Preparation and Characterization of Chitosan/β-GP Membranes for Guided Bone Regeneration

Bioabsorbable chitosan/β-glycerol phosphate (CS/β-GP) composite membranes were fabricated through a relatively PH neutral and mild sol-gel process for guided bone regeneration (GBR).Their structural properties,morphology,and tensile strength were investigated.FTIR and XRD analyses indicated that there were chemical bonds between the CS andβ-GP.SEM analysis revealed that the CS/β-GP composite membranes had a porous structure both at the surface and in sublayers.Even though the incorporation ofβ-GP in the CS matrix decreased the initial tensile strength of the membrane,the CS/β-GP membranes were still fit for GBR application with their tensile strength of roughly 1MPa.The concentration ofβ-GP was proportional to the pore size and thickness but was inversely proportional to the tensile strength of the CS/β-GP membrane.The present findings indicate that,based on its characteristics,the CS/β-GP composite membrane is a potential bioresorbable membrane for use in guided bone regeneration.     

Synthesis and Tribological Properties of Copper-alumina Nanocomposites Prepared by Coprecipitation Technique

The objective of this work is to study the synthesis of copper-alumina nanocomposites using the coprecipitation process and hot-pressing method, and investigate their mechanical properties. The effects of calcination temperature on the average size of composite particles and chemical composition after calcination were also analyzed. The sintering parameters including sintering temperature, hot pressure and packing time were optimized to fabricate the alumina nanoparticles reinforced copper matrix composites(CMCs). The density, microhardness and tribological properties of the CMCs reinforced with 1 wt%, 2 wt%, 3 wt%, 4 wt% and 5 wt% of alumina nanoparticles were investigated correspondingly. The results showed that the optimum preparation parameters for the CMCs were 900 ℃ of hot pressing temperature, 27.5 MPa of hot pressure and 2 hrs of packing time. The CMC reinforced with 2 wt% of alumina nanoparticles had the lowest wear rate, with the relative wear resistance of 3.13.     

Effect of Hot Extrusion on Microstructure and Properties of (ABOw+SiCp)/6061Al Composites Fabricated by Semi-solid Stirring Technique

6061Al matrix composites reinforced by 5vol.%ABOw and 15vol.%SiCp were fabricated by semi-solid stirring technique successfully at 640 ℃ for 40min with the stirring rate of 300 rpm,and the composites were extruded at a temperature of 500 ℃ using an extrusion ratio of 25:1 subsequently.Tensile tests were performed on as-casted and as-extruded(ABOw+SiCp)/6061Al composites at room temperature,and microstructures were observed by scanning electron microscope(SEM).SEM investigation showed that the as-extruded composite exhibited reduced porosity as well as a more uniform distribution of the reinforcements compared with the as-casted composite.The tensile tests results showed that the ultimate tensile strength and tensile elongation of as-extruded composite are higher than that of as-casted composite.     

An ultrahigh strength steel produced through deformation-induced ferrite transformation and Q&P process

In this work,DIFT technology and Q&P process were combined in order to introduce ultrafine-grained ferrite into the matrix of martensite and retained austenite to develop a new kind of advanced high strength steel,and two kinds of steels were investigated by this novel combined process.The newly designed process resulted in a sophisticated microstructure of a large amount of ferrite(about 5 m in diameter),martensite and a considerable amount of retained austenite for TRIP 780 steel.The ultimate tensile strength can reach about 1200 MPa with elongation above 16% for TRIP 780,that is much higher than the one solely treated by Q&P process.Tensile tests showed that both steels with the novel combined process achieved a good combination of strength and ductility,indicating that the new process is promising for the new generation of advanced high strength steels.     

Fabrication and densification enhancement of SiC-particulate-reinforced copper matrix composites prepared via the sinter-forging process

The fabrication of copper （Cu） and copper matrix silicon carbide （Cu/SiCp） particulate composites via the sinter-forging process was investigated. Sintering and sinter-forging processes were performed under an inert Ar atmosphere. The influence of sinter-forging time, temperature, and compressive stress on the relative density and hardness of the prepared samples was systematically investigated and subsequently compared with that of the samples prepared by the conventional sintering process. The relative density and hardness of the composites were enhanced when they were prepared by the sinter-forging process. The relative density values of all Cu/SiCp composite samples were observed to decrease with the increase in SiC content.     

