Wear and friction of Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites at various sliding speeds

The present study addresses the dry wear behavior of Al₂O₃ 6061 Aluminum particulate composite under different sliding speeds and applied load using pin-on-disk tribometer at room temperature. Three grades of the submicron particle composites containing 10, 20, and 30 vol.% Al₂O₃ were tested. The results illustrate that higher load and higher concentration of Al₂O₃ particles lead to higher wear rates. For 10 and 20% Al₂O₃ concentrations, the wear rate decreases with increasing sliding speed, while it increases for 30% Al₂O₃. The surface morphologies of the worn composites indicate that at lower sliding speeds abrasion is dominant, while at higher sliding speeds delamination and adhesion increases. Results also indicate that the friction coefficient between the composite and the mating steel surface decreases with increasing sliding speed to a steady state.     

The effect of Fe contents on the local structure and crystallization behavior of SiO<Subscript>2</Subscript>–CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The glass and glass ceramics containing SiO₂–CaO–Fe₂O₃–P₂O₅ were prepared by sol–gel method. The influence of the Fe contents on the crystallization and local structure of the glass and glass ceramics was systematically investigated. The crystal structure of the glass ceramics was identified by XRD characterization. Hematite phase can be precipitated from the glass matrix in all glass ceramics with various Fe contents, and the crystallographic parameters of hematite were determined by XRD Rietveld refinement. The crystallization kinetics of the glasses was investigated in detail. Relative low activation energies were obtained at low Fe contents. The local structure evolution of the glass and glass ceramics has been studied in-depth by means of FTIR and Mössbauer spectroscopy. Fe element is present both as network former and network modifier which significantly influenced the crystallization activation energies of the glasses. The results of this work may be of great significance for the material design and practical applications of bioactive magnetic glass ceramics for hyperthermia.     

Synthesis and optical limiting studies of HA<Subscript>P</Subscript> and HA<Subscript>P</Subscript>@SiO<Subscript>2</Subscript> core–shell nanoparticles

We report the spectral and optical limiting properties of two kinds of HA_P nanoparticles (pure HA_P and HA_P@SiO₂ core–shell nanoparticles) that were wet-chemically prepared and coated with silica by means of Stober method. The size, framework substitution and silica coating formation of the resultant particles were confirmed by Transmission Electron Microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy and Thermogravimetric analysis. The nonlinear optical limiting properties of HA_P and HA_P@SiO₂ nanoparticles suspended in ethylene glycol is studied at 532 nm using 5 ns Nd:YAG laser pulses. Observations indicate that effective three-photon absorption is found to be responsible for strong optical limiting characteristics in these nanoparticles and it is seen that the optical nonlinearity is enhanced in core–shell structures as compared with single counterparts. The nonlinear optical parameters calculated from the data show that these materials are efficient optical limiters.     

Compositional dependence of some physical properties of ZnO–PbO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Six glasses of the chemical composition 10ZnO–xPbO–(90−x) P₂O₅ were prepared. With an increase in PbO content a non-monotonous step like increase in the density, in the glass transition temperature, and in the refractive index was observed. From the Raman and IR spectra studied the evidence is given for the phosphate network depolymerization as PbO content increases. Increase in PbO content leads also to an increase in refractive index (n) up to n = 1.74, for x = 55, and to an increase in the glass transition temperature (T _g) from T _g = 270 °C (x = 30) to T _g = 360 °C (x = 55).

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Investigation of TaC–TaB<Subscript>2</Subscript> ceramic composites

The TaC–TaB₂ composition was sintered by spark plasma (SPS) at 1900–2100°C and applied pressure of 30 MPa. TaC and 2–3 wt% B₄C were used as starting powders. Densification process, phase evolution, microstructure and the mechanical properties of the composites were investigated. The results indicated that the TaC–TaB₂ composition could be SPS to 97% of theoretical density in 10 min at 2100°C. Addition of B₄C leads to an increase in the density sample from 76 to 97%. B₄C nano-powder resists grain growth even at high temperature 2100°C. The formation of TaB₂/carbon at TaC grain boundaries helps in pinning the grain boundary and inhibiting grain growth. The phase formation was associated with carbon and boron diffusion from the starting particles B₄C to form TaB₂ phases. TaC grain sizes decreased with increase in B₄C concentration. Samples with 2.0 wt% B₄C composition had highest flexure strength up to 520 MPa. The effect of B₄C addition on hardness measured by microhardness has been studied. Hardness of samples containing 3.0 wt% B₄C was 16.99 GPa.     

