The Experts below are selected from a list of 3174 Experts worldwide ranked by ideXlab platform
Kian Ping Loh - One of the best experts on this subject based on the ideXlab platform.
-
Self-assembly and selected area growth of zinc oxide nanorods on any surface promoted by an Aluminum precoat
Journal of Physical Chemistry B, 2004Co-Authors: Yee Wee Koh, Chow Kim Tan, Yong Lim Foo, Ming Lin, Kian Ping LohAbstract:We demonstrate a simple method to direct the self-assembly of ZnO nanorods on flat and curved surfaces in hydrothermal synthesis by precoating the substrate with a thin film of Aluminum (Al). The Al was transformed in the alkali hydrothermal environment into hydrotalcite-like zinc Aluminum Carbonate sheets, which provide a lattice-matched substrate for the self-assembly of ZnO nanorods. Selective growth of ZnO nanorods on the Al-patterned substrate as well as the high-density coating of carbon nanotubes by ZnO nanorods along the tangential and radial walls has been demonstrated using hydrothermal synthesis. The interfacial chemistry involved in the growth of ZnO and hydrotalcite-like zinc Aluminum Carbonate sheets is also discussed.
Mazhar Mehmood - One of the best experts on this subject based on the ideXlab platform.
-
Formation of porous α-alumina from ammonium Aluminum Carbonate hydroxide whiskers
Ceramics International, 2019Co-Authors: Jamil Ahmad, Muhammad Ismail Tariq, Rizwan Ahmad, Syed Mujtaba Ul-hassan, Mazhar Mehmood, Abdul Faheem Khan, Shabana Waseem, Shoaib Mehboob, Muhammad Tauseef TanvirAbstract:Abstract Ammonium Aluminum Carbonate hydroxide (AACH) whiskers prepared by hydrothermal technique were employed as precursor material for development of porous alumina. After compaction of AACH whiskers at 8 bars, calcination was performed at 650 °C followed by sintering at different temperatures. The sintered samples were characterized by XRD, FTIR, SEM and mercury intrusion porosimetry. Mechanical strength was determined by compression testing. At sintering temperatures of 1200 °C to 1400 °C, the % age porosity was around 80%. At 1500 °C, the percentage porosity decreased to 71%. The as-prepared AACH consisted of bundles of whiskers with diameters as thick as 0.7 µm, while an individual whisker had a diameter of about 100 nm with an aspect ratio of about 33. A two-phase mixture consisting of θ- and α-alumina was obtained at 1100 °C, while at 1200 °C and above, single phase α-alumina was formed. θ-alumina retained the bundle-like morphology. However, transformation to α-alumina was accompanied by formation of bead-like morphology. These beads were joined together through necks/stems within the whiskers as well as across the parallel-lying whiskers. These necks grew at 1300 °C to form aggregates with smooth surfaces. At 1400 °C, these aggregates started joining with each other by neck formation and at 1500 °C, a three-dimensional network was formed. For sintering temperatures of up to 1400 °C, pores with sizes around 260 nm were very stable. At 1500 °C, significant pore growth took place along with an overall densification. Therefore, number of pores with sizes of around 260 nm decreased and those with sizes around 10 µm, 1 µm and 5 nm increased. The compression strength of samples sintered at 1100 °C to 1300 °C was in the range of 3.4–4.3 MPa. At 1400 °C, the strength increased to 5.2 MPa, while at 1500 °C, it jumped to 10.8 MPa due to the formation of three-dimensional network.
-
Terahertz time domain spectroscopy of hydrothermally synthesized boehmite and ammonium dawsonite nanostructures
Infrared Physics & Technology, 2016Co-Authors: Shoaib Mehboob, Jamil Ahmad, Mazhar Mehmood, Muhammad Tauseef Tanvir, Mushtaq Ahmed, Izhar AhmadAbstract:Abstract The frequency dependent optical and dielectric properties of boehmite (AlOOH) and ammonium Aluminum Carbonate hydroxide (AACH) nanostructures, prepared at different temperatures via hydrothermal synthesis, were studied by using terahertz time domain spectroscopy (THz-TDS). The complex refractive indices, absorption coefficients and complex dielectric constants were determined and compared for different synthesis temperatures. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were also performed to confirm the formation of boehmite and AACH. Scanning electron microscopy (SEM) was performed to study the morphology of nanostructures. The study reveals the formation of AACH at higher temperatures and decrease in refractive index with increasing synthesis temperature. The higher absorption coefficient and lower refractive index and dielectric constant were observed for AACH than for boehmite.
