Carbonitride MXenes,such as Ti_(3)CNT_(x),Ti_(2)C_(0.5)N_(0.5)T_(x),and Ti_(4)(C_(0.2)N_(0.8))_(3)T_(x),have attracted much interest in the large family of two-dimensional(2D)nanomaterials.Like their carbide MXene cou...Carbonitride MXenes,such as Ti_(3)CNT_(x),Ti_(2)C_(0.5)N_(0.5)T_(x),and Ti_(4)(C_(0.2)N_(0.8))_(3)T_(x),have attracted much interest in the large family of two-dimensional(2D)nanomaterials.Like their carbide MXene counterparts,the nanolayered structure and functional groups endow carbonitride MXenes with an attractive combination of physical and chemical properties.More interestingly,the replacement of C by N changes the lattice parameters and electron distribution of carbonitride MXenes due to the greater electronegativity of N as compared to C,thus resulting in significantly enhanced functional properties.This paper reviews the development of carbonitride MXenes,the preparation of 2D carbonitride MXenes,and the current understanding of the microstructure,electronic structure,and functional properties of carbonitride MXenes.In addition,applications,especially in energy storage,sensors,catalysts,electromagnetic wave shielding and absorption,fillers,and environmental and biomedical fields,are summarized.Finally,their current limitations and future opportunities are presented.展开更多
Highly pure Al_(4)SiC_(4) powders were prepared by carbothermic reduction at 2173 K using Al_(2)O_(3),SiO_(2),and graphite as raw materials.The obtained Al_(4)SiC_(4) powders owned hexagonal plate-like grains with a d...Highly pure Al_(4)SiC_(4) powders were prepared by carbothermic reduction at 2173 K using Al_(2)O_(3),SiO_(2),and graphite as raw materials.The obtained Al_(4)SiC_(4) powders owned hexagonal plate-like grains with a diameter of about 200-300μm and a thickness of about 2-6μm.Based on the experimental results,the reaction of Al_(4)SiC_(4) formation and grain evolution mechanisms were determined from thermodynamic and first-principles calculations.The results indicated that the synthesis of Al_(4)SiC_(4) by the carbothermic reduction consisted of two parts,i.e.,solid-solid reactions initially followed by complex gas-solid and gas-gas reactions.The grain growth mechanism of Al_(4)SiC_(4) featured a two-dimensional nucleation and growth mechanism.The gas phases formed during the sintering process favored the preferential grain growth of(0010)and(110)planes resulting in formation of hexagonal plate-like Al_(4)SiC_(4) grains.展开更多
Two-dimensional(2D)MoB metal borides(MoB MBene)have attracted much attention due to their fascinating properties and functional applications.So far,work on the synthesis of 2D MoB nanosheets by acid or alkaline etchin...Two-dimensional(2D)MoB metal borides(MoB MBene)have attracted much attention due to their fascinating properties and functional applications.So far,work on the synthesis of 2D MoB nanosheets by acid or alkaline etching of MoAlB has not been very successful.It has been proposed that the 2D MoB MBene may be fabricated by chemical etching of a Mo_(2)AlB_(2) precursor,but further investigations were not performed possibly due to the difficult preparation of the metastable Mo_(2)AlB_(2) compound at high temperatures by solid-state reactions.Here,we report on the successful synthesis of the Mo_(2)AlB_(2) compound and 2D MoB nanosheets by the deintercalation of Al from MoAlB through a ZnCl_(2) molten salt etching approach at relatively low temperatures.The influence of etching temperature,etching time,and starting mixtures on the formation of desirable phases have been investigated.A pure Mo_(2)AlB_(2) compound was synthesized at temperatures below 600℃,while the 2D MoB MBene nanosheets were obtained at 700℃through the molten salt etching of MoAlB.In addition,the present work further confirms that the MoB MBene can be prepared by etching the as-synthesized Mo_(2)AlB_(2) precursor in LiF–HCl solution.Our work demonstrates that the molten salt etching is an effective method to prepare 2D MoB MBene.展开更多
Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vo...Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vol% SiC/MoAlB composite exhibited improved mechanical properties and enhanced oxidation resistance. A flexural strength of 380 MPa and a Vickers hardness of 12.7 GPa were achieved and increased by 24% and 51%, respectively, as compared with those for MoAlB, indicating the enhanced strengthening effect of SiC. Cyclic oxidation tests at 1200 and 1300 ℃ for 10 h in air showed that the 5 vol% SiC/MoAlB composite has better oxidation resistance than MoAlB due to the formation of a dense and continuous scale composed of Al_(2)O_(3) and SiO_(2), which prevents the oxygen inward diffusion and the evaporation of oxides. We expect that the general strategy of second phase reinforcing for materials will help to widen the applications of MoAlB composites.展开更多
