Mechanical properties of polydicyclopentadiene/graphite nanosheet composites prepared by reaction injection moulding

Abstract

Polydicyclopentadiene (PDCPD)/expanded graphite nanosheets treated with silane coupling agent (TEG) composites were prepared by simulating reaction injection moulding. Studies on the mechanical and tribological properties of the composites were carried out. The results showed that TEG of low content had an effect on reinforcing the PDCPD matrix. The incorporation of TEG in PDCPD greatly decreased wear rates and slightly increased friction coefficients under both dry sliding and oil lubricated conditions. The SEM images of the worn surface revealed their wear mechanisms. Unfilled PDCPD was characterised by spalling, with adhesive wear being the major wear form. Polydicyclopentadiene composites were characterised by plastic deformation, fatigue microcracking, spalling and ploughing effect in dry sliding. The wear forms for PDCPD composites under oil lubricated condition were also complicated, and several wear forms such as adhesive, abrasive and fatigue wears co-existed.     

Structural and electromagnetic properties of Ni0.5Zn0.5HoxFe2-xO4 ferrites

Ni-Zn ferrites with a nominal composition of Ni_0.5Zn_0.5Ho_xFe_2-xO₄ (x = 0–0.06) were prepared by conventional solid state reaction through using analytical-grade metal oxides powders as raw materials. The phase composition, microstructure, magnetic properties and dielectric performance of the as-prepared samples were investigated. The doped Ho³⁺ ions could enter into the crystal lattice of the resultant spinel ferrites, causing the expansion of the unit cell, reaching a saturated state when x = 0.015; and the additional Ho³⁺ ions would form a foreign HoFeO₃ phase at the grain boundary. The grain size and densification of the samples initially decreased after a small amount of Ho³⁺ ions was doped, but then increased with more Ho³⁺ ions added. The saturation magnetization decreased gradually with increasing substitution level of Ho³⁺ ions. The Curie temperature and coercivity raised initially and declined later with increasing content of Ho³⁺ ions in the samples, reaching their maximums of 305 °C with x = 0.015 and 2.99 Oe with x = 0.03, respectively. The variation of complex permeability versus Ho³⁺ ions substitution level presented an opposite trend to that of coercivity. The dielectric loss increased slightly after the introduction of a small amount of Ho³⁺ ions, but reduced significantly with more Ho³⁺ ions doped.     

Effects of Ni2+ concentration on the composition,structure, magnetic properties,and DC-bias superposition characteristics of NiCuZn ferrites

Ni_xCu_0.2Zn_yFe_1.98O₄ (x = 0.16, 0.26, 0.35, 0.43, 0.50; y = 0.8?x) ferrites were prepared via solid-state reaction. The influence of Ni²⁺ concentration on ferrites composition, microstructure, magnetic properties and DC-bias superposition characteristics was studied by XRD, SEM, XPS, and VSM. Then, the effect of magnetic properties on the DC-bias superposition characteristics was analyzed. The results showed that the ferrites sintered at 900 °C for 3 h were all in pure spinel phase with an average grain size of 7.5 μm and a relative density of about 5.15 g cm^?3. With the increase in Ni²⁺ concentration, the saturation magnetization (M_s) and coercivity (H_c) of ferrites increased, but the magnetocrystalline anisotropy constant (K₁) first increased and then decreased. And the M_s, H_c, and K₁ of the specimen with x = 0.43 were 63.62 emu·g^?1, 27.36 Oe, and 1813.17 Oe·emu·g^?1, respectively. In particular, the specimen of x = 0.50 achieved the best DC superposition characteristics, where the H_70% was about 220 A m^?1. The incremental permeability of the specimens decreased rapidly at a bias magnetic field <400 A m^?1. The variation mainly originated from the domain wall displacement, and the rate of decrease was influenced by both M_s and K₁. At a bias magnetic field ≥400 A m^?1, the incremental permeability of the specimens decreased slowly, mainly because the number of domain walls decreased until disappearing, and the specimens tended to become a single domain structure. And the rate of decrease of incremental permeability was mainly affected by K₁.     

