مجله مواد و فناوری های پیشرفته
سال سوم شماره 1 (بهار 1393)

Producing of today cutting tools without cemented carbides as a raw material is impossible. Requirements of industries to new cutting tools with high quality and performance in order to achieving better economical results, was caused to use of advanced processes in producing and improving of these tools. In this research, it is endeavored by changing sintering time, new properties and broadened fields of cemented carbide tools are obtained. For this purpose, samples of “K” type standard with WC(92%Wt), TaC(2%Wt) and Co(6%Wt) composition and “P” type standard withWC(80%Wt), TaC(5%Wt), TiC(5%Wt) and Co(10%Wt) composition which are suitable for cast iron and steel machining respectively, were processed. Microstructure of raw materials and products were investigated by light and scanning electron microscopy respectively. Samples were sintered at 1490±5°C for 1 to 10 hours in a 10-2torr vacuumed electric furnace. Analyzing of XRD patterns by software revealed desirable phases. Mechanical properties were analyzed by measuring of hardness changing from 1698HV30 to 1674HV30 for “K” type and 1389HV30 to 1347HV30 for “P” type samples. Transverse rupture strength of samples was measured after 4hr sintering and an increasing revealed up to 2991MPa for “K” type and 2710MPa for “P” type samples because of elimination of crack formation centers and after that decreased to 2610MPA and 2250MPa because of predominant of grain growth phenomenon, respectively. Also measurements of magnetic saturation and coercive force properties were done on sintered samples, which revealed reduction in both of these properties by increasing sintering time. No changing in density was observed.

Mechanical alloying of an elemental powder mixture with stoichiometric composition of Ti0.4Ni0.5Nb0.1 was conducted using planetary ball milling. The assessment of the formed phases was investigated using semi-empirical Miedema Model. In addition, the milled product was characterized using various techniques; X-ray diffraction studies revealed the formation of Ni(Ti) solid solution after the first hour of milling. However, dissolution of Nb was not found in neither of the other elements. After 7.5 h of milling, the formation of NiTi-based intermetallic compound begins while Nbis still remained as a free element. Finally, after 10h of milling, an amorphous phase was formed which remained for the next 10h. Field emission scanning electron microscopy investigations showed that a homogeneous structure is formed after 20h of milling, but further milling increases the product size due to agglomeration and cold welding of the relatively finer milling products. Transmission electron microscopy confirmed the presence of both the nano-crystalline NiTi intermetallic compound and amorphous phase. The experimental results were found to be in agreement with those of the thermodynamic calculations based on Miedema Model using Ni-Ti, Ni-Nb, Nb-Ti binary systems and Ni-Ti-Nb ternary system that predicted the formation of Ni(Ti) solid solution and immiscibility of Nb in Ti and Ni. In addition, a slight difference in the value of Gibss free energy of formation was found between the intermetallic compound and amorphous phase that confirms their presence in the final milled product. Keywords: NiTiNb, nano-structured materials, mechanical alloying, thermodynamic calculations based on Miedema Model

Dye-sensitized solar cells based on ordered mesoporous TiO2 films were fabricated by sol-gel technique. X-ray diffraction (XRD) analysis revealed that anatase phase was crystallized at 300 °C with initially crystallite size 3.2 nm and the crystallization was improved to 700 °C. Surface area analysis showed that the specific surface area of the films decreased from 163.43 to 87.15 m2/g and the pore size increased from 5.05 to 8.75 nm as the annealing temperature increased from 400 to 600 °C. The transmittance spectra that measured by UV/Vis spectrophotometer revealed that the transmittance maxima of the films decreased in the visible region and the absorption edges shifted to longer wavelengths. Photovoltaic measurements showed that the power conversion efficiency of the films initially enhanced to the maximum value of 3.61% with the increasing film thickness to 1.7 μm and then declined when the film thickness increased further.

In this study، Cu30-Ni70 alloy were synthesized by mechanical alloying. Different concentrations of carbon nanotubes were then distributed in the alloy to fabricate Cu-Ni/CNT nanocomposites. X-ray diffraction، scanning electron microscopy، vibrating sample magnetometer and 4point probe standard techniques were used to investigate the characteristics of the samples. XRD results of the alloy sample revealed that، homogeneous Cu30-Ni70 alloy was formed after 5 h of milling. The SEM micrographs of the specimens showed that CNTs have a significant effect on structural refinement of the nanocomposites. The finest microstructure was obtained in the sample containing 5 wt% CNTs. Decreasing the electrical resistivity values of the nanocomposites due to increasing the CNT contents showed that CNTs have been uniformly distributed in the samples. More ever، the distribution of CNTs in the matrix decreases the saturation magnetization and increases the coercivity of the nanocomposites.

