Effect of Nickel–Cobalt–Zinc Ferrite Filler on Magnetic and Thermal Properties of Thermoplastic Natural Rubber Composites

A sample of Ni_0.25Co_0.25Zn_0.5Fe₂O₄ ferrite was prepared by a double-staged sintering method in air. Thermoplastic natural rubber (TPNR) was prepared by melt blending of natural rubber (NR), liquid natural rubber (LNR), and high density polyethylene (HDPE) in an internal mixer Brabender Plasticorder PL 2000. Magnetic polymer composites were prepared from the ferrite and TPNR matrix using the same melt blending method at 135°C with mixing rate of 50 r.p.m. for 12 min. The fillers were varied from 5 to 30 weight percent. A uniform dispersion of the filler in the matrix was confirmed by thermogravimetric analysis (TGA). The density of the composites was determined using densitometer MD 200S. Magnetic properties were studied using a vibrating sample magnetometer (VSM) at room temperature (25°C). The results show that magnetization (M), saturation magnetization (M_S), remanent magnetization (M_R), initial susceptibility (χ_i) and initial permeability (μ_i) increase with increasing filler content at all compositions. The composites can be classified as soft magnetic materials as their coercivities are in the range of 30–36 Oe. The differential scanning calorimetric (DSC) results indicate that the glass transition temperature (T_g) and the melting point (T_m) of all the composites are independent of the filler content. The thermal conductivity of the composites was found to be in the range of 0.26 to 0.52 W m^?1 K^?1.     

Mechanical Properties and Microstructure of Nano-SiC–Al2O3 Composites Densified by Spark Plasma Sintering

Heterogeneous precipitation method has been used to produce 5 vol% SiC–Al₂O₃ powder, from aqueous suspension of nano-SiC, aqueous solution of aluminium chloride and ammonia. The resulting gel was calcined at 700°C. Nano-SiC–Al₂O₃ composites were densified using spark plasma sintering (SPS) process by heating to a sintering temperature at 1350, 1400, 1450, 1500 and 1550°C, at a heating rate of 600 °/min, with no holding time, and then fast cooling to 600°C within 2–3 min. High density composites could be achieved at lower sintering temperatures by SPS, as compared with that by hot-press sintering process. Bending strength of 5 vol% SiC–Al₂O₃ densified by SPS at 1450°C reached as high as 1000 MPa. Microstructure studies found that the nano-SiC particles were mainly located within the Al₂O₃ grains and the fracture mode of the nanocomposites was mainly transgranular fracture.     

Strength Properties and Microstructure of Diphase β—Sialon／Al2O3 Composites

Study on modules of rupture and microstructure of xphase bearing diphase β－Sialon and diphase β－Sialon/Al2O3 composites shows that MOR increases with tempera-ture rise up to a maximum oint and then decreases,For diphase β－Sialon materials,the maximum strength reaches 130 MPa-170 MPa at 1200℃;whereas for diphase β－Sialon/Al2O3 composites,the maximum strength reaches 200MPa-300 MPa at 1000℃,In the microstructure of th composite ,oblong crystals of x-phase and hexagonal prismatic crystals of β－Sialon are interlaced in the skeleton structure of corundum.This struture creates a distinctly intensifying effect on the strength of the composite.     

PVD Coating of Mg–AZ31 by Thin Layer of Al and Al–Si

Although magnesium alloys have the advantage of high specific strength, they have poor atmospheric corrosion resistance. An important method of improving the corrosion resistance is by applying a coating layer. In this work, the physical vapor deposition (PVD) technique is used for coating a magnesium (Mg) AZ31 sheet substrate with a thin layer of high purity aluminum (Al) and Al–12.6% Si. Aluminum is expected to be suitable as a coating layer on Mg sheets, due to its corrosion resistance and its formability. Before coating, the substrate was subjected to several consecutive surface preparations, including sand-blasting, mechanical grinding, mirror-like polishing, ultrasonic etching, and finally ion etching by magnetron sputtering (MS). PVD coating was conducted using a PVD machine with max electron beam power and voltage of 100 kW and 40 kV, respectively. This was either with or without plasma activation, and with variable substrate speeds ranging between 10 and 70 mm/s. During MS ion etching and coating, the substrate temperature increased. The substrate temperature increased with the application of plasma activation and with lower substrate speeds. The coating-layer thickness varied inversely with substrate speed. A thinner coat with finer morphology was obtained in the case of plasma activation. Other results included coating layer characteristics, diffusion between the AZ 31 substrate and the Al coating layer, adhesion of the coating layer to the substrate, and corrosion resistance by a humidity test.     

