CTAB assisted hydrothermal synthesis of ZnO/Co(OH)2 nano-composites: Mechanisms of synthesis and growth of composite

M. R. Vaezi 한양대학교 세라믹연구소 2014 Journal of Ceramic Processing Research Vol.15 No.6

In this paper, nano-composites of ZnO/Co(OH)2 were synthesized via Hydrothermal processing. Co(NO3)2.6H2O, Zn(NO3)2 • 4H2O (0.5 M, 200 ml) and KOH (2 M, 200 ml) were used as precursors. N_Cetyl_N,N,N,_tri methyl ammonium bromide (CTAB) was used as surfactant and its effects on the morphologie was investigated. The crystal growth mechanism was studied via Growth Unit Model and thermodynamics of cobalt oxide formation from its hydroxide under hydrothermal condition. Nano-rods and nano-hexagonals were prepared via hydrothermal synthesis with and without using CTAB, respectively. Also, the effects of hydrothermal periods on morphologies and particle growth were investigated in this paper. Xray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the products obtained.

Synthesis of nanosized SnO/ZnO coupled oxides via co-precipitation method

M. R. Vaezi 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.4

In this paper, SnO/ZnO nanocomposites have been produced via co-precipitation method for the first time. SnCl2, ZnCl2 and NaOH were used as precursors. The synthesized powders were characterized by X-Ray Diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer-Emmett-Teller adsorption isotherm (BET) and X-ray florescence (XRF) analyses. Effect of synthesis temperature on the obtained phases, particle size and morphology, crystallite size and specific surface area of produced nanocomposites have been discussed. It has been shown that at lower synthesis temperature only ZnO nanocrystals could be produced, however at higher temperatures SnO/ZnO nanocomposites could be formed and this co-existence of phases affects the powders crystallite sizes, morphologies, particle sizes and specific surface areas.

The fabrication of a dip- coated tin oxide thin film via solgel processing and a study of its gas sensing properties

M. R. Vaezi 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.6

In this paper, tin oxide, SnO2, thin films were coated on soda- lime glass substrates using the simple and economic processing route such as dip coating sol- gel method. In the preparation of a stable sol, instead of using only one alcohol, a combination of some alcohols without adding any surfactant and applying non- liquid tin chloride has been used. The effect of temperature, time, and thickness of the layers were studied. The phase and structural determination of samples were obtained by X-ray diffraction (XRD) analysis. Scanning electron microscopy (SEM) images were used for size and morphological evaluation of the thin films obtained. The gas- sensor response of tin dioxide thin films was determined by electrical sheet resistance measurements. After exposing the gas to different concentrations of ethanol, the effects of temperature, gas concentration, size, shape, dispersion of crystallite and thickness of the film on the sensor response were investigated. The best sensing responses are related to a two- times deposited layer with a thickness of about 299 nm heated at 400 ο C and 600 ο C. The first detection of gas concentration was at about 27.7 ppm ethanol at 300 ο C. Also, the level of response and recovery times of this sensor were 70 and 88 s, respectively.

MECHANICAL-ACTIVATED PHASE FORMATION OF NiTi IN THE PRESENCE OF NANOPARTICLES

M. FARVIZI,T. EBADZADEH,M. R. Vaezi,A. SIMCHI,김형섭 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2013 NANO Vol.8 No.5

Effect of Al2O3 nanoparticles (80 nm) on the grain structure and phase formation in Ni-50Ti system during high-energy mechanical alloying (MA) was studied. While the formation of NiTi B2 phase occurs progressively during MA, it is shown that the hard inclusions cause abrupt phase formation at short milling times, particularly at higher nano-Al2O3 contents. High-resolution transmission electron microscopy showed significant grain refinement in the presence of alumina nanoparticles to sizes less than 10 nm, which precedes the formation of semicrystalline structure and reduces the diffusion length and thus accelerates the phase formation. The composite powder reached steady-state MA condition at shorter milling times with finer grain structure and higher hardness.

Synthesis of nanostructured CuInSe2 (CIS) powder via solvothermal processing using diethylamine as a solvent

M. Najafi,M. R. Vaezi,S. K. Sadrnezhaad 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.6

In this paper, CuInSe2 nanostructures have been synthesized via a solvothermal method using diethyamine as a solvent. Various morphologies of CuInSe2 were obtained from the reaction of cupric chloride, indium chloride and selenium powder by changing the solvothermal conditions. The effect of the experimental parameters such as reaction time, temperature and concentration of the selenium powder were studied. The crystalline structures and morphologies of the products were characterized by means of X- ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) techniques,respectively. The results show that the morphology and dimensions of the CIS nanostructures obtained can be controlled through selective processing conditions. The optical properties and band gaps were estimated with a UV-Vis spectrophotometer. The electrical resistances of the samples were recorded by using four point probes.

