M. V. Kuznetsov

Porous biocompatible implants and tissue scaffolds synthesized by selective laser sintering from Ti and NiTi

An investigation of the technical aspects of producing sufficiently high strength porous biocompatible medical implants and tissue scaffolds from nitinol or pure titanium using selective laser sintering/ melting (SLS/M) is presented. In particular, the necessary processing parameters and procedures for successful laser synthesis of functionally graded implants have been established. Physical and mechanical properties, microstructure, corrosion behavior of the synthesized structures, as well as shape memory in porous layered nitinol structures made using laser synthesis are reported. Comparative morphological and histological results of SLS of porous titanium and nitinol made implants are also presented. Investigations were carried out on primary cultures of dermal fibroblasts and mesenchymal stromal human cells. The possibility of cultivating bone marrow on the porous carrier-incubator made from NiTi and pure titanium in vitro was determined. Sufficient understanding of the nature of laser synthesized titanium and nitinol structures was developed in order to determine their suitability for use as functional implants. This resulted in superior tissue to implant fixation and the development of minimally invasive surgical procedures.

Self-propagating high-temperature synthesis of lithium-chromium ferrites Li0.5Fe2.5-xCrxO4

Pure and chromium-substituted lithium ferrites have been made in air by self-propagating high-temperature synthesis (SHS), a combustion process involving the reaction of lithium peroxide, iron oxide, chromium oxide and iron or chromium metal powders. Three series of SHS samples were produced: by SHS only; by SHS followed by sintering at C for 2 h; and by SHS in a magnetic field of 1.1 T followed by sintering at C for 2 h. X-ray data showed that a cubic spinel ferrite was produced in all cases, with single-phase products achieved after sintering. Systematic changes in lattice parameter were seen both as a function of Cr content and, for the sintered samples, as a result of the field applied during SHS. Scanning electron microscopy showed that the crystallites had sizes of order . Electron microprobe analysis and EDAX indicated that the samples were homogeneous and had the expected Fe-to-Cr ratios. Mossbauer and magnetic hysteresis data showed that there were significant changes in sublattice occupancy and nett magnetization with Cr content. Coercive forces in the Cr-doped ferrites were larger than those in pure compositions. Some differences between Mossbauer and magnetization parameters of the sintered zero-field and applied-field SHS samples were observed.

Preparation of nickel nanoparticles for catalytic applications

Spherical oxidized nickel particles 15 to 200 nm in average size have been produced by a crucibleless aerosol method involving metal vapor condensation in an inert gas flow and oxidation processes. The particles have been characterized by scanning electron microscopy, X-ray microanalysis, X-ray diffraction, BET surface area measurements, and vibrating-sample magnetometry. The process parameters have been optimized for the preparation of particles with tailored size, specific surface area, and saturation magnetization. A dc electric field applied to the condensation zone during the oxidation process reduces the size and increases the extent of oxidation of the particles. We have studied low-temperature oxidation of carbon monoxide and propane on nickel nanopowders differing in particle size and extent of oxidation. The nanoparticles with optimized characteristics have been shown to have a marked catalytic effect on these processes.

Self-propagating high-temperature synthesis of barium-chromium ferrites BaFe12-xCrxO19 (0 <= x <= 6.0)

Pure and chromium substituted barium ferrites BaFe12-xCrxO19 (0 less than or equal to x less than or equal to 6.0) have been synthesised in air by self-propagating high-temperature synthesis (SHS): a combustion process involving a reaction of barium peroxide, iron oxide, chromium oxide and iron metal powder Two series of SMS samples were produced: series 1-zero field SHS, and series 2-SHS in a magnetic field of 1.1 T,both followed by sintering at 1200 degrees C for 2 h. X-ray data showed that hexagonal ferrites were produced, and systematic changes in lattice parameters were seen as a function of the Cr content. Scanning electron microscopy indicated crystallites of order 1 mu m. Energy dispersive x-ray analysis (EDAX) showed that the samples were homogeneous with the; expected Ba:Fe:Cr ratios. Mossbauer, x-ray and magnetic hysteresis data showed a progressive change in the sublattice occupancy and magnetization with Cr content. Some differences in magnetic: parameters were observed between series 1 and 2, implying that the use of a magnetic field during SHS can influence product microstructure. In particular the coercive forces in the Ct doped ferrites showed maxima at x = 1.5 and x = 1.0 for series 1 and 2 respectively, with the series 2 coercivities being consistently 40-50% smaller than their series 1 counterparts. This indicates that applied held SNS provides an alternative route to reducing coercivity in hexagonal ferrites in lieu of conventional approaches such as cationic doping.

