Nonconductive

Yuan J-Y, Shao Z and Gao C 1991 Alternative method of imaging surface topologies of nonconducting bulk specimens by scanning tunnelling microscopy Phys. Rev. Lett. 67 863... 

One example of a liquid-based ion-selective electrode is that for Ca +, which uses a porous plastic membrane saturated with di-(n-decyl) phosphate (Figure 11.13). As shown in Figure 11.14, the membrane is placed at the end of a nonconducting cylindrical tube and is in contact with two reservoirs. The outer reservoir contains di-(n-decyl) phosphate in di- -octylphenylphosphonate, which soaks into the porous membrane. The inner reservoir contains a standard aqueous solution of Ca + and a Ag/AgCl reference electrode. Calcium ion-selective electrodes are also available in which the di-(n-decyl) phosphate is immobilized in a polyvinyl chloride... 

Cera.micA.bla.tors, Several types of subliming or melting ceramic ablators have been used or considered for use in dielectric appHcations particularly with quartz or boron nitride [10043-11 -5] fiber reinforcements to form a nonconductive char. Fused siHca is available in both nonporous (optically transparent) and porous (sHp cast) forms. Ford Aerospace manufactures a 3D siHca-fiber-reinforced composite densified with coUoidal siHca (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see COMPOSITE MATERIALS, CERAMIC MATRIX). 

Polarization which can be induced in nonconducting materials by means of an externally appHed electric field is one of the most important parameters in the theory of insulators, which are called dielectrics when their polarizabiUty is under consideration (1). Experimental investigations have shown that these materials can be divided into linear and nonlinear dielectrics in accordance with their behavior in a realizable range of the electric field. The electric polarization PI of linear dielectrics depends linearly on the electric field E, whereas that of nonlinear dielectrics is a nonlinear function of the electric field (2). The polarization values which can be measured in linear (normal) dielectrics upon appHcation of experimentally attainable electric fields are usually small. However, a certain group of nonlinear dielectrics exhibit polarization values which are several orders of magnitude larger than those observed in normal dielectrics (3). Consequentiy, a number of useful physical properties related to the polarization of the materials, such as elastic, thermal, optical, electromechanical, etc, are observed in these groups of nonlinear dielectrics (4). 

Electrical Resistance—Conductivity. Most fillers are composed of nonconducting substances that should, therefore, provide electrical resistance properties comparable to the plastics in which they are used. However, some fillers contain adsorbed water or other conductive species that can gready reduce their electrical resistance. Standard tests for electrical resistance of filled plastics include dielectric strength, dielectric constant, arc resistance, and d-c resistance. 

Due to the strong ionic nature of lithium trifluoromethanesulfonate, it can increase the conductivity of coating formulations, and thereby enhance the dissipation of static electricity in nonconducting substrates (see Antistatic agents) (25). 

Induction furnaces utilize the phenomena of electromagnetic induction to produce an electric current in the load or workpiece. This current is a result of a varying magnetic field created by an alternating current in a cod that typically surrounds the workpiece. Power to heat the load results from the passage of the electric current through the resistance of the load. Physical contact between the electric system and the material to be heated is not essential and is usually avoided. Nonconducting materials cannot be heated directiy by induction fields. 

The heavy mineral sand concentrates are scmbbed to remove any surface coatings, dried, and separated into magnetic and nonmagnetic fractions (see Separation, magnetic). Each of these fractions is further spHt into conducting and nonconducting fractions in an electrostatic separator to yield individual concentrates of ilmenite, leucoxene, monazite, mtile, xenotime, and zircon. Commercially pure zircon sand typically contains 64% zirconium oxide, 34% siUcon oxide, 1.2% hafnium oxide, and 0.8% other oxides including aluminum, iron, titanium, yttrium, lanthanides, uranium, thorium, phosphoms, scandium, and calcium. 

Flexible Applications. The mainstay of the lead stabilizers in the United States is in flexible wine and cable coating appHcations. The nonconductive nature of lead stabilizers is unsurpassed by other classes of stabilizers. Rather high levels of stabilizers are necessary for these uses because... 

Because the corrosion resistance of lead and lead alloys is associated with the formation of the protective corrosion film, removal of the film in any way causes rapid attack. Thus the velocity of a solution passing over a surface can lead to significantly increased attack, particularly if the solution contains suspended particulate material. Lead is also attacked rapidly in the presence of high velocity deionised water. The lack of dissolved minerals in such water prevents the formation of an insoluble protective film. In most solutions, lead and lead alloys are resistant to galvanic corrosion because of the formation of a nonconductive corrosion film. In contact with more noble metals, however, lead can undergo galvanic attack which is accelerated by stray electrical currents. 

Fig. 8. Capacitance-based level measurement, nonconductive media.

When the process medium is electrically conductive (dielectric values > 10), the capacitor developed above does not work the iasulatiag material needed between the two conductive plates is lost. The conductive Hquid surrounding the probe acts as a short circuit to the tank wall (second plate of the capacitor). To reestabUsh the dielectric (iasulatiag material), the probe can be iasulated with a nonconductive material such as tetrafluoroethylene (TFE), poly(vinyhdene fluoride) (PVDF), poly(vinyl chloride) (PVC), etc. The capacitor exists between the probe rod, through the thickness of the iasulation (dielectric), to the conductive Hquid which is now acting as the second plate of the capacitor, or ground reference (Fig. 9). 

In nonmetaUic vessels, the second plate of the capacitor is missing and must be suppHed. A stiUweU probe, one with a concentric metal tube, is utilized. The concentric tube suppHes the second plate. StiUweU probes have numerous other uses. In appHcations of nonconductive media, a stiUweU probe is more sensitive and suppHes a greater amount of capacitance because the ground reference is so close to the probe. Further, if a tank waU offers a ground reference that is a varyiag distance to the probe, eg, a horizontal cylinder, the stiUweU offers a much more consistent (linear) ground reference. 

Portable fire extinguishers are classified according to appHcabiHty Class A for soHd combustibles Class B for flammable Hquids Class C for electrical fires that require a nonconducting agent and Class D for combustible metals. Water frequently is used for Class A extinguishers bicarbonates for Class B and Class BC carbon dioxide or Freon for Class C ammonium phosphate for Class ABC and powdered salt, sodium chloride, for Class D. 

---