Highly ordered vertically grown zinc oxide nanorods (ZnO NRs) were synthesized on ZnO-coated SiO2/Si substrate using zinc acetylacetonate hydrate as a precursor via a simple hydrothermal method at 85 °C. We used 0.05 M of ZnO solution to facilitate the growth of ZnO NRs and the immersion time was varied from 0.5 to 4 h. The atomic force microscopy revealed the surface roughness of ZnO seed layer used to grow the ZnO NRs. The morphology of vertically grown ZnO NRs was observed by field emission scanning electron microscopy. X-ray diffraction examination and transmission electron microscopy confirmed that the structure of highly ordered ZnO NRs was crystalline with a strong (002) peak corresponded to ZnO hexagonal wurtzite structure. The growth of highly ordered ZnO NRs was favorable due to the continuous supply of Zn2+ ions and chelating agents properties obtained from the acetylacetonate-derived precursor during the synthesis. Two-point probe current-voltage measurement and UV-vis spectroscopy of the ZnO NRs indicated a resistivity and optical bandgap value of 0.44 Ω.cm and 3.35 eV, respectively. The photoluminescence spectrum showed a broad peak centered at 623 nm in the visible region corresponded to the oxygen vacancies from the ZnO NRs. This study demonstrates that acetylacetonate-derived precursors can be used for the production of ZnO NRs-based devices with a potential application in biosensors.
The preparation of polystyrene/thermoplastic starch (PS/TPS) blends was divided into three stages. The first stage involved the preparation of TPS from sago starch. Then, for the second stage, PS was blended with TPS to produce a TPS/PS blend. The ratios of the TPS/PS blend were 20:80, 40:60, 60:40, and 80:20. The final stage was a modification of the composition of TPS/PS blends with succinic anhydride and ascorbic acid treatment. Both untreated and treated blends were characterized by their physical, thermal, and surface morphology properties. The obtained results indicate that modified blends have better tensile strength as the adhesion between TPS and PS was improved. This can be observed from SEM micrographs, as modified blends with succinic anhydride and ascorbic acid had smaller TPS dispersion in PS/TPS blends. The micrograph showed that there was no agglomeration and void formation in the TPS/PS blending process. Furthermore, modified blends show better thermal stability, as proved by thermogravimetric analysis. Water uptake into the TPS/PS blends also decreased after the modifications, and the structural analysis showed the formation of a new peak after the modification process.
In recent years considerable attention has been attracted to magnesium because of its light weight, high specific strength, and ease of recycling. Because of the growing demand for lightweight materials in aerospace, medical and automotive industries, magnesium-based metal matrix nanocomposites (MMNCs) reinforced with ceramic nanometer-sized particles, graphene nanoplatelets (GNPs) or carbon nanotubes (CNTs) were developed. CNTs have excellent material characteristics like low density, high tensile strength, high ratio of surface-to-volume, and high thermal conductivity that makes them attractive to use as reinforcements to fabricate high-performance, and high-strength metal-matrix composites (MMCs). Reinforcing magnesium (Mg) using small amounts of CNTs can improve the mechanical and physical properties in the fabricated lightweight and high-performance nanocomposite. Nevertheless, the incorporation of CNTs into a Mg-based matrix faces some challenges, and a uniform distribution is dependent on the parameters of the fabricating process. The characteristics of a CNTs reinforced composite are related to the uniform distribution, weight percent, and length of the CNTs, as well as the interfacial bonding and alignment between CNTs reinforcement and the Mg-based matrix. In this review article, the recent findings in the fabricating methods, characterization of the composite's properties, and application of Mg-based composites reinforced with CNTs are studied. These include the strategies of fabricating CNT-reinforced Mg-based composites, mechanical responses, and corrosion behaviors. The present review aims to investigate and conclude the most relevant studies conducted in the field of Mg/CNTs composites. Strategies to conquer complicated challenges are suggested and potential fields of Mg/CNTs composites as upcoming structural material regarding functional requirements in aerospace, medical and automotive industries are particularly presented.
