MEi Newsletter: 1996 Spring

630·365·9060

Materials Engineering, Inc.

47W605 I.C. Trail

Virgil, IL 60151

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		MEi Provides Assistance in Arson Investigations How to Read EDS Spectra MEi Involved in Local ASM Chapter MEi Speaks at CASMI Meeting 708, 312, 847, 815, 630 BINGO!
		MEi Provides Assistance in Arson Investigations Arson brings up images of a shady character with a gas can in an old warehouse. While the felonious crime of Arson has become more sophisticated, the purpose remains the same: to destroy property for gain by purposely setting a fire. The investigation.... The fire investigator makes a thorough examination of the fire site, often immediately after the fire. Through this examination, investigators can determine the location in which the fire initiated. From the evidence, the cause can usually be determined, as well as if the fire was arson or accidental. The problem... Many different incendiary devices are constantly being created in order to mislead fire investigators into thinking the fire is due to natural causes. Thanks to skilled fire investigators, experience and technological advances, the mystery of these devices and how they work is soon understood and exposed. The device... In recent years the use of thermite reactions as incendiary devices has gained popularity with arsonists because they are easily ignited with a match, burn quickly and can generate a very intense heat in excess of 4000(F. These substances are a mixture of copper oxide powders and other chemicals which can be home made or purchased commercially as products used for welding large copper bus bars together. The clue... When thermite reaction compounds are used to ignite a fire, they produce a characteristic burn pattern, and leave behind evidence. These compounds are rather unique in their chemical composition, containing common elements such as copper, iron, calcium, silicon and aluminum, but also contain more unusual elements, such as vanadium, titanium, tin, fluorine and manganese. While some of these elements are consumed in the fire, many are also left behind in the residue. The technology... MEi has conducted Energy Dispersive Spectroscopy (EDS) on minute traces of residue, identifying the presence of these chemical elements. The results, coupled with visual evidence at the scene, provide absolute certainty that thermite reaction compounds were present, indicating the fire was deliberately set, and not of natural causes. The photographs show a copper gas line where thermite reaction compounds were placed by an arsonist, causing a fire and destroying a house. EDS analysis of these samples identified the presence of chemical elements and was a key piece of evidence in determining that the fire was not an accident, but was deliberately set. Our experience... Materials Engineering, Inc., has a great deal of experience working with many insurance and fire investigators. These include registered Professional Engineers and registered Private Investigators who have been trained and educated in the field of fire investigation. Many have specialized in specific areas of fire investigation, such as Electrical Engineers with expertise in electrically initiated fires. Some of the investigators we work with have taught classes to Police and Fire departments. We have supported fire investigations with numerous laboratory tasks, including identification of chemicals present, analysis of electrical arcing, determining exposure temperature by looking for microstructural changes in metals or by knowledge of melting points. These tasks have helped fire investigators to determine if damage is the cause of a fire, or has been caused by the fire. While we are involved in a wide range of industrial, legal and insurance projects, few offer the satisfaction of supporting an arson investigation. How to Read EDS Spectra EDS is a powerful tool in identifying chemical elements in residues, particles, inclusions, corrosion products and filtrates, even if only a minute quantity is present. Contamination identification is one of the major services we provide to industry. However, we often receive phone calls from customers who need a little help in understanding exactly what 'that strange chart attached to the report' is. This article will provide an overview of EDS analysis. A little physics for background...(skip this paragraph is you don't remember your physics) In the scanning electron microscope (SEM), the sample is bombarded with electrons. Most of these electrons collide with and therefore interact with the orbital electrons in the atoms (remember the s, p,, d and f orbitals). Some of these electrons gain enough energy from the collisions to become free from their orbital. When this happens, it leaves a 'hole' on the atoms' orbital. An electron from an outer shell will jump down to the lower shell to fill the hole. This jump represents a change in energy for the electron, and so it releases an x-ray. This energy level of this x-ray is unique to the atom and is exactly the difference between the energy level of the orbitals. By measuring the energy level of this x-ray, the atom (or chemical element) can be. This is how EDS works. The EDS spectrum is a plot of energy level on the horizontal axis and counts on the vertical axis. As atoms have many different electrons that can jump between the levels, a single element has an EDS spectrum of a series of peaks, representing the jumps between the various orbital electrons. These peaks are often called the K, L, and M peaks, referring to which electron orbital shells they represent. Bigger (higher