In this study, hydroxyapatite (HAp) coated Mg matrix composites were fabricated for biodegradable implant applications. Spark plasma sintering was employed to fabricate the Mg-10 wt% ZnO composite substrates. HAp was coated on the surface of the sintered composites and pure Mg by a chemical solution treatment. SEM and optical micrographs of coated samples showed that HAp grew homogeneously and formed a layer on the entire surface of both pure sintered Mg and Mg composites. The immersion and polarization test results demonstrated that the HAp coating significantly improved the corrosion resistance of the sintered composites. While the HAp coating layer is not effective in the improvement of the pure Mg substrate, cell culture test results revealed that the HAp coating improved cell adhesion and proliferation on the composites effectively through 72 h, while no cell could survive on the uncoated composites after 72 h. In addition, the corrosion tests and cell culture test results indicated that the composite with longer sintering time has better corrosion resistance and cell viability than those of the composite with shorter sintering time. The findings suggested that the HAp-coated Mg-10 wt% ZnO-2.5 h + 10 min composite is a high-potential candidate for biodegradable implant applications.

BACKGROUND: Spirulina platensis contains a large amount of chlorophylls, chlorophyll a, that are starting materials to synthesize functionalized chlorins. Chlorin e6 (Ce6) as well as its derivatives are second generation sensitizers using in photodynamic therapy (PDT) of various cancers. In this study, we transfer chlorophyll a of S. platensis to Ce6derivatives and determine their several applications. AIM: to evaluate the effects of Ce6 derivatives to treat cancer cells. METHODS: Ce6 trimethylester was created from methyl pheophorbide a2 in S. platensis provided by the Hidumi Company, Nghe An province, Viet Nam. Hela cells were incubated with Ce6 trimethylester and the irradiated with the diode laser dose of 1.2 J/cm2/min through the system of filters £ 650 nm. MTT assay and clonogenic assay were used to determine survival rate and cloning efficiency of cells. Antimicrobial effect of Ce6 trimethylester with halogen light were studied with Propionibacterium acnes VTCC 0218 and Staphylococcus aureus VTCC 0173. RESULTS: From dry biomass (700 g) of S. platensis, after extracting chlorophyll a and methanolysis, 4.2 g of methyl pheophorbide a was obtained. The reaction to give Ce6 trimethylester with 82% yield was performed with potassium hydroxide (KOH) in MeOH/THF/CHCl3. After irradiation with a 650 nm laser at 1.2 J, the cell viability in all samples decreased with Ce6 trimethylester treatment, the survival declining trend of Hela cells treated with Ce6 trimethylester were proportional when concentration of Ce6 trimethylester increased. The rate of colony formation was declined as the concentration of Ce6 trimethylester treated was increased. The growth of both S. aureus and P. acnes can be inactivated by Ce6 trimethylester PDT. The MIC99 value against P. acnes VTCC 0218 and S. aureus VTCC 0173 of Ce6 trimethylester with halogen light was 1.25 μg/ml. CONCLUSION: The Ce6 trimethylester from S. platensis cultivated in Viet Nam could be used as a potential photosentizer for photodynamic therapy for treatment of cancer and acne.

Transparent MgAl₂O₄ceramic could be found in a wide range of applications for both military and civil sector due to its high melting point, good mechanical properties, small refractive index (1.71) and its ability to allow light in range from UV to mid-IR to pass through. In the present work, transparent MgAl₂O₄ was fabricated from metal nitrates via two steps. Firstly, the MgAl₂O₄ nanopowder was synthesized via solution combustion synthesis from the metal nitrates. Secondly, the powder was then consolidated by Pulsed Electric Current Sintering (PECS) technique to fabricate transparent ceramic. XRD patterns of the obtained powder showed the peaks of only MgAl₂O₄ phase. Besides, the atomic compositions of magnesium, aluminium and oxygen determined by EDX analysis were approximately corresponded to 1:2:4 of the molecular formula of MgAl₂O₄. After deagglomerating for 48 hours using soft ball-milling, the powder had the average particle of 27 nm. Transparent MgAl₂O₄ samples, which were sintered with two-step sintering mode of 1050^oC/60 minutes-1400^oC/20 minutes, permitted the transmission of visible and infrared light with the transmittance up to 80%, Vickers hardness of 14.2 GPa, and fracture toughness of 1.1 MPa.m^1/2. The results are a critical step toward fabrication of high-quality transparent ceramics from metal nitrates.

