Polycrystalline Cu 2 O nanowire arrays have been grown via porous alumina membranes using three-e... more Polycrystalline Cu 2 O nanowire arrays have been grown via porous alumina membranes using three-electrode electrochemical deposition. The effect of electrolyte, pH value, deposition potential, annealing temperature, and annealing atmosphere on the growth of Cu 2 O nanowire arrays has been investigated. On the other hand, ordered ZnO/AZO/PAM nanowire arrays have been prepared by seed layer assisted electrochemical deposition. The comprehensive of electrochemical process adopted (e.g. electrolytes, deposition parameters); various characterization techniques and the outcome of the results have been summarized in details. It is observed that the ZnO nanowire arrays are assembled into the nanochannel of porous alumina template with diameter of 120~140 nm. The crystalline structure of single ZnO nanowire is dependent on AZO seed layer. The nucleation and growth process of ZnO/AZO/PAM nanowires are interpreted by seed layer assisted growth mechanism.
Journal of Physics: Conference Series, Jan 1, 2010
A square Helmholtz coil has been designed and fabricated using commercial grade HTS BSCCO tape wi... more A square Helmholtz coil has been designed and fabricated using commercial grade HTS BSCCO tape with double pancake configuration. The present work is aimed at generating uniform magnetic field with a square Helmholtz coil pair useful in laboratory applications. It has an advantages over the circular Helmholtz coil which had been fabricated and validated by us earlier in terms of field uniformity. This coil is intended to be used as a background field/magnet for circular Helmholtz coil and possible characterization of High T c tapes. Design parameters details, magnetic field generated and the fabrication techniques o f this square Helmholtz coil have been described in this paper.
The fine grains of Al 2 O 3 -Cr 2 O 3 /Cr-carbide nanocomposites were prepared by employing recen... more The fine grains of Al 2 O 3 -Cr 2 O 3 /Cr-carbide nanocomposites were prepared by employing recently developed spark plasma sintering (SPS) technique. The initial materials were fabricated by a metal organic chemical vapor deposition (MOCVD) process, in which Cr(CO) 6 was used as a precursor and Al 2 O 3 powders as matrix in a spouted chamber. The basic mechanical properties like hardness, fracture strength and toughness, and the nanoindentation characterization of nanocomposites such as Elastics modulus (E), elastic work (W e ) and plastic work (W p ) were analyzed. The microstructure of dislocation, transgranular and step-wise fracture surface were observed in the nanocomposites. The nanocomposites show fracture toughness of (4.8 MPa m 1/2 ) and facture strength (780 MPa), which is higher than monolithic alumina. The strengthening mechanism from the secondary phase and solid solution are also discussed in the present work. Nanoindentation characterization further illustrates the strengthening of nanocomposites.
Mono to few-layer graphene were prepared on pre-annealed polycrystalline nickel substrates by che... more Mono to few-layer graphene were prepared on pre-annealed polycrystalline nickel substrates by chemical vapor deposition at a relatively low temperature of 800 C using fast cooling rate. It was observed that the reduced solubility of Carbon in Ni at low temperature and an optimum gas mixing ratio (CH 4 :H 2 = 60/80 (sccm)) can be used to synthesize mano-layer graphene that covers about 100 m 2 area. The number of graphene layers strongly depends upon the hydrogen and methane flow rates. An increase in the methane flow is found to increase the growth density of the single-layer graphene. The number of graphene layers was identified from micro-Raman spectra. The thinnest areas containing mono-layer graphene formed at small Ni grains surrounded by large Ni Grains can be explained in terms of Spinodal decomposition. Scanning tunneling microscopy observations of the graphene samples indicate that the graphene structure exhibits no defects, and extremely symmetry hexagon carbon at flat graphene surface is observed.
