Self-propagating Synthesis Research Articles

Self-propagating synthesis and CeO2 immobilization of zirconolite-rich composites using CuO as the oxidant

Synroc is recognized as the second generation waste matrice for HLW immobilization. In this research, one of the most important Synroc component, zirconolite, was rapidly synthesized using self-propagating plus quick pressing technique. As the surrogate of tetravalent actinides, CeO2 was introduced to replace the Zr site of zirconolite with nominal formulation of CaZr1−xCexTi2O7. The fraction of minor perovskite phase increases gradually as the CeO2 addition is elevated. The raw Ce4+ was mostly reduced to Ce3+ after SHS reaction, which leads it preferentially occupies the Ca site of perovskite rather than the Zr site of zirconolite. The Ce-bearing waste form (CC-3) exhibits excellent aqueous durability with 42 d normalized leaching rates of Ca, Cu, Zr and Ce in low values of 0.73, 4.97×10−5, 4.15×10−5 and 2.26×10−6gm−2d−1.

Microstructure and electrochemical properties of advanced Li-rich manganese based cathode material synthesized by self-propagating method

Li-rich manganese based cathode material is important in lithium-ion batteries that has received major research attention because of its high specific capacity (more than 250mAhg−1). This work investigates the impact of self-propagating synthesis (SHS) and characterization of Li1.2±xNi0.13±xCo0.13±xMn0.53±xO2 (x=0, 0.3). Li1.2Ni0.13Co0.13Mn0.53O2 delivers the initial capacity of 260.8mAhg−1 at the current rate of 0.1C. The initial capacity loss is attributed to the electrochemical activation of Li2MnO3 which results in the stabilization of the host structure of Li1.2±xNi0.13±xCo0.13±xMn0.53±xO2 (x=0, 0.3) in the following cycles. After 100 cycles, the sample with highest content of Li2MnO3 can remain 84% of the initial capacity. Li2MnO3 component is mainly helpful the stabilization of crystal structure and improvement of capacity, but is negative to the lithium diffusion ability reflected in the poor rate performance. The sample with optimized content of Li2MnO3 delivers the best electrochemical properties.

Self-propagating synthesis, mechanical property and aqueous durability of Gd2Ti2O7 pyrochlore

Synroc is recognized as the second generation waste form for the immobilization of high-level radioactive waste (HLW). In this paper, Gd2Ti2O7/Cu composite was rapidly synthesized by self-propagating high-temperature synthesis plus quick pressing (SHS/QP) using CuO as the oxidant and Ti as the reductant. Different TiO2/Ti ratios were explored to investigate the reactivity of the designed SHS reactions. The result shows that all designed reactions could be ignited and Gd2Ti2O7 pyrochlore was successfully prepared with Cu as the secondary phase. The sample performs an analogous self-encapsulated morphology with Gd2Ti2O7 core and Cu clapping. The synthesized pyrochlore-based waste form possesses high bulk density of 5.53g/cm3 and Vickers hardness of 1047.84 HV0.1. The aqueous durability is also evaluated. There are some fluctuations in the normalized leaching rate of Gd, but it is still acceptable and its average leaching rate is 1.97×10−4gm−2d−1.

Self-propagating synthesis and aqueous durability of Nd-bearing zirconolite-rich composites using Ca(NO3)2 as the oxidant

Synroc is recognized as the second-generation waste form for safety disposal of high-level radioactive waste (HLW). In this study, zirconolite-rich Synroc waste form was readily synthesized by self-propagating high-temperature plus quick pressing (SHS/QP) using Ca(NO3)2 as the oxidant and Ti as the reductant. As the surrogate of trivalent actinides, Nd2O3 was introduced to equally substitute the Ca and Zr sites of zirconolite with nominal stoichiometry of Ca1−xZr1−xNd2xTi2O7. The results demonstrate that zirconolite, perovskite and pyrochlore (Ca2Ti2O6) coexist as the ceramic components after SHS reaction. The introduction of Nd2O3 promotes the formation of perovskite. Nd is mostly incorporated into the Ca sites of these phases. The normalized elemental leaching rates of Ca and Nd are fairly constant in low values of 1.80 × 10−2 g m−2 d−1 and 6.12 × 10−4 g m−2 d−1 after 42 days.

