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<p>[QUOTE=&quot;GSDykes, post: 2253429, member: 73321&quot;]Various Methods for the Metallurgical Analyses of Coins</p><p>(In Nuce)</p><p><br /></p><p><br /></p><p>(1)</p><p><br /></p><p><font size="5"><b>SEM/EDS (Micro-Analysis):</b></font></p><p>Surface analyses, chemical analysis and imaging on a variety of materials are performed using a <a href="http://www.met-tech.com/SEM1.html" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.met-tech.com/SEM1.html" rel="nofollow"><span style="color: #000000"><b>Scanning Electron Microscope</b></span></a> (SEM). The Scanning Electron Microscope is equipped with an Energy Dispersive Spectrometer (EDS). SEM/EDS provides chemical analysis of the field of view or spot analyses of minute particles. More than 90 elements can be detected with most low-atomic number detectors using the SEM/EDS method. This micro-chemical analysis is also a NON-DESTRUCTIVE test. The equipment, takes up some space, and is quite expensive. But delivers great accuracy, and it can detect numerous metals at once. I personally, am not sure how well it works for a coin! Input invited!</p><p><br /></p><p><br /></p><p>(2)</p><p><br /></p><p>Typical <b>SPECTROGRAPHIC ANALYSIS:</b></p><p><br /></p><p><font size="5"><b> <b>(Bulk material and alloy certification):</b></b></font></p><p>An alternative to SEM/EDS, the Optical Emission Spectrometry (OES) technique utilizes a high-energy spark created across an argon-filled gap between an electrode and a sample of the material to be analyzed. The spark creates an emission of radiation from the excited sample surface with wavelengths characteristic of the elemental composition. The spectrum of radiation is separated into the distinct element lines and the intensity of each line is measured. Finally, these are precisely converted into concentration values for each element present. Typical applications involve determination of the alloying content of iron and steel, aluminum, copper, nickel, zinc, lead and many other metals and alloys. Optical Emission Spectrometry continues to be the reference technique for direct chemical analysis of solid metallic samples. The unmatched combination of accuracy, high speed, precision, stability and reliability have made it an indispensable tool for production and verification of quality metallurgical products. Since the metal to be tested must first be ground and inserted into an electrode it is obviously, DESTRUCTIVE.</p><p><br /></p><p><br /></p><p>(3)</p><p><br /></p><p><b>X-RAY FLUORESCENCE (XRF)</b></p><p><br /></p><p>Elements can absorb very specific frequencies of X-rays and, in turn, through a reshuffling of their electrons, kick out other, characteristic bands of X-rays. Xray fluorescence spectrometry utilizes this process to identify and quantify the elements found in a sample.The test is NON-DESTRUCTIVE. First, the X-rays are produced and sent to the sample. Fluorescent X-rays are then sent back to a detector, and the detector counts them. The algorithms then turn these counts into a concentration.</p><p><br /></p><p>While laboratory XRF instrumentation can be large, powerful, and imbued with complex and sophisticated competencies, the breed of portable instruments is designed to be taken to a work or research site. For the most popular of these—the handheld radar gun-like instruments—taking a measurement is essentially a matter of pointing at a sample and pulling the trigger.</p><p><br /></p><p><br /></p><p>(4)</p><p><br /></p><p><b>Optical Emission Spectroscopy (OES and AES)</b></p><p><br /></p><p>Optical emission spectroscopy (OES) or atomic emission spectroscopy (AES) are an important tool for fast and accurate elemental analysis of metals. Optical emission spectroscopy (OES) provides a non-evasive probe to investigate atoms, ions and molecules within a plasma. (AES) is a method of <a href="https://en.wikipedia.org/wiki/Chemical_analysis" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Chemical_analysis" rel="nofollow">chemical analysis</a> that uses the intensity of light emitted from a <a href="https://en.wikipedia.org/wiki/Flame" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Flame" rel="nofollow">flame</a>, <a href="https://en.wikipedia.org/wiki/Plasma_(physics)" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Plasma_(physics)" rel="nofollow">plasma</a>, <a href="https://en.wikipedia.org/wiki/Electric_arc" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Electric_arc" rel="nofollow">arc</a>, or <a href="https://en.wikipedia.org/wiki/Electric_spark" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Electric_spark" rel="nofollow">spark</a> at a particular wavelength to determine the quantity of an <a href="https://en.wikipedia.org/wiki/Chemical_element" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Chemical_element" rel="nofollow">element</a> in a sample. The wavelength of the <a href="https://en.wikipedia.org/wiki/Atomic_spectral_line" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Atomic_spectral_line" rel="nofollow">atomic spectral line</a> gives the identity of the element while the intensity of the emitted light is proportional to the number of <a href="https://en.wikipedia.org/wiki/Atom" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Atom" rel="nofollow">atoms</a> of the element. As usual in most spectrographic analysis techniques, the material tested is ground to a power, put into an electrode, or diluted with various acids and made into a plasma or spray. The light given off when &quot;sparked&quot; is measured on a or in a calibration scale. These two tests are DESTRUCTIVE.