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Our main research topics are the following:

 
      Metallic Glasses and Bulk Nanocomposite Materials  
      Thin Films, Foams and Micro/Nanostructures by Electrochemical Methods  
Lithographed Magnetic Structures
Permanent and Biodegradable Biomaterials
Mesoporous Materials
       
   
         
                               
         
 

METALLIC GLASSES - Led by E. Pellicer, M. D. Baró and J. Sort

Metallic glasses are a particular type of metallic materials with no long-range atomic order. Due to their amorphous character and the concomitant lack of dislocations, these materials exhibit mechanical properties that are quite different from those of other solid materials. For example, they can be twice as strong as steels, exhibit more elasticity and fracture toughness than ceramics and be less brittle than conventional oxide glasses. These materials also show good corrosion resistance basically due to the absence of grain boundaries. Apart from their technological use as structural materials, some metallic glasses have also found applications as soft magnetic materials (e.g., cores of high frequency transformers).

We investigate the mechanical properties of various families of bulk metallic glasses, based on Zr, Ti, Ni, Fe or rare earths. Whereas Zr-based and Fe-based BMGs are very hard and exhibit a large Young’s modulus, the rare-earth metallic glasses are relatively soft and show a low Young’s modulus. Results from nanoindentation experiments on this type of materials shed light on several issues such as the yielding criterion, strain rate effects or deformation-induced nanocrystallization. The latter effect has been used to generate arrays of ferromagnetic dots with perpendicular magnetic anisotropy at the surface of Fe-based glassy ribbons with in-plane magnetic anisotropy, an effect which could be used to fabricate ultra-high density magnetic recording media.

 

       
                     
           
       
 

NANOCOMPOSITE MATERIALS - Led by E. Pellicer and J. Sort

We investigate diverse types of nanocomposite materials: (i) metal-ceramic composites, (ii) nanocomposites formed by two metallic crystalline phases with distinct microstructure and (iii) inorganic-organic hybrid materials.

The overall mechanical behavior of composite materials depends on the mechanical properties of each of the constituent phases. New progress in the improvement of flow properties relies very much on finding combinations of strengthening mechanisms that lead to synergetic effects. Grain size reduction is one of the most appealing routes for improving strength. Enhanced mechanical properties are obtained in nanocomposites consisting of a nanoeutectic matrix with micrometer-sized dendrites embedded.

Nanocomposite materials can be also obtained by thermally-induced partial nanocrystallization of a metallic glass. These nanocrystals act as pinning sites for shear band propagation, thus hindering premature mechanical failure during deformation. Nanoparticles can be also purposely dispersed during the fabrication of metallic glasses or be obtained by other surface treatments, such as shot penning or ion irradiation.

Finally, organic-inorganic hybrid nanocomposites have attracted much interest because they can combine useful chemical, optical, magnetic and mechanical characteristics. In collaboration with the Department of Materials and Environmental Chemistry, Stockholm University in Sweden, we are currently studying the properties of hybrids composed of (i) nanofibrillated cellulose and titania nanoparticles and (ii) nanocrystalline cellulose and amorphous calcium carbonate, prepared in aqueous media. These bionanocomposites are especially appealing as they combine impressive properties with environmentally benign and energy efficient production routes.

         
     
       
THIN FILMS, FOAMS AND MICRO/NANOSTRUCTURES BY ELECTROCHEMICAL METHODS

Led by E. Pellicer, J.Fornell and J. Sort

Electrochemical methods are one of the powerful options for the synthesis of a great variety of materials including continuous or porous films of tuneable thickness, nanoparticles, nanorods, nanowires and nanotubes made of either single-phase or multi-phase (i.e., composite) materials. Electrochemical methods have many inherent advantages over physical deposition techniques such as simple set-up, low cost, low power demand and high compatibility with micro and nanofabrication technologies. We are interested in the growth of technologically relevant continuous metallic thin films by electrodeposition (e.g. Cu-Ni, Co-Ni, Co-W, CoNiReP) and in the scaling down of the synthetic procedures for the production of micro- and nanostructures (e.g. micropillars, nanowires and nanopillars). To this end, photo- and e-beam lithographed silicon based substrates and anodic alumina membranes (AAO) templates are used as matrices to accommodate the electrodeposited materials. Also, the synthesis of 3D hierarchically porous films by electrochemical means is tackled. Fully metallic (e.g. Cu-Ni) or composite (e.g. Cu-BiOCl) foams showing diverse properties (e.g. superhydrophobicity, ferromagnetism, photoluminescence or electrocatalytic characteristics) are pursued. Particular emphasis is given to new alloy compositions suitable for environmental / sustainable development applications (based on Fe, Cu or Al, without the presence of large amounts of costly noble metals or rare earths), obtained  using non-hazardous approaches. Finally, the synthesis of oxide nanotube arrays with tunable lengths and diameters by anodization of Ti-based alloys is investigated.

                   
                 
 
 

LITHOGRAPHED MAGNETIC STRUCTURES - Led by E.Pellicer, J. Nogués and J. Sort

This line of research aims at probing and understanding the fundamental reversal mechanisms of magnetic lithographed nanostructures, magnetic pillars or magnetic nanowires, sometimes consisting of multilayer structures, by systematically tuning patterning, exchange coupling conditions and dipolar interactions. The main goal is to study the magnetization reversal mechanisms in magnetic micro- and nano-structures composed of multiple components, giving special emphasis on how the reversal of the ferromagnet is modified due to the proximity and interactions with an adjacent antiferromagnet or another neighboring ferromagnet. Research is pursued on how to tailor the magnetization reversal in magnetic heterostructures, not simply by varying their shape, size, and separation, but by adding additional layers to which the ferromagnet can be exchange coupled. In parallel to the experiments, micromagnetic numerical simulations are also conducted. The simulations help to qualitatively and quantitatively interpret the experimental results. The investigated materials are suitable for applications in recording media, spintronics and wireless magnetically-actuated micro-/nano-electro-mechanical systems (MEMS/NEMS).

