High-affinity integration of hydroxyapatite nanoparticles with chemically modified silk fibroin

Hydroxyapatite (HA)-based nanocomposites were prepared by a co-precipitation method with silk fibroin (SF) serving as organic matrix. Silk fibroin was chemically modified with an alkali solution or an enzyme attempting to improve the interface between the mineral and the organic matrix. The influences of the alkali and enzyme pretreatments on microstructure and physicochemical properties of HA–SF composite were examined and compared. The results reveal that both the two kinds of pretreatments facilitate the formation of highly ordered three-dimensional porous network throughout the composites, increase the microhardness of the composite, and promote the preferential growth of HA crystallites along c-axis. Among all the as-prepared samples, the composite containing the enzyme pretreated SF shows desirable hierarchical microstructure with higher degree of organization and more uniform pore size distribution. Due to the enzyme pretreatment, HA crystallites undergo obvious changes in morphology from rod-like to␣whisker-like and in crystal growth towards more apparent epitaxy along c-axis. The alkali pretreatment induces the stronger chemical interactions between HA and SF and thus to strengthen the inorganic–organic interfacial adhesion. The newly developed HA–SF composites are expected to be attractive biomedical materials for bone repair and remodeling.     

Preferential Alignment of Hydroxyapatite Crystallites in Nanocomposites with Chemically Disintegrated Silk Fibroin

Hydroxyapatite (HAp) nanocrystals were prepared at room temperature by a coprecipitation method from Ca(OH)₂ and H₃PO₄, in the presence of chemically disintegrated silk fibroin (SF). Adsorbed amounts of cations on SF and crystallinity of HAp in the composite were increased by the chemical disintegration of SF higher order structure. Preferential alignment of c-axis of HAp crystallites along the longitudinal direction of ca. 150nm SF fibril was observed. These changes due to disintegration of SF were discussed in terms of the chemical interaction between HAp and SF. The resulted composite with preferential alignment of HAp nanocrystals is a good candidate as a starting material for bone substitutes.     

Microstructure and Chemical States of Hydroxyapatite/silk Fibroin Nanocomposites Synthesized via A Wet-mechanochemical Route

Hydroxyapaptite (HAp)/silk fibroin (SF) nanocomposites were prepared via a wet-mechanochemical route at room temperature. The results reveal that the inorganic phase in the composites is carbonate-substituted HAp containing 2.9–3.1 wt% of carbonate ions. The primary HAp crystals are rod-like in shape with a typical size of 20–30nm in length and 8–10nm in width, and lattice parameters a = 9.423, c = 6.888. The self-assembled HAp crystals along their c-axes aggregate into bundles, which are connected with SF fibrils. Consequently, a three-dimensional porous network is formed in the composite, which is beneficial to inducing new bone formation in practical implantation.     

Fabrication of metal-nanoparticle/carbon-fiber composites having a microtube-array morphology

In the current work, we succeeded in incorporation of Pt ions into sisal fiber (SF) – a biological matrix with a characteristic morphology of microtube array, and in subsequent in situ synthesis of Pt nanoparticles of ca. 3.6 nm. Carbonization of the SF with Pt nanopaticles at 400°C produced Pt-nanoparticle/carbon-fiber composite, preserving the initial microtube-array morphology of SF. It is interesting that the walls of neighboring microtubes and the middle lamella between these microtubes were fused by carbonization, and a homogeneous wall was formed. Although the size of Pt nanoparticles was enhanced to ca. 5.3 nm after carbonization, the solid matrices (from cellulose to carbon) acted as effective barriers against the growth of Pt nanoparticles. The Pt-nanoparticle/carbon-fiber composite combines several important aspects, including the morphologies of fiber and microtube-array, carbon matrix, and Pt nanoparticles. Thus it might be a novel type of catalyst and have potential applications in many fields.     