The effects of microstructure on the mechanical responses and damage evolution of spark-plasma-si... more The effects of microstructure on the mechanical responses and damage evolution of spark-plasma-sintered b-Si 3 N 4 -based ceramics has been evaluated through indentation tests. It was found that the nanoceramic and its coarse-grained counterpart exhibit similar elastoplastic behavior in their indentation responses. However, the increased hardness and ratio of elastic work to total work done in the nanoceramic suggest that resistance to plastic deformation is greater than that in the coarsergrained one. The microcracking behavior within the indented materials is also proposed. A finite-element analysis is used to estimate the distribution of compressive and shear stresses within the indented materials. The smaller grain size in bridging ceramic not only enhances the energy dissipation by formation of a higher density of intergranular microcracks along the weak grain boundary phase but also toughens the cracked solid through increasing resistance to plastic sliding and multi-cracks propagation. Prior to formation of the radial cracks, better damage tolerance of nanoceramic is thought to be achieved in this study.
Journal of the American Ceramic Society, Jan 1, 2007
Pure and 5 wt% of Ag-doped (La1−xYx)2Ba2CaCu5Oz superconducting compounds for x=0–0.5 have been p... more Pure and 5 wt% of Ag-doped (La1−xYx)2Ba2CaCu5Oz superconducting compounds for x=0–0.5 have been prepared. Analysis of X-ray diffraction patterns shows that the samples are essentially in the single-phase form and they could be refined using the P4/mmm space group in a tetragonal cell. The typical lattice parameters are found to be a=b=3.879 Å, c=11.646 Å for x=0 and a=b=3.856 Å, c=11.576 Å for x=0.5 samples. The detailed crystal structure parameters are presented. The average grain size values from scanning electron microscope images are found to be in the order of 1–3 μm. Temperature variations of ac susceptibility and electrical resistivity have been measured. Superconducting transitions with diamagnetic Tc ranging from 60 to 75 K have been observed, with the maximum Tc for the x=0.25 sample. Ag-doped samples exhibit improved inter-granular coupling and homogeneous oxygenation.
Fully dense β-Si3N4 based nanoceramics were consolidated by spark plasma sintering (SPS). A comme... more Fully dense β-Si3N4 based nanoceramics were consolidated by spark plasma sintering (SPS). A commercially available β-Si3N4 nano-powder was used as starting material. The sintering bulks were fabricated with a heating rate of 90 °C/min by varying SPS temperature from 1550 °C to 1700 °C, and the linear shrinkage was used to evaluate the sintering behavior of the nano-powder. The microstructures of the developed Si3N4 based ceramics were achieved, and the grain length, grain width, and aspect ratio for these sintering bulks were found to increase gradually with elevating sintering temperature. The hardness and fracture toughness are associated with the microstructural characteristics. The crack propagation and fracture behavior for these β-Si3N4 based nanoceramics have been observed for the specimens sintered at different sintering temperatures. Crack deflection is found to be one of the toughening mechanisms for these β-Si3N4 based nanoceramics.
Journal of The European Ceramic Society, Jan 1, 2011
Nanosized chromium carbide has been prepared by metal–organic chemical vapour deposition (MOCVD) ... more Nanosized chromium carbide has been prepared by metal–organic chemical vapour deposition (MOCVD) method in a fluidized bed and carburized in the mixture of CH4/H2 atmosphere in temperature range 700–850 °C. The carburization process involves carbon deposition on the outer surface of the Cr2O3 powder, followed by carbon diffusion into the powder, leading to formation of metastable Cr3C2−x phase and stable Cr3C2. The phase transformation from Cr2O3 to Cr3C2 via an intermediate state Cr3C2−x has been identified using electron-energy loss spectroscopy (EELS) and micro-Raman spectroscopy. We could hypothesize that the formation of carbon nanofilms surrounding the carbide crystallites provides the stress and assist the phase transformation from metastable Cr3C2−x to stable Cr3C2.
Single crystal SiC has been synthesized by a novel liquid phase epitaxy using mixture of (Sm:Co) ... more Single crystal SiC has been synthesized by a novel liquid phase epitaxy using mixture of (Sm:Co) as unique solvent. The synthesized high quality crystals have been characterized by field emission gun scanning electron microscopy and field emission gun transmission electron microscopy. The above analysis shows the epitaxial growth of single crystal SiC along [1 1 1] direction parallel to the Si wafer, followed by polycrystalline 3C–SiC and 6H–SiC whiskers. The formation mechanisms of single crystal SiC and SiC whiskers have been proposed.
