Evaluation of Mechanical and Erosive wear Characteristics of TiO<Subscript>2</Subscript> and ZnO Filled Bi-Directional E-glass Fiber Based Vinyl Ester Composites

This article presents the evaluation of mechanical and erosive wear characteristics of bi-directional E-glass fiber based vinyl ester composites filled with TiO₂ (titanium oxide) and ZnO (zinc oxide) of 10 wt.% and 20 wt.% respectively. The mechanical characterization of these composites is performed. The erosion rates of these composites have been evaluated at different impingement angles (30 ^°, 60 ^° and 90 ^°). The particles used for the erosion measurements were silica sand with the diameters of 300, 425 and 600 μm and impact velocities of 30, 50 and 70 m/s were used. A plan of experiments, based on the Taguchi design, was performed to acquire data in a controlled way. An orthogonal array L₂₇ (3 ¹³) and Analysis of variance (ANOVA) have been applied to investigate the influence of process parameters on the erosive wear behaviour of these composites. The tensile strength of composite specimens is found to decrease with filler loading while hardness, flexural strength, inter-laminar shear strength (ILSS) and impact strength increase. TiO₂ filled composites were observed to perform better than ZnO filled composites under erosive wear situations. The dominant wear mechanism is studied on the basis of micrographs of the worn-out surface of composite materials. Performance optimization of composites is done by using the VIKOR method.     

Investigation of Characterization and Mechanical Performances of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and SiC Reinforced PA6 Hybrid Composites

In this study, the influence of different weight percentages of alumina oxide (Al₂O₃) and silicon carbide (SiC) reinforcement on the mechanical properties of Polyamide (PA6) composite is investigated. Test specimens of pure PA6, 85 wt% PA6 + 10 wt% Al₂O₃ + 5 wt% SiC and 85 wt% PA6 +10 wt% SiC + 5 wt% Al₂O₃ are prepared using an injection molding machine. To investigate the mechanical behaviors tensile test, impact test, flexural test, and hardness test were conducted in accordance with ASTM standards. Experimental results indicated that the mechanical properties, such as tensile, impact, hardness, and flexural strength were considerably higher than the pure PA6. The tensile fracture morphology and the characterization of PA6 hybrid composites were observed by scanning electron microscope and Fourier transform infrared spectroscopic method. Further, thermogravimetric analysis confirms the thermal stability of PA6 hybrid composites. The reinforcing effects of Al₂O₃ and SiC on the mechanical properties of PA6 hybrid composites were compared and interpreted in this paper. Improved mechanical and thermal characteristics were observed by the addition of small amount of Al₂O₃ and SiC simultaneously reinforced with the pure PA6.     

Dry Sliding Friction and Wear Behavior of AA7075-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Composite

The present investigation is aimed at identifying the influence of Si₃N₄ reinforcement on the mechanical and tribological behavior of AA7075-Si₃N₄ composite. Five different composites of AA7075 aluminum alloy reinforced by silicon nitride particles have been fabricated by the stir casting route. The percentage of silicon nitride was varied from 0-8 wt%. The cast composites were tested for hardness, density and compression strength. Unidirectional friction and wear testing was carried out for all compositions under five different loading conditions (10 N, 20 N, 30 N, 40 N and 50 N) at a constant sliding speed of 1 m/s. SEM and EDS analysis was also carried out for worn surface analysis and elemental analysis of the composites. The hardness and compression strength of the composites exhibited an increasing trend with an increase in wt% of reinforcement in the base alloy, showing 20% improvement in hardness and around 50% improvement in compression strength for 8 wt% Si₃N₄ addition. The addition of Si₃N₄ particles led to an improvement in the wear resistance by 37% at low loads (10 N) and 61% at higher loads (50 N). The COF for all varied compositions at low load (10 N) and high load (50 N) ranges from 0.10 to 0.20 and 0.25 to 0.30 respectively. Moreover, the COF is observed to increase until 4 wt% and beyond it decreases. Microscopic studies of worn surfaces revealed a dominance of delamination wear at lower concentrations (0 wt% and 2 wt%) and ploughing at higher concentrations (6 wt% and 8 wt%). The developed composites exhibited better mechanical and anti-wear properties and could serve as potential candidates in sliding applications such as bearings, brake drums, gears, sprockets and brake rotors.     

