maryam sabetzadeh

To improve the hot section metallic parts durability in advanced gas-turbine operating in power generation and aircraft, thermal barrier coating (TBCs) are extensively utilized to increase their lifetime. The reason for applying coatings on these components is the improvement of their physical properties, mechanical properties, and outer look. The self-repairing ability of materials is very promising due to expanding the service time of materials and it is also beneficial in terms of human safety and financial aspects. In this review article, structure, properties, limitations, and the modification approaches of TBCs were studied. In addition, self-healing agents for TBCs including SiC, MoSi2, TiC were introduced, which release their oxide by reaction with air and O2 that are able to heal the pores/cracks in the coatings. In this regard, their coating methods, mechanism, and applications in TBCs were reviewed.

The population balance methods are employed to model sulfur vulcanization process of natural rubber (NR) compounds. The proposed primary models are so far empirical and/ or mechanistic and have various limitations that do not embody all reactions and formation of all the process products. In this work، the models are developed، using population balance methods that explicitly acknowledge the nature of all the formed species and the various types of reactions. The kinetic model can also accurately describe the complete cure responses including the scorch delay، cure time and the reversion for a wide range of compositions، using a single set of rate constants. In addition، the concentration profiles of all the reaction intermediates as a function of polysulfidic lengths are predicted. The population balance model provides a quantitative framework for explicitly incorporating mechanistically reasonable chemistry of the vulcanization process of different natural rubber compounds.

In this work, water absorption behaviour of biodegradable low density polyethylene-thermoplastic starch (LDPE-TPS) blends is investigated. Thermoplastic starch was prepared by melt mixing starch and glycerol (35 wt.%) using an internal mixer at 140 °C and rotor speed of 60rpm for 8 minutes. LDPE/TPS blends containing various amounts of starch (10-40 wt.%) were prepared with (3 wt.%) and without PE-g-MA using single screw extruder. Water absorption test was carried out at room temperature and using related standard methods. The results indicate that with increase in TPS content and also increasing the immersion time, water absorption increase unit the constant value is obtained. After 21 days of the immersion time, 10.5% and 16.3% increase in water absorption were obtained for uncompatibilized and compatibilized blends containing 40 wt.% TPS, respectively. The results also show that after immersion tests, the tensile properties such as ultimate tensile strength and Young's modulus decrease.

In this work, effect of maleic anhydride grafted- LDPE (PE-g-MA) on the mechanical, morphology and flow behavior of biodegradable LDPE-thermoplastic corn starch (TPS) blends were investigated. TPS was prepared by mixing neat starch and glycerol (35wt. %) at room temperature. The mixture then was melt-compounded using an internal mixer at 140oC, rotor speed of 60 rpm for 8 minutes. LDPE-TPS blends containing different contents of TPS (0-40wt. %) with (3wt. %) and without the addition of PE-g-MA, were prepared using a single-screw extruder. Surface morphology of the prepared blends was investigated by Scanning Electron Microscopy (SEM). Also, mechanical properties and flow behavior of the prepared samples were carried out by means of related standard test methods. Scanning electron micrographs of the samples show improvement in dispersion of the starch particles in LDPE matrix in the presence of PE-g-MA as a compatibilizer. Also, the results of mechanical properties indicate that as TPS concentration increases, the ultimate tensile strength, elongation at break, Young’s modulus and relative impact strength of the blends decrease. However, the compatibilized blends represent higher mechanical properties than the blends without any compatibilizer. Furthermore, the addition of starch to LDPE decreases the melt flow index values of the samples and subsequently increases their apparent viscosity.The results of rheological tests also indicate that as shear rate increases, the apparent viscosity of the samples decreases (shear thinning).

The changes in the behaviour of mechanical properties of low density polyethylene-thermoplastic corn starch (LDPE-TPCS) nanocomposites were studied by an adaptive neuro-fuzzy interference system. LDPE-TPCS composites containing different quantities of nanoclay (Cloisite®15A، 0. 5-3wt%) were prepared by extrusion process. In practice، it is difficult to carry out several experiments to identify the relationship between the extrusion process parameters and mechanical properties of the nanocomposites. In this paper، an adaptive neuro-fuzzy inference system (ANFIS) was used for non-linear mapping between the processing parameters and the mechanical properties of LDPE-TPCS nanocomposites. ANFIS model due to possessing inference ability of fuzzy systems and also the learning feature of neural networks، could be used as a multiple inputs-multiple outputs to predict mechanical properties (such as ultimate tensile strength، elongation-at-break، Young’s modulus and relative impact strength) of the nanocomposites. The proposed ANFIS model utilizes temperature، torque and Cloisite®15A contents as input parameters to predict the desired mechanical properties. The results obtained in this work indicated that ANFIS is an effective and intelligent method for prediction of the mechanical properties of the LDPE-TPCS nanocomposites with a good accuracy. The statistical quality of the ANFIS model was significant due to its acceptable mean square error criterion and good correlation coefficient (values > 0. 8) between the experimental and simulated outputs.