Key Engineering Materials Vol. 902

Abstract: We report on a development of the structural, optical and electrical properties of poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT:PSS) conducting polymer thin films. The PEDOT:PSS thin films were deposited by a controlled thin film applicator and their physical properties were found to be effectively modified by isopropanol. The deposited films were investigated by several techniques including XRD, UV–Vis, SPM and Hall-effect. Interestingly, by optimizing the PEDOTS:PSS/ISO volume ratio (v:v), we find that the film charge carriers type can be switched from p to n-type with a high bulk carriers concentration reaching 6×10¹⁷ cm^-3. Moreover, the film surface roughness becomes smoother and reaching a small value of only 1.9 nm. Such development of the PEDOT:PSS film properties makes it very promising to act as an electron transport layer for different energy applications.

Abstract: The main scope of the paper is to apply the Design of Experiment (DoE) method and to develop a predictive model of energy losses for non-oriented electrical steels. This approach permits us to determine a mathematical model, which is the predicted response (energy losses) as a function of input data (strip width and peak magnetic polarization) and experimental results. The presented DoE model is based on a classical central composite design of type 2ⁿ + 2n + 1 with two-levels (n = 2) and as a consequence only nine experimental points are necessary. The equation system that is associated with the model, generates a surface response equation, which permits the energy loss computation for different values of width strip and peak magnetic polarization. The DoE model was implemented, using different software packages as MathCad, Excel and OriginPro 2018, in the case of two types of electrical steels namely NO20 and M300-35A alloys that are used in small size electrical machines. In this case, the strain hardening phenomena at the cut edge becomes important, due to its negative impact on energy losses. The computed results were compared with the experimental data and errors lower than 5 % were determined.

Abstract: In this study, B₄C-TiB₂ ceramic composites were manufactured by hot pressing method. The raw materials for the in-situ synthesis of TiB₂ were TiO₂ and TiC. After being sintered at 1900°C for 60min under a pressure of 30MPa, compact composites samples with a TiB₂ volume fraction range from 0 to 11.05% were prepared. The relative density, fracture toughness and flexural strength of different sample were tested. Microstructures on the fracture surface were studied by SEM. The result shows that B₄C-TiB₂ ceramic composites sintered from B₄C-TiC had a better mechanical property than the one sintered from B₄C-TiO₂. When the content of TiB₂ (reacted from TiC) was 11.05vol.%, the strength and toughness of B₄C-TiB₂ ceramics can reach 598MPa and 6.45MPa·m^1/2. The toughening mechanisms of B₄C-TiB₂ composites include micro-crack toughening and energy consumption by the pulling out process of second phase.

Abstract: Metal-polymer composites are advanced materials for the aerospace, automotive and railway industry where details and elements of construction are affected by impact, cyclic and vibration loads. In the present work layered composites based on steel, aluminum alloy and rubber as intermediate layers were obtained by cold and hot bonding using adhesives. Adhesive lap-shear bond strength of layered composites fabricated by various techniques was determined using tensile shear test. To evaluate the mechanical behavior of layered metal-rubber composites under simulated operational conditions static, dynamic and cyclic, three points bending tests were carried out. The results of mechanical tests of these composites indicated that hot bonding is the most preferred fabrication method for the formation of increased mechanical characteristics.

Abstract: The effect of vulcanization processes and surface treatment of cellulose were investigated on tensile strength, degradation temperature, and morphological properties of cellulose/natural rubber composites. Cellulose was surface-treated with Si-69 silane coupling agent and used as reinforcing filler in natural rubber (NR). Different vulcanization processes including electron beam irradiation (EB-Cured) and sulphur vulcanization (S-Cured) were used to crosslink NR. The incorporation of both untreated and treated cellulose at various concentrations (5, 10, 15 and 20 phr) into NR was found to significantly improve the tensile strength and modulus. Notably, with addition of treated cellulose in NR, the tensile strength and modulus were considerably higher than that of the untreated cellulose for all curing system. SEM morphological analysis revealed a well dispersion of cellulose particles in NR matrix. Addition of cellulose slightly decreased the onset of degradation temperature of NR, however, the degradable temperature was found to be unchanged. The curing systems had shown an impact on tensile property of NR. S-Cured NR exhibited highest modulus of 2.23 MPa comparing to the EB-Cured NR (1.69 MPa) for the same amount of cellulose (20 phr), due to a stronger crosslink network. However, the curing system had no significant impact on degradation temperature of NR.

