Influences of the compositions and mechanical properties of HVOF sprayed bimodal WC-Co coating on its high temperature wear performance

In this work, the bimodal WC-Co coatings were sprayed by high-velocity oxygen-fuel (HVOF), and the conventional WC-Co coatings were also fabricated for comparison. The microstructure, mechanical properties and high temperature wear performance were investigated. The bimodal WC-Co coating presented denser structure (porosity lower than 1.0%), higher average hardness (1164 HV0.1) and fracture toughness (11.5 ± 1.4 MPa·m^1/2) than that of conventional coating. The Weibull analysis of microhardness data of the bimodal coating presents a mono-modal distribution. The friction coefficient and wear rate of the bimodal coating were 0.61 and 2.96 × 10^− 6 mm³·N^− 1·m^− 1, respectively, which is lower than that of conventional coating at the test temperature of 450 °C. The tribofilm could be formed on the worn surface of bimodal WC-Co coating, which is composed of WO₃ and CoWO₄. The formation of tribofilm could reduce friction and wear.     

Preparation,crystal structures and electrical conducting properties of new charge-transfer salts: (ET)2·SO3CF3 and (ET)·ClO4

Two new charge-transfer (CT) salts: (ET)₂·SO₃CF₃ and (ET)·ClO₄ were prepared by chemical oxidation of ET with AgSO₃CF₃ and AgClO₄, respectively. Their crystal structures were determined: monoclinic system, Cc, a=35.239(7) Å, b=6.5440(13) Å, c=14.646(3) Å, β=110.26(3)°, V=3168.5(11) Å³ for (ET)₂·SO₃CF₃; monoclinic system, C2/c, a=15.981(3) Å, b=10.627(2) Å, c=11.495(2) Å, β=120.61(3)°, V=1680.2(6) Å³ for (ET)·ClO₄. Electrical conductivity measurements indicate that (ET)₂·SO₃CF₃ shows semi-conducting behaviour with room temperature conductivity of 0.29 S cm⁻¹, while (ET)·ClO₄ is an insulator.     

Synthesis,photophysical and electrophosphorescent properties of a novel fluorinated rhenium(I) complex

A novel fluorinated rhenium complex, i.e., Re-BFPP (BFPP, 2, 3-bis(4-fluorophenyl)pyrazino[2,3-f][1,10]phenanthroline) was designed, synthesized and characterized by ¹H NMR and mass spectroscopy. The light-emitting and electrochemical properties of this complex were studied. The organic light-emitting diodes (OLEDs) employing Re-BFPP as a dopant emitter with the structures of ITO/m-MTDATA (10 nm)/NPB (20 nm)/CBP: X wt.% Re-BFPP (30 nm)/Bphen (10 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm) were successfully fabricated and a broad electroluminescent peak at 553 nm was observed. The 10 wt.% Re-BFPP doped device exhibited the maximum luminance of 6342 cd/m² and a peak current efficiency of 17.9 cd/A, corresponding to the power efficiency of 8.1 lm/W.     

Iridium(III) complexes with cyclometalated styrylbenzoimidazole ligands: Synthesis,electrochemistry and as highly efficient emitters for organic light-emitting diodes

Two phosphorescent iridium complexes (psbi)₂Ir(acac) and (ppbi)₂Ir(acac) (psbi = 1-phenyl-2-styryl-1H-benzo[d]imidazole, ppbi = 1-phenyl-2-(1-phenylprop-1-en-2-yl)-1H-benzo[d]imidazole, acac = acetylacetonate) were synthesized, and their photophysical, electrochemical and electroluminescent properties were also studied. Organic light-emitting devices with these two complexes as dopant emitters having the structure ITO/NPB (10 nm)/TCTA (20 nm)/x%Ir:CBP (y nm)/BCP (10 nm)/LiF (1 nm)/Al (100 nm) were fabricated. The device based on (psbi)₂Ir(acac) exhibited a maximum brightness of 56,162 cd m^?2, while the device based on (ppbi)₂Ir(acac) gave a maximum brightness of 31,232 cd m^?2. At high brightness of 1000 cd m^?2 and 10,000 cd m^?2, high current efficiencies of 25.7 cd A^?1 and 20.7 cd A^?1 were achieved, respectively, for the (psbi)₂Ir(acac)-based EL device. For the EL device based on (ppbi)₂Ir(acac), current efficiencies of 20.1 cd A^?1 at 1000 cd m^?2 and 14.2 cd A^?1 at 10,000 cd m^?2 were observed.     

