Low Melting Point Materials Research Articles

Characterization of drilled hole in low melting point material during low power microwave drilling process

Drilling of micro-holes for micro-electrical-mechanical systems and its applications are critical. In present work, micro-holes are drilled on a low melting point material, perspex. Microwave energy is used to drill holes through thermal ablation at 2.45 GHz. The drilled holes are analysed under field emission scanning electron microscope (FESEM) based on backscattering. The experimental results show a fine drilled hole with minimum heat affected zone (HAZ) and no delamination. A smooth curve with an average diameter of 846 micron was successfully drilled on a 5 mm thick perspex sample. Surface integrity around the hole was studied by atomic force microscope (AFM) through Ra, Rp, Rz, Rv, Rt, Rku and Rq values. AFM is used to generate values at three variants as near to hole, at average HAZ and at the end of HAZ boundary. Energy dispersive spectroscopy (EDS) is used to study the material degradation in terms of changes in composition at five different zones. The Vickers hardness tester at Hv0.05 was used to understand the hardness variation at three regions of HAZ. The XRD analysis was used to confirm the formation of the crystalline surface around the amorphous hole. The customised process is developed in-house to study the performance of microwave power, drill time, ablation, residue and (HAZ). The results confirm enhanced drilling of the hole at low power (90 W) by a steel alloy concentrator, which otherwise worsens with an increase of power beyond 180 W without significant variation in HAZ beyond 360 W.

Corrosion of MgAl<sub>2</sub>O<sub>4 </sub>Spinel with Different Al<sub>2</sub>O<sub>3</sub> Contents in Iron-Containing Gasifier Slag

The MgAl2O4 spinel ceramic specimens with five different alumina contents ( w(Al2O3)=66%,72%,78%,85%,90%) were prepared using alumina micropowder and magnesia micropowder as raw materials, after mixing, shaping, drying, and heating at 1800 °C. The crucible specimens were tested for slag corrosion with commercial gasifier slag at 1500 °C for 2 h under oxidazing and reducing atmosphere. The specimens before and after slag test were studied by analyzing the microstructure and element distributions of corroded specimens with XRD, SEM and EDS. The results show that the slow dissolution of spinel into slag was observed because a low melting point material was formed by spinel reacting with CaO and SiO2 in slag on the surface of the spinel block. Meanwhile, FeOx in the slag was absorbed around the surface of spinel block to form the multiple solid solution, which was composed of MgO-Al2O3-FeOx and had a denser microstructure. The absorption of FeOx in slag had contributed to the resistance to slag penetration for the spinel. The relationship between the absorption capacity of spinel on FeOx and the chemical composition of spinel was discussed.

Prototyping of biodegradable flat stents in pure zinc by laser microcutting and chemical etching

Cardiovascular stents are biomedical devices, which restore normal blood flow in the case of coronary artery obstructions. Biodegradable metals provide the possibility of a less-invasive treatment, where the stent is dissolved in body fluids after remodelling of the artery. Compared to Mg- and Fe-alloys, Zn and its alloys provide optimal corrosion rates as a more recent option. New Zn-alloys are under development and often need to be tested for corrosion and biological properties. However, Zn and its alloys still require further investigation in terms of the production routes involved for stent manufacturing. Especially at a prototyping stage, the extrusion of thin biodegradable tubes is an expensive and difficult process. This work investigates a novel manufacturing route consisting of laser microcutting and chemical etching of pure Zn sheets to develop inflatable devices that can take a tubular form. Initially, laser microcutting parameters were studied to understand the dross formation on a low melting point material. Chemical etching of the material with low corrosion resistance was investigated for the dross removal. Prototype flat stents were produced and expanded using a medical catheter.

