Jarosław Jakubowicz

Nanocrystalline titanium-type metal hydride electrodes prepared by mechanical alloying

Abstract Mechanical alloying (MA) was employed to produce nanocrystalline TiFe 1− x Ni x alloys ( x =0, 0.25, 0.5, 0.75 and 1.0). XRD analysis showed that, after 25 h of milling, the starting mixture of the elements had decomposed into an amorphous phase. Following annealing in high purity argon at 750°C for 0.5 h, XRD confirmed the formation of the CsCl-type structures with crystallite sizes of about 50 nm. These materials were used as negative electrodes for a Ni–MH x battery. With increasing nickel content in TiFe 1− x Ni x , the material shows an increase in discharge capacity which passes through a maximum for x =0.75. In the nanocrystalline TiFe 0.25 Ni 0.75 powder, discharge capacities of up to 155 mA h g −1 (at 40 mA g −1 discharge current) were measured. The titanium-based hydrogen storage alloys are attractive for secondary batteries, because of inexpensive raw materials.

Porous silicon formation by mechanical means

Porous silicon has been fabricated by both “top-down” techniques from solid silicon and “bottom-up” routes from silicon atoms and silicon-based molecules. Over the last 50 years, electrochemical etching has been the most investigated approach for chip-based applications and has been utilized to create highly directional mesoporosity and macroporosity. Chemical conversion of porous or solid silica is now receiving increasing attention for applications that require inexpensive mesoporous silicon in powder form. Very few techniques are currently available for creating wholly microporous silicon with pore size below 2 nm. This review summarizes, from a chronological perspective, how more than 30 fabrication routes have now been developed to create different types of porous silicon.

Surface analysis of polycrystalline and nanocrystalline LaNi5-type alloys

Abstract The chemical composition and the cleanness of the surface of polycrystalline and nanocrystalline LaNi 5 , LaNi 4.2 Al 0.8 , and LaNi 3 AlCo alloys were studied by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Results showed that the surface segregation under UHV conditions of lanthanum atoms in the mechanically alloyed nanocrystalline samples is significantly stronger compared to that of polycrystalline powders obtained from arc-melted ingots. On the other hand, the level of oxygen impurities trapped in the mechanically alloyed powder during the processing is practically the same as in the arc-melted ingots. Furthermore, we have estimated an average native oxide layer thickness of nanocrystalline LaNi 4.2 Al 0.8 as ∼5 nm. A strong segregation of the Fe impurities to the surface could be responsible for the observed slightly lower hydrogen storage capacity of the mechanically alloyed nanocrystalline LaNi 4.2 Al 0.8 compared to that of polycrystalline sample.

Magnetic properties of nanostructured Nd2(Fe,Co,Cr)14B/α-Fe magnets

The effect of intergrain exchange interactions on remanent magnetic polarization and intrinsic coercivity in nanostructured Nd12.6Fe67.8Co11.6Cr2B6/α-Fe magnets, with volume fractions of the soft magnetic phase of 0 and 37.5%, was studied experimentally and numerically. Epoxy bonded magnets were formed and values of 4πMr and JHc of 1.1 T and 760 kA m−1 were obtained, respectively.

Corrosion protection of nanocomposite Nd–Fe–B/α-Fe magnets

Abstract The magnetic properties and corrosion behaviour of two phase nanocomposite Nd 2 (Fe,Co,M) 14 B/α-Fe-type (M=Zr, AlCr) magnets have been investigated. In this work magnetic hardening was achieved by high-energy ball-milling (HEBM) of the Nd 2 Fe 14 B-type hard magnetic phase with 37.5 vol% of α-Fe as soft magnetic phase, followed by annealing. Fully dense Nd 2 (Fe,Co,M) 14 B/α-Fe-type magnets have been produced by hot pressing. The corrosion behaviour has been studied by potentiostatic measurements. For the Nd 12.6 Fe 66.8 Co 11.6 Al 1 Cr 2 B 6 /37.5 vol% α-Fe magnet, the corrosion rate was 0.037 mm year −1 . Effective protection against corrosion for nanocomposite Nd–Fe–Co–Al–Cr–B/α-Fe magnets was realised by surface coating with Zn metal.

Improved temperature and corrosion behaviour of nanocomposite Nd2(Fe,Co,M)14B/α-Fe magnets

Abstract The characteristics of the magnetic properties nanocomposite Nd 2 (Fe,Co,M) 14 B/α-Fe magnets obtained by high energy ball milling and powder metallurgy routes have been improved by appropriate Al–Cr, Cr, Zr additions. Using a single phase close to the stoichiometric composition, nanocomposite Nd 12.6 (Fe,Co,M) 81.4 B 6 /α-Fe magnets with better temperature stability are produced, due to the disappearance of the Nd-rich grain boundary phase in Nd 2 (Fe,Co) 14 B/α-Fe materials. If the content of the soft magnetic α-Fe phase in Nd 2 (Fe,Co,M) 14 B/α-Fe composities increases, the thermal stability of the coercivity increases, too. For a Nd 12.6 Fe 69.3 Co 11.6 Zr 0.5 B 6 /α-Fe magnet, containing 37.5 vol% α-Fe, the temperature coefficients (from 293 to 413 K) of remanence α ( J r ) and coercivity β ( J H c ) are: −0.07 and −0.35% K −1 , respectively. Nanocomposite magnets appears to be more corrosion resistant than sintered Nd–Fe–B magnets.

