Testing and Identifying Metals

Summary This chapter describes tests that verify the properties and quality of as received materials. These requirements may he referenced in specifications and performed as checks to prevent materials mix-ups. Types of identification markings used on products are also described. 

Many types of nondestructive, leak, corrosion evaluation and mechanical tests may be used to establish and verify quality requirements of the materials specification. In addition, identification markings enable materials to be checked for specification conformance. Field identification methods must be used when all else has failed, but their limitations must be understood. 

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The unit starts with a survey of the surroundings in which students familiarise themselves with the names, physical properties and uses of common metals. The use of symbols to represent metals is also introduced. Discussion of the physical properties which metals have in common then leads to the idea that different metals can be identified by their chemical properties. Students complete simple qualitative tests on known metals and use these tests to identify metals in common objects. 

Obtain a splint that has been soaked in a solution imknown to you. Perform the flame test and identify the imknown metallic element. 

Adds.—A free acid may be at once identified by its solubility in a holution of sodium carbonate and by being reprecipitated by concentrated hydrochloric acid. If a metal has been dis-coveied in the piehminary examination, a careful examination must be made for an organic acid. As the substance is insoluble ill water the metal will probably not be an alkali metal. Boil the substance with sodium carbonate solution. The sodium salt of the acid passes into solution and the metallic carbonate IS precipitated. Filter boil the filtrate with a slight excess of nitric acid, add excess of ammonia and boil until neutral, tests may then be applied in order to identify one of the common acids and the ni.p. determined but beyond this it is impossible to carry the investigation in a limited time. 

Mercury is a classical test to identify heterogeneous catalysts (bulk metal or colloids) due to its ability to poison metal(O) heterogeneous catalysts by formation of amalgam or adsorption on the metal surface [23]. If the catalytic activity remains unaffected when mercury is present, this fact represents an evidence for a homogeneous catalyst. But mercury can induce side reactions [23c] and also react with some molecular complexes [23c,24]. Consequently, the results obtained with mercury are not enough to conclude about the catalyst nature. From a practical point of view, it is important to use a large excess of Hg(0) with respect to the catalyst to favour the contact with it. 

The catalysts which have been tested for the direct epoxidation include (i) supported metal catalysts, (ii) supported metal oxide catalysts (iii) lithium nitrate salt, and (iv) metal complexes (1-5). Rh/Al203 has been identified to be one of the most active supported metal catalysts for epoxidation (2). Although epoxidation over supported metal catalysts provides a desirable and simple approach for PO synthesis, PO selectivity generally decreases with propylene conversion and yield is generally below 50%. Further improvement of supported metal catalysts for propylene epoxidation relies not only on catalyst screening but also fundamental understanding of the epoxidation mechanism. 

In related work a library of 1,458 peptide ligands and various metal salts was tested in hydrolysis reactions of (p-nitrophenyl)phosphates.35 An active substructure composed of polymer-bound histidine in combination with Eu3+ was identified by further dissecting the original hit structure. It needs to be pointed out that catalytically active polymer beads can also be tested for catalytic activity using IR-thermography. In a seminal paper this was demonstrated using 7,000 encoded polymer beads prepared by split-and-pool methods, specifically in the metal-free acylation of alcohols.36... 

Up to now, the sdB/sdOB stars, the classical sdOs and the extremely helium-rich luminous sdOs have been analyzed for the most important (and accessible) metal abundances. The analyses usually require extensive non-LTE line formation calculations to solve the statistical equilibrium in detailed model atoms simultaneously with the radiative transfer equations for all relevant frequencies. With the advent of computer codes based on modern powerful solution algorithms (Auer and Heasley, 1976 Werner and Husfeld, 1985) it has now become possible to test (and eventually remove) approximations necessary in older computations. This and the availability of improved atomic data make the non-LTE predictions more reliable, and obstacles in obtaining accurate abundance determinations come now mainly from the observational side where high-quality spectra are needed to identify and to measure weak... 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

Qualitative chemistry is an area of chemistry concerned with identifying substances. In Activity 9.1 you will perform a qualitative analysis to detect the presence of certain ions that, in turn, may reveal an art forgery. The ions could come from paints that were not available at the time of the artwork. In this qualitative analysis, metal ions (cations) and nonmetal ions (anions) are reacted with solvents and with each other. Then the cations and anions present are identified by the products produced. In addition, flame tests and pH determinations are used to identify ions. Qualitative analysis is an engaging opportunity for you to develop experience with chemical change and review solubility principles. Nowadays, however, most of the time a chemist analyzes a substance to detect ion content using quantitative analytical computerized instruments. 

Detection of hidden toxicants (those that do not express their toxicity because of the presence of a second toxicant) can be one of the most difficult aspects of TIE testing and can be difficult to identify when ammonia is the main toxicant (U.S. EPA, 1993b). Ammonia toxicity is attributable to the free or un-ionized (NH3, N) form as opposed to the ionized (NHfy, N) species (Thurston et al., 1981). The relative concentration of un-ionized ammonia increases proportionately with pH and water temperature. Although toxicity due to ammonia can be observed in a variety of effluents, it is commonly observed in effluent associated with metal mining and municipal discharges (Novak et al., 2002 U.S. EPA, 1999). Because of its ability to mask the presence of other toxicants, it may be more effective to address toxicity due to ammonia before proceeding with a full Phase I TIE. The approach would include the use of multiple species with differing sensitivities to ammonia (e.g., fish... 

The halides of all the metals except silver, lead, mercurous mercury, and cuprous copper are soluble in water, but with the ions of these metals, the halide ions give characteristic precipitates. The precipitates are valuable as tests for identifying either the halogens or the metals in qualitative analysis. 

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