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  • 1.
    Ekspong, Joakim
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stainless Steel as A Bi-Functional Electrocatalyst – A Top-Down Approach2019In: Materials, E-ISSN 1996-1944, Vol. 12, no 13, article id 2128Article in journal (Refereed)
    Abstract [en]

    For a hydrogen economy to be viable, clean and economical hydrogen production methods are vital. Electrolysis of water is a promising hydrogen production technique with zero emissions, but suffer from relatively high production costs. In order to make electrolysis of water sustainable, abundant, and efficient materials has to replace expensive and scarce noble metals as electrocatalysts in the reaction cells. Herein, we study activated stainless steel as a bi-functional electrocatalyst for the full water splitting reaction by taking advantage of nickel and iron suppressed within the bulk. The final electrocatalyst consists of a stainless steel mesh with a modified surface of layered NiFe nanosheets. By using a top down approach, the nanosheets stay well anchored to the surface and maintain an excellent electrical connection to the bulk structure. At ambient temperature, the activated stainless steel electrodes produce 10 mA/cm(2) at a cell voltage of 1.78 V and display an onset for water splitting at 1.68 V in 1M KOH, which is close to benchmarking nanosized catalysts. Furthermore, we use a scalable activation method using no externally added electrocatalyst, which could be a practical and cheap alternative to traditionally catalyst-coated electrodes.

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  • 2.
    Kumar Wagri, Naresh
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Jain, Neelesh Kumar
    Department of Mechanical Engineering, Indian Institute of Technology Indore, Indore, India.
    Petare, Anand
    Department of Mechanical Engineering, Indian Institute of Technology Indore, Indore, India.
    Das, Sudhansu Ranjan
    Department of Production Engineering, Veer Surendra Sai University of Technology, Burla, India.
    Tharwan, Mohammed Y.
    Mechanical Engineering Department, College of Engineering, Jazan University, KSA, Jazan, Saudi Arabia.
    Alansari, Abdulkarim
    Mechanical Engineering Department, College of Engineering, Northern Border University, Arar, Saudi Arabia.
    Alqahtani, Bader
    Mechanical Engineering Department, College of Engineering, Northern Border University, Arar, Saudi Arabia.
    Fattouh, Majed
    Department of Mechanical Engineering, Faculty of Engineering, University of Blue Nile, Damazeen, Sudan.
    Elsheikh, Ammar
    Department of Production Engineering and Mechanical Design, Tanta University, Tanta, Egypt.
    Investigation on the performance of coated carbide tool during dry turning of AISI 4340 alloy steel2023In: Materials, E-ISSN 1996-1944, Vol. 16, no 2, article id 668Article in journal (Refereed)
    Abstract [en]

    The machinability of materials is highly affected by their hardness, and it affects power consumption, cutting tool life as well as surface quality while machining the component. This work deals with machining of annealed AISI 4340 alloy steel using a coated carbide tool under a dry environment. The microhardness of annealed and non-annealed workpieces was compared and a significant reduction was found in the microhardness of annealed samples. Microstructure examination of the annealed sample revealed the formation of coarse pearlite which indicated a reduction of hardness and improved ductility. A commercially CVD multilayer (TiN/TiCN/Al2O3/ZrCN) coated cemented carbide cutting tool was employed for turning quenched and tempered structural AISI 4340 alloy steel by varying machining speed, rate of feed, and depth of cut to evaluate the surface quality, machining forces, flank wear, and chip morphology. According to the findings of experiments, the feed rate possesses a high impact on surface finish, followed by cutting speed. The prominent shape of the serrated saw tooth chip was noticed at a higher cutting speed. Machined surface finish and cutting forces during turning is a function of the wear profile of the coated carbide insert. This study proves that annealing is a low-cost and economical process to enhance the machinability of alloy steel.

