Preparation of ZrB2 based composites by reactive melt infiltration at relative low temperature

ZrB₂ based composites were prepared by a novel reactive melt infiltration process. The porous boron bars were used as preforms and infiltrated by the low melting Zr₂Cu intermetallic compound. Thermodynamics calculations revealed that B could react with liquid Zr₂Cu to form ZrB₂ as low as 1100 °C. Composites were prepared by heating the two materials to 1200 °C for 3 h in vacuum. The resultant composites were studied with XRD and SEM. ZrB₂ was identified to be the main constituent. The composites had a flexural strength of 414.3 MPa, a flexural modulus of 183.6 GPa, and a fracture toughness of 5.5 MPa m^1/2.     

Synthesis of H2Ti2O3·H2O nanotubes and their effects on the flame retardancy of bamboo fiber/high-density polyethylene composites

H₂Ti₂O₃·H₂O nanotubes (TNTs) were prepared through hydrothermal synthesis and dispersed in bamboo fiber/HDPE (BH) composites to improve the flame retardancy of the composites. TEM observation showed that TiO₂ particles were transformed into TNTs through hydrothermal treatment at 120 °C for 12 h in 8 M NaOH solution. Then, a cone calorimeter and a limiting oxygen index chamber were used to evaluate the effects of the TNTs on the flame retardancy of the BH composites. Results demonstrated that TNTs definitely improved the flame retardancy of BH composites by absorbing decomposition products from combustion due to its large specific area and tubular structure. Additionally, the TNTs reduced the free volume in the microzone, strengthened the molecular chain rigidity, and then contributed to the thermostability and flame retardancy of the BH composites.     

Effects of Si addition on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy

Effects of Si addition (1.0 wt.%) on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy have been investigated using scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS), X-ray diffraction (XRD), hardness measurements and tensile testing. The results indicated that the addition of Si led to the formation of Mg₂Si and (RE + Si)-rich particles, which enhanced the Young’s modulus of the alloy by 7 GPa while decreased the yield strength and ultimate strength by 10 MPa and 31 MPa, respectively. The tensile properties of the Mg–8Gd–4Y–Nd–Zr–Si alloy are as follows: Young’s modulus E = 51 GPa, yield strength σ_0.2 = 347 MPa, ultimate strength σ_b = 392 MPa and elongation δ = 2.7%. The increase in Young’s modulus was attributed to the formation of particles with high Young’s modulus, while the decrease in strength was ascribed to the decrease in volume fraction of metastable β′ precipitates caused by the consumption of rare earth atoms due to the formation of the rare earth containing particles.     

Sintering and technological properties of alumina/zirconia/nano-TiO2 ceramic composites

The present work focuses on studying the effect of nano TiO₂ (0.0–25 mass%) on the sintering behavior and mechanical properties of alumina/zirconia ceramic composites. Al₂O₃–ZrO₂–TiO₂ oxides mixture was sintered at 1600 °C to obtain the desired composites. The sinterability and the technological properties of these ceramic composites, i.e. the sintering parameters and microhardness as well as thermal shock resistance were investigated. Moreover, phase composition and microstructure of the sintered bodies were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results revealed that nano TiO₂ is a beneficial component for alumina/zirconia ceramic composites. The batch containing 20 mass% TiO₂ exhibited the highest sintering and mechanical properties as well as resistance to thermal shock. The obtained microstructure exhibited high compacted ceramic matrix composites.     

Effect of coupling agents on the dielectric properties of CaCu3Ti4O12/PVDF composites

