مجله مواد و فناوری های پیشرفته
سال چهارم شماره 3 (پاییز 1394)

During the last few decades، oxyfluoride glass ceramics containing fluoride nanocrystals have received more attention in photonic applications due to their low phonon energies (~500 1/cm) and favorable mechanical، thermal and chemical stability. Main purposes of the present research are investigation of the K2O role on their processing، crystallization behavior structure and transparency. Glasses in the SiO2- Al2O3- CaO- CaF2 system with different amounts of K2O additive (1. 5، 3 and 4. 5 weight ratio) were prepared by convenient melting process. DTA curves exhibited two exothermic peaks، one related to CaF2 crystallization (~ 700 °C) and the other which had not been interpreted clearly before (~ 900°C). XRD patterns، SEM images and EDX analysis confirmed the DTA results and revealed that the second exothermic peak was related to crystallization of anorthite. Glass ceramic samples were prepared on the basis of crystallization temperatures derived from DTA. The only precipitated crystalline phase in the glass samples heat treated on the basis of the first peak of DTA، was CaF2 With the aim of studying the transparency and structural changes of glass samples with different amounts of K2O content، transmittance in UV- Vis region and FT-IR spectra of them were studied. According to the better crystallization behavior and higher transparency in UV- Vis region (~87%)، the glass containing 4. 5 (weight ratio) K2O additive has been introduced as the best basic glass.

In this research، sol-gel bioactive glass in SiO2 -P2O5 – CaO - Na2O system using common nitrate precursors was investigated. Some parameters like water/alcohol/TEOS ratio، type of catalyst (acid or alkali) and temperature of heat treatment were also studied. Various precursors such as acetates، carbonates and chlorides were utilized to introduce Ca and Na in glass composition. Characterization of crystallization temperature، created phases and chemical groups in synthesis powder was accomplished by STA، XRD and FTIR analyses. Although above-mentioned parameters influence on final powder characteristics، their changes cannot induce amorphous phase development in composition with high amount of Na2O and sodium nitrate is always observed in their XRD patterns. Results indicated that by decreasing Na2O from 24. 4 %mol. to 13. 7 %mol. in glass composition، amorphous phase could be achieved.

In this research, three-dimensional graphene (3DG) was synthesized via thermal CVD method by using nickel foam in a tube furnace. This method consists of graphene growth on the nickel foam using Ar and H2 gases and ethanol carbon precursor, followed by removal of nickel foam by chemical etching. Finally, the synthesized graphene was characterized by XRD, SEM and Raman analyses. The electrical conductivity and work function of 3DG were determined by Van der Pauw method and UPS technique, respectively. The results indicated that the high porosity and good quality three-dimensional graphene was formed. The electrical conductivity and work function of 3DG were measured 4 s.cm-1 and 5 eV, respectively.

Lipases find great use in a broad number of biotechnology fields, especially dairy, detergents, drugs (ibuprofen, naproxen), chemicals, agriculture (pesticides, insecticides) and oil chemistry (the hydrolysis of fats and oils). In order to increase the half-life of the enzyme and repeated use of it, in this study the immobilization of lipase on the mesoporous silica SBA-15 has been investigated. For the first time, the effect of shortening rod channels on the adsorption capacity of porcine pancreatic lipase (PPL) has been studied. Due to the slowly diffusion of large lipase molecules, in addition to increase surface area by expanding the pore diameter, shortening of mesochannels can be considered as an effective parameter on the adsorption properties. Triblock copolymer Pluronic P123 and tetraethyl orthosilicate (TEOS) were used as structure directing agent and silica source in acidic media respectively. Tetramethylbenzidine (TMB) was used as a swelling agent for expanding pore diameter up to 10 nm. The well-ordered 2D hexagonal pore structure was obtained after prehydrolyzing silica for about 30 minutes. Shortening of rod mesochannels from 800nm to 100nm was also maintained in the presence of small amount of ZrOCl2.8H2O. Structural analysis by low angle XRD, nitrogen adsorption, scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy confirmed tuning effect of Zr in SBA-15 materials. The amount of lipases adsorbed on the mesoporous SBA-15 was determined by thermal gravimetric analysis. By optimizing synthesis parameters, the uptake capacity of PPL into the mesoporous silica was remarkably increased from 473.2 mg/g to 783.9 mg/g.

