In this paper, the nanometer permanent magnetic BaFe12O19 powder was synthesized by a novel method of independent nucleation and crystallization steps and subsequent heat treatment,during the synthesis, Ba(NO3)2, Fe(N...In this paper, the nanometer permanent magnetic BaFe12O19 powder was synthesized by a novel method of independent nucleation and crystallization steps and subsequent heat treatment,during the synthesis, Ba(NO3)2, Fe(NO3)2 and NH4HCO3·NH2COONH4 were used as starting materials. The effect of crystallization process and heat treatment conditions on the particle size, microstructure and magnetic properties of powder was studied by using XRD, TEM and vibration sample magnetometometer techniques.XRD results showed that the hematite, α Fe2O3, was the main phase in the powder at heat treatment temperatures below 650℃ and its amount in the powder was decreased with increasing temperature and small amount of α Fe2O3 was still remained after being heated at 900℃ for 8hrs. BaFe12O19 was formed about 650℃ and its amount increased in the powder as temperature raised and the higher temperature was needed to attain considerable amount of BaFe12O19 and ideal nanometer BaFe12O19 particle in the powder. The temperature between 40℃～60℃ in the crystallization process was favor to the formation of good BaFe12O19 crystal and to the good magnetic properties of the powder. TEM showed that the particle size in the powder increased with the enhancement of the temperature and the powder crystallized at 40℃ and heated at 800℃ for 8hrs afterwards had a very homogenous particle size distribution, and that the powder heated at 900℃ for 8hrs with the same crystalline condition as the former had a typical hexagonal shape and a chain aggregation. Specific saturation and residential magnetizations and coercive force of the powder increased monotonically with the increase of temperature, and reached 39.86A·m2·kg-1, 23.96A·m2·kg-1, 480kA·m-1 at 900℃, respectively.展开更多
High entropy alloys with the composition of FeCoNiA10.2Si0.2 were prepared by arc melting and induction melting, denoted by A1 and A2, respectively. The samples prepared by these two techniques have a face-centered cu...High entropy alloys with the composition of FeCoNiA10.2Si0.2 were prepared by arc melting and induction melting, denoted by A1 and A2, respectively. The samples prepared by these two techniques have a face-centered cubic （FCC） phase structure and a typical dendrite morphology. The tensile yield strength and maximum strength of A2 samples are about 280 and 632 MPa, respectively. Moreover~ the elongation can reach 41.7%. These two alloys prepared by the different methods possess the similar magnetic properties. The saturation magnetization and coercivity can reach 1.151 T and 1400 A/m for A1 samples and 1.015 T and 1431 A/m for A2 samples, respectively. Phases in A2 samples do not change, which are heat treated at different temperatures, then quenched in water. Only the sample, which is heat treated at 600~C for 3 h and then furnace cooled, has a new phase precipitated. Besides, the coercivity decreases obviously at this temperature. Cold rolling and the subsequent heat treatment cannot improve the magnetic properties effectively. However, cold rolling plays an important role in improving the strength.展开更多
Amorphous Ni-Fe-Co-Mn-Bi-Tm high entropy alloy films were firstly prepared by potentiostatic electro- deposition. The results indicate that the six elements can be co-deposited in an organic system of DMF （N,N-dimeth...Amorphous Ni-Fe-Co-Mn-Bi-Tm high entropy alloy films were firstly prepared by potentiostatic electro- deposition. The results indicate that the six elements can be co-deposited in an organic system of DMF （N,N-dimethylformamide）-CH3CN. The surface of the film is composed of compact and uniform particles with triangular cone shape and a particle size of 100-200 nm. A simple face-centered-cubic structure is identified by XRD patterns after the films were annealed under Ar atmosphere. The annealed alloy film shows soft magnetic properties and the magnetization decreases with Fe content decreasing.展开更多
Microwave absorbing properties of the carbonyl iron particles filled epoxy-silicone resin coatings showed visible degression when the coatings were heat treated at 300 ℃ with different time.The complex permittivity a...Microwave absorbing properties of the carbonyl iron particles filled epoxy-silicone resin coatings showed visible degression when the coatings were heat treated at 300 ℃ with different time.The complex permittivity and permeability of the coatings before and after heat treatment were measured.After heat treatment at 300 ℃,the real part of permittivity of the coatings increased with increasing treatment time and showed frequency dependence dielectric response.The complex permeability showed remarkable variation while the resonance frequency of the coatings heat treated at 300 ℃ shifted from 7 to 12 GHz.The electromagnetic results indicated that microwave absorbing properties of the coatings showed more dependent on the complex permeability.The results showed that the difference of the electromagnetic and microwave absorbing properties before and after heat treatment was mainly attributed to the crystalline state transition of carbonyl iron particles.展开更多
