Search results for "sintering"
showing 10 items of 165 documents
INFLUENCE OF MONOXIDES ADDITION ON SINTERING OF SODIUM-POTASSIUM NIOBATES SOLID SOLUTION
2008
ABSTRACT In this paper the preparation, structure and dielectric parameters of ceramics from different powders of pure potassium sodium niobate (KNN) and KNN doped with 1.0 wt% of Li2O, CdO, Bi2O3, MnO2, V2O5 and WO3 have been studied. The dopping of sintering aids did not affect the crystallographic structure of the ceramics significantly; all ceramic samples had a single-phase perovskite structure. Added elements Li2O, CdO, MnO2, V2O5 effectively decreased the sintering temperature of KNN (50°–80°C). All sintering aids influenced sinterability, microstructure and dielectric properties of ceramics. Dielectric constant for doped samples increased from 6000 up to 8000.
Enhanced thermoelectric properties of the n-type Magnéli phase WO2.90: reduced thermal conductivity through microstructure engineering
2014
The thermoelectric properties of the Magneli phase WO2.90 were investigated, with special attention to how the thermoelectric performance can be altered by changing its microstructure. Spark plasma sintering (SPS) allowed the direct preparation of large amounts of consolidated material. Adding Ta2O5 to the reaction mixture lead to the formation of solid solutions W1−xTaxO2.90via a concurrent reaction between WO3 and Ta2O5 during the SPS treatment. In addition, micron-sized inclusions containing tungsten surrounded by WOx embedded in a WO2.90 matrix were formed, which act as additional scattering centers. As a result, the thermal conductivity of the Ta-containing samples was reduced by ≈30% …
A dilatometric study of the Lao.8Sr0.2MnO3 sintering behaviour
1997
Abstract The sintering behaviour of La0.8Sr0.2MnO3 has been studied by dilatometry between 1100 and 1800 K in various oxygen potentials [pure oxygen, air and nitrogen (PO2 = 1 × 10−5 bar)]. The starting material was prepared by spray pyrolysis of aqueous solutions of nitrates. Two classical sinter stages, neck formation and grain growth respectively, were evidenced from dilatometric curves and this result was corroborated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The rate of densification was found to be directly dependent on oxygen partial pressure, the best conditions being in nitrogen. These results are discussed in terms of vacancy diffusion and oxygen …
Post-sintering heat treatment effect on the coercivity of sintered (Nd,Dy)15(Fe,Co,Mo,Al)77B8 permanent magnets
2000
Abstract The effect of heat treatment on the intrinsic coercivity, iHc and microstructure were investigated for sintered (Nd,Dy)15(Fe,Co,Mo,Al)77 B8 permanent magnet. The microstructure has been investigated by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray spectroscopy and Mossbauer spectroscopy. The observed behaviour of iHc may be caused by a superposition of the following effects: (i) the distribution of the nonmagnetic phases and the ratio of the amount of hard magnetic Nd2Fe14B-phase to the amount of the residual phases; (ii) homogeneous distribution of elements in the main phases; (iii) removing the stresses in the phases; and (iv) diffusion of Al, …
Synthesis of bulk FeAl nanostructured materials by HVOF spray forming and Spark Plasma Sintering
2006
Abstract This paper examines the efficiency of two consolidation processing techniques: High Velocity Oxy-Fuel (HVOF) spray forming and Spark Plasma Sintering (SPS) to obtain bulk nanostructured materials from an Y 2 O 3 reinforced Fe–40Al (at.%) milled powder. The microstructures of the sintered end-products were characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) in order to gain new insights in their microstructure formation mechanisms. HVOF spray forming is more effective to retain fine nanograins, in particular within retained unmelted powder particles. The drawbacks of this technique are that it inevitably leads to a high fraction of porosity…
Ti-Al Membranes for Microfiltration
2016
Porous membranes made of Ti – 48 at. % Al intermetallic compound was obtained by elemental powder synthesis. These disks can be used as microfiltration membranes due to their low pores size and interconnected porosity. During this study titanium (purity 99.5%) and aluminum (purity 99 %) with low particle size range were mixed in corresponding ratios. The powder mixture was pressed at 500 MPa and the samples were heat treated in two stages. In the first step is the forming of Al3Ti compound by a solid state reaction at a temperature of 640 °C, slightly below the melting point of aluminum. In the second step the Ti-Al compound was formed at the temperature of 1300 °C and the sintering the por…
Properties of spark plasma sintered nanostructured Zn1+xSb
2011
Engineering materials with specific physical properties has recently focused on the effect of nanoscopic inhomogeneities at the 10 nm scale. Such features are expected to scatter medium and long-wavelength phonons lowering thereby the thermal conductivity of the system without simultaneously decreasing the charge transport (phonon–glass electron–crystal concept). A new Zn1+xSb nanophase obtained by a wet chemical approach was densified by spark plasma sintering (SPS). Investigations on compounds subsumed as “Zn4Sb3” always suffer from its low thermal stability and the contamination of the nanoparticles with solvents and additives used in the synthesis. In order to gain insight into this com…
Control of barium ferrite decomposition during spark plasma sintering: Towards nanostructured samples with anisotropic magnetic properties
2014
Abstract The sintering of barium ferrite (BaM) nano-sized powders by spark plasma sintering was studied. At the surface of the samples, an iron-rich layer (magnetite) was formed due to the decomposition of BaM and segregation in the secondary phases. To prevent the formation of secondary phases different protection layers between the graphite mould and the sample were used. Their effect on the sample microstructure was studied by X-ray diffraction and scanning electron microscopy. The most suitable protection layer was a highly dense sintered disc of aluminium oxide. Using this dense protection layer, sintered discs of BaM with 82% of theoretical density and grains of 90 ± 50 nm were obtain…
Studies and Researches on the Obtaining of Sintered Gradual Porous Structures by Irregular Nickel Powders Sedimentation
2012
The aim of this work is to obtain sintered porous membranes with graded structure for microfiltration by sedimentation and sintering of metallic powders. Our previous studies have demonstrated the possibility of obtaining sintered porous materials with graded structure by sedimentation. In this paper, irregular nickel particles were used having a grain size in the 2-90 µm range evaluated using scanning electron microscopy and laser scattering particle size analyzer. The powders were sedimented into a sintering die in a sedimentation medium consisting of water and dispersant agent. After drying, the samples were sintered at 1000°C for 10 minutes in vacuum (~1•10-3 Pa). The structures obtaine…
Composition-related structural, thermal and mechanical properties of Ba1−xSrxTiO3ceramics (0 ≤x≤ 0.4)
2015
The Ba1−xSrxTiO3 (BST) ceramics were prepared by conventional ceramic method. The crystalline structure and morphology were studied by X-ray diffraction and scanning electron microscopy, respectively. Experimental results show that increase of sintering temperature leads to an uncontrolled precipitating of the phase with a lower content of Ti. The dielectric constant and specific heat as a function of composition and temperature were investigated. The increasing concentration of Sr ions leads to a shift of the Curie point below room temperature. To determine the elastic constants (the Young's modulus E, the shear modulus G and the Poisson's ratio v) of BST, a method of measurement of the lo…