Phase-pure calcium copper titanate (CaCu₃Ti₄O₁₂, CCTO) ceramic particles were synthesized via a sol–gel route. The CCTO was treated by bis[3-(triethoxysilyl)propyl]tetrasulfide (Si69) to give CCTO@Si69. The dielectric composites based on CCTO (or CCTO@Si69) and polyvinylidene fluoride (PVDF) were molded with desirable dielectric properties by mechanical mixing process and hot-pressing. The structures of CCTO and CCTO@Si69 were investigated by scanning electron microscopy (SEM) energy spectrum, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The stretching vibration of SO at 1096 cm⁻¹ in FTIR is an indication that chemical bond was formed between Si69 and CCTO. The influence of Si69 on the preparation and the dielectric properties of CCTO/PVDF dielectric composites were discussed. When the content of Si69 was 0.1 mL (relative to 1 g of CCTO), the dielectric constant (ε) (at a frequency of 1 kHz) of CCTO@Si69/PVDF composites reached the maximum value of 84, this value is 5.25 times that of an equal amount of CCTO of CCTO/PVDF composites (ε ≈ 16). The CCTO/PVDF and CCTO@Si69/PVDF composites had very stable dielectric properties over a wide range of temperatures (20–160 °C). These composites can be applied as high-energy–density capacitors in electronic and electrical engineering fields.     

Al3Ni2–Al composites with nanocrystalline intermetallic matrix produced by consolidation of milled powders

Mechanically alloyed nanocrystalline Al₆₃Ni₃₇ powder with a metastable structure of NiAl phase was mixed with 20, 30 and 40 vol.% of Al powder. The powder mixtures as well as pure powder of Al₆₃Ni₃₇ alloy were consolidated at 600 °C under the pressure of 7.7 GPa. The bulk materials were characterised by structural investigations (X-ray diffraction, light and scanning electron microscopy, energy dispersive spectroscopy), compression and hardness tests and measurements of density and open porosity. During the consolidation, the metastable NiAl phase transformed into the equilibrium Al₃Ni₂ intermetallic. The mean crystallite size of the Al₃Ni₂ intermetallic in the bulk materials is below 40 nm. The microstructure of the composite samples consists of Al₃Ni₂ intermetallic areas surrounded by lamellae-like Al regions. The hardness of the produced Al₃Ni₂–Al composites is in the range of 5–6.5 GPa (514–663 HV1), while that of the Al₃Ni₂ intermetallic is 9.18 GPa (936 HV1). The compressive strength of the composites increases with the decrease of Al content, ranging from 567 MPa to 876 MPa. The plastic elongation of the composites was increasing with the increase of Al content, while the Al₃Ni₂ intermetallic failed in the elastic region.     

Fabrication of HAp–8YSZ composite layer on Ti/TiO2 nanoporous substrate by EPD/MAO method

Zirconia/Hydroxyapatite composites containing 20–50 wt.% 8YSZ were prepared on Ti/TiO₂ substrates by electrophoretic deposition (EPD)/micro-arc oxidation (MAO) process. Titania, as an inner layer, was grown on the Ti plates using MAO treatment in order to form a strong join between substrate and HAp. These composites were produced by EPD in ethanol containing ZrO₂/HAp particles at 50, 100 and 150 V in 1 min. As-prepared samples were sintered at 900, 1100 and 1300 °C. HAp, β-TCP, CaZrO₃ phases were identified using X-ray diffractometry analysis (XRD). Scanning electron microscopy (SEM) utilized to study the surface morphology indicated a crack free microstructure at 1300 °C.     

High pressure behaviors of nanoporous anatase TiO2

High pressure behaviors of nanoporous anatase TiO₂ were studied using in situ Raman spectroscopy up to 37 GPa. The nanoporous anatase phase starts to transform into the baddeleyite phase with poor crystallinity at ～15.2 GPa, and the baddeleyite phase coexists with anatase phase up to 18.4 GPa. The baddeleyite form transforms into an amorphous phase above 20.5 GPa. Upon decompression, the amorphous phase recovers to the baddeleyite phase and then transforms to the α-PbO₂ phase. The phase transition from the baddeleyite phase to the amorphous form is reversible. The poor crystalline baddeleyite phase acts as an intermediate state in the amorphization process. The phase transitions of the nanoporous anatase TiO₂ are obviously different from the pressure-induced amorphization in the anatase TiO₂ nanoparticles. These results indicate that the porous microstructure plays important roles in the high pressure phase transitions of the nanoporous anatase TiO₂.     