Journal of The American Ceramic Society, Jan 1, 2010
Pure and Sm3+ (0.33, 0.46, 1.48, and 2.19 at.%)-doped ZrO2 thin films have been prepared using ra... more Pure and Sm3+ (0.33, 0.46, 1.48, and 2.19 at.%)-doped ZrO2 thin films have been prepared using radio-frequency (RF) sputtering technique. The phase composition and photoluminescence (PL) properties have been studied on these pure and doped thin films as a function of annealing temperature and doping concentration. Phase composition analysis indicates the increment in the monoclinic content and crystallite size of the pure sample with the increase in annealing temperature. Higher doping promotes the tetragonal phase of the material. From PL studies, Sm3+ (0.33 at.%)-doped zirconia thin film shows a stronger emission spectra than other higher doping. All doped samples exhibit a well-resolved emission series of Sm3+ at higher annealing temperatures. The effect of structural modifications on the PL spectra of the zirconia system has been investigated. Monoclinic phase promotes the luminescence efficiency of this system. PL study shows one to one correspondence with that of structural modification of zirconia system.
A conductive TiC nanopowder was incorporated into nanosized b-Si 3 N 4 -based powder and consolid... more A conductive TiC nanopowder was incorporated into nanosized b-Si 3 N 4 -based powder and consolidated by a spark plasma sintering (SPS) technique with a rapid heating process. The influence of the conductive phase on the microstructure development of the Si 3 N 4 matrix was demonstrated. After sintering, the conductive phase transformed into titanium oxycarbonitride. The Si 3 N 4 -based composite containing 5 wt% nano-TiC x O y N z shows a larger average grain size and aspect ratio than the monolithic Si 3 N 4 -based ceramic. This is possibly because a leakage current hops across the conductive titanium oxycarbonitride grains and causes Joule heating during sintering. The transmission electron microscopy analysis confirmed that dissolution-reprecipitation and coalescence occur. In addition, although the increasing amount of incorporated nano-TiC x O y N z (10 and 20 wt%) decreases the electrical resistivity of the composites, the pinning effect of the titanium-based phase significantly suppresses the grain growth of Si 3 N 4 matrix grains. b-Si 3 N 4 -based nanocomposites containing nanosized titanium oxycarbonitride were thus obtained in the present study.
Silicon carbide layers were grown on a Si substrate at a temperature below 1100 °C and pressure o... more Silicon carbide layers were grown on a Si substrate at a temperature below 1100 °C and pressure of 105 Pa. The synthesis was carried out in a tube furnace through cyclic heating process using methane as a carbon source and Sm–Co mixed powder as a solvent. The growth of SiC from rare earth Sm-based solvent is an innovative approach, and Co can promote the formation of solvent during the growth process. The structural and compositional analyses were carried out using X-ray diffraction, electron probe micro-analyzer, scanning electron microscopy and transmission electron microscopy. Results indicated that β-SiC was successfully fabricated on Si (1 1 1) substrate. The heterogeneous nucleation of β-SiC was found to be observed initially at the edge of triangle-shaped sites on Si (1 1 1) surface that formed due to the existence of Co, and then grew and expanded to form β-SiC film. The growth process of SiC via vapour–liquid–solid mechanism was also discussed in this study.► Successful synthesis of SiC using liquid phase technique below 1100 °C. ► The growth of SiC from rare earth Sm-based solvent is an innovative approach. ► Growth of β-SiC in <1 1 1> direction parallel to Si wafer. ► Appearance of some triangle-shape pits on Si (1 1 1) substrate after decomposition of Co–Si alloy. ► These triangle shaped pits promote the heterogeneous nucleation of SiC.
The densification behaviors of Al2O3–Cr2O3/Cr3C2 nanocomposites prepared by a Spark Plasma Sinter... more The densification behaviors of Al2O3–Cr2O3/Cr3C2 nanocomposites prepared by a Spark Plasma Sintering (SPS) were investigated in this work. The initial powders used for sintering were Al2O3–Cr2O3, which were prepared by metal organic chemical vapor deposition (MOCVD) in a spout bed. Different colors of the compacts such as green, purple and black were observed after densification process at different SPS temperatures from 1200 °C to 1350 °C. These changes of color were relevant to the existence of secondary phase of green Cr2O3, pink solid solution of Cr2O3–Al2O3 and black Cr3C2, which were formed under the different SPS temperature. The secondary phase of Cr2O3 retarded the processing of densification for spark plasma sintering at 1200 °C. The Cr2O3 reacted with Al2O3 to form solid solution of Cr2O3–Al2O3 and with carbon to form Cr3C2 as sintering temperature increased to 1350 °C. The characteristics of high heating rate, shorter sintering time for SPS and the formation of secondary phase of Cr3C2 effectively reduced the substrate's grain growth, making Al2O3–Cr2O3/Cr3C2 nanocomposites with small grain size.