             
 
PERMANENT AND BIODEGRADABLE BIOMATERIALS

Led by E. Pellicer, M. D. Baró, C. Nogués and J. Sort

We investigate the mechanical properties, corrosion resistance and cytotoxicity of different types of metallic materials (crystalline or amorphous) suitable for permanent orthopedic implants. Traditionally, 316L austenitic stainless steel and Co-Cr alloys have been employed as metallic orthopedic implants. However, these materials exhibit an exceedingly large Young’s modulus and can be cytotoxic. Ti–6Al–4V is currently the most widely used structural Ti-based material for the replacement of hard tissues in artificial joints. Nevertheless, the release of both V and Al ions from this alloy to the human body might cause long-term health problems, such as peripheral neuropathy, osteomalacia, and Alzheimer diseases. Elements like Nb, Zr, Mo or Ta are the safest that can be alloyed with titanium, leading to the so-called “second generation biomaterials”. Usually these alloys contain a large proportion of bcc-Ti solid solution and are known as beta-phase Ti alloys. Alternatively, Ti-based bulk metallic glasses have also attracted huge interest in recent years since they show higher strength and lower Young’s modulus than their crystalline counterparts. All these materials are produced and characterized in our Group.

In turn, the need for temporary implants such as plates, screws, pins, stents and sutures has recently prompted a lively research activity in the field of biodegradable materials. Polymers and metals have been advocated as potential bioabsorbable candidates. Compared to polymers, metals show superior mechanical properties (e.g. higher strength to bulk ratio) which make them the material of choice in many applications. Our research activity in this field focuses on the study of Mg-based amorphous and crystalline alloys. In collaboration with the Department of Cellular Biology, Physiology and Immunology at UAB, we study mouse preosteoblast cells adhesion onto the surfaces of these alloys. The obtained results in this field aim to provide baseline information to fathom out the mechanisms responsible for in vitro biocorrosion of this type of alloys and give some insights regarding their cytotoxicity in a physiological environment.

       
                           
                 
 

MESOPOROUS MATERIALS - Led by E. Pellicer and J. Sort

Among the synthesis pathways leading to nanostructured porous materials, the nanocasting route constitutes a facile, versatile, and easily-scalable procedure. We use the multi-step nanocasting concept to synthesize ordered mesoporous nanocomposite powders from diverse silica templates (e.g. SBA-15, SBA-16, and KIT-6). The obtained materials benefit from the long-range ordering and high specific surface area provided by the packing of the mesopores along with the functional and synergetic properties (e.g. magnetic and optical) arising from the phase constituents. We are interested in combining both different metal oxides (e.g. Co3O4-NiCo2O4) and metal chalcogenides – metal oxides (e.g. CdS-SiO2) in a single mesoporous structure with the aim to either produce novel physicochemical features or to enhance the properties of one of the phase constituents. Mesoporous dilute-oxide magnetic semiconductors (constituted of In2O3 doped with transition metals) are also being investigated.

   
 

EQUIPMENTS & FACILITIES

Shared equipments with:

"Laboratory of magnetic and thermal measurements" (Physics Department, UAB)

"Group of magnetic nanostructures" (Catalan Institute of Nanotechnology)

- Sample preparation

  • Glove Box System (<1ppm O2 & H2O)
  • Rapid solidification (melt spinnig, bulk casting...)
  • Several Ball milling Equipments with atmosphere control
  • Three Potentiostats/galvanostats
  • Sputtering Unit for the growth of metallic and oxide films (including magnetic)
  • Dip coating (EISA method) for the preparation of porous oxide films
  • Dealloying and Anodization setup

- Thermal Characterization   

  • Differential Scanning Calorimetry (up to 1000K)
  • Thermogravimetric/ Thermomagnetogravimetric analysis (up to 1300K)
  • Differential thermal analysis (up to 1500K)
  • Dilatometric analysis (up to 1200K)

- Thermal treatments

  • High vacuum; atmosphere controlled; maximum temperature 1700K
  • Sample hydrogenation

- Metallographic sample preparation

- Morphological characterization (optical microscopies transmission & reflection mode)

- Hardness: macro, micro, nanoidentation (with atomic and magnetic force microscopies)

- Magnetic characterization

  • AC Susceptometer (liquid helium temp up to RT)
  • Two Vibrating sample magnetometers (maximum field: 2.6 Tesla; temperatura range: 100-1000 K; magneto-electric option, up to 200 Volts)
  • MOKE (Magneto-optic Kerr efect), in collaboration with Prof. Nogués
  • SQUID, in collaboration with Prof. Nogués

- Mechanical characterization

  • Static mode (2kN; RT)
  • Dynamic mode (25kN; up to 1500K)
  • Charpy

- Electrochemical corrosion testing

- Density measurements (Archimedes method)

- Resistivity measurements (4 point contact)

Other UAB Facilities:

- Chemical ICP analysis

- Transmission electron microscopy with EDAX

- Scanning electron microscopy with EDAX

- X Ray diffraction (RT up to 700K)

- Cytotoxicity and Cell Adhesion studies (Department of Cellular Biology, Physiology and Immunology)

:: Research