Surface modification of cellulose nanofibers with alkenyl succinic anhydride for high-density polyethylene reinforcement

Hydrophobic cellulose nanofibers (CNFs) were prepared by surface modification using alkenyl succinic anhydride (ASA). The hydrophobicity of CNFs was varied by changing the degree of substitution (DS) from 0 to 0.83. Modified CNFs were mixed with high-density polyethylene (HDPE) using a twin-screw extruder and the resulting composites were injection molded. The tensile properties initially improved with increasing DS up to ∼0.3–0.5, and then decreased with further substitution. The tensile strength and modulus of 10 wt.% HDPE/CNF composites containing 8.8 wt.% ASA (DS: 0.44) were 43.4 MPa and 1.97 GPa, respectively. These values were both almost 70% higher than those of composites containing unmodified CNF, and 100% and 86% higher, respectively, than those for pure HDPE. X-ray computed tomography measurements showed that CNFs modified with a DS of 0.44 were dispersed uniformly within the resin matrix, whilst unmodified CNFs and those modified with a DS of 0.77 agglomerated within the composites.     

Microstructure,mechanical properties,and in vitro biocompatibility of spark plasma sintered hydroxyapatite–aluminum oxide–carbon nanotube composite

In the present work, HA reinforced with Al₂O₃ and multiwalled carbon nanotubes (CNTs) is processed using spark plasma sintering (SPS). Vickers micro indentation and nanoindentation of the samples revealed contrary mechanical properties (hardness of 4.0, 6.1, and 4.4 GPa of HA, HA–Al₂O₃ and HA–Al₂O₃–CNT samples at bulk scale, while that of 8.0, 9.0, and 7.0 GPa respectively at nanoscale), owing to the difference in the interaction of the indenter with the material at two different length scales. The addition of Al₂O₃ reinforcement has been shown to enhance the indentation fracture toughness of HA matrix from 1.18 MPa m^1/2 to 2.07 MPa m^1/2. Further CNT reinforcement has increased the fracture toughness to 2.3 times (2.72 MPa m^1/2). In vitro biocompatibility of CNT reinforced HA–Al₂O₃ composite has been evaluated using MTT assay on mouse fibroblast L929 cell line. Cell adhesion and proliferation have been characterized using scanning electron microscopy (SEM), and have been quantified using UV spectrophotometer. The combination of cell viability data as well as microscopic observations of cultured surfaces suggests that SPS sintered HA–Al₂O₃–CNT composites exhibit the ability to promote cell adhesion and proliferation on their surface and prove to be promising new biocompatible materials.     

In situ synthesis of hybrid-reinforced titanium matrix composites

Novel hybrid-reinforced (TiB + La₂O₃)/Ti composites were in situ synthesized utilizing the reaction between Ti, LaB₆ and B₂O₃ through homogeneous melting in a non-consumable vacuum arc remelting furnace. The thermodynamics of in situ synthesis reaction were analyzed. The phases in the composites were identified by X-ray diffraction (XRD) and the microstructures of the composites were examined by optical microscope (OM), backscattered scanning electron microscope (SEM) and field-emission SEM. Three kinds of reinforcements were found in the composites: La₂O₃ particles (diameter: ∼ 2 μm), TiB whiskers (width: ∼ 3 μm) and TiB plates (thickness: ∼ 1.5 μm). The reinforcements' sizes were fine and they were homogeneously distributed in the matrix.     

Effect of alumina particles loading on the mechanical properties of light-cured dental resin composites

The purpose of this study is to evaluate the effect of alumina (Al₂O₃) loading on the mechanical properties of dental resin composites (DRCs). The DRCs were prepared based on Al₂O₃ particles and bisphenol A-glycidyl methacrylate (Bis-GMA) was used as the base monomer. The silane-treated Al₂O₃ particles were mixed with the resin matrix in proportions of 40, 50, and 60 wt%, respectively. Resin matrix without filler was used as the control sample. The Vickers hardness (HV) and flexural modulus (FM) of the DRCs mixed with Al₂O₃ particles were found to be superior compared to the control sample; the values increased from 14.4 to 23.5 kg/mm² and 1.5 to 5.7 GPa, respectively. However, the flexural strength (FS) values of DRCs were slightly decreased as the filler loading increased i.e. from 84.5 to 74.2 MPa. The results also revealed statistically significant increases in the HV and FM. On the other hand, FS values showed significant decrease when filler loading was increased (P < 0.05).     

