مجله مواد و فناوری های پیشرفته
سال دوم شماره 4 (زمستان 1392)

Sedge (Carex riparia)، is a weed and waste product of agriculture. After the use of the organic elements as fuels، the leavings including large amounts of silica can be used as economically viable raw material for the production of silica based products. The purpose of this study is obtained of pure silica form sedge and also synthesis of ordered nano porous silica with hexagonal structure، type MCM-41 with hydrothermal method by silica source that extracted from sedge. To attain high-purity of the silica، the optimization of the process conditions of the burning temperature، hydrochloric acid leaching treatment of sedge biomass and acidic reflux process of sedge ash were conducted to remove the metallic impurities such as K، Na، Ca، Mg، Fe، P، etc. X-ray diffraction studies of obtained silica reveal increasing peak width (amorphousity) with decreasing burning temperature. X-ray Fluorescence (XRF) results show that high purity amorphous silica materials with 91. 13% were prepared from sedge by applying the 1N hydrochloric acid leaching، refluxing treatment and burning process at 600 C in electronic furnace. The synthesized MCM-41 were characterized by X-ray diffraction (XRD)، N2 physisorption measurements (BET)، Fourier transform infrared (FT-IR) spectrometry and scanning electron microscopy (SEM). X-ray diffraction pattern of the resulting MCM-41 revealed typical pattern of 2d-hexagonal mesophase. The other experimental results revealed that the specific surface area was 778 m2/g، total pore volume was 0. 745 cm3/g and average pore diameter was 3. 78 nm.

Development of composite scaffolds due to combing useful properties of two or more materials in order to meet mechanically and physiologically host tissue is increasing. Firstly، nano-Bio glass (nBG) powder was made with grain size between 55-65nm and then porous nBG of 30، 40 and 50%wt was produced by polyurethane sponge replication method. In order to increase the scaffoldsmechanical properties، they coated with 6%wt poly-Hydroxybutyrate (P3HB) for 30sec and 1min. XRD،XRF، SEM، FE-SEM and FT-IR were used in order to study the phase and elemental structure، morphology، grain size and functional groups، respectively. The scaffold including 30%wt nBG and 6%wt was used for evaluation of bioactivity. Biocompatibility of the scaffold was also tested in SBF solution for 4 weeks at 37 ºC. XRD، SEM and AAS results showed formation of HA on the surface of scaffold which prove the its biocompatibility، the result is showing that، the best scaffold is 30%wt nBG /6%wt P3HB with 75-87% porosity، which is a good candidate for bone tissue engineering.

Zinc oxide (ZnO) is a wide band-gap semiconductor oxide (3. 37 eV). ZnO nanoparticles have selective toxicity to bacteria but exhibit minimal effects on human cells. Ionic liquids (ILs) are a new class of chemical compounds which have many extraordinary properties and are able to create green chemical environments in order to perform chemical processes and are an appropriate alternative for organic and inorganic solvents. In this work ZnO nanoparticles were synthesized by a green method based on reaction of zinc acetate and sodium hydroxide in، IL 1-butyl-3-methyl imidazolium chloride under ultrasonic irradiation. Surface morphology and size of ZnO nanoparticles was characterized by scanning electron microscopy (SEM). X-ray diffraction pattern (XRD) indicated that ZnO has hexagonal wurtzite structure. Formation and purity of the ZnO nanoparticles was more confirmed with optical analyses such as UV-Vis spectroscopy and Fourier transform infrared spectroscopy (FT-IR). Specific surface area and porosity of synthesized ZnO was investigated by Brunaur-Emmett-Teller (BET) analysis. The antibacterial activity of ZnO nanoparticles against Escherichia coli (E. coli) was studied by a colony forming count (CFU) method. Results confirmed that the sample had high antibacterial activity.

This study investigated and compared mechanical and wear properties and microstructure of Al-5%Cu/SiC nanocomposites with 2، 4 and 8 weight percent of SiC. Powder metallurgy method was used to successfully fabricate the nanocomposites. After milling، the resulted powder was cold pressed into pellets at a pressure of 100 MPa. Then the samples were sintered at 590 °C for 1 hour in an argon atmosphere. Densitometry، hardness، compression and bending strength and wearing of pin on the disk tests were performed for all samples. The microstructure was examined by scanning electron microscopy (SEM) and optical microscopy. Phase analysis was conducted using XRD method. The sample with 4wt% of SiC had the maximum density and minimum porosity. However، the best compressive strength and bending strength results were obtained for samples with 0 and 2wt% SiC، respectively. In the wear resistance experiments، the proportion of the slope of the weight loss due to abrasion to distance travelled by the sample was 0. 039. In the nanocomposites studied there are some problems like unwetability and difference in thermal expansions between the matrix and the reinforcement; however، addition of up to 8wt% nano SiC can increase the hardness by 50%.

