Nitrogen has been demonstrated to be effective for the regeneration of Co3Mo3N from Co6Mo6N, albe... more Nitrogen has been demonstrated to be effective for the regeneration of Co3Mo3N from Co6Mo6N, albeit at higher temperature and longer duration than, when employing H2/N2. In some instances, incomplete regeneration yielding a mixture of the two line phases is observed, which has been interpreted on the possible basis of a crystallite size distribution. Temperature programmed reduction of Co3Mo3N, prepared so as to eliminate the possible contribution of NHx groups, demonstrates the significant production of ammonia although in much lower quantities than NHx–containing Co3Mo3N samples.Graphical Abstract
The 14 N/ 15 N isotopic exchange pathways over Co 3 Mo 3 N, a material of interest as an ammonia ... more The 14 N/ 15 N isotopic exchange pathways over Co 3 Mo 3 N, a material of interest as an ammonia synthesis catalyst and for the development of nitrogen transfer reactions, have been investigated. Both the homomolecular and heterolytic exchange processes have been studied, and it has been shown that lattice nitrogen species are exchangeable. The exchange behavior was found to be a strong function of pretreatment with ca. 25% of lattice N atoms being exchanged after 40 min at 600°C after N 2 pretreatment at 700°C compared to only 6% following similar Ar pretreatment. This observation, for which the potential contribution of adsorbed N species can be discounted, is significant in terms of the application of this material. In the case of the Co 6 Mo 6 N phase, regeneration to Co 3 Mo 3 N under 15 N 2 at 600°C occurs concurrently with 14 N 15 N formation. These observations demonstrate the reactivity of nitrogen in the Co−Mo−N system to be a strong function of pretreatment and worthy of further consideration.
The crystal chemistry and electronic structure of the layered nitride SrTiN 2 have been studied b... more The crystal chemistry and electronic structure of the layered nitride SrTiN 2 have been studied by powder neutron diffraction (PND) and density functional methods, respectively. PND investigations at room temperature, 80 K, and 2 K show that the tetragonal KCoO 2 structure (space group P4/nmm (No. 129), a) 3.8823(1) Å, c) 7.7008(1) Å, V) 116.068(1) Å 3 , Z) 2 at 298 K) is retained across the temperature range and confirm the structural model from previous room-temperature powder X-ray diffraction (PXD) studies. Furthermore, and importantly, PND data demonstrate that neither nitrogen nonstoichiometry nor substitution of O 2for N 3within the anion sublattice is a plausible mechanism for hole generation. Density functional calculations show that strong covalent bonding occurs within the TiN 2 layers and that Sr-N interactions are pivotal in determining the band structure at the Fermi level. Calculations predict metallic and paramagnetic behavior for SrTiN 2. These findings are confirmed by experimental measurements.
The pillars of Green Chemistry necessitate the development of new chemical methodologies and proc... more The pillars of Green Chemistry necessitate the development of new chemical methodologies and processes that can benefit chemical synthesis in terms of energy efficiency, conservation of resources, product selectivity, operational simplicity and, crucially, health, safety, and environmental impact. Implementation of green principles whenever possible can spur the growth of benign scientific technologies by considering environmental, economical, and societal sustainability in parallel. These principles seem especially important in the context of the manufacture of materials for sustainable energy and environmental applications. In this review, the production of energy conversion materials is taken as an exemplar, by examining the recent growth in the energy-efficient synthesis of thermoelectric nanomaterials for use in devices for thermal energy harvesting. Specifically, "soft chemistry" techniques such as solution-based, solvothermal, microwave-assisted, and mechanochemical (ball-milling) methods as viable and sustainable alternatives to processes performed at high temperature and/or pressure are focused. How some of these new approaches are also considered to thermoelectric materials fabrication can influence the properties and performance of the nanomaterials so-produced and the prospects of developing such techniques further.