The multi-elemental composition of in vitro—proliferated root tissues of Andrographis paniculata ... more The multi-elemental composition of in vitro—proliferated root tissues of Andrographis paniculata (Burm.f.) Wall. ex Nees was compared with that of the naturally grown in vivo plants. Trace elements namely Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Rb, Sr and Pb in addition to two macro-elements K and Ca were identified and quantified in root tissues of both sources using the energy dispersive X-ray fluorescence (ED-XRF) technique. ED-XRF analysis was performed using Mo K X-rays generated from a secondary molybdenum target. The elemental content of in vitro roots was found to be at par with that of naturally grown plants of the same species. This opens up a possibility of exploiting in vitro root cultures as a viable, alternative and renewable source of phytochemicals of relevance, besides providing a means for conservation of the valuable natural resources.
Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspe... more Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspect ratio, uniform pore size (120–140 nm), and ordered pore arrangement. The Cu2O nanowire arrays were prepared from the oxidization of Cu metal nanowire arrays. The electrochemical deposition potential of Cu metal nanowires (−180 mV vs. SCE) was determined from X-ray diffraction (XRD) patterns. The microstructure and chemical composition of Cu nanowire arrays were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). Results indicate that the Cu/Cu2O nanowire arrays assembled into the nanochannel of the porous alumina template with diameters of 120–140 nm. The valence of copper was controlled by the porous alumina template during the annealing process. Copper nanowires transformed to the Cu2O phase with the space limitation of the PAM template. Single-crystal Cu2O nanowire arrays were also obtained under the template embedded.
Polycrystalline Cu 2 O nanowire arrays have been grown via porous alumina membranes using three-e... more Polycrystalline Cu 2 O nanowire arrays have been grown via porous alumina membranes using three-electrode electrochemical deposition. The effect of electrolyte, pH value, deposition potential, annealing temperature, and annealing atmosphere on the growth of Cu 2 O nanowire arrays has been investigated. On the other hand, ordered ZnO/AZO/PAM nanowire arrays have been prepared by seed layer assisted electrochemical deposition. The comprehensive of electrochemical process adopted (e.g. electrolytes, deposition parameters); various characterization techniques and the outcome of the results have been summarized in details. It is observed that the ZnO nanowire arrays are assembled into the nanochannel of porous alumina template with diameter of 120~140 nm. The crystalline structure of single ZnO nanowire is dependent on AZO seed layer. The nucleation and growth process of ZnO/AZO/PAM nanowires are interpreted by seed layer assisted growth mechanism.
Journal of Physics: Conference Series, Jan 1, 2010
A square Helmholtz coil has been designed and fabricated using commercial grade HTS BSCCO tape wi... more A square Helmholtz coil has been designed and fabricated using commercial grade HTS BSCCO tape with double pancake configuration. The present work is aimed at generating uniform magnetic field with a square Helmholtz coil pair useful in laboratory applications. It has an advantages over the circular Helmholtz coil which had been fabricated and validated by us earlier in terms of field uniformity. This coil is intended to be used as a background field/magnet for circular Helmholtz coil and possible characterization of High T c tapes. Design parameters details, magnetic field generated and the fabrication techniques o f this square Helmholtz coil have been described in this paper.