Synthesis of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> mesoporous bioactive glasses with high P<Subscript>2</Subscript>O<Subscript>5</Subscript> content by evaporation induced self assembly process

Mesoporous bioactive glasses (MBGs) of the CaO–SiO₂–P₂O₅ system containing relatively high P₂O₅ contents (10–30 mol%) were prepared from a sol–gel. An evaporation-induced self-assembly (EISA) technique was used with poly(ethylene oxide)-block–poly(propylene oxide)-block–poly(ethylene oxide) (EO₂₀–PO₇₀–EO₂₀, P123) acting as a template. The structural, morphological and textural properties of MBGs were investigated by small-angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and a N₂ sorption/desorption technique. SAXRD and TEM results display the reduced long-range ordering of mesopores with increasing P₂O₅ content. N₂ sorption/desorption analysis shows that all three samples exhibit a type IV isotherm with type H1 hysteresis loops, characteristic of independent cylindrical slim pore channels and this material has a Barret–Joyner–Halenda (BJH) model pore size of ~4 nm and BET specific surface area ~430 m²/g. NMR results indicate a more condensed framework for samples with 30 mol% P₂O₅ than samples with 10 mol% P₂O₅. For in vitro bioactivity tests where samples were soaked in simulated body fluid (SBF), samples with 30 mol% P₂O₅ showed higher crystallinity than those with lower P₂O₅ contents Silicon concentration increased in SBF solution during the soaking period, which indicates MBGs can be degradable in SBF solution.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Evaluation of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Na<Subscript>2</Subscript>O–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> bioglass-ceramics for hyperthermia application

Magnetic bioglass ceramics (MBC) are being considered for use as thermoseeds in hyperthermia treatment of cancer. While the bioactivity in MBCs is attributed to the formation of the bone minerals such as crystalline apatite, wollastonite, etc. in a physiological environment, the magnetic property arises from the magnetite [Fe₃O₄] present in these implant materials. A new set of bioglasses with compositions 41CaO · (52 ? x)SiO₂ · 4P₂O₅  · xFe₂O₃ · 3Na₂O (2 ≤ x ≤ 10 mol% Fe₂O₃) have been prepared by melt quenching method. The as-quenched glasses were then heat treated at 1050°C for 3 h to obtain the glass-ceramics. The structure and microstructure of the samples were characterized using X-ray diffraction and microscopy techniques. X-ray diffraction data revealed the presence of magnetite in the heat treated samples with x ≥ 2 mol% Fe₂O₃. Room temperature magnetic property of the heat treated samples was investigated using a Vibrating Sample Magnetometer. Field scans up to 20 kOe revealed that the glass ceramic samples had a high saturation magnetization and low coercivity. Room temperature hysteresis cycles were also recorded at 500 Oe to ascertain the magnetic properties at clinically amenable field strengths. The area under the magnetic hysteresis loop is a measure of the heat generated by the MBC. The coercivity of the samples is another important factor for hyperthermia applications. The area under the loop increases with an increase in Fe₂O₃ molar concentration and the. coercivity decreases with an increase in Fe₂O₃ molar concentration The evolution of magnetic properties in these MBCs as a function of Fe₂O₃ molar concentration is discussed and correlated with the amount of magnetite present in them.     