Tensile properties of an aluminum matrix composite reinforced by SnO<Subscript>2</Subscript>-coated Al<Subscript>18</Subscript>B<Subscript>4</Subscript>O<Subscript>33</Subscript> whisker

Al18B4O33 whisker was coated by SnO2 particles using a chemical precipitation method, and an aluminum matrix composite reinforced by the coated whisker was fabricated by squeeze casting technique. It is found that the SnO2 coating can react with aluminum matrix during squeeze casting process, and Sn particles are induced near the interface between Al18B4O33 whisker and matrix. The tensile test at room temperature indicated that the tensile strength of Al18B4O33 whisker reinforced aluminum matrix composite can be enhanced by suitable content of SnO2 coating. The composites with various whisker coating contents exhibit maximum tensile plasticity at about 300 ℃, and the composite with a suitable whisker coating content could enhance its tensile plasticity evidently, which suggest that an Al18B4O33 whisker-Al composite with both high strength at room temperature and high formability at elevated temperature can be designed.     

Properties and Structure of Magnesium Matrix Composite Reinforced with CNTs

By using high pure Magnesium (99.9 wt% ) as matrix and multi-walled bended carbon nanotubes ( CNTs ) as reinforced phase, carbon nanotubes/magnesium matrix composite was prepared to the foundry method under the argon gas protection, and its mechanical properties were tested. The interface structure and component of plating and un-plating carbon nanotubes were analyzed by TEM and EDS , and the action mechanism was discussed. The experiment results show that the CNTs con strengthen mechanical properties of the nano-tube-reinforced Mg matrix composite, the tensile strength and elongation ratio are greatly improved. Furthermore, the plating CNTs are better than un-plating CNTs in strengthening effects. The tensile strength is inereased by 150% and the elongation ratio is increased by 30% than that of matrix when content of CNTs is 0.67 wt%.     

Atomic force microscope study of WC-10Co cemented carbide sintered from nanocrystalline composite powders

In order to compare the spark plasma sintedng （SPS） process plus hot isostatic press （HIP） with vacuum sintedng plus HIP, an investigation was carried out on the topography, microstructure and gain size distribution of nanocrystalline WC-10Co composite powder and the sintered specimens prepared by SPS plus HIP and by vacuum sintering plus HIP by means of atomic force microscopy （AFM）. The mechanical properties of the sintered specimens were also investigated. It is very easy to find cobalt lakes in the specimen prepared by vacuum sintering plus HIP process. But the microstructure of the specimen prepared by SPS plus HIP is more homogeneous, and the grain size is smaller than that prepared by vacuum sintering plus HIP. The WC-10Co ultrafine cemented carbide consolidated by SPS plus HIP can reach a relative density of 99.4%, and the transverse rupture strength （TRS） is higher than 3540 MPa, the Rockwell A hardness （HRA） is higher than 92.8, the average grain size is smaller than 300 nm, and the WC-10Co ultrafine cemented carbide with excellent properties is achieved. The specimen prepared by SPS with HIP has better properties and microstructure than that prepared by vacuum sintering with HIP.     

Superplasticity and superplastic bulging behavior of ZrO<Subscript>2</Subscript>/Ni nanocomposite

ZrO2/Ni nanocomposite was produced by pulse electrodeposition and its superplastic properties were investigated by the tensile and bulging tests. The as-deposited nickel matrix has a narrow grain size distribution with a mean grain size of 45 nm. A maximum elongation of 605% was observed at 723 K and a strain rate of 1.67×10-3s-1 by tensile test. Superplastic bulging tests were subsequently performed using dies with diameters of 1 mm and 5 mm respectively based on the optimal superplastic forming temperature. The effects of forming temperature and gas pressure on bulging process were experimentally investigated. The results indicated that ZrO2/Ni nanocomposite samples can be readily bulged at 723 K with H/d value (defined as dome apex height over the die diameter) larger than 0.5, indicating that the nanocomposite has good bulging ability. SEM and TEM were used to examine the microstructure of the as-deposited and bulged samples. The observations showed that significant grain coarsening occurs during superplastic bulging, and the microstructure is found to depend on the forming temperature.     

Effect of wet surface treated nano-SiO<Subscript>2</Subscript> on mechanical properties of polypropylene composite

Nano-SiO2/polypropylene composite was prepared by melt-blending process. The nano-SiO2 particles were organized by wet process surface treatment with silane coupling agent KH-570. The effect of mass fraction of nano-SiO2 particles and dosage of KH-570 on the toughening and strengthening of PP matrix were investigated based on the fractography of impact notch and the analysis of crystal structure by X-ray and dispersive structure of nano-SiO2 by TEM. Results show that the impact and flexural strength and modulus of the composite are improved obviously with low loading of nano-SiO2 （3 wt%-5 wt%）, and the izod impact strength of PP increases twice with 4 wt% nano-SiO2. The nano-SiO2 particles treated can disperse into the matrix resin, which has evident heterogeneous nucleation effects on the crystallization of PP. The optimal toughening and strengthening effects of PP matrix can be obtained when the content of nano-SiO2 and KH-570 are 4 wt% and 3 wt%, respectively.     

Comparative study of β-Si3N4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis (SHS) with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering (SPS). The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homo- geneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200°C lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa?m1/2.     