-
Single step hydrothermal synthesis of 3D urchin like structures of AACH and Aluminum oxide with thin nano-spikes
Ceramics International, 2012Co-Authors: Muhammad Abdullah, Mazhar Mehmood, Jamil AhmadAbstract:Abstract 3D urchins like ammonium Aluminum Carbonate hydroxide (AACH) nanostructures with nano-spikes of dia. 20–30 nm were synthesized by a simple, single step hydrothermal technique by using Aluminum nitrate and urea as precursor materials. It was found that morphology of the produced structure strongly depends upon the urea concentration. With increasing the amount of urea, the AACH particles having embedded rods like surface features transformed into 3D urchins. The added urea decomposed during hydrothermal treatment and increased the pH of the solution, which affected the morphology of the produced nanostructures. SEM, XRD, FTIR and TGA were employed to characterize the produced structures. On heating, the volatile ingredients of AACH were removed, leaving behind the alumina urchins.
-
Influence of Al2O3 whisker concentration on flexural strength of Al2O3(w)–ZrO2 (TZ-3Y) composite
Ceramics International, 2012Co-Authors: Muhammad Abdullah, Jamil Ahmad, Mazhar MehmoodAbstract:Abstract On investigating the possibility of using alumina whisker reinforced 3 mol% Yttria stabilized Tetragonal Zirconia (TZ-3Y) composite for bioceramic applications, presented here is the influence of varying whisker concentration (2, 5, 10, 15 and 20 wt%) on flexural strength of the composite. Whiskers of hydrothermally synthesized Ammonium Aluminum Carbonate Hydroxide (AACH) were used for composite synthesis. These whiskers transformed in situ into alumina during sintering. It was found that with addition of alumina whiskers, strength was increased and reached a maximum value of 1212±60 MPa and 1325±65 MPa, in pure and 1 wt% CTAB added samples respectively, at a concentration of 10 wt% Al 2 O 3 whiskers. The strength values of the synthesized composite can compete well with commercially available materials for dental applications.
-
Effect of sintering temperature on properties of Al2O3 whisker reinforced 3 mol% Y2O3 stabilized tetragonal ZrO2 (TZ-3Y) nanocomposites
Composites Part B: Engineering, 2012Co-Authors: Muhammad Abdullah, Jamil Ahmad, Mazhar MehmoodAbstract:Abstract In present study, effect of sintering temperature on density and hardness of 3 mol% yttria-stabilized tetragonal zirconia (referred to as TZ-3Y) composite reinforced with alumina whiskers (5, 10, 15 and 20 wt.%) has been studied. Initially, Ammonium Aluminum Carbonate Hydroxide (AACH) whiskers were added in TZ-3Y composite and transformed into alumina during sintering performed at different temperatures i.e. 1400, 1500 and 1650 °C. Results revealed that for all sintering temperatures, with increase in whisker concentration, sintered density decreased and hardness increased conversely. Maximum hardness of 14.47 GPa was achieved with 10 wt.% whiskers addition when sintered at 1500 °C. However, with addition of CTAB (1 wt.%) as deflocculating agent the hardness was further improved to 15.11 GPa. While sintering at 1650 °C a decrease in hardness was observed. It was mainly due to high temperature morphological change of whiskers i.e. transformation of whiskers into alumina rich grains.
Chenguang Liu - One of the best experts on this subject based on the ideXlab platform.
