The present study reports the formation of ultrafine hard particles of nanocomposite WC with different additions of ZrO2 powders (0.5 - 20 vol.%). The initial mixed powders of WC with the desired ZrO2 concentrations w...The present study reports the formation of ultrafine hard particles of nanocomposite WC with different additions of ZrO2 powders (0.5 - 20 vol.%). The initial mixed powders of WC with the desired ZrO2 concentrations were mechanically mixed for 360 ks (end-product) under argon gas atmosphere at room temperature, using high energy ball mill. The end-product consists of average grain size of about 17 nm in diameter. The obtained nanocomposite powders were consolidated into fully dense compact, using spark plasma sintering (SPS) technique in vacuum. The experimental results revealed that the consolidation step, which was conducted at 1673 K with uniaxial pressure ranging from 19.6 to 38.2 MPa for short time (0.18 ks), does not lead to dramatic grain growth in the powders so that the consolidated nanocomposite bulk objects maintain their nanocrystalline behavior, being fine grains with an average size of 63 nm in diameter. The relative densities of consolidated nanocomposite WC/ZrO2 materials increase from 99.1% for WC-0.5% ZrO2 to 99.93% for WC-20% ZrO2. The indentation fracture toughness of the composites can be tailored between 7.31 and 19.46 MPa/m1/2 by controlling the volume fraction of ZrO2 matrix from 0.5% to 20%. The results show that the Poisson’s ratio increased monotonically with increasing the ZrO2 concentrations to get a maximum value of 0.268 for WC-20% ZrO2. In the whole range of ZrO2 concentrations (0.5 - 20 vol.%), high hardness values (20.73 to 22.83 GPa) were achieved. The Young’s modulus tends to decrease with increasing the volume fraction of the ZrO2 matrix to reach a minimum value of 583.2 GPa for WC-20% ZrO2. These hard and tough WC/ZrO2 nanocomposites are proposed to be employed as higher abrasive-wear resistant materials.展开更多
Bismuth telluride thick films are suitable for thermoelectric (TE) devices covering large areas and operating at small-to-moderate temperature differences (20 - 200 K). High efficiency and high coefficient of performa...Bismuth telluride thick films are suitable for thermoelectric (TE) devices covering large areas and operating at small-to-moderate temperature differences (20 - 200 K). High efficiency and high coefficient of performance (COP) are expected to be achieved by using thick films in some cooling applications. Bismuth telluride thick films fabrication have been achieved with Galvanostatic and Potentionstatic deposition. Stoichiometric bismuth telluride thick film was obtained by Galvanostatic deposition at current density of 3.1 mAcm-2. Bismuth telluride films with average growth rate of 10 μmh-1 and different composition were obtained. Effects of current density and composition of electrolyte in Galvanostatic deposition were studied. The current density affected the film compactness, where films deposited at lower current density were more compact than those deposited at higher current density. The morphology of the films did not depend on the current density, but chemical composition was observed when different composition of electrolyte was used. Effects of distance between electrodes, composition of electrolyte solution, and stirring in Potentionstatic deposition were studied. The shorter the distance between electrodes, the higher the electric field, thus the higher current density was applied and the deposited film was less compact. The current density increased more rapidly with stirring during electrodeposition which leads to less compact film. Through this study, films electrode-posited from solution containing 0.013 M Bi(NO3)3.5 H2O, 0.01 M TeO2 and 1 M HNO3 at 3.1 mA cm-2 for 6 hours without stirring and with interelectrode distance of 4.5 cm were free-standing with average film thickness of 60 μm and optimum film composition of Bi2Te3. The crystallite size of the later films was found to be around 4.3 nm using Scherrer’s equation from XRD patterns. Also, negative Seebeck coefficient for the same samples was revealed with an average value of -82 μV.K-1.展开更多
The fabrication of nano porous silicon, nPSi, using alkali etching process has been studied and carried out. The surface chemistry of anisotropic etching of n-type Si-wafer is reviewed and the anisotropic chemical etc...The fabrication of nano porous silicon, nPSi, using alkali etching process has been studied and carried out. The surface chemistry of anisotropic etching of n-type Si-wafer is reviewed and the anisotropic chemical etching of silicon in alkaline solution using wetting agents is discussed. Transformation of crystallographic plane of n-Si (211) to nPSi (100) has occurred on using n-propanol as wetting agent. The rate of pore formation was 0.02478 - 0.02827 μm/min, which was heavily dependent upon the concentration of the etchant containing wetting agents, allowing patterned porous silicon formation through selective doping of the substrate. A particle size of 15 nm for porous nano-silicon was calculated from the XRD data. Porosity of PS layers is about 10%. Pore diameter and porous layer thickness are 0.0614 nm and 16 μm, respectively. The energy gap of the produced porous silicon is 3.3 eV. Furthermore, the combination of PS with Congo Red, which are nanostructured due to their deposition within the porous matrix is discussed. Such nano compounds offer broad avenue of new and interesting properties depending on the involved materials as well as on their morphology. Chemical route was utilized as the host material to achieve pores filling. They were impregnated with Congo Red, which gave good results for the porous silicon as a promising pH sensor.展开更多
