The Experts below are selected from a list of 39 Experts worldwide ranked by ideXlab platform
Haijiang Wang - One of the best experts on this subject based on the ideXlab platform.
-
Accelerated Conditioning for a proton exchange membrane fuel cell
Journal of Power Sources, 2012Co-Authors: Xiaozi Yuan, Haijiang Wang, Hui LiAbstract:Abstract A Conditioning process is usually needed for a newly fabricated proton exchange membrane (PEM) fuel cell to be activated. Depending on the membrane electrode assemblies, this process can take hours and even days to complete. To provide for Accelerated Conditioning techniques that can complete the process in a short time, this paper compares various reported methods to condition a PEM single cell. The major objectives are to identify Accelerated Conditioning approaches that can significantly reduce the Conditioning duration for the existing Conditioning regime in an operationally easy manner, and to understand the fundamental principles that govern Accelerated Conditioning. Various effects investigated include temperature, cycling steps, and cycling frequencies. Other techniques, such as short circuiting, hydrogen pumping, and hot water circulation, are also discussed. For each technique, measurements are taken using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV).
-
a review of Accelerated Conditioning for a polymer electrolyte membrane fuel cell
Journal of Power Sources, 2011Co-Authors: Xiaozi Yuan, Shengsheng Zhang, Haijiang WangAbstract:Abstract A newly fabricated polymer electrolyte membrane (PEM) fuel cell usually needs a so-called break-in/Conditioning/incubation period to activate it and reach its best performance. Typically, during this activation period the cell performance increases gradually, and then reaches a plateau without further increase. Depending on the membrane electrode assemblies, this process can take hours and even days to complete, which consumes a considerable amount of hydrogen fuel, leading to a higher operating cost. To provide for Accelerated Conditioning techniques that can complete the process in a short time period, this paper reviews established Conditioning protocols and reported methods to condition PEM single cells and stacks, in an attempt to summarize available information on PEM fuel cell Conditioning and the underlying mechanisms. Various techniques are arranged into two categories: on-line Conditioning and off-line Conditioning. For each technique, the experimental procedure and outcomes are outlined. Finally, weaknesses of the currently used Conditioning techniques are indicated and further research efforts are proposed.
Xiaozi Yuan - One of the best experts on this subject based on the ideXlab platform.
-
Accelerated Conditioning for a proton exchange membrane fuel cell
Journal of Power Sources, 2012Co-Authors: Xiaozi Yuan, Haijiang Wang, Hui LiAbstract:Abstract A Conditioning process is usually needed for a newly fabricated proton exchange membrane (PEM) fuel cell to be activated. Depending on the membrane electrode assemblies, this process can take hours and even days to complete. To provide for Accelerated Conditioning techniques that can complete the process in a short time, this paper compares various reported methods to condition a PEM single cell. The major objectives are to identify Accelerated Conditioning approaches that can significantly reduce the Conditioning duration for the existing Conditioning regime in an operationally easy manner, and to understand the fundamental principles that govern Accelerated Conditioning. Various effects investigated include temperature, cycling steps, and cycling frequencies. Other techniques, such as short circuiting, hydrogen pumping, and hot water circulation, are also discussed. For each technique, measurements are taken using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV).
-
a review of Accelerated Conditioning for a polymer electrolyte membrane fuel cell
Journal of Power Sources, 2011Co-Authors: Xiaozi Yuan, Shengsheng Zhang, Haijiang WangAbstract:Abstract A newly fabricated polymer electrolyte membrane (PEM) fuel cell usually needs a so-called break-in/Conditioning/incubation period to activate it and reach its best performance. Typically, during this activation period the cell performance increases gradually, and then reaches a plateau without further increase. Depending on the membrane electrode assemblies, this process can take hours and even days to complete, which consumes a considerable amount of hydrogen fuel, leading to a higher operating cost. To provide for Accelerated Conditioning techniques that can complete the process in a short time period, this paper reviews established Conditioning protocols and reported methods to condition PEM single cells and stacks, in an attempt to summarize available information on PEM fuel cell Conditioning and the underlying mechanisms. Various techniques are arranged into two categories: on-line Conditioning and off-line Conditioning. For each technique, the experimental procedure and outcomes are outlined. Finally, weaknesses of the currently used Conditioning techniques are indicated and further research efforts are proposed.
Hui Li - One of the best experts on this subject based on the ideXlab platform.
-
Accelerated Conditioning for a proton exchange membrane fuel cell
Journal of Power Sources, 2012Co-Authors: Xiaozi Yuan, Haijiang Wang, Hui LiAbstract:Abstract A Conditioning process is usually needed for a newly fabricated proton exchange membrane (PEM) fuel cell to be activated. Depending on the membrane electrode assemblies, this process can take hours and even days to complete. To provide for Accelerated Conditioning techniques that can complete the process in a short time, this paper compares various reported methods to condition a PEM single cell. The major objectives are to identify Accelerated Conditioning approaches that can significantly reduce the Conditioning duration for the existing Conditioning regime in an operationally easy manner, and to understand the fundamental principles that govern Accelerated Conditioning. Various effects investigated include temperature, cycling steps, and cycling frequencies. Other techniques, such as short circuiting, hydrogen pumping, and hot water circulation, are also discussed. For each technique, measurements are taken using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV).