Waste Management & Research: The Journal for a Sustainable Circular Economy, 2022
This article describes the catalytic cracking of low-density polyethylene over attapulgite clay a... more This article describes the catalytic cracking of low-density polyethylene over attapulgite clay and iron substituted tungstophosphate/attapulgite clay (Fe-POM/attapulgite) composite materials to evaluate their suitability and performance for recycling of plastic waste into liquid fuel. The prepared catalysts enhanced the yield of liquid fuel (hydrocarbons) produced in cracking process. A maximum yield of 82% liquid oil fraction with a negligible amount of coke was obtained for 50% Fe-POM/attapulgite composite. Whereas, only 68% liquid oil fractions with a large amount of solid black residue was produced in case of non-catalytic pyrolysis. Moreover, Fe-POM/attapulgite clay composites showed higher selectivity towards lower hydrocarbons (C5–C12) with aliphatic hydrocarbons as major fractions. These synthesised composite catalysts significantly lowered the pyrolysis temperature from 375°C to 310°C. Hence, recovery of valuable fuel oil from polyethylene using these synthesised catalysts...
A Tantalum Pentoxide (Ta2O5) based resistive nonvolatile memory device with bipolar switching beh... more A Tantalum Pentoxide (Ta2O5) based resistive nonvolatile memory device with bipolar switching behaviour was developed to demonstrate the new concept of memory in e-skin. The memory device showed stable switching behavior under preprogrammed voltage stimuli after an initial forming process. The memory cell was then integrated with a commercial tactile sensor with a new interface circuit, which enabled the switching of the memory cell through the electrical output from the sensor. This study provides a novel method for handling the transport and storage of large tactile data and will trigger advances towards memorable e-skin.
A composite MnO2@MOF-5 is prepared by in-situ incorporation of pre-synthesized MnO2 nanoparticles... more A composite MnO2@MOF-5 is prepared by in-situ incorporation of pre-synthesized MnO2 nanoparticles into metal organic framework, MOF-5, during synthesis. The product is characterized by Powder X-Ray diffraction analysis, Raman spectroscopy, Fourier transform infrared spectroscopy, Ultraviolet-Visible spectroscopy, Scanning Electron Microscopy, Energy Dispersive X-ray spectroscopy and elemental mapping, which support the formation of proposed composite materials. The oxygen evolution reaction activity of MnO2@MOF-5 composite is evaluated by cyclic voltammetry, linear sweep voltammetry and Chronoamperometric measurement under visible light. It is found that MnO2@MOF-5/NF has better durability and ability to produce current density of 10 mAcm-2 at only 324 mV overpotential with lower 71 mVdec-1 Tafel slope as compared to some of previously reported Mn-based catalysts for OER. Stability of these electrodes is evaluated by Chronoamperometric studies for 6000 seconds in presence of visible light and they showed constant current density. Furthermore, stability studied by continuous CV sweeps in 1.0 M NaOH at a scan rate of 100 mVs-1 shows that these materials are stable upto 100 cycles, which confirms the stability and durability of the electrodes.
Improvements in the thermoelectric performance of n-type Bi 2 Te 3 materials to more closely matc... more Improvements in the thermoelectric performance of n-type Bi 2 Te 3 materials to more closely match their p-type counterparts are critical to promote the continued development of bismuth telluride thermoelectric devices. Here the unconventional heteroatom dopant, niobium, has been employed as a donor in Bi 2 Te 3. Nb substitutes for Bi in the rhombohedral Bi 2 Te 3 structure, and exhibits multiple roles in its modulation of electrical transport and defect-induced phonon 2 scattering. The carrier concentration is significantly increased as electrons are afforded by aliovalent doping and formation of vacancies on the Te sites. Further, incorporation of Nb in the pseudo-ternary Bi 2-x Nb x Te 3-δ system increases the effective mass, m*, which is consistent with cases of "conventional" elemental doping in Bi 2 Te 3. Lastly, inclusion of Nb induces both point and extended defects (tellurium vacancies and dislocations, respectively), enhancing phonon scattering and reducing the thermal conductivity. As a result, an optimum zT of 0.94 was achieved in n-type Bi 0.92 Nb 0.08 Te 3 at 505 K, which is dramatically higher than an equivalent undoped Bi 2 Te 3 sample. This study suggests that not only is Nb an exciting and novel electron dopant for the Bi 2 Te 3 system, but also that unconventional dopants might be utilized with similar effects in other chalcogenide thermoelectrics.