Ni-Co-TiO2 nanocomposite coating prepared by pulse and pulse reversal methods using acetate bath

Ni-Co/nano TiO₂ (Ni-Co-TiO₂) composite coatings were prepared under pulse current and pulse reverse current methods using acetate bath. The microstructure and corrosion resistance of the coatings were characterized by means of XRD, SEM and EIS. Both the Ni-Co alloy and composite coatings exhibited single phase of Ni matrix with face centered cubic (fcc) crystal structure. The crystal orientation of the Ni-Co-TiO₂ composite coating was transformed from crystal face (2 0 0) to (1 1 1) compared with Ni-Co alloy coatings. The results showed that the microstructure and performances of the coatings were greatly affected by TiO₂ content on the deposits prepared by PC and PRC methods. The microhardness and corrosion resistance were enhanced in the optimum percentage of TiO₂ composite coatings. The PRC composite coatings were exhibited from compact surface, higher microhardness and good corrosion resistance compared with that of the PC composite coating.     

Laser cladding of in situ TiB2/Fe composite coating on steel

To enhance the wear resistance of mechanical components, laser cladding has been applied to deposit in situ TiB₂/Fe composite coating on steel using ferrotitanium and ferroboron as the coating precursor. The phase constituents and microstructure of the composite coating were investigated using X-ray diffraction (XRD), scanning electron micrograph (SEM) and electron probe microanalysis (EPMA). Microhardness tester and block-on-ring wear tester were employed to measure the microhardness and dry-sliding wear resistance of the composite coating. Results show that defect-free composite coating with metallurgical joint to the steel substrate can be obtained. Phases presented in the coating consist of TiB₂ and α-Fe. TiB₂ particles which are formed in situ via nucleation-growth mechanism are distributed uniformly in the α-Fe matrix with blocky morphology. The microhardness and wear properties of the composite coating improved significantly in comparison to the as-received steel substrate due to the presence of the hard reinforcement TiB₂.     

Hybrid Al + Al3Ni metallic foams synthesized in situ via laser engineered net shaping

A hybrid, Al?+?Al₃Ni metallic foam was synthesized in situ via laser engineered net shaping (LENS®) of Ni-coated 6061 Al powder in the absence of a foaming agent. During LENS® processing, the Ni coating reacted with the Al matrix, resulting in the simultaneous formation of a fine dispersion of Al₃Ni, and a high volume fraction of porosity. As a reinforcement phase, the intermetallic compound formed particles with a size range of 1–5?µm and a volume fraction of 63%, with accompanying 35–300?µm pores with a 60% volume fraction. The microstructure of the as-deposited Al?+?Al₃Ni composite foams was characterized using SEM, EDS, XRD and TEM/HRTEM techniques. The evolution of the microstructure was analyzed on the basis of the thermal field present during deposition, paying particular attention to the thermodynamics of the Al₃Ni intermetallic compound formation as well as discussing the mechanisms that may be responsible for the observed porosity. The mechanical behavior of the as-deposited material was characterized using compression and microhardness testing, indicating that the yield strength and hardness are 190?MPa and 320 HV, respectively, which represents an increase of over three times higher than that of annealed Al6061, or similar to heat-treated Al6061 fully dense matrix, and much higher than those of traditional Al alloy foams, and with a low density of 1.64?g/m³.     

Microstructure evolution of Fe-based WC composite coating prepared by laser induction hybrid rapid cladding

Fe + 50 wt.% WC composite coating was prepared by laser induction hybrid rapid cladding (LIHRC) on steel substrate. The phase and microstructure of the composite coating were investigated by X-ray diffraction (XRD), environmental scanning electron microscope (ESEM) and energy dispersive spectrum (EDS). The results showed that WC particles were dissolved almost completely to precipitate the coarse herringbone M₆C eutectic carbides and the fine dendritic M₆C carbides, and that the partially dissolved WC particles with an alloyed reaction layer were occasionally observed in the whole coating. The phases of the composite coating were composed of supersaturated solid solution α-Fe, retained austenite, Fe₃C, W₂C, M₆C and M₇C₃. The microstructure evolution in the composite coating was represented by the transformation of three parts such as Fe-based metallic matrix, dispersed carbides and incompletely dissolved WC particles. The microhardness of Fe-based WC composite coating was three times much higher than that of the substrate, but was relatively lower than that of Ni-based WC composite coating by LIHRC.     