-
Preparation of NiMo/γ-Al2O3 catalysts with large pore size for vacuum residue hydrotreatment
Materials Research Bulletin, 2013Co-Authors: Zhe Tang, Liu Yunqi, Chenguang LiuAbstract:gamma-Al2O3 supports with large pore size were prepared by using rod-like ammonium Aluminum Carbonate hydroxide (AACH) as precursors. The textural properties of supports are dependent on the different crystallinity of the as-prepared AACH. For investigating their catalytic performance, NiMo/gamma-Al2O3 hydrotreating catalysts were prepared by loading NiMo oxides on the supports and tested by using vacuum residue as reactant, and the results show that both pore structure and surface acid property of catalysts have significant influences on the catalytic activities for the hydrogenation and the removal of heteroatoms. (C) 2013 Elsevier Ltd. All rights reserved.
-
Fabrication of high-surface-area γ-alumina by thermal decomposition of AACH precursor using low-temperature solid-state reaction
Materials Research Bulletin, 2012Co-Authors: Yun Qi Liu, Zhe Tang, Ruiyu Zhao, Chenguang LiuAbstract:Abstract In this paper, systematical investigation has been made for the new simple synthesis pathway of catalytic alumina with high surface area through thermal decomposition of ammonium Aluminum Carbonate hydroxide (AACH), which has been prepared by a low-temperature solid-state reaction in non-aqueous system. The results indicate that the molar ratios of NH 4 HCO 3 /Al influence crystallinities and the morphologies of AACH. Well-crystallized AACH with nanorod morphology and low-crystallized AACH with cluster structure can be obtained with different molar ratios NH 4 HCO 3 /Al. The γ-Al 2 O 3 product with high surface area (511 m 2 /g) can be obtained from the calcination of AACH at 500 °C. Moreover, the results also indicate that crystallinities and morphologies of AACH affect their thermal decomposition behaviors. In addition, the formation of high-surface-area is possibly attributed to intracrystalline porosity of as-prepared γ-Al 2 O 3 .
-
Facile Synthesis of Ammonium Aluminum Carbonate Hydroxide Multilayered Nanofiber by Using Solid State Reaction
Advanced Materials Research, 2011Co-Authors: Yun Qi Liu, Chenguang LiuAbstract:In this paper, we make systematical investigation for the new synthesis pathway of AACH multilayered nanofiber, which has been prepared by a low-temperature solid-state reaction. The phase transformation sequence of AACH on heating is found that the precursor converts into γ-Al2O3 at 700-900°C and elevated temperature results in the θ-Al2O3 and α- Al2O3 crystal phase formation at 1000°C. With a higher calcination temperature at 1100°C, α- Al2O3 pattern appears. The specific surface area (SBET) of Aluminum oxide specie calcined at 500°C for 4h is still in 420.2m2/g. Meanwhile, it suggests a partial change in particle sizes and morphology of sample calcined at 500°C for 4h.
Wei-chin Chen - One of the best experts on this subject based on the ideXlab platform.
-
hydrothermal preparation of calcium Aluminum Carbonate sorbent for high temperature co2 capture in fixed bed reactor
Fuel, 2014Co-Authors: Wei-chin ChenAbstract:Abstract Calcium–Aluminum Carbonate (Ca–Al–CO 3 ) sorbents for CO 2 sorption were hydrothermally prepared and tested at 750 °C by thermal gravimetric (TG) analysis and fixed-bed reactor method. The Ca/Al molar ratios of the sorbents ranged from 1:1 to 30:1. As the Ca/Al molar ratio increased, the CO 2 sorption mass increased from 13.4 to 74.2 wt%. The capturing stability remained stable at 99% in TG analyzer and 76% in the reactor (10 cycles at 750 °C). The kinetic parameter, estimated by the kinetic control model, indicated that the model was consistent with the carbonation reaction of Ca–Al–CO 3 with CO 2 in the kinetically controlled reaction regime. The estimated activation energy ( E a ) of CO 2 sorption was 53.6 kJ/mol, slightly less than the typical E a of CaO carbonation reactions above 600 °C in fixed-bed reactors. This reduction may be partially attributed to the co-existence of Ca(OH) 2 and CaO nanoparticles in the synthetic Ca–Al–CO 3 sorbents.