We report here alumina-substituted Keggin tungstoborate/kaolin clay composite materials (KAB/kaol... more We report here alumina-substituted Keggin tungstoborate/kaolin clay composite materials (KAB/kaolin) as polyethylene cracking catalysts. KAB/kaolin composites with varying concentrations of KAB (10–50 wt.%) were synthesized by the wet impregnation method and successfully characterized by Fourier-transform infrared spectroscopy, powder X-ray diffraction, thermo-gravimetric analysis and scanning electron microscopy with energy dispersive X-ray spectroscopy analytical techniques. Use of KAB loaded kaolin composites as the catalyst for low-density polyethylene (LDPE) cracking exhibited a higher percentage of polymer conversion (99%), producing 84 wt.% of fuel oil and negligible amount (˂ 1 wt.%) of solid residue while thermal cracking produced ~22 wt.% residue. Furthermore, gas chromatography–mass spectrometry analysis of oil obtained by non-catalytic cracking exhibited a high selectivity to high molecular weight hydrocarbons (C13–C23) compared to the catalytic cracking where 70 mol.% o...
P2-Na 2/3 MO 2 materials have recently been investigated as promising high-capacity cathode hosts... more P2-Na 2/3 MO 2 materials have recently been investigated as promising high-capacity cathode hosts for Na-ion batteries. On the other hand, the Na-deficiency in these materials precludes a high energy density when coupled with Na-free anodes. As an alternative, O3-NaFeO 2 and its various derivatives such as NaFe 0.5 Mn 0.5 O 2 have been suggested and investigated. In this study, we dope Al in NaFe 0.5 Mn 0.5 O 2 and investigate Al-doping effects on the electrochemical properties of the Na + host. The Al-doped compound shows almost the same conductivity and diffusivity as the pristine structure. However, Al-doping enhances O3-P3 phase transition.
Although major difficulties are experienced for hydrogen- storage materials to meet performance r... more Although major difficulties are experienced for hydrogen- storage materials to meet performance requirements for mobile applications, alternative fuel cell feedstocks such as ammonia can be stored in the solid state safely at high capacity. We herein describe the NiX2 -NH3 (X=Cl, Br, I) systems and demonstrate their exceptional suitability for NH3 storage (up to 43 wt % NH3 with desorption that begins at 400 K). The structural effects that result from the uptake of NH3 were studied by powder X-ray diffraction (PXD), FTIR spectroscopy and SEM. NH3 release at elevated temperatures was followed by in situ PXD. The cycling capabilities and air stability of the systems were also explored. NH3 is released from the hexaammines in a three-step process to yield the diammine, monoammine and NiX2 dihalides respectively and (re)ammoniation occurs readily at room temperature. The hexaammines do not react with air after several hours of exposure.
The crossed compound parabolic concentrator (CCPC) is one of the most efficient non-imaging solar... more The crossed compound parabolic concentrator (CCPC) is one of the most efficient non-imaging solar concentrators used as a stationary solar concentrator or as a second stage solar concentrator. In this study, the CCPC is modified to demonstrate for the first time a new generation of solar concentrators working simultaneously as an electricity generator and thermal collector. The CCPC is designed to have two complementary surfaces, one reflective and one absorptive, and is named as an absorptive/reflective CCPC (AR-CCPC). Usually, the height of the CCPC is truncated with a minor sacrifice of the geometric concentration. These truncated surfaces rather than being eliminated are instead replaced with absorbent surfaces to collect heat from solar radiation. The optical efficiency including absorptive/reflective part of the AR-CCPC was simulated and compared for different geometric concentration ratios varying from 3.6Â to 4Â. It was found that the combined optical efficiency of the AR-CCPC 3.6Â/4Â remained constant and high all day long and that it had the highest total optical efficiency compared to other concentrators. In addition, the temperature distributions of AR-CCPC surfaces and the assembled solar cell were simulated based on those heat flux boundary conditions. It was shown that the addition of a thermal absorbent surface can increase the wall temperature. The maximum value reached 321.5 K at the front wall under 50°incidence. The experimental verification was also adopted to show the benefits of using absorbent surfaces. The initial results are very promising and significant for the enhancement of solar concentrator systems with lower concentrations.