Influence of Ranque-Hilsch vortex tube and nitrogen gas assisted MQL in precision turning of Al 6061-T6

Dry machining is undesirable to produce precision surface due to thermal adversities especially for a low melting point material such as Al 6061-T6. Likewise, the conventional flood cooling is neither economically viable nor eco-friendly. In this context, three novel cooling-lubrication (C/L) technologies namely the nitrogen gas cooling (NGC), nitrogen gas assisted minimum quantity lubrication (NGMQL) and Ranque-Hilsch vortex tube (RHVT) NGMQL are investigated along with the air cooling (AC) in turning with an attempt to reduce surface roughness (Ra) and tool flank wear (VBmax). The machining was conducted using uncoated WC insert at two-levels of cutting speed and feed rate; and, as medium of cooling/lubrication the nitrogen gas and/or canola oil is employed. The SEM and 3D topographic images were analyzed for the machined surfaces, worn tool surfaces and chips. Results showed that the RHVT-NGMQL revealed the least surface roughness and tool wear (∼75% improvement compared to other C/Ls). Notable wear modes were: in dry cutting the plastic deformation, BUE and adhesion; in NGC the BUE; in NGMQL the rubbing and adhesion; in RHVT-NGMQL the adhesion. In micro-level, no significant difference in chip structure was found for the studied C/L methods In addition, the Composite Desirability optimization was adopted to systematically minimize Ra and VBmax concurrently. It was found that the optimum speed vc = 160 m/min and feed rate f = 0.06 mm/rev under RHVT-NGMQL C/L condition has the potential to generate a precision surface with a roughness value <1.0 μm.

Hydrogen production using aluminum-based materials prepared by mechanical milling

Aluminum (Al)-based materials composited of different low melting point materials were prepared by mechanical ball-milling. Hydrogen production using these materials was investigated to help resolving the safety issues associated with the storage and transportation of hydrogen. The phase composition and microstructure of the Al-based composited materials were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. As observed in this study, the addition of low melting point metals (such as Sn, Bi and In) helped to lower the initial Al-water reaction temperature and to increase the yield in the production of hydrogen. Samples of optimized compositions, Al–6% Sn–4% Bi and Al–6% Sn–4% In, were found to exhibit high hydrogen production yields of up to 448 and 515 mL, respectively. Meanwhile, their hydrogen generation rates were increased.

A New Salt‐Baked Approach for Confining Selenium in Metal Complex‐Derived Porous Carbon with Superior Lithium Storage Properties

For lithium‐selenium batteries, commercial applications are hindered by the inferior electrical conductivity of selenium and the low utilization ratio of the active selenium. Here, we report a new baked‐in‐salt approach to enable Se to better infiltrate into metal‐complex‐derived porous carbon (Se/MnMC‐B). The approach uses the confined, narrow space that is sandwiched between two compact NaCl solid disks, thus avoiding the need for protection with argon or a vacuum environment during processing. The electrochemical properties for both lithium and sodium storage of our Se/MnMC‐B cathode were found to be outstanding. For lithium storage, the Se/MnMC‐B cathode (with 72% selenium loading) exhibited a capacity of 580 mA h g−1 after 1000 cycles at 1 C, and an excellent rate capability was achieved at 20 C and 510 mA h g−1. For sodium storage, a specific capacity of 535 mA h g−1 was achieved at 0.1 C after 150 cycles. These results demonstrate the potential of this approach as a new effective general synthesis method for confining other low melting point materials into a porous carbon matrix.

Experimental investigation of Microstructure and Mechanical properties of TIG welded Aluminium alloys

Aluminium and its alloys are used in fabrication because of their low weight, good corrosion resistance and weldability. Pure aluminium is soft and therefore not suitable for structures, which require strength. The Present investigation aims to compare the mechanical properties of non-heat treatable Aluminium alloy AA5083 and heat treatable. Aluminium alloy AA7020 using Tungsten Inert Gas welding. 5556A filler were used to weld AA7020 alloy and 5183A filler for AA5083 alloy. Effect of pulsing mode over conventional mode of GTA process were also investigated for AA5083 alloy. In this work, gas tungsten arc welding process has been selected because it is low heat input process. Low heat input process has selected because AA7020 and AA5083 were low melting point material. The alternating current (AC) power source has been selected because of better cleaning action and high heat concentration on the materials can be avoided. Mechanical testing like tensile test, impact test, bend and hardness test have been critically analysed and the properties were summarized and correlating with microstructure and SEM fractographs.

Experimental Investigation of Microstructure and Mechanical Properties of TIG Welded Aluminium Alloys.

