Friction electricity

Electric Friction Machine suitable for field use was invented by Baron von Ebner of Austria. After being improved in 1869, it was used in the blasting of Hoosac tunnel (Vol 2 of Encycl, pp B187-L B212-L)... 

At a molecular level, this slowdown is described in terms of two effects. One of these effects is called electrophoretic and the other, relaxational. The electrophoretie effect is easy to understand because it is a kind of electrical friction as one ion passes the other within electrical hailing distance, both ions slow down in recognition of the electrical existence of the other. 

In Franklin s time there were four known sources of electricity frictional, atmospheric (lightning), pyroelectricity (due to heating or cooling of certain substances) and animal electricity, as from the torpedo fish. All these sources yield what is somewhat inaccurately described as "static electricity. Since as we now know, the phenomena observed in connection with "static electricity are due to relatively small electric charges at high intensities it is not surprising that only scattered observations were made that indicated that electricity could be associated with chemical action. 

The electric friction cone penetrometer is shown in Figure 4.14. It is attached to a string of steel rods. Wires from the transducers are threaded through the center of the rods and continuously give the cone and side resistance (ASTM D5778). Results from typical penetrometer tests with friction measurements are presented in Figure 4.15 for both the... 

Electric friction cone penetrometer. (From De Ruiter, J., J. Soil Mech. Found. Div., 97,457-472,1971. Reprinted with permission of ASCE.)... 

Homemade AFM probes fabricated from metal microwires [79-81] (such as W, Ni, Pt, or Pt/Ir) where the end of the wire has been etched to form a sharp tip and then bent to form the cantilever, have also found much use as probes of the electrical, frictional, and topographical properties of sample substrates, in air or under vacuum. In many cases, the microwires are electrochemically etched using dissolution procedures borrowed from STM methodology for the production of sharp STM tips [10]. In some cases, the bent wire is flattened to form a beam- (or even V-)shaped cantilever [65, 82]. For C-AFM imaging measurements, solid metal microwire AFM probes are an attractive alternative to the metal-coated conventional AFM tips, as loss of probe conductivity due to wear, no longer poses a problem. 

Table 3.1 Fiber length, diameter, cell dimensions, density, electrical, frictional, and thermal properties... 

The two AC drive systems used on extruders are the adjustable transmission ratio drive and the adjustable frequency drive. The adjustable transmission ratio drive can be either a mechanical adjustable speed drive or an electric friction clutch drive. 

In the electric friction clutch drive, there is no direct mechanical connection between input and output shaft, eliminating mechanical friction and wear. Electrical forces are used to engage the input and output shaft. The three main types are hysteresis, eddy-current, and magnetic particle clutches. In the extrusion industry, the eddy-current drive has been widely applied in the past. The majority of the older extruders were equipped with eddy-current drives. 

OCCUPATIONAL SAFETY NOTE Personnel must exercise extreme caution whenever checking a gaseous fuel system for leaks. Any possibility of creating sparks, static electricity, friction, etc. must be avoided, as they could cause a fire or explosion. 

The first documented SECM-AFM probe is described in [6], fabricated from a 50 pm diameter Pt wire. In the arena of nanoscopic electrode fabrication [7] and the production of tips for electrochemical STM [8], procedures are well established for the electrochemical etching and insulation of microwires, to produce sharpened and insulated, except at the very apex of the tip, nanoelectrodes. In the AFM field, solid metal AFM probes, for the measurement of the electrical, frictional, and topographical properties of a substrate, have been fabricated previously, by hand, from metal microwires [9]. Thus, by combining the two methodologies together, it was possible to fabricate SECM-AFM probes. 

An alternative approach is to consider ions of charge z e accelerated by the electric field strengtii, E, being subject to a frictional force, Kj, that increases with velocity, v, and is given, for simple spherical ions of... 

It resembles polytetrafiuoroethylene and fiuorinated ethylene propylene in its chemical resistance, electrical properties, and coefficient of friction. Its strength, hardness, and wear resistance are about equal to the former plastic and superior to that of the latter at temperatures above 150°C. 

This thermoplastic shows good tensile strength, toughness, low water absorption, and good frictional properties, plus good chemical resistance and electrical properties. 

Dry nitrocellulose, which bums rapidly and furiously, may detonate if present in large quantities or if confined. Nitrocellulose is a dangerous material to handle in the dry state because of sensitivity to friction, static electricity, impact, and heat. Nitrocellulose is always shipped wet with water or alcohol. The higher the nitrogen content the more sensitive it tends to be. Even nitrocellulose having 40% water detonates if confined and sufftcientiy activated. AH large-scale processes use nitric—sulfuric acid mixtures for nitration (127—132). 

The dissipation factor (the ratio of the energy dissipated to the energy stored per cycle) is affected by the frequency, temperature, crystallinity, and void content of the fabricated stmcture. At certain temperatures and frequencies, the crystalline and amorphous regions become resonant. Because of the molecular vibrations, appHed electrical energy is lost by internal friction within the polymer which results in an increase in the dissipation factor. The dissipation factor peaks for these resins correspond to well-defined transitions, but the magnitude of the variation is minor as compared to other polymers. The low temperature transition at —97° C causes the only meaningful dissipation factor peak. The dissipation factor has a maximum of 10 —10 Hz at RT at high crystallinity (93%) the peak at 10 —10 Hz is absent. 

As a tme thermoplastic, FEP copolymer can be melt-processed by extmsion and compression, injection, and blow molding. Films can be heat-bonded and sealed, vacuum-formed, and laminated to various substrates. Chemical inertness and corrosion resistance make FEP highly suitable for chemical services its dielectric and insulating properties favor it for electrical and electronic service and its low frictional properties, mechanical toughness, thermal stabiUty, and nonstick quaUty make it highly suitable for bearings and seals, high temperature components, and nonstick surfaces. 

PTFE is outstanding in this group. In thin films it provides the lowest coefficient of friction (0.03—0.1) of any polymer, is effective from —200 to 250°C, and is generally unreactive chemically. The low friction is attributed to the smooth molecular profile of PTFE chains which allows easy sliding (57). Typical apphcations include chemical and food processing equipment, electrical components, and as a component to provide improved friction and wear in other resin systems. 

The fabric may also be given one or more of a number of other finishing treatments, either ia tandem with web formation and bonding or off-line as a separate operation, as a means of enhancing fabric performance or aesthetic properties. Performance properties iaclude functional characteristics such as moisture transport, absorbency, or repeUency flame retardancy electrical conductivity or static propensity abrasion resistance and frictional behavior. Aesthetic properties iaclude appearance, surface texture, and smell. 

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