A novel porous mullite ceramic with overlapping and interlocking mullite whiskers was prepared using in-situ whisker growth technology.Without the use of any pore-foaming agents,the formation of a porous structure was...A novel porous mullite ceramic with overlapping and interlocking mullite whiskers was prepared using in-situ whisker growth technology.Without the use of any pore-foaming agents,the formation of a porous structure was facilitated by the atomic rearrangement of Al_(2)O_(3) and SiO_(2) catalyzed with MoO_(3).The effects of the molar ratio of Al_(2)O_(3) to SiO_(2),MoO_(3) content,sintering time,and sintering temperature on the structure and properties of(xAl_(2)O_(3)·ySiO_(2))m(MoO_(3))n-T-t(T=sintering temperature,and t=sintering duration)ceramics were comprehensively studied.The molar ratio of Al_(2)O_(3) to SiO_(2) had a more significant effect on the morphology of the whiskers,while the other three conditions generally promote whisker growth.Under conditions of x:y=3:1.8,m:n=9:1,T=1300℃,and t=3 h,(3Al_(2)O_(3)·1.8SiO_(2))9(MoO_(3))1-1300℃-3 h ceramics exhibited a satisfactory compressive strength of 4.81 MPa at a density of 0.76 g/cm3.Microstructural analysis revealed that a multi-level reinforcement structure was obtained by the interlaced distribution of tiny and large whiskers,significantly increasing the crack deflection area and enhancing the crack deflection resistance when resisting external forces.After 100 thermal shock cycles between room temperature and 1300℃,the compressive strength retention rate was 77.13%.In addition,the multi-scale whisker-overlapping structure also has a high specific surface area(1.83 m^(2)/g),high porosity(74.18%),and small pore size(7.44μm).The thermal conductivity was as low as 0.260 W/(m·K),and the ceramic maintained a rear-side temperature below 200℃ when subjected to a 1300℃ butane flame.In addition,the regulatory mechanism between parameters,structure,and properties was analyzed in detail,providing data support for research on porous materials.展开更多
With the increasing penetration of wind power,using wind turbines to participate in the frequency regulation to support power system has become a clear consensus.To accurately quantify the inertia provided by the doub...With the increasing penetration of wind power,using wind turbines to participate in the frequency regulation to support power system has become a clear consensus.To accurately quantify the inertia provided by the doubly-fed induction generator(DFIG)based wind farm,the frequency response model of DFIG with additional frequency control is established,and then by using Routh approximation,the explicit expression of the virtual moment of inertia is derived for the DFIG gridconnected system.To further enhance the availability of the expression,an estimation method is proposed based on the matrix pencil method and the least squares algorithm for estimating the virtual moment of inertia provided by the wind farm.Finally,numerical results tested by a DFIG grid-connected system and a modified IEEE 30-bus system verify the derived expression of the virtual moment of inertia and the proposed estimation method.展开更多
基金supported by the Fundamental Research Funds for the Central Universities of Civil Aviation University of China(No.3122024050)the Undergraduate Innovation Project of Civil Aviation University of China(Nos.202410059049 and IECAUC2025043).
文摘A novel porous mullite ceramic with overlapping and interlocking mullite whiskers was prepared using in-situ whisker growth technology.Without the use of any pore-foaming agents,the formation of a porous structure was facilitated by the atomic rearrangement of Al_(2)O_(3) and SiO_(2) catalyzed with MoO_(3).The effects of the molar ratio of Al_(2)O_(3) to SiO_(2),MoO_(3) content,sintering time,and sintering temperature on the structure and properties of(xAl_(2)O_(3)·ySiO_(2))m(MoO_(3))n-T-t(T=sintering temperature,and t=sintering duration)ceramics were comprehensively studied.The molar ratio of Al_(2)O_(3) to SiO_(2) had a more significant effect on the morphology of the whiskers,while the other three conditions generally promote whisker growth.Under conditions of x:y=3:1.8,m:n=9:1,T=1300℃,and t=3 h,(3Al_(2)O_(3)·1.8SiO_(2))9(MoO_(3))1-1300℃-3 h ceramics exhibited a satisfactory compressive strength of 4.81 MPa at a density of 0.76 g/cm3.Microstructural analysis revealed that a multi-level reinforcement structure was obtained by the interlaced distribution of tiny and large whiskers,significantly increasing the crack deflection area and enhancing the crack deflection resistance when resisting external forces.After 100 thermal shock cycles between room temperature and 1300℃,the compressive strength retention rate was 77.13%.In addition,the multi-scale whisker-overlapping structure also has a high specific surface area(1.83 m^(2)/g),high porosity(74.18%),and small pore size(7.44μm).The thermal conductivity was as low as 0.260 W/(m·K),and the ceramic maintained a rear-side temperature below 200℃ when subjected to a 1300℃ butane flame.In addition,the regulatory mechanism between parameters,structure,and properties was analyzed in detail,providing data support for research on porous materials.
基金This work was supported in part by the National Science Foundation of China(No.51877015)the Science and Technology Foundation of State Grid Corporation of China(No.SGTYHT/19-JS-215).
文摘With the increasing penetration of wind power,using wind turbines to participate in the frequency regulation to support power system has become a clear consensus.To accurately quantify the inertia provided by the doubly-fed induction generator(DFIG)based wind farm,the frequency response model of DFIG with additional frequency control is established,and then by using Routh approximation,the explicit expression of the virtual moment of inertia is derived for the DFIG gridconnected system.To further enhance the availability of the expression,an estimation method is proposed based on the matrix pencil method and the least squares algorithm for estimating the virtual moment of inertia provided by the wind farm.Finally,numerical results tested by a DFIG grid-connected system and a modified IEEE 30-bus system verify the derived expression of the virtual moment of inertia and the proposed estimation method.