Aluminium and its alloys are used in fabrication because of their low weight, good corrosion resistance and weldability. Pure aluminium is soft and therefore not suitable for structures, which require strength. The Present investigation aims to compare the mechanical properties of non-heat treatable Aluminium alloy AA5083 and heat treatable. Aluminium alloy AA7020 using Tungsten Inert Gas welding. 5556A filler were used to weld AA7020 alloy and 5183A filler for AA5083 alloy. Effect of pulsing mode over conventional mode of GTA process were also investigated for AA5083 alloy. In this work, gas tungsten arc welding process has been selected because it is low heat input process. Low heat input process has selected because AA7020 and AA5083 were low melting point material. The alternating current (AC) power source has been selected because of better cleaning action and high heat concentration on the materials can be avoided. Mechanical testing like tensile test, impact test, bend and hardness test have been critically analysed and the properties were summarized and correlating with microstructure and SEM fractographs.

Bloating Mechanism for Artificial Light Weight Aggregate of Surface Modification with Coal ash

We manufacture artificial lightweight aggregates (ALWAs) using bottom-ash as the primary raw material. We coat the ALWA surfaces with low-melting point materials in order to enable them to bloat, which is essential to reduce the bulk density of the aggregate. Then, we sinter the prepared aggregates at 1000, 1100, and 1200℃ using either the direct or two-step firing schedules. Finally, we evaluate the properties of the fired samples through analyzing their bulk density, water absorption, and microstructure. The surface-modified samples result in a reduction of their bulk density by 0.3 ~ 0.4 g/㎤ regardless of the firing method used. Based on these results, we conclude that this approach could provide a viable method for the mass-production of ALWAs from industrial waste such as bottom-ash.

Investigation on the Clogging Behavior and Additional Wall Cooling for the Axial-Injection Cold Spray Nozzle

During the cold spray process, nozzle clogging always happens when spraying low-melting point materials, e.g., aluminum, significantly decreasing the working efficiency. In this paper, a comprehensive investigation was carried out to clarify the reason for inducing nozzle clogging and then to evaluate a home-made nozzle cooling device for preventing nozzle clogging. Computational fluid dynamics technique was employed as the main method with some necessary experiment validation. It is found that the particle dispersion and the high-temperature nozzle wall at the near-throat region are two dominant factors that cause nozzle clogging. The numerical results also reveal that the home-made cooling device can significantly reduce the nozzle wall temperature, which was validated by the experimental measurement. Besides, the aluminum coating build-up experiment further indicates that the additional cooling device can truly prevent the nozzle clogging.

Bed agglomeration characteristics of rice straw combustion in a vortexing fluidized-bed combustor

To investigate bed agglomeration characteristics, the combustion of pelletized rice straw was conducted in a bench-scale vortexing fluidized bed. Effects of bed temperature, superficial velocity, secondary gas velocities, and mass blended ratio of coal on the defluidization time were investigated. The alkali concentrations in different sections of the bed zone were also studied. The bed materials and agglomerates were analyzed using SEM/EDX to obtain the surface morphology and the compositions. The results revealed that the defluidization time is increased with superficial gas velocity and is decreased with bed temperature. Eutectic composition with low melting point materials promote defluidization at high temperatures. Effect of the secondary gas velocity on the defluidization time indicates different trends at different bed temperatures. The highest value of alkali concentration appears at upper bubbling zone. Coal ash can avoid the existence of a certain eutectic composition, and increases its melting point.

Magnetic Liquid Marbles: Toward “Lab in a Droplet”

Liquid marbles exhibit great potential for use as miniature labs for small‐scale laboratory operations, such as experiment and measurement. While important progress has been made recently in exploring their applications as microreactions, “on‐line” measurement of the components inside the liquid still remains a challenge. Herein, it is demonstrated that “on‐line” detection can be realized on magnetic liquid marbles by taking advantage of their unique magnetic opening feature. By partially opening the particle shell, electrochemical measurement is carried out with a miniaturized three‐electrode probe and the application of this technique for quantitative measurement of dopamine is demonstrated. Fully opened magnetic liquid marble makes it feasible to detect the optical absorbance of the liquid in a transmission mode. With this optical method, a glucose assay is demonstrated. Moreover, when magnetic particle shell contains low melting point material, e.g., wax, the liquid marble shows a unique encapsulation ability to form a rigid shell after heating, which facilitates the storage of the non‐volatile ingredients. These unique features, together with the versatile use as microreactors, enable magnetic liquid marbles to function as a miniature lab (or called “lab in a droplet”), which may find applications in clinical diagnostics, biotechnology, chemical synthesis, and analytical chemistry.