Adsorption and photocatalysis of nanocrystalline TiO2 particles prepared by sol–gel method for methylene blue degradation

Titanium dioxide (TiO₂) powders were synthesized by using TiO₂ colloidal sol prepared from titanium-tetraisopropoxide (TTIP) and used as a starting material by applying the sol–gel method. The effect of aging times and temperatures on physical and chemical properties of TiO₂ sol particles was systematically investigated. The results showed that the crystallinity and average particle size of TiO₂ can be successfully controlled by adjusting the aging time and temperature. The samples after calcination of TiO₂ powders were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and nitrogen adsorption measurements. In addition, the photocatalytic activity of synthesized TiO₂ powders was evaluated by studying the degradation of 10 ppm aqueous methylene blue dye under 32 W high pressure mercury vapor lamp with 100 mg of TiO₂ powders. The highest photocatalytic activity was observed in TiO₂ powder synthesized at 90 °C for 0 h attributed to the presence of anatase and rutile phases in an 80:20 ratio.     

Controlled retting of hemp fibres: Effect of hydrothermal pre-treatment and enzymatic retting on the mechanical properties of unidirectional hemp/epoxy composites

The objective of this work was to investigate the use of hydrothermal pre-treatment and enzymatic retting to remove non-cellulosic compounds and thus improve the mechanical properties of hemp fibre/epoxy composites. Hydrothermal pre-treatment at 100 kPa and 121 °C combined with enzymatic retting produced fibres with the highest ultimate tensile strength (UTS) of 780 MPa. Compared to untreated fibres, this combined treatment exhibited a positive effect on the mechanical properties of hemp fibre/epoxy composites, resulting in high quality composites with low porosity factor (α_pf) of 0.08. Traditional field retting produced composites with the poorest mechanical properties and the highest α_pf of 0.16. Hydrothermal pretreatment at 100 kPa and subsequent enzymatic retting resulted in hemp fibre composites with the highest UTS of 325 MPa, and stiffness of 38 GPa with 50% fibre volume content, which was 31% and 41% higher, respectively, compared to field retted fibres.     

Phase transition and microstructure evolution during the carbothermal preparation of Ti(C,N) powders in an open system

Phase transition and microstructure evolution during carbothermal reduction–nitridation of TiO₂ in an open system were investigated using XRD, TGA, SEM and laser particle analysis device. The results show that, the phase evolution sequences are: TiO₂ (anatase) → TiO₂(rutile) → Ti_nO_2n-1(n ? 4) → Ti₃O₅ → Ti(N,O) → Ti(C,N,O) → Ti(C,N). In the reaction process, the predominant reaction mechanism is TiO₂/C solid–solid reaction in the beginning and subsequent the gas–solid reactions mainly between oxides and CO, C and CO₂. The synthesizing powders gradually become finer in form of uniform spherical particles with the formation of cubic phase.     

Enhanced photocatalytic property of nanoporous TiO2/SiO2 micro-particles prepared by aerosol assisted co-assembly of nanoparticles

Nanoporous TiO₂/SiO₂ composite micro-particles were prepared by an aerosol assisted co-assembly (AACA) and their characteristics were investigated for photocatalytic application. The average diameter of resulting co-assembled TiO₂/SiO₂ particles was ranged 4–10 μm, and increased as the precursor concentration increased. The TiO₂/SiO₂ particles were spherical in shape and pores ranged 1–100 nm in diameter. Photocatalytic activity of the as-prepared nanoporous TiO₂/SiO₂ particles was evaluated by measuring the photodegradation of methylene blue (MB) and NO_x. Furthermore, the photocatalytic activity of nanoporous TiO₂/SiO₂ particles was compared with those of commercial TiO₂ nanoparticles and nanoporous TiO₂ particles. The nanoporous TiO₂/SiO₂ particles exhibited the highest photodegradation of MB and NO_x among three samples, which was 80% after 3 h and 55% at 10 min, respectively.     

