IOP Conference Series Materials Science and Engineering
Recently, in-situ observations were carried out by synchrotron X-ray radiography to observe the n... more Recently, in-situ observations were carried out by synchrotron X-ray radiography to observe the nucleation and growth in Al alloys during solidification. The nucleation and grain formation of a range of Al-Si and Al-Cu binary alloys were studied. When grain refiner was added to the alloys, the location of the nucleation events was readily observed. Once nucleation began it continued to occur in a wave of events with the movement of the temperature gradient across the field of view due to cooling. Other features observed were the settling of the primary phase grains in the Al-Si alloys and floating in the Al-Cu alloys, the effects of convection with marked fluctuation of the growth rate of the solid-liquid interface in the Al-Si alloys, and an absence of fragmentation. The microstructures are typical of those produced in the equiaxed zone of actual castings. These observations are compared with predictions arising from the Interdependence model. The results from this comparison have ...
ABSTRACT Vacuum deposited polymer-nanocomposites (PNCs) comprising alternate layers of metal (Al/... more ABSTRACT Vacuum deposited polymer-nanocomposites (PNCs) comprising alternate layers of metal (Al/Ag) (filler) and polymer (nylon-6) (matrix) have been investigated using chemical, impedance spectroscopy and microstructural characterisation techniques. Electron microscopy investigations revealed the morphology, nanostructure and phases of nano-scale core (metal)-shell (oxide) particles and metallic nano-islands in Al and Ag based PNCs respectively. Evaporation of Al yielded islands of angular core-shell nanoparticles in an Al-oxide/nylon-6 matrix whereas Ag yielded rounded, discrete nanoparticles in nylon-6 matrix. The high particle surface area and an affinity for oxygen formed oxide shells in Al nanoparticles and was critical to charge accumulation and enhanced dielectric behaviour; in contrast, Ag showed little oxidation and less charge accumulation. With an increase in the thickness of the deposited metal layer, Al formed a continuous film of particles whereas Ag condensed to form interconnected nano-islands. This microstructural study is useful in conceptualising better dielectrics based on PNCs.
The operation of electronic packages under exceptionally harsh environments presents a significan... more The operation of electronic packages under exceptionally harsh environments presents a significant challenge for the microelectronics industry, for example, in down-hole, well-logging and turbo-machinery applications. High temperature Au based solders are one potential candidate for die attachment for harsh environments and is already used in limited cases. For Au-Si die bonding, some of the Si is provided by diffusion from the Si die itself. Therefore, the interfacial reaction between the Si and Au-Si thin foil solder preform is a key factor in the control of the die bonding process. Unfortunately, during the die bonding process, defects such as voids, delaminations, and impurities are not unusual. These defects are caused by the assembly process, chemical impurities, soldering reactions, and thermal stresses. Understanding these defects is critical for the reliable performance of the devices after bonding. In this paper, optimization of the Au-Si eutectic die bonding has been perf...
A general computing framework was developed for solving the coupled non-linear phase field equati... more A general computing framework was developed for solving the coupled non-linear phase field equations in 3-D. The key components of the computing architecture comprises of the block structure adaptive mesh refinement (AMR) and distributed parallel computing scheme. Numerical tests on mesh adaptivity and parallel efficiency were performed by solving the 3-D phase field equations for dendrite growth and the computing capability was fully addressed by solving equiaxed and columnar multi-dendrite growth with random orientations. In addition, simulation of isothermal dendritic coarsening was performed and it was shown that by employing the parallel-AMR computing scheme, phase field simulations with comparable scales in both space and time to that of the real materials were realized and various insights into key aspects of competitive growth and coarsening were realized.
ABSTRACT A one-step scalable spray technique was used to fabricate solid-state supercapacitors wi... more ABSTRACT A one-step scalable spray technique was used to fabricate solid-state supercapacitors with multi-wall carbon nanotube/TiO2-nanoparticle/ionomer hybrid electrodes. The 3D electrode nanostructure was designed for mobile H+ ion generation and fast electron-ion dual conduction, achieving an unusual and highly attractive balance of energy (31.8 W h kg−1) and power (14.9 kW kg−1) densities at 1 A g−1 that are amongst highest reported for solid-state supercapacitors.
ABSTRACT Spray forming produces cast microstructures with comparatively low macro- and micro-stru... more ABSTRACT Spray forming produces cast microstructures with comparatively low macro- and micro-structural chemical segregation and is thus well-suited for the manufacture of complex chemistry, multi-component alloys that otherwise show strong elemental segregation. Although spray formed Ni superalloys have shown properties equivalent or superior to their conventionally cast/wrought counterparts, they have not been adopted commercially because of the difficulties in ensuring a high process yield and the complexity and associated cost of large-scale Ni superalloy melting. In this paper, we describe a hybrid arc spray forming (HASF) process in which costly, large-scale alloy melting as pre-cursor to spray forming is avoided by the use of a consumable wire feedstock. To achieve thermal conditions of melt spray forming – essential to produce a refined, polygonal grain structure – a customised secondary atomisation system has been developed. Fe-0.8 wt%C and Ni superalloy IN617 microstructures and preliminary mechanical properties suggested that hybrid arc spray forming may offer an attractive combination of convenience, low cost and mechanical performance.
