Yilong Dai

In vitro corrosion behavior and in vivo biodegradation of biomedical β-Ca3(PO4)2/Mg-Zn composites.

In this study 5, 10 and 15% β-Ca(3)(PO(4))(2)/Mg-Zn composites were prepared through powder metallurgy methods, and their corrosion behavior and mechanical properties were studied in simulated body fluid (SBF) at 37°C. The 10% β-Ca(3)(PO(4))(2)/Mg-Zn composite was selected for cytocompatibility assessment and in vivo biodegradation testing. The results identified the α-Mg, MgZn and β-Ca(3)(PO(4))(2) phases in these sintered composites. The density and elastic modulus of the β-Ca(3)(PO(4))(2)/Mg-6% Zn composite match those of natural bone, and the strength is approximately double that of natural bone. The 10% β-Ca(3)(PO(4))(2)/Mg-6% Zn composites exhibit good corrosion resistance, as determined by a 30 day immersion test and electrochemical measurements in SBF at 37°C. The 10% β-Ca(3)(PO(4))(2)/Mg-6% Zn composite is safe for cellular applications, with a cytotoxicity grade of ∼0-1 against L929 cells in in vitro testing. The β-Ca(3)(PO(4))(2)/Mg-6% Zn composite also exhibits good biocompatibility with the tissue and the important visceral organs the heart, kidney and liver of experimental rabbits. The composite has a suitable degradation rate and improves the concrescence of a pre-broken bone. The corrosion products, such as Mg(OH)(2) and Ca(5)(PO(4))(6)(OH)(2), can improve the biocompatibility of the β-Ca(3)(PO(4))(2)/Mg-Zn composite.

Microstructures and properties of Al-50%SiC composites for electronic packaging applications

Abstract Al–50%SiC (volume fraction) composites containing different sizes of SiC particles (average sizes of 23, 38 and 75 μm) were prepared by powder metallurgy. The influences of SiC particle sizes and annealing on the properties of the composites were investigated. The results show that SiC particles are distributed uniformly in the Al matrix. The coarse SiC particles result in higher coefficient of thermal expansion (CTE) and higher thermal conductivity (TC), while fine SiC particles decrease CTE and improve flexural strength of the composites. The morphology and size of SiC particles in the composite are not influenced by the annealing treatment at 400 °C for 6 h. However, the CTE and the flexural strength of annealed composites are decreased slightly, and the TC is improved. The TC, CTE and flexural strength of the Al/SiC composite with average SiC particle size of 75 μm are 156 W/(m·K), 11.6×10 −6 K −1 and 229 MPa, respectively.

Biodegradation performance of a chitosan coated magnesium-zinc-tricalcium phosphate composite as an implant

A Mg-Zn-tricalcium phosphate composite with a chitosan coating was prepared in this investigation to study its biodegradation performance both in vitro and in vivo conditions. The in vitro test results show that the immersion corrosion rate, the pH values of the simulated body fluids and the released metal ion concentration of the chitosan coated composite are all lower than those of the uncoated composite. The in vitro cytotoxicity test shows that the chitosan coated specimens is safe for cellular applications. When the chitosan coated composite is tested in vivo, the concentration of metal ions from the composite observed in the venous blood of Zelanian rabbits is less than the uncoated composite specimens. The chitosan coating slows down the in vivo degradation of the composite after surgery. In vivo testing also indicates that the chitosan coated composite is harmless to important visceral organs, including the heart, kidneys, and liver of the rabbits. The new bone formation surrounding the chitosan coated composite implant shows that the composite improves the concrescence of the bone tissues. The chitosan coating is an effective corrosion resistant layer that reduces the hydrogen release of the implant composite, thereby decreasing the subcutaneous gas bubbles formed.

Improvement of the mechanical properties and corrosion resistance of biodegradable β-Ca3(PO4)2/Mg-Zn composites prepared by powder metallurgy: the adding β-Ca3(PO4)2, hot extrusion and aging treatment

In this study, 10%β-Ca3(PO4)2/Mg-6%Zn (wt.%) composites with Mg-6%Zn alloy as control were prepared by powder metallurgy. After hot extrusion, the as-extruded composites were aged for 72h at 150°C. The effects of the adding β-Ca3(PO4)2, hot extrusion and aging treatment on their microstructure, mechanical properties and corrosion resistance were investigated. The XRD results identified α-Mg, MgZn phase and β-Ca3(PO4)2 phase in these composites. After hot extrusion, grains were significantly refined, and the larger-sized β-Ca3(PO4)2 particles and coarse MgZn phases were broken into linear-distributed β-Ca3(PO4)2 and MgZn phases along the extrusion direction. After aging treatment, the elements of Zn, Ca, P and O presented a more homogeneous distribution. The compressive strengths of the β-Ca3(PO4)2/Mg-Zn composites were approximately double those of natural bone, and their densities and elastic moduli matched those of natural bone. The immersion tests and electrochemical tests revealed that the adding β-Ca3(PO4)2, hot extrusion and aging treatment could promote the formation of protective corrosion product layer on the sample surface in Ringers solution, which improved corrosion resistance of the β-Ca3(PO4)2/Mg-Zn composites. The XRD results indicated that the corrosion product layer contained Mg(OH)2, β-Ca3(PO4)2 and hydroxyapatite (HA). The cytotoxicity assessments showed the as-extruded β-Ca3(PO4)2/Mg-Zn composite aged for 72h was harmless to L-929 cells. These results suggested that the β-Ca3(PO4)2/Mg-Zn composites prepared by powder metallurgy were promising to be used for bone tissue engineering.