Microwave adsorption of core–shell structure polyaniline/SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> composites

Polyaniline/strontium hexaferrites (PANI/SrFe₁₂O₁₉) composites were synthesized by the oxidative chemical polymerization of aniline in the presence of APS. X-ray powder diffraction of ferrites indicated that the structure of core materials is hexagonal with lattice constants around 5.886–5.885 Å. The structural in the character of the sol–gel was investigated with Fourier transform infrared spectrometer analysis. SEM and TEM photographs show that the particle size of core material is around 50–200 nm. After coating with polyaniline, the particle size of the core–shell of PANI/SrFe₁₂O₁₉ has grown up to 100~300 nm. In the magnetization for the PANI/SrFe₁₂O₁₉ composites, it was found that the saturation magnetization (M _s) and coercivity (H _c) decreased after polyaniline coating. The composite under applied magnetic field exhibited the hysteretic loops of the ferromagnetic behavior, such as high saturation magnetization (M _s = 18.9 emu/g) and coercivity (H _c = 3850.0 Oe). The conductivity of the core–shell materials increased with increasing amounts of polyaniline as the temperature increased from 0 to 50 °C, the conductivity increased by about 13%. The polymerization mechanism for the core–shell composites was also investigated. The composite specimens of core–shell PANI/SrFe₁₂O₁₉ and thermal plastic resin (TPR) had band-width microwave absorption due to reflection losses from ?27.3 to ?37.4 dB at frequencies between 10.5 and 11.8 GHz as observed by High-frequency network analyzer.     

Effect of sintering temperatures on properties of BaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass/silica composites for CBGA package

BaO–B₂O₃–SiO₂–Al₂O₃ (BBSA) glass/silica composites synthesized by solid-state reaction method were developed for CBGA packages, and the effects of sintering temperature (900–950 °C) on the phase transformation, microstructure, thermal, mechanical and electrical properties were investigated. XRD results show that the major phases quartz and cristobalite, and the minor phase BaSi₂O₅ are detected in BBSA composites. Furthermore, it was found that the quartz phase transforms to cristobalite phase at 930–940 °C. The formation of cristobalite phase with higher coefficient of thermal expansion (CTE) led to the increase of CTE value of BBSA composites. However, excessive cristobalite phase content would degrade the mechanical properties and the linearity of thermal expansion of the ceramics. BBSA composites sintered at 920 °C exhibited excellent properties: low dielectric constant and loss (ε_r = 6.2, tanδ = 10^?4 at 1 MHz), high bending strength (179 MPa), high CTE (12.19 ppm/°C) as well as superior linearity of the thermal expansion.     

Mechanochemical behavior of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al–Fe powder mixtures to produce Fe<Subscript>3</Subscript>Al–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite powder

Mechanical treatment of Fe₂O₃, Al and Fe powder mixtures was carried out in a high energy ball mill to synthesize Fe₃Al–Al₂O₃ intermetallic matrix nanocomposite. Different compositions including 3Fe + Al, Fe₂O₃ + 2Al, 3Fe₂O₃ + 8Al and Fe₂O₃ + 3Al+Fe were chosen in this study. Phase development and structural changes occurring during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during MA, Fe₂O₃, Al, and Fe react to give a nanocrystalline Fe₃Al intermetallic compound matrix. The presence of pure Fe in initial powder mixture changed the modality of mechanochemical process from sudden to gradual reaction. The Fe₃Al–Al₂O₃ compound had a finer microstructure and particles size compared to the Fe₃Al compound.     

Phytic acid derived bioactive CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> gel-glasses

The possibility of using phytic acid as a precursor to synthesize CaO–P₂O₅–SiO₂ glasses by sol–gel method has been explored and the pseudo ternary phase diagram has been established. It was shown that gel-glasses over a broader range of compositions could be prepared compared to other phosphorus precursors or melt-quenching method. Furthermore, phytic acid was found to assist calcium being incorporated into glass networks. In vitro tests in simulated body fluid (SBF) were performed on the above gel–glasses and it was found that they were bioactive over a much broader compositional range especially at high phosphate content, thus enabling one to design bioactive materials with various degradation rates by adjusting the phosphate content.     