This work investigates the structural formation and analyses of titania membranes (TM) prepared using different vacuum exposure times for molecular weight (MW) cut-off performance and oil/water separation. Titania membranes were synthesized via a sol-gel method and coated on macroporous alumina tubes followed by exposure to a vacuum between 30 and 1200 s and then calcined at 400 °C. X-ray diffraction and nitrogen adsorption analyses showed that the crystallite size and particle size of titania increased as a function of vacuum time. All the TM membranes were mesoporous with an average pore diameter of ~3.6 nm with an anatase crystal morphology. Water, glucose, sucrose, and polyvinylpyrrolidone with 40 and 360 kDa (PVP-40 kDa and PVP-360 kDa) were used as feed solutions for MW cut-off and hexadecane solution for oil filtration investigation. The TM membranes were not able to separate glucose and sucrose, thus indicating the membrane pore sizes are larger than the kinetic diameter of sucrose of 0.9 nm, irrespective of vacuum exposure time. They also showed only moderate rejection (20%) of the smaller PVP-40 kDa, however, all the membranes were able to obtain an excellent rejection of near 100% for the larger PVP-360 kDa molecule. Furthermore, the TM membranes were tested for the separation of oil emulsions with a high concentration of oil (3000 ppm), reaching high oil rejections of more than 90% of oil. In general, the water fluxes increased with the vacuum exposure time indicating a pore structural tailoring effect. It is therefore proposed that a mechanism of pore size tailoring was formed by an interconnected network of Ti-O-Ti nanoparticles with inter-particle voids, which increased as TiO₂ nanoparticle size increased as a function of vacuum exposure time, and thus reduced the water transport resistance through the TM membranes.
The fourth rail transit is an interesting topic to be shared and accessed by the community within that area of expertise. Several ongoing works are currently being conducted especially in the aspects of system technical performances including the rail bracket component and the sensitivity analyses on the various rail designs. Furthermore, the lightning surge study on railway electrification is significant due to the fact that only a handful of publications are available in this regard, especially on the fourth rail transit. For this reason, this paper presents a study on the electrical performance of a fourth rail Direct Current (DC) urban transit affected by an indirect lightning strike. The indirect lightning strike was modelled by means of the Rusck model and the sum of two Heidler functions. The simulations were carried out using the EMTP-RV software which included the performance comparison of polymer-insulated rail brackets, namely the Cast Epoxy (CE), the Cycloaliphatic Epoxy A (CEA), and the Glass Reinforced Plastic (GRP) together with the station arresters when subjected by 30 kA (5/80 µs) and 90 kA (9/200 µs) lightning currents. The results obtained demonstrated that the GRP material has been able to slightly lower its induced overvoltage as compared to other materials, especially for the case of 90 kA (9/200 µs), and thus serves better coordination with the station arresters. This improvement has also reflected on the recorded residual voltage and energy absorption capacity of the arrester, respectively.
The demand for composite materials in high-voltage electrical insulation is escalating over the last decades. In the power system, the composite glass-fiber-reinforced polymer has been used as an alternative to wood and steel crossarm structures due to its superior properties. As a composite, the material is susceptible to multi-aging factors, one of which is the electrical stress caused by continuous and temporary overvoltage. In order to achieve a better insulation performance and higher life expectancy, the distribution of the stresses should firstly be studied and understood. This paper focuses on the simulation work to better understand the stress distribution of the polyurethane foam-filled glass-fiber-reinforced polymer crossarm due to the lightning transient injection. A finite-element-based simulation was carried out to investigate the behavior of the electric field and voltage distribution across the sample using an Ansys Maxwell 3D. Electrical stresses at both outer and inner surfaces of the crossarm during the peak of lightning were analyzed. Analyses on the electric field and potential distribution were performed at different parts of the crossarm and correlated to the physical characteristics and common discharge location observed during the experiment. The results of the electric field on the crossarm indicate that both the outer and internal parts of the crossarm were prone to high field stress.
