Synthesis of carbon nitride powder by selective etching of TiC0.3N0.7 in chlorine-containing atmosphere at moderate temperature

We reported the synthesis of carbon nitride powder by extracting titanium from single inorganic precursor TiC_0.3N_0.7 in chlorine-containing atmosphere at ambient pressure and temperature not exceeding 500 °C. The TiC_0.3N_0.7 crystalline structure acted as a template, supplying active carbon and nitrogen atoms for carbon nitride when it was destroyed in chlorination. X-ray diffraction data showed that the obtained carbon nitride powders were amorphous, which was in good agreement with transmission electron microscope analysis. The composition and structure of carbon nitride powders were analyzed by employing Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Results indicated that disorder structure was most likely for the carbon nitride powders and the N content depended greatly on the chlorination temperature. Thermal analysis in flowing N₂ indicated that the mass loss started from 300 °C and the complete decomposition occurred at around 650 °C, confirming the low thermal stability of the carbon nitride material.     

Microstructure and mechanical properties of titanium carbonitride whisker reinforced β-sialon matrix composites

The microstructure, hardness, fracture toughness and thermal shock resistance were investigated for 15 vol.% TiC_0.3N_0.7 whisker reinforced β-sialon (Si_6−zAl_zO₂N_8−z with z=0.6) composites with additions of three different volume fractions 2, 5 and 20 vol.%, of an yttrium-containing glass oxynitride phase. The composites were prepared by hot pressing at 1750°C for 90 min under a uniaxial pressure of 30 MPa in nitrogen atmosphere. The TiC_0.3N_0.7 whiskers were found to survive without deteriorating in morphology or reacting with the β-sialon matrix and/or the glass phase. The TiC_0.3N_0.7 whiskers had no obvious influence on the matrix microstructure, but their presence improved both the hardness and the fracture toughness of the composites. The highest hardness was obtained for the whisker composite with 2 vol.% glass phase (H_v=18.6 GPa). The fracture toughness and thermal shock resistance improved with increasing glass content. The whisker reinforced composite containing 20 vol.% glass showed the highest fracture toughness (K_1C=6.8 MPa m^1/2). No unstable crack extension occurred during the thermal shock test of the obtained composites in the temperature interval 90-700°C, but above 700°C severe oxidation of the whiskers precludes further evaluation of thermal shock properties by the indentation-quench method applied.     

A simple route to prepare nanocrystalline titanium carbonitride

Nanocrystalline titanium carbonitride, TiC_0.7N_0.3, has been synthesized directly by a simple reaction route of TiCl₄ and C₃N₃C1₃ using sodium as the reductant at 600°C. The composition of the powders has been investigated by X-ray powder diffraction. Transmission electron microscopy image reveals that the average size of the obtained particles is about 30 nm.     

Synthesis,characterization and formaldehyde gas sensitivity of La0.7Sr0.3FeO3 nanoparticles assembled nanowires

La_0.7Sr_0.3FeO₃ nanoparticles assembled nanowires were synthesized by a hydrothermal method assisted with cetyltrimethylammonium bromide (CTAB). The hydrothermal temperature was 180 °C and the annealed temperature was 700 °C. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology, composition and structural properties of the materials. The results showed that the La_0.7Sr_0.3FeO₃ nanoparticles assembled nanowires had a high aspect ratio (the largest aspect ratio >100); the size of the nanoparticles was about 20 nm and the diameter of the nanowires was about 100–150 nm. The growth mechanism of La_0.7Sr_0.3FeO₃ nanowires was discussed. Gas sensors were fabricated by using La_0.7Sr_0.3FeO₃ nanowires. Formaldehyde gas sensing properties were carried out in the concentration range of 0.1–100 ppm at the optimum operating temperature of 280 °C. The response and recovery times to 20 ppm formaldehyde of the sensor were 110 s and 50 s, respectively. The gas sensing mechanism of La_0.7Sr_0.3FeO₃ nanowires was investigated.     

