Mevlüt Gürbüz

Development of antibacterial electrospun chitosan/poly(vinyl alcohol) nanofibers containing silver ion-incorporated HAP nanoparticles

Chitosan/poly(vinyl alcohol) (CS/PVA) nanofibers with a diameter in the range of 60–70 nm were prepared by electrospinning method. The effect of CS/PVA blend ratio and process parameters on the morphology and diameter of nanofibers was investigated by SEM analysis. The FT-IR and differential scanning calorimetry analysis of nanofibers revealed that intermolecular hydrogen bonds were formed between CS and PVA. Weight fractions of polymers in the electrospun nonwoven fibers mats were determined by thermal gravimetric analysis and were close to ratio of polymers in the blend solution. The silver ion (Ag+)-incorporated nanocrystalline hydroxyapatite (HAP) particles, determined as about 70 nm in diameter, were synthesized by wet chemical method. These nanoparticles were added to the CS/PVA blend solution in order to increase antibacterial activity of electrospun fibers. It was observed that the synthesized nanofibers including Ag+-incorporated HAP nanoparticles exhibited antibacterial efficiency against Escherichia coli. The antibacterial electrospun CS/PVA nanofibers are the potential candidate for biomedical applications, because they provide an efficient way to fulfill new requirements for material properties.

Analyses of the modulatory effects of antibacterial silver doped calcium phosphate-based ceramic nano-powder on proliferation, survival, and angiogenic capacity of different mammalian cells in vitro.

In this study, the antibacterial, cytotoxic, and angiogenic activities of silver doped calcium phosphate-based inorganic powder (ABT or PAG) were systematically investigated. ABT powders containing varying silver content were fabricated using a wet chemical manufacturing method. Antibacterial efficiencies of the ABT powders were investigated using a standard test with indicator bacteria and yeast. The cytotoxic effects of ABT on three different fibroblast cells and human umbilical vein endothelial cells (HUVECs) were assessed using MTT assay. ABT powder exhibits concentration-related cytotoxicity characteristics. Apoptotic activity, attachment capability, and wound healing effects were examined on fibroblasts. The angiogenic activity of ABT was investigated by tube formation assay in HUVECs; 10 μg ml(-1) and 100 μg ml(-1) concentrations of the highest metal ion content of ABT did not disrupt the tube formation of HUVECs. All these tests showed that ABT does not compromise the survival of the cells and might impose regeneration ability to various cell types. These results indicate that silver doped calcium phosphate-based inorganic powder with an optimal silver content has good potential for developing new biomaterials for implant applications.

The effect of sintering time, temperature, and graphene addition on the hardness and microstructure of aluminum composites

Currently, graphene is used in aluminum matrix composite manufacturing due to its superior mechanical properties. However, few detailed studies exist on the effect of the process conditions such as sintering temperature (TS), time (tS), and a number of graphene nanoplatelets. Therefore, the effects of different sintering times (tS = 60, 120, 180, 300 min), sintering temperatures (TS = 550, 600, 630℃), and graphene addition (0.1, 0.3, 0.5 wt%) on apparent density and hardness were reported in detail in this study. The crystal structure and microstructure of fabricated composites by powder metallurgy method were examined with X-ray diffractometer and scanning electron microscopy. Apparent density and mechanical properties were tested by density meter and micro Vickers hardness tester. The results indicated that the best sintering time, sintering temperature, and graphene addition were determined to be 180 min, 630℃, and 0.1 wt%, respectively, for the best hardness of composite. The hardness of composite increased from 38 to 57 HV when compared with pure aluminum under the best process conditions.

Effect of process parameters on hardness and microstructure of graphene reinforced titanium composites

In this study, the effect of the sintering time, temperature and graphene amount on titanium properties was examined for the first time in detail. From the results, the highly dense (4.39 g/cm3), most hard (from 390 HV to 566 HV) and improved microstructure for 0.15 wt% graphene addition were performed at 1100℃ for 120 min. The titanium composite properties have been reduced with increasing graphene due to damaged graphene and titanium carbide formation above 0.30 wt% graphene. To summarise, when pure titanium is compared with graphene reinforced titanium composites, the properties enhanced due to dislocation and fine grain strengthening mechanisms.

Electrospray deposition of SnO2 films from precursor solution

The electrospray deposition (ESD) of SnO2 films from SnCl4.5H2O precursor solution was performed for gas sensor applications. Deposition time, solution flow rate and solution concentration were the main control parameters in the ESD process. The morphological properties of the deposited films were characterised by scanning electron microscopy. X-ray diffraction and energy dispersive X-ray analyses were employed to confirm the crystal phases and composition of the films. The best coatings with an island of particle agglomerates were observed at a flow rate of 0.12 ml min−1, for 60 min, and at a 0.05M concentration. The crystallisation of SnO2 films was observed at 650°C. The grain size and surface morphology of the films were influenced by the sol concentrations. Larger grain size and cracked surface were observed by increasing the sol concentration. The film thickness of 6 µm and a grain size of less than 100 nm were achieved.