Ti_(2)AlC,a MAX phase ceramic,has an attractive self-healing ability to restore performance via the oxidation-induced crack healing mechanism upon healing at high temperatures in air(high oxygen partial pressures).How...Ti_(2)AlC,a MAX phase ceramic,has an attractive self-healing ability to restore performance via the oxidation-induced crack healing mechanism upon healing at high temperatures in air(high oxygen partial pressures).However,such healing ability to repair damages in vacuum or low oxygen partial pressure conditions remains unknown.Here,we report on the self-healing behavior of Ti_(2)AlC at a low oxygen partial pressure of about 1 Pa.The experimental results showed that the strength recovery depends on both healing temperature and time.After healing at 1400℃for 1–4 h,the healed samples exhibited the recovered strengths even exceeding the original strength of 375 MPa.The maximum recovered strength of~422 MPa was achieved in the healed Ti_(2)AlC sample after healing at 1400 for 4 h,about 13%higher than the original strength.Damages were healed by the formed℃TiCx from the decomposition of Ti_(2)AlC.The decomposition-induced crack healing as a new mechanism in the low oxygen partial pressure condition was disclosed for the MAX ceramics.The present study illustrates that key components made of Ti_(2)AlC can prolong their service life and keep their reliability during use at high temperatures in low oxygen partial pressures.展开更多
Changing the N content in the Ti_(3)AlC_(2−y)N_(y) MAX phase solid solutions allows for the fine-tuning of their properties.However,systematic studies on the synthesis and properties of Ti_(3)AlC_(2−y)N_(y) solid solu...Changing the N content in the Ti_(3)AlC_(2−y)N_(y) MAX phase solid solutions allows for the fine-tuning of their properties.However,systematic studies on the synthesis and properties of Ti_(3)AlC_(2−y)N_(y) solid solution bulks have not been reported thus far.Here,previously reported Ti_(3)AlC_(2−y)N_(y) solid solution bulks(y=0.3,0.5,0.8,and 1.0)were synthesized via hot pressing of their powder counterparts under optimized conditions.The prepared Ti_(3)AlC_(2−y)N_(y) bulks are dense and have a fine microstructure with grain sizes of 6–8μm.The influence of the N content on the mechanical properties,electrical conductivities,and coefficients of thermal expansion(CTEs)of the prepared Ti_(3)AlC_(2−y)N_(y) bulk materials was clarified.The flexural strength and Vickers hardness values increased with increasing N content,suggesting that solid solution strengthening effectively improved the mechanical properties of Ti_(3)AlC_(2−y)N_(y).Ti_(3)AlCN(y=1)had the highest Vickers hardness and flexural strength among the studied samples,reaching 5.54 GPa and 550 MPa,respectively.However,the electrical conductivity and CTEs of the Ti_(3)AlC_(2−y)N_(y) solid solutions decreased with increasing N content,from 8.93×10^(−6) to 7.69×10^(−6) K^(−1) and from 1.33×10^(6) to 0.95×10^(6) S/m,respectively.This work demonstrated the tunable properties of Ti_(3)AlC_(2−y)N_(y) solid solutions with varying N contents and widened the MAX phase family for fundamental studies and applications.展开更多
基金Fundamental Research Funds for the Central Universities,Grant/Award Numbers:2023YJS061,2023JBZY019。
文摘Carbonitride MXenes,such as Ti_(3)CNT_(x),Ti_(2)C_(0.5)N_(0.5)T_(x),and Ti_(4)(C_(0.2)N_(0.8))_(3)T_(x),have attracted much interest in the large family of two-dimensional(2D)nanomaterials.Like their carbide MXene counterparts,the nanolayered structure and functional groups endow carbonitride MXenes with an attractive combination of physical and chemical properties.More interestingly,the replacement of C by N changes the lattice parameters and electron distribution of carbonitride MXenes due to the greater electronegativity of N as compared to C,thus resulting in significantly enhanced functional properties.This paper reviews the development of carbonitride MXenes,the preparation of 2D carbonitride MXenes,and the current understanding of the microstructure,electronic structure,and functional properties of carbonitride MXenes.In addition,applications,especially in energy storage,sensors,catalysts,electromagnetic wave shielding and absorption,fillers,and environmental and biomedical fields,are summarized.Finally,their current limitations and future opportunities are presented.
基金the National Science Fund for Excellent Young Scholars of China(No.51522402)the National Natural Science Foundation of China(Nos.51572019 and U1460201)the Central Universities of FRF-TP-15-006C1 for financial support.
文摘Highly pure Al_(4)SiC_(4) powders were prepared by carbothermic reduction at 2173 K using Al_(2)O_(3),SiO_(2),and graphite as raw materials.The obtained Al_(4)SiC_(4) powders owned hexagonal plate-like grains with a diameter of about 200-300μm and a thickness of about 2-6μm.Based on the experimental results,the reaction of Al_(4)SiC_(4) formation and grain evolution mechanisms were determined from thermodynamic and first-principles calculations.The results indicated that the synthesis of Al_(4)SiC_(4) by the carbothermic reduction consisted of two parts,i.e.,solid-solid reactions initially followed by complex gas-solid and gas-gas reactions.The grain growth mechanism of Al_(4)SiC_(4) featured a two-dimensional nucleation and growth mechanism.The gas phases formed during the sintering process favored the preferential grain growth of(0010)and(110)planes resulting in formation of hexagonal plate-like Al_(4)SiC_(4) grains.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.2022YJS088)the National Natural Science Foundation of China(Grant No.52275171).
