Electrical chloride impurity

Impurity atoms can form solid solutions in ceramic materials much as they do in metals. Solid solutions of both substitutional and interstitial types are possible. For an interstitial, the ionic radius of the impurity must be relatively small in comparison to the anion. Because there are both anions and cations, a substitutional impurity substitutes for the host ion to which it is most similar in an electrical sense If the impurity atom normally forms a cation in a ceramic material, it most probably will substitute for a host cation. For example, in sodium chloride, impurity Ca and ions would most likely substitute for Na and Cl ions, respectively. Schematic representations for cation and anion substitutional as well as interstitial impurities are shown in Figure 12.21. To achieve any appreciable sohd solubility of substituting impmity atoms, the ionic size and charge must be very nearly the same as those of one of the host ions. For an impurity ion having a charge different from that of the host ion for which it substitutes, the crystal must compensate for this difference in charge so that electroneutrality is maintained with the solid. One way this is accomplished is by the formation of lattice defects—vacancies or interstitials of both ion types, as discussed previously. 

The presence of ions in solution is what gives a sodium chloride solution the ability to conduct electricity. If positively and negatively charged wires are dipped into the solution, the ions in the solution respond to the charges on the wires. Chloride anions move toward the positive wire, and sodium cations move toward the negative wire. This directed movement of ions in solution is a flow of electrical current. Pure water, which has virtually no dissolved ions, does not conduct electricity. Any solution formed by dissolving an ionic solid in water conducts electricity. Ordinary tap water, for example, contains Ionic Impurities that make It an electrical conductor. 

The electrical performance of the encapsulant is greatly dependent on its purity. Ionic impurities, such as sodium, potassium and chlorides, are harmful contaminants in the encapsulant. It has long been shown that ionic materials. 

In 1909, Dr. E. Weintraub of the General Electric Company ran high-potential alternating current arcs between cooled copper electrodes in a mixture of boron chloride with a large excess of hydrogen (51), obtaining pure fused boron which differed greatly in properties from the impure amorphous product of earlier workers. 

Lead compounds are generally added to polyvinyl chloride in electrical formulations in order to stabilize them against thermal decomposition 7 p.h.r. of National Lead Tribase XL modified tribasic lead sulfate was used throughout the present study. Since the stabilizer itself is an ionic impurity, it is remarkable to note that it actually increases volume resistivity (Table IV). 

In summary, the volume resistivity of polyvinyl chloride plasticized by liquid or elastomeric plasticizers, or internally plasticized by copolymerization, was intermediate between the inherent volume resistivities of the pure components and combined the contributions of each of them. The presence of ionic soluble impurities in liquid plasticizers provided mobile ions which conducted electricity and thus lowered volume resistivity. Copolymerization with 2-ethylhexyl acrylate provided an excellent balance of softness and flexibility with high volume resistivity further studies of internal plasticization by copolymerization are therefore recommended. 

Insulators. Some solids have wide spacing between the occupied and the unoccupied energy states—2 eV or more. Such solids are called insulators since normal electric fields cannot cause extensive motion of the electrons. Examples are diamond, sodium chloride, sulfur, quartz, mica. They are poor conductors of electricity and heat and are usually transparent to light (when not filled with impurities or defects). 

For nonmetallic substances, the electrons cannot move as freely as in the case of metals because their energy bands are essentially completely full or empty. The electrical conductivity in nonmetallic materials is dominated by another mechanism, i.e., the defect mechanism, instead of electron conduction. In ionic crystals such as salts (e.g., sodium chloride), two types of ions, cations and anions, are driven to move by the electrical force qE once an electrical field is applied. The ions can move only by the defect mechanism that is, they exchange position with a vacancy of the same type. At the room temperature, the fraction of vacancies for salt is very small (of the order of 10-17) with low exchange frequency (of the order of 1 Hz) so that electrical conductivity is extremely low. Although impurities and high temperature can affect electrical conductivity by a large factor, nonmetallic materials generally have very low electrical conductivity and these substances are widely used as electrical insulators. 

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