Synthesis of Micron and Submicron Nickel and Nickel Oxide Particles by a Novel Laser–Liquid Interaction Process

The laser–liquid–solid interaction is a new technique for synthesis of nickel and nickel oxide particles. The process uses a continuous-wave CO₂ laser beam as the source of thermal energy required to induce precipitation reactions in solution. The uniqueness of the process is the synthesis reaction taking place in a localized region, which allows better control of the chemical reaction. Porous nickel and nickel oxide powders have been synthesized by laser-induced reactions between a nickel nitrate hexahydrate [Ni(NO₃)₂·6H₂O] precursor and 2-ethoxyethanol-based mixtures. Nickel powders were produced after irradiating a solution of the precursor salt and a 2-ethoxyethanol and d-sorbitol mixture. Crystalline nickel oxide (NiO) powders were isolated after irradiating a solution containing the precursor salt and a 2-ethoxyethanol and water mixture. Powders containing both nickel and nickel oxide crystalline phases were produced after irradiating a solution of the precursor salt and 2-ethoxyethanol. The mean particle diameter is found to be sensitive to irradiation time, substrate thermal conductivity, irradiation power density, and solution concentration. It is hypothesized that nucleation and growth of crystalline phases occurring in irradiated solutions are thermal driven.     

Production of alumina fibre through jute fibre substrate

Alumina fibre has been produced using jute fibre as substrate material at temperatures lower than 1600 C in a reducing atmosphere. Processed jute fibre was chemically pretreated by saturation with Al₂Cl₆ · 12H₂O, coked and then pyrolysed to obtain alumina fibre. Chemical pretreatment conditions have been determined by following weight loss measurements of the jute fibre at 0.1 to 0.6 N solutions of NaOH, KOH, NH₄OH, Na₂CO₃, K₂CO₃, HCl and acetic acid. The effect of heat treatment on the jute fibre and jute fibre + aluminium salt has been studied from 150 to 1600 C. Trace elements present (Fe₂O₃, SiO₂, K₂O, Na₂O, CaO, MgO, ZnO, MnO, V₂O₅, P₂O₅, CuO) on heat-treated products have been determined by atomic absorption spectrometry. Optical and scanning electron micrographs of representative samples showing growth mechanism are presented. The effect of copper, nickel and platinum catalysts and fluxing agents such as K₂O and Na₂O in fibre formation has also been examined. Particle size and surface area analyses of intermediate and final products have been carried out. Changes in 2 values are plotted for various products from X-ray diffraction studies. It is conceived that the porous surface of cellulosic fibrils in the jute fibre adsorbs the AlCl₃ molecules which decompose to oxide and are gradually shaped to the fibrous form during the course of thermal treatment in a reducing atmosphere and due to the high surface area.     

Preparation of nanosized perovskite LaNiO3 powder via amorphous heteronuclear complex precursor

Nanosized lanthanum nickel oxide powder LaNiO₃ with perovskite structure was successfully synthesized at a relatively low calcination temperature by using an amorphous heteronuclear complex LaNi(DTPA) · 6H₂O as a precursor. The precursor decomposed completely into nickel oxide above 600°C based on the DTA and TGA results. XRD demonstrated that nanosized LaNiO₃ crystalline powder with pure perovskite structure was obtained after the calcination temperature increased to 700°C. The effects of calcination time and temperature were also examined by XRD and TEM. The results indicated the grain size and the crystal size of LaNiO₃ increased with the calcination temperature from 600°C to 900°C, and were less influenced by the heat-treatment time. The electrical resistivity of the powder decreased when the calcination temperature increased. It can be concluded that it is a useful way to synthesize nanosized perovskite oxides using an amorphous complex as a precursor, and this method can be easily quantitatively controlled.     