Microwave dielectric ceramics are extensively used in systems utilized at microwave frequencies for example mobile telephone and satellite devices. In this study ceramics with 0. 88Ba ([Zn0. 6Co0. 4] 1/3،Nb2/3) O3–0. 1Ba (Ga1/2Ta1/2) O3–0. 02BaZrO3 composition were prepared through the conventional ceramic processing; i. e. mixing and milling of the starting powders، calcination at 1100°C، second milling and sintering of pressed samples at different temperatures. The study showed that increasing sintering temperature resulted in an increase in density so that the highest density was observed at 1500°C. There was also an increase in quality factor (Q´f) when sintering temperature was increased; Q´f was about 16،000 GHz at 1500°C. The increase in quality factor is mainly due to the increase in density. Since superlattice reflections were not observed in XRD spectrum، the increase in quality factor can not be related to an increase in ordering degree. The presence of ordering can also be evaluated by changes in c/a ratio (c and a are lattice parameters of the hexagonal superlattice structure) and changes in lattice distortion. None of these two methods were able to show the existence of ordering.

Friction stir processing was carried out on an AZ31 substrate with and without introduction of nano-sized TiC powder. Clusters of TiCwere found in the fabricated layer with a non-uniform distribution. Applied additional passes resulted in gradual break-up of TiC clusters; a nano-composite layer with a uniform dispersion of nano-sized TiC reinforcements in a matrix of fine grains (~3mm) was achieved after three further passes. This layerexhibited a micro hardness and yield strength of ~91HV and 290MPa، respectively. These values are found to be ~1. 5 and 1. 3 times of those of the as-received AZ31 substrate، respectively. Enhancement of mechanical properties is attributed to dispersion of nano-sized hard reinforcements in a matrix of fine grains. The layer produced without introduction of TiC powder showed a microstructure of fine grains (~5. 5mm). However، it exhibited a lower micro hardness and yield strength than those of the as-received AZ31; this softening is related to dissolution of an intermetallic compound phase during the thermo-mechanical phenomena associated with friction stir processing.

Mechanical Activation Assisted Self-Propagating High-Temperature Synthesis (MASHS)، as an advanced method in early decades is used for synthesis of advanced engineering compounds and composites. In this research influence of type and pressure of combustion environment on synthesis of nano-structured composite characteristics included reinforced ZrB2 field by ZrC which has effective and important applications as a heat protective shield in supersonic and re-entry vehicles industry was studied. Raw materials powder were mixed stoichiometrically according to 2ZrO2+B2O3+C+7Mg=ZrB2+ZrC+7MgO chemical equation and activated for 10 hours by a ball mill machinery. Used environments for this study were vacuumed، continuous flow of Argon inert gas and pressurized argon atmosphere reactor chambers. Studies revealed that by changing the tack from vacuum to continuous flow of Argon and then to pressurized Argon، the process became more and more controllable and because of this، arbitrary phases of our own accord nano-composite were synthesized.

Interaction of silver nanoparticles with bacterium depends on their size and shape. Although many studies have been recently done about synthesis and investigating reaction of spherical silver nanoparticles to bacterium، few studies have been performed in terms of shape of such nanoparticles. In this research، triangular structure nanosilver particles were synthesized and their antibacterial behavior on three conventional bacterium i. e. Escherichia Coli، Staphylococcus aureus and Pseudomonas aeruginosa were assessed. At first، silver nitrate solution and deionized water in the presence of polyvinyl pyrrolidone were prepared. Sodium citrate and sodium borohydrate were then added to the solution. Hydrogen peroxide acted as an oxidizing agent. Transmission Electron Microscope (TEM) analysis showed that distribution of triangular shaped nanosilver particle size was broad and in the range of 7-65 nm. This triangular formed nanosilver had a sharp edges and vertexes. The UV spectroscopy of blue-color solution showed two peaks in the range of 331nm and 627 nm which reflected anisotropic and the formation of triangular structure of silver nanoparticles. The halo test results represented that halo diameter for gram positive S. aureus was smaller than the other gram negative bacterium.

In this study، the effects of heat treatment on the microstructure and pitting corrosion resistance of super duplex stainless steel welds have been investigated. The results showed that step annealing treatments in the temperature range of 550–1000 °C resulted in a precipitation of sigma phase and Cr2N along the ferrite/austenite and ferrite/ferrite boundaries. At this temperature range، the metastable pits mainly nucleated around the precipitates formed in the grain boundary and ferrite phase. Above 1050 °C، the microstructure contains only austenite and ferrite phases. At this condition، the critical pitting temperature of samples successively arrived to the highest value obtained in this study.