Electrophoretic Deposition of SnO2 Nanoparticles and Its LPG Sensing Characteristics

Homogenized nanoparticles (60 nm) in acetylacetone mediums, both with and without iodine, were deposited onto platinum coated alumina substrate and interdigital electrodes using the electrophoretic deposition (EPD) method for gas sensor applications. Homogeneous and porous film layers were processed and analyzed at various coating times and voltages. The structure of the deposited films was characterized by a scanning electron microscopy (SEM). The gas sensing properties of the films were investigated using liquid petroleum gas (LPG) for various lower explosive limits (LEL). The results showed that porous, crack-free, and homogeneous films were achieved for 5 and 15 sec at 100 and 150 V EPD parameters using an iodine-free acetylacetone based suspension. The optimum sintering for the deposited nanoparticles was observed at 500°C for 5 min. The results showed that the sensitivity of the films was increased with the operating temperature. The coated films with EPD demonstrated a better sensitivity for the 20 LEL LPG concentrations at a 450°C operating temperature. The maximum sensitivity of the sensors at 450°C to 20 LEL LPG was 30.

Energy harvesting with multilayer piezoelectric ceramics

Energy harvesting from piezoelectric ceramic components can be achieved in three ways. These are impact induced, continues vibration induced, and decaying vibration induced. Defining the necessary characteristic of piezoelectric materials in ATILA provides the preliminary knowledge of expectation result of multilayer product under vibration condition. In this study, continues vibration induced energy harvesting over the multilayer ceramic were studied. Experimental studies were performed on the multilayer piezoelectric ceramics with 10×10 mm size with twenty six layer and 2mm thickness. FEM studies on multilayer were performed with ATILA finite element modeling program. In addition, experimental setup was modeled in ATILA to have the possible experimental results. Finally, experimental and modelled properties of samples were compared as a function of voltage, power, and charge.

Development of Photochromic Coatings on Ceramic Tiles

Photochromic materials are sensitive to light when such a material exposed to the sunlight or UV irradiation, it can change color very quickly and turn back to its original uncolored form by removing light resource. Photochromic powder at different ratios in polymeric gel were prepared and coated on ceramic surfaces by using spray technique. This coating technique provided to form homogeneous layer structure on surface. By using polymeric gel, photochromic coatings were occurred at low temperatures with good adhesion. After heat treatment fast response photochromic coatings were achieved. Surface morphology of coatings on ceramic surfaces were investigated by scanning electron microscopy (SEM), the photochromic effect and optical characterization of coatings were analyzed by using Minolta 3600-d spectrophotometer.

Induction Heated Sintering and Mechanical Properties of Electrosprayed Nano YSZ

ABSTRACT In this study, YSZ nanopowder for gas turbine blades was used to deposit a film on Ni-based superalloy with electrospray deposition method. Then, the coated substrates were sintered with high-frequency induction heated sintering system which is yet not so popular in this field. Effect of nanosized YSZ and sintering method on the crystal structure and microstructures of coated materials were studied by X-ray diffraction and scanning electron microscopy. The best parameters for ESD of YSZ in 2-propanol were achieved at an applied potential of 7 kV, a flow rate of 0.05 mL/min and at aduration of 15 min. Results showed that YSZ coating was highly dense with non-cracked surface, uniform in thickness at 15 min total sintering time. Surface roughness, microhardness, and resistance to friction were measured as 0.41 μm, 348 HV and 0.14, respectively. GRAPHICAL ABSTRACT

Mechanical and tribological behaviours of aluminium matrix composites reinforced by graphene nanoplatelets

ABSTRACT In the present study, the effects of graphene content (0.1, 0.3, 0.5 wt-%) on the mechanical and tribological properties of aluminium matrix composites were reported. The experimental results reveal that the best apparent density (2.58 ± 0.02 g cm−3), highest Vickers hardness (57 ± 2.5 HV), lowest mass loss (1.6 and 9.7 mg for 10 N and 40 N), and lowest wear rate (12 × 10−5 and 18 × 10−5 mm3/Nm for 10 N and 40 N) were obtained at aluminium–0.1% graphene composite when compared with pure aluminium. The ultimate compressive strength of composites increases from 106 ± 4 to 138 ± 4 MPa with increasing graphene nanoplatelet contents. All results showed that graphene has been a very effective reinforcement and solid-lubricant material for Al matrix composites.