Fabrication and Property of SiC Ceramic with Large Thickness/Diameter Ratios

Silicon carbide ceramics with different thicknesses/diameter ratios were prepared by using ultra-fine silicon carbide powder with the sintering additives of 1.0 wt% boron and 1.5 wt% carbon.The influence of thickness/diameter ratio on the microstructure and density of SiC ceramics was investigated in detail.The experimental results show that the addition of boron and carbon sintering aids can promote the densification process of SiC ceramic,leading to the low sintering temperature and improve mechanical properties.At 1950 ℃,SiC ceramic with a density of 99% exhibits Young's modulus,hardness,and flexural strength of 476 MPa,28.3 GPa,and 334 MPa,respectively.It is found that long holding time has a positive effect on the uniformity of the microstructure and density distribution of SiC ceramics with large thickness/diameter ratios.Additionally,the sintering additive of boron can solid-solve into SiC,and then facilitate the phase transformation of SiC to form 6H-SiC and 4H-SiC composite ceramics.     

Effects of activated sintering process on properties and microstructure of W-15Cu alloy

The effects of activated sintering technology of H2 atmosphere sintering on the microstructure and properties of W-15Cu alloy using ultrafine W-15Cu composite powder fabricated by spray drying calcining-continuous reduction technology were investigated.The experimental results showed that W-15Cu alloy,consolidated by activated sintering technology of H2 atmosphere sintering for 1 h at 1300 ℃,with 98.5 % relative density,transverse rupture strength 1218 MPa,Vickers hardness HV0.5 378,average grain size about 1.2 μm and thermal conductivity 192 W/m·K,was obtained.In comparison to the normal sintering process,activated sintering process to W-15Cu alloy could be achieved at lower sintering temperature.Furthermore,better properties in activated sintered compacts were obtained,and activated sintering process resulted in finer microstructure and excellent properties.     

Evolution of microstructure and high temperature tensile properties of as-extruded Ti Bw reinforced near-α titanium matrix composite subjected to heat treatments

The Ti Bw reinforced near-α titanium matrix composite(Ti-5.8 Al-3.4 Zr-4.0 Sn-0.4 Mo-0.4 Nb-0.4 Si-0.06 C) was successfully synthesized by powder metallurgy and hot extrusion route. The effects of solution and aging temperature on the microstructure and high temperature tensile properties of the composite were investigated. The results revealed that the fine transformed β phase can be obtained by the solution treatment at β phase region and aging treatment, no other precipitates were observed. The α2 phase(Ti3 Al) can be acquired when the solution treated at α+β phase region followed by aging treatment. With increasing the aging temperature from 500 to 700°C for 5 h, the size of α2 precipitates increases from about 5 to about 30 nm. The Ti Bw are stable without any interfacial reaction during the heat treatments. The high temperature tensile properties show that the composite performed by solution and aging treatment exhibits good strengthening effects. With increasing the aging temperature from 500 to 700°C, the strength of the composite increases at the expense of elongation due to the increment of α2 precipitates.The strength of the composite at 600°C increases by 17% to 986 MPa after 1000°C/2 h/AC and 700°C/5 h/AC heat treatment.     

Fabrication of solid-phase-sintered SiC-based composites with short carbon fibers

Solid-phase-sintered Si C-based composites with short carbon fibers（Csf/SSi C） in concentrations ranging from 0 to 10wt% were prepared by pressureless sintering at 2100°C. The phase composition, microstructure, density, and flexural strength of the composites with different Csf contents were investigated. SEM micrographs showed that the Csf distributed in the SSi C matrix homogeneously with some gaps at the fiber/matrix interfaces. The densities of the composites decreased with increasing Csf content. However, the bending strength first increased and then decreased with increasing Csf content, reaching a maximum value of 390 MPa at a Csf content of 5wt%, which was 60 MPa higher than that of SSi C because of the pull-out strengthening mechanism. Notably, Csf was graphitized and damaged during the sintering process because of the high temperature and reaction with boron derived from the sintering additive B4C; this graphitization degraded the fiber strengthening effect.     

Microstructure and Properties of Fe-12Cr-2.5W-xSi-0.4Ti-0.3Y2O3 Alloys

Fe-12Cr-2.5W-x Si-0.4Ti-0.3Y₂O₃ alloys were fabricated by mechanical alloying and vacuum sintering. The effect of sintering temperature and Si content on the microstructure and properties of the alloy was investigated systematically. The experimental results show that the relative density and tensile strength of the alloy were increased with the elevating of sintering temperature and Si content within a certain range.The alloy with 1wt% Si sintered at 1 350 ℃ exhibited supe...     