Structure and mechanical properties of low temperature magnetron sputtered nanocrystalline (nc-)Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings

This paper reports on the structure and mechanical properties of ~ 2 μm thick nanocomposite (nc-) Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings deposited on 100Cr6 steel substrates, using low temperature (~ 200 °C) DC reactive magnetron sputtering. The carbon content was varied with acetylene partial pressure in order to obtain single layer coatings with different a-C:H carbon phase fractions. The nanocrystalline Ti(N,C) phase is approximately stoichiometric for all coatings and the a-C:H phase fraction increases from 31 to 47 at.% as the coatings stoichiometry changed from TiC_1.34 N_0.51 to TiC_2.48 N_0.48, respectively. TiC_1.34 N_0.51 coatings showed the highest nanoindentation hardness (H) of ~ 14 GPa and a modulus (E_r) of ~ 144 GPa; H reduced to < 6 GPa and E_r to < 70 GPa for TiC_2.48 N_0.48 coatings. nc-Ti(N,C)/a-C:H coatings are promising candidates for applications where better matching of the modulus between a relatively low modulus substrate, hard loading support layer and low modulus-high H/E ratio top layer is required.     

Preparation and characterization of nano-sized Sr0.7Ca0.3TiO3 crystallines by low temperature aqueous synthesis method

Nano-sized calcium strontium titanate (Sr_0.7Ca_0.3TiO₃) particles were prepared by low temperature aqueous synthesis method at temperature as low as 90 °C and under ambient pressure. To improve the morphology and crystallinity of the particles, the hydrothermal treatment was used. The lattice structure, particle size, particle morphology, and hydroxyl defects of Sr_0.7Ca_0.3TiO₃ particles were investigated by using XRD, TEM, FE-SEM, TG and FT-IR measurements. The as-prepared particles with size about 100 nm were single cubic phase crystallines which consist of aggregates of small rounded nanocrystals about 10 nm in diameter. However, in as-prepared crystallines, a hydroxyl group was detected as a lattice defect. After the hydrothermal treatment, the hydroxyl groups in Sr_0.7Ca_0.3TiO₃ nanoparticles were partially released from the perovskite lattice. The morphology and crystallinity of the hydrothermally treated particles were observably improved.     

Behavior of N atoms after thermal nitridation of Si1 − xGex surface

Behavior of N atoms after thermal nitridation of Si_1 − xGe_x (100) surface in NH₃ atmosphere at 400 °C was investigated. X-ray photoelectron spectroscopy (XPS) results show that N atomic amount after nitridation tends to increase with increasing Ge fraction, and amount of N atoms bonded with Ge atoms decreases by heat treatment in H₂ at 400 °C. For nitrided Si_0.3Ge_0.7(100), the bonding between N and Si atoms forms Si₃N₄ structure whose amount is larger than that for nitrided Si(100). Angle-resolved XPS measurements show that there are N atoms not only at the outermost surface but also beneath surface especially in a deeper region around a few atomic layers for the nitrided Si(100), Si_0.3Ge_0.7(100) and Ge(100). From these results, it is suggested that penetration of N atoms through around a few atomic layers for Si, Si_0.3Ge_0.7 and Ge occurs during nitridation, and the N atoms for the nitrided Si_0.3Ge_0.7(100) dominantly form a Si₃N₄ structure which stably remains even during heat treatment in H₂ at 400 °C.     

Symmetry breaking and electrical conductivity of La0.7Sr0.3Cr0.4Mn0.6O3−δ perovskite as SOFC anode material

This work is focused on nanocrystalline solid oxide fuel cell synthesis and characterization (SOFC) anodes of La_0.7Sr_0.3Cr_0.4Mn_0.6O_3−δ (perovskite-type) with Nickel. Perovskite-type oxide chemical reactivity, nucleation kinetics and phase composition related with La_0.7Sr_0.3Cr_0.4Mn_0.6O_3−δ–NiO to La_0.7Sr_0.3Cr_0.4Mn_0.6O_3−δ–Ni transformation have been analyzed. SOFC anode powders were obtained by sol–gel synthesis, using polyvinyl alcohol as an organic precursor to get a porous cermet electrode after sintering at 1365 °C and oxide reduction by hydrogen at 800 °C/1050 °C for 8 h in a horizontal tubular reactor furnace under 10% H₂/N₂ atmosphere. Composite powders were compressed into 10-mm diameter discs with 25–75 wt% Ni.     