Thermal stability of aluminide coatings are affected by chemical and phase changes of the coating and coating/substrate interface. In this paper the coating thickness and structure stabilities within interfaces of both simple and silicon-modified aluminide coatings with GTD-111 superalloy substrate were investigated. The coatings were prepared by high-activity pack aluminizing and slurry aluminizing, respectively. Thermal stability test was conducted in 950? C for 1000 h. Microstructural changes of the coatings during high temperature exposure were characterized by optical and scanning electron microscopes. The results indicated that the substrate/coating interfaces in both coatings comprised of two diffusion layers of PID and SID during 100-1000 h of the high-temperature exposure. However, it was found that Si has a minor effect on the phase morphology and widening of the PID and SID in the aluminide coatings.

Fe2O3 thin film with 300 nm thickness is deposited on FTO substrate using electrodeposition technique. After deposition, samples were annealed at 300°C for 30 min. X ray diffraction (XRD), scanning electron microscopy (SEM), Cyclic voltammetry (CV), choronometry and UV/Vis spectrophotometric analysis were used for studying the structure, morphology, electrochromic and optical properties of synthesized thin films, respectively. Based on our results, α-Fe2O3 nanoparticles with 40 nm size were uniformly distributed on FTO surface thin film. We have used two different electrolytes LiClO4 – PC and LiOH for investigation of electrochromic behavior of thin films. Results showed that this behavior depends on the electrolyte type in the potential range of -1.5 to 1 V.

In the present study, production of the composite nano powder of Co/VC by mechanochemical method from Co3O4, V2O5, and graphite as the starting materials with magnesium as the reduction agent was investigated. For this purpose, the materials powder mixture was milled in accordance with stoichiometric reaction in a high energy ball mill with the ball-to-powder ratio of 20:1 under argon atmosphere for different durations. After 10min of milling, combustion occurred and the XRD results indicated that magnesium has reduced vanadium and cobalt oxides (V2O5 and Co3O4) and has changed into magnesium oxide; also, graphite has reacted with the metallic vanadium to form vanadium carbide, which means that the reaction has been completed. Based on the adiabatic temperature of the reaction (Tad~ 3932.014), the reaction was identified as a mechanically inducted self-sustaining one or MSR. The crystallite sizes of vanadium carbide and cobalt calculated by the Williamson-Hall equation were 50 and 10nm, respectively. Finally, the magnesium oxide phase was deleted from the system via leaching process in 0.9% hydrochloric acid and the composite powder of Co/VC was obtained.

In this research ZnO hexagonal nanorods solved in hydrothermal with 0.05M and 0.025M concentrations(MEA) has been grown at 2.5 and 5hours on the FTO. For construction of solid phase of solar cell, combination of CH3NH3PbI3, Spiro-OMeTAD and gold has been used. For investigation of structural and optical specification of nano rods by SEM, XRD, DRS and determining photo electro chemical parameters of cell by voltage-current analysis has been done. Results has been shown that efficiency is reached from 5.42% to 6.41% because of increasing the synthesis time by two times which is caused to increase the average length of nanorods from 300 nm to 650nm. By 50 percent decreasing of concentration of MEA, the average diameter of the nanorods has been decreased from 95 nm to 50 nm and finally efficiency of the cell has been 1.5% decreased. Results has also been shown that the efficiency of synthesis nanorods with fully concentration of MEA during 5 hours is 6.41% and the efficiency of produced nanorods with half of concentration of MEA during 2.5 hours is 4.98%.