Effect of CuO as a dopant in TiO2 on ammonia and hydrogen sulphide sensing at room temperature

The heterogeneous nanocomposites of CuO doped TiO₂ nanoparticles were synthesized using sol gel method by varying the concentration of CuO as 0.1, 0.5 and 1 mol% for the sensing of ammonia and hydrogen sulphide. The substitutional doping of CuO in TiO₂ matrix was confirmed by the X-ray diffraction. Average crystallite size of the doped nanocomposites was found to reduce with increase in concentration of CuO. The 0.1 mol% CuO doped TiO₂ nanocomposites showed highest sensitivity to ammonia (97%) with response time of 2 s, while 1 mol% was selective to H₂S gas (77%) with response time of 45 s for 50 ppm of each gas at room temperature.     

Microstructure and wear resistance of low temperature hot pressed TiB2

Fine-grained TiB₂ compacts have been hot pressed to 98–99% theoretical density at 1400 °C. The compacts were consolidated from sub-micron powders prepared by a high-energy ball milling technique. Titanium diboride (TiB₂) powders were obtained from the milling of commercially synthesized TiB₂ and also from the mechanical alloying (MA) of Ti and B precursors. The formation of TiB₂ from Ti and B powders by mechanical alloying was found to reach completion after 3 h, and wear debris from steel mill vials and media introduced 0.8 to 1.5 wt% Fe in the sintered compacts. The dry erosion resistance of the highest density compacts was examined using an ASTM standard test with an abrasive jet of Al₂O₃ impinging at a normal angle of incidence. Steady-state erosion rates of 0.5 mm³/kg of erodent compare favorably with the measured value of 9 mm³/kg for commercial, fine-grained WC–Co cermets under identical conditions. Microstructures, fracture surfaces, and erosion craters were also examined by electron microscopy.     

WC–ZrO2 composites: processing and unlubricated tribological properties

In the present work, we report the processing and properties of WC–6 wt.% ZrO₂ composites, densified using the pressureless sintering route. The densification of the WC–ZrO₂ composites was carried out in the temperature range of 1500–1700 °C with varying time (1–3 h) in vacuum. The experimental results indicate that significantly high hardness of 22–23 GPa and moderate fracture toughness of ∼5 MPa m^1/2 can be obtained with 2 mol% Y-stabilized ZrO₂ sinter-additive, sintered at 1600 °C for 3 h. Furthermore, the friction and wear behavior of optimized WC–ZrO₂ composite is investigated on a fretting mode I wear tester. The tribological results reveal that a moderate coefficient of friction in the range from 0.15 to 0.5 can be achieved with the optimised composite. An important observation is that a transition in friction and wear with load is noted. The dominant mechanisms of material removal appear to be tribochemical wear and spalling of tribolayer.     

AC conduction mechanism and battery discharge characteristics of (PVC/PEO) polyblend films complexed with potassium chloride

New K⁺ ion-conducting polymer blend electrolyte films based on amorphous polymer poly(vinyl chloride) (PVC) and semicrystalline polymer poly(ethylene oxide) (PEO) complexed with KCl salt were prepared using a solution-cast technique. The maximum value of ionic conductivity of a PVC/PEO:KCl (42.5:42.5:15) system is 8.29 × 10⁻⁶ S/cm at 303 K. The absorption edge was found at 4.30 eV for undoped film, while it was observed at 4.03 and 3.93 eV for 10 and 15 wt% KCl doped films, respectively. The direct band gaps for these pure and salt doped PVC/PEO films were found to 4.10, 3.86 and 3.74 eV, respectively, whereas the indirect band gaps were determined as 4.15, 3.72 and 3.64 eV. Transference number values showed that the charge transport in this electrolyte system is predominantly due to ions (t_ion = 0.97). The discharge capacity for PVC/PEO:KCl (42.5:42.5:15) polymer blend electrolyte system is 11 μA/h.     

