THE EFFECT OF PROCESSING PARAMETERS ON SOL GEL SYNTHESIS OF β-SiC NANO POWDER

Mono dispersed nano SiC particles with spherical morphology were synthesized in this project by hydrolysis and condensation mechanism during sol gel processing. pH, temperature and precursor’s ratio considered as the main parameters which could influence particles size. According to DLS test results, the smallest size of particles in the sol (<5nm) was obtained at pH<4. It can be observed from rheology test results optimum temperature for achieving nanometeric gel is about 60 ˚C. The optimum pH values for sol stabilization was (2-5) determined by zeta potentiometery. Si 29NMR analysis was used in order to get more details on final structure of gel powders resulted from initial sol. X-ray diffraction studies showed sythesized powder consists of β-SiC phase. Scanning electron microscopy indicated agglomerates size in β-SiC synthesis is less than 100 nm. Finally, TEM studies revealed morphology of β-SiC particles treated in 1500˚C and after 1hr aging is spherical with (20-30) nm siz

Investigation of Photocatalytic Properties of NiO/TiO2 Layers Grown via PEO/EPD Method

Titanium dioxide-nickel oxide porous coatings were synthesized by Plasma Electrolytic Oxidation (PEO)/ ElectroPhoretic Deposition (EPD) in one step and within a short time. The main purpose of this research was to increase photocatalytic activity of titanium oxide by increasing surface area and coupling of titanium oxide with nickel oxide. Applied voltage effects on phase structure, surface morphology and photocatalytic efficiency of coatings were studied. Phase structure and surface morphology of the synthesized catalysts were investigated by XRD and SEM, respectively. Photocatalytic efficiency of the samples was studied through measuring the decomposition rate of 4-chlorophenol. The results showed that the coatings mainly consisted of anatase and nickel oxide phases whose amounts in coatings increased with the voltage. There was an enhancement of the photocatalytic efficiency in TiO2/NiO composite coatings compared with TiO2 coatings. Besides, there was an optimum amount of NiO to reach maximum photocatalytic efficiently

EFFECT OF ZrO2 PARTICLE SIZE ON MORPHOLOGY and SYNTHESIS OF NANO CaZrO3Via MOLTEN SALT METHOD

Well crystallized pure calcium zirconate (CaZrO3 ) nanopowder was successfully synthesized using the molten-salt method. CaCl2 , Na 2CO3, micro-ZrO 2and nano-ZrO 2 were used as starting materials. On heating, Na2CO3 reacted with CaCl 2to form NaCl and CaCO 3. Nano CaZrO 3 was formed by reacting equimolar amounts of in situformed CaCO 3 (or CaO) and ZrO 2 in molten Na 2CO3-NaCl eutectic mixture. CaZrO 3 particle size and synthesis temparture was tailored as a function of ZrO 2particle size. Due to the usage of nano-ZrO 2 , the molten salt synthesis (MSS) temperature was decreased and possible impurity phases in the final product were suppressed. The synthesis temperature was lowered to 800°C and soaking time of the optimal synthesis condition was reduced to 3h. After washing with hot-distilled water, the n-ZrO2sample heated at 800°C for 3h, was single phase CaZrO 3with 70-90 nm in particle size, while the m-ZrO 2sample heated at 1000°C for 3h, was single phase CaZrO 3 with 250-400 nm in particle size. Based on the TEM observation and thermodynamic analysis, the synthesized CaZrO 3 grains retained the morphology of the ZrO2 nanopowders, which indicated that a template formation mechanism play a dominant role in synthesis proces

Sintering behavior of an ultrafine alumina powder shaped by pressure filtration and dry pressing

Master sintering curve (MSC) was used as a practical approach to analyse the sintering behavior of an ultrafine alumina powder. Non-isothermal sintering was carried out at three heating rates. The concept of the MSC has been used to investigate the effect of different shaping methods, i.e. dry pressing (DP) and pressure filtration (PF) on the apparent activation energy for sintering. Although no change in the dominant densification mechanism is expected, the interplay between different diffusion mechanisms taking place during the heating ramp may be affected by the shaping method. Values of 605 +/- 15 and 700 +/- 20 kJ/mol were determined for PF and DP samples, respectively. The lower activation energy for PF samples may be explained by the higher green density and homogeneity, smaller pore size in comparison with the DP samples. Furthermore, the mechanical properties (hardness and fracture toughness) of the samples are presented. (C) 2010 Elsevier B.V. All rights reserved

Sintering behavior of nano alumina powder shaped by pressure filtration

In the present study, the sintering behavior of a commercial nano alumina powder with an initial particle size of 100 nm was investigated. The shrinkage response of the powder formed by pressure filtration (PF) during non-isothermal sintering was measured in a laser assisted dilatometer at three different heating rates of 2, 10 and 25 degrees C min(-1) up to 1400 degrees C. In order to calculate the activation energy of sintering, constant rate of heating (CRH) was employed and the activation energy was found to be 608 +/- 20 kJ mol(-1) for iso-density method. The heating rate was demonstrated to have a vital role on densification behavior and final grain size. The mean grain size of the full dense specimens decreased from 875 to 443 nm when the heating rate increased from 2 to 25 degrees C min(-1). (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Spark plasma sintering of TaC-HfC UHTC via disilicides sintering aids

Ta0.8Hf0.2C ceramic has the highest melting point among the known materials (4000 degrees C). Spark plasma sintering is a new route for consolidation of materials, specially ultra high temperature ceramics (UHTCs), which are difficult to be sintered at temperatures lower than 2000 degrees C. The purpose of this study is to consolidate Ta0.8Hf0.2C by spark plasma sintering at low temperature using MoSi2 and TaSi2 as sintering aid. In this regard, effect of different amounts of sintering aids and carbides ratio on densification behavior and mechanical properties of Ta1-xHfxC were investigated. Fully consolidation of Ta0.8Hf0.2C was achieved in presence of 12 vol.% sintering aid after sintering at 1650 degrees C for 5 min under 30 MPa. The first stage of sintering was due to plastic deformation of sintering aids particles and consequent rearrangement. The second stage was occurred via Ta1-xHfxC solid solution and liquid phase formation