Transient multiphysics simulations are performed to investigate the thermal and electric performa... more Transient multiphysics simulations are performed to investigate the thermal and electric performance of a thermoelectric generator (TEG) module placed between hot and cold blocks. Effects of heat radiation, thermal and electric contact on the TEG are examined and the simulated results are compared with experimental data. The predicted temperature difference across the TEG module and the electric voltage and power are in very good agreement with the experimental data. The radiation effect on the thermal and electric performance is negligible and the temperature at the interface of the TEG module substrates is predicted to be non-uniform. The peak temperatures are found in the both ends of the legs, and the maximum Joule heat is generated at the leg ends connected with the hot substrate.
Physica C: Superconductivity and its Applications, 1989
The effects of varying oxygen content on the superconducting transition temperature T , resistivi... more The effects of varying oxygen content on the superconducting transition temperature T , resistivity, and crystal structure of HoBa 2Cu 0 (0 < x < 1 have been investigated. The variation of T 2 w~th-is very similar to that previously reported by several authors for YBa Cu 3 0 7 ax [1,2]. In particular a plateau in the T vs x curve is observe for values of x between 0.3 and 0.4 witR the value of T ,(10 % onset measured magnetically) remaining relatively constaný at about 55 K. The width of the superconducting transition , as measured both resistively and magnetically, is substantially narrower for x= 0.35 + 0.05 than for slightly larger or smaller values of x. High resolution powder x-ray diffraction analysis was used to measure the lattice constants of both the orthorhombic and tetragonal phases as x was varied. With increasing x the temperature coefficient of the resistivity changed from positive (metallic) for x < 0.2 to negative (semiconducting) for x > 0.3. Since the general shape of the T vs x curve was unaffected by the complete substitution of cmagnetic Ho for Y, these results suggest an ordering of the oxygen vacancies in the a-b plane and the existence of an ordered compound with a Tc of 55 K.
Synthesis of Cesium & potassium salts of aluminum substituted Keggin tungstoborate • Catalytic cr... more Synthesis of Cesium & potassium salts of aluminum substituted Keggin tungstoborate • Catalytic cracking of polyethylene produced 80wt.-% liquid hydrocarbons • Liquid oil showed very high selectivity to gasoline range hydrocarbons • Al-substituted tungstoborates are excellent catalyst for acid catalyzed reactions *Highlights (for review)
Nitrogen has been demonstrated to be effective for the regeneration of Co3Mo3N from Co6Mo6N, albe... more Nitrogen has been demonstrated to be effective for the regeneration of Co3Mo3N from Co6Mo6N, albeit at higher temperature and longer duration than, when employing H2/N2. In some instances, incomplete regeneration yielding a mixture of the two line phases is observed, which has been interpreted on the possible basis of a crystallite size distribution. Temperature programmed reduction of Co3Mo3N, prepared so as to eliminate the possible contribution of NHx groups, demonstrates the significant production of ammonia although in much lower quantities than NHx–containing Co3Mo3N samples.Graphical Abstract
The 14 N/ 15 N isotopic exchange pathways over Co 3 Mo 3 N, a material of interest as an ammonia ... more The 14 N/ 15 N isotopic exchange pathways over Co 3 Mo 3 N, a material of interest as an ammonia synthesis catalyst and for the development of nitrogen transfer reactions, have been investigated. Both the homomolecular and heterolytic exchange processes have been studied, and it has been shown that lattice nitrogen species are exchangeable. The exchange behavior was found to be a strong function of pretreatment with ca. 25% of lattice N atoms being exchanged after 40 min at 600°C after N 2 pretreatment at 700°C compared to only 6% following similar Ar pretreatment. This observation, for which the potential contribution of adsorbed N species can be discounted, is significant in terms of the application of this material. In the case of the Co 6 Mo 6 N phase, regeneration to Co 3 Mo 3 N under 15 N 2 at 600°C occurs concurrently with 14 N 15 N formation. These observations demonstrate the reactivity of nitrogen in the Co−Mo−N system to be a strong function of pretreatment and worthy of further consideration.