铈掺杂镍锌铁氧体的制备与性能研究

用高分子凝胶法制备了稀土元素铈掺杂的镍锌铁氧体粉Ni0.5Zn0.5CexFe2-xO4,并对产物结构和电磁性能进行了表征。结果表明,当Ce3+的掺杂摩尔数x为0.1时,800℃煅烧后会形成立方晶系尖晶石结构的镍锌铁氧体晶相。与Ni0.5Zn0.5Fe2O4铁氧体相比,在8.2~12.4 GHz频率范围内掺杂铈元素的Ni0.5Zn0.5Ce0.1Fe1.9O4铁氧体的tanδm值降低,而其tanδe值升高,平均值可达0.527。     

Mechanosynthesis of nanostructured magnetic Ni-Zn ferrite

Nanocrystalline Ni-Zn ferrite (NiZnFe₂O₄) was directly produced by high energy ball milling of stoichiometric mixture of ZnO, NiO, Fe₂O₃ powders. X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), simultaneous thermal analysing (STA), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM) were carried out to characterize the structural, chemical and magnetic aspects of NiZnFe₂O₄ compound. The formation of NiZnFe₂O₄ phase appeared to involve two stages; development of Zn ferrite by diffusion of ZnO in Fe₂O₃ followed by diffusion of NiO in Zn ferrite to form Ni-Zn ferrite. The crystallite size of final product after 60 h of ball milling time was estimated to be 18 nm which increased to 45 nm after annealing at 800 °C for 4 h. After annealing of ball milled powders, the saturation magnetization was increased and coercivity was decreased as lattice defects and internal strain reduced.     

Effect of sintering on the microstructure and mechanical properties of alloy titanium-wollastonite composite fabricated by powder injection moulding process

Composite biomaterials are in high demand in the medical field of today. The combination of bioactive wollastonite (WA) glass ceramic with the biocompatibility of alloy titanium (Ti6Al4V) could be a good candidate for implant applications. The rheological properties of Ti6Al4V/WA feedstock show a pseudoplastic behaviour with low activation energy. The feedstock was successfully injected as a green part with no defects. The green part was solvent debound for 6?h in heptane and thermal debound in an argon environment for 1?h. The brown part was successfully sintered at 1300?°C for 3?h with 5?°C/min heating and cooling rates. The average sintered density was 4.12?g/cm³; which is 97.5% from the theoretical density. The highest Young's modulus obtained was 18.10?GPa; which is in the range of human bone strength. EDX analysis shows that by increasing sintering temperature, the level of oxygen decreased. Cell viability test shown an absorbance increased with days increasing indicated that the cellular were proliferated on the composite Ti6Al4V/WA composite which also proved that the composite was non-toxic. This indicates that the Ti6Al4V/WA composite is suitable for bone implant applications.     

Microstructure and properties of lightweight fibrous porous mullite ceramics prepared by vacuum squeeze moulding technique

A novel fibrous porous mullite network with a quasi-layered microstructure was produced by a simple vacuum squeeze moulding technique. The effects of organic binder content, inorganic binder and adsorbent on the microstructure and the room-temperature thermal and mechanical properties of fibrous porous mullite ceramics were systematically investigated. An anisotropy microstructure without agglomeration and layering was achieved. The fibrous porous mullite ceramics reported in this study exhibited low density (0.40 g/cm³), low thermal conductivity (~0.095 W/(m K)), and high compressive strength (~2.1 MPa in the x/y direction). This study reports an optimal processing method for the production of fibrous porous ceramics, which have the potential for use as high-temperature thermal insulation material.     

Effect of Zn substitution on the structural and magnetic properties of nanocrystalline NiFe2O4 ferrites

Nanocrystalline Ni_1?xZn_xFe₂O₄ (where, x = 0.0, 0.2, 0.4, 0.6, 0.8 & 1) samples were synthesized through solution combustion technique using oxylyl de-hydrazide (ODH) as a fuel and the effect of dopant and its concentration on the structural and magnetic properties was investigated. As-prepared samples were characterized using different characterization techniques such as, XRD, SEM-EDS, TEM and Raman spectroscopy for their phase-purity, crystallinity, surface morphology and elemental composition; also magnetic properties were investigated through EPR, Mossbauer spectroscopy and vibrating sample magnetometer (VSM). Rietveld fitted XRD and Raman studies confirm the formation of cubic spinel structured ferrites and substitution of Zn ion at Ni site without formation of impurity phases. No other structural changes were observed and the structure remains in cubic phase with increase of Zn concentration. SEM and TEM micrographs reveal that the particles are agglomerated and the particles size were found in the nano range. Also good stoichiometric composition was observed in all the compositions of Zn substituted Ni ferrite samples. Magnetic measurements (VSM) reveal that pure Ni ferrites exhibits soft magnetic behaviour. Further the ferromagnetic behaviour suppressed with the substitution of diamagnetic Zn ion and with increase of its concentration in Ni ferrites, which was further evidenced in the Mossbauer spectroscopic results. At room temperature, electronic paramagnetic resonance spectra exhibits a broad resonance signal with Lande's g factor varies from 2.23 to 1.95 with increase in Zn content, which is attributed to spin exchange interactions between Fe³⁺, Ni²⁺ and Zn²⁺ ions also asymmetric EPR spectra was observed. The investigated results show that, Zn substitution has greater impact on the magnetic properties of Ni ferrites due to the diamagnetic nature of Zn, which inturn alters the cationic distribution and the exchange interactions between Ni-Fe and Fe-Fe.     