Jovan Tatar - One of the best experts on this subject based on the ideXlab platform.
-
Hygrothermal Conditioning of wet-layup CFRP-concrete adhesive joints modified with silane coupling agent and core-shell rubber nanoparticles
Construction and Building Materials, 2019Co-Authors: Syed Ahnaf Morshed, Arkabrata Sinha, Qian Zhang, Jovan TatarAbstract:Abstract The adhesive bond between externally bonded fiber-reinforced polymer (FRP) repairs and the concrete substrate can significantly deteriorate under hygrothermal conditions. The present study evaluated the epoxy adhesive toughening with core–shell rubber (CSR) nanoparticles and concrete surface functionalization with an epoxy-functional silane coupling agent as a means of improving the bond durability under hygrothermal exposure. To determine the effect of environmental degradation, beam bond test specimens were subjected to control conditions (standard laboratory conditions: 23 ± 2 °C and RH 50 ± 10%) and a hygrothermal Accelerated Conditioning protocol (ACP) (water immersion at 45 ± 1 °C) for 8 weeks. Bond test results indicate that CSR toughening and silane coupling agent can improve FRP-concrete adhesive bond strength retention following Accelerated Conditioning by up to 15% over that of neat epoxy. Following Accelerated Conditioning, CFRP coupons prepared with CSR-modified epoxy retain their mechanical properties, while the CFRP prepared with the neat epoxy exhibited a significant reduction in strength (40%) and elongation (54%). CSR nanoparticles demonstrated good compatibility with the base epoxy resin, as evidenced by differential scanning calorimetry (DSC) glass transition temperature measurements.
-
Durability of wet lay-up FRP bonded to concrete with nanomodified epoxy adhesives
Journal of Adhesion, 2018Co-Authors: Syed Ahnaf Morshed, Qian Zhang, Tyler J. Young, William M. Chirdon, Jovan TatarAbstract:ABSTRACTExternally bonded fiber-reinforced polymer (FRP) composites represent a simple and economical solution for repairing and strengthening concrete structures. However, the potential for debonding failure in such strengthening systems becomes prominent when FRP-concrete bonds undergo environmental degradation induced by moisture. Low-viscosity Bisphenol A diglycidyl ether (DGEBA)-based epoxy adhesives are most commonly utilized in the engineering practice to bond wet-layup FRP to the concrete surface. This study evaluated the effects of the addition of commercial surface-modified nanosilica (SMNS), core-shell rubber (CSR) nanoparticles, and multi-walled carbon nanotubes (MWCNT) to neat epoxy on the mechanical properties of the adhesive, and strength and durability of FRP-concrete adhesively bonded joints. To determine the effects of environmental degradation, all specimens were subjected to the following environments: control – 23°C at RH 50 ± 10% for 18 weeks; and Accelerated Conditioning protocol (A...
-
Comparison of laboratory and field environmental Conditioning on FRP-concrete bond durability
Construction and Building Materials, 2016Co-Authors: Jovan Tatar, H. R. HamiltonAbstract:Abstract Assessment of bonded FRP durability by means of Accelerated Conditioning is sometimes thought to be too harsh compared to ambient environmental conditions; consequently, this may result in underestimate of the actual durability. To assess the efficacy of utilizing Accelerated Conditioning protocols (ACP) for FRP-concrete bond durability testing, results from laboratory and field conditions (Sunshine Skyway Bridge in Tampa, FL) were compared. Direct tension pull-off test patches were applied to the approach span girders and notched beam three-point bending test specimens were placed on the dolphins adjacent to the bridge. These results were compared to notched beam specimens exposed to ACP. Testing indicated that characteristics of the FRP-concrete bond failure modes changed in some of the field samples within 6 months of field exposure, which may be an indication of durability problems. Moreover, ACP under elevated temperatures (60 °C) of notched three-point bending test resulted in a 36% loss of strength compared to no strength degradation after 18 months of field Conditioning.
-
Bond Durability Factor for Externally Bonded CFRP Systems in Concrete Structures
Journal of Composites for Construction, 2016Co-Authors: Jovan Tatar, H. R. HamiltonAbstract:Lack of understanding and confidence in the long-term performance of externally bonded fiber-reinforced polymer (FRP) composites in concrete structures still inhibits their application in repair of aged structures. While synergistic effects of multiple exposure conditions can be severe, it is generally agreed that the single most significant issue with externally bonded FRP composites is their susceptibility to degradation when exposed to moisture. This research utilized small-beam three-point bending test specimens to study FRP-concrete bond performance when subjected to Accelerated Conditioning environments (immersion in water and exposure to high humidity at elevated temperatures). Bond strength retention (Rb) was determined by dividing the conditioned strength by the average control strength. Test results from the present research were combined with other test data to form a database of over 700 test results. By utilizing an apparent analogy of FRP-concrete bonded systems to adhesive anchors, a bond durability factor (BDF) that quantifies loss in bond capacity due to Accelerated Conditioning is determined equivalently as a characteristic test value for adhesive anchors. Given their resistance to the environment, only carbon-fiber-reinforced polymer (CFRP) composites were examined. For the purpose of the analyses, and based on available data, it was determined that all CFRP systems may be split into three categories: wet-layup without putty, wet-layup with putty, and precured laminate. BDF corresponding to wet-layup without putty was determined to be 0.60. BDF for wet-layup with putty was not established due to the observed sensitivity to increasing Conditioning temperature. CFRP laminate specimens failed prematurely by composite rupture or at the adhesive-composite interface; BDF was not determined as long term durability data corresponding to FRP-concrete bond failure mode was not available.
