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X-Ray Diffraction Analysis of

Lipstick and Gunpowder Samples

Raheem Balogun ca3rbalogun@yahoo.com

Samantha Berstler berstlers@yahoo.com

Brian Kutsop kutsop2@aol.com

Abstract Using polycrystalline x-ray diffraction (XRD), we analyzed the chemical components of lipstick and gunpowder. Our three lipstick samples, although from the same manufacturer, were processed slightly differently. After obtaining an experimental pattern from the lipstick sample using a rotating Philips Expo diffractometer, we used the Philips HighScore computer program to compare our diffraction pattern with those from the International Center of Diffraction Data (ICDD). With this program, we were able to identify four distinct phases in each sample, representing about 98-99% of their crystalline material. We were unable to account for a small portion of data, but this represented less than 1% of the lipstick’s composition. As we expected, the three samples had a high degree of chemical similarity. However the XRD process was sensitive enough to identify small differences both in terms of trace compounds and in terms of the relative percent composition of the phases. To analyze the black powder, we repeated the same method. Like with our lipstick samples, we used the Philips HighScore program to identify its components; we successfully found its major phase and were able to list six other possible compounds present. However, our smokeless gun powder sample lacked a sufficiently crystalline character needed for XRD, and we were unable to generate substantial data about it.

1 Introduction Our experiment demonstrated how the technique polycrystalline x-ray diffraction (XRD) can be used to determine such information. By shooting an x-ray beam through a sample and then comparing the intensity value of the deflected light with the angle of the incident beam, XRD analysis determines the distance between planes of atoms in a compound. When Sir W. H. Bragg

and his son first used this technique in 1913, they were able to create a model of simple crystalline compounds like table salt, NaCl. Now, chemists have amassed huge databases of the unique diffraction patterns for countless compounds. When powder mixtures are analyzed, computers can match the complex patterns generated during the XRD analysis with known patterns from these databases. Chemists continue to use XRD precisely because it identifies the crystalline

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components of mixtures quickly, easily, and accurately. XRD is an extremely valuable tool for chemists interested in studying the makeup or structure of the potentially new compounds they have created. Drug companies frequently use XRD to analyze their new products because, if they can find even a slightly unique variation present, they are eligible to apply for a patent. Commercial manufacturers send various processing batches to labs for XRD analysis in order to obtain information about why their products react a certain way or how the companies can more easily mass-produce their wares. Finally, forensic scientists are able to use XRD analysis to identify the unique diffraction pattern of the commercial substance in question. After obtaining a subpoena, they can then use companies’ private diffraction databases in order to identify the manufacturer, product, and even batch number of the substance. Sometimes, this information can prove invaluable for detective work. In this paper, we present the basic theory and process of polycrystalline XRD analysis. We then discuss how our data was interpreted and analyzed to reveal important, and possibly

hidden, information about the chemical composition of the samples. 2 Background X-ray diffraction (XRD) is a nondestructive analytical process in which substances are penetrated by parallel x-ray beams. The technique is generally limited to crystalline materials or mixtures with a large degree of crystalline or periodic character. But since any substance whose constituent atoms, molecules, or ions are arranged in a repeating three-dimensional pattern is considered crystalline, most solids can be analyzed using XRD. Even seemingly non-crystalline substances like chocolate, cookies, or lipstick are often periodic enough to be successfully analyzed. The XRD process requires three major steps: creating x-ray radiation, aiming the radiation at the sample, and then collecting the reflected radiation using a detector. 2.1 The Creation of X-rays Fundamentally x-rays are a form of electromagnetic radiation, exactly identical to visible light except for x-rays’ higher frequency and smaller wavelength. Although technically any entity with wavelike

Figure 1: Cross-section of a sealed x-ray tube [1]

