Introduction
Introduced dielectric properties of the inorganic medium material, also involves the dielectric constant, dielectric loss factor and dielectric strength.
The dielectric constant is also called media constants, dielectric coefficients or electric capacitors. It is a coefficient that represents the characteristics of the insulation capability, indicated by letter ε, the unit is a method / meter
if A material having a high dielectric constant is placed in an electric field, and the strength of the field will have a considerable decline in the dielectric.
Loss
Factor is only related to the medium, and its size can be used as a criterion of the insulating material.
The medium is called the dielectric strength of the dielectric strength of the dielectric state.
Common solvent dielectric constant:
H2O (water) 78.5
HCOOH (formic acid) 58.5
CH3COOH (acetic acid) 6.15
CH3COOC2H5 (ethyl acetate) 6.02
HCON (CH3) 2 (N, N-dimethylformamide) 36.7
CH3OH (methanol) 32.7
C2H5OH (ethanol) 24.5
CH3CH2CH2-OH (n-propanol) 20.1
CH3CH2CH2CH2-OH (n-butanol) 17.8
N-C6H13OH (n-hexanol) 13.3
CH3COCH3 (acetone) 20.7
C6H6 (benzene) 2.28
CCL4 (carbon tetrachloride) 2.24
N-C6H14 (n-hexane) 1.88
CH3SOCH3 (dimethyl sulfoxide, DMSO) 47.2
Features
refers to substance molecules The response characteristics of the binding charge (only in the molecular linear range) to the external electric field, which is mainly from relative dielectric constant εr ', relative dielectric loss factor εr〃, medium loss angle Tanδ and medium equivalent Impedance and other parameters are characterized.
Oil and water (pure water) are insulator. But the dielectric performance of pure water is much higher than the oil. When the relative dielectric constant is taken, the dielectric constant of water is 81, while the transformer oil is between 3-5.
High polymer
High polymer dielectric properties refer to the high polymer under an electric field, showing the properties of static energy storage and loss, usually with dielectric Constant and dielectric losses are expressed.
(1) dielectric polarization
Most of the high polymer is an excellent electrical insulator, high resistivity, low dielectric loss, high high frequency And high breakdown strength. However, under the action of the external electric field, more or less relative displacement of the price electron or the nucleus causes the redistribution of charge, referred to as polarization. It has the following polarizations: (1) Electronic polarization, (2) atomic polarization, (3) dipole polarization. The first two generated dipole tormes induced dipole moment, and the latter is a permanent dip polarization.
(2) Dielectric loss
The polymer is oriented in an alternating electric field, accompanied by energy consumption, so that the medium itself is heated, which is referred to as a polymer. Dielectric loss.
Commonly used multiple dielectric constants simultaneously represents the properties of dielectric constants and dielectric losses:
(3) Factors affecting dielectricity
1 Structure
The larger polarity is polarized, and it is generally increasing. The position of the polar group is also sensitive to the position of the polar group (such as on the side group), which is smaller.
Crosslinking, orientation or crystallization increases the intensity of the molecular action, reduces the intensive force, and increases molecular weight.
2 frequency and temperature
and mechanical relaxation similar
3 foreign objects
Plasticizer added to reduce the system viscosity It is conducive to tendency to polarize, and dielectric loss peak moves to low temperature. The presence of polar plasticizers or conductive impurities will increase.
The polymer is used as an electrical insulating material or a capacitor material, and the smaller the dielectric loss is required, the better in the case of plastic high frequency welding or high frequency "heat treatment", etc. good.