Self-propagating synthesis and characterization of Ca1−xZr1−xNd2xTi2O7 using CuO as the oxidant

Zirconolite-rich composite was rapidly synthesized from self-propagating plus quick pressing using CuO as the oxidant. As the surrogate of trivalent actinides, Nd2O3 was introduced to equally substitute the Ca and Zr sites of zirconolite (nominally Ca1−xZr1−xNd2xTi2O7). The original 2M-zirconolite transforms to identically structured Nd-bearing calcium zirconium titanium oxide (CZTO) after Nd2O3 addition. Nd mostly substitutes the Ca sites of CZTO and perovskite. The aqueous durability of Nd-bearing waste form (CN-3) was evaluated. The normalized leaching rates (42d) of Ca, Cu and Nd are in low values of 0.6, 3.3×10−4 and 1.6×10−5gm−2d−1.

Environmental problems of wood biomass processing. Waste processing lignin

in this paper the ecological problems of wood biomass processing are analyzed. The strongest attention is drawn to the problem of recycling and processing waste materials containing lignin with the help of high temperature self-propagating synthesis.

Study of Cermet Synthesis from Powders Prepared by Chemical Dispersion of Al–Mg (20 wt.%)-Alloy

Powders are obtained containing metal particles during chemical dispersion of Al–Mg (20 wt.%)-alloy. A method of high-temperature self-propagating synthesis is used in order to prepare cermet. Reaction sintering in a filtering combustion regime for a powder workpiece is implemented by heating in air at 550 – 600°C followed by initiation of metal exothermic reaction combustion.

Mössbauer spectroscopy in analyzing products of the self-propagating synthesis of ferrates

A rapid method for producing Na and K ferrates via self-propagating high-temperature synthesis is proposed. To obtain ferrates, samples are prepared under different conditions by changing the ratio of reacting substances, the synthesis temperature, and the duration of mixture heating. The method proposed for ferrate production is quick and easy to use and has practical applications.

Microstructure evolution and formation mechanism of laser-ignited SHS joining between Cf/Al composites and TiAl alloys with Ni–Al–Ti interlayer

In this study, Cf/Al composites and TiAl alloys were joined by a new method named laser-ignited self-propagating synthesis (SHS). Mixed powders of 63.0Ni–31.9Al–5.1Ti (wt%) were used as joining interlayer. Perfect joint was got. The microstructure evolution and formation mechanism of the SHS joint were investigated by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Results show that localized melting occurs on both sides. One γ-Ni0.35Al0.30Ti0.35 and two Ni–Al reaction layers form, respectively, in the TiAl/interlayer and Cf/Al/interlayer interfaces. The combustion of Ni–Al–Ti interlayer begins with the sharp reaction of Ni and Al. The interlayer product is a eutectic organization of NiAl and Al-rich γ.

Phase and morphology studies of B4C–SiC nanocomposite powder synthesized by MASHS method in B2O3, Mg, C and Si system

In this study, ultra fine B4C–SiC composite powder was prepared by mechanically activated self-propagating synthesis (MASHS) method from the raw material of B2O3, Si, C and Mg. Initially the synthesized samples contained MgO, B4C, SiC and a small amount of magnesium borates, residual carbon and silicon. XRD analysis after acid leaching of combustion products showed a great effect of acid leaching on removing the impurities. The remaining substances significantly reduced by increasing the energy of milling. The comparison of diffraction patterns after synthesis and after acid leaching showed that acid leaching had moved the peaks to the lower angles. This is due to the development of solid solution and a decrease in contraction stress during the synthesis. Optimum sample prepared with milling parameter of ball to powder ratio of 20:1, rotation speed 300rpm and milling time of 12h and synthesized at 1000°C furnace temperature. The average crystallite size of B4C and SiC were calculated less than 15nm. These values are consistent with the TEM results while most of grain size was less than 30nm. The particle size analysis of optimum sample indicated that 99.7% of synthesized nanocomposite agglomerated particles were less than 1000nm.

Self-propagating high-temperature synthesis of highly dispersed titanium-carbide phase from powder mixtures in the aluminum melt

The self-propagating synthesis (SHS) of titanium carbide particles in an aluminum melt made from a mixture of titanium and carbon powders with the addition of a chloride-containing flux, aluminum, or haloid salt (Na2TiF6) during the fabrication of the Al-10% TiC alloy is investigated. It is shown that the use of these additives makes it possible to reduce the size of synthesized particles of the TiC carbide phase to ultradispersed (0.17–0.35 μm) and nanosize (smaller than 0.1 μm) levels.