Protonation-induced rearrangements in Langmuir films and redox properties of Langmuir–Blodgett films of 2-(n-alkyl)fulleropyrrolidines

The effect of protonation of the pyrrolidine ring nitrogen of 2-(n-alkyl)fulleropyrrolidines, C₆₀pyr–C_m (m=4, 6, 8, 10 and 12), on the properties of the Langmuir and Langmuir–Blodgett (LB) films was investigated. The isotherms of both surface pressure (π) and surface potential change (ΔV) versus area per molecule (A) for the Langmuir films of C₆₀pyr–C_m were determined simultaneously. It was found that the longer the alkyl chain of the fulleropyrrolidine the larger is the film compressibility, κ, i.e., κ(C₆₀pyr–C₄)=(2.1±0.4)×10⁻² m mN⁻¹, κ(C₆₀pyr–C₈)=(3.5±0.4)×10⁻² m mN⁻¹ and κ(C₆₀pyr–C₁₂)=(4.1±0.5)×10⁻² m mN⁻¹, as expected for the liquid surface films. The values of surface area at zero surface pressure (A₁) differ in the range 0.6 nm² molecule⁻¹ (for m=4–8) to 1.4 nm² molecule⁻¹ (for m=10–12), indicating that all 2-(n-alkyl)fulleropyrrolidines form multilayer or aggregated films on neutral water subphase. However, acidification of the water subphase increases the A₁ values for all investigated fulleropyrrolidines up to ca. 1.9 nm² molecule⁻¹, i.e., the value corresponding to maximum area occupied by a fulleropyrrolidine at horizontal orientation in a monolayer film. Apparently, 2-(n-alkyl)fulleropyrrolidinium cations formed at low pH are markedly de-aggregated in the films and their orientation is changed due to protonation of the pyrrolidine nitrogen. Similarly, however, less pronounced effects are observed if ionic strength of the subphase solution, I, is increased in the range 0≤I≤1.0 mol dm⁻³ NaCl. The Langmuir films formed on a water subphase were the most stable with respect to the LB transfer onto 5 MHz Au–quartz crystal vibrators. Simultaneous cyclic voltammetry and piezoelectric microgravimetry at an electrochemical quartz crystal microbalance of these films showed at least two electroreductions where the fulleropyrrolidine mono anions were stable with respect to dissolution.     

Preparation of self-organized porous anodic niobium oxide microcones and their surface wettability

Porous anodic niobium oxide with a pore size of ～10 nm was formed at 10 V in glycerol electrolyte containing 0.6 mol dm^?3 K₂HPO₄ and 0.2 mol dm^?3 K₃PO₄ at 433 K. After prolonged anodizing for 5.4 ks, niobium oxide microcones develop on the surface. X-ray diffraction patterns of the anodized specimens revealed that the initially formed anodic oxide is amorphous, but an amorphous-to-crystalline transition occurs during anodizing. As a consequence of the preferential chemical dissolution of the initially formed amorphous oxide, due to different solubility of the amorphous and crystalline oxides, crystalline oxide microcones appear on the film surface after prolonged anodizing. The surface is superhydrophilic. After coating with fluorinated alkylsilane, the surface becomes superhydrophobic with a contact angle of 158° for water. The surface is also oil repellent, with a contact angle as high as 140° for salad oil.     

Etching mechanisms during plasma jet machining of silicon carbide

The material removal of the C- and Si-face of 4H-SiC using a 13.56 MHz RF excited plasma jet source at atmospheric pressure using helium as feed gas and CF₄ as reactive gas has been investigated. Additionally O₂ is provided together with the peripherally injected N₂ shielding gas and it is shown that a decrease of the etching rate with an increase of the O₂ gas flow occurs.Furthermore, etching experiments under sample heating have been carried out for different [CF₄]/[O₂] mixtures to obtain the activation energy of fluorine and oxygen with the surface. A minimum in the etching rate at a temperature of approximately 150 °C has been found. Therefore XPS and SEM analyses have been carried out for surfaces etched at sample temperatures of 25 °C, 150 °C and 400 °C showing an elevated fraction of silicon oxides and film thickness at 150 °C.     