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characteristics can be used for diffraction—including all electromagnetism and particles like neutrons and electrons––x-rays are particularly useful for two reasons. First, their high frequency indicates that they possess high energy and can easily pass through most macroscopic objects, and more importantly, x-rays’ wavelength is in the range of 0.5 – 2.5 Angstroms [1]. Since the distance between atomic layers in most compounds is also of a comparable size, x-rays are the most logical form of electromagnetic radiation to use. Generally, these waves are formed in the laboratory using simple x-ray tubes. An example is shown in Figure 1 on the previous page. The main component of an x-ray tube is a tungsten filament; tungsten is ideal for its high melting point, large number of electrons, and low eletronegativity. Large electric currents, usually about 40 kilovolts, are then sent through the filament, causing it to emit electrons. Thus, in order to create a constant flow of electrons, a stable current must always be present. For this reason, most diffractometers often have their own generators. The electrons created by the current are then propelled forward by the anode that surrounds the filament. They travel rapidly toward the metal cathode, usually made from copper. During this violent collision and rapid deceleration, most of the electrons’ energy is converted into heat. This eventually creates high temperatures in the tube, and the opposite side of the copper target must be cooled by a continuous flow of water in order to keep it from melting. However when the electron strikes the target, it transfers a small degree of energy to the electrons in the copper atoms. These electrons are excited to a higher energy level, become unstable, and then quickly return to ground

level. In the process, they emit energy in the form of x-ray radiation in all directions. 2.2 The Diffraction Process For these x-rays to be considered useful, they must be focused at the sample. Therefore the x-ray tube has a small window, usually made from Beryllium, which allows only x-rays moving in the same direction to exit the device. The beams then pass through a Soller slit. Generally made from many closely-spaced pieces of foil, the slit ensures that only parallel x-rays waves continue toward the sample. The parallel x-rays continue toward the sample at some incidence angle. They enter the sample, but the majority of the waves pass directly through it, unaffected. Some of the waves, however, do reflect off the various planes of atoms. The diffraction process itself indicates why crystalline character is necessary. When diffraction occurs, x-rays reflect symmetrically about the line perpendicular to the planes of diffraction. Because the planes are separated by a certain amount of space, the x-rays that reflect off lower planes will have to travel a longer distance than those that reflect at planes near the surface. (See Figure 2 on the following page) If this longer distance is equal to an integral number of wavelengths, then the periodicity of the waves will remain in phase after diffraction and interfere constructively, therefore increase the intensity of the beams. Otherwise, the once parallel waves will be out of phase after diffraction and experience destructive interference, thereby decreasing the intensity. These properties are summarized by Brag’s equation:

nλ = 2dsinθ where n equals an integer, λ equals the wavelength of X-ray beams, d equals the

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Figure 2: This is the derivation of Bragg’s Law. Constructive inference occurs only when:

nλ = AB + BC, AB = BC nλ = 2AB sinθ = AB/d, AB = dsinθ nλ = 2dsinθ, l = 2dhklsinθhkl [2]

distance between atomic planes, and θ equals the angle of incidence. In other words, an integral number of wavelengths (nλ) is equal to the extra distance traveled by another x-ray (2dsinθ). XRD is all about finding at the angles at which constructive interference creates large intensities. Because this occurs much less often than destructive interference, sudden peaks in intensity can be used to derive key information about the substance being tested, such as an element’s structure or a compound’s constituents. 2.3 Detection of Diffracted X-rays Finally, a detector must be able to measure the intensity of the reflected x-rays beams. Generally the detector has some way to “count” the photons striking it; this is then sent to a computer as a number with an

arbitrary unit. The simplest way to accomplish detection is to use photographic film. When x-rays hit the film, they cause it to glow. Photons with a great intensity create a brighter region than those with a lesser intensity. Computers can now read the film and convert intensity of each pixel to a quantifiable number. Charge-coupled device (CCD) detectors have also become increasingly popular. These proportional counters use a metal cylinder, usually made from a second-row transition metal, which is filled with vertical rods and a quenching gas. When x-rays strike the metal rods, the photoelectric effect creates a voltage difference. The difference is read and recorded by the computer monitoring the system. Finally, the quenching gas resets the voltage in the vertical bars, which can then be used to record more data. 3 Method We obtained three similar lipstick samples from a single manufacturer and two distinct types of gunpowder, black powder and smokeless gun powder. (See Figure 3 on the following page.) The lipstick required rudimentary sample preparation. We removed a small portion of the lipstick from the tube and placed it on the center of a small, 10 mm metal disc. We then placed another disc, which had a hole in the middle, over this disc so that the lipstick was neatly contained. To ensure that the sample was flat, we used a glass slide to flatten and then wipe away the excess lipstick. We then loaded our three experimental samples, along with a known silicon-based polymer, into the Philips Expo Machine. We programmed this diffractometer to use fairly industry-standard settings: the electric

