Comparison of Beta Backscatter and X-ray Fluorescence Methods to Measure Coating Thickness

This work compares and assesses the effectiveness of beta backscatter (BB) and x-ray fluorescence (XRF) for measuring the thickness of gold coatings on two substrates: silicon and an iron-nickel alloy. A set of samples of known gold coating thickness, ranging from 0.5 – 4.0 microns, was measured in each case along with the substrate alone. In BB the number of electrons (beta particles from a very small radioactive source, Pm-147 in this case) backscattered from a sample in a fixed time period is counted. The XRF method uses x-rays generated in the sample from a primary x-ray beam of higher energy (e.g. 50 kV). The spectrum of the outgoing x-rays is collected and all the peaks in that spectrum are identified. The peak intensities for the primary peaks of each element can be quantified and the data summarized. The data from both methods was recorded in Excel and the data plot using IGOR, a data visualization software package. Both methods are capable of measuring coating thickness, BB is simple and easy to use but the compositions of both the coating and substrate must be a known and standards are required in order for calibration. XRF gives intensities for each element in the coating-substrate system that can be seen, however the data takes longer to interpret and it is limited by the energy of the characteristic x-rays from each element. XRF can also identify unexpected elements, e.g. nickel seen between the gold and the silicon in this work. Although we used standards with XRF in this work, there is software that can be used for standardless XRF thickness measurements if the composition of all of the layers and the substrate is known. This suggests potential future research directions

Radiographic Image Quality Enhancement by the Use of Copper Filters

In x-radiography, filters are often used in order to improve the overall image quality. Filters achieve this by making the x-ray beam have less energy spread, resulting in a cleaner image. Step wedges of different materials were used to compare radiographic density with and without a copper filter to identify the effect of the copper filter at different energies and exposure times. The step wedges used were CRS 1018 (cold rolled steel), Stainless Steel 304L, Al 1100, Al 6061 T6, titanium, copper, PTFE (polytetrafluoroethylene or Teflon), brass, carbon, magnesium, phenolic, tungsten, and tantalum. Out of the 14 step wedges tested, only 12 produced useful data, as tungsten and tantalum were both too dense to produce any useable images and data points. In the given time, we were able to run a total of 6 different series of tests at the following parameters: 130kV for 15min, 130kV for 5min, and 70kV for 5min; all with and without a copper filter. From the resulting data we were able to identify certain trends and patterns of the copper filter that held true across all materials. In every case the use of a copper filter lowers the radiographic density of every step on every material under any conditions

Radiographic Density of Selected Materials at Different Thicknesses

X-rays are widely used in medicine and materials science to identify impurities or fractures within the target object. In material science, x-rays can be used to identify the thickness of samples with different material densities. The current method is to collect a radiograph using estimated conditions, evaluate the results, then make changes to the conditions. The residual image can be rescanned making it possible to obtain an image of lower radiographic density. By tabulating or graphing the effects of energy changes and rescans, a more informed choice of conditions is possible. For this study, six materials were chosen with a material density ranging from 1.74-16.65 g/cc. During each experiment, different voltages are used and several rescans are taken if the residual image on the film plate was not erased. When comparing the rescans, the largest drop in radiographic density occurred between the original scan and the first rescan. The relative amount of radiographic density decreased is lower after each scan. The percent change in radiographic density between rescans ranged from 4-12% overall. As the material density or thickness increased, the data consistently showed the radiographic density decreased. The denser, thicker materials may only need a few rescans at the higher voltages, and less dense, thinner materials may need more. The change in voltage showed a similar trend as that of the rescans. The voltages used in this experiment were too high for most of the materials and thicknesses, but some general trends were observed

C-Ring Contaminate Identification by Spectroscopy and Elemental Mapping

A silver plated steel c-ring used to seal two steel pieces together was found to have contamination upon disassembly. Auger and x-ray fluorescence spectroscopy and mapping were used to identify the contaminate as molybdenum disulfide lubricant. Recommendations were made to avoid such contamination in the future