The fine grains of Al 2 O 3 -Cr 2 O 3 /Cr-carbide nanocomposites were prepared by employing recen... more The fine grains of Al 2 O 3 -Cr 2 O 3 /Cr-carbide nanocomposites were prepared by employing recently developed spark plasma sintering (SPS) technique. The initial materials were fabricated by a metal organic chemical vapor deposition (MOCVD) process, in which Cr(CO) 6 was used as a precursor and Al 2 O 3 powders as matrix in a spouted chamber. The basic mechanical properties like hardness, fracture strength and toughness, and the nanoindentation characterization of nanocomposites such as Elastics modulus (E), elastic work (W e ) and plastic work (W p ) were analyzed. The microstructure of dislocation, transgranular and step-wise fracture surface were observed in the nanocomposites. The nanocomposites show fracture toughness of (4.8 MPa m 1/2 ) and facture strength (780 MPa), which is higher than monolithic alumina. The strengthening mechanism from the secondary phase and solid solution are also discussed in the present work. Nanoindentation characterization further illustrates the strengthening of nanocomposites.
Mono to few-layer graphene were prepared on pre-annealed polycrystalline nickel substrates by che... more Mono to few-layer graphene were prepared on pre-annealed polycrystalline nickel substrates by chemical vapor deposition at a relatively low temperature of 800 C using fast cooling rate. It was observed that the reduced solubility of Carbon in Ni at low temperature and an optimum gas mixing ratio (CH 4 :H 2 = 60/80 (sccm)) can be used to synthesize mano-layer graphene that covers about 100 m 2 area. The number of graphene layers strongly depends upon the hydrogen and methane flow rates. An increase in the methane flow is found to increase the growth density of the single-layer graphene. The number of graphene layers was identified from micro-Raman spectra. The thinnest areas containing mono-layer graphene formed at small Ni grains surrounded by large Ni Grains can be explained in terms of Spinodal decomposition. Scanning tunneling microscopy observations of the graphene samples indicate that the graphene structure exhibits no defects, and extremely symmetry hexagon carbon at flat graphene surface is observed.
The effects of microstructure on the mechanical responses and damage evolution of spark-plasma-si... more The effects of microstructure on the mechanical responses and damage evolution of spark-plasma-sintered b-Si 3 N 4 -based ceramics has been evaluated through indentation tests. It was found that the nanoceramic and its coarse-grained counterpart exhibit similar elastoplastic behavior in their indentation responses. However, the increased hardness and ratio of elastic work to total work done in the nanoceramic suggest that resistance to plastic deformation is greater than that in the coarsergrained one. The microcracking behavior within the indented materials is also proposed. A finite-element analysis is used to estimate the distribution of compressive and shear stresses within the indented materials. The smaller grain size in bridging ceramic not only enhances the energy dissipation by formation of a higher density of intergranular microcracks along the weak grain boundary phase but also toughens the cracked solid through increasing resistance to plastic sliding and multi-cracks propagation. Prior to formation of the radial cracks, better damage tolerance of nanoceramic is thought to be achieved in this study.
Journal of the American Ceramic Society, Jan 1, 2007
Pure and 5 wt% of Ag-doped (La1−xYx)2Ba2CaCu5Oz superconducting compounds for x=0–0.5 have been p... more Pure and 5 wt% of Ag-doped (La1−xYx)2Ba2CaCu5Oz superconducting compounds for x=0–0.5 have been prepared. Analysis of X-ray diffraction patterns shows that the samples are essentially in the single-phase form and they could be refined using the P4/mmm space group in a tetragonal cell. The typical lattice parameters are found to be a=b=3.879 Å, c=11.646 Å for x=0 and a=b=3.856 Å, c=11.576 Å for x=0.5 samples. The detailed crystal structure parameters are presented. The average grain size values from scanning electron microscope images are found to be in the order of 1–3 μm. Temperature variations of ac susceptibility and electrical resistivity have been measured. Superconducting transitions with diamagnetic Tc ranging from 60 to 75 K have been observed, with the maximum Tc for the x=0.25 sample. Ag-doped samples exhibit improved inter-granular coupling and homogeneous oxygenation.
Fully dense β-Si3N4 based nanoceramics were consolidated by spark plasma sintering (SPS). A comme... more Fully dense β-Si3N4 based nanoceramics were consolidated by spark plasma sintering (SPS). A commercially available β-Si3N4 nano-powder was used as starting material. The sintering bulks were fabricated with a heating rate of 90 °C/min by varying SPS temperature from 1550 °C to 1700 °C, and the linear shrinkage was used to evaluate the sintering behavior of the nano-powder. The microstructures of the developed Si3N4 based ceramics were achieved, and the grain length, grain width, and aspect ratio for these sintering bulks were found to increase gradually with elevating sintering temperature. The hardness and fracture toughness are associated with the microstructural characteristics. The crack propagation and fracture behavior for these β-Si3N4 based nanoceramics have been observed for the specimens sintered at different sintering temperatures. Crack deflection is found to be one of the toughening mechanisms for these β-Si3N4 based nanoceramics.
