The Experts below are selected from a list of 2526 Experts worldwide ranked by ideXlab platform
Anna P Goldstein - One of the best experts on this subject based on the ideXlab platform.
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correction nanoscale structure and superhydrophobicity of sp 2 Bonded Boron nitride aerogels
Nanoscale, 2016Co-Authors: Thang Pham, Anna P Goldstein, James P Lewicki, S O Kucheyev, Cheng Wang, Thomas P Russell, Marcus A Worsley, Leta WooAbstract:Correction for ‘Nanoscale structure and superhydrophobicity of sp2-Bonded Boron nitride aerogels’ by Thang Pham et al., Nanoscale, 2015, 7, 10449–10458.
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nanoscale structure and superhydrophobicity of sp 2 Bonded Boron nitride aerogels
Nanoscale, 2015Co-Authors: Thang Pham, Anna P Goldstein, James P Lewicki, S O Kucheyev, Cheng Wang, Thomas P Russell, Marcus A Worsley, Leta WooAbstract:Aerogels have much potential in both research and industrial applications due to their high surface area, low density, and fine pore size distribution. Here we report a thorough structural study of three-dimensional aerogels composed of highly crystalline sp2-Bonded Boron nitride (BN) layers synthesized by a carbothermic reduction process. The structure, crystallinity and bonding of the as-prepared BN aerogels are elucidated by X-ray diffraction, 11B nuclear magnetic resonance, transmission electron microscopy, and resonant soft X-ray scattering. The macroscopic roughness of the aerogel's surface causes it to be superhydrophobic with a contact angle of ∼155° and exhibit high oil uptake capacity (up to 1500 wt%). The oil can be removed from the BN aerogel by oxidizing in air without damaging the crystalline porous structure of the aerogel or diminishing its oil absorption capacity.
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synthesis of highly crystalline sp2 Bonded Boron nitride aerogels
ACS Nano, 2013Co-Authors: Michael Rousseas, Anna P Goldstein, Marcus A Worsley, Leta Woo, William Mickelson, Alex ZettlAbstract:sp2-Bonded Boron nitride aerogels are synthesized from graphene aerogels via carbothermal reduction of Boron oxide and simultaneous nitridation. The color and chemical composition of the original gel change dramatically, while structural features down to the nanometer scale are maintained, suggesting a direct conversion of the carbon lattice to Boron nitride. Scanning and transmission electron microscopies reveal a foliated architecture of wrinkled sheets, a unique morphology among low-density, porous BN materials. The converted gels display a high degree of chemical purity (>95%) and crystalline order and exhibit unique cross-linking structures.
Alex Zettl - One of the best experts on this subject based on the ideXlab platform.
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synthesis of highly crystalline sp2 Bonded Boron nitride aerogels
ACS Nano, 2013Co-Authors: Michael Rousseas, Anna P Goldstein, Marcus A Worsley, Leta Woo, William Mickelson, Alex ZettlAbstract:sp2-Bonded Boron nitride aerogels are synthesized from graphene aerogels via carbothermal reduction of Boron oxide and simultaneous nitridation. The color and chemical composition of the original gel change dramatically, while structural features down to the nanometer scale are maintained, suggesting a direct conversion of the carbon lattice to Boron nitride. Scanning and transmission electron microscopies reveal a foliated architecture of wrinkled sheets, a unique morphology among low-density, porous BN materials. The converted gels display a high degree of chemical purity (>95%) and crystalline order and exhibit unique cross-linking structures.
Prashant Karandikar - One of the best experts on this subject based on the ideXlab platform.
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structural evolution in reaction Bonded silicon carbide and Boron carbide composites rbsbc
Ceramics International, 2018Co-Authors: Tianshi Wang, Yuying Zhang, Prashant KarandikarAbstract:Abstract Reaction-Bonded silicon carbide and Boron carbide composites (RBSBC) are promising for laser mirror, armor and other applications. However, the structural evolution in RBSBC has not been fully understood. From microscopic characterization and thermodynamic analysis, we propose the mechanisms which can successfully explain observed microstructures, e.g., core-rim structure in SiC grains and plate-like SiC inside B 4 C grains, respectively. In addition, we find that the pre-existing SiC particles may hinder the formation of polygonal SiC in Si and lead to more B 4 C dissolution during the fabrication of RBSBC due to its lower B 4 C percentage than that in corresponding reaction-Bonded Boron carbide composites (RBBC). We believe that the results would shed light on potential fabrication optimization of RBSBC.