Discharge behavior and electrochemical properties of Mg–Al–Sn alloy anode for seawater activated battery

Abstract Mg–Al–Sn alloy is one of the new developed anode materials for seawater activated batteries. The potentiodynamic polarization, galvanostatic discharge and electrochemical impedance spectroscopy of Mg–6%Al–1%Sn and Mg–6%Al–5%Sn (mass fraction) alloys in seawater were studied and compared with the commercial AZ31 and AP65 alloys. The results show that the Mg–6%Al–1%Sn alloy obtains the most negative discharge potential of average –1.611 V with a electric current density of 100 mA/cm 2 . EIS studies reveal that the Mg–Al–Sn alloy/seawater interfacial electrochemical process is determined by an activation controlled reaction. The assembled prototype batteries with Mg–6%Al–1%Sn alloy as anodes and AgCl as cathodes exhibit a satisfactory integrated discharge properties.

Effects of chitosan coating on biocompatibility of Mg–6%Zn–10%Ca3(PO4)2 implant

Abstract A Mg–6%Zn–10%Ca 3 (PO 4 ) 2 composite with a chitosan coating was prepared to study its in vivo biodegradation properties. The chitosan dissolved in a 0.2% acetic acid solution was applied on the surface of Mg–6%Zn–10%Ca 3 (PO 4 ) 2 composite specimens and solidified at 60 °C for 30 min to form the coating. The cytotoxicity evaluation of chitosan coated specimens is at level 0, which indicates that such coating is safe for cellular applications. The in vivo tests of chitosan coated composite show that the concentration of metal ions from the composite measured in the venous blood of Zelanian rabbits is less than that from the uncoated composite specimens. The chitosan coating impedes the in vivo degradation of the composite after surgery. The in vivo testing also indicates that the chitosan coated composite is harmless to important visceral organs, including the heart, kidneys and liver of the rabbits. The new bone formation surrounding the chitosan coated composite implant shows that the composite improves the concrescence of the bone tissues. And the chitosan coating is an effective corrosion resistant layer that reduces the hydrogen release of the implant composite, thereby decreasing the subcutaneous gas bubbles formed.

Effects of gallium on electrochemical discharge behavior of Al–Mg–Sn–In alloy anode for air cell or water-activated cell

Abstract In order to evaluate the electrochemical properties of aluminum alloy anode under high current densities in alkaline electrolyte, the galvanostatic discharge, potentiodynamic polarization and hydrogen evolution tests of three experimental Al–Mg–Sn–In–(Ga) alloys were performed. The results show that the alloying element gallium improves the working potentials of experimental Al–Mg–Sn–In alloys under different discharge current densities. The average working potentials of the alloys containing gallium can reach –1.3 V under current density ranging from 650 to 900 mA/cm 2 , while those of alloy without Ga are only –1.0 V. Such phenomenon is attributed to the solid solution which can form amalgam with aluminum matrix. Such an amalgam can form the hydrolyzed species during the discharge process and lead to the corrosion infiltrating into aluminum matrix.

Compressive properties and energy absorption characteristics of open-cell nickel foams

Abstract Open-cell nickel foams with different relative densities and pre-stretching degrees were subjected to room temperature quasi-static compressive tests to explore their compressive properties. The compressive properties of the nickel foams including yield strength, elastic modulus, energy absorption density and energy absorption efficiency were calculated accurately. The results show that the compressive properties of yield strength, elastic modulus and energy absorption density increase with the increase of relative density of nickel foams. The compressive properties are sensitive to the pre-stretching degree, and the values of yield strength, elastic modulus and energy absorption density decrease with the increase of pre-stretching degree. However, the energy absorption efficiency at the densification strain state exhibits the independence of relative density and pre-stretching degree. The value of energy absorption efficiency reaches its peak when the strain is at the end of the collapse plateau region.

Microstructure and Mechanical Properties of AA1235 Aluminum Foil Stocks Produced Directly from Electrolytic Aluminum Melt

A new process is developed to obtain high-quality AA1235 aluminum foil stocks and to replace the traditional manufacture process. During the new manufacture process, AA1235 aluminum sheets are twin-roll casted directly through electrolytic aluminum melt (EAM), and subsequently the sheets are processed into aluminum foil stocks by cold rolling and annealing. Microstructure and mechanical properties of the AA1235 aluminum sheets produced through such new process are investigated in each state by optimal microscope, scanning electron microscopy, X-ray diffraction, orientation imaging microscopy, transmission electron microscopy, etc. The results show that compared with the traditional AA1235 aluminum foil stocks produced through re-melted aluminum melt (RAM), the amount of impurities is decreased in the EAM aluminum foil stocks. The EAM aluminum foil stock obtains less β-FeSiAl5 phases, but more α-Fe2SiAl8 phases. The elongation of EAM aluminum foil stocks is improved significantly owing to more cubic orientation. Especially, the elongation value of the EAM aluminum foil stocks is approximately 25 pct higher than that of the RAM aluminum foil stocks. As a result, the EAM aluminum foil stocks are at an advantage in increasing the processing performance for the aluminum foils during subsequent processes.

The effects of rolling deformation on Al-27%Si alloys prepared by powder metallurgy for electronic packaging applications

Al-27%Si alloys were prepared with 99.9% pure aluminium powder and 99.9% pure silicon powder through powder metallurgy. The sintered experimental alloy ingots were homogenized at 773 K for 2 h and hot rolled to sheets with 3 mm in thickness with several rolling passes. The results show that silicon grains were broken down to streamline with small size ranging from 5 μ m to 40 μ m after rolling. Thermal conductivity, relative density and gas-tightness of Al-27%Si alloys were increased to 143.8W/m·K (28°C), 99.3%, 2×10-8Pa· m3/S through rolling deformation. There was no significant change with coefficient of thermal expansion of Al-27%Si alloy. Rolling deformation can decrease the amount of holes in Al-27%Si alloy prepared through powder metallurgy.