Aqueous suspensions of multi-wall carbon nanotubes (MWNTs) in dilute H2SO4 were sprayed onto both... more Aqueous suspensions of multi-wall carbon nanotubes (MWNTs) in dilute H2SO4 were sprayed onto both sides of a Nafion membrane and dried to fabricate flexible solid-state supercapacitors. A single cell with MWNT-only electrodes had a capacitance of 57 F g(-1) per electrode at 2 mV s(-1) and 44 F g(-1) at 150 mV s(-1) but with low H(+) mobility. Cells with MWNT + ionomer hybrid electrodes showed higher H(+) mobility, and the electric double layer (EDL) capacitance increased to 145 F g(-1) at 2 mV s(-1) and 91 F g(-1) at 150 mV s(-1). The energy and power densities of one electrode charged to 1 V at 1 A g(-1) were 12.9 Wh kg(-1) and 3.3 kW kg(-1) respectively. Three solid-state supercapacitor cells connected in series charged to 3 V at 1 and 2 A g(-1) provided a device power density of 8.9 kW kg(-1) at 1 A g(-1) and 9.4 kW kg(-1) at 2 A g(-1), the highest for all-solid-state EDL supercapacitors.
We present a detailed study of the evolution and nature of metallic core-oxide shell particles an... more We present a detailed study of the evolution and nature of metallic core-oxide shell particles and the role of nanostructure in the physics of enhanced polarization in polymer-nanocomposite (PNC) based dielectrics. Nylon-6 based PNCs consisting of aluminium (core)-aluminium oxide (shell) nanoparticles were fabricated by a vacuum deposition technique. Their resulting high polarizability was closely related to the formation and chemistry of the core-shell structure that was revealed by transmission electron microscopy to comprise a highly-defective, strained and non-stoichiometric semi-crystalline/amorphous Al-oxide shell.
IOP Conference Series Materials Science and Engineering
Recently, in-situ observations were carried out by synchrotron X-ray radiography to observe the n... more Recently, in-situ observations were carried out by synchrotron X-ray radiography to observe the nucleation and growth in Al alloys during solidification. The nucleation and grain formation of a range of Al-Si and Al-Cu binary alloys were studied. When grain refiner was added to the alloys, the location of the nucleation events was readily observed. Once nucleation began it continued to occur in a wave of events with the movement of the temperature gradient across the field of view due to cooling. Other features observed were the settling of the primary phase grains in the Al-Si alloys and floating in the Al-Cu alloys, the effects of convection with marked fluctuation of the growth rate of the solid-liquid interface in the Al-Si alloys, and an absence of fragmentation. The microstructures are typical of those produced in the equiaxed zone of actual castings. These observations are compared with predictions arising from the Interdependence model. The results from this comparison have ...
ABSTRACT Vacuum deposited polymer-nanocomposites (PNCs) comprising alternate layers of metal (Al/... more ABSTRACT Vacuum deposited polymer-nanocomposites (PNCs) comprising alternate layers of metal (Al/Ag) (filler) and polymer (nylon-6) (matrix) have been investigated using chemical, impedance spectroscopy and microstructural characterisation techniques. Electron microscopy investigations revealed the morphology, nanostructure and phases of nano-scale core (metal)-shell (oxide) particles and metallic nano-islands in Al and Ag based PNCs respectively. Evaporation of Al yielded islands of angular core-shell nanoparticles in an Al-oxide/nylon-6 matrix whereas Ag yielded rounded, discrete nanoparticles in nylon-6 matrix. The high particle surface area and an affinity for oxygen formed oxide shells in Al nanoparticles and was critical to charge accumulation and enhanced dielectric behaviour; in contrast, Ag showed little oxidation and less charge accumulation. With an increase in the thickness of the deposited metal layer, Al formed a continuous film of particles whereas Ag condensed to form interconnected nano-islands. This microstructural study is useful in conceptualising better dielectrics based on PNCs.