Effect of plasma nitriding on electrodeposited Ni–Al composite coating

In this study plasma nitriding is applied on nickel–aluminum composite coating, deposited on steel substrate. Ni–Al composite layers were fabricated by electro-deposition process in Watt’s bath containing Al particles. Electrodeposited specimens were subjected to plasma atmosphere comprising of N₂–20% H₂, at 500 °C, for 5 h. The surface morphology investigated, using a scanning electron microscope (SEM) and the surface roughness was measured by use of contact method. Chemical composition was analyzed by X-ray fluorescence spectroscopy and formation of AlN phase was confirmed by X-ray diffraction. The corrosion resistance of composite coatings was measured by potentiodynamic polarization in 3.5% NaCl solution. The obtained results show that plasma nitriding process leads to an increase in microhardness and corrosion resistance, simultaneously.     

Preparation and characterization of Y3Al5O12 (YAG) nano-powder by co-precipitation method

YAG precursor was synthesized by a co-precipitation method from a mixed solution of aluminum and yttrium nitrates with aqueous ammonia as the precipitator. The structure, phase evolution and morphology of YAG precursor and the sintered powders were studied by means of IR, TG/DTA, XRD, TEM methods. It was found the precursor with approximate composition of Al(OH)₃·0.3[Y₂(OH)₅·(NO₃)₂·2H₂O] directly transformed to pure-YAG phase at 800 °C and no intermediate phases were detected. YAG nanocrystalline powders from sintering the precursor at different temperatures were less-aggregated and the diameters of the grains were about 40-100 nm. BET surface area of the particles decreased with increase of calcination temperature and the powder sintered at 800 °C can be used for fabrication of transparent YAG ceramics.     

TiCxNy and TiCx-TiN films obtained by CVD in an ultrasonic field

TiC _x N _y mono- and TiC_x-TiN double-layer films with a thickness of 30 to 100 m were prepared on a carbon steel (C: 0.6 to 0.7%) substrate by CVD in an ultrasonic field (ultrasound frequency: 19kHz; power: 10 to 20Wcm^–2). The moderate deposition conditions for obtaining an adherent and thick film of TiC _x N _y were: substrate temperature: 1050° C; H₂, N₂, TiCl₄ and CH₄ flow rates: 6.2, 4.0, 0.9 and 0.26 to 2.0 ml sec^–1, respectively. The growth rate, grain size and degree of 2 2 0 preferred orientation were found to decrease with increase in CH₄ concentration. TiC _x N _y film on carbon steel had a Vickers microhardness of 1800 to 2600 and an adhesion strength to the substrate of more than 120 kg cm^–2. A TiC _x -TiN (x0.5) double-layer film was obtained at 1050° C by a controlled alternative deposition of TiC _x or TiN. Quasiepitaxial growth of crystallites in the double layers was found to prevail in both coatings of TiC _x (220)/TiN (220)/steel and TiN (200)/TiC_x (200)/steel.     

A nanometre-sized porous phase in iron-carbon-boron system

A porous phase is detected in a Fe-0.28 wt.%C-0.1 wt.%B alloy. The porous phase is mainly located at the grain boundary region and the pore size ranges from about 10 nm to 500 nm. The chemical composition of the porous phase is very close to Fe₃(B_0.7C_0.3) with an orthorhombic lattice. The result shows an opportunity to produce bulk steel matrix composites with a porous second phase.     

Deposition and characterization of BN/Si(0 0 1) using tris(dimethylamino)borane

Boron nitride thin films could be deposited on Si(0 0 1) by chemical vapor deposition (CVD) at atmospheric pressure using a single source precursor. IR absorption spectra of films deposited between 750 and 1000°C using B[N(CH₃)₂]₃ (tris(dimethylamino)borane, TDMAB) as the boron and nitrogen source showed a peak absorption at ∼1360 cm⁻¹ characteristic of the in-plane vibrational mode seen in h-BN. It was noted that the mode at 800 cm⁻¹ is very weak. The observed growth rate varied exponentially with temperature in the range 850-900°C. Ellipsometry measurements were used to investigate the thickness and optical constant of the films. The refractive index, slightly lower than the bulk material, is close to 1.65-1.7 depending on the surface morphology of the films. The surface morphology of thin layers has been observed by atomic force microscopy with an increase of the surface roughness from 0.3 to 3.5 nm as the growth temperature increases from 800 to 950°C.     