Synthesis and characterization of NiO-YSZ for SOFCs

Nickel oxide and yttria-stabilized zirconia ceramic materials were prepared by three methods: physical mixture, a modified Pechini route, and impregnation with Ni(NO₃)₂·6H₂O. Temperature-programmed reduction (TPR) analysis showed the presence of different reduction peaks for each sample and that the reduction temperature was influenced by the employed preparation procedure. Nickel oxide species are completely reduced at temperatures up to 1000 °C and their temperature-programmed reduction profiles indicated that a higher temperature reduction corresponds to a higher calcination temperature. Furthermore, the composites synthesized through impregnation presented nickel oxide species more easily reducible than those prepared by the two other methods. Scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) evidenced a larger nickel oxide coating on yttria-stabilized zirconia for the composite synthesized through the impregnation method. The electrical conductivity of impregnation sample was 117 S cm⁻¹ at 850 °C, a value three times higher than that of the physical mixture.     

Preparation and characterization of NiO nanorods by thermal decomposition of NiC2O4 precursor

Synthesis of nickel oxide (NiO) nanorods was achieved by thermal decomposition of the precursor of NiC₂O₄ obtained via chemical reaction between Ni(CH₃COO)₂·2H₂O and H₂C₂O₄·2H₂O in the presence of surfactant nonyl phenyl ether (9)/(5) (NP-9/5) and NaCl flux. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structure features and chemical compositions of the as-made nanorods. The results showed that the as-prepared nanorods is composed of NiO with diameter of 10–80 nm, and lengths ranging from 1 to 3 micrometers. The mechanism of formation of NiO nanorods is also discussed.     

Phase equilibria in the system CdO-B2O3-GeO2 at 800°C

Phase equilibria in the system CdO-B₂O₃-GeO₂ were investigated at 800° C using X-ray powder diffraction techniques. The binary phases reported previously as produced by solid-state reactions were confirmed and, in addition, a new one CdO·2GeO₂ was found. The ternary phase diagram was solved and a new phase CdO·B₂O₃·GeO₂ was discovered. X-ray powder data are given for both these new phases. Solid solution effects were investigated for the primary and binary phases by comparison of patterns; no solid solutions were detected. The relationship of the phase diagram to the composition of photoconductive oxide glasses is discusssed in the light of previous suggestions made of possible mechanisms responsible for the photoelectric effects.     

Preparation of Ni particles by ultrasonic spray pyrolysis of NiCl2·6H2O precursor containing ammonia

The preparation of nickel particles from nickel ammine complex was studied by ultrasonic spray pyrolysis in the presence and the absence of hydrogen. In the presence of H₂ (about 9 vol.%), nickel particles were formed at 500 °C, which is much lower than that reported. Metallic nickel, together with NiO, was obtained as a major phase at 400 °C. In the absence of H₂, metallic Ni was also obtained, but higher temperature (e.g. 900 °C) was needed. It is suggested that the addition of NH₃·H₂O and NH₄HCO₃ to NiCl₂·6H₂O precursor changes the reaction pathway of Ni formation. By careful control, spherical, solid and well-distributed Ni particles of about 0.5 m were obtained at a residence time of 7–9 s in the aerosol reactor.     

Chemical vapour deposition of aluminium based micro- and nanostructured surfaces for biological applications

Aluminium hydride oxide, HAlO, an Al-compound with hydrogen and oxygen directly bound to aluminium is produced by chemical vapour deposition (CVD). At higher process-temperatures a second material, Al·Al₂O₃, can be obtained. These materials differ not only in chemical composition, but also in surface morphology. While the first forms a smooth structural surface, the second builds up a highly chaotic surface composed of nanowires.The different behaviour of normal human dermal fibroblasts (NHDF) on these surfaces in terms of proliferation and differentiation was studied. NHDF have the possibility to differentiate into their contractile form, the myofibroblast (MF), as a response to the contact with a given surface or upon induction by growth factors.We were able to show, that cell compatibility and proliferation on HAlO and on Si-wafers are comparable, whereas NHDF do not proliferate on Al·Al₂O₃. MF differentiation could be seen on both, HAlO and Si-wafer, but not on Al·Al₂O₃.     