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generator created an electrical current at 45kV and 40mA. The x-ray tube’s anode was made from copper. When the x-rays exited the tube, they passed through a divergence slit that blocked all x-rays except those in a 0.9570° range. Before the x-rays were detected, they passed through another receiving slit that was .3 mm in length. Using the computer, we entered the parameters we wanted for our experiment. Since diffraction is ineffective at both very low and very high angles, we only programmed the diffractometer to angle x-rays at 2θ values between 5° and 100° (exclusive). We set the step size at every 0.02°2θ, and at this position data then was recorded for 1 second. The diffractometer scanned the sample continuously and throughout the experiment rotated the sample, thus increasing its randomness. The silicon control sample was analyzed first. We observed that its experimental data matched its known pattern, and thus we verified that the machine was properly calibrated for our samples. The machine then loaded the lipstick samples.

In order to comply with the parameters we set, the diffractometer tested each sample for 1 hour and 20 minutes. Thus we allowed the machine to run overnight in a secure room. After the diffraction data collection was complete, we used the Philips HighScore program to indentify the phases in the lipstick. The computer automatically generated a graph of the 2-theta incidence angle versus intensity. Present on this graph were peaks, which were indicative of d-spaces. Each compound’s unique XRD pattern consists of a number of peaks at certain locations and of certain sizes. We removed some of the background noise and normalized our graph until we obtained an appropriate number of recognizable peaks (typically a quantity between 75 and 125). The computer program then matched the peaks in our pattern to known patterns in the International Center of Diffraction Data (ICDD) database from 2003. This generated a list of possible compounds present, based on the peak size and height, in order of probability. We programmed the ICDD to ignore compounds containing noble gases, lanthanoids, or actinoids since such elements would not be found in commercial lipstick.

Figure 3: On the left appears an image of one grain of smokeless gunpowder. On the right appears an image of three grains of black powder. Each sample is shown at a magnification of 600x.

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After the computer returned its results, we manually analyzed this list by checking to see if (1) the compound was a possible, logical component of lipstick and (2) the peaks of the components matched the most important peaks of our graph. In this way we indentified the phases of the lipstick. The powder gunpowder samples proved trickier to analyze. At first we repeated the procedure we used with the lipstick. This proved sufficient for the black powder sample. However the smokeless gunpowder, which we could not easily grind, was placed on the slide in irregular clumps. We even tried to create an acetone monolayer over it, but this combination of factors created such high background noise that the diffraction pattern was useless. We then decided to use another diffractometer with an air detector and more powerful rotating anode generator, the Enraf-Nonius FR571. Our team could more easily prepare the sample for this type of device. We placed a tiny portion of gunpowder on a thin capillary. The capillary was held in place between the x-ray tube and the detector. Since we knew that we were looking for potassium nitrate, we only scanned between 5° and 55°. Using the Philips HighScore program, we repeated our basic phase identification method with the two samples of gunpowder. 4 Results As we expected, the lipstick samples were similar but not identical. Lipstick sample 39 was composed of 36.6% synthetic Barite (BaSO4), 21.9% Paraffin ((CH2)x), 19.1% Anatase (TiO2), and 22.4% Muscovite (Al3Si3O10). Lipstick sample 40 also contained 33.5% Barite and 19.3% Muscovite, but we also found 19.9% synthetic Anatase and traces of synthetic Hematite (Fe2O3) and

Aluminum hydroxide Al(OH)3. Again, sample 41 contained 40.0% synthetic Barite, 17.6% Paraffin, and 18.7% Anatase but also 23.8% dehydroxylated Muscovite. These percentages are based on the normalized score the computer assigned to each compound; the score was based on the probability that the compound was in the sample. This is not a precise measurement of the percent composition of the lipstick, but the numbers are useful for comparing relative percentages among the samples. It is evident, for example, that barite is found in substantially different quantities in all three samples. See the figures 4 – 7 in the appendix for 2θ versus intensity graphs for each lipstick sample. The red lines above the graphs represent recognizable peaks, and the lines topped with black represent those for which we were unable to account. The gray bars below the graphs illustrate the peaks that coincide with the PDFs of the substances our team determined were in the lipstick sample. Figure 7 compares the diffraction patterns of the three samples. The graphs’ high degree of similarity reveals the lipsticks’ similar composition. Nonetheless, small differences in the patterns exist. XRD analysis is sensitive enough to use these differentiate between the three compositions. For each sample, all but one or two major peaks were identified. These peaks represented trace elements that were present in the lipstick at only about 1% levels. Finally, the base curve of the three graphs indicates the quantity of organic or non-crystalline material in the samples (probably present as oil in the lipstick). Sample 39 had the largest base curve followed by sample 40 and sample 41; this indicates that sample 39 was also probably the most liquid in character. Our first gunpowder sample, the smokeless gunpowder, proved to have such little