Previous works have shown that wearable antennas can operate ideally in free space; however, degradation in performance, specifically in terms of frequency shifts and efficiency was observed when an antenna structure was in close proximity to the human body. These issues have been highlighted many times yet, systematic and numerical analysis on how the dielectric characteristics may affect the technical behavior of the antenna has not been discussed in detail. In this paper, a wearable antenna, developed from a new electro-textile material has been designed, and the step-by-step manufacturing process is presented. Through analysis of the frequency detuning effect, the on-body behavior of the antenna is evaluated by focusing on quantifying the changes of its input impedance and near-field distribution caused by the presence of lossy dielectric material. When the antenna is attached to the top of the body fat phantom, there is an increase of 17% in impedance, followed by 19% for the muscle phantom and 20% for the blood phantom. These phenomena correlate with the electric field intensities (V/m) observed closely at the antenna through various layers of mediums (z-axis) and along antenna edges (y-axis), which have shown significant increments of 29.7% in fat, 35.3% in muscle and 36.1% in blood as compared to free space. This scenario has consequently shown that a significant amount of energy is absorbed in the phantoms instead of radiated to the air which has caused a substantial drop in efficiency and gain. Performance verification is also demonstrated by using a fabricated human muscle phantom, with a dielectric constant of 48, loss tangent of 0.29 and conductivity of 1.22 S/m.
Efficient solar driven photoelectrochemical (PEC) response by enhancing charge separation has attracted great interest in the hydrogen generation application. The formation of one-dimensional ZnO nanorod structure without bundling is essential for high efficiency in PEC response. In this present research work, ZnO nanorod with an average 500 nm in length and average diameter of about 75 nm was successfully formed via electrodeposition method in 0.05 mM ZnCl₂ and 0.1 M KCl electrolyte at 1 V for 60 min under 70 °C condition. Continuous efforts have been exerted to further improve the solar driven PEC response by incorporating an optimum content of TiO₂ into ZnO nanorod using dip-coating technique. It was found that 0.25 at % of TiO₂ loaded on ZnO nanorod film demonstrated a maximum photocurrent density of 19.78 mA/cm² (with V vs. Ag/AgCl) under UV illumination and 14.75 mA/cm² (with V vs. Ag/AgCl) under solar illumination with photoconversion efficiency ~2.9% (UV illumination) and ~4.3% (solar illumination). This performance was approximately 3-4 times higher than ZnO film itself. An enhancement of photocurrent density and photoconversion efficiency occurred due to the sufficient Ti element within TiO₂-ZnO nanorod film, which acted as an effective mediator to trap the photo-induced electrons and minimize the recombination of charge carriers. Besides, phenomenon of charge-separation effect at type-II band alignment of Zn and Ti could further enhance the charge carrier transportation during illumination.
This study intended to address the problem of damaged (collapsed, cracked and decreased soil strength) road pavement structure built on clay soil due to clay soil properties such as low shear strength, high soil compressibility, low soil permeability, low soil strength, and high soil plasticity. Previous research reported that ground granulated blast slag (GGBS) and fly ash can be used for clay soil stabilizations, but the results of past research indicate that the road pavement construction standards remained unfulfilled, especially in terms of clay's subgrade soil. Due to this reason, this study is carried out to further investigate soil stabilization using GGBS and fly ash-based geopolymer processes. This study investigates the effects of GGBS and ratios of fly ash (solid) to alkaline activator (liquid) of 1:1, 1.5:1, 2:1, 2.5:1, and 3:1, cured for 1 and 7 days. The molarity of sodium hydroxide (NaOH) and the ratio of sodium silicate (Na2SiO3) to sodium hydroxide (NaOH) was fixed at 10 molar and 2.0 weight ratio. The mechanical properties of the soil stabilization based geopolymer process were tested using an unconfined compression test, while the characterization of soil stabilization was investigated using the plastic limit test, liquid limit test, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results showed that the highest strength obtained was 3.15 MPA with a GGBS to alkaline activator ratio of 1.5 and Na2SiO3 to NaOH ratio of 2.0 at 7 days curing time. These findings are useful in enhancing knowledge in the field of soil stabilization-based geopolymer, especially for applications in pavement construction. In addition, it can be used as a reference for academicians, civil engineers, and geotechnical engineers.