Abstract: This study investigated characteristics of moisture desorption for polylactic acid (PLA) filaments. The filaments tend to absorb moisture from humid air, led to moisten filaments. The absorption of even small amounts of moisture by filaments during storage and/or 3D printing, degraded the quality of final parts, and therefore, caused manufacturing problems. In this work, the filaments were subjected to humid conditions to achieve various moisture concentrations (0.75, 1.3 and 1.87 wt.%). Warm air-drying processes are used to reduce the moisture for different times (1, 2, 3, 4, 5 and 6 hours) and temperature (40, 50 and 60 °C). It was founded that the moisture from the polylactic acid (PLA) filaments can be discovered the moisture by use 60 degree of temperature in 5 hours warm air-drying process.

Abstract: Enhancement of the room temperature vulcanization silicone rubber (RTV) tracking resistance with various filler loadings of synthesized wollastonite against electrical surface tracking was prepared. The X-ray diffraction (XRD), Scanning electron microscope (SEM), and X-ray fluorescent (XRF) techniques were involved in characterizing the synthesized substances. The test method IEC-60587 standard was employed to evaluate the surface tracking resistance. The results obtained from the XRF technique confirmed that the raw materials could be synthesized for wollastonite, while the XRD and SEM techniques revealed the formation of wollastonite (CaSiO₃) associated with gehlenite (Ca₂Al₂SiO₇). Moreover, it was found that the electrical surface tracking resistance of composite insulation takes a long time to track when the filler loading is increased more than 5 phr.

Abstract: Hematite (α-Fe₂O₃) is a low-cost n-type semiconductor with significant absorption of visible light owing to its low bandgap energy of 2.1 eV. The wide applications of hematite in renewable energy and environmental remediation continuously entice more studies. However, the low absorbance of solar energy in the UV-range significantly limits the efficiency of many photocatalytic materials. In this study, we tried to dope α-Fe₂O₃ with silver via chemical precipitation method to lower the bandgap energy and widen its absorbance. The effects of doping hematite with Ag on the structure, morphology, elemental composition, and optical absorbance were determined by characterizing the samples via X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and UV-Vis spectroscopy, respectively. It was observed from the XRD patterns that the α-Fe₂O₃ crystallizes in hexagonal structure with lattice parameters a = 5.0380 Å and c = 13.7720 Å for the pure α-Fe₂O₃. Doping with 0.1M and 0.2M AgNO₃ leads to a greater value of the lattice parameters indicating successful doping. SEM images show that the hematite formed was composed of particles with irregular shapes that have sizes in the range 0.865-0.883 μm. Excess silver particles were deposited on the surface of hematite. UV-Vis spectra show that there is a red-shift in the absorption band of the Ag-doped hematite. A notable decrease in the bandgap energy of the undoped α-Fe₂O₃ was observed from ~2.2eV to ~2.0eV with the increase in the amount of the dopant in the hematite as determined using Tauc’s plot.

Abstract: Shelf life in ground and tree nuts are often assessed based on aesthetic appearance, nut integrity, color and most importantly, taste and edibleness. Nuts with considerable level of rancidity and free fatty acids due to degradation of oils indicate expiration or decay. We prepared a shellac-lemongrass oil blend coating using food-grade ingredients and assessed its potential to extend shelf life of Pili nut (Canarium ovatum) kernels. A glossy, hard but considerably brittle coating for the pili kernels were prepared with varying numbers of layers. On average, the mass of coating added per dip is 0.10 g, and the thickness of 5-layers of coating is 0.3 mm. The obtained reflectance spectra of the coated pili kernels implied the translucent nature of the coating, but becomes opaque as the number of layers are increased. Peroxide value (PV) and free fatty acid value (FFAV), were also measured at 10 days after application of coating. PV was lowest in the nuts with 5 coating layers, while this treatment did not reduce FFAV. These results indicate the effectiveness of our coatings in preventing peroxide production probably by blocking oxygen penetration and ultraviolet exposure, which are important triggers production of peroxide and other free radicals. Further tests and time-series experiments are planned to assess the dynamics of peroxide levels and the overall potential of our coating technology for Pili nut.

Abstract: Kapok fibers were used as a filtering medium in a column-type filtration set-up to separate diesel from water molecules in dynamic conditions. The amount of diesel flowing out the filtration system with respect to time was monitored. The times wherein the diesel first came out the filtering system (breakthrough time) were shorter at higher influent concentration and faster flow rate. Meanwhile, the total sorbed diesel molecules in the filtering system were increasing with the influent concentration while invariant with flow rate. The shorter breakthrough time was associated with the higher amount of diesel molecules that could be sorbed at a shorter time and the rate at which the overall processes of sorption-desorption-resorption proceeded. On the other hand, the sorption capacity of the system was viewed to be affected by the amount of moving diesel molecules that would interact with the kapok fibers and/or surface-sorbed diesel molecules but not by the contact time.