Electrical and microstructural properties of Yb-doped CeO2

Nanopowdered Ce1−xYbxO2−δ solid solutions (0 ≤ x ≤ 0.2) were synthesized by a self-propagating room temperature synthesis. XRD and SEM were used to study the properties of these materials as well as the Yb solubility in CeO2 lattice. Results showed that all the obtained powders were solid solutions with a fluorite-type crystal structure and with nanometric particle size. The average size of Ce1−xYbxO2−δ particles was approximately 3 nm. Electrochemical impedance spectroscopy for the sintered pellets depicted that it was possible to separate Rbulk and Rgb in the temperature interval of 550–800 °C. The activation energy for the bulk conduction was 1.03 eV and for grain boundary conduction was 1.14 eV. Grain boundary resistivity dominates over the other resistivities. These measurements confirmed that Yb3+-doped CeO2 material had a potential as electrolyte for intermediate-temperature solid oxide fuel cell applications.

Fabrication of Silicon Carbide Quantum Dots via Chemical-Etching Approach and Fluorescent Imaging for Living Cells

A simple chemical-etching approach is used to prepare the silicon carbide quantum dots (QDs). The raw materials of silicon carbide (SiC) with homogeneous nanoparticles fabricated via self-propagating combustion synthesis are corroded in mixture etchants of nitric and hydrofluoric acid. After sonication and chromatography in the ultra-gravity field for the etched products, aqueous solution with QDs can be obtained. The microstructure evolution of raw particles and optical properties of QDs were measured. Different organophilic groups on the surface like carboxyl, oxygroup, and hyfroxy were produced in the process of etching. Fluorescent labeling and imaging for living cells of Aureobasidium pulluans were investigated. The results indicated that SiC QDs were not cytotoxic and could stably label due to the conjugation between organophilic groups of QDs and specific protein of cells, it can be utilized for fluorescent imaging and tracking cells with in vivo and long-term-distance. Moreover, mechanism and specificity of mark were also analyzed.

Effect of alloying and temperature of deformation on the grain structure and phase composition of Ni3Al intermetallic

The structure of Ni3Al intermetallic alloyed with boron and hafnium is studied at various temperatures of deformation by means of diffraction and scan electron microscopy. The alloy was produced through self-propagating synthesis. The phase composition of the alloy is determined. The effect of doping with boron and hafnium on the alloy structure morphology is revealed.

SPS Method for Manufacturing Carbide Materials

Due the rapid heating rate combined with high pressure by the Spark Plasma Sintering (SPS) technologies possible manufacture a wide range of novel materials with exceptional properties that cannot be achieved using conventional sintering techniques. Hard metals are, from a technical point of view, one of the most successful composite materials. An overview of the metallurgical reactions during the SPS sintering process of powder mixtures for the manufacture of hard metals is presented. The relatively complex phase reactions in the multi-component system TiC-Mo-W-Ni are discussed. There were elaborated a new technology for the fabrication of nanocrystalline hard metals of a new class assigned for the production of articles with high different characteristics. Elaborated materials are characterized by high melting temperature, hardness, wear-resistance, and satisfactory strength at high temperature and corrosive resistance. Through the use of developed technology and the appropriate structural condition gives possibility to achieve high physical-mechanical characteristics. Obtaining of composite materials via elaborated technology is available from the corresponding complex compounds and directly consisting elements too. In this case High-temperature Self-propagation Synthesis (SHS) and spark plasma sintering/synthesis (SPS) process are united and during a single operation it is possible to get not only the powder materials but at the same time obtain required details.

Self-Propagating Combustion Synthesis and Characterization of ODS Fe-Base Superalloy Powders

A new method was employed to synthesize nanosized Y2O3 dispersion strengthened Fe-base superalloy powders using self-propagating combustion. A concentrated solution of nitrates of iron and yttrium was used as oxidizer, malic acid as fuel to fabricate Fe2O3/Y2O3 powders at low temperature. Afterwards, uniform and fine Fe/2wt.%Y2O3 powders were obtained by selective reduction with hydrogen, on the surface of which dispersive Y2O3 particles of the mean size of 30 - 50 nm were observed.

Self-propagating High-temperature Synthesis of Simulated An3+-Contained Radioactive Graphite in N2 Atmosphere