Influence of Re-adhesion on the Wear and Friction of Glass Fibre–Reinforced Polyester Composites

Based on the well-known pin-on-disc test rig, a new test setup for online measuring of wear and friction behaviour of polymer matrix composites has been developed. In contrast to a traditional friction-and-wear test rig, a steel pin and composite disc are used for studying the influence of wear debris and fibre orientation. During sliding, a thin adhesive film is possibly formed on the wear track of a composite disc, consisting of wear debris that is squeezed under the steel pin and that finally smoothens onto the composite surface. By optical microscopy, it was observed that most of the debris particles originate from the edges of the wear track. The thin film deforms continuously, with large and dark wear particles observed at the edge of the wear track. A lower coefficient of friction is achieved when the particles are re-adhered to the mating surface. The film formation mechanism depends on the normal force, sliding velocity, and bulk composite structure: because pultruded composite profiles are presently used with a layered structure, a change in film properties is observed depending on the wear depth.     

Preparation and sealing effects of Mg–Al–Si–Ba–O-based glass-ceramic coatings on NTC thermistors

Herein, Mg–Al–Si–Ba–O-based glass ceramics were studied as potential candidates to protect Mn–Co–Ni–O-based negative temperature coefficient (NTC) thermistors at high temperatures such as 900 °C. The ceramics were prepared in three glass formulations (1#: 15MgO–15Al₂O₃-44.7SiO₂–25BaO, 2#: 17MgO–17Al₂O₃–41SiO₂–25BaO and 3#: 17MgO–17Al₂O₃–41SiO₂–20BaO–5Y₂O₃ (in mol%)) and their glass-transition temperatures (T_g) were determined using the differential scanning calorimetry (DSC) method. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the parent glasses and glass-ceramic coatings. The sealing effects of the glass ceramics were examined by conducting an insulation test. The glass-ceramic sealing structures were subjected to 1000 thermal shock cycles at temperatures varying from room temperature to 900 °C. Notably, the sealing structure of glass-ceramic coating 1# was compact at a T_g of 760.9 °C. The glass-ceramic coatings effectively maintained the NTC properties of the sensitive ceramics in all three formulations. Interestingly, the glass-ceramic coating 3# containing Y₂O₃ demonstrated an increase in electrical resistance. Both the NTC thermistors coated with 1# and 2# glass formulations successfully passed 1000 thermal shock cycles without visible failures, and their resistance change ratios were well below the requisite 20%.     

The Effect of Yttrium Oxide on the Microstructure and Properties of Ceramics Based on Lanthanum Hexaaluminate Synthesized by the Sol–Gel Method

The effect of a sintering aid, yttrium oxide, on the properties of ceramic materials based on lanthanum hexaaluminate synthesized by a sol–gel method is studied. The synthesis of a sol of ternary oxide composition conducted via hydrolysis of a mixed salt solution leads to the formation of particles with a nucleus – shell-type structure. The synthesis of lanthanum hexaaluminate with the participation of these particles proceeds at 1000 – 1100°C, and the sintering of ceramic at 1400 – 1500°C. Ceramic based on yttrium-containing lanthanum hexaaluminate exhibits improved strength properties.     

Mechanical and Bioactive Behavior of Hydroxyapatite–Wollastonite Sintered Composites

The effect of wollastonite amount on the mechanical and bioactive properties of several hydroxyapatite-wollastonite sintered composites was evaluated. The wollastonite reinforcement effect was assessed by measuring hardness and reduced elastic modulus on the materials, using nanoindentation methods. Bioactive properties were analyzed by soaking these materials in a simulated body fluid (SBF) for various periods of time. The analyses reveal an enhancement of hardness and reduced elastic modulus with the addition of wollastonite. In addition, the interaction of these materials with an SBF produces a bone-like apatite layer on their surfaces, which is thicker when the wollastonite is in a higher proportion.     

Influence of additives on microstructure and property of microarc oxidized Mg–Si–O coatings

Ceramic coatings were fabricated on ZK60 magnesium alloy substrate by microarc oxidation (MAO) in Na₂SiO₃–KOH base electrolyte with four kinds of additives (i.e. KF, NH₄HF₂, C₃H₈O₃ and H₂O₂). The effects of these additives on microstructure and property of coatings were investigated. The surface morphology, phase composition and corrosion resistance of the ceramic coatings were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and simulation body fluid (SBF) immersion test respectively. It is found that different additives can change the spark discharge phenomenon during microarc oxidation. It is proved that both potassium fluoride (KF) and ammonium bifluoride (NH₄HF₂) promote discharge and accelerate reaction while the introduce of glycerol (C₃H₈O₃) leads to the refining of sparks and reduction of thermal effects. Results also demonstrate that the introduce of hydrogen peroxide (H₂O₂) contributes to the increase of coating surface roughness and enlargement of surface micropore size. XRD results indicate that the ceramic coatings are mainly composed of Mg₂SiO₄, MgSiO₃ and SiO₂. The introduce of H₂O₂ hinders the reaction between SiO₂ and MgO and creates favorable conditions for the formation of the MgO phase. The ceramic coatings formed in base electrolyte containing 7 g/L NH₄HF₂ and 5 mL/L C₃H₈O₃ exhibit the highest corrosion resistance.     

