Mauro Callisti

Electronic metal-support interaction enhanced oxygen reduction activity and stability of boron carbide supported platinum

Catalysing the reduction of oxygen in acidic media is a standing challenge. Although activity of platinum, the most active metal, can be substantially improved by alloying, alloy stability remains a concern. Here we report that platinum nanoparticles supported on graphite-rich boron carbide show a 50–100% increase in activity in acidic media and improved cycle stability compared to commercial carbon supported platinum nanoparticles. Transmission electron microscopy and x-ray absorption fine structure analysis confirm similar platinum nanoparticle shapes, sizes, lattice parameters, and cluster packing on both supports, while x-ray photoelectron and absorption spectroscopy demonstrate a change in electronic structure. This shows that purely electronic metal-support interactions can significantly improve oxygen reduction activity without inducing shape, alloying or strain effects and without compromising stability. Optimizing the electronic interaction between the catalyst and support is, therefore, a promising approach for advanced electrocatalysts where optimizing the catalytic nanoparticles themselves is constrained by other concerns.

Selective oxidation-induced strengthening of Zr/Nb nanoscale multilayers

The paper presents a new approach, based on controlled oxidation of nanoscale metallic multilayers, to produce strong and hard oxide/metal nanocomposite coatings with high strength and good thermal stability. The approach is demonstrated by performing long term annealing on sputtered Zr/Nb nanoscale metallic multilayers and investigating the evolution of their microstructure and mechanical properties by combining analytical transmission electron microscopy, nano-mechanical tests and finite element models. As-deposited multilayers were annealed at 350 °C in air for times ranging between 1 and 336 h. The elastic modulus increased by ?20% and the hardness by ?42% after 15 h of annealing. Longer annealing times did not lead to changes in hardness, although the elastic modulus increased up to 35% after 336 h. The hcp Zr layers were rapidly transformed into monoclinic ZrO2 (in the first 15 h), while the Nb layers were progressively oxidized, from top surface down towards the substrate, to form an amorphous oxide phase at a much lower rate. The sequential oxidation of Zr and Nb layers was key for the oxidation to take place without rupture of the multi-layered structure and without coating spallation, as the plastic deformation of the metallic Nb layers allowed for the partial relieve of the residual stresses developed as a result of the volumetric expansion of the Zr layers upon oxidation. Moreover, the development of residual stresses induced further changes in mechanical properties in relation to the annealing time, as revealed by finite element simulations.

Parylene C topographic micropattern as a template for patterning PDMS and Polyacrylamide hydrogel

Parylene C is a well-known polymer and it has been mainly employed as a protective layer for implantable electronics. In this paper, we propose a new approach to use Parylene C as a versatile template for patterning soft materials potentially applicable as scaffolds in cardiac tissue engineering (TE). Parylene C substrates were anisotropically patterned through standard lithographic process with hydrophilic channels separating raised hydrophobic strips. Ridges and grooves of the template are 10 µm width and depth ranging from 1 to 17 µm. Polydimethylsiloxane (PDMS) and Polyacrylamide (PAm) hydrogel have been chosen as soft polymers to be moulded. Thanks to their chemical and physical properties PDMS and PAm hydrogel mimic the extracellular matrix (ECM). PDMS was spin coated on micropatterned Parylene C obtaining composite substrates with 460 nm and 1.15 µm high grooves. The Young’s modulus of the composite Parylene C/PDMS was evaluated and it was found to be almost half when compared to PDMS. PAm hydrogel was also printed using collagen coated micro-grooved Parylene C. Optical micrographs and fluorescence analysis show the successful topographic and protein pattern transfer on the hydrogel.

Structural characterization of Si-ion irradiated Zr/Nb nano-multilayers with different individual layer thicknesses

XRD and HR-TEM analyses of Si-ion irradiated Zr/Nb nanoscale multilayers with different individual layer thicknesses.

Investigation of nano-sized debris released from CoCrMo secondary interfaces in total hip replacements: Digestion of the flakes: INVESTIGATION OF NANO-SIZED DEBRIS RELEASED FROM CoCrMo

The in vivo release of wear debris and corrosion products from the metallic interfaces of total hip replacements is associated with a wide spectrum of adverse body reactions and systemic manifestations. The origin of debris and the electrochemical conditions at the sites of material loss both play a role in determining the physicochemical characteristics of the particles, and thus influence their in vivo reactivity. Debris retrieved from revised CoCrMo tapers and cement-stem interfaces consists of heterogeneous flakes that comprise mechanically mixed metal particles, corrosion products and organic material. Detailed investigation of the size and composition of the metal debris contained within these composites requires the digestion of the flakes to release the small metal particles. Here, we compare alkaline and enzymatic digestion methods that both aim to fragment the flakes and reveal their smallest building blocks. The characterization of debris cleaned with both methods revealed crystalline Cr oxide nanoparticles and clusters. Comparison between the treatments showed that the alkaline method is more efficient in fragmenting the flakes and provided cleaner and generally smaller nanoparticles than exhibited in debris released with the enzymatic treatment. The provision of cleaner nanoparticles from the alkaline method also allows the physicochemical properties of the particles to be more clearly identified.

Deformation behaviour of Zr/Nb nano-multilayers: XRD and FIB/SEM data

Structure and deformation behaviour of as-deposited Zr/Nb NMMs investigated by XRD, Nanoindentation and FIB/SEM.Dataset to support: Callisti, Mauro and Polcar, Tomas (2017) Combined size and texture-dependent deformation and strengthening mechanisms in Zr/Nb nano-multilayers. Acta MaterialiaFunded by EPSRC (South of England Analytical Electron Microscope , EP/K040375/1, 2013 to 2017).

Structural characterisation of Zr/Nb nanoscale metallic multilayers

Structural characterisation of Zr/Nb nanoscale metallic multilayers through X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM).Dataset to support: Monclus, Miguel A. et al (2016) Selective oxidation-induced strengthening of Zr/Nb nanoscale multilayers. Acta MaterialiaFunding: Multiscale Modelling and Materials by Design of interface-controlled Radiation Damage in Crystalline Materials (RADINTERFACES, 263273), 2011 to 2014. Virtual Design, Virtual Processing and Virtual Testing of Metallic Materials (VIRMETAL, 669141), 2015 to 2020. South of England Analytical Electron Microscope (EPSRC; EP/K040375/1), 2013 to 2017.