On the structural and magnetic properties of La-substituted NiCuZn ferrites prepared using egg-white

Ni_0.50Cu_0.25Zn_0.25La_xFe_2−xO₄ ferrites (with x = 0.00–0.09) were prepared by a simple method using metal nitrates and freshly extracted egg white. The proper calcination temperature for ferrites formation was estimated using thermo-gravimetry technique (TG). The samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared spectroscopy (FT-IR) measurements. XRD of the powders calcined at 550 °C for 2 h showed single-phase crystalline cubic ferrites with crystallite sizes in the range 17.2–21.6 nm. Both the lattice parameter and X-ray density are found to increase by the addition of rare earth ion. TEM image showed agglomerated nano-particles with irregular sizes and shapes. FT-IR spectra showed two absorption bands (ν₁ and ν₂) attributed to stretching vibration of tetrahedral and octahedral complex Fe³⁺–O²⁻, respectively. The shifting of the ν₂ band towards lower frequencies indicates the preference of lanthanum ions to occupy the octahedral sites. The effect of La-substitution on the magnetic properties was studied using vibrating sample magnetometry (VSM) and susceptibility measurements. The decrease in the saturation magnetization with increasing La content can be attributed to the decreasing of Fe³⁺–Fe³⁺ interactions in the octahedral sites. Coercivity shows size dependent behavior due to the combination of surface effect and surface anisotropy. The obvious decrease in the Curie temperature (T_C) with increasing La content indicates that the highly paramagnetic character of La³⁺ ions decreases the ferromagnetic region at the expense of the paramagnetic one.     

Impact of Dy on structural,dielectric and magnetic properties of Li-Tb-nanoferrites synthesized by micro-emulsion method

A series of Dy-doped Li–Ni ferrites of the following composition Li_0.5Ni_0.48Tb_0.02Dy_xFe_2−xO₄ (0.2≤x≥0) was synthesized by the microemulsion method. The X-ray diffraction (XRD) analysis indicated that Li_0.5Ni_0.48Tb_0.02Dy_xFe_2−xO₄nano-crystalline ferrites exhibited the single-phase spinel structure. The lattice parameter was determined by the Nelson-Riley refinement technique and it increased by increasing the Dy contents. The crystallite size was computed from the Debye Scherrer's formula and it was in range from 27 to 40 nm. The thermal decomposition process was studied by the thermogravimetric analysis and the annealing temperature observed was 980 °C. The real and complex parts of dielectric constant decreases very sharply in the lower frequency region, but in the higher frequency region, the real and complex part of dielectric constant show variable values with Dy contents. The dielectric tangent loss (tan δ) decreases exponentially with Dy contents. The magnitude of the ac conductivity decreases in certain frequency region, as the Dy contents are increased. The possible mechanisms contributing to the above behavior are discussed. The results of these nanocrystalline ferrites are very suitable materials for microwave device applications.     

Microstructure and properties of B4C-SiC composites prepared by polycarbosilane-coating/B4C powder route

B₄C-SiC composites with fine grains were fabricated with hot-pressing pyrolyzed mixtures of polycarbosilane-coated B₄C powder without or with the addition of Si at 1950 °C for 1 h under the pressure of 30 MPa. SiC derived from PCS promoted the densification of B₄C effectively and enhanced the fracture toughness of the composites. The sinterability and mechanical properties of the composites could be further improved by the addition of Si due to the formation of liquid Si and the elimination of free carbon during sintering. The relative density, Vickers hardness and fracture toughness of the composites prepared with PCS and 8 wt% Si reached 99.1%, 33.5 GPa, and 5.57 MPa m^1/2, respectively. A number of layered structures and dislocations were observed in the B₄C-SiC composites. The complicated microstructure and crack bridging by homogeneously dispersed SiC grains as well as crack deflection by SiC nanoparticles may be responsible for the improvement in toughness.     

