Metal replacement strip

In the field of electrowinning and electrorefining of metals, titanium has an advantage as a cathode, upon which copper particularly can be deposited with finely balanced adhesion that allows the electrodeposited metal to strip easily when required. Titanium anodes are also being employed as a replacement for lead or graphite in the production of electrolytic manganese dioxide. 

Some polymers (PEG or PEG-like) have low cloud points (the critical solution temperature) in water. If these polymers support the formation of an ABS, metal ion stripping by temperature programming may be possible. Rogers et al. [35] have found that UCON (a random copolymer of ethylene oxide and propylene oxide) can replace PEG-2000 and give better extraction of TcO in certain ABSs. UCON has a cloud point around 50 C and can form an ABS with salt solutions at lower salt concentrations [68]. TcO " can be extracted into the UCON-rich phase, and the UCON-rich phase can be separated, heated, and the two new phases separated again [35]. Thus, metal ions can be stripped from a polymer-rich phase directly into water. This technique shows promise, but more research is needed to define clearly the conditions necessary for a successful separation. 

Ch oline in the form of choline base (hydroxide) is a strong organic base with a pH of approximately 14. This product can have industrial apphcations where it is important to replace inorganic bases with organic materials. Ch oline base is currently used in the formulation of photoresist stripping products for use in the printed wire board industry. Dilute aqueous solutions (5%) of ch oline base that have very low concentrations of metallic ions have been utilized for apphcations in the semiconductor industry. 

X-ray diffraction patterns yield typical 1.2—1.4 nm basal spacings for smectite partially hydrated in an ordinary laboratory atmosphere. Solvating smectite in ethylene glycol expands the spacing to 1.7 nm, and beating to 550°C collapses it to 1.0 nm. Certain micaceous clay minerals from which part of the metallic interlayer cations of the smectites has been stripped or degraded, and replaced by expand similarly. Treatment with strong solutions of... 

Gas-fired water heaters use the same general method of construction, except that the elements are replaced with a burner beneath the tank. The combustion products from the burner are vented through a flue made out of the same thickness steel as the tank, that goes up through the center of the tank. To increase heat transfer from the hot flue gases to the inner wall of the flue, a baffle is inserted down the flue. This baffle is a twisted strip of sheet metal with folds and tabs on it. The folds and tabs are designed to... 

When a strip of zinc metal is added to a solution of copper(II) sulfate, the blue color slowly fades, and the zinc metal is replaced by copper metal (Figure 4-13). As copper ions in the solution are reduced to copper metal, zinc atoms are oxidized to Zn cations. This is an example of a metal displacement reaction, in which a metal ion in solution (Cu ) is displaced by another metal (Zn) by means of a redox reaction. Figure 4-13 also shows molecular views of this displacement reaction. 

Focal plane detectors are used primarily to detect ions separated in space by, for example, magnetic sector analyzers (see Section 2.2.2). The objective of an ideal focal plane detector is to simultaneously record the location of every ion in the spectrum. In many ways the photoplate (see Section 2.3.1) is the original focal plane detector, but it has today been more or less replaced with designs that rely on EM detectors (see Section 2.3.3). A common arrangement is to allow the spatially disperse ion beams simultaneously to impinge on an MCP (see Section 2.3.3.2). The secondary electrons generated by the ion impacts then strike a one- or two-dimensional array of metal strips and the current from the individual electrodes is recorded. A tutorial on the fundamentals of focal plane detectors is found in Reference 283. Reference 284 provides a relatively recent review of MS detector-array technology. 

In your previous chemistry course, you compared the reactivities of metals. You may recall that, when a piece of zinc is placed in an aqueous solution of copper(II) sulfate, the zinc displaces the copper in a single displacement reaction. This reaction is shown in Figure 10.1. As the zinc dissolves, the zinc strip gets smaller. A dark red-brown layer of solid copper forms on the zinc strip, and some copper is deposited on the bottom of the beaker. The blue colour of the solution fades, as blue copper(ll) ions are replaced by colourless zinc ions. 

Zinc metal reacts spontaneously with an aqueous solution of copper sulfate when they re placed in direct contact. Zinc, being a more reactive metal than copper (it s higher on the activity series of metals presented in Chapter 8), displaces the copper ions in solution. The displaced copper deposits itself as pure copper metal on the surface of the dissolving zinc strip. At first, the reaction may appecir to be a simple single replacement reaction, but it s also a redox reaction. 

FIGURE 12.2 (a) When a strip of zinc is placed in a beaker of copper(II) sulfate solution, copper is deposited on the zinc and the blue copper(II) ions are gradually replaced by colorless zinc ions, (b) The residue in the beaker is copper metal. No more copper ions can be seen in solution. See Fig. 12.3 for an atomic view of the processes involved. 

When it is desirable to prevent corrosion of iron, a new anode, such as a zinc (Zn) or magnesium (Mg) strip, is connected to the surface of the iron. These metals are stronger reducing agents than iron and will be more easily oxidized. As oxidation occurs, the zinc or magnesium, rather than the iron, will furnish electrons. These sacrificial anodes will erode instead of the iron. They must be replaced periodically, but the iron will remain intact. (See Figure 6.12.)... 

In the 1980s, zinc precipitation was replaced by a method involving the passing of the solution over activated carbon to adsorb the precious metals, which are then stripped from the charcoal by a hot caustic solution. Electrowinning removes the precious metals from this solution, depositing them on the cathode. One benefit of this process is that the filtration or deareation steps of the zinc precipitation are not required. Thus the environmental hazard of the zinc salts is eliminated. 

When copper or iron strips were placed in water after long exposure to benzyl bromide vapors, they showed much greater dissolution than unexposed strips (Table IV) (97). Replacement of water by deuterium oxide as the reaction medium yielded CHjD as the primary gaseous products (97). While this would arise from the hydrolysis of a metal-methyl bond ... 

The various steps that characterize the transport of metal species through SLMs can be described with the help of Figure 31.4. Step 1 The metal species, after diffusing to the source-membrane interface, react with the metal carrier, ions are simultaneously released into the feed solution (counter-transport, acidic carrier) or ions accompany the metal ions into the membrane (cotransport, neutral, or basic carriers). Step 2 The metal-carrier complex diffuses across the membrane because its concentration gradient is negative. Step 3 At the membrane-receiver interface the metal-carrier complex releases metal ions into the aqueous phase, ions replace M ions into the membrane (counter-transport) or X ions are simultaneously released together with M ions into the strip solution (cotransport). Step 4 The uncomplexed carrier diffuses back across the membrane. 

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