In this study، to investigate the mechanical properties of Cu / graphene nanocomposite using by mechanical alloying process of cold pressing of the Taguchi experimental design is used when variables such as percentage of graphene، milling time، pressure pressing and sintered temperatures used in this study. In this article the effect of graphene on the mechanical properties of copper / graphene nanocomposite has been studied. For this operation، the mechanical alloying powders in a ball mill for 20 hours maximum wear under argon atmosphere was carried out. Powder particle morphology by scanning electron microscopy، X-ray diffraction analysis of the powder mixture model and Raman spectra analyze has been used for graphene detect. According to the results mechanical properties are improved such that the highest compressive strength (MPa562) and highest hardness (3/63 BHN) are achieved in the Al composite reinforced with5/0 % and 2/0 % graphene respectively.

Nanostructured TiO2–SnO2 films were prepared by a facile aqueous sol–gel route. The prepared sols showed particle size in nano-meter scale. X-ray diffraction (XRD) analysis revealed that phase composition of the films depend on Sn:Ti molar ratio and annealing temperature. Moreover, SnO2 retarded the anatase to rutile transformation. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO2- SnO2 binary mixed oxide, being 3 nm. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited films had nanostructured morphology with the average grain size in the range 20-40 nm. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications towards low concentrations of CO gas at low operating temperature of 200°C.

Graphite powders were used in this project and pellets were made under the pressure of 10 bar. Sodium hydro carbonate was used to dope with graphite. Sodium salt powder were poured inside the pellets and heat treated for 5 hours in vacuum at 800̊ C. XRD analysis showed a shift of characteristic peak of graphite. After that, in order to storehydrogen in the pellets, hydrogen was generated and purged to the pellets in the sealed chamber. The chamber was cooled to 80̊ k to make hydrogen adsorption possible. The pellets were exposed to hydrogen for different times and the hydrogen pressure was 1 MP. DSC analysis in argon atmosphere was carried out to assess hydrogen storage. The results showed that after 20 minutes the pellets doped with sodium could adsorb hydrogen which is good for hydrogen storage.

An experimental study was conducted to determine the abrasive wear behavior of different weight percentage fiberglass and silicon carbide powder filled polyester composites. The effect of glass fiber and SiC powder concentration and sliding distance on the weight loss of composites has been analyzed. The weight loss depends on fiber glass and powders concentration. The weight loss decreases with the increase of sliding distance and wear resistance increases with the decrease of percentage of weight loss. Strength characteristics on the material depending on the type and quantity of fillers have been tested. Sample having 1 weight percentage (wt%) of fiber glass and 3 percentage (wt%) of SiC show the maximum strength. Density of the Nano composites tends to decrease with adding filler into matrix, While porosity percentage and water absorption percentage of the Nano composites tend to increase. At least morphologies and microstructures of samples were characterized by various techniques such as X-Raydiffraction (XRD), Scanning electron microscopy (SEM), nevertheless the X-Ray diffraction could not identify the phases because of the small percentage of reinforcements.

Acidification is a common harm to historical wood works and the issue of deacidification, inconserving and restoring historical wood works, is mentioned using ammonia along with alcoholic solvent (usually methanol), as a deacidifire, is a common approach to deacidification of historical wood works. But using this deacidifire also has its own problems. One of the problems of using ammonia solvent in methanol is the superficiality of the deacidification and low penetration in wood which causes reacidification of wood after a short period. Being poisonous, for both ammonia and methanol, and dangers of using them for the wood restorers are other radical problems of using these solvents for deacidification of historical wood works. Also, permanent damage of wood compositions while conserving and restoring the wood works causes changes and problems. Recently, using nano materials in the science of conservation and restoration of historical works is being examined. One of the examined cases has been alkalized dispersion of nano particles of calcium hydroxide in isopropanol for deacidification of historical wood, paper and cloth. The results of the deacidification on these material which have been mentioned is very noticeable. In this research we compared traditional method for deacidification of iranian historical wood works (using ammonia in a alkoholic solvent) with a new method have been examined recently in Stokholm Museum for deacidification of acidified wood of the historical ship Vasa(using alkalized dispersion of nano particles of calcium hydroxide). We examined three types of permanent wood; Buttonwood, Pearswood and Walnutwood, and two types of historical wood; safavid Buttonwood and qajari Buttonwood. For feasibility study of using alkalized dispersion of nano particles of calcium hydroxide for deacidification of historical wood works, we perpended on results of these examinations; pH examinations, weight examinations, SEM images, Atomic Absorption, comparing solvation of samples in deacidifires with examination of changing in their color.

Separation of sulfuric acid with TOA from acidic solution for many metals ion recovery through solvent extraction method has been investigated. The effect of concentration of TOA as an extractant and octanol as modifier has been studied. Also the effect of temperature and water adsorption has been studied. An organic phase containingTOA as extractant, octanol as modifier and Kerosene as diluent. Increase in the TOA concentration leads to an increase of the amount of acid extracted in the organic phase. Adsorption of sulfuric acid with TOA is an exothermic reaction.stoichiometric coefficients of sulfuric acid in this reaction has been determinated by slope analysis method. It has been shown that 3 moles of TOA extracts 2moles of sulfuric acid and 3 moles of water.