The self-propagation synthesis (SHS) technology is characterized exclusively in multiple aspects, including: higher reaction rate, simplified procedure, shortened flow-process, facilitated process, lower energy consumption and remote control. In order to evaluate the performance of the self-propagating high-temperature synthesis (SHS) to treat An3+- contained radioactive graphite in N2 atmosphere, in our study, with the exothermic reaction (3C + 4Al + 3TiO2 = 2Al2O3 + 3TiC + Q), we used the following raw powdery materials including graphite (C), aluminum (Al), titanium dioxide (TiO2) and neodymium oxide (Nd2O3, where Nd3+ was used to simulate An3+). After a serial pretreatment including mixing, refinement and formation, a self-developed SHS reactive facility was used to prepare the simulated waste form for the An3+-contained radioactive graphite. Then, X-ray diffractometer(XRD) and scanning electron microscope (SEM) were used to test and analyze the morphology, phase composition and solid solubility of the prepared waste forms. According to the results, the samples with the adding Nd2O3 of 0∼16 wt% could maintain the self-sustainable reaction. And in the designed reaction, the Nd2O3 solid solubility was 1 wt%. The samples were mainly in pieces, with grain sized mainly in 5∼10μm. The samples without adding Nd2O3 content were composed of Al2O3, TiC, C, TiO2 and AlN. With adding Nd2O3 content of 1 wt%, the samples were composted of Al2O3, TiC, C, TiO2, AlN and NdAlO3. While in case of adding Nd2O3 content of over 1 wt%, the occurrence of the Nd2O3 phase was observed in the XRD patterns of the samples.

Research on preparation optimization of nano CeB6 powder and its high temperature stability

High temperature self-propagating synthesis (SHS) process is very rapid, the reaction process becomes un-controlled after the SHS reaction is ignited. So the initial reaction conditions will have great effects on phase compositions and microstructures of reaction products. In this paper, the effects of the proportioning amount of Mg on the yield ratio and particle sizes of CeB6 were studied. The SHS reaction products and leached products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the SHS products consisted of MgO, CeB6 and little Mg3B2O6. The single CeB6 phase was contained after the SHS reaction products were leached. The purity of CeB6 was higher than 99.0 mass%, and the minimum particle sizes of CeB6 were within 30–70 nm. When the proportioning amount of Mg was 25% more than the theoretic amount, the yield of CeB6 was 68.68%. The antioxidant ability of CeB6 was rather stronger, which was oxidized step by step, and the initial oxidation temperature was 750 °C, which indicated that it had good high temperature stability. The apparent activation energies of oxidation reactions of CeB6 were 200.09 and 312.10 kJ/mol, respectively, and reaction orders were 0.69 and 0.40, respectively.

Self-Propagating Synthesis of Ti-Al-C Powder Mixtures

Self-propagating synthesis of Ti-Al-C powder mixture was used for fabrication of master alloys suited to industrial scale manufacturing of Al-TiC composites. The cold compacted powder pellets were heated in a protective atmosphere until the melting point of aluminium. Then the temperature of pellets increased rapidly due to intense exothermic reaction between molten Al and Ti, resulting in simultaneous formation of Al3Ti and Al4C3. When the temperature exceeded ~1090°C, TiC particles started to form as a result of the mutual reaction between Al3Ti and Al4C3. Resulting reaction products consisted of fine (~Subscript textub>2µm) TiC particles uniformly distributed in the Al matrix. The composition of powder mixture was optimized to attain master alloy pellets containing ~50 vol.% TiC. Such pellets were then diluted in molten aluminium to produce Al+TiC composites. In-situ formation of TiC in Al matrix provided favourable interfacial quality, which avoided dewetting and rejection of particles from molten aluminium. The parameters for composite casting were optimized in order to reduce the effect of reversible reaction leading to undesired formation of Al3Ti or Al4C3. The final composites showed significantly increased Young’s modulus and strengths. The potential of using the approach for the fabrication of fine, nearly spherical TiC particulate reinforced Ti composites is briefly discussed. The simple process is very promising for economical manufacturing of highly efficient lightweight structural materials.

EPR and photoluminescence properties of green light emitting LaAl11O18:Mn2+ phosphors

The LaAl11O18:Mn2+ powder phosphor has been prepared using a self-propagating synthesis. Formation and homogeneity of the LaAl11O18:Mn2+ phosphor has been verified by X-ray diffraction and energy dispersive X-ray analysis respectively. The EPR spectra of Mn2+ ions exhibit resonance signals with effective g values at g≈4.8 and g≈1.978. The signal at g≈1.978 exhibits six-line hyperfine structure and is due to Mn2+ ions in an environment close to tetrahedral symmetry, whereas the resonance at g≈4.8 is attributed to the rhombic surroundings of the Mn2+ ions. It is observed that the number of spins participating in resonance for g≈1.978 increases with decreasing temperature obeying the Boltzmann law. Upon 451nm excitation, the photoluminescence spectrum exhibits a green emission peak at 514nm due to 4T1 (G)→6A1 (S) transition of Mn2+ ions. The crystal field parameter Dq and Racah inter-electronic repulsion parameters B and C have been evaluated from the excitation spectrum.