The operation of electronic packages under exceptionally harsh environments presents a significan... more The operation of electronic packages under exceptionally harsh environments presents a significant challenge for the microelectronics industry, for example, in down-hole, well-logging and turbo-machinery applications. High temperature Au based solders are one potential candidate for die attachment for harsh environments and is already used in limited cases. For Au-Si die bonding, some of the Si is provided by diffusion from the Si die itself. Therefore, the interfacial reaction between the Si and Au-Si thin foil solder preform is a key factor in the control of the die bonding process. Unfortunately, during the die bonding process, defects such as voids, delaminations, and impurities are not unusual. These defects are caused by the assembly process, chemical impurities, soldering reactions, and thermal stresses. Understanding these defects is critical for the reliable performance of the devices after bonding. In this paper, optimization of the Au-Si eutectic die bonding has been perf...
A general computing framework was developed for solving the coupled non-linear phase field equati... more A general computing framework was developed for solving the coupled non-linear phase field equations in 3-D. The key components of the computing architecture comprises of the block structure adaptive mesh refinement (AMR) and distributed parallel computing scheme. Numerical tests on mesh adaptivity and parallel efficiency were performed by solving the 3-D phase field equations for dendrite growth and the computing capability was fully addressed by solving equiaxed and columnar multi-dendrite growth with random orientations. In addition, simulation of isothermal dendritic coarsening was performed and it was shown that by employing the parallel-AMR computing scheme, phase field simulations with comparable scales in both space and time to that of the real materials were realized and various insights into key aspects of competitive growth and coarsening were realized.
ABSTRACT A one-step scalable spray technique was used to fabricate solid-state supercapacitors wi... more ABSTRACT A one-step scalable spray technique was used to fabricate solid-state supercapacitors with multi-wall carbon nanotube/TiO2-nanoparticle/ionomer hybrid electrodes. The 3D electrode nanostructure was designed for mobile H+ ion generation and fast electron-ion dual conduction, achieving an unusual and highly attractive balance of energy (31.8 W h kg−1) and power (14.9 kW kg−1) densities at 1 A g−1 that are amongst highest reported for solid-state supercapacitors.
ABSTRACT Spray forming produces cast microstructures with comparatively low macro- and micro-stru... more ABSTRACT Spray forming produces cast microstructures with comparatively low macro- and micro-structural chemical segregation and is thus well-suited for the manufacture of complex chemistry, multi-component alloys that otherwise show strong elemental segregation. Although spray formed Ni superalloys have shown properties equivalent or superior to their conventionally cast/wrought counterparts, they have not been adopted commercially because of the difficulties in ensuring a high process yield and the complexity and associated cost of large-scale Ni superalloy melting. In this paper, we describe a hybrid arc spray forming (HASF) process in which costly, large-scale alloy melting as pre-cursor to spray forming is avoided by the use of a consumable wire feedstock. To achieve thermal conditions of melt spray forming – essential to produce a refined, polygonal grain structure – a customised secondary atomisation system has been developed. Fe-0.8 wt%C and Ni superalloy IN617 microstructures and preliminary mechanical properties suggested that hybrid arc spray forming may offer an attractive combination of convenience, low cost and mechanical performance.
Aqueous suspensions of multi-wall carbon nanotubes (MWNTs) in dilute H2SO4 were sprayed onto both... more Aqueous suspensions of multi-wall carbon nanotubes (MWNTs) in dilute H2SO4 were sprayed onto both sides of a Nafion membrane and dried to fabricate flexible solid-state supercapacitors. A single cell with MWNT-only electrodes had a capacitance of 57 F g(-1) per electrode at 2 mV s(-1) and 44 F g(-1) at 150 mV s(-1) but with low H(+) mobility. Cells with MWNT + ionomer hybrid electrodes showed higher H(+) mobility, and the electric double layer (EDL) capacitance increased to 145 F g(-1) at 2 mV s(-1) and 91 F g(-1) at 150 mV s(-1). The energy and power densities of one electrode charged to 1 V at 1 A g(-1) were 12.9 Wh kg(-1) and 3.3 kW kg(-1) respectively. Three solid-state supercapacitor cells connected in series charged to 3 V at 1 and 2 A g(-1) provided a device power density of 8.9 kW kg(-1) at 1 A g(-1) and 9.4 kW kg(-1) at 2 A g(-1), the highest for all-solid-state EDL supercapacitors.
We present a detailed study of the evolution and nature of metallic core-oxide shell particles an... more We present a detailed study of the evolution and nature of metallic core-oxide shell particles and the role of nanostructure in the physics of enhanced polarization in polymer-nanocomposite (PNC) based dielectrics. Nylon-6 based PNCs consisting of aluminium (core)-aluminium oxide (shell) nanoparticles were fabricated by a vacuum deposition technique. Their resulting high polarizability was closely related to the formation and chemistry of the core-shell structure that was revealed by transmission electron microscopy to comprise a highly-defective, strained and non-stoichiometric semi-crystalline/amorphous Al-oxide shell.
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Papers by Patrick Grant