V<Subscript>2</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>5</Subscript>/SiO<Subscript>2</Subscript> as a Heterogeneous Catalyst in the Synthesis of bis(indolyl)methanes Under Solvent Free Condition

The heterogeneous catalyst of V₂ O ₅/SiO₂ was prepared and characterized with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy. XRD of the silicon dioxide used reveals the amorphous nature while the spectrum of the prepared catalyst shows sharp intense peaks at about (20.2, 26.1, 31.0 and 47.3^°) and less intense sharp peaks at about (51.1, 55.2, 57.1 and 60.4^°) indicating formation of a crystalline phase with orthorhombic geometry. The FTIR spectra of the catalyst showed characteristic vibration stretching bands of V ?O at their specified position. An efficient and facile approach for the synthesis of bis(indolyl)methanes through a catalytic one pot reaction. Indole and aromatic aldehydes were stirred in the presence of a catalytic amount of the prepared and characterized heterogeneous catalyst V₂ O ₅/SiO₂ at 50^°C under solvent free condition. This procedure has advantages in competition with the previously reported methods, in terms of high yield, green catalyst, mild reaction condition, simple procedure, lack of toxicity, low cost, and simplicity of workup.     

B4C reinforced NiTi-based composites: Microstructure and wear performance

In this study, NiTi–x wt.% B₄C (x = 0, 2, and 4) composites were consolidated with spark plasma sintering method, and the effects of boron carbide reinforcement addition on the microstructure and wear behavior of samples were investigated. Identification of the constituent phases of samples by the X-ray diffraction method plus Rietveld analysis revealed that the stability of the martensite phase increased in the composite samples because of mismatch stresses between the NiTi matrix phase and the reinforcing particles, which increases the density of the dislocations and facilitates the diffusion process that subsequently leads to the formation of stable intermetallics. The results of hardness test indicated that the hardness value increased from 3.67 GPa for pure NiTi to 10.99 GPa for NiTi–4 wt.% B₄C. Results of wear test revealed that boron carbide reinforced composite specimens had higher wear resistance, whereas wear rate of NiTi sample was 3.6 × 10⁻³ mm³/N m, and it reached to .21 × 10⁻³ mm³/N m for NiTi–4 wt.% B₄C. Investigation of microstructure by scanning electron microscopy images and EDS analysis revealed that the wear mechanism in NiTi samples was abrasive and the addition of B₄C to NiTi changed the wear mechanisms from abrasive to a combination of oxidation, adhesive, and delamination mechanisms.     

Thermal and neutron shielding properties of <Superscript>10</Superscript>B<Subscript>2</Subscript>O<Subscript>3</Subscript>/polyimide hybrid materials

In this study, ¹⁰B₂O₃/polyimide (PI) hybrid materials were synthesized with the aim to improve their thermal stability and neutron shielding properties. 3,3′-Diaminodiphenyl sulfone (DADPS) reacted with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl-2-pyrrolidone (NMP) and mixed with amine functionalized ¹⁰B₂O₃ to prepare a series of poly (amic acid), meanwhile, corresponding PIs were obtained via the thermal imidization procedures. The morphologies and structures of the prepared hybrid materials were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The thermooxidative and flame retardancy properties of the PI films were examined by thermogravimetric analysis (TGA) and limiting oxygen ındex (LOI). The experimental results showed that as the amount of functionalized ¹⁰B₂O₃ was increased, flame retardant properties of the hybrid films were increased. Hybrid materials were also irradiated with thermal neutrons. The neutron shielding properties increasing depends on the amount and the distribution of the ¹⁰B isotope.     

Low-weight TiAl<Subscript>3</Subscript> composites by thermal explosion

Dispersion-strengthened TiAl₃-based material with uniform structure and high compression strength (σ_c ≈ 850 MPa) was SHS-produced from Ti–Al–B₄C blends in a mode of thermal explosion by using the B₄C particles coated with a TiB₂/TiC layer as a strengthening agent and preliminary mechanical activation of Ti–Al powder mixtures. The Ti + 3Al mixtures were mechanically activated in a planetary mill for 3 or 6 min and then 10 or 20 wt % of coated B₄C particles were added. Pelleted samples were placed into a reaction chamber and heated in an electric furnace under Ar to a self-ignition temperature. The process was optimized and recommended for practical implementation.     

Optoelectronic Properties of Al/n-Si/ Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>/Au Photosensor

We have fabricated an Al/n-Si/Bi₄Ti₃O₁₂/Au photodiode by the sol-gel method. The photoelectrical response of the diode was measured under dark and various light intensity conditions. The photocurrent of the diode increases with increase in light intensity. The light sensitivity value of the photosensor was measured and observed to increase from 5.06 × 10^?8 (under dark) to 2.34 × 10^?4 A (under 100 mW/cm²). Furthermore, other parameters for instance, ideality factor and barrier height of the photosensors were calculated. The ideality factor and barrier height of the Al/n-Si/Bi₄Ti₃O₁₂/Au photosensor were found to be 3.01 and 0.86 eV respectively. Also capacitance-voltage (C-V) characteristics were measured. The C-V graph indicates changeable behavior with the varying frequency. The value of capacitance and the interface state density D_it value decrease with increase in frequency. Thus, the obtained results indicate that the Al/n-Si/Bi₄Ti₃O₁₂/Au photosensor can be used as a photosensor in optoelectronic applications.     