Journal of The European Ceramic Society, Jan 1, 2011
Nanosized chromium carbide has been prepared by metal–organic chemical vapour deposition (MOCVD) ... more Nanosized chromium carbide has been prepared by metal–organic chemical vapour deposition (MOCVD) method in a fluidized bed and carburized in the mixture of CH4/H2 atmosphere in temperature range 700–850 °C. The carburization process involves carbon deposition on the outer surface of the Cr2O3 powder, followed by carbon diffusion into the powder, leading to formation of metastable Cr3C2−x phase and stable Cr3C2. The phase transformation from Cr2O3 to Cr3C2 via an intermediate state Cr3C2−x has been identified using electron-energy loss spectroscopy (EELS) and micro-Raman spectroscopy. We could hypothesize that the formation of carbon nanofilms surrounding the carbide crystallites provides the stress and assist the phase transformation from metastable Cr3C2−x to stable Cr3C2.
Single crystal SiC has been synthesized by a novel liquid phase epitaxy using mixture of (Sm:Co) ... more Single crystal SiC has been synthesized by a novel liquid phase epitaxy using mixture of (Sm:Co) as unique solvent. The synthesized high quality crystals have been characterized by field emission gun scanning electron microscopy and field emission gun transmission electron microscopy. The above analysis shows the epitaxial growth of single crystal SiC along [1 1 1] direction parallel to the Si wafer, followed by polycrystalline 3C–SiC and 6H–SiC whiskers. The formation mechanisms of single crystal SiC and SiC whiskers have been proposed.
Journal of The American Ceramic Society, Jan 1, 2010
Pure and Sm3+ (0.33, 0.46, 1.48, and 2.19 at.%)-doped ZrO2 thin films have been prepared using ra... more Pure and Sm3+ (0.33, 0.46, 1.48, and 2.19 at.%)-doped ZrO2 thin films have been prepared using radio-frequency (RF) sputtering technique. The phase composition and photoluminescence (PL) properties have been studied on these pure and doped thin films as a function of annealing temperature and doping concentration. Phase composition analysis indicates the increment in the monoclinic content and crystallite size of the pure sample with the increase in annealing temperature. Higher doping promotes the tetragonal phase of the material. From PL studies, Sm3+ (0.33 at.%)-doped zirconia thin film shows a stronger emission spectra than other higher doping. All doped samples exhibit a well-resolved emission series of Sm3+ at higher annealing temperatures. The effect of structural modifications on the PL spectra of the zirconia system has been investigated. Monoclinic phase promotes the luminescence efficiency of this system. PL study shows one to one correspondence with that of structural modification of zirconia system.
A conductive TiC nanopowder was incorporated into nanosized b-Si 3 N 4 -based powder and consolid... more A conductive TiC nanopowder was incorporated into nanosized b-Si 3 N 4 -based powder and consolidated by a spark plasma sintering (SPS) technique with a rapid heating process. The influence of the conductive phase on the microstructure development of the Si 3 N 4 matrix was demonstrated. After sintering, the conductive phase transformed into titanium oxycarbonitride. The Si 3 N 4 -based composite containing 5 wt% nano-TiC x O y N z shows a larger average grain size and aspect ratio than the monolithic Si 3 N 4 -based ceramic. This is possibly because a leakage current hops across the conductive titanium oxycarbonitride grains and causes Joule heating during sintering. The transmission electron microscopy analysis confirmed that dissolution-reprecipitation and coalescence occur. In addition, although the increasing amount of incorporated nano-TiC x O y N z (10 and 20 wt%) decreases the electrical resistivity of the composites, the pinning effect of the titanium-based phase significantly suppresses the grain growth of Si 3 N 4 matrix grains. b-Si 3 N 4 -based nanocomposites containing nanosized titanium oxycarbonitride were thus obtained in the present study.