Imaging of Explosive Emission Cathode and Anode Plasma in a Vacuum-Sealed Vircator High-Power Microwave Source at 250 A/cm&lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;\(^{2}\) &lt;/tex-math&gt;&lt;/inline-formula&gt;

Cold cathode operation under high current densities leads to explosive electron emission (EEE) that contributes to early A-K gap closure. Hence, inconsistent vacuum conditions and, if utilized in a high power microwave device, degradation of microwave output power are observed. The EEE centers are known to produce localized plasmas on the surface of the cathode that release and ionize the electrode material. Further, low melting point material in the anode is released due to electron bombardment accompanied by a significant surface temperature increase. Postmortem analysis has revealed particles up to 50 μm in diameter embedded in the opposite electrode. High speed ICCD imaging during A-K gap operation enabled resolving the plasma's spatial characteristics in time. Images of cathode and anode plasma during the operation of a virtual cathode oscillator at 250 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> under ultrahigh vacuum conditions are presented.

Gastroretentive extended-release floating granules prepared using a novel fluidized hot melt granulation (FHMG) technique.

The objective of this work was to investigate the feasibility of using a novel granulation technique, namely, fluidized hot melt granulation (FHMG), to prepare gastroretentive extended-release floating granules. In this study we have utilized FHMG, a solvent free process in which granulation is achieved with the aid of low melting point materials, using Compritol 888 ATO and Gelucire 50/13 as meltable binders, in place of conventional liquid binders. The physicochemical properties, morphology, floating properties, and drug release of the manufactured granules were investigated. Granules prepared by this method were spherical in shape and showed good flowability. The floating granules exhibited sustained release exceeding 10 h. Granule buoyancy (floating time and strength) and drug release properties were significantly influenced by formulation variables such as excipient type and concentration, and the physical characteristics (particle size, hydrophilicity) of the excipients. Drug release rate was increased by increasing the concentration of hydroxypropyl cellulose (HPC) and Gelucire 50/13, or by decreasing the particle size of HPC. Floating strength was improved through the incorporation of sodium bicarbonate and citric acid. Furthermore, floating strength was influenced by the concentration of HPC within the formulation. Granules prepared in this way show good physical characteristics, floating ability, and drug release properties when placed in simulated gastric fluid. Moreover, the drug release and floating properties can be controlled by modification of the ratio or physical characteristics of the excipients used in the formulation.

Study on Mechanical Materials with Overview of Connection and Separation Devices

Different kinds of mechanical materials in connection and separation devices have been widely used in spacecraft engineering and keep on innovating and improving. Pyrotechnic and non-pyrotechnic devices have their own advantages and drawbacks and the application of new materials such as SMA (shape memory alloy) and low-melting point materials has become a new and striving issue. Different kinds of connection and separation devices and their prime mechanical materials will be presented in details in this paper.

Application of X-Ray Microtomography to Quantify the Liquid Fraction of M2 Steel for Semi-Solid Forming Process

Thixoforging, one variant of semi-solid metal processing in which the metallic alloys are processed at low liquid fraction (0.1&lt; Fl &lt; 0.3), is used to produce complex parts with high mechanical properties. Steel thixoforging faces more challenges as compared to that of low melting point materials due to high processing temperature and lack of understanding of the thermomechanical behavior of materials in the given conditions. It is crucial to study the microstructure at the semi-solid state to improve the understanding of the thixoforging process since the material behavior strongly depends on main parameters: the liquid fraction, its distribution as well as the coherence of the solid skeleton. The microstructure has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Here, the characterization of the volume percentage and distribution of liquid fraction at the semi-solid state with high energy 3D X-ray microtomography was investigated on M2 steel grade as a ‘model’ alloy. The obtained results have been compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They showed a good correlation making both approaches very efficient for the study of the liquid zones at the semi-solid state.