文摘Two-dimensional(2D)MoB metal borides(MoB MBene)have attracted much attention due to their fascinating properties and functional applications.So far,work on the synthesis of 2D MoB nanosheets by acid or alkaline etching of MoAlB has not been very successful.It has been proposed that the 2D MoB MBene may be fabricated by chemical etching of a Mo_(2)AlB_(2) precursor,but further investigations were not performed possibly due to the difficult preparation of the metastable Mo_(2)AlB_(2) compound at high temperatures by solid-state reactions.Here,we report on the successful synthesis of the Mo_(2)AlB_(2) compound and 2D MoB nanosheets by the deintercalation of Al from MoAlB through a ZnCl_(2) molten salt etching approach at relatively low temperatures.The influence of etching temperature,etching time,and starting mixtures on the formation of desirable phases have been investigated.A pure Mo_(2)AlB_(2) compound was synthesized at temperatures below 600℃,while the 2D MoB MBene nanosheets were obtained at 700℃through the molten salt etching of MoAlB.In addition,the present work further confirms that the MoB MBene can be prepared by etching the as-synthesized Mo_(2)AlB_(2) precursor in LiF–HCl solution.Our work demonstrates that the molten salt etching is an effective method to prepare 2D MoB MBene.
基金This work was supported by the National Natural Science Foundation of China(No.51772020)Beijing Government Funds for the Constructive Project of Central Universities.
文摘Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vol% SiC/MoAlB composite exhibited improved mechanical properties and enhanced oxidation resistance. A flexural strength of 380 MPa and a Vickers hardness of 12.7 GPa were achieved and increased by 24% and 51%, respectively, as compared with those for MoAlB, indicating the enhanced strengthening effect of SiC. Cyclic oxidation tests at 1200 and 1300 ℃ for 10 h in air showed that the 5 vol% SiC/MoAlB composite has better oxidation resistance than MoAlB due to the formation of a dense and continuous scale composed of Al_(2)O_(3) and SiO_(2), which prevents the oxygen inward diffusion and the evaporation of oxides. We expect that the general strategy of second phase reinforcing for materials will help to widen the applications of MoAlB composites.
基金supported by the National Natural Science Foundation of China(No.52275171)the PreResearch Program in National 14th Five-Year Plan(No.80923010304).
文摘Ti_(2)AlC,a MAX phase ceramic,has an attractive self-healing ability to restore performance via the oxidation-induced crack healing mechanism upon healing at high temperatures in air(high oxygen partial pressures).However,such healing ability to repair damages in vacuum or low oxygen partial pressure conditions remains unknown.Here,we report on the self-healing behavior of Ti_(2)AlC at a low oxygen partial pressure of about 1 Pa.The experimental results showed that the strength recovery depends on both healing temperature and time.After healing at 1400℃for 1–4 h,the healed samples exhibited the recovered strengths even exceeding the original strength of 375 MPa.The maximum recovered strength of~422 MPa was achieved in the healed Ti_(2)AlC sample after healing at 1400 for 4 h,about 13%higher than the original strength.Damages were healed by the formed℃TiCx from the decomposition of Ti_(2)AlC.The decomposition-induced crack healing as a new mechanism in the low oxygen partial pressure condition was disclosed for the MAX ceramics.The present study illustrates that key components made of Ti_(2)AlC can prolong their service life and keep their reliability during use at high temperatures in low oxygen partial pressures.
基金supported by the Fundamental Research Funds for the Central Universities(Nos.2023YJS061 and 2023JBZY019).
文摘Changing the N content in the Ti_(3)AlC_(2−y)N_(y) MAX phase solid solutions allows for the fine-tuning of their properties.However,systematic studies on the synthesis and properties of Ti_(3)AlC_(2−y)N_(y) solid solution bulks have not been reported thus far.Here,previously reported Ti_(3)AlC_(2−y)N_(y) solid solution bulks(y=0.3,0.5,0.8,and 1.0)were synthesized via hot pressing of their powder counterparts under optimized conditions.The prepared Ti_(3)AlC_(2−y)N_(y) bulks are dense and have a fine microstructure with grain sizes of 6–8μm.The influence of the N content on the mechanical properties,electrical conductivities,and coefficients of thermal expansion(CTEs)of the prepared Ti_(3)AlC_(2−y)N_(y) bulk materials was clarified.The flexural strength and Vickers hardness values increased with increasing N content,suggesting that solid solution strengthening effectively improved the mechanical properties of Ti_(3)AlC_(2−y)N_(y).Ti_(3)AlCN(y=1)had the highest Vickers hardness and flexural strength among the studied samples,reaching 5.54 GPa and 550 MPa,respectively.However,the electrical conductivity and CTEs of the Ti_(3)AlC_(2−y)N_(y) solid solutions decreased with increasing N content,from 8.93×10^(−6) to 7.69×10^(−6) K^(−1) and from 1.33×10^(6) to 0.95×10^(6) S/m,respectively.This work demonstrated the tunable properties of Ti_(3)AlC_(2−y)N_(y) solid solutions with varying N contents and widened the MAX phase family for fundamental studies and applications.
