Yuri G. Morozov

Self-propagating high-temperature synthesis of SrFe12O19 from reactions of strontium superoxide, iron metal and iron oxide powders

Abstracts are not published in this journal

Convenient, low energy routes to hexagonal ferrites MFe12O19(M=Sr, Ba) from SHS reactions of iron, iron oxide and MO2 in air

Thermal initiation of a mix of metal superoxide (MO2 , M=Sr, Ba), iron and iron powder in air induces a self propagating reaction with velocity 0.5 mm s–1 and the formation of predominantly MFe12O19 . Heating the mixture to 1150 °C for 2 h produces pure crystalline MFe12O19 . The ferrites were characterised by X-ray powder diffraction (Rietveld analysis), FTIR, VSM magnetism, EDAX/SEM, electron probe analysis and Mossbauer spectroscopy. The ferrites showed good purity, coercivity, remanence and hysteresis loops compared to commercial samples. Preparation of ferrite solid solutions MxM′yFe12O19 (M=Sr, Ba, Pb) was investigated.

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.

Combustion synthesis of alkaline-earth substituted lanthanum manganites; LaMnO3, La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3

Alkaline-earth substituted lanthanum manganites La1 − xAxMnO3 (A = Ca, Sr; x = 0, 0.4) were synthesized in air by self-propagating high-temperature synthesis (SHS): a combustion process involving the reaction of lanthanum(III) oxide, calcium oxide (or carbonate), strontium peroxide, manganese metal powder and sodium perchlorate. A very sensitive thermal imaging method was used to study the combustion characteristics of the SHS-process. This method is based on the continuous measurement of the combustion process using an IR-camera and software developed by MIKRON Instrument Co., Inc. (M9100 Pyrovision Series – Imaging Pyrometer). X-Ray powder diffraction, scanning electron microscopy (SEM)/energy dispersive analysis by X-rays (EDAX), infrared spectroscopy and vibrating sample magnetometry were carried out on all samples. X-Ray diffraction data showed that single-phase orthorhombic LaMnO3 and monoclinic La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3 were formed. Magnetic properties were found to transform from antiferromagnetic for LaMnO3 to weak ferromagnetic for La0.6Ca0.4MnO3 to strong ferromagnetic for La0.6Sr0.4MnO3. The experimental results show the SHS route is useful for the synthesis of multicomponent Mn-based oxides. The thermal imaging work enables accurate monitoring of the SHS combustion process and enabled velocity of propagation, maximum temperature, cooling rates, synthesis wave width and synthesis wave path to be determined with high precision.

Combustion synthesis of chromium-substituted lithium ferrites Li0.5Fe2.5−xCrxO4 (x≤2.0): Rietveld analysis and magnetic measurements

Abstract Pure and chromium-substituted lithium ferrites Li 0.5 Fe 2.5− x Cr x O 4 ( x ≤2.0) 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. Reactions were performed in zero field and in an applied magnetic field of 1.1 T. Both the zero field and the applied field SHS reactions proceeded with a synthesis wave which spread out from the point of initiation. Notably the applied field synthesis waves were faster and hotter than their zero field counterparts. The products from the SHS reaction were ground and sintered at 1150°C for 2 h. Rietveld analysis of the powder X-ray data on the sintered samples showed that in all cases a cubic spinel ferrite was produced which showed a decrease in the lattice parameter with increasing Cr content. The x =0 applied field sample showed 87% superstructured and 13% disordered LiFe 2.5 O 4 whilst the zero field sample showed 30% superstructured LiFe 2.5 O 4 and 70% disordered LiFe 2.5 O 4 . X-ray line broadening indicated crystallites of order 70–90 nm in all samples. Electron microprobe analysis and EDAX showed that the samples were homogeneous and had the expected Fe to Cr ratios. Mossbauer and magnetic hysteresis data showed a significant change in sublattice occupancy and net magnetisation with Cr content. Coercive forces in the Cr-doped ferrites were larger than in pure compositions. Samples prepared in an applied magnetic field exhibited smaller coercivity and saturation magnetisation compared to those prepared in zero magnetic field.

Dual-wavelength generation by vertical external cavity surface-emitting laser

A high-power dual-wavelength AlGaInAs / GaAs laser operating in a vertical external-cavity surface emitting geometry, grown by molecular beam epitaxy, is reported. The active regions of the laser are separated by an optical long-wave-pass filter to prevent absorption of short-wavelength radiation in the long-wavelength gain area. The maximum output power achieved at 15 degrees C was 0.75 W at lambda approximately 966 nm and 1.38 W at lambda approximately 1047 nm for the pump power of 21.2 W.

Advanced Ways and Experimental Methods in Self-Propagating High-Temperature Synthesis (SHS) of Inorganic Materials

New experimental methods for investigations of phase formation during SHS have been established. First experiments using penetrating synchrotron radiation and energy dispersive detectors for different classes of complex inorganic materials were carried out at ESRF (Grenoble, France) and Daresbury (UK). A new and very sensitive thermal imaging method (Thermal Imaging Technique (TIT)) based on continuous registration of the whole combustion process by using highly sensitive IR-camera and software developed by MIKRON Instruments Co. (USA) was used for precise registration of the combustion parameters. SHS was performed on different types of pure and doped complex inorganic materials in pellet and powder form in a range of dc magnetic fields up to 20 T and in electrical field strengths up to ±220 kV/m. The dc magnetic field was applied during the reaction, supplied either by a permanent magnet (transverse, up to 1.1 T) or by an electromagnet (longitudinal, up to 20 T). The dc electrical field was applied along the direction of the combustion wave front propagation. The combined processes of SHS and SLS (Selective Laser Sintering) of 3D articles for different powdered compositions were optimized with laser irradiation power.

Electrochemistry and Dynamic Ionography of Self-Propagating High-Temperature Synthesis (SHS)

The results of a new potentiometric technique for in situ diagnostics of self-propagating high-temperature synthesis (SHS) of different complex oxides are presented. This technique is based on electrochemical processes. The characteristic peaks attributed to the electric responses from cation streams of alkali, alkaline-earth and some elements of group VI are discovered and the respective routes of the corresponding chemical reactions found.