Cationic and radical polymerization of N-vinyl-2-phenylpyrrole: Synthesis of electroconducting,paramagnetic and fluorescent oligomers

Cationic polymerization of N-vinyl-2-phenylpyrrole (catalysts: Me₃SiCl, CF₃COOH, BF₃·OEt₂, HCl, WCl₆, FeCl₃, complex LiBF₄–dimethoxyethane, catalysts concentration 1–2 wt%, 20–70 °C, 24–48 h) affords oligomers (molecular weight 1400–1700) of a unexpected structure with alternating 2-phenylpyrrole and ethylydene units, the yields reaching 63%. The oligomers structure has been supported by isolation and identification of the corresponding dimer, N-vinyl-2-phenyl-5-[N-(2-phenyl-1H-pyrrol-1-yl)ethyl]-1H-pyrrole. Radical polymerization of the same monomer (AIBN, 1.5–4 wt%, 60–80 °C, 40–60 h or UV irradiation or both) gives oligomers (molecular weight 2100–3000) of normal structure having polyethene backbone with pendant 2-phenylpyrrole groups in up to 40% yields. The oligomers of both types are semiconductors (1.3 × 10^?6–3.6 × 10^?6 S/cm) after doping with I₂, paramagnetic (4.2 × 10¹⁷–8.7 × 10¹⁷ g^?1) and fluorescent in a near UV region (λ 355–363 nm, acetonitrile).     

Synthesis,crystal structure and two-photon absorption of a cadmium complex constructed by DMIT ligand

The cadmium complex [(CH₃)₄N][Cd(C₃S₅)₂]·H₂O constructed by 1,3-dithiole-2-thione-4,5-dithiolato (DMIT) ligand has been synthesized and its structure has been determined by means of X-ray single crystal diffraction. Its two-photon absorption (TPA) has been studied in acetonitrile solution using open-aperture Z-scan technique with 20 picosecond (ps) pulses at wavelength 1064 nm. Its TPA coefficient β was determined to be 4.475 × 10^?10 m/W, corresponding the TPA cross-section σ₂ is 3.95 × 10^?53 (m⁴ s/photon molecule).     

Plasma electrolytic oxidation of hafnium

This paper presents the results of the investigation of plasma electrolytic oxidation (PEO) of hafnium. Atoms ionized during the PEO micro-discharging were identified using optical emission spectroscopy. The spectral line shape analysis of the hydrogen Balmer line H_β indicated the presence of two types of micro-discharges characterized by electron number densities of around 2.5·10²¹ m^− 3 and 1.3·10²² m^− 3. Scanning electron microscopy and X-ray diffraction were employed to investigate surface morphology and phase composition of the PEO coatings obtained. The coatings were crystalline and composed of monoclinic HfO₂. Diffuse reflectance spectroscopy has shown that HfO₂ coatings have a broad absorption band in the range from 200 nm to 400 nm. Optical band gap of HfO₂ coatings was around 5.4 eV, as estimated from absorption spectra. Photoluminescence measurements show that HfO₂ coatings have broad emission band in the visible region, with a maximum at around 480 nm. The highest photoluminescence was obtained for the excitation wavelength of 270 nm. Intensity of photoluminescence increased with PEO time and is related to an increase of oxygen vacancy defects in HfO₂ coatings formed during the process.     

Effect of sintering temperature on the structure and properties of polycrystalline cubic boron nitride prepared by SPS

The polycrystalline cubic boron nitride (PcBN) with Si₃N₄–AlN–Al₂O₃–Y₂O₃ ceramic system as binding agents was prepared by spark plasma sintering (SPS). The starting materials Si₃N₄, AlN, Al₂O₃, Y₂O₃, and cBN in the ratio of 22:14:10:4:50 were heated to a sintering temperature between 1250 °C and 1450 °C at a heating rate of 300 °C/min, with a holding time of 5 min in nitrogen atmosphere. The microstructure, phase constitution, microhardness and fracture toughness of the prepared PcBN were then studied. It was shown that the Si₃N₄–AlN–Al₂O₃–Y₂O₃–cBN polycrystalline materials were densified in a very short sintering time resulting in materials with relative densities of more than 95%. When the sintering temperature increased, the microhardness and fracture toughness of prepared PcBN were also increased. The microhardness of PcBN prepared at 1250–1450 °C was between 28.0 ± 0.5 GPa and 48.0 ± 0.9 GPa, and its fracture toughness K_IC was from 7.5 ± 0.2 MPa m^1/2 to 11.5 ± 0.3 MPa m^1/2. Microstructure study showed that the ceramic-binding agents bonded with cubic boron nitride particles firmly. Our work demonstrated that spark plasma sintering technology could become a novel method for the preparation of PcBN cutting materials.     

Reaction spark plasma sintering of niobium diboride

Niobium diboride (NbB₂) is synthesized and consolidated by the spark plasma sintering technique. Elemental reactants such as niobium (Nb) and boron (B) were subjected to two stage heat treatment, initially at 1200 °C for synthesis and followed by densification at the temperatures in the range of 1700 °C to 1900 °C. High dense NbB₂ (~ 97.7%ρ_th) is obtained at 1900 °C after 15 min holding period. Load application during heat treatment stage is found to improve the sinterability of the niobium diboride compacts. Hardness, elastic modulus and indentation fracture toughness of the high dense NbB₂ are measured as 20.25 GPa, 539 GPa and 4 MPa m^1/2 respectively.     