Relationships between the anisotropy of longitudinal wave velocity and hydroxyapatite crystallite orientation in bovine cortical bone

Quantitative ultrasound (QUS) is now widely used for evaluating bone in vivo, because obtained ultrasonic wave properties directly reflect the visco-elasticity. Bone tissue is composed of minerals like hydroxyapatite (HAp) and a collagen matrix. HAp crystallites orientation is thus one parameter of bone elasticity. In this study, we experimentally investigated the anisotropy of ultrasonic wave velocity and the HAp crystallites orientation in the axial-radial and axial-tangential planes in detail, using cylindrical specimens obtained from the cortical bone of three bovine femurs. Longitudinal bulk wave propagation was investigated by using a conventional ultrasonic pulse system. We used the one cycle of sinusoidal pulse which was emitted from wide band transmitter. The nominal frequency of the pulse was 1 MHz. First, we investigated the anisotropy of longitudinal wave velocity, measuring the anisotropy of velocity in two planes using cylindrical specimens obtained from identical bone areas. The wave velocity changed due to the rotation angle, showing the maximum value in the direction a little off the bone axis. Moreover, X-ray pole figure measurements also indicated that there were small tilts in the HAp crystallites orientation from the bone axis. The tilt angles were similar to those of the highest velocity direction. There were good correlations between velocity and HAp crystallites orientation obtained in different directions. However, a comparatively low correlation was found in posterior bone areas, which shows the stronger effects of bone microstructure. In the radial-tangential plane, where the HAp crystallites hardly ever align, weak anisotropy of velocity was found which seemed to depend on the bone microstructure.     

Electrodeposition and tribological properties of Ni-SrSO4 composite coatings

Ni-SrSO₄ composite coatings were electrodeposited on superalloy Inconel 718 from a Watts electrolyte containing a SrSO₄ suspension. Ni-SrSO₄ coatings were investigated by scanning electron microscope, microhardness tester, and friction and wear tester in sliding against a bearing steel ball under unlubricated condition. The incorporation of SrSO₄ into Ni matrix increases the microhardness of electrodeposited coatings. Ni-SrSO₄ composite coating exhibits a distinctly low friction coefficient and a small wear rate as contrasted with pure Ni coating and the substrate. The effect of SrSO₄ particles on microstructure and tribological properties of Ni-SrSO₄ composite coatings is discussed.     

Surface modification of Al-20Si alloy by high current pulsed electron beam

Hypereutectic Al-20Si (Si 20 wt.%, Al balance)alloy surface was treated with high current pulsed electron beam (HCPEB) under different pulse numbers. The results indicate that HCPEB irradiation induces the formation of metastable structures on the treated surface. The coarse primary Si particle melts, producing a “halo” microstructure with primary Si as the center on the melted surface. A supersaturated solid solution of Al is formed in the melted layer caused by Si atoms dissolving into the Al matrix. Cross-section structure analysis shows that a 4 μm remelted layer is formed underneath the top surface of the HCEPB-treated sample. Compared with the matrix, the Al and Si elements in the remelted layer are distributed uniformly. In addition, the grains of the Al-20Si alloy surface are refined after HCPEB treatment, as shown by TEM observation. Nano-silicon particles are dispersed on the surface of remelted layer. Polygonal subgrains, approximately 50-100 nm in size, are formed in the Al matrix. The hardness test results show that the microhardness of the α(Al) and eutectic structure is increased with increasing pulse number. The hardness of the “halo” microstructure presents a gradient change after 15 pulse treatment due to the diffusion of Si atoms. Furthermore, hardness tests of the cross-section at different depths show that the microhardness of the remelted layer is higher than that of the matrix. Therefore, HCPEB technology is a good surface modification method for enhancing the surface hardness of hypereutectic Al-20Si alloy.     

稀土CeO_2对镍基纳米Al_2O_3激光熔覆复合涂层组织和性能的影响

采用激光熔覆技术在45钢基体上制备了不同CeO2含量的镍基纳米Al2O3复合涂层,对熔覆层进行了微观组织分析和显微硬度测试。结果表明,随着CeO2含量的增加,熔覆层组织由亚共晶向共晶组织转变;加入1.0%CeO2对镍基纳米Al2O3熔覆层的组织起到明显的细化和净化作用,枝晶生长的方向性减弱,组织趋向均匀,熔覆涂层的显微硬度值比未加稀土的涂层提高了60-95HV0.2。     

Calcination of Rod-like Hydroxyapatite Nanocrystals with an Anti-sintering Agent Surrounding the Crystals