Carbon-based particles, such as graphite and graphene, have been widely used as a filler in magnetorheological elastomer (MRE) fabrication in order to obtain electrical properties of the material. However, these kinds of fillers normally require a very high concentration of particles to enhance the conductivity property. Therefore, in this study, the nanosized Ni-Mg cobalt ferrite is introduced as a filler to soften MRE and, at the same time, improve magnetic, rheological, and conductivity properties. Three types of MRE samples without and with different compositions of Mg, namely Co0.5Ni0.2Mg0.3Fe2O4 (A1) and Co0.5Ni0.1Mg0.4Fe2O4 (A2), are fabricated. The characterization related to the micrograph, magnetic, and rheological properties of the MRE samples are analyzed using scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and the rheometer. Meanwhile, the effect of the nanosized Ni-Mg cobalt ferrites on the electrical resistance property is investigated and compared with the different Mg compositions. It is shown that the storage modulus of the MRE sample with the nanosized Ni-Mg cobalt ferrites is 43% higher than that of the MRE sample without the nanomaterials. In addition, it is demonstrated that MREs with the nanosized Ni-Mg cobalt ferrites exhibit relatively low electrical resistance at the on-state as compared to the off-state condition, because MRE with a higher Mg composition shows lower electrical resistance when higher current flow occurs through the materials. This salient property of the proposed MRE can be effectively and potentially used as an actuator to control the viscoelastic property of the magnetic field or sensors to measure the strain of the flexible structures by the electrical resistance signal.
This paper presents the mechanical and microstructural characteristics of a lightweight aggregate geopolymer concrete (LWAGC) synthesized by the alkali-activation of a fly ash source (FA) before and after being exposed to elevated temperatures, ranging from 100 to 800 °C. The results show that the LWAGC unexposed to the elevated temperatures possesses a good strength-to-weight ratio compared with other LWAGCs available in the published literature. The unexposed LWAGC also shows an excellent strength development versus aging times, up to 365 days. For the exposed LWAGC to the elevated temperatures of 100 to 800 °C, the results illustrate that the concretes gain compressive strength after being exposed to elevated temperatures of 100, 200 and 300 °C. Afterward, the strength of the LWAGC started to deteriorate and decrease after being exposed to elevated temperatures of 400 °C, and up to 800 °C. Based on the mechanical strength results of the exposed LWAGCs to elevated temperatures of 100 °C to 800 °C, the relationship between the exposure temperature and the obtained residual compressive strength is statistically analyzed and achieved. In addition, the microstructure investigation of the unexposed LWAGC shows a good bonding between aggregate and mortar at the interface transition zone (ITZ). However, this bonding is subjected to deterioration as the LWAGC is exposed to elevated temperatures of 400, 600 and 800 °C by increasing the microcrack content and swelling of the unreacted silicates.
Aggregates can be categorized into natural and artificial aggregates. Preserving natural resources is crucial to ensuring the constant supply of natural aggregates. In order to preserve these natural resources, the production of artificial aggregates is beginning to gain the attention of researchers worldwide. One of the methods involves using geopolymer technology. On this basis, this current research focuses on the inter-particle effect on the properties of fly ash geopolymer aggregates with different molarities of sodium hydroxide (NaOH). The effects of synthesis parameters (6, 8, 10, 12, and 14 M) on the mechanical and microstructural properties of the fly ash geopolymer aggregate were studied. The fly ash geopolymer aggregate was palletized manually by using a hand to form a sphere-shaped aggregate where the ratio of NaOH/Na2SiO3 used was constant at 2.5. The results indicated that the NaOH molarity has a significant effect on the impact strength of a fly ash geopolymer aggregate. The highest aggregate impact value (AIV) was obtained for samples with 6 M NaOH molarity (26.95%), indicating the lowest strength among other molarities studied and the lowest density of 2150 kg/m3. The low concentration of sodium hydroxide in the alkali activator solution resulted in the dissolution of fly ash being limited; thus, the inter-particle volume cannot be fully filled by the precipitated gels.
The utilisation of rice husk ash (RHA) as an aluminosilicate source in fire-resistant coating could reduce environmental pollution and can turn agricultural waste into industrial wealth. The overall objective of this research is to develop a rice-husk-ash-based geopolymer binder (GB) fire-retardant additive (FR) for alkyd paint. Response surface methodology (RSM) was used to design the experiments work, on the ratio of RHA-based GB to alkyd paint. The microstructure behaviour and material characterisation of the coating samples were studied through SEM analysis. The optimal RHA-based GB FR additive was formulated at 50% wt. FR and 82.628% wt. paint. This formulation showed the result of 270 s to reach 200 °C and 276 °C temperature at equilibrium for thermal properties. Furthermore, it was observed that the increased contents of RHA showed an increment in terms of the total and open porosities and rough surfaces, in which the number of pores on the coating surface plays an important role in the formation of the intumescent char layer. By developing the optimum RHA-based GB to paint formulation, the coating may potentially improve building fire safety through passive fire protection.