Studies on wear behavior of nano-intermetallic reinforced Al-base amorphous/nanocrystalline matrix in situ composite

Resistance to wear is an important factor in design and selection of structural components in relative motion against a mating surface. The present work deals with studies on fretting wear behavior of in situ nano-Al₃Ti reinforced Al–Ti–Si amorphous/nanocrystalline matrix composite, processed by high pressure (8 GPa) sintering at room temperature, 350, 400 or 450 °C. The wear experiments were carried out in gross slip fretting regime to investigate the performance of this composite against Al₂O₃ at ambient temperature (22–25 °C) and humidity (50–55%). The highest resistance to fretting wear has been observed in the composites sintered at 400 °C. The fretting wear involves oxidation of Al₃Ti particles in the composite. A continuous, smooth and protective tribolayer is formed on the worn surface of the composite sintered at 400 °C, while fragmentation and spallation leads to a rougher surface and greater wear in the composite sintered at 450 °C.     

Friction and wear properties of αFeSi2–Si alloy,ReSi1.8 and MoSi2 in ethyl alcohol

In this study, Fe–X at% Si alloy (X=70.5, 80.0 and 96.0), Re–64.3 at% Si and Mo–66.7 at% Si disk specimens were prepared by spark plasma sintering, and their friction and wear properties were investigated when they were slid against Si₃N₄ ball specimens in ethyl alcohol. The friction and wear properties of Si ingots were also examined. Fe–70.5 at% Si, Fe–80.0 at% Si, Fe–96.0 at% Si and Re–64.3 at% Si disk specimens exhibited friction coefficients as low as 0.15. It is considered that the low friction of the Fe–70.5 at% Si, Fe–80.5 at% Si and Fe–96.0 at% Si disk specimens was due to the formation of low friction silicon alkoxide and polyoxysilane on the worn surfaces of the disk specimens and the paired ball specimens. Re–64.3 at% Si disk specimens exhibited the highest microvickers hardness of all the disk specimens prepared in this study. In addition, the microvickers hardness of the Fe–X at% Si (X=70.5, 80.0, 96.0 and 100) disk specimen increased with increasing the Si content. Moreover, it was difficult to obtain dense Fe–90.0 at% Si disk specimens by sintering the annealed and crushed Fe–90.0 at% Si powder. However, dense Fe–96.0 at% Si disk specimens could be obtained by sintering the Fe–90.0 at% Si powder at 1403 K.     

Tribological properties of Ni3Al produced by pressure-assisted volume combustion synthesis

The production of Ni₃Al was performed under an uniaxial pressure of 150 MPa at 1050 °C for 1 h. The formation temperature of Ni₃Al was determined to be 655 °C. The presence of Ni₃Al was confirmed by XRD analysis. SEM analysis revealed that the Ni₃Al phase has very low porosity. The relative density and microhardness of test materials were 97.8% and about 359±31 HV_1.0, respectively. The specific wear rate of Ni₃Al was 0.029 mm³/N m for 2 N, 0.017 mm³/N m for 5 N and 0.011 mm³/N m for 10 N, respectively. The distribution of alloying elements was determined by energy-dispersive spectroscopy (EDS).     

Preparation,characterization, electrical conductivity and dielectric studies of Na2SO4 and V2O5 composite solid electrolytes

Composite solid electrolytes (1 − x) Na₂SO₄–(x) V₂O₅ were prepared and characterized by various techniques such as XRD, FT-IR, DTA and SEM. AC impedance spectroscopy revealed that the contribution of grain is strong enough over the grain boundary. Arrhenius plot of the Na₂SO₄ shows a sharp increase in conductivity at 523 K due to the structural phase transition (phase V → I). Composites show the enhanced ionic conductivity than the pristine Na₂SO₄ over the entire temperature range. The maximum conductivity σ = 0.003 S cm⁻¹ at 773 K with the lowest activation energy of 0.28 eV was observed for the x = 0.4 sample. The enhanced value of dielectric constant and dielectric loss in the case of composites was obtained because of increase of conductivity, resulted from the increase of space charge polarization and charge motion.     

