Optimization of forward pulsed currents for combining the precision shaping and polishing of nickel micro mould tools to reduce demoulding defects.

Precise tooling is vital for defect-free production of micro injection moulded (µ-IM) or hot-embossed products. The demoulding stage of such moulding and forming processes poses a serious challenge to the integrity of thin miniature features because of friction, adhesion, and thermal stresses. Typically, micro moulds involve geometrically textured patterns or features such as linear ridges, pillars, channels, and holes, the characteristic dimensions of which range from 10 to 300 µm. Realistically complex mould designs, containing precision micro features (enhanced fillet radius and positive draft angle) and high surface quality, are presented in this work. Electropolishing based on forward pulse currents (PC) has been used to shape and polish Ni micro moulds that contain sets of micron-scaled linear ridges and star patterns in order to ease the separation of moulded polymeric parts from the metallic mould during ejection and demoulding. The use of forward pulsed currents improved the mould design by increasing the fillet radii and draft angle while keeping the surface roughness low and maintaining a good surface shine. An optimization study of forward PC using a green solution of nickel sulfamate varied EP times (0-70 min) and duty cycles (40, 50, 60, and 70%) at a process conditions of 2.8 V, 50 °C, and 250 rpm. The best topographical and morphological changes were observed for a typical microfluidic channel (w × h, 100 × 110 µm) with an EP time of 70 min and 50% duty cycle: fillet radius increased by 3.8 µm, draft angle by 3.3°, and the channel width reduced by 11.4% while surface roughness changed by 8.6% and surface shine improved by 48.9%. Experimental validation was performed using hot embossing wherein the electropolished Ni mould replicated the micro channels and star patterns in PMMA chips with notably fewer burrs, material pile up, and no feature distortion. Moreover, there was a reduction in the side wall roughness of micro channels in PDMS casting with electropolished Ni mould by 16%. Hence, this work presents a significant scientific contribution to improving the efficiency of micro mould tools and reduces the defects caused by friction and adhesion in replicated polymeric parts.

Unveiling the tribological potential of MXenes-current understanding and future perspectives.

Reducing energy consumption and CO2 emissions by improving the tribological performance of mechanical systems relies on the development of new lubrication concepts. Two-dimensional (2D) materials have been the subject of extensive tribological research due to their unique physical and chemical properties. 2D transition metal carbides, nitrides, and carbonitrides (MXenes), with their tuneable chemistry and structure, are a relatively new addition to the family of 2D materials. MXenes' good strength and stiffness, easy-to-shear ability, capability to form wear-resistant tribofilms, and the possibility to control their surface chemistry make them appealing candidates to be explored for tribological purposes. This review provides a comprehensive overview of MXenes' tribology, covering their structure-property relationship, synthesis approaches, deposition methods to generate MXene coatings for tribological purposes, and their fundamental tribological mechanisms. Furthermore, detailed insights into studies exploring MXenes' tribological performance from the nano- to the macro-scale are presented with special emphasis on their use as self-lubricating solid lubricants, lubricant additives, and reinforcement phases in composites.

Electropolishing and Shaping of Micro-Scale Metallic Features.

Electropolishing (EP) is most widely used as a metal finishing process. It is a non-contact electrochemical process that can clean, passivate, deburr, brighten, and improve the biocompatibility of surfaces. However, there is clear potential for it to be used to shape and form the topology of micro-scale surface features, such as those found on the micro-applications of additively manufactured (AM) parts, transmission electron microscopy (TEM) samples, micro-electromechanical systems (MEMs), biomedical stents, and artificial implants. This review focuses on the fundamental principles of electrochemical polishing, the associated process parameters (voltage, current density, electrolytes, electrode gap, and time), and the increasing demand for using environmentally sustainable electrolytes and micro-scale applications. A summary of other micro-fabrication processes, including micro-milling, micro-electric discharge machining (EDM), laser polishing/ablation, lithography (LIGA), electrochemical etching (MacEtch), and reactive ion etching (RIE), are discussed and compared with EP. However, those processes have tool size, stress, wear, and structural integrity limitations for micro-structures. Hence, electropolishing offers two-fold benefits of material removal from the metal, resulting in a smooth and bright surface, along with the ability to shape/form micro-scale features, which makes the process particularly attractive for precision engineering applications.zx3.

In vitro antilithiatic activity of the hydro-alcoholic extract of Cinnamomum zeylanicum Blume bark on calcium oxalate crystallization.

OBJECTIVE: The study examines the effect of the hydro-alcoholic extract of Cinnamomum zeylanicum Blume bark on crystallization of calcium oxalate. METHODS: The antilithiatic effect of various concentrations of the hydro-alcoholic extract of C. zeylanicum was investigated at various stages of stone formation, using Cystone as a standard reference drug. The effect on calcium oxalate crystallization was evaluated by measuring the change in turbidity over time, during crystal nucleation, growth and aggregation, in the metastable solution of calcium chloride and sodium oxalate. The slope from the change in turbidity over time was measured using a spectrophotometer at 620 and 214 nm in respective tests. The inhibition rate was estimated by comparing turbidity in the presence and absence of extract. Crystals formed under experimental conditions were observed under a light microscope, and number and shape of the crystals were assessed in a randomly selected field. Phytochemical analysis and high-performance thin-layer chromatography of the extract was also carried out. RESULTS: C. zeylanicum significantly reduced crystal nucleation at concentrations of 4, 8 and 10 mg/mL (P < 0.001). The inhibition percentage of crystal growth was between 28.30% and 92.46% in the presence of C. zeylanicum extract and from 20.76% to 64.15% with various concentrations of Cystone. The maximum inhibition of crystal growth was obtained from C. zeylanicum at 2 mg/mL (92.46%). Microscopic examination revealed a reduction in the number and size of crystals. In the aggregation assay, the inhibition percentage of C. zeylanicum was between 16.27% and 100%, while Cystone was from -214.68% to 100% at different concentrations. The highest (100%) inhibition of aggregation was found at 4 mg/mL of both the test and standard drugs. CONCLUSION: We found that C. zeylanicum hydro-alcoholic extract has notable inhibitory effects on various stages of crystallization, in terms of turbidity of solution, as well as the crystal size, number and morphology.