This paper investigates the changed in the microstructure in HAZ of the dissimilar weld between carbon steel and 304 austenitic stainless steel. Continuous cooling transformation diagrams (CCT), peak temperature profiles and cooling rates can be used to predict the change in the microstructure of the HAZ during the welding process. Optical microscopy, X -ray, SEM and TEM were used to determine the phases which formed in HAZ of carbon steel and austenitic stainless steel. The results of this study indicate that grain size in HAZ depended on the temperature at that point could be reached during the welding. Fully Martensitic layer observed at the interface in carbon side due to the combination of the rapid cooling subsequent to weld and local chemical composition. Cooling rate played the rule on forming Widmanstatten ferrite, Bainite and Pearlite. On the other hand, microstructures and grain size in HAZ of austenitic stainless steel were not affected by temperature and cooling rate. Carbides precipitation (M23C6, M7C3), however, were found in the boundary of grains.

In the present work, FeMn13-40 wt.% TiC composite was fabricated by Pulsed Electric Current Sintering (PECS) process at different temperatures between 990 and 1020^oC under a pressure of 60 MPa with a holding time of 5 min in the vacuum. Phases identification was done using the X-ray diffraction. The relative density, microstructure and hardness of the samples were characterized. The results showed that the relative density of FeMn13-TiC composite increased with the increase of sintering temperature. The highest relative density (96.19%) and the hardness (70.54 HRC) of the sample were achieved by PECS process, namely sintering at the temperature of 1020^oC under the applied pressure of 60 MPa for 5 min.

Transparent MgAl2O4 ceramics were fabricated by pulsed electric current sintering (PECS) employing two-step sintering mode. First, nanoscale MgAl2O4 powders were produced by solution combustion synthesis from hydrated nitrate compounds and urea. Subsequently, the synthesized powders were sintered by PECS with a heating rate of 100oC/min under an applied pressure of 100 MPa. The sintering process was conducted according to two-step heating profile. At the first step, the temperature increased to 1050, 1100, and 1150oC, followed by a dwell time of 60 min. The second-step sintering was carried out at 1300, 1350, and 1400oC for 20 min. The transparent ceramics sintered at 1050oC/ 60 min – 1400oC/ 20 min exhibited transmittance over 80% in infrared range. In addition, transparent samples presented a Vickers hardness up to 30 GPa for sintering mode of 1150oC/ 60 min – 1400oC/ 20 min.

Highly porous alumina (Al2O3) was prepared by sintering of Al2O3 powder using ammonia bicarbonate (NH4HCO3) as a pore-forming agent and chromia (Cr2O3) as a sintering additive. In order to investigate the influence of particle shape and size on the characterization of sintered porous Al2O3, the starting Al2O3 powders included commercial disk micro-sized powder and synthesized spherical nanopowder. The nanoscale Al2O3 powder was produced via combustion synthesis route. At the optimal pore-forming agent concentration, the porous Al2O3 sintered by nanoparticles had a smaller pore size and a lower total porosity than the one prepared by microparticles. The differences of open porosity and closed porosity between porous Al2O3 synthesized by micro and nano-scale powders with and without Cr2O3 dopant were also discussed. In addition, the compressive strength of porous Al2O3 achieved by nano-sized powders, especially with Cr2O3 dopant, had a higher value in comparison with the one prepared by micro-sized powders.

The objective of the present work is to investigate the feasibility of the synthesis of copper matrix composite reinforced with in-situ nanosized Al2O3 ¬particle powder via combustion synthesis method from metal nitrates followed by reducing process at high temperature. The starting nitrates Cu(NO3)2.3H2O and Al(NO3)3·9H2O composition corresponds to Cu-30%Al2O3. X-ray Diffraction (XRD) patterns of the obtained powders indicated the presence of the oxides CuO and CuAl2O4. The powder had the size of 75 ± 10 nm after deagglomerating by soft ball milling for 24h. After reducing in CO at 1000oC for 3h, the peaks of the oxides were no longer observed and were replaced by the peaks of Cu and -Al2O3. The morphology of the reduced powders observed by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analysis showed a well distribution of the -Al2O3 particles within the Cu matrix with an average particle size of 40 nm.