The objective of this study was to establish the dielectric properties of CoFe2O4 nanoparticles with particle sizes that varied from 28.6 to 5.8 nm. CoFe2O4 nanoparticles were synthesized using a chemical coprecipitat...The objective of this study was to establish the dielectric properties of CoFe2O4 nanoparticles with particle sizes that varied from 28.6 to 5.8 nm. CoFe2O4 nanoparticles were synthesized using a chemical coprecipitation method. The particle sizes were calculated accord-ing to the Scherrer formula using X-ray diffraction （XRD） peaks, and the particle size distribution curves were constructed by using field-emission scanning electron microscopy （FESEM） images. The dielectric permittivity and loss tangents of the samples were determined in the frequency range of 1 kHz to 1 MHz and in the temperature range of 300 to 10 K. Both the dielectric permittivity and the loss tangent were found to decrease with increasing frequency and decreasing temperature. For the smallest CoFe2O4 nanoparticle size, the dielectric per-mittivity and loss tangent exhibited their highest and lowest values, respectively. This behavior is very useful for materials used in devices that operate in the microwave or radio frequency ranges.展开更多
The dielectric and thermal analysis of copper doped Magnesium Hydrogen Maleate Hexahydrate single crystals are studied for the first time. The dielectric constant, loss tangent, a.c. conductivity and a.c. activation e...The dielectric and thermal analysis of copper doped Magnesium Hydrogen Maleate Hexahydrate single crystals are studied for the first time. The dielectric constant, loss tangent, a.c. conductivity and a.c. activation energy were measured with variation of frequency in the range 50 Hz to 1 MHz. Dielectric studies reveal that the present crystal under investigation show good optical quality. The melting point and final compound after decomposition were determined using the DTA/TG analysis.展开更多
Mixed Mg-Cr Nano ferrites having the compositional formula MgCrxFe2-xO4 (where x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were synthesized using Citrate-Gel auto combustion method. Structural characterization was carri...Mixed Mg-Cr Nano ferrites having the compositional formula MgCrxFe2-xO4 (where x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were synthesized using Citrate-Gel auto combustion method. Structural characterization was carried out by XRD Analysis which confirmed the formation of single phase cubic spinel structure without any impurity peak. The dielectric properties such as Dielectric constant (ε'), Dielectric Loss tangent (tan δ) and AC conductivity (σAC) of Mg-Cr nano ferrites were studied at room temperature in the frequency range of 2 Hz - 2 MHz using Agilent E4980A Precision LCR meter. The dielectric constant, loss tangent and AC conductivity shows a normal behavior with frequency. A qulitative explanation is given for composition and frequency dependance of the dielectric constant, dielectric loss tangent and AC conductivity of the nano ferrite. The loss tangent for the synthesized samples was found to be decreased from 0.09 to 0.054 in higher frequency region showing the potential applications of these materials in high frequency micro wave devices. On the basis of these results the explanation of dielectric mechanism in Mg-Cr ferrites is suggested.展开更多
Si/C/B powders were synthesized by carbothermal reduction of xerogels containing boride. Colorless, transparent and monolithic gel was obtained by using tetraethoxysilane, saccharose, tributyl borate, ethanol and dist...Si/C/B powders were synthesized by carbothermal reduction of xerogels containing boride. Colorless, transparent and monolithic gel was obtained by using tetraethoxysilane, saccharose, tributyl borate, ethanol and distilled water as starting materials. When the xerogel was fired at 1 600℃in the static argon atmosphere, the XRD pattern commences to show the crystallite peak corresponding with C.β-SiC was synthesized at 1 700℃, but amorphous remainders could not be eliminated completely. The XRD results show that the boron possibly enters into the silica network, leading to the formation of borosiloxane. Microstructure ofβ-SiC powders consists of agglomerated particles with diameters ranging from 30 to 100 nm. Though the samples prepared at 1 600℃and 1 700℃have better dielectric loss tangent than the sample at 1 500℃due to exiting crystalline material, the dielectric constant and dielectric loss tangent of three samples reveal lower values.展开更多