The effect of large magnetic fields on solid state combustion reactions: novel microstructure, lattice contraction and reduced coercivity in barium hexaferrite

Combustion reactions of BaO2, Fe2O3 and Fe performed in large applied fields have revealed unexpected modifications in the microstructure of the multiphase combustion product, and in the lattice parameters and coercivity of monophase BaFe12O19 obtained by post-production grinding and sintering.

Electric field-assisted levitation-jet aerosol synthesis of Ni/NiO nanoparticles

Ni/NiO powdered nanoparticles with average sizes 10–30 nm were prepared by a levitation-jet method involving the condensation of Ni metal vapour in a mixture of helium with various amounts of air or oxygen. The process was undertaken with the application of a DC electric field up to 6.5 kV cm−1. The particles were characterized by X-Ray diffraction, transmission electron microscopy, BET adsorption and vibrating sample magnetometry. It was found that the intensity of the applied electric field and partial oxygen pressure correlated with the main structural and magnetic parameters of the nanoparticles, such as average particle size, residual ratio of nickel, coercivity and maximum magnetisation. The specific surface area of the particles correlated with the magnitude of the external electric field. Room-temperature hysteresis loops of weakly oxidized nanoparticles show ferromagnetic-like behaviour, whereas the strongly oxidized ones exhibit a low-field ferromagnetic feature superimposed to a paramagnetic signal, regardless of the particle size. Magnetic measurements allowed for the estimation of the residual metal Ni content in the powdered nanoparticles, which can be as low as 0.04 at.% depending on oxygen partial pressure and external electric field strength.

Low-threshold mode instability in Yb 3+ -doped few-mode fiber amplifiers

Spatio-temporal instability of the fundamental mode in Yb(3+)-doped few-mode PM fiber amplifiers with a core diameter of 8.5 μm was registered at 2-30 Watts pump power. Both experimental and theoretical analysis revealed the nonlinear power transformation of the LP(01) fundamental mode into high-order modes. Numerical simulation revealed self-consistent growth of the higher-order mode and traveling electronic index grating accompanying the population grating induced by the mode interference field (due to different polarizability of the excited and unexcited Yb(3+) ions). Experimental results and numerical calculations showed the increase of the instability threshold along with an increase of the signal frequency bandwidth.

Porous titanium and nitinol implants synthesized by SHS/SLS: Microstructural and histomorphological analyses of tissue reactions

The comparative microstructural analyses and histomorphological studies of tissue reactions to porous titanium and nitinol implants synthesized by Selective Laser Sintering (SLS) are presented for a rat model for bone implants. It was discovered that the surface of porous pegs of titanium and nitinol made by SHS/SLS has a significantly favorable structure to the mechanical interlocking with bone and soft tissues. Histological analysis of decalcified paraffin sections after implant removal could only show that trabecular bone structures and marrow cavities were observed around the porous implants. In the connective tissue of the remaining implant beds the following cells: macrophages, fibroblasts, adipocytes and lymphocytes are discernible. It was shown that the nitinol synthesized by combined SHS/SLS technique has a developed and ordered microstructure.

Laser-induced combustion synthesis of 3D functional materials: computer-aided design

Selective Laser-induced Sintering (SLS) of mixed powders of Ni + Ti; Ni + Al; Ti + Al; TiO2 + ZrO2 + PbO; Al(Al2O3) + Zr(ZrO2); BaO2 + Fe2O3 + Cr2O3 + Fe and Li2O2 + Fe2O3 + Cr2O3 + Fe is presented. Optimization of the process using computer-aided 2D and 3D movement of the laser beam enabled porous monoliths to be prepared of chosen net shape.

Convenient, rapid synthesis of rare earth orthochromites LnCrO3 by self-propagating high-temperature synthesis

Abstract Lanthanide orthochromites of general formula LnCrO 3 (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu) and YCrO 3 have been made by self-propagating high-temperature synthesis (SHS). Four different SHS reactions were found to form LnCrO 3 : reaction of Ln 2 O 3 , Cr and CrO 3 with NaClO 4 or Ba (ClO 4 ) 2 in air; reaction of Ln 2 O 3 , Cr and CrO 3 in oxygen; reaction of LnCl 3 , CrCl 3 and NaO 2 or Na 2 O 2 in air and reaction of Ln (NO 3 ) 3 , Cr and melamine in air. Reactions were studied by DTA and TGA experiments which showed exotherms and weight losses associated with the initiation temperatures ( ca. 350°C) of the SHS reactions. Maximum reaction temperature T c and propagation velocity U c were measured for selected reactions. X-ray powder diffraction showed a single phase orthorhombic perovskite structure was produced in all reactions. Systematic changes in the lattice parameters, cell volume and pycnometrical densities were seen as a function of lanthanide atomic number. SHS prepared LnCrO 3 samples were all shown to be weak antiferromagnets. IR spectra for the LnCrO 3 materials showed bands at 635, 480, 440, 350 and 180 cm −1 .