Structure and magnetic properties of Nd2(Fe,Co,Al,Cr)14B/α-Fe nanocomposite magnets

Abstract The structure, magnetic properties and corrosion behaviour of two-phase nanocomposite Nd 2 (Fe,Co,Al,Cr) 14 B/α-Fe-type magnets, which have tetragonal/cubic Nd 2 Fe 14 B/α-Fe structure, have been investigated. The magnetic hardening was achieved by high-energy ball-milling (HEBM) of the Nd 2 Fe 14 B-type hard magnetic phase with different vol.% of α-Fe as soft magnetic phase, followed by annealing. Fully dense Nd 2 (Fe,Co,Al,Cr) 14 B/α-Fe type magnets have been produced by hot pressing. Magnets with good corrosion resistance as well as high temperature stability have been produced. The corrosion resistance is improved in the case of Co-, Al-, Cr-doped nanocomposite magnets with a volume fraction of the soft magnetic phase of 37.5 vol.%. Effective protection against corrosion was realised also by surface coating with Zn metal.

Magnetic properties of nanocomposite Nd2(Fe,Co,M)14B/α-Fe-bonded magnets

Abstract Nanocomposite Nd 12.6 Fe 69.8− x Co 11.6 M x B 6 /α-Fe (M=Al-Cr, V, Cr, Ni, Zr or Mo) powders, with a volume fraction of magnetically soft α-Fe phase of 10 and 37.5%, have been prepared by a high-energy ball-milling (HEBM) and annealing. Enhanced remanent magnetic polarizations up to 1.15 T were obtained. It has been found that addition of a small amount of Al-Cr, Cr, Zr or Mo to Nd 12.6 Fe 69.8− x Co 11.6 M x B 6 /α-Fe can improve the intrinsic coercivity and the hysteresis squareness of the Nd 2 (Fe,Co) 14 B/α-Fe-based nanocomposite materials. The improvements may be related to refined grain sizes realized by these additives. Bonded magnets of J r and J H c ranging from 0.81 T and 840 kA m −1 to 1.10 T and 760 kA m −1 have been produced from Nd 12.6 Fe 67.8 Co 11.6 Cr 2 B 6 /α-Fe, with a 10 and 37.5% volume fraction of soft α-Fe phase, respectively.

Nanostructured Titanium-10 wt% 45S5 Bioglass-Ag Composite Foams for Medical Applications

The article presents an investigation on the effectiveness of nanostructured titanium-10 wt% 45S5 Bioglass-1 wt% Ag composite foams as a novel class of antibacterial materials for medical applications. The Ti-based composite foams were prepared by the combination of mechanical alloying and a “space-holder” sintering process. In the first step, the Ti-10 wt% 45S5 Bioglass-1 wt% Ag powder synthesized by mechanical alloying and annealing mixed with 1.0 mm diameter of saccharose crystals was finally compacted in the form of pellets. In the next step, the saccharose crystals were dissolved in water, leaving open spaces surrounded by metallic-bioceramic scaffold. The sintering of the scaffold leads to foam formation. It was found that 1:1 Ti-10 wt% 45S5 Bioglass-1 wt% Ag/sugar ratio leads to porosities of about 70% with pore diameter of about 0.3–1.1 mm. The microstructure, corrosion resistance in Ringer’s solution of the produced foams were investigated. The value of the compression strength for the Ti-10 wt% 45S5 Bioglass-1 wt% Ag foam with 70% porosity was 1.5 MPa and the Young’s modulus was 34 MPa. Silver modified Ti-10 wt% 45S5 Bioglass composites possess excellent antibacterial activities against Staphylococcus aureus. Porous Ti-10 wt% 45S5 Bioglass-1 wt% foam could be a possible candidate for medical implants applications.

Nd2(Fe,Co,M)14B-type magnet powders produced by the HDDR process

Abstract The relationship between the various HDDR processing parameters and the magnetic properties of Nd 2 (Fe,Co,M) 14 B-type materials with partial replacement of Fe by Zr, V, Cr, Ga and Al or Al–Cr have been studied. Aligned anisotropic powders show values of ( BH ) max ∼ 180 kJ m −3 for Nd 16 Fe 66.4− x Co 11.6 M x B 6 (M x =Zr 0.5 , Cr 0.25 and Al 1 Cr 2 ) materials.