Hydrotalcite-like compounds obtained by anion exchange reactions

The synthesis of nickel aluminium hydroxypicrate, [Ni₃Al(OH)₈] (C₆O₇N₃H₂)·nH ₂O, and lithium aluminium hydroxypicrate, [Al₂Li(OH)₆] (C₆O₇N₃H₂)·nH ₂O by anion exchange is described. Picric acid and the corresponding hydroxycarbonates were used as starting materials. The new compounds were characterized by chemical analyses, electron microscopy, infrared spectroscopy and X-ray diffraction. The results obtained indicate that both are hydrotalcite-like compounds where the picrate anion lies between the basic layers. The thermal decomposition of the compounds was studied by differential thermal and thermogravimetric analysis.     

Comparison of some properties of neodymium-doped silica glasses prepared by sol-gel and melting

Samples with 10Nd₂O₃·5CaO·17Al₂O₃·68SiO₂ composition (mol %) were prepared by the sol-gel method and by melting. The structure of the samples was investigated by X-ray diffraction, scanning electron microscopy, infrared spectroscopy, a.c. susceptibility measurements and electron spin resonance. The gel-derived sample heat-treated between 250 and 700°C is amorphous and has a granular microstructure. In the samples heat-treated at 800, 900 and 1000°C we detected by X-ray diffraction AlNdO₃ crystalline particles. The melted sample was amorphous and the micrograph shows a glass matrix containing particles. The infrared measurements show structural changes produced by the heat-treatment of the gel samples. The magnetic susceptibility data indicates that neodymium oxide is present in these samples as Nd³⁺-O-Nd³⁺ aggregates with an antiferromagnetic interaction.     

Interface studies on crystallized alumina-silica fibre-reinforced Al-Si alloy composites

On applying heat treatments to the amorphous alumina-silica fibre (55% Al₂O₃, 45% SiO₂), the mullite crystal is separated out, and the crystallinity depends on the heat treatment parameters. The crystallized alumina-silica fibre shows higher hardness than amorphous alumina-silica fibre and a remarkable stability to chemical reaction with molten metal. The primary interfacial reaction zone product was found to be 2MgO · SiO₂.     

Mechanical and thermal properties of silicon-carbide composites fabricated with short Tyranno® Si-Zr-C-O fibre

Silicon carbide (SiC) composites reinforced with 10–50 mass% (10.5–51.2 vol%) of short Tyranno® Si-Zr-C-O fibre (average length 0.5 mm) and 0–10 mol% of Al₄C₃as a sintering aid were fabricated using the hot-pressing technique. Firstly, the effect of Si-Zr-C-O fibre addition on the relative density (bulk density/true density) of the SiC composite hot-pressed at 1800 °C for 30 min was examined by fixing the amount of Al₄C₃to be 5 mol%. Although the relative density was reduced to 87.4% for 10 mass% of Si-Zr-C-O addition, further increases in the amount of Si-Zr-C-O fibre increased density to a maximum of 92.8% at 40 mass% of fibre addition. Secondly, the effect of varying the amount of Al₄C₃addition on the relative density was examined by fixing the amount of Si-Zr-C-O fibre to be 40 mass%. The optimum amount of Al₄C₃addition for the fabrication of dense SiC composite was found to be 5 mol%. The fracture toughness of the hot-pressed SiC composites with 20–40 mass% of Si-Zr-C-O fibre addition (amount of Al₄C₃: 5 mol%) was 3.2–3.4 MPa · m^1/2and approximately 1.5 times higher than that (2.39 MPa · m^1/2) of the hot-pressed SiC composite with no Si-Zr-C-O fibre addition. SEM observation showed evidence of Si-Zr-C-O fibre debonding and pull-out at the fracture surfaces. The hot-pressed SiC composite with 5 mol% of Al₄C₃and 40 mass% of Si-Zr-C-O fibre additions showed excellent heat-resistance at 1300 °C in air due to the formation of a SiO₂layer at and near exposed surfaces.     

Phase transformation of calcia-alumina-magnesia fibres produced by inviscid melt spinning

CaO-Al₂O₃-MgO (CAM) ceramic fibre produced via inviscid melt spinning (IMS) was investigated for phase transformation. Differential thermal analysis (DTA) on the as-spun CAM fibre gave two transformation peaks, one for exothermic peak at around 927°C and the other for endothermic one at around 1100°C. In order to identify each phase transformation x-ray diffraction (XRD) analysis was performed on the CAM fibres heat-treated to each phase transformation completion temperature. The exothermic peak was determined to represent crystallization of remaining amorphous phase in the as-spun CAM fibre. The endothermic peak was determined to correspond to transformation of non-equilibrium CaO · Al₂O₃ phase to equilibrium 3CaO· 5Al₂O₃ phase.     