The crystal chemistry and electronic structure of the layered nitride SrTiN 2 have been studied b... more The crystal chemistry and electronic structure of the layered nitride SrTiN 2 have been studied by powder neutron diffraction (PND) and density functional methods, respectively. PND investigations at room temperature, 80 K, and 2 K show that the tetragonal KCoO 2 structure (space group P4/nmm (No. 129), a) 3.8823(1) Å, c) 7.7008(1) Å, V) 116.068(1) Å 3 , Z) 2 at 298 K) is retained across the temperature range and confirm the structural model from previous room-temperature powder X-ray diffraction (PXD) studies. Furthermore, and importantly, PND data demonstrate that neither nitrogen nonstoichiometry nor substitution of O 2for N 3within the anion sublattice is a plausible mechanism for hole generation. Density functional calculations show that strong covalent bonding occurs within the TiN 2 layers and that Sr-N interactions are pivotal in determining the band structure at the Fermi level. Calculations predict metallic and paramagnetic behavior for SrTiN 2. These findings are confirmed by experimental measurements.
The pillars of Green Chemistry necessitate the development of new chemical methodologies and proc... more The pillars of Green Chemistry necessitate the development of new chemical methodologies and processes that can benefit chemical synthesis in terms of energy efficiency, conservation of resources, product selectivity, operational simplicity and, crucially, health, safety, and environmental impact. Implementation of green principles whenever possible can spur the growth of benign scientific technologies by considering environmental, economical, and societal sustainability in parallel. These principles seem especially important in the context of the manufacture of materials for sustainable energy and environmental applications. In this review, the production of energy conversion materials is taken as an exemplar, by examining the recent growth in the energy-efficient synthesis of thermoelectric nanomaterials for use in devices for thermal energy harvesting. Specifically, "soft chemistry" techniques such as solution-based, solvothermal, microwave-assisted, and mechanochemical (ball-milling) methods as viable and sustainable alternatives to processes performed at high temperature and/or pressure are focused. How some of these new approaches are also considered to thermoelectric materials fabrication can influence the properties and performance of the nanomaterials so-produced and the prospects of developing such techniques further.
Waste Management & Research: The Journal for a Sustainable Circular Economy, 2022
This article describes the catalytic cracking of low-density polyethylene over attapulgite clay a... more This article describes the catalytic cracking of low-density polyethylene over attapulgite clay and iron substituted tungstophosphate/attapulgite clay (Fe-POM/attapulgite) composite materials to evaluate their suitability and performance for recycling of plastic waste into liquid fuel. The prepared catalysts enhanced the yield of liquid fuel (hydrocarbons) produced in cracking process. A maximum yield of 82% liquid oil fraction with a negligible amount of coke was obtained for 50% Fe-POM/attapulgite composite. Whereas, only 68% liquid oil fractions with a large amount of solid black residue was produced in case of non-catalytic pyrolysis. Moreover, Fe-POM/attapulgite clay composites showed higher selectivity towards lower hydrocarbons (C5–C12) with aliphatic hydrocarbons as major fractions. These synthesised composite catalysts significantly lowered the pyrolysis temperature from 375°C to 310°C. Hence, recovery of valuable fuel oil from polyethylene using these synthesised catalysts...
A Tantalum Pentoxide (Ta2O5) based resistive nonvolatile memory device with bipolar switching beh... more A Tantalum Pentoxide (Ta2O5) based resistive nonvolatile memory device with bipolar switching behaviour was developed to demonstrate the new concept of memory in e-skin. The memory device showed stable switching behavior under preprogrammed voltage stimuli after an initial forming process. The memory cell was then integrated with a commercial tactile sensor with a new interface circuit, which enabled the switching of the memory cell through the electrical output from the sensor. This study provides a novel method for handling the transport and storage of large tactile data and will trigger advances towards memorable e-skin.
A composite MnO2@MOF-5 is prepared by in-situ incorporation of pre-synthesized MnO2 nanoparticles... more A composite MnO2@MOF-5 is prepared by in-situ incorporation of pre-synthesized MnO2 nanoparticles into metal organic framework, MOF-5, during synthesis. The product is characterized by Powder X-Ray diffraction analysis, Raman spectroscopy, Fourier transform infrared spectroscopy, Ultraviolet-Visible spectroscopy, Scanning Electron Microscopy, Energy Dispersive X-ray spectroscopy and elemental mapping, which support the formation of proposed composite materials. The oxygen evolution reaction activity of MnO2@MOF-5 composite is evaluated by cyclic voltammetry, linear sweep voltammetry and Chronoamperometric measurement under visible light. It is found that MnO2@MOF-5/NF has better durability and ability to produce current density of 10 mAcm-2 at only 324 mV overpotential with lower 71 mVdec-1 Tafel slope as compared to some of previously reported Mn-based catalysts for OER. Stability of these electrodes is evaluated by Chronoamperometric studies for 6000 seconds in presence of visible light and they showed constant current density. Furthermore, stability studied by continuous CV sweeps in 1.0 M NaOH at a scan rate of 100 mVs-1 shows that these materials are stable upto 100 cycles, which confirms the stability and durability of the electrodes.