-
Effects of hygrothermal Conditioning on epoxy adhesives used in FRP composites
Construction and Building Materials, 2015Co-Authors: B. Paige Blackburn, Jovan Tatar, Elliot P. Douglas, H. R. HamiltonAbstract:Durability of FRP composites and their bond to concrete is essential to structural integrity of an FRP repair. Epoxy adhesives are used to form FRP composites, and as a bonding medium between the FRP and concrete substrate. Susceptibility of epoxy to the negative effects of water and high temperature affects the longevity of FRP repairs in hygrothermal environmental conditions. The presented work investigates the effects of such environments on the curing kinetics of epoxy. Competing effects of plasticization and post-cure during Accelerated Conditioning are discussed; recommendations targeting researchers, practitioners, and manufacturers are made based on the research findings.
H. R. Hamilton - One of the best experts on this subject based on the ideXlab platform.
-
Comparison of laboratory and field environmental Conditioning on FRP-concrete bond durability
Construction and Building Materials, 2016Co-Authors: Jovan Tatar, H. R. HamiltonAbstract:Abstract Assessment of bonded FRP durability by means of Accelerated Conditioning is sometimes thought to be too harsh compared to ambient environmental conditions; consequently, this may result in underestimate of the actual durability. To assess the efficacy of utilizing Accelerated Conditioning protocols (ACP) for FRP-concrete bond durability testing, results from laboratory and field conditions (Sunshine Skyway Bridge in Tampa, FL) were compared. Direct tension pull-off test patches were applied to the approach span girders and notched beam three-point bending test specimens were placed on the dolphins adjacent to the bridge. These results were compared to notched beam specimens exposed to ACP. Testing indicated that characteristics of the FRP-concrete bond failure modes changed in some of the field samples within 6 months of field exposure, which may be an indication of durability problems. Moreover, ACP under elevated temperatures (60 °C) of notched three-point bending test resulted in a 36% loss of strength compared to no strength degradation after 18 months of field Conditioning.
-
Bond Durability Factor for Externally Bonded CFRP Systems in Concrete Structures
Journal of Composites for Construction, 2016Co-Authors: Jovan Tatar, H. R. HamiltonAbstract:Lack of understanding and confidence in the long-term performance of externally bonded fiber-reinforced polymer (FRP) composites in concrete structures still inhibits their application in repair of aged structures. While synergistic effects of multiple exposure conditions can be severe, it is generally agreed that the single most significant issue with externally bonded FRP composites is their susceptibility to degradation when exposed to moisture. This research utilized small-beam three-point bending test specimens to study FRP-concrete bond performance when subjected to Accelerated Conditioning environments (immersion in water and exposure to high humidity at elevated temperatures). Bond strength retention (Rb) was determined by dividing the conditioned strength by the average control strength. Test results from the present research were combined with other test data to form a database of over 700 test results. By utilizing an apparent analogy of FRP-concrete bonded systems to adhesive anchors, a bond durability factor (BDF) that quantifies loss in bond capacity due to Accelerated Conditioning is determined equivalently as a characteristic test value for adhesive anchors. Given their resistance to the environment, only carbon-fiber-reinforced polymer (CFRP) composites were examined. For the purpose of the analyses, and based on available data, it was determined that all CFRP systems may be split into three categories: wet-layup without putty, wet-layup with putty, and precured laminate. BDF corresponding to wet-layup without putty was determined to be 0.60. BDF for wet-layup with putty was not established due to the observed sensitivity to increasing Conditioning temperature. CFRP laminate specimens failed prematurely by composite rupture or at the adhesive-composite interface; BDF was not determined as long term durability data corresponding to FRP-concrete bond failure mode was not available.
-
Effects of hygrothermal Conditioning on epoxy adhesives used in FRP composites
Construction and Building Materials, 2015Co-Authors: B. Paige Blackburn, Jovan Tatar, Elliot P. Douglas, H. R. HamiltonAbstract:Durability of FRP composites and their bond to concrete is essential to structural integrity of an FRP repair. Epoxy adhesives are used to form FRP composites, and as a bonding medium between the FRP and concrete substrate. Susceptibility of epoxy to the negative effects of water and high temperature affects the longevity of FRP repairs in hygrothermal environmental conditions. The presented work investigates the effects of such environments on the curing kinetics of epoxy. Competing effects of plasticization and post-cure during Accelerated Conditioning are discussed; recommendations targeting researchers, practitioners, and manufacturers are made based on the research findings.