Wear behavior of Al(OH)<Subscript>3</Subscript>-GF/epoxy composites in low velocity

Effects of fiber content, size, and weave form, and addition of particles on wear behaviors of epoxy composites are studied widely, while little investigation is paid on thermal effect in friction. In this study, effects of Al(OH)₃ powder on wear behavior of glass fiber reinforced epoxy composites are investigated. The experimental results show that within 6 wt%, the addition of Al(OH)₃ powder could decrease the friction surface temperature, friction coefficient, and wear mass loss of the composites. The decrease is attributed to the heat absorption when Al(OH)₃ powder decomposes. However, when the content of Al(OH)₃ powder increases to 9 wt%, the temperature, the friction coefficient, and the wear mass loss increase to nearly equal to those of pure epoxy resin-based composites. It is considered resulting from the decrease in mechanical property, which could lead to more serious fatigue wear. In a word, within a proper content, the addition of Al(OH)₃ powder in epoxy could increase the resistance to wear and friction.     

Effect of Reinforcement Volume Fraction on the Wear Behavior of Al-SiC<Subscript><Emphasis Type="Bold">p</Emphasis></Subscript> Composites Prepared by Spark Plasma Sintering

Most investigations on MMCs were carried out using conventional methods. Employing a different approach, this study concentrated on compaction, hardness and wear behavior of Al-SiC composites with different reinforcement volume fractions (5–15%) by spark plasma sintering method. Hardness and density test results of the composite samples used in this study were significantly higher than conventionally produced composites. Such increase in density and hardness resulted in lower wear rate. To study the effect of applied load on samples wear behavior, wear tests were carried out under 1, 3 and 10 N loads with 0.07 m/s sliding rate. Results revealed that in all the applied loads, composite samples had lower wear rates and lower friction coefficients than those of unreinforced aluminum. Conversely, increase in volume fraction of reinforcement particles led to decrease in wear rates and friction coefficients of the composite specimens which were more tangible in Al-15%SiC sample. Obtained data showed that by increasing the applied load, friction coefficient and wear rate increased in all the samples. Also dominant wear mechanism was determined using SEM micrographs of sample surfaces after wear tests.     

Effect of a novel intumescent retardant for ABS with synergist Al(H<Subscript>2</Subscript>PO<Subscript>2</Subscript>)<Subscript>3</Subscript>

A novel intumescent flame retardant (IFR), containing ammonium polyphosphate (APP) and poly(hexamethylene terephthalamide) (PA6T), was prepared for acrylonitrile–butadiene–styrene (ABS). Limiting oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA) were used to investigate the flammability property and thermal stability of the IFR/ABS systems. It was found that the flame retardancy of the IFR/ABS systems was improved significantly. When the components of the IFR were 25% APP and 5% PA6T, the LOI value of IFR/ABS system reached to the maximum of 29, but only UL-94V-1 rating was passed. Thus, Al(H₂PO₂)₃ was incorporated into ABS/APP/PA6T system as a synergistic agent, it was found 2% addition of Al(H₂PO₂)₃ caused PA6T/APP/PA6T/Al(H₂PO₂)₃ (70/23.3/4.7/2) to pass V-0 rating of UL-94 test. Meanwhile, the TGA curves indicated that PA6T could be effective as a charring agent and there was a synergistic reaction between PA6T and APP, which effectively promoted the char formation of IFR/ABS composites. Moreover, the residual char obtained after the LOI test of the IFR/ABS was characterized by Fourier transform infrared spectra (FTIR). Results indicated that P–O–C chemical bond was formed in the residual char, which could indicate the cross-linking reaction between PA6T and APP could occur. Furthermore, scanning electron microscopy (SEM) was used to investigate the morphology of the residual char formed in the LOI tests. It was revealed that both ABS/APP/PA6T (70/25/5) and PA6T/APP/PA6T/Al(H₂PO₂)₃ (70/23.3/4.7/2) formed uniform and compact intumescent charred layers.     

