Effect of Milling Conditions on Microstructure and Properties of AA6061/halloysite Composites

AbstractIn this work, AA6061 matrix composites reinforced with halloysite nanotubes (HNT) were fabricated using respectively, mechanical alloying and uniaxial pressing and hot extrusion. Halloysite, being a clayey mineral of volcanic origin which is characterized by large specific surface, high porosity, high ion exchange and easy mechanical and chemical treatment can be used as alternative reinforcement of metal matrix composite materials. Halloysite nanotubes have recently become the subject of research attention as a new type of reinforcement for improving the mechanical, thermal and fire-retardant performance of polymers. Application of halloysite as the reinforcement in metal matrix composites is the original invention of the authors and it has been patented (PL Patent 216257). The powders morphology, particle size and apparent density of newly developed nanostructural composites were studied as a function of milling time, ball-to-powder ratio and milling speed. Obtained composite powders of aluminium alloy matrix reinforced with 10wt.% of halloysite nanotubes were characterized by SEM analysis. Microstructural observation reveals that mechanical alloying generate a uniform dispersion of nanoparticles in the AA6061 matrix. AA6061 reinforced with 10wt.% HNT composite powder has been fabricated at vial rotation speed of 400rpm within only 6h of ball milling. It has been proven that milling speed and ball-to-powder ratio has a significant effect on the time required to achieve a morphological change in the powder being mechanically alloyed. Moreover, it has been confirmed that the use of mechanical alloying leads to high degree of deformation, which – coupled with a decrease in grain size below 100nm and the dispersion of the reinforcing refined particles – causing increase of composite hardness. Manufacturing conditions allow to achieve an improvement of mechanical properties compared with the base material

Mechanical characterisation and crashworthiness performance of additively manufactured polymer-based honeycomb structures under in-plane quasi-static loading

ABSTRACTAdditive manufacturing technology is suitable for producing energy-absorbing devices with tunable mechanical properties and improved crashworthiness performance. In this study, the mechanical properties and macrostructural crushing behaviour of five additively manufactured polymer-based honeycomb structures (HS) are investigated. Subjected to in-plane loading, the experimental results of the HS are compared with numerical findings and theoretical predictions. Results indicate that deformation modes and overall crushing performance are influenced by utilising different parent materials. The polymer HS made from polyethylene terephthalate glycol gives the best overall crushing performance over the other polymers and polymer-fibre reinforcement HS. However, the crush force efficiency of HS made from polylactic acid is the least promising. The polymer-fibre reinforced HS outperforms some of the pure polymer-based ones in terms of specific energy absorption and shows a characteristic lightweight advantage. Hence, spotting it as a promising energy absorber utilised for crashworthiness application especially where ultra-lightweight property is highly desired

SECM study of hydrogen photogeneration in a 1,2-dichloroethane | water biphasic system with decamethylruthenocene electron donor regeneration

This paper reports light driven hydrogen evolution reaction (HER) at 1,2-dichloroethane | water (DCE | W) interface using photoexcited decamethylruthenocene (DMRc) as electron donor. DMRc is in situ regenerated by electroreduction of its oxidized form (DMRc+) formed during HER as a by-product. This enables continuous HER using small amount of DMRc. Proton transfer from the acidic aqueous phase to the DCE phase is ensured by negative chemical polarization of the liquid | liquid interface. The reduction of protons in DCE occurs only after excitation of DMRc by light. Voltammetry performed with the organic droplet-modified glassy carbon electrode immersed in the aqueous electrolyte solution of various anions, indicated that oxidation of DMRc is followed by an anion insertion from water into the organic phase. We demonstrate that DMRc can be electrochemically regenerated at the microelectrode positioned close to the interface between two immiscible electrolyte solutions (ITIES) by the scanning electrochemical microscopy. Regeneration of the electron donor allows further development of biphasic system towards continuous hydrogen generation platform

Scanning electrochemical microscopy determination of hydrogen flux at liquid|liquid interface with potentiometric probe

