Current methods

Determining Residual Austenite with the Eddy Current Method. 

The eddy current method is used for the quantitative evaluation of residual austenite contents in the martensite struaure. 

The principle physical phenomenon of applying the eddy current method for evaluating the amount of residual austenite in the structure of quenched steel is magnetic induction, involving the influence of the changeable magnetic field on the studied area, found under the probe. 

The detection of residual austenite in fact requires average frequency, however for comparison reasons (reference) with a different recognized method, it is recommended to use high frequency, as with high frequency of eddy currents the penetration depth is comparable in the diffraction method and eddy current method. 

Nondestructive Cracks and Corrosion Testing by Eddy Current Method. 

The realized experiments have shown the large possibilities of analysis by the eddy currents method. They allow, besides the verification of the coating and the determination of its thickness, to give an overview on the percentage of the main chemical components of the controlled samples coating by a deepened processing. 

Abstract An Eddy current method applying a High Temperature Superconductor ( HTS ) DC SQUID sensor operating at Uquid nitrogen temperature (77K) is presented. The method is developed for the detection of surface or surface near defects. We compare the performance of the SQUID system with the performance gained from a commercial Eddy current system, while using identical probes. The experimental data are obtained on defects in gas turbine blades. The advantage of planar conformable probes for the use with the SQUID is discussed. 

Remote Field Eddy Current (RFEC) technology is a variation of the conventional eddy-current method, developed for detecting flaws at any point in the walls of (particularly) ferromagnetic (Fe) tubes and pipes from the inside diameter. 

There are difficulties of detecting defects in axial canal because of solid sediment layer of 1. 2 mm thick on the canal surface. When using known defectoscope devices a preliminary labor-intensive mechanical treatment of the axial canal surface is needed. The experience of application of different methods of rotor axial canal control in multifunction automatic device ROTOR - K has pointed to the fact that the most effective method is eddy current one [1]. All the dangerous cracks were just detected by the eddy current method, the part of the cracks were not... 

This work presents two procedures of quantitative evaluation of the material discontinuities, using the eddy current method. One of the procedures concerns the long surface or subsurface crack-type discontinuities in a flat conductive body. The second procedure allows a quantitative evaluation of short discontinuities, such as voids, inclusions etc. 

The eddy current method allows to evalute the state of stress in ferromagnetic material. The given method is used for determining own stress as well as that formed in effect of outside load. With regard to physical principles of own stress analysis, the dependence between the magnetic permeability and the distance between atomic surfaces is utilized. 

Dybiec Cz. Eddy current method for defecting intercrystalline corrossion Materials XXIII KKBN, Szczyrk 1994. 

Czeslaw Dybiec, Ste n Jankowski, Sylwia Wloarczyk, Control of stress and structural changes using the eddy current method. Materials XXX KKBN Szczyrk 1996. 

At present, all over the world the X-ray television systems, instruments based on magnetic heat and eddy-current methods are used to check the air-passengers luggage and to check staff when entering the hazardous objects. In banks, security services and etc. the optic-television and endoscopic technical vision systems are widely used. 

Many methods have been developed to detemrine surface structure we have mentioned several in the previous section and there are many more. To get an idea of their relative usage and importance, we here examine historical statistics. We also review the kinds of surface structure drat have been studied to date, which gives a feeling for the kinds of surface structures tliat current methods and technology can most easily solve. This will provide an overview of the range of surfaces for which detailed surface structures are known, and those for which very little is known. 

A completely new method of determining siufaces arises from the enormous developments in electron microscopy. In contrast to the above-mentioned methods where the surfaces were calculated, molecular surfaces can be determined experimentally through new technologies such as electron cryomicroscopy [188]. Here, the molecular surface is limited by the resolution of the experimental instruments. Current methods can reach resolutions down to about 10 A, which allows the visualization of protein structures and secondary structure elements [189]. The advantage of this method is that it can be apphed to derive molecular structures of maaomolecules in the native state. 

M and A R Leach 1994. Current Methods for Site-Directed Structure Generation. Journal of nputer-Aided Molecular Design 8 467-475. 

Residual Current Even in the absence of analyte, a small current inevitably flows through an electrochemical cell. This current, which is called the residual current, consists of two components a faradaic current due to the oxidation or reduction of trace impurities, and the charging current. Methods for discriminating between the faradaic current due to the analyte and the residual current are discussed later in this chapter. 