Study of electrochemical properties and the charge/discharge mechanism for Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>/MnO<Subscript>2</Subscript>-AC hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO₂-AC) were prepared by a method in which KMnO₄ was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li₄Mn₅O₁₂ and MnO₂-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g⁻¹ was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g⁻¹ in 1 mol L⁻¹ Li₂SO₄ solution. The charge/discharge mechanism of Li₄Mn₅O₁₂ and MnO₂-AC was discussed.     

A method for determining the charge state of chromium in Cr-doped Bi<Subscript>12</Subscript>SiO<Subscript>20</Subscript> and Bi<Subscript>12</Subscript>TiO<Subscript>20</Subscript> materials

A chemical method for determination of the charge state of chromium in B₂O₃-based materials (Bi₁₂SiO₂₀ and Bi₁₂TiO₂₀ single crystals) in a wide Cr concentration range (1 × 10^–5 – 2 × 10^–2 wt.%)is proposed. The method is based on a color reaction between Cr⁶⁺ and diphenylcarbazide in an acid medium.Translated from Novye Ogneupory, No. 8, pp. 61 – 63, August, 2004.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanofiller on ion conductivity,transmittance, and glass transition temperature of PEI:LiTFSI:PC:EC polymer electrolytes

In the present study, ion conductivity, optical properties, and glass transition temperatures are characterized for polymer electrolytes composed of poly(ethyleneimine) (PEI), lithium bis(trifluoromethane)sulfonylimide (LiTFSI) salt, propylene carbonate (PC), and ethylene carbonate (EC). It was doped with nanoceramic particles in different ratio (0–15 wt.%) to see the effect of ceramic particles. The salt concentration was fixed as 1.04 mol.kg^?1. Although valuable improvement in ion conductivity could not be achieved due to nano-Al₂O₃ fillers, ion conductivity results are placed between 10^?2 and 10^?4 S/cm. Differential scanning calorimetry (DSC) measurements and optical measurements of all electrolytes were performed between ?80 and 140 °C, in the wavelength range between 400 and 700 nm for sample with 80 μm thickness, respectively. The results showed that transmittance of electrolytes decreased monotonically for increasing Al₂O₃ contents. In particular, its transmittance value at 550 nm where human sight is at its greatest sensitivity went from 100% without nanoparticles to 50% for 15 wt% of Al₂O₃.     

Electrical properties of lead-free 0.98(Na<Subscript>0.5</Subscript>K<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript>-0.02Ba(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> piezoelectric ceramics by optimizing sintering temperature

Lead-free 0.98(Na_0.5K_0.5)NbO₃-0.02Ba(Zr_0.52Ti_0.48)O₃ [0.98NKN-0.02BZT] ceramics were fabricated by the conventional mixed oxide method with sintering temperature at 1,080°C to 1,120°C. The results indicate that the sintering temperature obviously influences the structural and electrical properties of the sample. For the 0.98NKN-0.02BZT ceramics sintered at 1,080°C to 1,120°C, the bulk density increased with increasing sintering temperature and showed a maximum value at a sintering temperature of 1,090°C. The dielectric constant, piezoelectric constant [d ₃₃], electromechanical coupling coefficient [k _p], and remnant polarization [P _r] increased with increasing sintering temperature, which might be related to the increase in the relative density. However, the samples would be deteriorated when they are sintered above the optimum temperature. High piezoelectric properties of d ₃₃ = 217 pC/N, k _p = 41%, dielectric constant = 1,951, and ferroelectric properties of P _r = 10.3 μC/cm² were obtained for the 0.98NKN-0.02BZT ceramics sintered at 1,090°C for 4 h.     

Improvement in dielectric and mechanical performance of CaCu<Subscript>3.1</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12.1</Subscript> by addition of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

The properties of CaCu_3.1Ti₄O_12.1 [CC3.1TO] ceramics with the addition of Al₂O₃ nanoparticles, prepared via a solid-state reaction technique, were investigated. The nanoparticle additive was found to inhibit grain growth with the average grain size decreasing from approximately 7.5 μm for CC3.1TO to approximately 2.0 μm for the unmodified samples, while the Knoop hardness value was found to improve with a maximum value of 9.8 GPa for the 1 vol.% Al₂O₃ sample. A very high dielectric constant > 60,000 with a low loss tangent (approximately 0.09) was observed for the 0.5 vol.% Al₂O₃ sample at 1 kHz and at room temperature. These data suggest that nanocomposites have a great potential for dielectric applications.     