Effect of Biopolymer Blend Matrix on Structural,Optical and Biological Properties of Chitosan–Agar Blend ZnO Nanocomposites

The present research is focused on the development of ecofriendly biopolymer blend based nanocomposites to enhance the effect of cytotoxic activity. Novel eco-friendly synthesis of pure Chitosan–Agar blend and Chitosan–Agar/ZnO nanocomposites was successfully synthesized by in-situ chemical synthesis method. The influence of Chitosan–Agar (1:1 wt/wt%) concentrations (0.1, 0.5, 1 and 3 g) was studied. The presence of ZnO nanoparticles in Chitosan–Agar polymer matrix was confirmed by UV, FTIR, XRD, FESEM, EDAX and TEM. The crystallite size of the nanocomposites in the range of 12–17 nm is observed from XRD analysis. PL and UV reveal that Nanocomposites shows an blue shift by increase in the blend concentrations. TEM analysis shows that 0.1 and 3 g of Chitosan–Agar/ZnO Nanocomposites are in spindle and spherical shape with polycrystalline nature. The prepared Nanocomposites shows the respectable Antibacterial activity against Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Pseudomonas aureginosa and Klebsilla pneumonia) bacteria. The potential toxicity of Chitosan–Agar/ZnO nanocomposites was studied for normal (L929) and breast cancer cell line (MB231). The result of this investigation shows that the Chitosan–Agar/ZnO nanocomposites deliver a dose dependent toxicity in normal and cancer cell line.     

Processing and Characterisation of Epoxy–SiC Functionally Graded Polymer Matrix Composites

This paper proposed preparing and investigating the Epoxy–Silicon carbide composite for aerospace applications. In recent years aerospace industries concentrated in low weight, high strength and high thermal resistance materials. Polymer matrix composite can provide a better solution for the statement mentioned above. This study thermosetting study Epoxy and SiC materials have mixed in centrifugal casting with the ratio of 5%-SiC and resin. The microstructural evaluation is carried by Scanning Electron microscopic and investigating the tensile and hardness properties of the Epoxy– SiC Functionally Graded Polymer Matrix Composites. The wear and fracture analyse were investigated, and the results were discussed. the results show the SiC has provided the higher strength for composite, and its mixing percentage has control the weight of the polymer composite.

     

The influence of the mixed alkaline earth effect on the structure and properties of (Ca,Mg)–Si–Al–O–N glasses

Alkaline earth oxynitride glasses of (Ca, Mg)–Si–Al–O–N with different CaO/(CaO + MgO) molar ratios (0, 0.25, 0.5, 0.75, and 1) were successfully prepared using the sol-gel method, and their structural compositions were characterised by Raman and FT-IR techniques. The glass dynamic properties of thermal expansion coefficient, glass transition temperature (T_g), and static properties of density, molar volume, Vickers hardness and compressive strength were systematically measured and analysed. The results showed that the static properties exhibited an overall regular change as the CaO/(CaO + MgO) ratio gradually increased, while the dynamic properties had an obvious mixed alkaline earth effect, which represented the appearance of an extreme value point in CaO/(CaO + MgO) mole ratios of 0.25 and 0.75, respectively. The typical thermal expansion coefficient and T_g of mixed alkaline earth oxynitride glasses deviated far from the linear connection between single alkaline earth oxynitride glasses. Raman spectra and infrared spectra revealed that the ratio value of the Q³/(Q²+Q⁴) decreased (Qⁿ: n = no. of bridging anions joining SiO₄ tetrahedra) in the mixed alkaline earth oxynitride glasses with increasing the amount of Ca, confirming that Ca decreased the crosslinking between individual tetrahedra via the transformation of Q³ species into Q² and Q⁴ species.     

Improving the Mechanical and Wear Properties of Mg–Mg2Si In-Situ Composite via Hybrid SiCp and Hot Working

Silicon - Numerous investigations have been performed on Mg/SiCp or Mg-Si systems; however, there is a shortage of research papers about Mg-Mg2Si-SiCp in the literature. Therefore, the structural...     