Electrical and magnetic properties of ZrO2-doped lithium-titanium-zinc ferrite ceramics

This report documents the effect of 0–3 wt% ZrO₂ additive on the electrical and magnetic properties of LiTiZn ferrite. Ferrite powder of Li_0.65Fe_1.6Ti_0.5Zn_0.2Mn_0.05O₄ composition was synthesised at 900 °C for 4 h in air. Ferrite ceramics doped with ZrO₂ were sintered at 1010 °C for 2 h in air. A spreading resistance analysis showed that LiTiZn ferrites exhibited nonuniform distribution of depth DC resistivity, which varied in the range of (0.25–2.3) × 10⁹ Ω⋅cm depending on the amount of additive. Zirconia also affected the magnetic properties of ferrite so that the magnetisation increased and the initial permeability decreased as the ZrO₂ content increased. In addition, the Curie temperature varied. The permeability spectra measured in the frequency range from 10 MHz to 18 GHz changed depending on the zirconia content.     

Microstructure and mechanical properties of a Pt-Rh alloy produced by powder metallurgy and subjected to plastic working

The paper presents the results of investigations of the Pt-Rh8 wires produced by powder metallurgy. The powder was consolidated by isostatic pressing followed by sintering. Examinations of the microstructure and the microhardness of the wires thus obtained showed that this treatment yields solid wires characterized by fine-grained microstructure and low porosity. The wires have better mechanical properties than those produced by plastic treatment of moulded alloys.     

High-performance inductive couplers based on novel Ce3+ and Co2+ ions co-doped Ni-Zn ferrites

High-performance inductive couplers require Ni-Zn ferrites of high saturation magnetization, Curie temperature, permeability and application frequency. However, for inductive couplers some of these properties run against each other in one ferrite. To balance these requirements, in this work, novel Ni-Zn ferrite ceramics co-doped by Ce³⁺ and Co²⁺ ions with chemical formula Ni_0.4Zn_0.5Co_0.1Ce_xFe_2-xO₄ (x = 0–0.06) were designed and fabricated by a molten salt method. For the acquired ferrites, both Ce³⁺ and Co²⁺ ions could come into the lattices. The initially doped Co²⁺ ions would cause a slightly decreased grain size and dramatically reduced the specimen densification, but the further added Ce³⁺ ions could effectively inhibit the density reduction, while the grain size continues to dwindle. The additional Ce³⁺ ions would generate a foreign CeO₂ phase in the acquired specimens. The sole doping of Co²⁺ ions would aggrandize the saturation magnetization of ferrites, but the introduction of Ce³⁺ ions would cause its decrease. However, with an appropriate doping level, the Ce³⁺ and Co²⁺ ions co-doped ferrites could preserve a relatively high saturation magnetization, while the Curie temperature and cut-off frequency of the ferrites are dramatically augmented, although the permeability would be somewhat reduced. The as-acquired ferrites were simulated to apply in inductive couplers, revealing that the devices manufactured by the Ni_0.4Zn_0.5Co_0.1Ce_xFe_2-xO₄ ferrites had significantly high maximum operating frequency, compared with that of the one manufactured by pure Ni_0.5Zn_0.5Fe₂O₄ ferrite.     

Improvement of wetability,sinterability, mechanical and electrical properties of Al2O3-Ni nanocomposites prepared by mechanical alloying

The wetability improvement and particle size reduction of alumina/Ni composites through mechanical alloying were addressed. Their effect on the sinterability (at high temperature), mechanical and electrical properties were studied. Al₂O₃ matrix nanocomposites reinforced with different volume fractions of Ni up to 10 vol% were prepared by mechanical alloying. The milled powders were cold pressed and sintered at different firing temperatures up to 1600 °C. The morphology of powders and the microstructure of sintered bodies were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), respectively. Furthermore, relative density, apparent porosity, mechanical properties and electrical resistivity of the sintered composites were investigated. The results revealed that Al₂O₃ matrix was successfully coated with Ni thin film through mechanical alloying; the thickness of coat was increased with increasing the Ni content. Moreover, the increasing of both Ni content and sintering temperature up 1600 °C, led to a remarkable increase in the relative density and facture toughness of the sintered specimen. On the other hand, microhardness and elastic modulus were decreased with increasing of Ni content, while they increased significantly with the increase of sintering temperature. The electrical resistivity was decreased with increasing Ni content and sintering temperature.     

Microstructure and mechanical properties of (Ti,W)C cermets prepared by ultrafast spark plasma sintering

To explore the impact of the sintering rate on the microstructure and mechanical properties of cermets, the preparation of (Ti,W)C cermets by ultrafast sintering via spark plasma sintering (SPS) is reported. Compared with a slow heating rate, the electric field produced by an ultrafast heating rate enhances the liquid phase mass transfer of the metal binder phase, thus achieving rapid densification of (Ti,W)C cermets and effectively inhibiting abnormal grain growth. However, an excessive heating rate will lead to an “overflow” phenomenon, which reduces the grain growth difficulty and the bonding strength between grains. The results show that when the heating rate is 500 °C/min, the liquid phase mass transfer is moderate, the densification degree is the highest and the mechanical properties are excellent. The flexural strength, Vickers hardness and fracture toughness are 1340.90 ± 23.55 MPa, 18.42 ± 0.46 GPa and 11.96 ± 0.23 MPa?m^1/2, respectively.     