-
Hydrothermal preparation of calcium–Aluminum Carbonate sorbent for high-temperature CO2 capture in fixed-bed reactor
Fuel, 2014Co-Authors: Wei-chin ChenAbstract:Abstract Calcium–Aluminum Carbonate (Ca–Al–CO 3 ) sorbents for CO 2 sorption were hydrothermally prepared and tested at 750 °C by thermal gravimetric (TG) analysis and fixed-bed reactor method. The Ca/Al molar ratios of the sorbents ranged from 1:1 to 30:1. As the Ca/Al molar ratio increased, the CO 2 sorption mass increased from 13.4 to 74.2 wt%. The capturing stability remained stable at 99% in TG analyzer and 76% in the reactor (10 cycles at 750 °C). The kinetic parameter, estimated by the kinetic control model, indicated that the model was consistent with the carbonation reaction of Ca–Al–CO 3 with CO 2 in the kinetically controlled reaction regime. The estimated activation energy ( E a ) of CO 2 sorption was 53.6 kJ/mol, slightly less than the typical E a of CaO carbonation reactions above 600 °C in fixed-bed reactors. This reduction may be partially attributed to the co-existence of Ca(OH) 2 and CaO nanoparticles in the synthetic Ca–Al–CO 3 sorbents.
Jamil Ahmad - One of the best experts on this subject based on the ideXlab platform.
-
Formation of porous α-alumina from ammonium Aluminum Carbonate hydroxide whiskers
Ceramics International, 2019Co-Authors: Jamil Ahmad, Muhammad Ismail Tariq, Rizwan Ahmad, Syed Mujtaba Ul-hassan, Mazhar Mehmood, Abdul Faheem Khan, Shabana Waseem, Shoaib Mehboob, Muhammad Tauseef TanvirAbstract:Abstract Ammonium Aluminum Carbonate hydroxide (AACH) whiskers prepared by hydrothermal technique were employed as precursor material for development of porous alumina. After compaction of AACH whiskers at 8 bars, calcination was performed at 650 °C followed by sintering at different temperatures. The sintered samples were characterized by XRD, FTIR, SEM and mercury intrusion porosimetry. Mechanical strength was determined by compression testing. At sintering temperatures of 1200 °C to 1400 °C, the % age porosity was around 80%. At 1500 °C, the percentage porosity decreased to 71%. The as-prepared AACH consisted of bundles of whiskers with diameters as thick as 0.7 µm, while an individual whisker had a diameter of about 100 nm with an aspect ratio of about 33. A two-phase mixture consisting of θ- and α-alumina was obtained at 1100 °C, while at 1200 °C and above, single phase α-alumina was formed. θ-alumina retained the bundle-like morphology. However, transformation to α-alumina was accompanied by formation of bead-like morphology. These beads were joined together through necks/stems within the whiskers as well as across the parallel-lying whiskers. These necks grew at 1300 °C to form aggregates with smooth surfaces. At 1400 °C, these aggregates started joining with each other by neck formation and at 1500 °C, a three-dimensional network was formed. For sintering temperatures of up to 1400 °C, pores with sizes around 260 nm were very stable. At 1500 °C, significant pore growth took place along with an overall densification. Therefore, number of pores with sizes of around 260 nm decreased and those with sizes around 10 µm, 1 µm and 5 nm increased. The compression strength of samples sintered at 1100 °C to 1300 °C was in the range of 3.4–4.3 MPa. At 1400 °C, the strength increased to 5.2 MPa, while at 1500 °C, it jumped to 10.8 MPa due to the formation of three-dimensional network.
