جستجوی مقالات مرتبط با کلیدواژه "graphite" در نشریات گروه "مهندسی شیمی، نفت و پلیمر"

Research subject:

 Global warming is the most important worldwide problem. CO2 is one of the greenhouse gasses and its emission to the atmosphere causes global warming to increase. Porous adsorbents are great candidates for CO2 adsorption and graphene aerogels are porous nanostructures with very low density and hierarchical porosity which is suitable for CO2 adsorption. The source of pristine graphite for graphene oxide synthesis as a precursor plays a vital role in graphene aerogel nanostructure.  

Research approach:

 In the current study, graphene oxide by modified Hummers method was synthesized with three different graphite sources. Graphene aerogels were prepared with synthesized graphene oxides via hydrothermal and freeze-drying methods to investigate their effect on graphene aerogel nanostructure. Finally, the CO2 adsorption of graphene aerogels was evaluated. The samples were characterized by FTIR, XRD, SEM, and BET analysis.

 The results indicated that the source of graphite has a significant role in the process of oxidation of graphene oxide by the modified Hummers method. XRD results of graphene oxides showed successful oxidation of graphite. The normalizing FTIR peaks of graphene oxides showed different intensities of oxygenated functional group peaks. FE-SEM results of graphene aerogels showed that less oxidation of graphite powder caused agglomeration of graphite plates and thick walls were formed. The macropore size in the structure of obtained aerogels (GAB and GAE) was 2.28 and 3.84 µm respectively which affected the CO2 adsorption. Larger pores led to easier mass transfer of CO2 molecules and higher CO2 adsorption was achieved. Moreover, the high meso and micro surface area (111 and 115 m2/g respectively) in GAE increased CO2 adsorption up to 1.04 mmol/g compared to GAB (0.724 mmol/g).

Research Subject: 

Because of the constant deterioration of environmental conditions, the world faces energy and clean water shortage. To address the water crisis issue, the solar steam generation system has been considered as a suitable technology for seawater desalination due to its competitive features, such as no carbon dioxide emission, low energy consumption, and high efficiency. In modern solar steam generation systems, solar energy is harvested by a photothermal absorber and then converted into thermal energy to heat a certain volume of water and produce steam. Then, the generated steam condenses on the inner surface of the cover, and clean water is collected. The five key features required for solar steam generation system are: high light absorption, low heat losses and heat localization, proper water transfer, and the ability to float on the water surface.

In this study, a solar steam generation system based on a graphite absorber layer is built, and its performance is improved using nickel plasmonic nanoparticles.
In order to investigate the dependency of the performance on the structure, two different layers including cotton and polyester felts are used to transfer water controllable. In this study, the water evaporation rate, surface temperature, and efficiency of the devices are evaluated.

Thermal efficiency and evaporation rate for the system based on the pure graphite absorber is 68.17% and 0.97 kg/m2.h, which increases to 93.57% and 1.37 kg/m2.h, respectively by adding nickel nanoparticles. Using two cotton and PS water managers reveals the importance of the thermal energy and mass transfer balancing in the systems, which strongly affects the devices performance.

Polymer nanofibers have attracted much industrial interest over the past decade. In general, these fibers are suitable for a variety of applications including medical applications, insulation, capacitors, advanced aerospace technologies, and so on. Specifically in aerospace technology, the used materials must be thermally stable with suitable electrical conductivity. However, many of these polymer nanofibers suffer from low temperature degradation and low electrical conductivity, limiting their use in many potential applications. Graphite has unique properties such as high conductivity and high thermal stability. This exceptional material can be included as a nanoparticle in polymer nanofibers to modify electrical and thermal properties.The aim of this research was to investigate the effect of addition of graphite nanoparticle on thermal and electrical propertiesof polymer fibers.

For this purpose, polyvinyl alcohol 72000 (PVA) as a non-conductive polymer and graphite nanoparticles were used. Polyvinyl alcohol-graphite nanofibers were synthesized method by electrospinning technique under optimized parameters. The optimum conditions for the electrospinning process were: PVA concentration of 8%, applied voltage of 22 Kv, flow rate of 10 ml and tip/collector distance of 20 cm.