Silicon carbide layers were grown on a Si substrate at a temperature below 1100 °C and pressure o... more Silicon carbide layers were grown on a Si substrate at a temperature below 1100 °C and pressure of 105 Pa. The synthesis was carried out in a tube furnace through cyclic heating process using methane as a carbon source and Sm–Co mixed powder as a solvent. The growth of SiC from rare earth Sm-based solvent is an innovative approach, and Co can promote the formation of solvent during the growth process. The structural and compositional analyses were carried out using X-ray diffraction, electron probe micro-analyzer, scanning electron microscopy and transmission electron microscopy. Results indicated that β-SiC was successfully fabricated on Si (1 1 1) substrate. The heterogeneous nucleation of β-SiC was found to be observed initially at the edge of triangle-shaped sites on Si (1 1 1) surface that formed due to the existence of Co, and then grew and expanded to form β-SiC film. The growth process of SiC via vapour–liquid–solid mechanism was also discussed in this study.► Successful synthesis of SiC using liquid phase technique below 1100 °C. ► The growth of SiC from rare earth Sm-based solvent is an innovative approach. ► Growth of β-SiC in <1 1 1> direction parallel to Si wafer. ► Appearance of some triangle-shape pits on Si (1 1 1) substrate after decomposition of Co–Si alloy. ► These triangle shaped pits promote the heterogeneous nucleation of SiC.
The densification behaviors of Al2O3–Cr2O3/Cr3C2 nanocomposites prepared by a Spark Plasma Sinter... more The densification behaviors of Al2O3–Cr2O3/Cr3C2 nanocomposites prepared by a Spark Plasma Sintering (SPS) were investigated in this work. The initial powders used for sintering were Al2O3–Cr2O3, which were prepared by metal organic chemical vapor deposition (MOCVD) in a spout bed. Different colors of the compacts such as green, purple and black were observed after densification process at different SPS temperatures from 1200 °C to 1350 °C. These changes of color were relevant to the existence of secondary phase of green Cr2O3, pink solid solution of Cr2O3–Al2O3 and black Cr3C2, which were formed under the different SPS temperature. The secondary phase of Cr2O3 retarded the processing of densification for spark plasma sintering at 1200 °C. The Cr2O3 reacted with Al2O3 to form solid solution of Cr2O3–Al2O3 and with carbon to form Cr3C2 as sintering temperature increased to 1350 °C. The characteristics of high heating rate, shorter sintering time for SPS and the formation of secondary phase of Cr3C2 effectively reduced the substrate's grain growth, making Al2O3–Cr2O3/Cr3C2 nanocomposites with small grain size.
The multi-elemental composition of in vitro—proliferated root tissues of Andrographis paniculata ... more The multi-elemental composition of in vitro—proliferated root tissues of Andrographis paniculata (Burm.f.) Wall. ex Nees was compared with that of the naturally grown in vivo plants. Trace elements namely Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Rb, Sr and Pb in addition to two macro-elements K and Ca were identified and quantified in root tissues of both sources using the energy dispersive X-ray fluorescence (ED-XRF) technique. ED-XRF analysis was performed using Mo K X-rays generated from a secondary molybdenum target. The elemental content of in vitro roots was found to be at par with that of naturally grown plants of the same species. This opens up a possibility of exploiting in vitro root cultures as a viable, alternative and renewable source of phytochemicals of relevance, besides providing a means for conservation of the valuable natural resources.
Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspe... more Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspect ratio, uniform pore size (120–140 nm), and ordered pore arrangement. The Cu2O nanowire arrays were prepared from the oxidization of Cu metal nanowire arrays. The electrochemical deposition potential of Cu metal nanowires (−180 mV vs. SCE) was determined from X-ray diffraction (XRD) patterns. The microstructure and chemical composition of Cu nanowire arrays were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). Results indicate that the Cu/Cu2O nanowire arrays assembled into the nanochannel of the porous alumina template with diameters of 120–140 nm. The valence of copper was controlled by the porous alumina template during the annealing process. Copper nanowires transformed to the Cu2O phase with the space limitation of the PAM template. Single-crystal Cu2O nanowire arrays were also obtained under the template embedded.
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Papers by Pramoda Nayak