Effect of starting materials on the wear performance of NiTi-based composites

Farvizi, M.,Ebadzadeh, T.,Vaezi, M.R.,Yoon, E.Y.,Kim, Y.J.,Kang, J.Y.,Kim, H.S.,Simchi, A. Elsevier Sequoia [etc.] 2015 Wear: An international journal on the science and Vol.334 No.-

NiTi alloys have exhibited significant potential as a matrix of wear resistant composites. In this study, in order to examine the effect of starting materials on the wear performance of NiTi-based composites, both elemental Ni/Ti and prealloyed NiTi powders were used to fabricate NiTi-6wt% nano-Al<SUB>2</SUB>O<SUB>3</SUB> composites using hot isostatic pressing (HIP). Nanoindentation and microhardness test results indicate that the composite samples produced from the elemental Ni/Ti powders exhibited higher hardness and lower pseudoelasticity properties than those of the samples fabricated from the prealloyed NiTi powders; this is attributed to the higher amount of Ni<SUB>3</SUB>Ti/NiTi<SUB>2</SUB> phases in the samples from the elemental powders. The wear test results also confirm the superior performance of the composite samples produced from the elemental powders. The high-resolution transmission electron microscopy studies of the wear debris demonstrate that the heavy local plastic deformation induced during the wear test appeared to inhibit the pseudoelasticity during the wear process. Hence, it can be deduced that the role of the hardness enhancement is more pronounced than that of the pseudoelasticity reduction in the wear performance of NiTi-based composite samples.

Microstructural characterization of HIP consolidated NiTi-nano Al₂O₃ composites

Farvizi, M.,Ebadzadeh, T.,Vaezi, M.R.,Yoon, E.Y.,Kim, Y.J.,Kim, H.S.,Simchi, A. Elsevier Sequoia 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.606 No.-

The microstructure and phase transformational behavior of NiTi-based composites reinforced with 6wt.% of α-alumina nanoparticles have been investigated. Two kinds of starting materials, elemental Ni-Ti and prealloyed austenitic NiTi, were used to prepare the composites. The samples were consolidated using a hot isostatic pressing method. The X-ray diffraction results showed that while unreinforced NiTi mainly contained B2 phase at room temperature, martensitic B19' phase appeared in the microstructure after addition of the α-alumina nanoparticles. The differential scanning calorimetry measurements indicated that the martensitic transformation temperatures were elevated in the composite samples, but the transformational enthalpy was reduced in comparison with the NiTi sample. It is believed that the generation of thermal mismatch stress during the sintering and the formation of small contents of NiTi<SUB>2</SUB>/Ni<SUB>3</SUB>Ti intermetallics in the composite samples are responsible for this increment of the martensitic transformation temperatures. Also, due to the nanometric size of α-Al<SUB>2</SUB>O<SUB>3</SUB>, a larger fraction of the matrix is disturbed by the presence of the nanoparticles, which yields the formation of effective barriers to the thermally induced martensitic transformation in the nanocomposite samples. The high-resolution transmission electron microscopy studies of the samples confirmed the higher defect density and partial microplastic deformation in the composite samples.

Effect of nano Al₂O₃ addition on mechanical properties and wear behavior of NiTi intermetallic

Farvizi, M.,Ebadzadeh, T.,Vaezi, M.R.,Kim, H.S.,Simchi, A. Scientific and Technical Press ; Elsevier Science 2013 Materials & design Vol.51 No.-

It has been found that the high wear resistance of NiTi alloy is mainly attributed to its pseudoelasticity which is only effective within a small temperature range. It is believed that pseudoelasticity becomes ineffective by applying high-load wear condition which yields plastic deformation and temperature increment during wear test. Therefore, the enhanced wear resistance can be obtained from the improvement of mechanical property of the alloy without much reduction of pseudoelasticity. In this study, a low weight percentage of hard Al<SUB>2</SUB>O<SUB>3</SUB> nanoparticles were added to NiTi atomized powders. The resultant powder mixture was homogenized by ball milling and sintered in a vacuum furnace in order to improve the wear property of the composite in comparison with the NiTi alloy. The results demonstrated that the addition of nanoparticles increased the stability of martensite phase. Nanoindentation test results showed that both hardness and elastic modulus were considerably increased in the composite samples in comparison with pure NiTi, while the pseudoelasticity was not significantly reduced. The worn surfaces were investigated using a scanning electron microscope equipped with energy dispersive X-ray. The wear test results confirmed the improved wear performance of NiTi matrix after the addition of nanoparticles under both low and high loads can be mainly attributed to superior mechanical properties combined with pseudoelasticity effect of the composite samples.

A comparison between hydrothermally prepared Co3O4 via H2O2 assisted and calcination methods

S. E. Hashemi Amiri,M. R. Vaezi,A. Esmaielzadeh Kandjani 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.3

In this paper Co3O4 nanoparticles were synthesized via two different synthesis procedures. In the first method, hydrothermally synthesized β-Co(OH)2 particles were calcined at different temperatures. In the other method, H2O2 was used to eliminate the production of cobalt hydroxide. The amount of H2O2 was the main variable investigated in this study. All samples synthesized via these methods, were investigated for their structure, morphology, specific surface area and magnetization. The results showed that an increase in the temperature of the post heat treatment substantially increased particle sizes and consequently decreased the specific surface area of nanoparticles which influences magnetization. In the H2O2 assisted route, the minimum amount of the oxidant necessary for the complete elimination of the β-Co(OH)2 phase and production of the pure Co3O4 phase was determined to be 0.25 volume fraction. In the H2O2 assisted method, due to elimination of the post heat treatment, the nanoparticles become smaller with a higher specific surface area in comparison with the calcination method. However, the magnetic properties of the nanoparticles in the H2O2 assisted method are influenced by changing the amount of H2O2.