Papers by Keyword: Nanocrystallite

Abstract: Sr2CeO4 nanocrystallites were prepared by a sonochemical process with a later heat treatment using CeO2 and SrCO3 as source materials. The influence of processing factors on the phase composition and morphology of the crystallites were investigated. Results show that nano-Sr2CeO4 monophase could be prepared at the calcining temperature up to 800oC for 2h. Particle size of Sr2CeO4 crystallites decrease with the increase of ultrasonic irradiation power. Around 20-30nm Sr2CeO4 crystallites can be obtained at 800oC when ultrasonic irradiation power reaches 300W.

Abstract: The nanocrystallites in a metal matrix composite (MMC) have wide importance in the sintering area. The nanocrystallites have been related with properties such as hardness and density of 316L steel matrixes. The Y2O3 and TaC dispersion in steel crystalline structures affects these properties and the sintering process. This study analyze: the 316L steel, Y2O3 and TaC crystallite size; TaC and Y2O3 dispersion in milled powder composite; MMC nanocrystallite size and micro-strain during milling process of 316L-(CFC) steel and the effects of dispersion in sintered MMC. The alloy was submitted to high energy milling. MMC was characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The diffraction was analyzed by Rietveld’s refinement method, DBWS 9807 program, and crystallite size and micro-strain were performed using Scherrer’s equation and Williamson-Hall’s method.

Abstract: Using the methods of scanning electron microscopy (SEM), Auger electron spectrometry (AES), fast electron diffraction (FED) in the “on reflection” regime and wavelength dispersive spectrometry (WDS) a complex investigation of the hierarchical sequence of amorphous Beilby layer formation has been studied due to the self-organizing dissipative processes, associated with extensive cold work, on the surface of an Fe-Cr-Ni-Al-La alloy, with high (>40%) chromium content. It was established that, the surface layer (≤1μm thickness) of the mechanically polished specimen of Fe-44%Cr-1%Ni-4%Al-0.3%La alloy consists of the amorphous Beilby layer and that its adjacent matrix layer, crushed due to the plastic deformation, formed an entropy “excited” functional system, which at the temperature of 1200°C in laboratory atmosphere permits the formation of an oxide surface layer with a micro-wrinkles modulated structure of uniform thickness, in the form of mixture of nanocrystallites (100÷500nm) made of oxides of atoms constituting the basic metallic matrix. Beneath this layer a thin alumina scale is observed to form. Increasing the oxidation temperature causes the regrowth of nanocrystallites and also the recrystallization processes, accompanied by solid-phase reactions between oxide nano-particles. This leads to scale delamination at the superficial oxide thin uniform alumina layer interface. The Al2O3 layer is characterized by high adherence with metallic substrate and provides protective features against both high temperature (1200°C) oxidation of the matrix and resistance to abrasion. By the pretreatment at 1200°C of the investigated alloy’s surface modified specimens, there forms a low thickness (several microns) scale which has ultra fine graininess (~1μ) with no porosity and blocked grain boundaries short-circuit diffusion paths. This gives to the scale the ability to protect the metallic matrix against high temperature gas (and other aggressive environment) corrosion.

Abstract: Electrolytical layers of Ni-Mo alloys with polypyrrole, polytiofene and polyethylene were deposited on steel substrate (St3S, 4 cm2). After structural analyses of as quenched samples performed by X-ray diffraction it was noticed that the solid solution of Mo in Ni is observed. After annealing in an argon atmosphere the solid solution of Mo in Ni is becomeing more stable and crystalites are growing to the size of 200 – 300 Å. After annealing in an air atmosphere X-ray diffraction patterns show presence of phases: NiO, MoO, NiCO3, Mo2N. The unit cell parameters of solid solution after annealing are smaller than parameters of as quenched samples what means that the solid solution has been decomposing.

Abstract: The mechanical properties of the 316L stainless steel subjected to surface mechanical attrition treatment (SMAT) have been studied, these properties are hardness, tensile properties and wear resistance. The research shows that the thickness of the hardened layer increases with the increasing of the treating time. The refined microstructure in the treated layer led to increasing in hardness, strength, and wear resistance. It is obvious that the surface layer hardness and bulk yield strength are increasing when the SMAT time reaches 5 minutes. The increase of surface layer wear resistance is obvious when the SMAT time is 15 minutes. The SEM observation of the wear scars shows that the nanocrystalline layer might reduce the effect of adhesive wear of 316L stainless steel. Therefore, the wear mechanism changes from adhesive abrasion to grinding particle abrasion after SMAT.

Abstract: The size effect of magnetocaloric effect (MCE) in CoCr2O4 has been investigated by comparing two samples with different crystal sizes. One is bulk CoCr2O4 sample (referred as A), and the other is a nanocrystalline CoCr2O4 sample (referred as B). It has been found that crystal size dramatically affects the magnetic properties and MCE for CoCr2O4, and that the nanocrystalline material is more favorable for application than the bulk material. The above results are explained in terms of the effect of small size and its distribution for sample B on the intrinsic magnetic properties and magnetic entropy change.

Abstract: Electron beam lithography combined with electrophoretic deposition was investigated to fabricate micropatterned barium titanate (BTO) with nanostructures. High quality resist molds with micropatterns of microgrids and microdot arrays were prepared on Pt/Ti/SiO2/Si substrate by electron beam lithography. BTO nanocrystallites in a pseudo-cubic perovskite phase with an average particle size of about 10 nm were synthesized by a high-concentration sol-gel process. Well-dispersed and stable suspensions of barium titanate nanocrystallites were synthesized. Then, BTO microlines, microgrids and microdot arrays were electrophoretically deposited on micropatterned Pt/Ti/SiO2/Si substrate from these suspensions. The microstructure and properties of the BTO micropatterns were evaluated.