文摘In this paper, the nanometer permanent magnetic BaFe12O19 powder was synthesized by a novel method of independent nucleation and crystallization steps and subsequent heat treatment,during the synthesis, Ba(NO3)2, Fe(NO3)2 and NH4HCO3·NH2COONH4 were used as starting materials. The effect of crystallization process and heat treatment conditions on the particle size, microstructure and magnetic properties of powder was studied by using XRD, TEM and vibration sample magnetometometer techniques.XRD results showed that the hematite, α Fe2O3, was the main phase in the powder at heat treatment temperatures below 650℃ and its amount in the powder was decreased with increasing temperature and small amount of α Fe2O3 was still remained after being heated at 900℃ for 8hrs. BaFe12O19 was formed about 650℃ and its amount increased in the powder as temperature raised and the higher temperature was needed to attain considerable amount of BaFe12O19 and ideal nanometer BaFe12O19 particle in the powder. The temperature between 40℃～60℃ in the crystallization process was favor to the formation of good BaFe12O19 crystal and to the good magnetic properties of the powder. TEM showed that the particle size in the powder increased with the enhancement of the temperature and the powder crystallized at 40℃ and heated at 800℃ for 8hrs afterwards had a very homogenous particle size distribution, and that the powder heated at 900℃ for 8hrs with the same crystalline condition as the former had a typical hexagonal shape and a chain aggregation. Specific saturation and residential magnetizations and coercive force of the powder increased monotonically with the increase of temperature, and reached 39.86A·m2·kg-1, 23.96A·m2·kg-1, 480kA·m-1 at 900℃, respectively.
文摘High entropy alloys with the composition of FeCoNiA10.2Si0.2 were prepared by arc melting and induction melting, denoted by A1 and A2, respectively. The samples prepared by these two techniques have a face-centered cubic （FCC） phase structure and a typical dendrite morphology. The tensile yield strength and maximum strength of A2 samples are about 280 and 632 MPa, respectively. Moreover~ the elongation can reach 41.7%. These two alloys prepared by the different methods possess the similar magnetic properties. The saturation magnetization and coercivity can reach 1.151 T and 1400 A/m for A1 samples and 1.015 T and 1431 A/m for A2 samples, respectively. Phases in A2 samples do not change, which are heat treated at different temperatures, then quenched in water. Only the sample, which is heat treated at 600~C for 3 h and then furnace cooled, has a new phase precipitated. Besides, the coercivity decreases obviously at this temperature. Cold rolling and the subsequent heat treatment cannot improve the magnetic properties effectively. However, cold rolling plays an important role in improving the strength.
基金Supported by the National Natural Science Foundations of China(No.20873184)the Science and Technology Planning Project of Guangdong Province,China(No.2008B010600040)the Foundation of Potentially Important Natural Science Research and Young Teacher Starting-up Research of Sun Yat-Sen University,China
文摘Amorphous Ni-Fe-Co-Mn-Bi-Tm high entropy alloy films were firstly prepared by potentiostatic electro- deposition. The results indicate that the six elements can be co-deposited in an organic system of DMF （N,N-dimethylformamide）-CH3CN. The surface of the film is composed of compact and uniform particles with triangular cone shape and a particle size of 100-200 nm. A simple face-centered-cubic structure is identified by XRD patterns after the films were annealed under Ar atmosphere. The annealed alloy film shows soft magnetic properties and the magnetization decreases with Fe content decreasing.
基金supported by the Fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,China (No. KP200901)
文摘Microwave absorbing properties of the carbonyl iron particles filled epoxy-silicone resin coatings showed visible degression when the coatings were heat treated at 300 ℃ with different time.The complex permittivity and permeability of the coatings before and after heat treatment were measured.After heat treatment at 300 ℃,the real part of permittivity of the coatings increased with increasing treatment time and showed frequency dependence dielectric response.The complex permeability showed remarkable variation while the resonance frequency of the coatings heat treated at 300 ℃ shifted from 7 to 12 GHz.The electromagnetic results indicated that microwave absorbing properties of the coatings showed more dependent on the complex permeability.The results showed that the difference of the electromagnetic and microwave absorbing properties before and after heat treatment was mainly attributed to the crystalline state transition of carbonyl iron particles.
