Electrical conductivity cells

In general, it can be said that, often of necessity, the detector cell may be relative large with a low aspect ratio and thus, would theoretically produce serious band dispersion. In practice the predicted dispersion is reduced by deign of the inlet and outlet tubes, as discussed above, to ensure maximum secondary flow in the cell and thus, minimize dispersion. The success of the procedure to reduce detector cell dispersion depends on the type of detector and the principle of detection. For example.it is far easier to design a low dispersion electrical conductivity cell than a low dispersion UV absorption cell. 

Methods. The differential heats of adsorption of reagents and the differential heat of their interaction on the nickel oxide surface were measured in a Calvet microcalorimeter with a precision of 2 kcal. per mole. The apparatus has been described (18). For each adsorption of a single gas, small doses of gas are allowed to interact with a fresh nickel oxide sample (100 to 200 mg.) placed in the calorimeter cell maintained at 30°C. At the end of the adsorption of the last dose, the equilibrium pressure is, in all cases, 2 torr. Duplication of any adsorption experiment on a new sample gives the same results within 2 kcal. per mole of heat evolved and 0.02 cc. of gas adsorbed per gram. Electrical conductivities of the nickel oxide sample are measured in an electrical conductivity cell with platinum electrodes (1) by a d.c. bridge. 

Fio. 6.47. Electrical conductivity cell (a) section through flow-through conductivity cell showing arrangement of electrodes (6) screw-in cell inserted in pipeline... 

The nature of the tracer dictates the detection system. For the liquid phase, quite often the tracers (e.g., NaCl, H2S04, etc.) are such that the detection probe is directly inserted into the reactor and continuous monitoring of the concentration at any fixed position is obtained by means of an electrical conductivity cell and a recorder. In this case, no external sampling of liquid is necessary. If the tracer concentration measurement requires an analytical procedure such as titration, etc., sampling of the liquid is required. For the solid phase, a magnetic tracer is sometimes used. The concentration of a solid-phase tracer can also be measured by a capacitance probe if the tracer material has a different dielectric constant than the solid phase. In general, however, for solid and sometimes gas phases, some suitable radioactive tracer is convenient to use. The detection systems for a radioactive tracer (which include scintillation counters, a recorder, etc.) can be expensive. Some of the tracers for the gas, liquid, and solid phases reported in the literature are summarized in Table 3-1. 

For the analysis of ammonium, the sample carrier stream consists of 10 mM NaOH + 0.2 M Na-citrate. This converts ammonium into NH -gas which penetrates the PTFE membrane and travels into the gas receiver stream, in this case consisting of 50 pm HCl. Here as well, an electric conductivity cell is used for the measurements. To provide a steady and impulse-free flow of the solutions, a multichannel peristaltic pump is used. The flow rates in both cases were set to approx. 

An early example of a dew point meter was developed by the British Coal Research Association (BCURA) reported by Flint [1948]. The dew point meter consists of a glass thimble located at the end of the probe inserted into the flue gas. The thimble is progressively cooled by an air stream and the surface temperature measured by means of a suitable thermocouple. The junction of the thermocouple is fused into the glass and forms one electrode of an electrical conductivity cell. When condensation occurs the aqueous acid film produced on the surface of the... 

Electrical conductivity cell. Impedance is a measure of the total opposition to the flow of a sinusoidal alternating current in a circuit containing resistance, inductance, and capacitance. Inductance and capacitance together are called the reactive part of the circuit. The changes in impedance that occur in a microbial culture can be measured by placing two metal electrodes into the culture medium and introducing an alternating potential into the circuit. 

An electrically conducting cell growth substrate is required for imaging analysis with a CAMECA IMS-3f SIMS ion microscope because the sample is held at 4,500 V in the high vacuum sample chamber of the instrument. 

Electron conduction through electrically conductive cell components. 