Tensile properties of in situ synthesized (TiB + La2O3)/β-Ti composite

A novel (TiB + La₂O₃)/Ti-alloy composite was In situ synthesized through homogeneously melting in a non-consumable vacuum arc remelting furnace. Ti–35Nb–2Ta–3Zr β titanium alloy was chosen as the matrix Ti-alloy and different mass fractions of LaB₆ were chosen as additions. Microstructure observations were examined by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The phase analysis was identified by X-ray diffraction (XRD). Largest ultimate tensile strength around 580 MPa and highest elongation around 30% is obtained in 0.1% LaB₆-additioned specimen. The appearance of too many La₂O₃ particles and the reduction of oxygen in the matrix alloy also attribute much to the strength and plasticity of (TiB + La₂O₃)/Ti composites. Lower ultimate tensile strength around 526 MPa is obtained in 0.5% LaB₆-additioned specimen.     

Microstructural characteristics and evolution of Ti2AlN/TiAl composites with a network reinforcement architecture during reaction hot pressing process

The microstructural evolution of TiAl matrix composites with a novel network distribution of Ti₂AlN particle reinforcement was studied. The composites were synthesized by reaction hot pressing method using pure Al and nitrided Ti powders as initial materials. Pure Ti powders nitrided at 600 °C for a certain time in an atmosphere of flowing nitrogen turned into new compound Ti(N) powders, which have a shell of titanium nitrides (such as TiN, Ti₂N and TiN_0.3) and a core of Ti–N solid solution. Within the composites synthesized, Ti₂AlN particles, produced by in situ reaction, exhibit a network distribution. The special shell/core structure of the compound Ti(N) powders contributes to this architecture. Nitriding time of the Ti powders greatly affects the microstructure of the composites. Increasing the nitriding time is beneficial to the distribution of Ti₂AlN particles in a continuous network form. However, too long nitriding time can result in the aggregation of Ti₂AlN particles and thus destroy the uniformity of the network structure. The in-situ synthesized Ti₂AlN/TiAl composites with uniform network structure have a superior mechanical property, and their compressive strengths at 800 °C and 1000 °C are 1112 MPa and 687 MPa, respectively.     

Development of NiFe-CNT and Ni3Fe-CNT nanocomposites by mechanical alloying

NiFe-CNT and Ni₃Fe-CNT nanocomposites were fabricated by high energy mechanical alloying method. X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and optical microscopy were employed for evolution of phase composition, morphology and microstructure of the powder particles. Ball milled powders were heat treated at 500 °C for 1 h to release the milling induced stresses. Bulk samples were prepared by sintering of cold pressed (300 MPa) samples at 1040 °C for 1 h. XRD patterns of powders, as-milled and after annealing at 500 °C did not show any peak related to CNTs or excess phases due to the interaction between CNTs and matrix. SEM micrographs showed that the addition of CNTs caused a reduction of powder particles size. The hardness value of as-milled NiFe and Ni₃Fe powders reach to 660 and 720 HV, respectively. According to optical microscopy evaluations, the amount and size of the porosities of the composites bulk samples decreased in comparison with matrix ones.     

Synthesis of conducting ferromagnetic nanocomposite with improved microwave absorption properties

The present paper reports the synthesis of polyaromatic amine–ferromagnetic composite with nanosize TiO₂ (～70–90 nm) and γ-Fe₂O₃ (～10–15 nm) particles via in situ emulsion polymerization. Magnetic and conductivity studies demonstrate that the conducting ferromagnetic composite possesses saturation magnetization (M_S) value of 26.9 emu g^?1 and conductivity of the order of 0.46 S cm^?1, which are measured by vibrating sample magnetometer and four-probe technique, respectively. It is observed that the presence of the nanosized γ-Fe₂O₃ in the polyaniline–TiO₂ matrix affects the electromagnetic shielding property of the composite. Polyaniline–TiO₂–γ-Fe₂O₃ nanocomposite has shown better shielding effectiveness due to absorption (SE_A ～ 45 dB) than the polyaniline-γ-Fe₂O₃ (SE_A ～ 8.8 dB) and polyaniline–TiO₂ (SE_A ～ 22.4 dB) nanocomposite. The polymer composites were further characterized by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) technique.