Scanning electrochemical microscopy potentiometric determination of local hydrogen concentration and its flux next to the liquid|liquid interface was demonstrated. This method is based on the shift of open circuit potential of Pt-based reversible hydrogen electrode. The detection system was verified with a system generating hydrogen under galvanostatic conditions. Then, it was applied to aqueous|1,2-dichloroethane interface where hydrogen is produced with decamethylferrocene as electron donor

Inducible Nitric Oxide Synthase (iNOS) Is a Novel Negative Regulator of Hematopoietic Stem/Progenitor Cell Trafficking

Nitric oxide (NO) is a gaseous free radical molecule involved in several biological processes related to inflammation, tissue damage, and infections. Based on reports that NO inhibits migration of granulocytes and monocytes, we became interested in the role of inducible NO synthetase (iNOS) in pharmacological mobilization of hematopoietic stem/progenitor cells (HSPCs) from bone marrow (BM) into peripheral blood (PB). To address the role of NO in HSPC trafficking, we upregulated or downregulated iNOS expression in hematopoietic cell lines. Next, we performed mobilization studies in iNOS−/− mice and evaluated engraftment of iNOS−/− HSPCs in wild type (control) animals. Our results indicate that iNOS is a novel negative regulator of hematopoietic cell migration and prevents egress of HSPCs into PB during mobilization. At the molecular level, downregulation of iNOS resulted in downregulation of heme oxygenase 1 (HO-1), and, conversely, upregulation of iNOS enhanced HO-1 activity. Since HO-1 is a negative regulator of cell migration, the inhibitory effects of iNOS identified by us can be at least partially explained by its enhancing the HO-1 level in BM cells

Evidence for the Involvement of Sphingosine-1-Phosphate in the Homing and Engraftment of Hematopoietic Stem Cells to Bone Marrow

The α-chemokine stromal-derived factor 1 (SDF-1), which binds to the CXCR4 receptor, directs migration and homing of CXCR4+ hematopoietic stem/progenitor cells (HSPCs) to bone marrow (BM) stem cell niches. Nevertheless, it is also known that CXCR4-/- fetal liver-derived hematopoietic stem cells engraft into BM and that blockade of CXCR4 by its antagonist AMD3100 does not prevent engraftment of HSPCs. Because of this finding of SDF-1-CXCR4-independent BM homing, the unique role of SDF-1 in HSPC homing has recently been challenged. While SDF-1 is the only chemokine that chemoattracts HSPCs, other chemoattractants for these cells have recently been described, including the bioactive phosphosphingolipid sphingosine-1-phosphate (S1P). To address the potential role of S1P in homing of HSPCs to BM, we performed hematopoietic transplants into mice deficient in BM-expressed sphingosine kinase 1 (Sphk1-/-) using hematopoietic cells from normal control mice as well as cells from mice in which floxed CXCR4 (CXCR4fl/fl) was conditionally deleted. We observed the presence of a homing and engraftment defect in HSPCs of Sphk1-/- mice that was particularly profound after transplantation of CXCR4-/- BM cells. Thus, our results indicate that BM-microenvironment-expressed S1P plays a role in homing of HSPCs. They also support the concept that, in addition to the SDF-1-CXCR4 axis, other chemotactic axes are also involved in homing and engraftment of HSPCs

H2O2 generation at carbon paste electrode with decamethylferrocene solution in 2-nitrophenyloctyl ether as a binder. The catalytic effect of MoS2 particles

Here, we report hydrogen peroxide generation at 2-nitrophenyloctyl ether (NPOE)-water interface with decamethylferrocene as an electron donor. The progress of this reaction was detected by the observation of color change of the organic and aqueous phases in series of shake-flask experiments. The shape change of cyclic voltammograms recorded at carbon paste electrode with decamethylferrocene solution in NPOE also indicates (electro)catalytic reaction. Hydrogen peroxide was electrochemically detected at Pt microelectrode tip positioned in front of carbon paste electrode. For this purpose, scanning electrochemical microscopy (SECM) approach curves were recorded. Analogous experiments demonstrated the possibility of electrochemical regeneration of the electron donor. The (electro)catalytic effect of MoS2 on hydrogen peroxide generation was found by both shake-flask and SECM experiments