文摘The present study reports the formation of ultrafine hard particles of nanocomposite WC with different additions of ZrO2 powders (0.5 - 20 vol.%). The initial mixed powders of WC with the desired ZrO2 concentrations were mechanically mixed for 360 ks (end-product) under argon gas atmosphere at room temperature, using high energy ball mill. The end-product consists of average grain size of about 17 nm in diameter. The obtained nanocomposite powders were consolidated into fully dense compact, using spark plasma sintering (SPS) technique in vacuum. The experimental results revealed that the consolidation step, which was conducted at 1673 K with uniaxial pressure ranging from 19.6 to 38.2 MPa for short time (0.18 ks), does not lead to dramatic grain growth in the powders so that the consolidated nanocomposite bulk objects maintain their nanocrystalline behavior, being fine grains with an average size of 63 nm in diameter. The relative densities of consolidated nanocomposite WC/ZrO2 materials increase from 99.1% for WC-0.5% ZrO2 to 99.93% for WC-20% ZrO2. The indentation fracture toughness of the composites can be tailored between 7.31 and 19.46 MPa/m1/2 by controlling the volume fraction of ZrO2 matrix from 0.5% to 20%. The results show that the Poisson’s ratio increased monotonically with increasing the ZrO2 concentrations to get a maximum value of 0.268 for WC-20% ZrO2. In the whole range of ZrO2 concentrations (0.5 - 20 vol.%), high hardness values (20.73 to 22.83 GPa) were achieved. The Young’s modulus tends to decrease with increasing the volume fraction of the ZrO2 matrix to reach a minimum value of 583.2 GPa for WC-20% ZrO2. These hard and tough WC/ZrO2 nanocomposites are proposed to be employed as higher abrasive-wear resistant materials.
文摘Bismuth telluride thick films are suitable for thermoelectric (TE) devices covering large areas and operating at small-to-moderate temperature differences (20 - 200 K). High efficiency and high coefficient of performance (COP) are expected to be achieved by using thick films in some cooling applications. Bismuth telluride thick films fabrication have been achieved with Galvanostatic and Potentionstatic deposition. Stoichiometric bismuth telluride thick film was obtained by Galvanostatic deposition at current density of 3.1 mAcm-2. Bismuth telluride films with average growth rate of 10 μmh-1 and different composition were obtained. Effects of current density and composition of electrolyte in Galvanostatic deposition were studied. The current density affected the film compactness, where films deposited at lower current density were more compact than those deposited at higher current density. The morphology of the films did not depend on the current density, but chemical composition was observed when different composition of electrolyte was used. Effects of distance between electrodes, composition of electrolyte solution, and stirring in Potentionstatic deposition were studied. The shorter the distance between electrodes, the higher the electric field, thus the higher current density was applied and the deposited film was less compact. The current density increased more rapidly with stirring during electrodeposition which leads to less compact film. Through this study, films electrode-posited from solution containing 0.013 M Bi(NO3)3.5 H2O, 0.01 M TeO2 and 1 M HNO3 at 3.1 mA cm-2 for 6 hours without stirring and with interelectrode distance of 4.5 cm were free-standing with average film thickness of 60 μm and optimum film composition of Bi2Te3. The crystallite size of the later films was found to be around 4.3 nm using Scherrer’s equation from XRD patterns. Also, negative Seebeck coefficient for the same samples was revealed with an average value of -82 μV.K-1.
文摘The fabrication of nano porous silicon, nPSi, using alkali etching process has been studied and carried out. The surface chemistry of anisotropic etching of n-type Si-wafer is reviewed and the anisotropic chemical etching of silicon in alkaline solution using wetting agents is discussed. Transformation of crystallographic plane of n-Si (211) to nPSi (100) has occurred on using n-propanol as wetting agent. The rate of pore formation was 0.02478 - 0.02827 μm/min, which was heavily dependent upon the concentration of the etchant containing wetting agents, allowing patterned porous silicon formation through selective doping of the substrate. A particle size of 15 nm for porous nano-silicon was calculated from the XRD data. Porosity of PS layers is about 10%. Pore diameter and porous layer thickness are 0.0614 nm and 16 μm, respectively. The energy gap of the produced porous silicon is 3.3 eV. Furthermore, the combination of PS with Congo Red, which are nanostructured due to their deposition within the porous matrix is discussed. Such nano compounds offer broad avenue of new and interesting properties depending on the involved materials as well as on their morphology. Chemical route was utilized as the host material to achieve pores filling. They were impregnated with Congo Red, which gave good results for the porous silicon as a promising pH sensor.