O＇－Sialon－ZrO_2复合材料的显微结构与力学性能的研究

研究了Ｏ＇－Ｓｉａｌｏｎ－ＺｒＯ２复合材料的显微结构与力学性能的关系。结果表明，Ｏ＇－Ｓｉａｌｏｎ形成连续网络编织状结构。ＺｒＯ２加入量较少时充当填充结构骨架的作用；ＺｒＯ２加入量增多时（至４０％），会有更多的ＺｒＯ２形成聚集体。随着ＺｒＯ２引入量的增加，材料的常温抗折强度提高，但高温抗折强度下降。Ｏ＇－Ｓｉａｌｏｎ的编织状结构可能阻碍晶界滑移。这种复合材料的高温抗折强度在１４００℃为１１２～１７３ＭＰａ。     

Sintered TiO2 powder containing metallic Co binder prepared via mechanical carbonization,and its mechanical properties

A TiO₂-Co-a composite powder was prepared via carbonizing and selective oxidation processing of a Ti-Co alloy. The conventionally mixed TiO₂-Co-c composite powder and pure TiO₂ were sintered at 1100, 1200, 1300, 1400?°C, respectively. The structural characterization was performed using X-ray diffraction, field emission scattering electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The sintered samples were more densified, and melted bonding occurred at temperature higher than 1300?°C. The flexural strength and fracture toughness of the TiO₂-Co-a sample were higher than those of the TiO₂ and TiO₂-Co-c sintered at temperature higher than 1300?°C, while the Vickers hardness of TiO₂-Co-a was the lowest at all sintering temperatures. The sintered TiO₂-Co-a sample was more ductile and strengthened than the TiO₂-Co-c sample with added metallic Co binder via mechanical mixing. The enhanced mechanical properties of the TiO₂-Co-a sample were due to the fine dispersion of the metallic Co binder wetted with a TiO₂ matrix.     

Microstructure and mechanical properties of hydroxyapatite obtained by gel-casting process

In the present work, well-shaped HAp green bodies were obtained by the gel-casting process with 50 vol.% slurry. After drying, the microstructure and pore distribution of the green body were investigated. The density, compressive strength and flexural strength of the green body were 1.621 g/cm³, 32.6 ± 3.2 MPa and 13.8 ± 1.0 MPa, respectively. After pressureless sintering at the range of 1100–1300 °C for 2 h, the relative density of the final product ranges from 71.8 to 97.1% th. The maximum value of flexural strength, elastic modulus, hardness and fracture toughness were 84.6 ± 12.6 MPa, 138 ± 7 GPa, 4.45 ± 0.18 GPa and 0.95 ± 0.13 MPa m^1/2, respectively. SEM images show a compact and uniform microstructure; the average grain size was found by using the linear intercept method. XRD and FTIR determined the phase and the radical preserved after sintering.     

Design,fabrication, and magnetic properties of novel (Ni,Cr,Zr)-co-doped M-type barium ferrite ceramics

Multicomponent co-doping is an effective method to balance the counteracting magnetic properties of ferrite ceramics. In this work, novel (Ni,Cr,Zr)-co-doped M-type barium hexaferrites (BaFe_12-3xNi_xCr_xZr_xO₁₉, x = 0–0.8) were designed and synthesized by traditional solid-state reaction. Thermogravimetric analysis indicated that NiO would participate in the formation of secondary phase NiFe₂O₄ in the as-synthesized powder. Through traditional solid-state sintering, by using the synthesized pure-phase magnetic powders, almost full-dense ceramics were fabricated. Visual high-temperature deformation analysis revealed that there was no obvious difference in the sintering behavior and densification temperature of the ceramics with different compositional x, due to the low sintering activity of the as-synthesized magnetic powders. And X-ray diffraction analysis indicated that all the fabricated ceramics are of pure-phase M-type barium ferrite, and the lattice parameter c/a firstly increased as x raised up to 0.4 and then remained almost unchanged with further increased x, even if the lattice distortion became heavier. Microstructure examination revealed that the grain size monotonously decreased as the quantity of the substituent ions increased. The remnant magnetization and coercivity of the fabricated ceramics decreased monotonously as x increased, while the saturated magnetization could be maintained till the samples with x ≤ 0.4. Taking all the parameters into consideration, the samples with x = 0.4 might be a good candidate for transformer cores.