atomic number elements) atoms have higher energy levels, and will generally appear on the right side of the plot. These include iron, copper, nickel, and chromium. Smaller atoms (lower atomic number elements) have lower energy levels and will generally appear on the left side of the plot. These include chlorine, silicon, aluminum and carbon. The peaks will always be located at the same energy levels on the horizontal axis. Many of the peaks do overlap so a skilled operator will insure that he has correctly identified an element by looking for the second and third peaks for each element. While all elements will show more than one peak, if the concentration is low, multiple peaks may not be visible on the spectrum. Likewise, elements with very low atomic number, (carbon, oxygen) typically show only one peak. Most commercially available EDS analysis equipment has software which assist the user in identifying and the peaks. The first figure shows a typical EDS spectrum for a stainless steel, with peaks for iron, chromium, nickel and silicon. Notice that all the peaks are not the same height. This is due to higher concentrations of iron than chromium or nickel in stainless steel. However, the height is not always an exact measurement of concentration. Other variables in the atoms and the SEM affect peak height. EDS equipment takes into account these factors and can be used to calculated quantitative amounts of the elements. A typical application of EDS is to identify the contamination on the surface of a metal. While examining the sample in the SEM, we 'align the crossbars' on the contamination and generate an EDS spectrum. However, and the contaminant is small, the electron beam penetrates through it into the base metal. Therefore, the spectrum shows the elements present in the contamination and the base metal. You must mentally subtract out the base metal elements to know what is in the contamination. This is why we will usually publish base metal spectrum for comparison. The second spectrum is of a residue on a stainless steel component. As you can see, many peaks are present. By subtracting iron, chromium, nickel and silicon found in the first spectrum, the contamination can be identified as containing mostly chlorine, with lesser amounts of sodium and potassium and a trace of sulfur. Summary of EDS spectra interpretation 1 If the peak is present, then the element is present. 2 Peaks for a given element are always located in the same place on the horizontal axis. 3 Most elements generate more than one peak. This is normal 4 Higher peaks indicate greater concentration, but not this is not linear 5 Quantitative analysis can provide a weight percent, but use this data with caution. 6 Be sure to subtract off base metal peaks to find out what is in the contaminant. 7 Call us if you have any questions about the data in your report. MEi Involved in Local ASM Chapter This year, Bill Durako is serving as secretary for the Rockford Chapter of ASM International, and will become Vice Chairman next year. ASM International, formerly known as the American Society for Metals, has long been the largest technical society for Materials and Metallurgical Engineers. In this position, he works with the 12 member executive committee in a variety of chapter activities. One of the major activities is planning the meetings and arranging speakers. Please give us a call if you or someone from your company would like to make a technical presentation at an ASM meeting. We are always looking for interesting materials related topics and good speakers. MEi, along with Charles Kawin Company, sponsored a TV give away as an attendance prize at this year's monthly ASM meetings. By sponsoring such activities, we hope to encourage members to become more involved in the ASM chapter. We are open to consider sponsoring a similar activity with your technical society, so give us a call. We enjoy being active in technical societies because they offer a good opportunity to have technical conversations in a relaxed social environment. Through the years, the staff at Materials Engineering has been involved in ASTM, NSPE, ASME, SAMPE, TMS-AIME, ACerS, SAE, and ASM. We hope to see you there! MEi Speaks at CASMI Meeting We have an open offer to any of our customers and friends to prepare a presentation for your local technical society meeting. Just give us a call, we'll be glad to do it. Last November, Bill Durako spoke to a full house of members and guests of the Chicago Area Spring Manufactures Institute (CASMI) meeting. The meeting was one of the best attended CASMI meetings of the year, with nearly sixty people present. The title of the presentation was "Why Do Springs and Things Fail?", covering the subject of failure analysis in general, with the majority of the talk citing examples involving springs. Materials Engineering has looked at many springs through the years, dealing with failure analysis, processing problems, design issues, plating problems, hydrogen embrittlement, heat treating and corrosion issues. 708, 312, 847, 815, 630 BINGO! It is time once again to play area code bingo. With large increases in phone lines for computers and cellular phones, Ma Bell has let it be known that the 708 area code will soon be filled up, requiring new areas codes (and mass confusion). I am sure this is not news to many of you who are already dealing with these changes. Unfortunately, MEi is not immune to these changes. As of August 3, 1996, we will change to area code 630. To permit a smooth transition, we will be sending out a reminder to all of our customers as the time of change approaches.
		Next: 1996 Fall Newsletter