Microstructure and mechanical properties of silicon carbide fibre-reinforced aluminium nitride composite

SiC continuous fibre (15 vol%)/AlN composite was fabricated using a sintering additive of 4Ca(OH)₂ · Al₂O₃ by hot-pressing at 1650 °C and 17.6 MPa in vacuum. Analytical transmission electron microscopy and scanning electron microscopy were used to investigate the microstructure of as-fabricated and crept SiC fibre/AlN composites. The room-temperature mechanical and high-temperature creep properties of the composite were investigated by four-point bending. The incorporation of SiC fibre into AlN matrix improved significantly the room-temperature mechanical properties. This improvement could result from the crack deflections around the SiC fibres. However, the incorporation degraded severely the high-temperature creep properties under oxidizing atmosphere. This could be attributed to the development of the pores and various oxides at the matrix grain boundary and matrix/fibre interface during creep test.     

Interface analysis in Al and Al alloys/Ni/carbon composites

Nature of fibre/matrix interfaces existing in Al/C composites were investigated depending on the presence of a nickel interlayer deposited on carbon fibres and on the composition of the aluminium matrix. Auger and electron microprobe analyses were used. The role of the nickel layer on the chemical evolution of the system after a 96 h heat treatment at 600°C is discussed. The presence of this nickel layer limits the diffusion of carbon into aluminium, and thereby, eliminates the formation of a carbide interphase, Al₃C₄, which is known to lower the mechanical properties of Al/C composites. The mechanisms differ according to the composition of the matrix. In the case of pure aluminium, an Al-Ni intermetallic is formed after thermal annealing. It does not react with the carbon fibre and so inhibits the growth of Al₃C₄. In the case of the alloyed matrix (AS7G0.6), the dissolution of the Ni sacrificial layer, after annealing, does not lead to the same Al-Ni intermetallic but a thin nickel layer remain in contact with the carbon fibre avoiding formation and growth of Al₃C₄ carbide. This difference of behaviour is tentatively ascribed to the presence of silicon that segregates at the fibre/matrix interface.     

Pack cementation process for the formation of refractory metal modified aluminide coatings on nickel-base superalloys

The vapour phase compositions of a series of pack powder mixtures containing elemental Al and Hf or W powders as depositing sources and CrCl₃·6H₂O or AlF₃or CrF₃as activators were analysed in an attempt to further develop the pack cementation process to codeposit Al and Hf or W to form diffusion coatings on nickel base superalloys. The results suggested that Al could be codeposited with Hf, but not with W, from the vapour phase. Compared with both AlF₃and CrF₃, CrCl₃·6H₂O has been shown to be a more suitable activator for codepositing Al with Hf. The optimum coating temperature was identified to be in the range of 1050°C to 1150°C. Based on the thermochemical analysis, a series of coating deposition studies were undertaken, which confirmed that codeposition of Al and Hf could be achieved at a deposition temperature of 1100°C in the CrCl₃·6H₂O activated packs containing elemental Al and Hf powders. The coating obtained had a multilayer structure consisting of a Ni₇Hf₆Al₁₆top layer and a NiAl layer underneath, followed by a diffusion zone, which revealed that the coating was formed by the outward Ni diffusion. It is suggested that the compositions suitable for codeposition of Al and Hf could be effectively identified by comparing the vapour pressures of HfCl₄and HfCl₃with that of AlCl in the packs activated by chloride salts. It has also been experimentally demonstrated that, although W could not be deposited from the vapour phase, a high volume of fine W particles can be entrapped into the outer NiAl coating layer formed by the outward Ni diffusion using a modified pack configuration. This leads to the formation of a composite coating layer with W particles evenly distributed in a matrix of NiAl. It is suggested that this modified pack process could be similarly applied to develop nickel aluminide coatings containing other refractory metals that may not be codeposited with Al from the vapour phase.     