In vitro dissolution behavior of SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–F glass–ceramic system

Herein, we report the results of the in vitro dissolution tests, which were carried out by immersing the selected glass-ceramic samples in artificial saliva (AS) for various time periods of up to 42 days. In our experiments, the SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass ceramics with different crystal morphology and crystal content were used and a comparison is also made with the baseline glass samples (without any crystals). The bioactivity of the samples was probed by measuring the changes in pH, ionic conductivity and ionic concentration of AS following in vitro dissolution experiments. High resistance of the selected glass-ceramic samples against in vitro leaching has been demonstrated by minimal weight loss (<1%) and insignificant density change, even after 6 weeks of dissolution in artificial saliva. While XRD analysis reveals the change in surface texture of the crystalline phase, FT-IR analysis weakly indicated the Ca-P compound formation on the leached surface. The experimental measurements further indicate that the leaching of F(-), Mg(2+) ions from the sample surface commonly causes the change in the surface chemistry. Furthermore, the presence of (Ca, P, O)-rich mineralized deposits on the leached glass-ceramic surface as well as the decrease in Ca(2+) ion concentrations in the leaching solutions (compared to that in the initial AS solution) provide evidences of the moderate bioactive or mild biomineralisation behaviour of investigated glass-ceramics.     

Preparation and characterization of Li<Subscript>2</Subscript>O–CaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> glasses as bioactive material

The aim of the present investigation was to study the role of Al₂O₃ in the Li₂O–CaO–P₂O₅–SiO₂ bioactive glass for improving the bioactivity and other physico-mechanical properties of glass. A comparative study on structural and physico-mechanical properties and bioactivity of glasses were reported. The structural properties of glasses were investigated by X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and the bioactivity of the glasses was evaluated by in vitro test in simulated body fluid (SBF). Density, compressive strength, Vickers hardness and ultrasonic wave velocity of glass samples were measured to investigate physical and mechanical properties. Results indicated that partial molar replacement of Li₂O by Al₂O₃ resulted in a significant increase in mechanical properties of glasses. In vitro studies of samples in SBF had shown that the pH of the solution increased after immersion of samples during the initial stage and then after reaching maxima it decreased with the increase in the immersion time. In vitro test in SBF indicated that the addition of Al₂O₃ up to 1.5 mol% resulted in an increase in bioactivity where as further addition of Al₂O₃ caused a decrease in bioactivity of the samples. The biocompatibility of these bioactive glass samples was studied using human osteoblast (MG-63) cell lines. The results obtained suggested that Li₂O–CaO–Al₂O₃–P₂O₅–SiO₂-based bioactive glasses containing alumina would be potential materials for biomedical applications.     

Thermophysical Properties of Ceramic Filler-Added BaO–ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> Glass Composites for Barrier Ribs of Plasma Display Panels

The capability of BaO–ZnO–B₂O₃–P₂O₅ glass in hosting various ceramic fillers (up to 20 mass% of Al₂O₃, TiO₂, and ZnO) has been investigated. All the investigated filler-added glasses have demonstrated a reasonable densification at 550 °C to form stable ceramic filler-glass composites. Modifications of the thermophysical properties, such as coefficient of thermal expansion (CTE), glass transition temperature, and dilatometric softening temperature, by the addition of the fillers have been investigated and correlated to phase and microstructural evolution. The CTE of the fabricated composites with varying filler addition is well correlated with theoretical predictions based on the Turner equation considering the modification by phase evolution, which indicates the thermal property tuning potential of the BZBP-based glass composites for application to barrier ribs of plasma display panels.     

Characterization of Li<Subscript>2</Subscript>S–P<Subscript>2</Subscript>S<Subscript>5</Subscript>–Cu composite electrode for all-solid-state lithium secondary batteries

Electrochemical performance of the Li₂S–P₂S₅–Cu composite materials was examined in all-solid-state lithium secondary batteries. The 80Li₂S·20P₂S₅ (mol.%) solid electrolyte with the addition of Cu was partially used as an active material with lithium source in all-solid-state cells. The initial discharge capacity of 110 mAh g⁻¹ (normalized by the weight of 80Li₂S·20P₂S₅–Cu), which corresponds to 400 mAh g⁻¹ (normalized by the weight of Li₂S), was obtained in the cell using the 80Li₂S·20P₂S₅–Cu composite electrode with the molar ratio of Li₂S/Cu = 48/52. Cycling performance and reaction mechanism of the electrode in the solid-state cell were investigated.     