 Scanning electron microscopy (SEM) studies showed that produced PVA fibers were smooth, continuous without any bead, with a diameter of about 350 nm. The PVA / graphite nanofibers were also smooth but much thinner (about 200 nm) than PVA fibers at the same processing parameters. Moreover, X-ray patterns of PVA/graphite nanofibers include peaks of graphite particles in the structure and slso the suppression of crystallinity.  According to the results of 4 point probe teste, by increasing weight percentage of graphite in the fibers, electrical conductivity increased up to 0.5 . The thermal behavior of PVA nanofibers after mixing with graphite was also investigated by differential calorimetry analysis (DSC) and TGA. It was demonstrated that PVA / graphite nanofibers are thermally stable up to 300 ° C.

suspension polymerization of styrene in the presence of graphite was carried out. The polymerization reaction kinetics was investigated to gain better insight into manipulating process parameters. The particle size distribution and thermal conductivity of the foams were studied by considering different parameters.

Product characterization and the reaction thermal kinetics were evaluated using differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), particle size distribution and thermal conductivity measurements. The effect of graphite and initiator concentration on the reaction kinetics was investigated.

The results showed that the graphite profoundly reduced the rate of reaction and consequently caused instability in the suspension. By manipulating the process variables such as increasing the amount of stabilizers (1 to 2%) and initiator (up to 0.6% by wt), their frequency and injection time, the polymerization of styrene in the presence of graphite was done. The beads were spherical and the superfine (less than 420 μm) proportion of the product was less than 5%. Through the pre-expansion process, the beads were expanded and the cell structure was uniform. The pentane content of the beads was sufficient (~7% by wt) to successfully sinter the pre-expanded beads in the final molding process. Final foams had 0, 1 and 1.5% graphite. By increasing the graphite content, the thermal conductivity of the foams was decreased. Graphite-containing foams were better thermal insulators than conventional expandable polystyrene. Therefore, for a specific thermal duty, a smaller amount of graphite-containing expandable polystyrene rather than conventional polystyrene is required and consequently, the total cost of the insulation is reduced.

In this study the fabrication of printed heaters using conductive film prepared by nano graphite and nano copper was investigated. One of the features of this heater, is high stability and low energy consumption, which makes it possible to build a heater by producing high temperature. Initially, nano copper was produced by using the polyol method, in which polyvinylpyrrolidone was used as a protective agent. According to the scanning electron microscopy(SEM) analysis, the copper nanoparticles had a size range of about 35±9 nm. The copper particles were confirmed by XRD to be crystalline copper with a face-centered cubic (fcc) structure. In addition, graphite, 1-methyl-2-pyrrolidinone (as film solvent) and copper nanoparticles (to increase film conductivity), a conductive film with a weight percentage of 60.21% was prepared. The optimum film resistivity, which was printed as a conductive film on the glass surface with dimensions of 10 x 1 cm, and dried by the oven at 170 °C, was 126.8 ohms. Finally, when the film was connected to a 24 V supply, temperature of the film increased to200°C. Due to its stability and uniform heat, the heater can be used in the electronics industry.

Nano composites of graphene oxide and modified nanoclay (Cloisite 15A) were produced based on 80 phr chlorobutyl and 20 phr natural rubber according to inner liner recipe. The results show modified nano fillers have remarkable change in dispersion in the matrix. Subsequently Improved cured products properties. Exfoliation of graphen oxide and Cloisite 15A was confirmed by XRD and TEM. In the case of graphite intercalation has happened. Also physical and mechanical properties of this composite was studied.

Electrically conductive coatings are mainly required for static charge dissipation and electromagnetic/radio frequency interference (EMI/RFI) shielding. Electrically conductive coatings are prepared by the incorporation of the metallic pigments/graphite or carbon black onto the binder. In the present investigation, a study on the correlation between electrical, percolation threshold, filler volume concentration and some other physical and mechanical properties for graphite filled epoxy coating was carried out through an examination of the filler concentration dependence of the volume resistivity and othermechanical properties. The impact strength of epoxy resin filled with graphite was also investigated. A decrease in impact strength with an increase in filler content was observed. It is found that there are two critical threshold, in plot of electrical resistivity v.s. filler volume concentration. The adhesion of the filled resin to substrate was also determined by pull-off test. A decrease in the adhesion to substrate with an increase in filler content was observed in Then to find out the correlation between filler concentration and viscoelastic behavior of the system tensile test carried out. Then for expand a theory that can explain the transfer between insulator-semiconductor and semiconductor-conductor behavior of graphite filled system images was gived by SEM and optical microscopy and also oil absorption (for determine CPVC) test carried out. All data show that formation of internal network by graphite particles and particle by particle contact of them is the reason of formation a conductive network in epoxy system. J. Color Sci. Tech. 2(2008), 129-140.© Institute for Colorants, Paint and Coatings.