-
Terahertz time domain spectroscopy of hydrothermally synthesized boehmite and ammonium dawsonite nanostructures
Infrared Physics & Technology, 2016Co-Authors: Shoaib Mehboob, Jamil Ahmad, Mazhar Mehmood, Muhammad Tauseef Tanvir, Mushtaq Ahmed, Izhar AhmadAbstract:Abstract The frequency dependent optical and dielectric properties of boehmite (AlOOH) and ammonium Aluminum Carbonate hydroxide (AACH) nanostructures, prepared at different temperatures via hydrothermal synthesis, were studied by using terahertz time domain spectroscopy (THz-TDS). The complex refractive indices, absorption coefficients and complex dielectric constants were determined and compared for different synthesis temperatures. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were also performed to confirm the formation of boehmite and AACH. Scanning electron microscopy (SEM) was performed to study the morphology of nanostructures. The study reveals the formation of AACH at higher temperatures and decrease in refractive index with increasing synthesis temperature. The higher absorption coefficient and lower refractive index and dielectric constant were observed for AACH than for boehmite.
-
Single step hydrothermal synthesis of 3D urchin like structures of AACH and Aluminum oxide with thin nano-spikes
Ceramics International, 2012Co-Authors: Muhammad Abdullah, Mazhar Mehmood, Jamil AhmadAbstract:Abstract 3D urchins like ammonium Aluminum Carbonate hydroxide (AACH) nanostructures with nano-spikes of dia. 20–30 nm were synthesized by a simple, single step hydrothermal technique by using Aluminum nitrate and urea as precursor materials. It was found that morphology of the produced structure strongly depends upon the urea concentration. With increasing the amount of urea, the AACH particles having embedded rods like surface features transformed into 3D urchins. The added urea decomposed during hydrothermal treatment and increased the pH of the solution, which affected the morphology of the produced nanostructures. SEM, XRD, FTIR and TGA were employed to characterize the produced structures. On heating, the volatile ingredients of AACH were removed, leaving behind the alumina urchins.
-
Influence of Al2O3 whisker concentration on flexural strength of Al2O3(w)–ZrO2 (TZ-3Y) composite
Ceramics International, 2012Co-Authors: Muhammad Abdullah, Jamil Ahmad, Mazhar MehmoodAbstract:Abstract On investigating the possibility of using alumina whisker reinforced 3 mol% Yttria stabilized Tetragonal Zirconia (TZ-3Y) composite for bioceramic applications, presented here is the influence of varying whisker concentration (2, 5, 10, 15 and 20 wt%) on flexural strength of the composite. Whiskers of hydrothermally synthesized Ammonium Aluminum Carbonate Hydroxide (AACH) were used for composite synthesis. These whiskers transformed in situ into alumina during sintering. It was found that with addition of alumina whiskers, strength was increased and reached a maximum value of 1212±60 MPa and 1325±65 MPa, in pure and 1 wt% CTAB added samples respectively, at a concentration of 10 wt% Al 2 O 3 whiskers. The strength values of the synthesized composite can compete well with commercially available materials for dental applications.
-
Effect of sintering temperature on properties of Al2O3 whisker reinforced 3 mol% Y2O3 stabilized tetragonal ZrO2 (TZ-3Y) nanocomposites
Composites Part B: Engineering, 2012Co-Authors: Muhammad Abdullah, Jamil Ahmad, Mazhar MehmoodAbstract:Abstract In present study, effect of sintering temperature on density and hardness of 3 mol% yttria-stabilized tetragonal zirconia (referred to as TZ-3Y) composite reinforced with alumina whiskers (5, 10, 15 and 20 wt.%) has been studied. Initially, Ammonium Aluminum Carbonate Hydroxide (AACH) whiskers were added in TZ-3Y composite and transformed into alumina during sintering performed at different temperatures i.e. 1400, 1500 and 1650 °C. Results revealed that for all sintering temperatures, with increase in whisker concentration, sintered density decreased and hardness increased conversely. Maximum hardness of 14.47 GPa was achieved with 10 wt.% whiskers addition when sintered at 1500 °C. However, with addition of CTAB (1 wt.%) as deflocculating agent the hardness was further improved to 15.11 GPa. While sintering at 1650 °C a decrease in hardness was observed. It was mainly due to high temperature morphological change of whiskers i.e. transformation of whiskers into alumina rich grains.