We report the crystallization of electrodeposited germanium (Ge) thin films on n-silicon (Si) (100) by rapid melting process. The electrodeposition was carried out in germanium (IV) chloride: propylene glycol (GeCl₄:C₃H₈O₂) electrolyte with constant current of 50 mA for 30 min. The measured Raman spectra and electron backscattering diffraction (EBSD) images show that the as-deposited Ge thin film was amorphous. The crystallization of deposited Ge was achieved by rapid thermal annealing (RTA) at 980 °C for 1 s. The EBSD images confirm that the orientations of the annealed Ge are similar to that of the Si substrate. The highly intense peak of Raman spectra at 300 cm(-1) corresponding to Ge-Ge vibration mode was observed, indicating good crystal quality of Ge. An additional sub peak near to 390 cm(-1) corresponding to the Si-Ge vibration mode was also observed, indicating the Ge-Si mixing at Ge/Si interface. Auger electron spectroscopy (AES) reveals that the intermixing depth was around 60 nm. The calculated Si fraction from Raman spectra was found to be in good agreement with the value estimated from Ge-Si equilibrium phase diagram. The proposed technique is expected to be an effective way to crystallize Ge films for various device applications as well as to create strain at the Ge-Si interface for enhancement of mobility.
The effects of annealing temperatures on composition and strain in Si x Ge1-x, obtained by rapid melting growth of electrodeposited Ge on Si (100) substrate were investigated. Here, a rapid melting process was performed at temperatures of 1000, 1050 and 1100 °C for 1 s. All annealed samples show single crystalline structure in (100) orientation. A significant appearance of Si-Ge vibration mode peak at ~400 cm-1 confirms the existence of Si-Ge intermixing due to out-diffusion of Si into Ge region. On a rapid melting process, Ge melts and reaches the thermal equilibrium in short time. Si at Ge/Si interface begins to dissolve once in contact with the molten Ge to produce Si-Ge intermixing. The Si fraction in Si-Ge intermixing was calculated by taking into account the intensity ratio of Ge-Ge and Si-Ge vibration mode peaks and was found to increase with the annealing temperatures. It is found that the strain turns from tensile to compressive as the annealing temperature increases. The Si fraction dependent thermal expansion coefficient of Si x Ge1-x is a possible cause to generate such strain behavior. The understanding of compositional and strain characteristics is important in Ge/Si heterostructure as these properties seem to give significant effects in device performance.
This present study evaluates the effect of silica modulus (Ms) and curing temperature on strengths and the microstructures of binary blended alkali-activated volcanic ash and limestone powder mortar. Mortar samples were prepared using mass ratio of combined Na2SiO3(aq)/10 M NaOH(aq) of 0.5 to 1.5 at an interval of 0.25, corresponding to Ms of 0.52, 0.72, 0.89, 1.05 and 1.18, respectively, and sole 10 M NaOH(aq). Samples were then subjected to ambient room temperature, and the oven-cured temperature was maintained from 45 to 90 °C at an interval of 15 °C for 24 h. The maximum achievable 28-day strength was 27 MPa at Ms value of 0.89 cured at 75 °C. Samples synthesised with the sole 10 M NaOH(aq) activator resulted in a binder with a low 28-day compressive strength (15 MPa) compared to combined usage of Na2SiO3(aq)/10 M NaOH(aq) activators. Results further revealed that curing at low temperatures (25 °C to 45 °C) does not favour strength development, whereas higher curing temperature positively enhanced strength development. More than 70% of the 28-day compressive strength could be achieved within 12 h of curing with the usage of combined Na2SiO3(aq)/10 M NaOH(aq). XRD, FTIR and SEM + EDX characterisations revealed that activation with combined Na2SiO3(aq)/10 M NaOH(aq) leads to the formation of anorthite (CaAl2Si2O8), gehlenite (CaO.Al2O3.SiO2) and albite (NaAlSi3O8) that improve the amorphosity, homogeneity and microstructural density of the binder compared to that of samples synthesised with sole 10 M NaOH(aq).