On-line measurement for dielectric loss angle can effectively monitor the insulation condition of capacitive equipment in power systems. Synthetic relative measuring methods not only markedly overcome the shortcomings...On-line measurement for dielectric loss angle can effectively monitor the insulation condition of capacitive equipment in power systems. Synthetic relative measuring methods not only markedly overcome the shortcomings of traditional absolute measuring methods but also greatly improve the accuracy of dielectric loss angle measurement. However, synthetic relative measuring methods based on two or three pieces of capacitive equipment do not have the characteristic of generality. In this paper, a principle of synthetic relative measuring method is presented. The example of application for synthetic relative methods based on three and four pieces of capacitive equipment running in the same phase is taken to present the failure judgment matrices for N pieces of equipment. According to these matrices, the fault condition of N pieces of capacitive equipment can be watched, which is more general. Then some problems needing to be concerned along with two diagnostic methods used in diagnostic system are introduced. Finally, two programmable flow charts for the two methods are given and corresponding examples demonstrate their feasibility in practice.展开更多
The paper presents the results of studies surface microrelief, frequency-temperature characteristics of the imaginary part of the dielectric permittivity and dielectric loss of PE+TlInSe2 composite materials in 25。C ...The paper presents the results of studies surface microrelief, frequency-temperature characteristics of the imaginary part of the dielectric permittivity and dielectric loss of PE+TlInSe2 composite materials in 25。C - 150。C temperature and 25 Hz - 1 MHz frequency range before and after application of the aluminum nano-particles with a size of 50 nm. The change in the amount of semicon-ductor filler TlInSe2 and aluminum nano-particles changes the state of the surface and the frequency-temperature characteristics of composite materials PE+xvol.%TlInSe2, which allows to obtain composites with the desired dielectric permittivity and dielectric loss.展开更多
In this research work, (Bi<sub>2</sub>O<sub>3</sub>Fe<sub>2</sub>O<sub>3</sub>)<sub>0.4</sub>(Nb<sub>2</sub>O<sub>5</sub>)<sub>...In this research work, (Bi<sub>2</sub>O<sub>3</sub>Fe<sub>2</sub>O<sub>3</sub>)<sub>0.4</sub>(Nb<sub>2</sub>O<sub>5</sub>)<sub>0.6</sub> was made by the solid state reaction method. Samples were sintered at four different temperatures (850°C, 925°C, 1000°C and 1150°C) to study the effect of sintering temperature on the various properties of the samples. X-ray diffraction analysis confirmed that single phase Bi<sub>1.721</sub>δ<sub>0.089</sub>Fe<sub>1.056</sub>Nb<sub>1.134</sub>O<sub>7</sub> was found when sintering temperature increased. At the same time, larger grain size was found when sintering temperature increased. From variation of dielectric loss with respect to frequency, a small peak was found when sample was sintered at higher temperature (1150°C). Dielectric constant of the sample decreases with the increase of frequency for all the samples. With the variation of temperature, DC resistivity of the samples showed that resistivity decreases with the increase of measuring temperature which indicates semiconducting nature.展开更多
In the light of fractal geometry theory, the characteristics of coal's electric parameters (including dielectric constant, alternating conductivity, dielectric loss angle tangent and electric polarization constant...In the light of fractal geometry theory, the characteristics of coal's electric parameters (including dielectric constant, alternating conductivity, dielectric loss angle tangent and electric polarization constant) were studied by using literature data. The results are shown that the electrical properties of coal have fractal characteristic. The fractal dimensions of dielectric, alternating conductivity, dielectric loss angle tangent were obtained, and are relative to the content of pyrite sulfur, heat and ash content of coal.展开更多
文摘The objective of this study was to establish the dielectric properties of CoFe2O4 nanoparticles with particle sizes that varied from 28.6 to 5.8 nm. CoFe2O4 nanoparticles were synthesized using a chemical coprecipitation method. The particle sizes were calculated accord-ing to the Scherrer formula using X-ray diffraction （XRD） peaks, and the particle size distribution curves were constructed by using field-emission scanning electron microscopy （FESEM） images. The dielectric permittivity and loss tangents of the samples were determined in the frequency range of 1 kHz to 1 MHz and in the temperature range of 300 to 10 K. Both the dielectric permittivity and the loss tangent were found to decrease with increasing frequency and decreasing temperature. For the smallest CoFe2O4 nanoparticle size, the dielectric per-mittivity and loss tangent exhibited their highest and lowest values, respectively. This behavior is very useful for materials used in devices that operate in the microwave or radio frequency ranges.
文摘The dielectric and thermal analysis of copper doped Magnesium Hydrogen Maleate Hexahydrate single crystals are studied for the first time. The dielectric constant, loss tangent, a.c. conductivity and a.c. activation energy were measured with variation of frequency in the range 50 Hz to 1 MHz. Dielectric studies reveal that the present crystal under investigation show good optical quality. The melting point and final compound after decomposition were determined using the DTA/TG analysis.