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  • 3. Mosconi, Dario
    et al.
    Giovannini, Giorgia
    Maccaferri, Nicolò
    Serri, Michele
    Agnoli, Stefano
    Garoli, Denis
    Electrophoretic Deposition of WS2 Flakes on Nanoholes Arrays—Role of Used Suspension Medium2019In: Materials, E-ISSN 1996-1944, Vol. 12, no 20, p. 3286-3286Article in journal (Refereed)
    Abstract [en]

    Here we optimized the electrophoretic deposition process for the fabrication of WS2 plasmonic nanohole integrated structures. We showed how the conditions used for site-selective deposition influenced the properties of the deposited flakes. In particular, we investigated the effect of different suspension buffers used during the deposition both in the efficiency of the process and in the stability of WS2 flakes, which were deposited on an ordered arrays of plasmonic nanostructures. We observed that a proper buffer can significantly facilitate the deposition process, keeping the material stable with respect to oxidation and contamination. Moreover, the integrated plasmonic structures that can be prepared with this process can be applied to enhanced spectroscopies and for the preparation of 2D nanopores.

  • 4. Orqusha, Nimet
    et al.
    Phal, Sereilakhena
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Berisha, Avni
    Tesfalidet, Solomon
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Experimental and Theoretical Study of the Covalent Grafting of Triazole Layer onto the Gold Surface2020In: Materials, E-ISSN 1996-1944, Vol. 13, article id 2927Article in journal (Other academic)
    Abstract [en]

    Finding novel strategies for surface modification is of great interest in electrochemistry and material sciences. In this study, we present a strategy for modification of a gold electrode through covalent attachment of triazole (TA) groups. Triazole groups were electrochemically grafted at the surface of the electrode by a reduction of in situ generated triazolediazonium cations. The resulting grafted surface was characterized before and after the functionalization process by different electrochemical methods (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS)) confirming the presence of the grafted layer. The grafting of TA on the electrode surface was confirmed using analysis of surface morphology (by atomic force microscopy), the thickness of the grafted layer (by ellipsometry) and its composition (by X-ray photoelectron spectroscopy). Density functional theory (DFT) calculations imply that the grafted triazole offers a stronger platform than the grafted aryl layers.

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  • 5.
    Qu, Chengjuan
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB). Department of Orthopaedics, Traumatology and Hand Surgery, Kuopio University Hospital, Kuopio, Finland.
    Kaitainen, Salla
    Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
    Kröger, Heikki
    Department of Orthopaedics, Traumatology and Hand Surgery, Kuopio University Hospital, Kuopio, Finland.
    Lappalainen, Reijo
    Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
    Lammi, Mikko
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB). Key Laboratory of Trace Elements and Endemic Diseases, National Health and Family Planning Commission, School of Public Health of Health Science Center, Xi’an Jiaotong University, Xi’an, China.
    Behavior of human bone marrow-derived mesenchymal stem cells on various titanium-based coatings2016In: Materials, E-ISSN 1996-1944, Vol. 9, no 10, article id 827Article in journal (Refereed)
    Abstract [en]

    The chemical composition and texture of titanium coatings can influence the growth characteristics of the adhered cells. An enhanced proliferation of the human mesenchymal stem cells (hMSCs) would be beneficial. The present study was aimed to investigate whether titanium deposited at different atmospheres would affect the cell growth properties, cellular morphology, and expression of surface markers of hMSCs. Titanium-based coatings were deposited on silicon wafers under oxygen, nitrogen, or argon atmospheres by ultra-short pulsed laser deposition using two different gas pressures followed by heating at 400 °C for 2 h. The characteristics of the coated surfaces were determined via contact angle, zeta potential, and scanning electron microscopy (SEM) techniques. Human MSCs were cultivated on differently coated silicon wafers for 48 h. Subsequently, the cell proliferation rates were analyzed with an MTT assay. The phenotype of hMSCs was checked via immunocytochemical stainings of MSC-associated markers CD73, CD90, and CD105, and the adhesion, spreading, and morphology of hMSCs on coated materials via SEM. The cell proliferation rates of the hMSCs were similar on all coated silicon wafers. The hMSCs retained the MSC phenotype by expressing MSC-associated markers and fibroblast-like morphology with cellular projections. Furthermore, no significant differences could be found in the size of the cells when cultured on all various coated surfaces. In conclusion, despite certain differences in the contact angles and the zeta potentials of various titanium-based coatings, no single coating markedly improved the growth characteristics of hMSCs.

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