Current, electrical collector

The bipolar junction transistor (BIT) consists of tliree layers doped n-p-n or p-n-p tliat constitute tire emitter, base and collector, respectively. This stmcture can be considered as two back-to-back p-n junctions. Under nonnal operation, tire emitter-base junction is forward biased to inject minority carriers into tire base region. For example, tire n type emitter injects electrons into a p type base. The electrons in tire base, now minority carriers, diffuse tlirough tire base layer. The base-collector junction is reverse biased and its electric field sweeps tire carriers diffusing tlirough tlie base into tlie collector. The BIT operates by transport of minority carriers, but botli electrons and holes contribute to tlie overall current. 

An ion beam causes secondary electrons to be ejected from a metal surface. These secondaries can be measured as an electric current directly through a Faraday cup or indirectly after amplification, as with an electron multiplier or a scintillation device. These ion collectors are located at a fixed point in a mass spectrometer, and all ions are focused on that point — hence the name, point ion collector. In all cases, the resultant flow of an electric current is used to drive some form of recorder or is passed to an information storage device (data system). 

Ions arrive at one end of each element of a multipoint collector and trigger a cascade of electrons, which moves toward the opposite end and is detected electronically. The resulting electric current corresponds to the ion current. 

A carbon rod is used as a current collector for the positive electrode in dry cells. It is made by heating an extruded mixture of carbon (petroleum coke, graphite) and pitch which serves as a binder. A heat treatment at temperatures of about 1100 °C is used to carbonize the pitch and to produce a solid structure with low resistance. For example, Takahashi [23] reported that heat treatment reduced the specific resistance from 1 Q cm to 3.6xlO"1Qcm and the density increased from 1.7 to 2.02 gem- 1. Fischer and Wissler [24] derived an experimental relationship [Eq. (1)] between the electrical conductivity, compaction pressure, and properties of graphite powder ... 

The main criteria for the selection of the current collector material in a central sulfur cell or for the cell case material in a central sodium cell are corrosion resistance to sulfur and sodium polysulfides, good electrical conductivity, and low costs. This cost argument has led to coated materials which have been compared with nickel—chromium alloys (Inconel 600). 

Now let us consider a model for a SC device that comprises two electrodes (anode and cathode), each of them being electrically connected to a current collector fabricated of A1 foil. Let two of such collectors have a certain thickness of SAi- As an electrode material, an activated carbon powder is considered below. Anode and cathode are interposed with a separator of thickness Ss. The electrodes and separator are impregnated with electrolyte. In this paper we mostly focus on the optimization of SC performance by varying the electrode thickness, while some other effects will briefly be considered in the next section. 

Now an equivalent circuit, which takes into account both the ion transport along the TC and the charge transfer through the carbon electrode material to the current collector, may be represented as in Fig. 2, wherein N = a(c)/4r, Cm and Rm are the total NP capacitance and resistance in a unit electrode volume (defined here as a product of a unit electrode area and the tier thickness), Re is the electrical resistance of an electrode in the same unit... 

The main components of a PEM fuel cell are the flow channels, gas diffusion layers, catalyst layers, and the electrolyte membrane. The respective electrodes are attached on opposing sides of the electrolyte membrane. Both electrodes are covered with diffusion layers, and the flow channels/current collectors. The flow channels collect current from the electrodes while providing the fuel or oxidant with access to the electrodes. The gas diffusion layer allows gases to diffuse to the electro-catalysts and provides electrical contact throughout the catalyst layers. Within the anode catalyst layer, the fuel (typically H2) is oxidized to produce electrons and protons. The electrons travel through an external circuit to produce electricity, while the protons pass through the proton conducting electrolyte membrane. Within the cathode catalyst layer, the electrons and protons recombine with the oxidant (usually 02) to produce water. 

CHO+, which reacts with water formed in the flame to form H30+, allowing a measurable electrical current to flow across an electrode gap. A schematic representation of an FID is shown in Fig. 14.7, showing the fuel and oxidant flows, flame tip, location of the flame and collector electrode. Like the carrier gas, the fuel (hydrogen) and oxidant (air) gases must be highly pure and carefully flow controlled. For each GC, the manufacturer provides recommendations. 

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