Note: Mechanically and chemically stable colloidal probes from silica particles for atomic force microscopy

In this note we present a novel approach to prepare colloidal probes for atomic force microscopy by sintering. A central element of this procedure is the introduction of an inorganic "fixation neck" between the cantilever and a micrometer-sized silica particle that is acting as probe. This procedure overcomes previous restrictions for the probe particles, which had to be low melting point materials, such as borosilicate glass or latex particles. The here-presented colloidal probes from silica can withstand large mechanical forces. Additionally, they have high chemical resistivity due to the absence of adhesives and the well-studied surface chemistry of colloidal silica.

Modelling of the Effect of Process Parameters on Tensile Strength of Friction Stir Welded Aluminium Alloy Joints

Friction stir welding (FSW) process is a promising solid-state joining process with the potential to join low-melting point material, particularly, aluminium alloy. The most attractive reason for joining aluminium alloy with this process is the avoidance of the solidification defects formed by conventional fusion welding processes. In this article, an attempt has been made to develop an empirical relationship between FSW variables and tensile strength. Central composite rotatable design was used by considering four factor and five levels, which enables to quantify the direct and interactive effect of four numeric factors, that is, tool rotational speed, welding speed, axial force, and tapered pin diameter on the tensile strength. The developed relationship is useful for prediction of tensile strength in friction stir welded AA6082 aluminium alloy joints at 95% confidence level. It will also be helpful for selection of process variable to obtain desired strength of the joint. Furthermore, the optimized capabilities in design-expert software were used to numerically optimize the input parameters. At the optimal parameters, three experiments were conducted to compare the predicted value of tensile strength with the experimental value.

Microstructural Evolution and Thermal Stability Characterization of a High Temperature Die Attach Lead-Free System

There is a need for electromechanical devices capable of operating in high temperature environments (&amp;gt;200°C) for a wide variety of applications. Today's wide-bandgap (WBG) semiconductor based power electronics have demonstrated a potential of operating above 400°C, however they are still limited by packaging. Among the most promising alternative is the Au-Sn eutectic solder, which have been widely used due to its excellent mechanical and thermal properties. However, the operating temperature of this metallurgical system is still limited to ∼250°C owing to its melting temperature of 280°C. Therefore, a higher temperature resistant system is much needed, but without affecting the current processing temperature of ∼325°C typically exhibited in most high temperature Pb-Free solders. This paper presents the development and characterization of a fluxless die attach soldering process based on gold enriched solid liquid inter-diffusion (SLID). A low melting point material (eutectic Au-Sn) was deposited in the face of a substrate, whereas a high melting point material, gold in this instance, was deposited in its mating substrate. Deposition of all materials was performed using a jet vapor deposition (JVD) equipment where thicknesses were controlled to achieve specific compositions in the mixture. Sandwiched coupons where isothermally processed in a vacuum reflow furnace. SEM and EDS were employed to reveal the microstructural evolution of the samples in order to study the interfacial reactions of this fluxless bonding process. Mechanical characterization of the each individual intermetallic phase was achieved by nanoindentation. Differential scanning calorimetry demonstrated the progression of the SLID process by quantifying the remaining low melting point constituent as a function of time and temperature. Post-processed samples confirmed the inter-diffusion mechanism as evidenced by the formation of sound joints that proved to be thermally stable up to ∼490°C after the completion of the SLID process.

Mechanical Properties and Microstructure of SS400 Friction Stir Welds Pursuant to Welding Distance

FSW have advantage as defect such as porosity, metallic compounds decrease than other welding process. So, FSW was researched about low melting point materials. However, welding of high melting point and high strength materials attract attention because of high mechanical properties was needed due to industrial development. In this study, FSW is enforced using the kind of high melting point materials as SS400(SPHC). However, the tool must have super heat-resisting and abrasion resistance. So, WC-X%Co tool was manufactured by SPS method. The result, welding is successfully practice using WC-X%Co tool to 50m without fracture of tool.