Hydrogen and Hydrogen Peroxide Formation in Trifluorotoluene-Water Biphasic Systems

Hydrogen or hydrogen peroxide can be generated in liquid-liquid biphasic systems, where the organic phase contains sufficiently strong electron donor (whose redox potential is lower than the potential of reversible hydrogen electrode). H2O2 generation with acidified aqueous phase occurs prior to H2 evolution when oxygen is present. No other organic solvent than highly toxic 1,2-dichloroethane (DCE) has been reported in biphasic system for H2 or H2O2 generation. In this work, we have used trifluorotoluene (TFT) instead of carcinogenic DCE, and studied these reactions in TFT-water biphasic system. To evaluate H2 flux, scanning electrochemical microscopy potentiometric approach curves to the TFT-water interface were recorded. H2O2 was detected voltametrically at a microelectrode located in the vicinity of the interface. H2 and H2O2 are formed and both reactions occur also in the absence of a hydrophobic salt in the organic phase. Their thermodynamics was discussed on the basis of Gibbs energies determined electrochemically with droplet-modified electrodes. The results show that DCE can be replaced by a noncarcinogenic solvent and the biphasic system for H2 and H2O2 generation can be simplified by elimination of the uncommon hydrophobic salt from the organic phase

Hydrogen Peroxide Generation at Liquid|Liquid Interface under Conditions Unfavorable for Proton Transfer from Aqueous to Organic Phase

The charge transfer processes across the interface between two immiscible electrolyte solutions (ITIES) can be employed for energy storage and conversion, solvent extraction, or sensing or in life sciences. Among them are catalytic reactions, which have only been recently studied. Here H2O2 generation is studied with decamethylferrocene (DMFc) as electron donor at the interface between tetrahexylammonium perchlorate solution in 1,2- dichloroethane (1,2-DCE) and aqueous HClO4. These conditions are unfavorable for proton transfer across ITIES because of positive Galvani potential difference. Voltammetry with 1,2-DCE droplet modified electrode shows that DMFc oxidation is accompanied by ClO4− insertion into the organic phase. The reaction progress was followed by UV−vis spectroscopy, voltammetry, and scanning electrochemical microscopy (SECM). In the first and last method, horseradish peroxidase was used as catalyst. It is concluded that O2 is reduced to H2O2 at the liquid|liquid interface not only under conditions when proton transfer to organic phase is strongly favored, namely, when Galvani potential difference is negative (Angew. Chem., Int. Ed. 2008, 47, 4675−4678)

Catalysis of water oxidation in acetonitrile by iridium oxide nanoparticles

Water oxidation catalysed by iridium oxide nanoparticles (IrO2 NPs) in water–acetonitrile mixtures using [RuIII(bpy)3]3+ as oxidant was studied as a function of the water content, the acidity of the reaction media and the catalyst concentration. It was observed that under acidic conditions (HClO4) and at high water contents (80% (v/v)) the reaction is slow, but its rate increases as the water content decreases, reaching a maximum at approximately equimolar proportions (≈25% H2O (v/v)). The results can be rationalized based on the structure of water in water–acetonitrile mixtures. At high water fractions, water is present in highly hydrogen-bonded arrangements and is less reactive. As the water content decreases, water clustering gives rise to the formation of water-rich micro-domains, and the number of bonded water molecules decreases monotonically. The results presented herein indicate that non-bonded water present in the water micro-domains is considerably more reactive towards oxygen production. Finally, long term electrolysis of water–acetonitrile mixtures containing [RuII(bpy)3]2+ and IrO2 NPs in solution show that the amount of oxygen produced is constant with time demonstrating that the redox mediator is stable under these experimental conditions