Physico-chemical and catalytic properties of Mg–Al hydrotalcite and Mg–Al mixed oxide supported copper catalysts

The Mg–Al hydrotalcite (HT) and Mg–Al mixed oxide supported copper catalysts containing 3–3.5 wt.% copper in finely dispersed form were synthesized and characterized. The effect of support nature on physico-chemical and catalytic properties of supported copper species were studied. The loading of copper on the supports was observed to be influencing the surface acidic, basic and reducibility properties, and catalytic behavior in dehydrogenation of benzyl alcohol. The high basicity and intercalated copper ions in Mg–Al hydrotalcite supported copper sample showed multifunctional activity in catalytic transformations of alcohols (primary, secondary and aromatic alcohols).     

Preparation and Properties of Novel Quaternized Metal–Polymer Matrix Nanocomposites

A new class of PANI/Sn(II)SiO₃/FCNTs nanocomposite was synthesized by mixing polyaniline into the gel of Sn(II)SiO₃ followed by FCNTs (Polyaniline/Sn(II)SiO₃/Functionalized Carbon nanotubes). The physico-chemical characterization was carried out by scanning electron microscope, XRD (X-ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), ultraviolet–visible spectroscopy, and simultaneous thermogravimetric analysis studies. The ion-exchange capacity (1.2 meq/g) and distribution studies were also determined to understand the ion-exchange capabilities. The DC electrical conductivity studies revile it in the range of 3–5 × 10^?3 S/cm. On the basis of distribution studies, ion-selective membrane electrode was designed for Hg(II). The analytical utility of this membrane was established by using it as an indicator electrode in electrometric titrations.     

Reaction Synthesis and Mechanical Properties of TiB2–AlN–SiC Composites

TiB₂–AlN–SiC (TAS) ternary composites were prepared by reactive hot pressing at 2000°C for 60 min in an Ar atmosphere using TiH₂, Si, Al, B₄C, BN and C as raw powders. The phase composition was determined to be TiB₂, AlN and β-SiC by XRD. The distribution of elements Al and Si were not homogeneous, which shows that to obtain a homogeneous solid solution of AlN and SiC in the composites by the proposed reaction temperatures higher than 2000°C or time duration longer than 60 min are needed. The higher fracture toughness (6·35±0·74 MPa·m^1/2 and 6·49±0·73 MPa·m^1/2) was obtained in samples with equal molar contents of AlN and SiC (TAS-2 and TAS-5) in the TAS composites. The highest fracture strength (470±16 MPa) was obtained in TAS-3 sample, in which the volume ratio of TiB₂/(AlN+SiC) was the nearest to 1 and there was finer co-continuous microstructure. ©     

Preparation,Mechanical and Electrical Properties of Glass and Jute–Epoxy/Epoxy Polyurethane Composites

Glass and jute (treated and untreated) composites of epoxy resin of 1,1′-bis(3-methyl-4-hydroxy phenyl)cyclohexane(EMC) cured using 20% triethylamine as a hardener (G-EMCT-20 and J-EMCT-20) and EMC- polyurethane of toluene diisocyanate (J-EMCPU and TJ-EMCPU) have been prepared by a hand layup technique under 27.58 MPa pressure and at 150°C for 4 h. G-EMCT-20, J-EMCT-20, J-EMCPU and TJ-EMCPU showed 275, 96.5, 37.3 and 31.5 MPa tensile strength; 351, 84, 10 and 24 MPa flexural strength; 5837, 2758, 1277 and 1619 MPa elastic modulus; 24.6, 7.1, 1.9 and 1.6 kV/mm electric strength; and 1.4 × 10¹³, 1.1 × 10¹¹, 7.7 × 10¹⁰ and 3.6 × 10¹⁰ ohm cm volume resistivity, respectively. Fairly good to excellent mechanical and electrical properties of the composites indicated their industrial applications in building and construction, electrical and electronic industries.     

Crystallization Behavior,Mechanical Properties,and Chemical Resistance of Leucite–Fluoroapatite Glass-Ceramic Glazes

The roles of Li₂O and B₂O₃ and heat-treatment condition on crystallization behavior and flowability of leucite–fluoroapatite-based glass-ceramic glazes were investigated. The thermal expansion coefficient, mechanical, and chemical properties of the optimum specimen were determined. Glaze firing was performed in the 650–1100°C interval, in one and two step processes. Based on the results, B₂O₃ was more effective than Li₂O in point of flowability view. Also, the microstructures varied with the adopted firing process, so that the two-step heat-treated sample showed superior mechanical properties than the one-step heat-treated specimens.