فصلنامه مواد پیشرفته در مهندسی
سال سی و دوم شماره 1 (بهار 1392)

In this research, M-type Mn-Zr doped Ba-ferrites powders with a general chemical composition of BaFe10.6(ZrxMn1- x)O19 (x= 0, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1) were synthesized and prepared by a solid state method, and were then mixed with an Araldite + hardner and processed into polymer matrix composite specimens. Phase analyses of synthesized samples were performed by an XRD technique and magnetic properties of the composite specimens were measured using a hysteresis graph system. EM absorbtion characteristics of the composite samples in the (8-12 GHz) frequency ranges were determined using a VNA system.Among the compositions investigated in the present work, the highest absorbtion of 11.25 dB accured in BaFe10.6Zr0.28Mn1.12O19 (x= 0.2) at a frequency of 8.4 GHz. Based on EM absorbtion behaviors and magnetic properties, BaFe10.6Zr0.28Mn1.12O19 is classified as a potential EM absorber material.

To improve mechanical properties of hydroxyapatite as the main mineral constituent of hard tissue, titania reinforcement was added to hydroxyapatite structure. HAp/TiO2 nanocomposites were prepared successfully by in situ precipitation processes at room temperature and 70°C. Fallowing that, hydroxyapatite/titania bodies were fabricated by hot isostatic pressing at 1200°C under a pressure of 200 MPa. Characterization of mechanical behavior of compacts indicated that mechanical properties of hydroxyapatite/titania samples are relatively higher in relation to pure hydroxyapatite. SEM images showed that the HAp/TiO2 nanocomposites demonate excellent chemical and structural uniformity. TEM observation revealed that different morphology for hydroxyapatite/titania nanocomposites could be obtained due to titania crystalline structure. XRD and FTIR results indicated the formation of high temperature crystalline phase of titania (rutile)at room temperature and low temperature phase of its (anatase) at 70ºC.

In this study, magnetite (Fe3O4) nanoparticles were synthesized by chemical co-precipitation from the solution containing iron salts in alkaline medium under N2 gas and room temperature. Magnetite nanoparticles were characterized by X- ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), Brunauer-Emmet-Teller (BET), and vibrating-sample magnetometer (VSM). The rheological properties of magnetite ferrofluid were examined by rheology apparatus. The biocompatibility and cytotoxity of magnetite nanoparticles were evaluated by 3T3 and fibroblast cells. The results showed that the Fe3O4 magnetite nanoparticles coated by polyvinyl alcohol (PVA) could be an appropriate candidate for biomedical applications.

Carbon fiber composite is one of the most important materials in aerospace engineering applications. For fabrication of this composite, optimum polymerization and carbonization cycles of phenolic resin were obtained [1]. Then, carbon/phenolic composite was fabricated by mixing different weight percentages of T700 carbon fiber with phenolic resin, and the flexural strength of specimens was examined. The samples were pyrolyzed at 1100°C to form high temperature phenolic matrix. Because of high porosity of samples, the composite was impregnated to increase the density and reduce porosity. The maximum flexural strength of samples was obtained with 40 wt. % of fiber. With addition of TiO2 and ZrO2 nanoparticles to carbon/phenolic composite, thermal and mechanical improvement was measured. The samples were examined by ablation test and microstructures of composites were analyzed by SEM.

This study aims to characterize and evaluate the applicability of Polyhedral Oligomeric Silsesquioxane (POSS)/ Poly (carbonate-urea) Urethane (PCU) nanocomposite films as a temporary skin substitute by means of FTIR, MTT assay, cell proliferation assay and SEM studies. FTIR spectra showed all the characteristic peaks of POSS/PCU nanocomposite. The indirect cytotoxicity of membranes was investigated by MTT assay. In MTT test, L929 mouse fibroblasts were exposed to the extract of the films for 24 h. MTT results showed no sign of cell cytotoxicity for the extracts at the extraction times up to14 days.Menwhile, it was found that POSS nanocages have a stimulating effect on L929s. In cell proliferation assay, L929s were cultured on the films for 3, 7 and 14 days. The cells showed a high rate of proliferation in direct contact with the biomaterial after 7 and 14 days. Morphology and density of the cells on the nancomposite surface was investigated through SEM observations. SEM micrographs showed that the cells adhered well on the surface after 3 days of culture. Moreover, after 7 days, cell density increased so substantially that a cell layer was formed on the membranes.

Short life of current total hip replacement metallic implants is generally dependent on the aseptic loosening of the implant, which occurs due to mismatch of elastic modulus between bone and metallic implant materials. Decreasing in elastic modulus of implant could be successful. Forsterite is biocompatible and bioactive ceramic which has suitable mechanical properties. In presented research the composite materials based on Co-Cr-Mo alloy with 10, 15 and 20wt% of forsterite nanopowder as reinforcement were fabricated and mechanical behavior of the composites were evaluated. Composites were fabricated by ball milling, cold pressing and sintering. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used for characterization and evaluation phase composition and microstructure of the composites. Density, microhardness,compressive strength and elastic modulus of fabricated composites were evaluated. Obtained results showed elastic modulus of composite materials based on Co-Cr-Mo alloy reinforced with 10, 15 and 20wt% of forsterite nanopowder decreased significantly. Results also showed that the compressive strength of Co-base alloy composites reinforced with 10, 15 and 20 wt% forsterite were lower than cast Co-Cr-Mo alloy. With increasing in the content of reinforcement, compressive strength of the composites were decreased. Microhardness of prepared composites were higher than cast Co-Cr-Mo alloy. With increasing in content of bioceramic reinforcement, microhardness of the composites were increased.

In this study, mullite– irconia composite samples were prepared by reaction sintering of alumina and zircon powder via gel casting process. Gel casting is a new ceramic forming technique. This process is based on the casting of slurry, containingceramic powder, dispersant and premix monomer solution. To achieve stabilized, high solid loading 80 wt%) and castable slurry, the rheological properties of slurry were optimized. The monomers polymerized the slurry to form gelled specimens. After gelation, the specimens were unmolded, then dried out under controlled condition. Burning out and sintering of the specimens was carried out in the range of 1400-1700°C. Apparent porosity and bulk density of the sintered samples were measured by soaking in water. Crystalline phase evolution and microstructure were determined by XRD and SEM techniques. Results showed that the reaction sintering and mullite formation was completed at 1700°C due to very slow diffusion of Al3+ ions within amorphous silica formed at the decomposition of zircon. The sintered samples at this temperature also showed the lowest apparent porosity (≈ 4%) and the highest bulk density (≈3.40 gr/cm-3).

The effects of temperature, time and atmosphere on microstructure and magnetic properties of NiF 2O4 glassceramic were investigated utilizing differential thermal analysis, X-ray diffraction, vibrating sample magnetometer and scanning electron microscope techniques. Various compositions were studied in the Na2O-NiO-Fe2O3-B2O3 SiO2 system to obtain amorphous phase. The sample heat-treated in graphite bed at 5100C for 1 hr showed higher magnetization than the one heattreated in the air under the same condition. XRD analysis showed the presence of nickel ferrite and some non-magnetic phases such as sodium borate and silicate phases in the heat treated samples. The maximum magnetization of samples reduced by increasing the holding time from 1hr to 3 hr at 5100C. Increment of temperature to 7000C increased the amount of NiFe2O4 and maximum magnetization.