A comparison of the reciprocating sliding wear behaviour of steel based metal matrix composites processed from self-propagating high-temperature synthesised Fe–TiC and Fe–TiB2 masteralloys

Steel matrix particulate composites were processed by direct addition of various powders to molten medium carbon steel. Fe–TiC and Fe–TiB₂ powders were produced using a self-propagating high-temperature synthesis (SHS) reaction and consisted of a dispersion of fine TiC (5–10 μm) and TiB₂ particles (2–5 μm), respectively in an iron binder.Addition of the Fe–TiC powder to the steel resulted in the formation of a metal matrix composite containing a homogeneous dispersion of TiC particles. However, addition of the Fe–TiB₂ powder resulted in the formation of a parasitic Fe₂B phase and TiC within the steel microstructure. In response to this an SHS masteralloy composed of Fe–(50% TiB₂+50%Ti) was manufactured which, when added to steel, prevented the formation of Fe₂B and resulted in a composite containing a mixture of TiB₂ and TiC particles.Dry reciprocating sliding wear behaviour of the three composite materials and their unreinforced counterpart was investigated at room temperature against a white cast iron counterface. Relative wear behaviour of the materials varied as a function of load. In all cases, the composite manufactured by addition of Fe–TiB₂ (yielding Fe₂B and TiC phases in the steel) exhibited wear rates greater than three times that of the unreinforced alloy. However, improvements in wear resistance over the base steel of up to two and a half times were observed with the other composites where the desired TiC and/or TiB₂ phases were retained in the steel. Scanning electron microscopy has been used to interpret wear behaviour in relation to both the as-cast microstructures of the composites and the wear scar microstructures observed.     

Wear characteristics of Cr3C2–NiCr and WC–Co coatings deposited by LPG fueled HVOF

Wear behavior of the HVOF deposited Cr₃C₂–NiCr and WC–Co coatings on Fe-base steels were evaluated by the pin-on-disc mechanism. The constant normal load applied to the pin was 49 N and sliding distance was 4500 m with velocity of 1 m/s, at ambient temperature and humidity. The specific wear rate of WC–Co coating was 3 mm³/N m and Cr₃C₂–NiCr coating was 5.3 mm³/N m. SEM/EDAX and XRD techniques were used to analyze the worn out surface and wear debris. The Fe₂O₃ was identified as the major phase in the wear debris. The wear mechanism is mild adhesive wear in nature.     

Cavitation erosion of Fe–Mn–Si–Cr shape memory alloys

Cavitation erosion tests of three Fe–Mn–Si–Cr shape memory alloys were carried out at speed 34 and 45 m/s using a rotating disc rig, and their cavitation damage has been investigated by comparison with a referring 13Cr–5Ni–Mo stainless steel used for hydraulic turbine vanes. The research results proved that the cavitation erosion of the Fe–Mn–Si–Cr shape memory alloys is a failure of low cycle fatigue and fracture propagates along grain boundaries. After 48 h cavitation erosion the cumulative mass losses of the studied alloys at speed 45 m/s are more than theirs at speed 34 m/s; however, the effect of velocity on cavitation damage of the Fe–Mn–Si–Cr alloys is much lower than that of 13Cr–5Ni–Mo stainless steel. The cumulative mass loss of the 13Cr–5Ni–Mo stainless steel are 26.3 mg at speed 45 m/s and 3.2 mg at speed 34 m/s, and the mass losses of the Fe–Mn–Si–Cr alloys are within the range of 3.6–7.3 mg at speed 45 m/s and 2.0–4.1 mg at speed 34 m/s. The surface elasticity of the Fe–Mn–Si–Cr shape memory alloys is better than that of the 13Cr–5Ni–Mo stainless steel, and the effect of surface elasticity on cavitation damage increases with velocity. The excellent surface elasticity of the cavitation-induced hexagonal closed-packed (h.c.p.) martensite plays a key role in contribution of phase transformation to the cavitation erosion resistance of the Fe–Mn–Si–Cr shape memory alloys. The cavitation damage of the studied alloys at speed 45 m/s mainly depends on their surface elasticity, and the variation of 48 h cumulative mass loss (Δm) as a function of the elastic depth (h_e) can be expressed as Δm=2.695+[1371.94/(4(h_e−46.83)²+12.751)] with a correlation factor of 0.99345.     

A comparative study on the wear properties of coarse-grained Al6061 alloy and nanostructured Al6061–Al2O3 composites

Wear behavior of nanostructured Al6061 alloy and Al6061–Al₂O₃ nanocomposites produced by milling and hot consolidation were investigated. The samples were characterized by hardness test, pin-on-disk wear test, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Nanocomposites containing 3 vol% Al₂O₃ showed a maximum hardness of 235 HV and optimum wear rate of 4×10⁻³ mg/m. Increasing the amount of Al₂O₃ up to 5 vol% resulted in decrease in hardness values (∼112 HV) and a sharp rise in wear rate (∼18×10⁻³ mg/m).     

