Hom Dhakal

Binder free 2D aligned efficient MnO2 micro flowers as stable electrodes for symmetric supercapacitor applications

Herein, δ-MnO2 micro-flower thin films are grown directly onto a stainless steel mesh via a simple rotational chemical bath deposition technique. Moreover, the influence of the concentration of precursor ratio of MnSO4u2006:u2006KMnO4 is investigated and the obtained samples are designated as M1 (KMnO4u2006:u2006MnSO4 = 3u2006:u20061), M2 (KMnO4u2006:u2006MnSO4 = 3u2006:u20062) and M3 (KMnO4u2006:u2006MnSO4 = 3u2006:u20063). The concentration of MnSO4 as a starting material has a significant influence on the reaction kinetics, which subsequently alters the morphology and also the electrochemical performance. Among these three electrodes, the M1 electrode exhibits a high specific capacitance of 376 F g−1 at a current density of 5 mA cm−2 and a high specific energy of 52 W h kg−1, which is higher than M2 (specific capacitance 312 F g−1 and specific energy 43 W h kg−1) and M3 (specific capacitance 283 F g−1 and specific energy 39 W h kg−1) electrodes. Due to the interesting performance of the M1 based electrode, the symmetric device is fabricated using two electrodes M1 (3u2006:u20061) and represented as SSM/M1//M1/SSM. The device provides a maximum specific capacitance of 87 F g−1 and specific energy density of 32 W h kg−1 at a current density of 5 mA cm−2. In addition, the symmetric device of the M1 electrode also exhibits good cycle stability showing 138% capacitance retention up to 2500 cycles. The enhanced electrochemical performance could be attributed to the direct growth of micro-flowers of MnO2 on a stainless steel mesh, which provides more pathways for easy diffusion of electrolyte ions into the electrode. This study provides new insight and pathways for the development of low-cost and high-performance energy storage devices.

Philosophical study on composites and their drilling techniques

Due to the advancement in the properties, design and manufacturing of fibre-reinforced polymer composite materials, especially the natural or bio-based types, their wide applications have been significantly enhanced compared to the conventional materials (metals and alloys). With this trend, there is a strong interest and importance in understanding the machinability of these materials. Machinability of these materials depends, among other parameters, on properties of fibres and matrices, drilling conditions, parameters and techniques. Among the machining operations of these composites, drilling is the most crucial and common operation. Hence, this chapter focuses on better understanding of biocomposites and various composite conventional and non-conventional drilling techniques. The primary aim of this chapter, therefore, is to provide comparative analysis between conventional and non-conventional drilling of composite materials.

The post-impact response of flax/UP composite laminates under low velocity impact loading:

Flax fibre-reinforced unsaturated polyester composite laminates were fabricated by vacuum bagging process and their impact and post-impact responses were investigated through experimental testing and finite element simulations. Samples of 60u2009mmu2009×u200960u2009mmu2009×u20096.2u2009mm were cut from the composite laminates and were subjected to a low-velocity impact loading to near perforation using hemispherical steel impactor at three different energy levels, 25, 27 and 29u2009Joules. Post-impact was employed to obtain full penetration. The impacted composite plates were modelled with various lay-ups using finite element software LS-DYNA (LS-DYNA User’s Manual 1997) to provide a validated finite element model for the future investigation in the field. The effects of impact and post-impact on the failure mechanisms were evaluated using scanning electron microscopy. Parameters measured were load bearing capability, energy absorption and damage modes. The results indicate that both peak load and the energy absorption were reduced significantly after the post-impact events. Consequently, it was observed from the visual images of the damages sites that the extent of damage increased with increased incident energy and post-impact events.

Ultrasound‐assisted green economic synthesis of hydroxyapatite nanoparticles using eggshell biowaste and study of mechanical and biological properties for orthopedic applications

Nanostructured hydroxyapatite (HAp) is the most favorable candidate biomaterial for bone tissue engineering because of its bioactive and osteoconductive properties. Herein, we report for the first time ultrasound-assisted facile and economic approach for the synthesis of nanocrystalline hydroxyapatite (Ca10 (PO4 )6 (OH)2 ) using recycled eggshell biowaste referred as EHAp. The process involves the reaction of eggshell biowaste as a source of calcium and ammonium dihydrogen orthophosphate as a phosphate source. Ultrasound-mediated chemical synthesis of hydroxyapatite (HAp) is also carried out using similar approach wherein commercially available calcium hydroxide and ammonium dihydrogen orthophosphate were used as calcium and phosphate precursors, respectively and referred as CHAp for better comparison. The prepared materials were characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy to determine crystal structure, particle morphology, and the presence of chemical functional groups. The nanocrystalline EHAp and CHAp were observed to have spherical morphology with uniform size distribution. Furthermore, mechanical properties such as Vickers hardness, fracture toughness, and compression tests have been studied of the EHAp and CHAp samples showing promising results. Mechanical properties show the influence of calcination at 600°C EHAp and CHAp material. After calcination, in the case of EHAp material an average hardness, mechanical strength, elastic modulus, and fracture toughness were found 552 MPa, 46.6 MPa, 2824 MPa, and 3.85 MPaxa0m1/2 , respectively, while in the case of CHAp 618 MPa, 47.5 MPa, 2071 MPa, and 3.13 MPaxa0m1/2 . In vitro cell studies revealed that the EHAp and CHAp nanoparticles significantly increased the attachment and proliferation of the hFOB cells. Here, we showed that EHAp and CHAp provide promising biocompatible materials that do not affect the cell viability and proliferation with enhancing the osteogenic activity of osteoblasts. Moreover, hFOB cells are found to express Osteocalcin, Osteopontin, Collagen I, Osteonectin, BMP-2 on the EHAp and CHAp bone graft. This study demonstrates the formation of pure nanocrystalline HAp with promising properties justifying the fact that the eggshell biowaste could be successfully used for the synthesis of HAp with good mechanical and osteogenic properties. These findings may have significant implications for designing of biomaterial for use in orthopedic tissue regeneration.

Finite element analysis on conventional drilling of natural fibre-reinforced polymer bio-composites

Finite element analysis (FEA) on conventional drilling of two biocomposite materials, consist of hybrid woven flax-basalt and woven basalt fibre with vinyl ester matrix, designated as composite materials A and B respectively, has been conducted. The simulation results using LS-DYNA and ANSYS software depict that different reinforcements (flax and basalt fibres) of the composite materials significantly influenced the degree of resistance, strength, deformation and elasticity exhibited during the machining process. It was observed that drillinginduced damage were experienced in different degrees by the materials. The quality of the holes produced was affected by the characteristics of these materials, when experimentally validated. Also, significant differences in tensile strength and impact of the drilling operation on the plies of the two materials were observed. Material A experienced higher stress and lower tensile strength, resulting into a higher level of push-out delamination, uncut-fibre and fibre pull-out, among other rampant drilling-induced damage, than material B. Both materials possessed high stress and deformation, which were more at the edges (entry and exit) of the drilled holes rather than the centre point where the drill impacted the hole. The equivalent elastic strain further shows a high level of impact at the surface of material A, unlike material B. Comparatively, the composite material B (woven basalt fibre reinforced polymer) has a better machinability when compared with hybrid material A (woven flax-basalt). Hence, it implies that the FRP composite materials responded to damage differently under same machining (drilling) process and condition.