Wear resistance of electrodeposited Ni–B and Ni–B–Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite coatings

The wear resistance of electrodeposited (ED) Ni–B and Ni–B–Si₃N₄ composite coatings is compared. The effect of incorporation of Si₃N₄ particles in the ED Ni–B matrix on the surface morphology, structural characteristics and microhardness has been evaluated to correlate the wear resistance. The wear mechanism of ED Ni–B and Ni–B–Si₃N₄ composite coatings appears to be similar; both involve intensive plastic deformation of the coating due to the ploughing action of the hard counter disc. However, the extent of wear damage is relatively small for ED Ni–B–Si₃N₄ composite coatings.     

Structural investigations of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–CaO glass system by FT-IR and EPR spectroscopies

xV₂O₅·(100 − x)[0.7P₂O₅·0.3CaO] glass system was obtained for 0 ≤ x ≤ 35 mol% V₂O₅. In order to obtain information regarding their structure, several techniques such as X-Ray diffraction, FT-IR, and EPR spectroscopies were used. X-Ray diffraction patterns of investigated samples are characteristic of vitreous solids. FT-IR spectra of 0.7P₂O₅·0.3CaO glass matrix and its deconvolution show the presence in the glass structure of all structural units characteristic to P₂O₅. Their number are increasing for x ≤ 3 mol% V₂O₅ then, for higher content of vanadium ions, the number of phosphate structural units are decreasing leading to a depolymerization of the structure. The structural units characteristic to V₂O₅ were not evidenced but their contribution to the glass structure can be clearly observed. EPR revealed a well resolved hyperfine structure (hfs) typical for vanadyl ions in a C_4v symmetry for x ≤ 3 mol% V₂O₅. For 5 < x < 20 mol% V₂O₅ the spectra show a superposition of two EPR signals one due to a hfs structure and another consisting of a broad line typical for associated V⁴⁺–V⁴⁺ ions. For x ≥ 20 mol% V₂O₅ only the broad line can be observed. The composition dependence of the line-width suggests the presence of dipole–dipole interaction between vanadium ions up to x ≤ 5 mol% V₂O₅ and superexchange interactions between vanadium ions for x > 5 mol% V₂O₅.     

Synthesis,bioactivity and preliminary biocompatibility studies of glasses in the system CaO–MgO–SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–CaF<Subscript>2</Subscript>

New compositions of bioactive glasses are proposed in the CaO–MgO–SiO₂–Na₂O–P₂O₅–CaF₂ system. Mineralization tests with immersion of the investigated glasses in simulated body fluid (SBF) at 37°C showed that the glasses favour the surface formation of hydroxyapatite (HA) from the early stages of the experiments. In the case of daily renewable SBF, monetite (CaHPO₄) formation competed with the formation of HA. The influence of structural features of the glasses on their mineralization (bioactivity) performance is discussed. Preliminary in vitro experiments with osteoblasts’ cell-cultures showed that the glasses are biocompatible and there is no evidence of toxicity. Sintering and devitrification studies of glass powder compacts were also performed. Glass-ceramics with attractive properties were obtained after heat treatment of the glasses at relatively low temperatures (up to 850°C).     

Structural investigation of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–K<Subscript>2</Subscript>O glass system with antibacterial potential

The xV₂O(1?x)[0.8 P₂O₅ ? 0.2 K₂O] glass system with 0 ≤ x ≤ 50 mol% was prepared and the structural changes induced in these glasses by increasing the vanadium oxide content were investigated by IR and ESR spectroscopies. The dual behaviour role of V₂O₅ oxide, as network modifier (for x ≤ 10 mol%) and the network former (x ≥ 20 mol%), as a consequence of phosphate network depolymerization and P–O–V and V–O–V linkages appearance was also highlighted. The antibacterial effect of the glasses with x ≤ 20 mol% V₂O₅ content was tested by optical density (OD) measurements. A linear correlation between the amount of vanadium and the antibacterial effect was evidenced.