Improvement of single-walled carbon nanotube transparent conductive films using substrate pretreatment

This study sought to improve the characteristics of single-walled carbon nanotube (SWCNT) transparent conductive films (TCFs), such as their sheet resistance and transparency, by applying pre-treatments to their PET substrates. Oxygen–argon plasma pretreatment was found to increase the surface energies of the PET substrates from 33.9 to 74.2 mJ/m², which improves the electric conductivity of the SWCNT-TCFs and provides a lower sheet resistance at a given light transmittance. Polymer electrolyte solution pretreatment was used to vary the surface functionality and modulate the surface charges quantitatively, as confirmed by the measurement of the resulting substrate zeta potentials, which varied between ?45.8 and 18.2 mV. When the surfaces became negatively charged through pretreatment, the electric conductivities of the SWCNT-TCFs were increased. Both pre-treatments also improve the adsorption of SWCNTs onto the PET substrates and reduce the loss of coating solution during the spray deposition of SWCNTs.     

Processing and properties of sintered reaction-bonded silicon nitride with Y2O3–MgSiN2: Effects of Si powder and Li2O addition

The effects of Si powder and Li₂O addition on the processing, thermal conductivity and mechanical properties of sintered reaction-bonded silicon nitride (SRBSN) with Y₂O₃–MgSiN₂ sintering aids were studied. Addition of Li₂O provides a less-viscous liquid phase that results in a more uniform and finer pore structure in RBSN with the coarser Si powders, but the pore structure plays a less important role in the densification of RBSN. The thermal conductivity of SRBSN without porosity decreases with increased Al impurity content and also decreases with the Li₂O addition regardless of the Si purity. The impurest coarse Si powder produces the lowest thermal conductivity (93 W m⁻¹ K⁻¹) but the highest four-point bending strength (∼700 MPa) and a higher fracture toughness (∼10 MPa m^1/2). However, the purer fine Si powder produces the highest thermal conductivity (119 W m⁻¹ K⁻¹) and highest toughness (∼11 MPa m^1/2) but the lowest strength (∼500 MPa).     

Preparation and properties of hot-pressed NbMo-matrix composites reinforced with ZrB2 particles

The NbMo-matrix composites reinforced with (0–60 vol%) ZrB₂ were fabricated by hot-pressing at 2400 °C for 10 min under a pressure of 50 MPa in dynamic vacuum in the induction heating furnace specially designed in our institute. The optimum ZrB₂ content in NbMo solid solution was determined to be 30 vol% for excellent comprehensive mechanical property. NbMo-30 vol% ZrB₂ has the highest density of 99.63%, the most uniform microstructure, high fracture toughness of 5.75 MPa m^1/2. The highest ZrB₂ concentration that reacts with NbMo solid solution is at the range of 30 to 45 vol%. The types of the formed niobium borides were decided by the original ratio of Nb to B. The distribution of Mo and Zr was mutually exclusive in low ZrB₂ content composites, however, there was Mo₂Zr in high ZrB₂ content composite. Except for NbMo-45 vol% ZrB₂, the compressive strength increased with ZrB₂ content (from 927.09 MPa to 1635.91 MPa). The Young's modulus values were directly proportional to ZrB₂ content. The fracture toughness (from 6.34 MPa m^1/2 to 3.99 MPa m^1/2) was inversely proportional to ZrB₂ content. The big residual ZrB₂ particles in high ZrB₂ content samples such as NbMo-45 vol% ZrB₂ and NbMo-60 vol% ZrB₂ was the main reason for nonhomogeneous microstructure, low density (94.09% and 94.83%, respectively) and low fracture toughness (4.58 MPa m^1/2 and 3.99 MPa m^1/2, respectively).     

Synthesis of macroscopic SiC nanowires at the gram level and their electrochemical activity with Pt loadings

Macroscopic SiC nanowires (SiCNWs) were successfully synthesized at the gram level (2–4 g h^?1) by using a simple solid–vapor reaction of silicon powders and carbon oxides, assisted by ZnS. This results in a promising material for a wide range of applications. The obtained products possess a small size of 10–30 nm and a good single-crystal structure. In addition, a specific surface area of 1.6 m² g^?1 was achieved. A high electrochemical activity to H₂ adsorption/desorption and methanol oxidation was observed from cyclic voltammograms in H₂SO₄ and H₂SO₄/CH₃OH solutions after loading with 50 wt.% Pt. Furthermore, a high catalytic performance for oxygen reduction at ～0.57 V and good chemical stability were displayed. The novel SiCNW-supported catalyst shows potential for fuel cells with long lifetimes.     