Sintering-free nanocrystals of calcined hydroxyapatite (HAp) having a rod-like morphology were fabricated by calcination at 800°C for 1 h with an anti-sintering agent surrounding original HAp particles and the agent was subsequently removed after calcination. The original HAp particles having a rod-like morphology with a size ranging from 30 to 80 nm (short axis) and 300 to 500 nm (long axis) were prepared by wet chemical process, and poly(acrylic acid, calcium salt) (PAA-Ca) was used as the anti-sintering agent. In the case of calcination without additives, the mean size of HAp crystals dispersed in an ethanol medium increased by about 4 times and the specific surface area of the crystals exhibited a 25% decrease compared to those of the original HAp particles because of calcination-induced sintering among the crystals. On the other hand, the HAp crystals calcined with the anti-sintering agent, PAA-Ca, could be dispersed in an ethanol medium at the same size as the original particles, and they preserved the specific surface area after calcination. These results indicate that PAA-Ca and/or its thermally decomposed product, CaO, surrounded the HAp particles and protected them against calcination-induced sintering during calcination. The HAp crystals calcined with PAA-Ca showed high crystallinity, and no other calcium phosphate phases could be detected after washing with water.     

Effect of Polyethylene Functionalization on Mechanical Properties and Morphology of PE/SiO2 Composites

In this study composites of high density polyethylene (HDPE) with various SiO₂ content were prepared by melt compounding using maleic anhydride grafted polyethylene (PE-g-MAH) as a compatibilizer. The composites containing 2, 4 and 6% by weight of SiO₂ particles were melt-blended in a co-rotating twin screw extruder. In all composites, polyethylene-graft-maleic anhydride copolymer (PE-g-MAH, with 0.85% maleic anhydride content) was added as a compatibilizer in the amount of 2% by weight. Morphology of inorganic silica filler precipitated from emulsion media was investigated. Mechanical properties and composite microstructure were determined by tensile tests and scanning electron microscopy technique (SEM). Tensile strength, yield stress, Young's modulus and elongation at break of PE/SiO₂ composites were mainly discussed against the properties of PE/PE-g-MAH/SiO₂ composites. The most pronounced increase in mechanical parameters was observed in Young's modulus for composites with polyethylene grafted with maleic anhydride. The increase in the E-modulus of PE/PE-g-MAH/SiO₂composites was associated with the compatibility and improvement of interfacial adhesion between the polyethylene matrix and the nanoparticles, leading to an increased degree of particle dispersion. This finding was verified on the basis of SEM micrographs for composites of PE/PE-g-MAH/4% by weight of SiO₂. The micrographs clearly documented that addition of only 2 wt% of the compatibilizer changed the composite morphology by reducing filler aggregates size as well as their number. Increased adhesion between the PE matrix and SiO₂ particles was interpreted to be a result of interactions taking place between the polar groups of maleic anhydride and silanol groups on the silica surface. These interactions are responsible for reduction of the size of silica aggregates, leading to improved mechanical properties.     

Processing pathway effects in CoCrCuNi+X (Fe,Mn) high-entropy alloys

A parallel study of mechanical alloying and solidification was carried out on FCC high-entropy alloys (HEAs) CoCrCuNi, CoCrCuFeNi and CoCrCuMnNi to investigate the effects of each processing methods on the resulting microstructure, crystal structure and microhardness. Elemental powders were mechanically alloyed followed by spark plasma sintering (SPS) at 800°C and 900°C to achieve densified discs, while arc melting was carried out from bulk pieces of the elemental metals followed by furnace annealing at 800°C and 900°C for 5?h. Both processing routes resulted in a primary FCC phase with secondary Cu-rich FCC segregation as interdendrites for the solidified alloys and particle boundaries for the SPS alloys, with the exception of a small amount of σ phase present in the SPS processed alloys. The solidification of the CoCrCuNi, CoCrCuFeNi and CoCrCuMnNi HEAs resulted in typical dendritic microstructure, followed by the precipitation of a small Cr-rich phase in the CoCrCuMnNi alloy after annealing. The grain size of the mechanically alloyed powder was approximately 20?nm from the Scherrers equation and the SPS processed HEAs consisted of a Cu-rich phase in the particle boundaries, forming cobblestone-like microstructure. The microhardness was examined in the as-cast, annealed and SPS states. It was found that the SPS processed samples had an increased microhardness by a factor of 2.5.     