Preparation and Properties of 1-octadecanol/1,3:2,4-di-(3,4-dimethyl) Benzylidene Sorbitol/Expanded Graphite Form-stable Composite Phase Change Material

A 1-octadecanol(OD)/1,3:2,4-di-(3,4-dimethyl) benzylidene sorbitol(DMDBS)/expander graphite(EG) composite was prepared as a form-stable phase change material(PCM) by vacuum melting method. The results of field emission-scanning electron microscopy(FE-SEM) showed that 1-octadecanol was restricted in the three-dimensional network formed by DMDBS and the honeycomb network formed by EG. X-ray diffraction(XRD) and Fourier transform infrared spectroscopy(FT-IR) results showed that no chemical reaction occurred among the components of composite PCM in the preparation process. The gel-to-sol transition temperature of the composite PCMs containing DMDBS was much higher than the melting point of pure 1-octadecanol. The improvements in preventing leakage and thermal stability limits were mainly attributed to the synergistic effect of the three-dimensional network formed by DMDBS and the honeycomb network formed by EG. Differential scanning calorimeter(DSC) was used to determine the latent heat and phase change temperature of the composite PCMs. During melting and freezing process the latent heat values of the PCM with the composition of 91% OD/3% DMDBS/6% EG were 214.9 and 185.9 kJ·kg~(-1), respectively. Its degree of supercooling was only 0.1 ℃. Thermal constant analyzer results showed that its thermal conductivity(κ) changed up to roughly 10 times over that of OD/DMDBS matrix.     

Fabrication of high strength carbon nanotube/7055Al composite by powder metallurgy combined with subsequent hot extrusion

Bimodal carbon nanotube reinforced 7055Al(CNT/7055Al) composites containing coarse grain bands and ultra-fine grain zones were fabricated by high energy ball milling, vacuum hot pressing followed by hot extrusion. The effect of extrusion temperature varied from 320℃ to 420℃ on the microstructure evolution and tensile properties were investigated. Microstructure observation indicates that the elongated coarse grain bands aligned along the extrusion direction after extrusion. The width of the coarse grain bands increased, and the length of the coarse grain bands increased firstly and then decreased with the increase of extrusion temperature. The grain size of the ultra-fine grain zones changed little after hot extrusion, but the ultra-fine grains coarsened after subsequent heat treatment, especially for the composite extruded at low temperature of 320℃. By observing the CNT distribution, it was found that the higher temperature extrusion was beneficial to the CNT orientation along the extrusion direction.Furthermore, a precipitated free zone formed at the boundary between the coarse grain band and the ultra-fine grain zone as the composite extruded at high temperature of 420℃. As the result of the comprehensive influence of the above microstructure, the tensile strength of the composite extruded at moderate temperature of 370℃ reached the highest of 826 MPa.     

Nafion/Silicon Oxide Composite Membrane for High Temperature Proton Exchange Membrane Fuel Cell

Nafion/Silicon oxide composite membranes were produced via in situ sol-gel reaction of tetraethylorthosilicate （TEOS） in Nafion membranes. The physicochemical properties of the membranes were studied by FT-IR,TG-DSC and tensile strength. The results show that the silicon oxide is compatible with the Nation membrane and the thermo stability of Nation/Silicon oxide composite membrane is higher than that of Nation membrane. Furthermore, the tensile strength of Nation/Silicon oxide composite membrane is similar to that of the Nation membrane. The proton conductivity of Nation/Silicon oxide composite membrane is higher than that of Nation membrane. When the Nation/Silicon oxide composite membrane was employed as an electrolyte in H2/O2 PEMFC, a higher current density value （1 000 mA/cm^2 at 0.38 V） than that of the Nafion1135 membrane （100 mA/cm^2 at 0.04 V） was obtained at 110 ℃.     

Mechanical and morphological properties of highly dispersed carbon nanotubes reinforced cement based materials

Stable homogeneous suspensions of multi-walled carbon nanotubes (MWCNTs) were prepared using gum arabic (GA) as dispersant and were incorporated to Portland cement paste. The dispersion was examined by ultraviolet visible spectroscopy (UV-vis), and the concentration measurement shows that the optimum concentration of GA is 0.45 g L-1. The dispersibility of the surface-modified MWCNTs in aqueous solution and cement matrix were investigated by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), and the mechanical properties of the composites were investigated. The results show that the addition of the treated nanotubes can improve both the flexural strength and the compressive strength of the Portland cement composite significantly. The flexural strength of the composite increases up to 43.38% with the MWCNT concentration of 0.08% (by weight of cement). The porosity and pore size distribution of the composites were measured by mercury intrusion porosimetry (MIP), and the results indicate that the cement paste doped with MWCNTs obtained lower porosity and concentrated pore size distribution. The morphological structure was analyzed by field emission scanning electron microscopy (FESEM) and EDS. It is shown that MWCNTs act as bridges and networks across cracks and voids, which transfer the load in case of tension, and the interface bond strength between the nanotubes and matrix is very strong.