Preparation and electrical behavior study of the ceramic interconnect La0.7Ca0.3CrO3−δ with CeO2-based electrolyte Ce0.8Sm0.2O1.9

Based on the conventional interconnect La_0.7Ca_0.3CrO_3−δ, a novel ceramic interconnect for intermediate temperature solid oxide fuel cells was developed. In the air, the electrical conductivities of La_0.7Ca_0.3CrO_3−δ + 5%Ce_0.8Sm_0.2O_1.9 at 600, 700 and 800 °C were 96.7, 146.3 and 687.8 S cm⁻¹, respectively, which increased significantly as compared with La_0.7Ca_0.3CrO_3−δ under the same conditions. Similarly, in pure hydrogen, La_0.7Ca_0.3CrO_3−δ + 3%Ce_0.8Sm_0.2O_1.9 possessed the maximal electrical conductivities which were 4.2, 5.3 and 7.1 S cm⁻¹, respectively at 600, 700 and 800 °C. The crystal structures of La_0.7Ca_0.3CrO_3−δ, La_0.7Ca_0.3CrO_3−δ + 5%Ce_0.8Sm_0.2O_1.9 and La_0.7Ca_0.3CrO_3−δ + 10%Ce_0.8Sm_0.2O_1.9 were single phase with hexagonal symmetry, cubic phase plus some doped ceria impurity and orthorhombic phase plus some doped ceria impurity, respectively. The difference between the crystal structures may account for the difference between the electrical conductivities. The electrical conductivities and sinterability of La_0.7Ca_0.3CrO_3−δ were increased by introducing Ce_0.8Sm_0.2O_1.9, whereas the other properties were not influenced.     

Preparation of titanium carbonitride nanoparticles from a novel refluxing-derived precursor

Titanium carbonitride (TiC_xN_1 − x) nanoparticles were prepared from a novel refluxing-derived precursor. The organic/inorganic hybrid precursor was prepared by two-stage refluxing method using hydrous TiO₂ as titania source and n-Dodecane as carbon source. The precursor was heat-treated to 1350 °C in flowing nitrogen to get TiC_xN_1 − x nanoparticles. Electron microscopy photographs showed the particle size ranged from 20 to 60 nm. X-ray powder diffraction pattern indicated that the product was face-centered cubic TiC_xN_1 − x with a lattice constant a = 4.2872 Å and average crystallite sizes of 33.4 nm. Long time refluxing results in Alkane dehydrogenation and the formation of coke occur and promotes the coke to large scale impinge on TiO₂ nanoparticles as carbon source in the carbothermal reduction-nitridation reaction.     

Synthesis and performance of LiMn0.7Fe0.3PO4 cathode material for lithium ion batteries

Pure and carbon-containing olivine LiMn_0.7Fe_0.3O₄ were synthesized at 600 °C by the method of solid-state reaction. Structure, surface morphology and charge/discharge performance of LiMn_0.7Fe_0.3O₄ were characterized by X-ray diffraction, scanning electron microscopy, and electrochemical measurement, respectively. The prepared materials with and without carbon both show the single olivine structure. The morphologies of primary particles are greatly affected by the addition of carbon. Large particles (500-1000 nm) and densely sintered blocks were observed in pure LiMn_0.7Fe_0.3PO₄, which made the insertion and extraction of lithium ions difficult. Battery made from this sample can not charge and discharge effectively. The carbon-containing LiMn_0.7Fe_0.3PO₄ has a small particle size (100-200 nm) and a regular appearance. This material demonstrates high reversible capacity of about 120 mAh g⁻¹, perfect cycling performance, and excellent rate capability. It is obvious that the addition of carbon plays an important role in restricting the particle size of the material, which helps to prepare LiMn_0.7Fe_0.3PO₄ with excellent electrochemical performance. The electrochemical reaction resistance is much lower in the partly discharged state than in the fully charged or fully discharged state by the measurement of ac impedance for carbon-containing LiMn_0.7Fe_0.3PO₄. It is indicated that the mixed-valence of Fe³⁺/Fe²⁺ or Mn³⁺/Mn²⁺ is beneficial to the transfer of electron which happens between the interface.     