Mechanical and tribological behavior of nanostructured copper–alumina cermets obtained by Pulsed Electric Current Sintering

Nanostructured Cu–Al₂O₃ powders obtained by the reduction of CuO with Al in a high energy ball mill were successfully consolidated by Pulsed Electric Current Sintering (PECS). The effect of the composition and microstructure of these PECS Cu–Al₂O₃ cermets on their strength was investigated. The friction and wear behavior of these cermets were studied under reciprocating sliding against corundum at 23 °C and 50% RH, and compared to the behavior of coarse grained PECS sintered pure copper. The effect of grain size on the coefficient of friction was masked by the formation of a surface tribolayer. The wear depth recorded on Cu–Al₂O₃ is lesser than half the one on coarse grained copper. Surface and subsurface deformation studied through FIB cross-sections showed that delamination and oxidative wear were active on Cu and Cu–Al₂O₃ cermets respectively under the current sliding test conditions. PECS Cu–Al₂O₃ cermets showed a good thermal stability even at 600 °C.     

Friction and wear characterization of sintered low alloyed chromium steels for structural components

Sintered and sintered/gas nitrided cylinders made of low alloyed chromium steel Astaloy CrL + 0.45 C at 7.25 g/cm³ density, have been tested for scuffing resistance and wear rate in a crossed cylinders test setup lubricated with a commercial SAE 10W40 engine oil at 90 °C. The results show large potential of 1 h gas nitriding of the sintered chromium steel cylinders. The nitrided cylinders experienced safe wear at 1000 MPa and scuffing at 1100 MPa at 2.5 m/s. At 0.5 and 0.1 m/s at least up to 800 MPa the wear was mild, as sintered chromium cylinders showed scuffing at pressure lower than 320 MPa and limited wear at 0.5 and 0.1 m/s.     

Spray pyrolysed Mn:Co3O4 thin film electrodes via non-aqueous route and their electrochemical parameter measurements

Present work explains the preparation of manganese incorporated cobalt oxide thin film electrodes on stainless steel by spray pyrolysis technique, via non-aqueous (methanolic) media. Structural, morphological and electrochemical characterizations of the prepared samples were made by means of XRD, SEM and electrochemical measurements. Structural elucidation confirms Co₃O₄ has face centred cubic and Mn₃O₄ has tetragonal body centred cubic structure with polycrystalline nature. Surface morphological observation shows the continuous semi porous film growth with spherical grains. Cyclic voltammetry reveals the mixed capacitive behaviour with maximum specific capacitance 605.35 F/g at the scan rate 1 mV/s in 1 M KOH electrolyte. Chronopotentiometric measurement gives energy density 33.5 Wh/kg, power density 2 kW/kg and Columbic efficiency 99.23%. Electrochemical impedance study was carried out in the frequency range 1 mHz to 1 MHz to see the internal resistance. Randles equivalent circuit was developed by using ZsimpWin software to search the circuitry parameters associated with the cell.     

On the film thickness dependence of shear strengths in sliding,boundary-layer friction

The density functional theory calculated pressure-dependent shear strength S of a four-layer slab of KCl on a Fe(1 0 0) substrate is compared to previous calculations for a bilayer slab to gauge the effect of film thickness on the shear properties of the film. It is found that the shear strength varies with pressure as S = S₀ + αP, where P is the contact pressure. The resulting calculated values for the four-layer slab are S₀〈1 0〉 = 62 ± 15 and S₀〈1 1〉 = 65 ± 11 MPa while α〈1 0〉 and α〈1 1〉 are 0.06 ± 0.01. The values are very close to those calculated for the bilayer slab of S₀〈1 0〉 = 64 ± 9 and S₀〈1 1〉 =69 ± 8 MPa and α〈1 0〉 and α〈1 1〉 of 0.05 ± 0.01, and in reasonable agreement with the experiment values. These results suggest that the thickness of the film does not have a profound effect on the shear properties.     