Effects of composition and cooling rate on the microstructure of?Sn–3.7Ag–0.9Zn–Bi solders

The effects of Bi addition, of less than 3 wt.%, and applied cooling rate on the solidified microstructure of the eutectic Sn–3.7Ag–0.9Zn (weight percent, hereafter) solder were investigated. As observed by microstructural analysis, the increase of Bi content favors the separation of the β-Sn and AgZn intermetallic compounds (IMCs) in the eutectic Sn–Ag–Zn solder. And there are some Bi precipitates formed along with the primary β-Sn dendrites as the concentration of Bi exceeds 2%. As the applied cooling rate increases, the microstructure of the Sn–3.7Ag–0.9Zn–Bi solder is refined, and the segregation of Bi is restrained. By increasing the amount of Bi, the microhardness of the solder increases.     

Fortification of Ni–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite coatings prepared by pulse and direct current methods

Ni–Y₂O₃ nanocomposite coatings were prepared under direct current (DC) and pulse current (PC) using acetate bath. The microstructure and corrosion resistance of the coatings were characterized by means of XRD, SEM, AFM, and EIS. The results showed that the microstructure and performances of the coatings were greatly affected by Y₂O₃ content on the deposits prepared by DC and PC methods. The microhardness and corrosion resistance were enhanced in the optimum percentage of Y₂O₃ composite coatings. The PC composite coatings were exhibited compact surface, higher microhardness, and good corrosion resistance compared with that of the DC composite coatings.     

Ti6Al4V合金表面激光沉积复合涂层的组织和性能

为了增强Ti6Al4V钛合金的耐磨性,采用激光沉积制造方法在其表面上制备了以原位生成的TiC颗粒和直接添加的WC颗粒为增强相的耐磨涂层,观察了各涂层的微观组织,并测量了涂层的显微硬度和涂层在室温大气条件下的摩擦磨损性能。结果表明各涂层和基体呈现冶金结合,原位自生的TiC和部分熔化的WC颗粒均能够均匀弥散分布于基体上,由于增强相颗粒的弥散强化及激光沉积组织的细晶强化作用,基材的硬度和耐磨性均得到了提高。原位自生的TiC涂层比WC涂层硬度梯度分布平缓,但耐磨性稍差。     

Simple synthetic route for hydroxyapatite colloidal nanoparticles via a Nd:YAG laser ablation in liquid medium

Pulsed laser ablation (PLA) in liquid medium was successfully employed to synthesize hydroxyapatite (HAp) colloidal nanoparticles. The crystalline phase, particle morphology, size distribution and microstructure of the HAp nanoparticles were investigated in detail. The obtained HAp nanoparticles had spherical shape with sizes ranging from 5 to 20 nm. The laser ablation and the nanoparticle forming process were studied in terms of the explosive ejection mechanism by investigating the change of the surface morphology on target. The stoichiometry and bonding properties were studied by using XPS, FT-IR and Raman spectroscopy. A molar ratio of Ca/P of the prepared HAp nanoparticles was more stoichiometric than the value reported in the case of ablation in vacuum.     

Structural,spectral and dielectric properties of piezoelectric–piezomagnetic composites

Composite materials of spinel ferrite (SF) NiZnFe₂O₄ (NZF) and barium titanate (BT) BaTiO₃ were prepared by double sintering ceramic technique. X-ray diffraction patterns for the composite system (1–x) NZF+x BT, showed the presence of mainly of 2 phases, hence confirming the successful preparation of the composite. Some structural and microstructural parameters like porosity, X-ray density, particle size and lattice constant were deduced from the analysis of X-ray data for both phases. Scan electron microscope (SEM) analysis shows nearly a homogeneous microstructure with good dispersion of BT grains as well as the presence of some pores. There was also an enlargement of BT grains with increasing its content. Infra red (IR) spectra of the composite system indicate that BT content affects the intermolecular character of the SF phase. A rise in the dielectric constant occurred at high temperature which was attributed to the effect of space change resulting from the increase of the change carriers in the paramagnetic region. The dielectric loss (tan δ) decreased by increasing BT content.