نشریه علم و مهندسی سرامیک
پیاپی 1 (تابستان 1391)

In the current investigation، zirconia nanopowders with zirconia nanoparticles content of 0 and 10 %wt was synthesized via chemical co-precipitation method. Zirconium oxycloride and cerium nitrate salts were used as the precursors. Calcined nanopowder of zirconia was added through synthesis processing of the two types of 0 and 10%wt zirconia nanopowders. Appropriate calcined temperature of dried powders and physical properties of the resultant powders were studied by Differential Thermal Analysis (DTA)، X-ray diffraction (XRD)، specific surface area measurement by BET method، Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). Added zirconia nanoparticles act as heterogeneous sites، so crystallite size was enlarged. The compaction behavior of the calcined powders revealed that however less value in the slope of the raw density curve on the pressure logarithm (α=A3/A2)، caused in better compressibility of the specimen. Based on the results، raw density increasing in the sample without zirconia particle (%0 wt) was higher than the sample with zirconia particle content of 10% wt.

In this research، magnetite iron oxide nanoparticles were synthesized via coprecipitation method and their colloidal stability was investigated using 3 different comb polymeric surfactants based on polyacrylic acid-co-polyethylene glycol acrylate in water media. The difference of these surfactants is in tree type of polyethylene glycol with molecular weights of 1000، 2000 and 4000 which is connected to hydrophobic acrylate chain. The effects of synthesis temperature and time on particle sizes were studied. The temperature and time range was determined 27-90C and 10-40 min، respectively. To synthesis of magnetite nanoparticles، ferric and ferrous chlorides were precipitated with pH adjustment using ammonia (25 wt %) solution. The size distribution and stability of particles were studied via dynamic light scattering (DLS) and turbidimetry، respectively. The attachment of surfactants on nanoparticles was studied using fourier transform infrared spectroscopy (FTIR). Results showed that the particle sizes are different related to molecular weights of polyethylene glycol in comb polymeric surfactants. The com polymeric surfactant with polyethylene glycol Mw=2000 was lead to lower mean particle size and better stability relative to others. Moreover it was revealed that the best magnitude colloidal stability was with 22 wt % from comb polymeric surfactant having polyethylene glycol Mw=2000 at 70C for 20 min. The hydrodynamic size of particles was 80nm in this condition.

Titanium nitride and carbonitride have high melting point and good chemical resistance to slag. Composites of Ti (C،N) and TiN with oxides and non-oxide ceramic have potential application in structural and refractory industries. In this paper the synthesis of MgAl2O4-Ti (C،N) composites by aluminothermic reduction from MgO، Al and TiO2 mix in coke bed was investigated. The effect of carbon black and sugar to above mix was also determined. The bodies after pressing، were fired in coke bed in temperature range 1200-1600˚C in electrical furnace. MgTi2O5، Corundum، rutile and suboxides of titanium phases were present at 1200-1300˚C in the microstructure. By increasing the temperature to 1400 and 1600˚C for sugar and carbon black containing samples respectively، MgAl2O4 and Ti (C،N) phases were established as main phases.

In this research، stable mesostructured titania sols were synthesized employing P123 block copolymer as soft template under controlled hydrolysis of titanium isopropoxide (TTIP) in alcoholic media. In order to study the effect of Hexane additive on the sol characteristics and aggregation of the P123 unimers، two molar ratios of Hexane to P123 (H/P) of 60 and 240 were used in the sol composition. The effect of addition stage of Hexane to the sol and aging time (at 50 ˚Cfor 1 and 14 days) on the size distribution of unimeric clusters were also investigated by dynamic light scattering (DLS) technique. It was shown that the stage of addition has a marked effect on the size distribution of the clusters formed. Comparison ofDLS plots for the prepared sols with and without Hexane revealed a shift towards smaller sizes for the former. Further، no signs of micelle formation could be detected for the sample containing the highest Hexane content، based on DLS results. However، for the sample with H/P molar ratio of 60 aged for 1 and 14 days،rising sizes of the clusters close to P123 micelle size was noticed. This reached to 19 nm for the sample with 60 H/Pmolar ratio aged for 14 days. Finally، micelle formation and micellar aggregation will be discussed for the system studied here.

Wet chemical methods are the most widely used routes for biphasic calcium phosphate bioceramics synthesis in which control of synthesis condition and reaction factors are very important. To predict and control the synthesis condition، mathematical models can be used. Artificial neural networks are computational tools inspired by the nervous systems of living organisms that help us to get better understanding about the complicated problems. Powders were synthesized using aqueous solution containing different calcium /phosphorus ratio. HNO3 and NH4OH were used to adjust the pH of the solution mixture during the process. The precipitation was calcined at 1100˚ C for one hour. The chemical composition and Ca/P ratio were determined by inductively coupled plasma atomic emission spectroscopy. Phase identification of powders and evaluation of the functional groups of specimens were carried out by X-ray diffraction and Fourier transform infrared spectroscopy respectively. Four three-layered feed forward networks with ten neurons in the hidden layer، linear sigmoid stimulation and Levenberg-Marquardt learning algorithm were trained using data obtained from the experiments designed in four different patterns. The best result was obtained with the network consists of 80% training process، 15% validation process and 5% testing process samples by changing number of samples in each step. To ensure optimal performance of four networks، each network was studied using four new data. The predicted results show a good comparison with those obtained experimentally.

In this study، bioactive glass coating was used for improvement of surface and bioactivity of stainless steel 316L. Bioactive glass was made by sol–gel technique and thermal properties of the prepared powder were studied using differential thermal analysis (DTA). Stainless steel was immersed in the solution and afterward، effect of heat treatment by CO2 laser with 5 and 10 w and an electrical furnace was investigated. The structural and topographical properties of the glasses were studied using، XRD، FTIR، SEM and AFM techniques. The results showed، the sample was prepared by sol-gel method after heat treatment in furnace has been partially crystallized to hydroxyapatite. Whereas، the samples were prepared by laser remained amorphous.

In the work presented here، attempt is made to study the effect of different carbon supports on the electrochemical behavior of Pt/Carbon supports. In this respect، the carbon mesoporous samples (CMK-3) prepared by hard templating method were functionalized with Nickel oxide، Carbon nanotube and Platinum. Then all the materials have been characterized by XRD (Low&high)، N2 adsorption–desorption isotherms، transmission electron microscopy (TEM) and high-resolution field emission scanning electron (FESEM). The results showed the mesostructural structure has been destroyed by functionalization of CMK3 with NiO and CNT. Furthermore، The WAXRD patterns revealed the formation of smaller Pt crystallites in relative to Vulcan supports. Finally، obtaining the polarization curves for the fabricated MEAs with Pt loading of 0. 5 mg cm-2 demonstrated that the CMK3-CNT-20Pt catalyst shows a considerably better performance than the other samples.