Improvements in the thermoelectric performance of n-type Bi 2 Te 3 materials to more closely matc... more Improvements in the thermoelectric performance of n-type Bi 2 Te 3 materials to more closely match their p-type counterparts are critical to promote the continued development of bismuth telluride thermoelectric devices. Here the unconventional heteroatom dopant, niobium, has been employed as a donor in Bi 2 Te 3. Nb substitutes for Bi in the rhombohedral Bi 2 Te 3 structure, and exhibits multiple roles in its modulation of electrical transport and defect-induced phonon 2 scattering. The carrier concentration is significantly increased as electrons are afforded by aliovalent doping and formation of vacancies on the Te sites. Further, incorporation of Nb in the pseudo-ternary Bi 2-x Nb x Te 3-δ system increases the effective mass, m*, which is consistent with cases of "conventional" elemental doping in Bi 2 Te 3. Lastly, inclusion of Nb induces both point and extended defects (tellurium vacancies and dislocations, respectively), enhancing phonon scattering and reducing the thermal conductivity. As a result, an optimum zT of 0.94 was achieved in n-type Bi 0.92 Nb 0.08 Te 3 at 505 K, which is dramatically higher than an equivalent undoped Bi 2 Te 3 sample. This study suggests that not only is Nb an exciting and novel electron dopant for the Bi 2 Te 3 system, but also that unconventional dopants might be utilized with similar effects in other chalcogenide thermoelectrics.
We report here alumina-substituted Keggin tungstoborate/kaolin clay composite materials (KAB/kaol... more We report here alumina-substituted Keggin tungstoborate/kaolin clay composite materials (KAB/kaolin) as polyethylene cracking catalysts. KAB/kaolin composites with varying concentrations of KAB (10–50 wt.%) were synthesized by the wet impregnation method and successfully characterized by Fourier-transform infrared spectroscopy, powder X-ray diffraction, thermo-gravimetric analysis and scanning electron microscopy with energy dispersive X-ray spectroscopy analytical techniques. Use of KAB loaded kaolin composites as the catalyst for low-density polyethylene (LDPE) cracking exhibited a higher percentage of polymer conversion (99%), producing 84 wt.% of fuel oil and negligible amount (˂ 1 wt.%) of solid residue while thermal cracking produced ~22 wt.% residue. Furthermore, gas chromatography–mass spectrometry analysis of oil obtained by non-catalytic cracking exhibited a high selectivity to high molecular weight hydrocarbons (C13–C23) compared to the catalytic cracking where 70 mol.% o...
P2-Na 2/3 MO 2 materials have recently been investigated as promising high-capacity cathode hosts... more P2-Na 2/3 MO 2 materials have recently been investigated as promising high-capacity cathode hosts for Na-ion batteries. On the other hand, the Na-deficiency in these materials precludes a high energy density when coupled with Na-free anodes. As an alternative, O3-NaFeO 2 and its various derivatives such as NaFe 0.5 Mn 0.5 O 2 have been suggested and investigated. In this study, we dope Al in NaFe 0.5 Mn 0.5 O 2 and investigate Al-doping effects on the electrochemical properties of the Na + host. The Al-doped compound shows almost the same conductivity and diffusivity as the pristine structure. However, Al-doping enhances O3-P3 phase transition.
Although major difficulties are experienced for hydrogen- storage materials to meet performance r... more Although major difficulties are experienced for hydrogen- storage materials to meet performance requirements for mobile applications, alternative fuel cell feedstocks such as ammonia can be stored in the solid state safely at high capacity. We herein describe the NiX2 -NH3 (X=Cl, Br, I) systems and demonstrate their exceptional suitability for NH3 storage (up to 43 wt % NH3 with desorption that begins at 400 K). The structural effects that result from the uptake of NH3 were studied by powder X-ray diffraction (PXD), FTIR spectroscopy and SEM. NH3 release at elevated temperatures was followed by in situ PXD. The cycling capabilities and air stability of the systems were also explored. NH3 is released from the hexaammines in a three-step process to yield the diammine, monoammine and NiX2 dihalides respectively and (re)ammoniation occurs readily at room temperature. The hexaammines do not react with air after several hours of exposure.