Preparation of Ti<Subscript>2</Subscript>AlN by reactive sintering

Reactive sintering of 2Ti–AlN mixtures at T = 1300°C for τ = 2 h in an argon atmosphere was used to prepare Ti₂AlN containing below 1 wt % TiN and exhibiting a laminate structure typical of MAX compounds. At lower values of T and τ, the TiN content of products increased. Sintering in vacuum yielded a material containing up to 20 wt % TiN. Contrary to our expectations, mechanical activation of green blends was found to increase the TiN content of sintered materials, due to intensification of thermal dissociation of AlN and elimination of Al, which shifts equilibrium toward two-phase Ti₂AlN–TiN composite. Relative density of green compacts was found to produce little or no influence on phase composition of products.     

Chemical and electrochemical characterization of TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> atomic layer depositions on AZ-31 magnesium alloy

In this study, innovative TiO₂/Al₂O₃ mono/multilayers were applied by atomic layer depositions (ALD) on ASTM-AZ-31 magnesium/aluminum alloy to enhance its well-known scarce corrosion resistance. Four different configurations of ALD layers were tested: single TiO₂ layer, single Al₂O₃ layer, Al₂O₃/TiO₂ bilayer and Al₂O₃/TiO₂/Al₂O₃/TiO₂ multilayer deposited using Al[(CH₃)]₃ (trimethylaluminum, TMA), and TiCl₄ and H₂O precursors. All depositions were performed at 120°C to obtain an amorphous-like structure of both oxide layers. The four coatings were then investigated using different techniques, such as scanning electron microscope (SEM), stylus profilometer, glow discharge optical emission spectrometry (GDOES) and polarization curves in 0.05-M NaCl solution. The thickness of all the coatings was around 100 nm. The layers compositions were successfully investigated by the GDOES technique, although obtained data seem to be affected by substrate roughness and differences in sputtering rates between ceramic oxides and metallic magnesium alloy. Corrosion resistance showed to be strongly enhanced by the nanometric coatings, giving lower corrosion current densities in 0.05-M NaCl media with respect to the uncoated substrate (from 10⁻⁴ to 10⁻⁶ A/cm² for the single layers and from 10⁻⁴ to 10⁻⁸ A/cm² for the bi- and multilayers). All polarization curves on coated samples also showed a passive region, wider for the bi-layer (from −0.58 to −0.43 V with respect to Ag/AgCl) and multilayer (from −0.53 to −0.38 V with respect to Ag/AgCl) structures.     

Polystyrene-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite solid polymer electrolyte for lithium secondary battery

In a common salt-in-polymer electrolyte, a polymer which has polar groups in the molecular chain is necessary because the polar groups dissolve lithium salt and coordinate cations. Based on the above point of view, polystyrene [PS] that has nonpolar groups is not suitable for the polymer matrix. However, in this PS-based composite polymer-in-salt system, the transport of cations is not by segmental motion but by ion-hopping through a lithium percolation path made of high content lithium salt. Moreover, Al₂O₃ can dissolve salt, instead of polar groups of polymer matrix, by the Lewis acid-base interactions between the surface group of Al₂O₃ and salt. Notably, the maximum enhancement of ionic conductivity is found in acidic Al₂O₃ compared with neutral and basic Al₂O₃ arising from the increase of free ion fraction by dissociation of salt. It was revealed that PS-Al₂O₃ composite solid polymer electrolyte containing 70 wt.% salt and 10 wt.% acidic Al₂O₃ showed the highest ionic conductivity of 9.78 × 10^-5 Scm^-1 at room temperature.     

Crystal structure of Pb<Subscript>6</Subscript>O[(Si<Subscript>6</Subscript>Al<Subscript>2</Subscript>)O<Subscript>20</Subscript>]

The crystal structure of Pb₆O[(Si₆Al₂)O₂₀)] is investigated using X-ray diffraction. The compound has tetragonal symmetry, space group I4/mmm, a = 11.7162(10) Å, c = 8.0435(12) Å, and V = 1104.13(2) ų. The structure is refined to R ₁ = 0.036 for 562 unique reflections with [F ₀] ≥ 4σF. The structure contains two symmetrically independent positions of the Pb²⁺ cations coordinated by five O atoms (Pb²⁺-O^2? = 2.34–2.68 Å). The TO₄ tetrahedra (T = Si, Al) form tubular [(Si₆Al₂)O₂₀] chains extended along the c axis. The O₄ oxygen atom is not bonded to the Si and Al atoms and is octahedrally coordinated by six Pb atoms with the formation of an oxo-centered OPb₆ octahedron. The assumption is made that, in some of lead silicate and aluminosilicate glasses, a number of oxygen atoms are located outside the tetrahedral structure and represent segregation centers of the Pb²⁺ cations due to the formation of oxo-centered complexes.