Direct current power

Brown, T. andj. L. Cadick. Electrochemical Processes Need Direct Current Power, Chem. Eng, p. 127, Oct. 22, (1979). 

Galvanostatic polarisation—constant direct current power units, or banks of accumulators or dry cells used in conjunction with a variable resistance. 

A numerically controlled filament winder has been designed and constructed. The distance between the head-stock and tail-stock is six feet. Clearance between the centers emd the body of the winder is adjustable, but a specimen several feet in diameter could presently be fabricated. The mandrel and carriage are each driven by one horsepower, direct current motors with a maximum 2000 revolutions per minute. Three phase, 480 volt alternating current is transformed to a 90 volt, direct current power supply. A gear... 

The insertion is monopolar when the electrode functions exclusively as either the anode or the cathode and in this case it is connected with one of the poles of the electric source as shown in Figure 6.22 (a-f). Since the voltage for a single cell is very small (of the order of one to a few volts) several cells are usually connected in series and parallel combinations such that the overall potential drop corresponds to the available direct current power source. With bipolar insertions, however, there are a number of electrodes in each cell which function as anodes on one side and as cathodes on the other apart from the end electrodes, these are not directly connected to the electric source. 

During the separation a direct current power supply is used to provide either a constant voltage or current across the capillary. The accuracy and stability of this applied voltage or current is essential to ensure reproducible migration times. 

The power section consists of twenty cell-stack assemblies (CSAs). Each CSA contains approximately 450 individual Tuel cells, stacked one above the other. Manifolds on the CSAs direct the fuel gas to the anode side of the fuel cells and the air to the cathode side. Electrochemically. the CSAs convert the hydrogen and oxygen inlo direct-current power according to the following reaction ... 

The basic design of the iontophoretic devices is a direct current power source and two electrodes. Platinum is the commonly used material for the electrodes, since it is nontoxic, has high oxidation voltage, slow degradation, and low ion release (Figure 26.1). 

Power Supply and Process Control Unit. Electrodialysis systems use large amounts of direct current power the rectifier required to convert AC to DC and to control the operation of the system represents a significant portion of a plant s capital cost. A typical voltage drop across a single cell pair is in the range 1 -2 V and the normal current flow is 40 mA/cm2. For a 200-cell-pair stack containing 1 m2 of membrane, the total voltage is about 200-400 V and the current about... 

An electrolytic cell is similar to a voltaic cell, but there are some slight differences. One of the first differences is the source of electrons. In the voltaic cell, the source of the electrons is the spontaneous oxidation that occurs at the anode. Because no spontaneous reactions occur in an electrolytic cell, the source of electrons is a DC (direct current) power supply. The power supply forces electrons to the cathode rather than the potential of the half-reactions. The cathode in an electrolytic cell acquires a negative charge (which is opposite from a voltaic cell) because electrons are being forced onto it, while the anode takes on a positive charge (which is opposite from a voltaic cell) because electrons are being removed from it by the power supply. 

When an aqueous solution of a weak acid, HA, in a suitable container is connected to the terminals of a direct current power source (through inert platinum electrodes), electrolysis takes place. At the cathode, where reduction or the gain of electrons occurs, water dissociates and the anion A is liberated (ignoring the hydronium ion H30+) ... 

A calutron consists essentially of an intense source of uranium ions, a way to accelerate the ions to high energy within a vacuum system, and a way to collect the uranium-235 and uranium-238 ions after they have moved in separate arcs between the poles of a very large electromagnet. The components at the heart of the system are ion sources, collectors, and high-voltage, regulated direct-current power supplies (Lore, 1973 London, 1961 USDoE, 1980). 

For the purpose of this text, an operational amplifier consists of a series of solid-state components designed to have certain fimctional characteristics. A schematic representation of an operational amplifier, given in Figure 6.1(a), shows 5 leads attached to the operational amplifier. The vertical leads, marked Vs+ and Vs-, provide power to the amplifier and are connected to a direct-current power supply. The two leads on the left, termed the noninverting (-I-) and the inverting (—) input, have potentials V+ and VL, respectively. The output potential is Vq. 

Although modern electrophoresis equipment and systems vary considerably in form and degree of automation, the essential components common to all systems (Figure 5-1) include two reservoirs (1), which contain the buffer used in the process a means of delivering current from a power supply via platinum or carbon electrodes (2), which contact the buffer, and a support medium (3) in which separation takes place connecting the two reservoirs. In some systems, wicks (4) may connect the medium to the buffer solution or directly to the electrodes. The entire apparatus is enclosed (5) to muiimize evaporation and protect both the system and the operator. The direct current power supply sets the polarity of the electrodes and defivers current to the medium. 

Equation (3) and (4) mean that the supply of the energetic e is needed to split water. This is the basic principle of water-electrolysis. The PEMFC is just the reverse operation of the SPE. Hydrogen fuel is decomposed into 2e and 2H+ by the catalytic cathode. The protons pass through the solid polymer (electrolyte) and arrive at the anode (A) to react with the electrons and the supplied oxygen. Then, water is produced. The electrons come to A via the external resistance. This fuel cell generates, ideally, about 1 V-direct current power. A stack of the cells is constructed to give the output power with, for example, 25 kW, which is set together to drive the vehicles. 

The principle of an impressed current system involves the supply of a protective current from some direct current power source, e.g. storage batteries, rectifiers or d.c. generators, through an auxiliary anode. Fig. 15.4 illustrates the arrangement. 

Cathodic protection (CP) is an electrical method of mitigating corrosion on metallic structures that are exposed to electrolytes such as soils and waters. Corrosion control is achieved by forcing a defined quantity of direct current to flow from auxiliary anodes through the electrolyte and onto the metal structure to be protected. Theoretically, corrosion of the structure is completely eliminated when the open-circuit potentials of the cathodic sites are polarized to the open-circuit potentials of the anodic sites. The entire protected structure becomes cathodic relative to the auxiliary anodes. Therefore, corrosion of the metal structure will cease when the applied cathodic current equals the corrosion current. There are two basic methods of corrosion control by cathodic protection. One involves the use of current that is produced when two electrochemically dissimilar metals or alloys (Table 19.1) are metallically connected and exposed to the electrolyte. This is commonly referred to as a sacrificial or galvanic cathodic protection system. The other method of cathodic protection involves the use of a direct current power source and auxiliary anodes, which is commonly referred to as an impressed-current cathodic protection system. Then cathodic protection is a technique to reduce the corrosion rate of a metal surface by making it the cathode of an electrochemical cell [3]. 

In the case of EMM, the workpiece acts as the anode and the tool acts as the cathode, i.e., two electrodes immersed in an electrolyte solution and connected by an external direct current power source. The gap between the tool and the workpiece, which is known as the lEG, is filled up with... 

Direct-current power supply (a regular power supply used for agarose gel electrophoresis will do), capacitor-discharge unit (for delivery of an exponentially decaying pulse for circuit, see Fromm et al., 1985), and stainless-steel electrodes (6-mm gap, 3 X 9-mm electrode surface area) were homemade. 

When charging a capacitor, with a capacitance C and an internal resistance R, by connecting it to a direct-current power supply of voltage E, at each instant the current that flows in the circuit is given by ... 

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