Micrometer-scaled OFET channel patterns fabricated by using PEDOT/PSS microfibers

We have easily fabricated channel patterns of organic field-effect transistors (OFETs), in which channel lengths were 5 μm, by using wet-spun poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) microfibers with diameters of ca. 5 μm. Pentacene-based FETs with a top-contacted configuration, showed a hole mobility of 0.13 cm² V^?1 s^?1 and on/off current ratio of 9.4 × 10⁴. The device also showed large current of ca. 160 μA (V_D = ?50 V; V_G = ?50 V), reflecting shorter channel length of the devices. We have evaluated self-assembled monolayer (SAM) through measurements of water contact angle and by Zisman plot. As a result, critical surface tension of the octadecyltrichlorosilane (OTS)-treated SiO₂ surface is 17 mN m^?1 which is consistent with that of well-known SAM. We also well analyzed the cross-sections of the device by a scanning transmission electron microscopic (STEM) technique. The results indicated that the thicknesses of the pentacene layer in the channel part and Au layer in the source/drain part were ca. 30 and 30 nm, respectively. Furthermore, it is also indicated that the 100-nm grains of the pentacene were well adhered on the surface of the SAM-formed SiO₂ layer.     

Mechanosynthesis of rhenium carbide at ambient pressure and temperature

We report the synthesis of Re₂C at ambient pressure and temperature. The formation of rhenium carbide (Re₂C) from the elements was obtained by mechanochemical treatment after 640 min of milling. The microscopy analysis shows polyhedral particle agglomerates with diameters of less than 600 nm. Thermogravimetric analysis results revealed the stability of material at up to 800 °C as well as chemical and surface analysis of polyhedral particles which show oxidative properties and a surface area of 2.0 m² g^− 1, respectively.     

Synthesis,characterization, and dc conductivity of hydrogen-bonding dibenzotetrathiafulvalene (DBTTF) based salts

The synthesis, characterization, and dc conductivity of organic conductors, 1-[2-(1,3-benzodithiol-2-ylidene)-1,3-benzodithiol-5-yl]ethylammonium tetrafluoroborate ([DBTTFCH(Me)NH₃⁺]BF₄^?) and 1-[2-(1,3-benzodithiol-2-ylidene)-1,3-benzodithiol-5-yl]ethylammonium bromide ([DBTTFCH(Me)NH₃⁺]Br^?) salts are presented. These salts are prepared by mixing the corresponding primary amine and Brønsted acid in a one-to-one ratio without electrochemical oxidation. The change in the electronic state of insulating DBTTFCH(Me)NH₂ into conductive [DBTTFCH(Me)NH₃⁺]X^? (X = BF₄ and Br) salts and the carrier generation upon salt formation were confirmed by diffuse reflectance (UV–vis) and ESR spectra. The concentration of localized radicals is estimated to be 1 radical/3.3 units and 1 radical/1.8 units for BF₄ and Br salts, respectively. The possible carrier generation mechanism is proposed by ¹H NMR and ESI-TOF-MS spectroscopic analyses. The dc conductivity and the activation energy are σ_rt = 2.3 × 10^?3 S/cm with 0.24 eV for the BF₄ salt, and σ_rt = 1.3 × 10^?3 S/cm with 0.21 eV for the Br salt.     

Coercivity enhancement in boron-enriched stoichiometric REFeB melt-spun alloys

Considerable enhancement of magnetic properties was attained in initially stoichiometric nanophase RE₁₂Fe₈₂B₆ melt-spun alloys (RE = Nd, Nd + Pr) by means of an excess B content (10 at%) and additions of Zr and Co (2% and 7%, respectively). The intrinsic coercivity exhibited a marked improvement (with respect to the stoichiometric 6 at% B alloy), within the range 50–65%, with a maximum of 1161 ± 14 kA m⁻¹ for the B-rich and Zr-containing alloy, together with an excellent combination of remanence and energy density values of 0.90 ± 0.01 T and 137 ± 4 kJ m⁻³, respectively. Further Co addition led to a Curie temperature increase, while preserving high coercivity (1176 ± 31 kA m⁻¹) and useful energy densities (119 ± 4 kJ m⁻³). Results were interpreted on the basis of alloy microstructural features and on variations of the intrinsic magnetic properties, supported by micromagnetic calculations.