Tribological behavior of NiAl matrix composites with addition of oxides at high temperatures

NiAl, NiAl–Cr–Mo alloy and NiAl matrix composites with addition of oxides (ZnO/CuO) were fabricated by powder metallurgy route. It was found that some new phases (such as NiZn₃, Cu_0.81Ni_0.19 and Al₂O₃) are formed during the fabrication process due to a high-temperature solid state reaction. Tribological behavior was studied from room temperature to 1000 °C on an HT-1000 ball-on-disk high temperature tribometer. The results indicated that NiAl had high friction coefficient and wear rate at elevated temperatures, while incorporation of Cr(Mo) not only enhanced mechanical properties evidently but also improved high temperature tribological properties. Among the sintered materials, NiAl matrix composite with addition of ZnO showed the lowest wear rate at 1000 °C, while CuO addition into NiAl matrix composite exhibited the self-lubricating performance and the best tribological properties at 800 °C.     

Wear behavior of electroless Ni–P–B4C composite coatings

In this research, the wear of electroless Ni–P and Ni–P–B₄C composite coatings was reviewed. Auto catalytic reduction of Ni in nickel sulfate and sodium hypophosphate bath including suspended B₄C particles with different concentration was used to create composite coatings with 12, 18, 25 and 33 vol.% of B₄C particles. Coatings 35 μm thick were heat treated at 400 °C for one hour in an argon atmosphere and the wear resistance and friction coefficient of heat-treated samples were determined by block-on-ring tests. All wear tests were carried out at 24 °C, 35% moisture, 0.164 m/s sliding speed and about 1000 m sliding distance. Graphs show that an electroless Ni–P–B₄C composite coating with 25 vol.% of B₄C had the best wear resistance against a CK45 steel counterface.     

Fabrication of resistance type humidity sensor based on CaCu3Ti4O12 thick film

A resistance type humidity sensor has been fabricated from an assembly of CaCu₃Ti₄O₁₂ thick film, Ag interdigitated electrodes, and an Al₂O₃ ceramic substrate. The humidity sensing properties were measured using the direct current (DC) analysis method. The results show that the electrical properties of the CaCu₃Ti₄O₁₂ thick film are dependent on humidity and applied voltage. At low humidity, the film exhibited low conductivity and behaved as an insulator. However, at high humidity, the conductivity of the film increased due to the enhancement of ion conduction. These outcomes indicate that the measured resistance is highly dependent on the applied bias voltage within the whole humidity range i.e. 20–90% relative humidity (RH) at ambient temperature. The response and recovery times as well as sensitivity were determined to be around 2.8 min, 25 min, and 98.2%, respectively. Therefore, it is concluded that CaCu₃Ti₄O₁₂ thick film has good humidity sensing properties and has high potential in the application for fabrication of high-performance humidity sensors.     

Effect of bovine serum constituents on the surface of the tribological pair alumina/alumina nanocomposites for total hip replacement

Alumina has been widely used in the fabrication of hip joint replacement due to its excellent properties. But one of its drawbacks is the low fracture toughness, which can be enhanced with the addition of a second ceramic phase of nanometer size. Another property to be improved is its wear resistance under severe rubbing conditions. In this work Yttria Tetragonal Zirconia Polycrystal, Y-TZP (TZ-8YS, 100 nm), TiO₂ (PS-25, 50 nm) and Co (Nilaco, 28 nm) were added to Al₂O₃ (AKP 50, 300 nm). These starting powders were mixed and hot pressed, in order to fabricate alumina nanocomposites. Mechanical properties of the nanocomposites were estimated using the indentation method. Wear tests were carried out using a ball-on-plate tribometer, with a frequency of 1 Hz, at a load of 49 N, for 1 h. Alumina balls were used as the counterface. Distilled water and fetal bovine serum solution (FBSS) were the environments. The specific wear rate was within 10^?8 to 10^?7 mm³/N m and the coefficient of friction was around 0.3–0.7. Keeping in mind that wear is a process that starts on the surface and it is related to the physical chemistry of the surfaces, techniques such as scanning electron microscopy (SEM), and X-ray photoelectron spectrometry (XPS) were used to elucidate the role played by the proteins and phospholipids present in the fetal bovine serum solution and the new chemical specie formed on the surface.