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raman spectroscopic characterization of the core rim structure in reaction Bonded Boron carbide ceramics
Applied Physics Letters, 2015Co-Authors: Phillip Jannotti, Ghatu Subhash, James Zheng, Virginia Halls, Prashant Karandikar, S Salamone, Michael K AghajanianAbstract:Raman spectroscopy was used to characterize the microstructure of reaction Bonded Boron carbide ceramics. Compositional and structural gradation in the silicon-doped Boron carbide phase (rim), which develops around the parent Boron carbide region (core) due to the reaction between silicon and Boron carbide, was evaluated using changes in Raman peak position and intensity. Peak shifting and intensity variation from the core to the rim region was attributed to changes in the Boron carbide crystal structure based on experimental Raman observations and ab initio calculations reported in literature. The results were consistent with compositional analysis determined by energy dispersive spectroscopy. The Raman analysis revealed the substitution of silicon atoms first into the linear 3-atom chain, and then into icosahedral units of the Boron carbide structure. Thus, micro-Raman spectroscopy provided a non-destructive means of identifying the preferential positions of Si atoms in the Boron carbide lattice.
Nahum Frage - One of the best experts on this subject based on the ideXlab platform.
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low temperature processing of reaction Bonded Boron carbide composites
Advanced Engineering Materials, 2014Co-Authors: Nahum Frage, H Dilman, Shmuel Hayun, M P DarielAbstract:The present paper is concerned with the fabrication of fully dense B4C-Mg, B4C-AZ91 alloy, and B4C-Mg,Si (eutectic) composites at a significantly lower (750–1000 °C) temperature range. The key feature of the novel approach is based on the Mg-vapor atmosphere, under which the infiltration process is carried out. This approach has also been used to fabricate B4C-Al composites at a low temperature. The microstructure and the mechanical properties of the composites are described and discussed. It was concluded that the formation of the deleterious aluminum carbide (Al4C3) depends on the presence of free carbon in the Boron carbide powders. The suggested approach for low temperature fabrication of reaction Bonded composites under Mg vapor can be further expanded to other boride and carbide phases.
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reaction Bonded Boron carbide magnesium silicon composites
International Journal of Applied Ceramic Technology, 2014Co-Authors: Matan Cafri, Alon Malka, H Dilman, M P Dariel, Nahum FrageAbstract:Reaction-Bonded Boron carbide was manufactured by infiltrating porous Boron carbide preforms at 1273 K with a Mg-Si eutectic alloy. The resulting composite material consists, in addition to the original B4C, of SiC, Mg2Si, and a Mg-rich complex boride/carbide Mgx(Al,Si)y(B,C)z phase. The composites display high hardness (1700 HV), Young's modulus (356 MPa) and a moderate bending strength (230 MPa). The ballistic efficiency (of about 6.7), as determined by the depth of penetration method, is much higher than that of alumina and similar to that of silicon-infiltrated reaction-Bonded composites.
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reaction Bonded Boron carbide recent developments
Advances in Applied Ceramics, 2012Co-Authors: M P Dariel, Nahum FrageAbstract:AbstractReaction Bonded Boron carbide composites are among the hardest ceramics with low specific gravity values, a combination that makes them eminently suitable for light armour applications. The present review covers the main issues involved in the reaction bonding process based on the infiltration of Boron carbide preforms with molten silicon. The importance of achieving high green density values before infiltration is emphasised. Separate sections deal with the morphology of the composite material, the thermodynamics of its microstructure formation, the static mechanical properties and the dynamic mechanical properties at strain rates up to 105 s−1. All along the review, emphasis is placed on describing the effect of free carbon presence in the initial preform on the morphology and properties of the final composite.