Fabrication of ultrafine tungsten-based alloy powders by novel soda reduction process

A novel reduction method has been developed to fabricate ultrafine tungsten heavy alloy powders, with ammonium metatungstate (AMT), iron(II) chloride tetrahydrate (FeCl₂·4H₂O), nickel(II) chloride hexahydrate (NiCl₂·6H₂O) as source materials and sodium tungstate dihydrate (Na₂WO₄·2H₂O) as a reductant. In the preparation of mixtures the amounts of the source components were chosen so as to obtain alloy of 93W-5Ni-2Fe composition (wt.%). The obtained powders were characterized by X-ray diffraction, XPS, field-emission scanning microscope (FESEM), and chemical composition was analyzed by EDX.     

Kinetic dissociation of nickel titanate and nickel tungstate in oxygen potential gradients

Nickel titanate (NiTiO₃) and nickel tungstate (NiWO₄) were exposed to oxygen potential gradients at 1400 and 1100° C, and they were found to dissociate into their constituent oxides, namely, NiO and TiO₂, and WO₃ and NiO, respectively. This is consistent with the non-equilibrium phenomenon of kinetic decomposition. In the case of nickel titanate, at the low-oxygen-potential side, TiO₂ was formed as sharp needle-like structures within the titanate matrix, while at the high-oxygen-potential side, NiO was formed. In contrast, NiO was formed at the lower-oxygen-potential side in the case of nickel tungstate, while WO₃ volatized off from the high-oxygen-potential side. This indicated that W diffuses faster than Ni in tungstates. In both cases, there were significant macroscopic shifts of the oxide with respect to the original position, established with Pt markers, towards the high-oxygen-potential side.     

Fabrication and properties of SiC fibre-reinforced Li2O·Al2O3·6SiO2 glass-ceramic composites

Ta₂O₅, Nb₂O₅ and TiO₂ were used separately as additives to a Li₂O·Al₂O₃·6SiO₂ glass-ceramic composition, to act as nucleating dopants and to aid the formation of an interfacial carbide layer (TaC and NbC) between the fibre and matrix in SiC fibre uniaxially reinforced glass-ceramic composites, The composites exhibited high modulus of rupture (>800 MPa) and fracture toughness (K _IC > 15 MPam^1/2). The interfacial amorphous carbon rich layer and carbide layer were responsible for lowered interfacial shear strength but permitted high composite fracture toughness. The composite with the TiO₂ additive in the matrix showed a lower flexural strength (<500MPa) and a smaller K _IC (-11 MPam^1/2) which resulted from the high interfacial shear strength between the SiC fibre and the matrix due to the formation of the interfacial TiC layer.     

Addition of Urea or Biuret on Synthesis of Rhabdophane-Type Neodymium and Cerium Phosphates

Urea or biuret was added to the thermal synthetic system of Rhabdophane-type neodymium and cerium phosphates. The mixture of a rare earth compound, a phosphorus compound, and an additive [CO(NH₂)₂ or NH(CONH₂)₂] was heated at 150°C or 300°C for 20 hr, and the thermal products were analyzed by the XRD, FT-IR, and BET methods. H₃PO₄ and (NH₄)₂HPO₄ were used for phosphorus compounds, and for rare earth compounds, Nd₂O₃, Nd(NO₃)₃ · 6H₂O, NdCl₃ · 6H₂O, Nd₂(CO₃)₃ · 8H₂O, CeO₂, Ce(NO₃)₃ · 6H₂O, CeCl₃ · 7H₂O, and Ce₂(CO₃)₃ · 8H₂O were used. Urea and biuret worked not only as a dispersing agent but also as a reactant. By the addition of biuret, the thermal products changed from cerium oxide to Rhabdophane-type cerium phosphate in the system using CeCl₃ · 7H₂O and (NH₄)₂HPO₄. Addition of urea or biuret influenced the specific surface area of Rhabdophane-type neodymium and cerium phosphates. Furthermore, to increase the reactivity of the raw solid materials, mechanical treatment was performed. The mixture of diammonium hydrogenphosphate and a rare earth compound was ground with water and then heated. The influence of the addition of urea or biuret was also studied in these systems.