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crystalline characteristic that we were unable to collect sufficient data about it. The diffraction pattern yielded background noise, one main broad peak, and finally only background noise. Thus we could not analyze the gunpowder. As shown in Figure 8, the diffraction pattern of the gunpowder indicates a lack of crystalline character. Conversely, the black powder produced a graph with peaks, as we expected. However we assumed that the gunpowder’s broad peak was caused by the presence of an amorphous polymer such as polyethylene. Furthermore, we were able to identify a small second peak at about 12°2θ (6.9Å d-spacing). Since polymers generally have a 4.1Å d-spacings (peak at 22°2θ), this means that the powder’s polymer matrix may contain an intercalated oxidizer such as Nitrate. Although the black powder analysis yielded an acceptable graph, indicating a reasonable level of crystalline character, we had difficulty accurately identifying its major phases. This was probably due to its irregularity on the glass slide, which may have created nonrandom absorption patterns. We successfully identified Niter (KNO3) as a major component. Other possibilities include elemental Sulfur (S8), Cesium gold oxide (Cs3AuO), Lithium nitride (Li2.94N), Sodium boron hydride (NaBH4), Anatase (TiO2), and P-nitrotoluene (C7H6NO2). 5 Related Work In a 2007 article in Forensic Science Communications, Johny T. Abraham, S. K. Shukla, and A. K. Singh argued that x-ray diffraction is such an important and accurate tool that the FBI should consider compiling a database of diffraction data [3]. Specifically they highlighted the problems of identifying lipstick smears and suggested that the government focus on compiling lipstick

diffraction patterns for potential future reference. 6 Conclusion Using the Philips diffractometer, we studied three samples of lipstick and two samples of gunpowder. We studied a graph of the 2-theta angles of the incident beam versus the intensity of the reflected light, two quantities that can be related via Bragg’s Law. Finally we used the Philips HighScore program to match our experimental results with known diffraction patterns from the ICDD. Our XRD analysis successfully identified four phases of our lipstick samples, representing 98-99% of their crystalline composition. We were able to identify Nitrate and a few other possible components in black gunpowder. Although we were not able to analyze the smokeless gunpowder using XRD, we were able to surmise its general composition. Our work demonstrates the usefulness of XRD. By identifying key components of seemingly identical substances, XRD analysis can prove an invaluable tool for chemists, manufacturers, and forensic scientists. 6 Acknowledgements We would like to thank Dr. Thomas Emge of Rutgers University and Omodunni Titi Osunfisan for their guidance and assistance throughout this project. We would also like to thank the NJ Governor’s School of Engineering and Technology, especially Donald M. Brown, Director, and Blase Ur, Program Coordinator. Much appreciation goes to Rutgers University School of Engineering, including Dr. Yogesh Jaluria, Outgoing Interim Dean, Dr. Thomas Farris, Dean, and the NJ Governor’s School Board of Overseers. Finally, we would like to acknowledge our 2009 program sponsors: Rutgers University, the Rutgers University

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School of Engineering, the Motorola Foundation, Morgan Stanley, PSEG, Silver Line Building Products, and the families of 2001-2008 program alumni. References [1] B. D. Cullity and S. R. Stock. Elements

of X-ray Diffraction, 2001. [2] J. H. Reibenspies. “Lecture Notes,”

2009. [3] J. T. Abraham, S. K. Shukla, and A. K.

Singh. Forensic Science Communications, April 2007.

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Appendix

Figure 4: 2θ (position) versus intensity (counts) graph for lipstick sample 39

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Figure 5: 2θ (position) versus intensity (counts) graph for lipstick sample 40

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Figure 6: 2θ (position) versus intensity (counts) graph for lipstick sample 41

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Figure 7: Comparison of the three lipstick diffraction patterns

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Figure 8: 2θ versus intensity graph for the smokeless gunpowder (red) and the black powder (blue)