Spark Plasma and Rate Controlled Sintering of High-Melting Point Nanocomposites

Over the last decade, nano-structured materials, including nanocrystalline monolithic aggregates and nano-composites, became the object of increasing interest. To consolidate the nanocomposites and achieve desired properties the new technological processes have been applied. Rate Controlled Sintering and Spark Plasma Sintering are successfully used to obtain near fully dense high melting nanocomposites with grain size within nanometric scale and make sintering process faster and cheaper. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3507

Synthesis of Ni/NiO Nanopowder by Thermal Decomposition of Nickel Acetate Amine

Ni/NiO nanopowders have been synthesized using thermal decomposition of nickel acetate hexaammine in air. Obtained powders have been characterized by IR-spectroscopy, XRD and TG, DTA, DTG and HR TEM. Thermal decomposition of nickel ammine complexes occurs with forming nickel hydroxide, carbonate and hydroxocarbonate ammines precursors. Mean particle size of nickel and nickel oxide phases in powders depends on temperature. In the temperature range from 350 to 500 degrees Celsius the particle size of nickel oxide has grown from 5 to 25 nm and nickel from 50 to 55 nm. Particle size of 5 nm for nickel hydroxide ammine remained unchanged with temperature. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3481

Size effects in radiospectroscopy spectra of ferroelectric nanopowders

The theoretical and experimental investigation of ferroelectric nanopowders is performed. The manifestation in radiospectroscopy spectra of size driven ferroelectric-paraelectric phase transition at some critical particle average size was the main goal of the consideration. In theoretical part the size effect for the materials with ferroelectric tetragonal phase and cubic paraelectric phase was considered allowing for the spontaneous polarization inhomogeneity inside a particle and distribution of particle sizes. In ESR the transformation of the spectra from tetragonal symmetry to cubic symmetry with decreasing of nanoparticle sizes was calculated. Measurements of Fe3+ ESR spectra in nanopowder of BaTiO3 were carried out at room temperature. The decrease of intensity of tetragonal symmetry ESR lines of Fe3+ and appearance of cubic symmetry line with asymmetry of the shoulders was observed with the average sizes decrease with complete disappearance of tetragonal spectrum at average size less or equal 40 nm. The comparison of the theory with experiment was carried out. The value of critical size Rc = 40 nm was extracted from ESR data. The asymmetry and broadening of right hand side shoulder of ESR cubic symmetry line was shown to be related to contribution of paramagnetic centers in the vicinity of the particles surface. The deconvolution of the cubic line allowed to show, that this region size is about 3 nm.Comment: 10 pages, 8 figure

Kinetics of CxNy formation on electrode surface through electrochemical method

Powded CxNy coatings were deposited from acetonitrile on Ni, Si, and C surfaces at a voltage of 500-2000 V by the electrochemical method. Electrolysis products were analyzed by IR spectroscopy, X-ray phase analysis and electron microscopy. According to FTIR data, at frequencies 1370 and 1530 cm-1, absorption bands characteristic for stretching C-N and C=N oscillations are observed. The obtained results indicate that the deposition process occurs in different manner in each specific case, i.e., the kinetics of the electrode depends on the electrode material (Ni, Si, and C)

Doped Barium Titanate at Intermediate Stages of Synthesis of ВТО

This paper presents the results of synthesis and characterization of calcium 0doped nanocrystalline barium titanate powder with different concentration of doped elements ((Ba1-xCax) TiO3, were x 0; 0.02; 0.06; 0.1; 0.16; 0.2), produced by oxalate route. Calcium additives were added on the surface the samples of semidecomposed barium titanil oxalate. For synthesis were used simultaneously decomposition of unstable barium, titanium compositions and calcium salts. The semidecomposed barium titanil oxalate and doped barium titanate characterization carried out by specific surface area measurements, TEM, X-Ray. It is experimentally shown that Са2+ introduction reduces lattice parameter for samples that related with replacement of barium by calcium. Solubility of calcium in barium titanate nanopowders increase from 10 at % up to 16 at %. The second phase appears at 20 at %. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3547

Monitoring of the morphologic reconstruction of deposited ablation products in laser irradiation of silicon

Using electron microscopy, atomic force microscopy, X-ray microanalysis, and IR spectroscopy, it was established that, in the regime of continuous laser irradiation of silicon at P = 170 W in different gaseous atmospheres with an oxygen impurity, SiOx composite films with a complex morphology form. The main components of ablation products are clusters that form during flight of ablation products and as a result of separation of SiOx-clusters from the zone of the irradiation channel. The roughness and density of the films depend on the heating temperature of the target surface and the type of deposited clusters

The layer by layer selective laser synthesis of ruby

In the work, features of the layer-by-layer selective laser synthesis (SLS) of ruby from an Al2O3-Cr2O3 mixture are considered depending on the irradiation power, the laser beam traverse speed, the height and amount of the backfill of powder layers. It has been established that, under irradiation, a track consisting of polycrystalline textured ruby forms. The morphology of the surface of the track and its crystalline structure are determined by the irradiation conditions

Neck growth kinetics during microwave sintering of nickel powder

a b s t r a c t Model experiments on initial stage of microwave sintering of nickel powder showed anomalous neckgrowth rate during isothermal soaking, which is not the case for conventional sintering. Neck growth was determined as a function of time. Values for the neck growth exponent in the neck growth equation, (x/a) n = Bt, of 5.2, 5.4, 5.8, and 5.9 were found for within the temperature range 700-950 • C, respectively. The evidences of formation of liquid phase during microwave sintering have been revealed, that may support enhancement of mass transfer during sintering process. The activation energy of 48 kJ mol −1 was found for microwave sintering of nickel, according to sphere-to-sphere model. Value revealed is significantly lower then values for conventional sintering (136 kJ mol −1 ), and is on same level with activation energy for diffusion of metals in liquid state. An explanation and analysis of this phenomenon has been attempted

Microstructural development and evolution of liquid phase sintered Cr-Cu composites

Features of the microstructure formation of Cr-Cu composites under impregnation followed by liquid phase sintering of reduced and electrolytic chromium powders at 1200°C in a vacuum of (2-4)×10-3Pa have been studied. The refractory component particle size distribution in the microstructure of samples with reduced chromium sintered for 60 min is shown to obey a normal logarithmic law; with distribution parameters being sensitive to the volume fraction of the refractory particles. The calculated values of the dihedral angle are close to the value of one of the modes in the experimental dihedral angle distribution for the microstructure of electrolytic chromium based samples (115°). The interfacial and interparticle surface energies ratio σsl/σss>0.5 is shown to correspond to theory for the Crs-Cul system in equilibrium, which indicates the presence of skeleton structure elements in the course of composition formation under liquid phase sintering (including the case of excess liquid phase). Experimentally determined interparticle and interfacial surface areas, solid particle contiguity and continuity are discussed in terms of concurrent diffusion-controlled particle coarsening (in Lifshitz, Slyozov and Wagner theory) and particle coalescence (in German’s model). The kinetics of shrinkage for the composites with 50...55 % solid-phase volume-fractions at heating and isothermal sintering in a vacuum at a temperature of 1200°C in terms of linearly viscous rheological theory are discussed