_x)₂O₇ series and result in a minimum value of the Young’s modulus at x = 0.3 and a maximum value of the coefficient of thermal expansion at x = 0.2. At lower temperatures, the thermal conductivity of Gd₂Zr₂O₇ was significantly reduced by Ti⁴⁺ doping, and its composition dependence was accurately modeled by taking into account the phonon scattering by mass and strain fluctuations at the B site.