</p><p><br /></p><p><br /></p><p><br /></p><p>(5)</p><p><br /></p><p><b>COIN DRY WEIGHT AND DENSITY:</b></p><p><br /></p><p><b>Density = mass/volume </b></p><p><br /></p><p>These tests are usually the least expensive to perform. And are NON-DESTRUCTIVE. Pure metal compositions are the easiest to evaluate. But with accurate charts and prior measurement comparisons, various alloys can be perceived, or at least recognized. Density can indicate a change in the composition of a material, or a defect in a product, such as a crack or a bubble in cast parts (known as voids), for instance in coins or in bars et cetera.</p><p><br /></p><p>The production of accurate charts of various coins and their alloys -- showing each coins specific gravity, is a first step. Very little work has been done in this area of numismatics.</p><p><br /></p><p>A general rule is: The higher the temperature, the lower the density. Coins should be tested at normal room temperatures 62-75 degrees F. as well as the distilled water. Scales should be in a very calm environment, no drafts, best if inside a glass chamber! Both the buoyancy and the displacement methods are suitable for density determination on porous solids. To determine the bulk density of porous material, the sample can also be covered in a wax or latex coating or layer to prevent liquid from entering open pores.</p><p><br /></p><p><br /></p><p>Accuracy requires that the temperatures be stable, and that the porosity of the coin is evaluated, if needed. There are formulas which can be incorporated to consider/calculate the effect of the coin&#039;s pores in the specific gravity test. If a high degree of precision is required, the existing conditions must be allowed for. With care a coin could be coated with a wax to seal all pores, but this is undesirable, especially with rare coins. One can simply agitate the water to loosen the air bubbles, et cetera. Technically speaking, the weighing instrument does not show the mass of the samples–the value given in the equations–but rather the weight value for the samples in air. For more precise results, use the weight values obtained after air buoyancy correction. When using the buoyancy method, the immersion level of the pan hanger assembly is affected when the sample is immersed, which produces additional buoyancy. This must also be considered in more precise calculations. In general, density determination procedures require very careful work; it is especially important to make sure the temperature remains constant during testing. With porous material: bulk density relates to the total volume including open and closed pores – true density relates to the solid volume. Most coins have very very tiny pores, which should have a minimal effect upon the outcome. Ancient and very corroded coins may require numerous measurements and averaging to reflect the actual specific gravity.</p><p><br /></p><p>Bubbles entering the liquid when the sample is immersed can also affect results; bubbles adhering to the test piece will distort the measurement results. This can be reduced with practice, and with certain additives which can assist with breaking the H20&#039;s surface tension, and as mentioned, via agitation.</p><p><br /></p><p><br /></p><p><br /></p><p>The following link gives the formulas required, and the necessary steps to achieve very accurate specific gravity tests of various materials. These are only useful if you have a laboratory set-up. Home-made kits can work just fine, with care, and can give useful results.</p><p><br /></p><p><b><a href="http://www.dcu.ie/sites/default/files/mechanicalengineering/PDFS/manuals/De-nsityDeterminationManual.pdf" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.dcu.ie/sites/default/files/mechanicalengineering/PDFS/manuals/De-nsityDeterminationManual.pdf" rel="nofollow">www.dcu.ie/sites/default/files/mechanicalengineering/PDFS/manuals/De-nsityDeterminationManual.pdf</a></b></p><p><b><br /></b></p><p>or search Google for<b> Densitydeterminationmanual.pdf</b></p><p><br /></p><p>Wikipedia also has some good basic information:</p><p><br /></p><p><b><a href="https://en.wikipedia.org/wiki/Density" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://en.wikipedia.org/wiki/Density" rel="nofollow">https://en.wikipedia.org/wiki/Density</a></b></p><p><br /></p><p><br /></p><p>Here is a periodic table listed as per descending densities!!</p><p><br /></p><p><b><a href="http://www.science.co.il/PTelements.asp?s=Density" target="_blank" class="externalLink ProxyLink" data-proxy-href="http://www.science.co.il/PTelements.asp?s=Density" rel="nofollow">http://www.science.co.il/PTelements.asp?s=Density</a></b></p><p><br /></p><p><br /></p><p><font size="3">courtesy of Mr. Gary Dykes</font>[/QUOTE]</p><p><br /></p>

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