Characterization and optoelectronic properties of sol-gel-derived CuFeO2 thin films

In this study, CuFeO₂ thin films were deposited onto quartz substrates using a sol-gel and a two-step annealing process. The sol-gel-derived films were annealed at 500 °C for 1 h in air and then annealed at 600 to 800 °C for 2 h in N₂. X-ray diffraction patterns showed that the annealed sol-gel-derived films were CuO and CuFe₂O₄ phases in air annealing. When the films were annealed at 600 °C in N₂, an additional CuFeO₂ phase was detected. As the annealing temperature increased above 650 °C in N₂, a single CuFeO₂ phase was obtained. The binding energies of Cu-2p_3/2, Fe-2p_3/2, and O-1s were 932.5 ± 0.1 eV, 710.3 ± 0.2 eV and 530.0 ± 0.1 eV for CuFeO₂ thin films. The chemical composition of CuFeO₂ thin films was close to its stoichiometry, which was determined by X-ray photoelectron spectroscopy. Thermodynamic calculations can explain the formation of the CuFeO₂ phase in this study. The optical bandgap of the CuFeO₂ thin films was 3.05 eV, which is invariant with the annealing temperature in N₂. The p-type characteristics of CuFeO₂ thin films were confirmed by positive Hall coefficients and Seebeck coefficients. The electrical conductivities of CuFeO₂ thin films were 0.28 S cm^− 1 and 0.36 S cm^− 1 during annealing at 650 °C and 700 °C, respectively, in N₂. The corresponding carrier concentrations were 1.2 × 10¹⁸ cm^− 3 (650 °C) and 5.3 × 10¹⁸ cm^− 3 (700 °C). The activation energies for hole conduction were 140 meV (650 °C) and 110 meV (700 °C). These results demonstrate that sol-gel processing is a feasible preparation method for delafossite CuFeO₂ thin films.     

Effect of thermal stress on magnetic domain patterns of multiferroic Bi1-xDyxFeO3 thin films

Effect of temperature on magnetic domain structure of Bi_0.7Dy_0.3FeO₃ (BDFO) multiferroic thin films is studied in situ using magnetic force microscopy (MFM). Initially, as the temperature increases the domains start aligning from irregular to more distinct stripe pattern. However, above 250 °C, the domain alignment is disturbed. The systematic change in the domain configuration with temperature, suggests a strong thermal history of the system. The randomness in domain alignment caused above 250 °C is correlated to internal stress developed during ferromagnetic to paramagnetic phase transition occurring in BDFO. Indirect experimental evidence is given to support the explanation based on stress.     

Hydrothermal synthesis and characterization of bismuth titanate regular tetrahedron crystallites

Bi₁₂TiO₂₀ (BTO) single crystals were synthesized by a hydrothermal process in KOH solution at 180 °C for 4 h from Ti(OC₄H₉)₄ and Bi(NO₃)₃·5H₂O compounds. The effects of processing parameters on the growth and morphology of BTO single crystals were investigated. The KOH concentration, reaction time and temperature had a great effect on the phase composition and morphology of the resultant crystals. BTO phase could not be obtained with KOH concentrations lower than 3 M or higher than 5 M. XRD, SEM and TEM were used to characterize the samples. BTO single crystals were regular tetrahedron in morphology and 10 μm or so in size.     

Structural and mechanical properties of multi-element (AlCrMoTaTiZr)Nx coatings by reactive magnetron sputtering

(AlCrMoTaTiZr)N_x high-entropy films were deposited on silicon wafer and cemented carbide substrates from a single alloy target by reactive RF magnetron sputtering under a mixed atmosphere of Ar and N₂. The effect of nitrogen flow ratio R_N on chemical composition, morphology, microstructure, and mechanical properties of the (AlCrMoTaTiZr)N_x films was investigated. Nitrogen-free alloy film had an amorphous structure, while nitride films with at least 37 at.% N exhibited a simple NaCl-type FCC (face-centered cubic) structure. Mixed structures occurred in films with lower nitrogen contents. Films with the FCC structure were thermally stable without phase decomposition at 1000 °C after 10 h. The (AlCrMoTaTiZr)N film deposited at R_N = 40% exhibited the highest hardness of 40.2 GPa which attains the superhard grade. The main strengthening mechanisms for this film were grain-size and solid-solution strengthening. A residual compressive stress of 1.04 GPa was small to account for the observed hardness. The nitride film was wear resistant, with a wear rate of 2.8 × 10^− 6 mm³/N m against a loaded 100Cr6 steel ball in the sliding wear test. These high-entropy films have potential in hard coating applications.