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microstructural evolution during the infiltration of Boron carbide with molten silicon
Journal of The European Ceramic Society, 2010Co-Authors: Shmuel Hayun, M P Dariel, Amir Weizmann, Nahum FrageAbstract:Abstract The previously reported model that accounts for the formation of the core-rim structure in reaction-Bonded Boron carbide composites (RBBC) is expanded and validated by additional experimental observations and by a thermodynamic analysis of the ternary B–C–Si system. The microstructure of the RBBC composites consists of Boron carbide particles with a core-rim structure, β-SiC and some residual silicon. The SiC carbide particles have a polygonal shape in composites fabricated in the presence of free carbon, in contrast to the plate-like morphology when the initial Boron carbide is the sole source of carbon. In the course of the infiltration process, the original B4C particles dissolve partly or fully in molten silicon, and a local equilibrium is established between Boron carbide, molten silicon and SiC. Overall equilibrium in the system is achieved as a result of the precipitation of the ternary Boron carbide phase B12(B,C,Si)3 at the surface of the original Boron carbide particles and leads to the formation of the rim regions. This feature is well accounted for by the “stoichiometric saturation” approach, which takes into account the congruent dissolution of B4C particles. The SiC phase, which precipitates form the silicon melt adopts the β-allotropic structure and grows preferably as single plate-like particles with an {1 1 1}β habit plane. The morphology of the SiC particles is determined by the amount of carbon available for their formation.
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the effect of particle size distribution on the microstructure and the mechanical properties of Boron carbide based reaction Bonded composites
International Journal of Applied Ceramic Technology, 2009Co-Authors: Shmuel Hayun, M P Dariel, Amir Weizmann, Nahum FrageAbstract:The presence of unreacted, free silicon lowers the mechanical properties of reaction-Bonded Boron carbide. The fraction of free silicon can be reduced by increasing the green density of the initial Boron carbide performs. The use of multimodal Boron carbide mixtures allows attaining 75% green density. After reaction bonding with molten silicon, the composites consist of four phases, namely the original B 4 C particles, the B 12 (B,C,Si) 3 phase, product of the dissolution―precipitation process, β-SiC, and residual Si. The volume fraction of residual Si in the composites is in the 8―10% range. The infiltrated composites display elevated values of the mechanical properties with a high Weibull modulus.
Leta Woo - One of the best experts on this subject based on the ideXlab platform.
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correction nanoscale structure and superhydrophobicity of sp 2 Bonded Boron nitride aerogels
Nanoscale, 2016Co-Authors: Thang Pham, Anna P Goldstein, James P Lewicki, S O Kucheyev, Cheng Wang, Thomas P Russell, Marcus A Worsley, Leta WooAbstract:Correction for ‘Nanoscale structure and superhydrophobicity of sp2-Bonded Boron nitride aerogels’ by Thang Pham et al., Nanoscale, 2015, 7, 10449–10458.
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nanoscale structure and superhydrophobicity of sp 2 Bonded Boron nitride aerogels
Nanoscale, 2015Co-Authors: Thang Pham, Anna P Goldstein, James P Lewicki, S O Kucheyev, Cheng Wang, Thomas P Russell, Marcus A Worsley, Leta WooAbstract:Aerogels have much potential in both research and industrial applications due to their high surface area, low density, and fine pore size distribution. Here we report a thorough structural study of three-dimensional aerogels composed of highly crystalline sp2-Bonded Boron nitride (BN) layers synthesized by a carbothermic reduction process. The structure, crystallinity and bonding of the as-prepared BN aerogels are elucidated by X-ray diffraction, 11B nuclear magnetic resonance, transmission electron microscopy, and resonant soft X-ray scattering. The macroscopic roughness of the aerogel's surface causes it to be superhydrophobic with a contact angle of ∼155° and exhibit high oil uptake capacity (up to 1500 wt%). The oil can be removed from the BN aerogel by oxidizing in air without damaging the crystalline porous structure of the aerogel or diminishing its oil absorption capacity.
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synthesis of highly crystalline sp2 Bonded Boron nitride aerogels
ACS Nano, 2013Co-Authors: Michael Rousseas, Anna P Goldstein, Marcus A Worsley, Leta Woo, William Mickelson, Alex ZettlAbstract:sp2-Bonded Boron nitride aerogels are synthesized from graphene aerogels via carbothermal reduction of Boron oxide and simultaneous nitridation. The color and chemical composition of the original gel change dramatically, while structural features down to the nanometer scale are maintained, suggesting a direct conversion of the carbon lattice to Boron nitride. Scanning and transmission electron microscopies reveal a foliated architecture of wrinkled sheets, a unique morphology among low-density, porous BN materials. The converted gels display a high degree of chemical purity (>95%) and crystalline order and exhibit unique cross-linking structures.