The mote electropositive metals react with cryohte, Hberating aluminum or aluminum monofluotide (22,23). The reduction of cryohte by magnesium is a current method for removal of magnesium in the refining of aluminum. Upon contact with strong acids cryohte Hberates hydrogen fluoride. 

The vapor pressure, of soHd iodine has been redetermined using the gas current method and by a static method using a flexible metallic diaphragm (27,28). The data from the gas current method are weU represented by equation 2 (27) ... 

Bromine occurs ia the form of bromide ia seawater and ia natural brine deposits (see Chemicals frombrine). Chloride is also present. In all current methods of bromine production, chlorine, which has a higher reduction potential than bromine, is used to oxidize bromide to bromine. 

Separation Techniques. Current methods for separating fatty acids are by solvent crystaUi2ation or by the hydrophili2ation process. Other methods that have been used in the past, or perhaps could be used in the future, are panning and pressing, solvent extraction, supercritical fluid extraction, the use of metal salts in assisting in separation, separations using urea complexes, and adsorption/desorption. 

Crystallinity is low the pendent allyl group contributes to the amorphous state of these polymers. Propylene oxide homopolymer itself has not been developed commercially because it cannot be cross-baked by current methods (18). The copolymerization of PO with unsaturated epoxide monomers gives vulcanizable products (19,20). In ECH—PO—AGE, poly(ptopylene oxide- o-epichlorohydrin- o-abyl glycidyl ether) [25213-15-4] (5), and PO—AGE, poly(propylene oxide-i o-abyl glycidyl ether) [25104-27-2] (6), the molar composition of PO ranges from approximately 65 to 90%. 

Electrochemical Impedance Spectroscopy (EIS) and AC Impedance Many direct-current test techniques assess the overall corrosion process occurring at a metal surface, but treat the metal/ solution interface as if it were a pure resistor. Problems of accuracy and reproducibility frequently encountered in the application of direct-current methods have led to increasing use of electrochemical impedance spectroscopy (EIS). 

Location of faults by the direct current method is based on the application of Ohm s Law. It is assumed that, because of the good pipe coating, virtually no current passes into the measured span and that the longitudinal resistance R is known. When the fault-locating current, I, is fed in and takes a direct path via the foreign line to the protected pipeline, the fault distance is determined from the voltage drop AU over the measured span ... 

Where there is a high protection current requirement, and for long pipelines, the impressed current method is almost always recommended, since it can provide for the increased protection current requirements resulting from branched pipelines by raising the output voltage. The following factors should be taken into... 

The impressed current method with metal oxide-coated niobium anodes is usually employed for internal protection (see Section 7.2.3). In smaller tanks, galvanic anodes of zinc can also be used. Potential control should be provided to avoid unacceptably negative potentials. Pure zinc electrodes serve as monitoring and control electrodes in exposed areas which have to be anodically cleaned in the course of operation. Ag-AgCl electrodes are used to check these reference electrodes. 

Three types of anodic protection can be distinguished (1) impressed current, (2) formation of local cathodes on the material surface and (3) application of passivating inhibitors. For impressed current methods, the protection potential ranges must be determined by experiment (see information in Section 2.3). Anodic protection with impressed current has many applications. It fails if there is restricted current access (e.g., in wet gas spaces) with a lack of electrolyte and/or in the... 

Current methods for removing sulfur from the hydrogen sulfide gas streams are typically a combination of two processes the Claus Process followed by the Beaven Process, SCOT Process, or the Wellman-Land Process. 

The A -fluoroamide reactants were initially prepared by fluorination of amides with fluoroxytnfluoromethane [63 Current methods involve the direct fluorination of amide reagents with elemental fluorine under a variety of conditions [48. 64, 65, 66, 67, 68, 69, 71, 72, 73, 74, 76, 81. 82] (Tables 3a and 3b)... 

Tesla arrived in New York in 1884 and was hired by Edison. Edison understood Tesla s ability but remained unconvinced by his new employee s insistence on the use of alternating current for electrical power transmission. Nevertheless, Tesla accepted his assignment to work on improving Edison s direct-current method, which was then in use. Working long hours Tesla increased the system output and asked Edison for a 50,000 bonus, which Tesla understood he was to receive. Edison refused, claiming that the bonus had only been a joke. Tesla quit Edison s employ, and thereafter relations were strained between the two men. 

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