Two major sources of ultrasound are employed, namely ultrasonic baths and ultrasonic immersion hom probes [79, 71]- The fonuer consists of fixed-frequency transducers beneath the exterior of the bath unit filled with water in which the electrochemical cell is then fixed. Alternatively, the metal bath is coated and directly employed as electrochemical cell, but m both cases the results strongly depend on the position and design of the set-up. The ultrasonic horn transducer, on the other hand, is a transducer provided with an electrically conducting tip (often Ti6A14V), which is inuuersed in a three-electrode thenuostatted cell to a depth of 1-2 cm directly facing the electrode surface. 

Mercury cells are operated to maintain a 21—22 wt % NaCl concentration in the depleted brine and thus preserve good electrical conductivity. The depleted brine is dechlorinated and then resaturated with soHd salt prior to recycling back to the electroly2er. 

A dimensionally stable anode consisting of an electrically conducting ceramic substrate coated with a noble metal oxide has been developed (55). Iridium oxide, for example, resists anode wear experienced ia the Downs and similar electrolytic cells (see Metal anodes). 

Specific Conductance. The specific conductance depends on the total concentration of the dissolved ioni2ed substances, ie, the ionic strength of a water sample. It is an expression of the abiUty of the water to conduct an electric current. Freshly distilled water has a conductance of 0.5—2 ]lS/cm, whereas that of potable water generally is 50—1500 ]lS/cm. The conductivity of a water sample is measured by means of an a-c Wheatstone-bridge circuit with a null indicator and a conductance cell. Each cell has an associated constant which, when multiphed by the conductance, yields the specific conductance. 

In a battery, the anode and cathode reactions occur ia different compartments, kept apart by a separator that allows only ionic, not electronic conduction. The only way for the cell reactions to occur is to mn the electrons through an external circuit so that electrons travel from the anode to the cathode. But ia the corrosion reaction the anode and cathode reactions, equations 8 and 12 respectively, occur at different locations within the anode. Because the anode is a single, electrically conductive mass, the electrons produced ia the anode reaction travel easily to the site of the cathode reaction and the 2iac acts like a battery where the positive and negative terminals are shorted together. 

Almost all the methods described for the nickel electrode have been used to fabricate cadmium electrodes. However, because cadmium, cadmium oxide [1306-19-0], CdO, and cadmium hydroxide [21041-95-2], Cd(OH)2, are more electrically conductive than the nickel hydroxides, it is possible to make simple pressed cadmium electrodes using less substrate (see Cadmium and cadmium alloys Cadmium compounds). These are commonly used in button cells. 

PIa.tes, Plates are the part of the cell that ultimately become the battery electrodes. The plates consist of an electrically conductive grid pasted with a lead oxide—lead sulfate paste which is the precursor to the electrode active materials which participate in the electrochemical charge—discharge reactions. 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

C), (cmVohm geqmv) K = Ci/R = specific conductance, (ohm cm) h C = solution concentration, (gequiv/ ) Ot = conductance cell constant (measured), (cm ) R = solution electrical resistance, which is measured (ohm) and/(C) = a complicated function of concentration. The resulting equation of the electrolyte diffusivity is... 

The electrical conductivity also increases with increasing metal oxide content, due to the high mobility of the metal ions. For example several glass compositions have been used as solid electrolytes in galvanic cells in which other metal ions apart from the alkaline and alkaline earth ions have been incorporated. The electrochemical cell... 

Electrical conductivity is of interest in corrosion processes in cell formation (see Section 2.2.4.2), in stray currents, and in electrochemical protection methods. Conductivity is increased by dissolved salts even though they do not take part in the corrosion process. Similarly, the corrosion rate of carbon steels in brine, which is influenced by oxygen content according to Eq. (2-9), is not affected by the salt concentration [4]. Nevertheless, dissolved salts have a strong indirect influence on many local corrosion processes. For instance, chloride ions that accumulate at local anodes can stimulate dissolution of iron and prevent the formation of a film. Alkali ions are usually regarded as completely harmless, but as counterions to OH ions in cathodic regions, they result in very high pH values and aid formation of films (see Section 2.2.4.2 and Chapter 4). 

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