In this study, simultaneous adsorption of cationic dyes was investigated by using binary component solutions. Thiourea-modified poly(acrylonitrile-co-acrylic acid) (TMPAA) polymer was used as an adsorbent for uptake of cationic dyes (malachite green, MG and methylene blue, MB) from aqueous solution in a binary system. Adsorption tests revealed that TMPAA presented high adsorption of MG and MB at higher pH and higher dye concentrations. It suggested that there are strong electrostatic attractions between the surface functional groups of the adsorbent and cationic dyes. The equilibrium analyses explain that both extended Langmuir and extended models are suitable for the description of adsorption data in the binary system. An antagonistic effect was found, probably due to triangular (MG) and linear (MB) molecular structures that mutually hinder the adsorption of both dyes on TMPAA. Besides, the kinetic studies for sorption of MG and MB dyes onto adsorbent were better represented by a pseudo-second-order model, which demonstrates chemisorption between the polymeric TMPAA adsorbent and dye molecules. According to experimental findings, TMPAA is an attractive adsorbent for treatment of wastewater containing multiple cationic dyes.
Melting aluminium waste to produce a secondary bulk material is such an energy-intensive recycling technique that it also indirectly threatens the environment. Hot press forging is introduced as an alternative. Mixing the waste with another substance is a proven practice that enhances the material integrity. To cope with the technology revolution, a finite element is utilised to predict the behaviour without a practical trial. Utilising commercial software, DEFORM 3D, the conjectures were demonstrated scientifically. The flow stress of the material was modified to suit the material used in the actual experiment. It is acknowledged that the stress⁻strain had gradually increased in each step. Due to the confined forming space, the temperature decreased by ~0.5% because the heat could not simply vacate the area. A reduction of ~10% of the flesh observed in the simulation is roughly the same as in the actual experiment. Above all, the simulation abides by the standards and follows what has been done previously. Through the finite element utilisation, this study forecasted the performance of the recycled composite. The results presented may facilitate improvement of the recycling issue and conserve the environment for a better future.
Solid-state recycling, which involves the direct recycling of scrap metal into bulk material using severe plastic deformation, has emerged as a potential alternative to the conventional remelting and recycling techniques. Hot press forging has been identified as a sustainable direct recycling technique that has fewer steps and maintains excellent material performance. An experimental investigation was conducted to explore the hardness and density of a recycled aluminum-based metal matrix composite by varying operating temperature and holding time. A mixture of recycled aluminum, AA6061, and aluminum oxide were simultaneously heated to 430, 480, and 530 °C and forged for 60, 90, and 120 min. We found a positive increase in microhardness and density for all composites. The hardness increased approximately 33.85%, while density improved by about 15.25% whenever the temperature or the holding time were increased. Based on qualitative analysis, the composite endures substantial plastic deformation due to the presence of hardness properties due to the aluminum oxide embedded in the aluminum matrix. These increases were significantly affected by the operating temperature; the holding time also had a subordinate role in enhancing the metal matrix composite properties. Furthermore, in an effort to curb the shortage of primary resources, this study reviewed the promising performance of secondary resources produced by using recycled aluminum and aluminum oxide as the base matrix and reinforcement constituent, respectively. This study is an outline for machining practitioners and the manufacturing industry to help increase industry sustainability with the aim of preserving the Earth for our community in the future.
The primary motivation of developing ceramic materials using geopolymer method is to minimize the reliance on high sintering temperatures. The ultra-high molecular weight polyethylene (UHMWPE) was added as binder and reinforces the nepheline ceramics based geopolymer. The samples were sintered at 900 °C, 1000 °C, 1100 °C, and 1200 °C to elucidate the influence of sintering on the physical and microstructural properties. The results indicated that a maximum flexural strength of 92 MPa is attainable once the samples are used to be sintered at 1200 °C. It was also determined that the density, porosity, volumetric shrinkage, and water absorption of the samples also affected by the sintering due to the change of microstructure and crystallinity. The IR spectra reveal that the band at around 1400 cm-1 becomes weak, indicating that sodium carbonate decomposed and began to react with the silica and alumina released from gels to form nepheline phases. The sintering process influence in the development of the final microstructure thus improving the properties of the ceramic materials.