The crossed compound parabolic concentrator (CCPC) is one of the most efficient non-imaging solar... more The crossed compound parabolic concentrator (CCPC) is one of the most efficient non-imaging solar concentrators used as a stationary solar concentrator or as a second stage solar concentrator. In this study, the CCPC is modified to demonstrate for the first time a new generation of solar concentrators working simultaneously as an electricity generator and thermal collector. The CCPC is designed to have two complementary surfaces, one reflective and one absorptive, and is named as an absorptive/reflective CCPC (AR-CCPC). Usually, the height of the CCPC is truncated with a minor sacrifice of the geometric concentration. These truncated surfaces rather than being eliminated are instead replaced with absorbent surfaces to collect heat from solar radiation. The optical efficiency including absorptive/reflective part of the AR-CCPC was simulated and compared for different geometric concentration ratios varying from 3.6Â to 4Â. It was found that the combined optical efficiency of the AR-CCPC 3.6Â/4Â remained constant and high all day long and that it had the highest total optical efficiency compared to other concentrators. In addition, the temperature distributions of AR-CCPC surfaces and the assembled solar cell were simulated based on those heat flux boundary conditions. It was shown that the addition of a thermal absorbent surface can increase the wall temperature. The maximum value reached 321.5 K at the front wall under 50°incidence. The experimental verification was also adopted to show the benefits of using absorbent surfaces. The initial results are very promising and significant for the enhancement of solar concentrator systems with lower concentrations.
Transient multiphysics simulations are performed to investigate the thermal and electric performa... more Transient multiphysics simulations are performed to investigate the thermal and electric performance of a thermoelectric generator (TEG) module placed between hot and cold blocks. Effects of heat radiation, thermal and electric contact on the TEG are examined and the simulated results are compared with experimental data. The predicted temperature difference across the TEG module and the electric voltage and power are in very good agreement with the experimental data. The radiation effect on the thermal and electric performance is negligible and the temperature at the interface of the TEG module substrates is predicted to be non-uniform. The peak temperatures are found in the both ends of the legs, and the maximum Joule heat is generated at the leg ends connected with the hot substrate.
Physica C: Superconductivity and its Applications, 1989
The effects of varying oxygen content on the superconducting transition temperature T , resistivi... more The effects of varying oxygen content on the superconducting transition temperature T , resistivity, and crystal structure of HoBa 2Cu 0 (0 < x < 1 have been investigated. The variation of T 2 w~th-is very similar to that previously reported by several authors for YBa Cu 3 0 7 ax [1,2]. In particular a plateau in the T vs x curve is observe for values of x between 0.3 and 0.4 witR the value of T ,(10 % onset measured magnetically) remaining relatively constaný at about 55 K. The width of the superconducting transition , as measured both resistively and magnetically, is substantially narrower for x= 0.35 + 0.05 than for slightly larger or smaller values of x. High resolution powder x-ray diffraction analysis was used to measure the lattice constants of both the orthorhombic and tetragonal phases as x was varied. With increasing x the temperature coefficient of the resistivity changed from positive (metallic) for x < 0.2 to negative (semiconducting) for x > 0.3. Since the general shape of the T vs x curve was unaffected by the complete substitution of cmagnetic Ho for Y, these results suggest an ordering of the oxygen vacancies in the a-b plane and the existence of an ordered compound with a Tc of 55 K.
Synthesis of Cesium & potassium salts of aluminum substituted Keggin tungstoborate • Catalytic cr... more Synthesis of Cesium & potassium salts of aluminum substituted Keggin tungstoborate • Catalytic cracking of polyethylene produced 80wt.-% liquid hydrocarbons • Liquid oil showed very high selectivity to gasoline range hydrocarbons • Al-substituted tungstoborates are excellent catalyst for acid catalyzed reactions *Highlights (for review)
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