文摘Mixed Mg-Cr Nano ferrites having the compositional formula MgCrxFe2-xO4 (where x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were synthesized using Citrate-Gel auto combustion method. Structural characterization was carried out by XRD Analysis which confirmed the formation of single phase cubic spinel structure without any impurity peak. The dielectric properties such as Dielectric constant (ε'), Dielectric Loss tangent (tan δ) and AC conductivity (σAC) of Mg-Cr nano ferrites were studied at room temperature in the frequency range of 2 Hz - 2 MHz using Agilent E4980A Precision LCR meter. The dielectric constant, loss tangent and AC conductivity shows a normal behavior with frequency. A qulitative explanation is given for composition and frequency dependance of the dielectric constant, dielectric loss tangent and AC conductivity of the nano ferrite. The loss tangent for the synthesized samples was found to be decreased from 0.09 to 0.054 in higher frequency region showing the potential applications of these materials in high frequency micro wave devices. On the basis of these results the explanation of dielectric mechanism in Mg-Cr ferrites is suggested.
基金Project(50572090) supported by the National Natural Science Foundation of China
文摘Si/C/B powders were synthesized by carbothermal reduction of xerogels containing boride. Colorless, transparent and monolithic gel was obtained by using tetraethoxysilane, saccharose, tributyl borate, ethanol and distilled water as starting materials. When the xerogel was fired at 1 600℃in the static argon atmosphere, the XRD pattern commences to show the crystallite peak corresponding with C.β-SiC was synthesized at 1 700℃, but amorphous remainders could not be eliminated completely. The XRD results show that the boron possibly enters into the silica network, leading to the formation of borosiloxane. Microstructure ofβ-SiC powders consists of agglomerated particles with diameters ranging from 30 to 100 nm. Though the samples prepared at 1 600℃and 1 700℃have better dielectric loss tangent than the sample at 1 500℃due to exiting crystalline material, the dielectric constant and dielectric loss tangent of three samples reveal lower values.
文摘On-line measurement for dielectric loss angle can effectively monitor the insulation condition of capacitive equipment in power systems. Synthetic relative measuring methods not only markedly overcome the shortcomings of traditional absolute measuring methods but also greatly improve the accuracy of dielectric loss angle measurement. However, synthetic relative measuring methods based on two or three pieces of capacitive equipment do not have the characteristic of generality. In this paper, a principle of synthetic relative measuring method is presented. The example of application for synthetic relative methods based on three and four pieces of capacitive equipment running in the same phase is taken to present the failure judgment matrices for N pieces of equipment. According to these matrices, the fault condition of N pieces of capacitive equipment can be watched, which is more general. Then some problems needing to be concerned along with two diagnostic methods used in diagnostic system are introduced. Finally, two programmable flow charts for the two methods are given and corresponding examples demonstrate their feasibility in practice.
文摘The paper presents the results of studies surface microrelief, frequency-temperature characteristics of the imaginary part of the dielectric permittivity and dielectric loss of PE+TlInSe2 composite materials in 25。C - 150。C temperature and 25 Hz - 1 MHz frequency range before and after application of the aluminum nano-particles with a size of 50 nm. The change in the amount of semicon-ductor filler TlInSe2 and aluminum nano-particles changes the state of the surface and the frequency-temperature characteristics of composite materials PE+xvol.%TlInSe2, which allows to obtain composites with the desired dielectric permittivity and dielectric loss.
文摘In this research work, (Bi<sub>2</sub>O<sub>3</sub>Fe<sub>2</sub>O<sub>3</sub>)<sub>0.4</sub>(Nb<sub>2</sub>O<sub>5</sub>)<sub>0.6</sub> was made by the solid state reaction method. Samples were sintered at four different temperatures (850°C, 925°C, 1000°C and 1150°C) to study the effect of sintering temperature on the various properties of the samples. X-ray diffraction analysis confirmed that single phase Bi<sub>1.721</sub>δ<sub>0.089</sub>Fe<sub>1.056</sub>Nb<sub>1.134</sub>O<sub>7</sub> was found when sintering temperature increased. At the same time, larger grain size was found when sintering temperature increased. From variation of dielectric loss with respect to frequency, a small peak was found when sample was sintered at higher temperature (1150°C). Dielectric constant of the sample decreases with the increase of frequency for all the samples. With the variation of temperature, DC resistivity of the samples showed that resistivity decreases with the increase of measuring temperature which indicates semiconducting nature.
基金Supported by Key Project of Chinese National Programs for Fundamental Research Development(973 Project 2005CB221502)
文摘In the light of fractal geometry theory, the characteristics of coal's electric parameters (including dielectric constant, alternating conductivity, dielectric loss angle tangent and electric polarization constant) were studied by using literature data. The results are shown that the electrical properties of coal have fractal characteristic. The fractal dimensions of dielectric, alternating conductivity, dielectric loss angle tangent were obtained, and are relative to the content of pyrite sulfur, heat and ash content of coal.