The Effect of High Pressure Hydrogen on Volatiles in Polymers Buna-N and Viton A

Thermal desorption spectroscopy (TDS) was used to monitor the outgassing as a function of temperature for polymers in the range of 30°C to 200°C. Mass spectra were taken while samples were heated in vacuum at 1°C per minute to the maximum temperature and held there for a dwell time of three hours. Samples of Buna-N and Viton A not exposed (ne), and exposed to high pressure (100MPa) helium and hydrogen (He/H2), and argon and hydrogen (Ar/H2) were studied. During these experiments Buna-N(ne) lost ~8% of its weight, Buna-N(Ar/H2) lost 18% of its weight, and Buna-N(HeH2) lost ~8% of its weight. All the Viton A samples lost The mass spectra of the non-exposed samples show greater release of volatiles than the exposed samples. The samples exposed to Ar/H2 release less volatiles than those exposed to He/H2. In the graphs comparing pressure changes for Buna-N, all the samples peak at different temperatures. The (ne) sample peaks at ~85°C, while the exposed samples have a shoulder at ~90°C but do not peak until 200°C. All of the Viton A samples have a peak at ~85°C with the ArH2 sample having a much higher amount of outgassing. The ArH2 shows increasing pressure when the sample gets to the 200°C dwell point implying a peak at higher temperature would release more tightly trapped species. The other two Viton sample show pressure is still falling at 200°C. TDS has been shown to be a useful tool in the study of the effect of high pressure gases on these materials. Future work should include a more detailed examination of the time/temperature evolution of the individual masses seen in this data. There are plans for similar experiments using hydrogen only as well as experiments where the high pressure hydrogen is cycled

Oxidation of zirconium alloys in 2.5 kPa water vapor for tritium readiness.

A more reactive liner material is needed for use as liner and cruciform material in tritium producing burnable absorber rods (TPBAR) in commercial light water nuclear reactors (CLWR). The function of these components is to convert any water that is released from the Li-6 enriched lithium aluminate breeder material to oxide and hydrogen that can be gettered, thus minimizing the permeation of tritium into the reactor coolant. Fourteen zirconium alloys were exposed to 2.5 kPa water vapor in a helium stream at 300 C over a period of up to 35 days. Experimental alloys with aluminum, yttrium, vanadium, titanium, and scandium, some of which also included ternaries with nickel, were included along with a high nitrogen impurity alloy and the commercial alloy Zircaloy-2. They displayed a reactivity range of almost 500, with Zircaloy-2 being the least reactive

Non destructive testing of test objects.

In order to determine the visibility of various features by different techniques and in different settings, several test objects containing wires have been used as standards. Examples are shown of the use of x-ray and active thermal imaging for the detection of inclusions. The effect of x-ray accelerating voltage and confounding materials on the x-ray images is shown. Calculated transmission functions for selected materials at a range of voltages are given. The effect of confounding materials, finishes, and textures on thermography is shown and on x-radiography is discussed

Contamination and solid state welds.

Since sensitivity to contamination is one of the verities of solid state joining, there is a need for assessing contamination of the part(s) to be joined, preferably nondestructively while it can be remedied. As the surfaces that are joined in pinch welds are inaccessible and thus provide a greater challenge, most of the discussion is of the search for the origin and effect of contamination on pinch welding and ways to detect and mitigate it. An example of contamination and the investigation and remediation of such a system is presented. Suggestions are made for techniques for nondestructive evaluation of contamination of surfaces for other solid state welds as well as for pinch welds. Surfaces that have good visual access are amenable to inspection by diffuse reflection infrared Fourier transform (DRIFT) spectroscopy. Although other techniques are useful for specific classes of contaminants (such as hydrocarbons), DRIFT can be used most classes of contaminants. Surfaces such as the interior of open tubes or stems that are to be pinch welded can be inspected using infrared reflection spectroscopy. It must be demonstrated whether or not this tool can detect graphite based contamination, which has been seen in stems. For tubes with one closed end, the technique that should be investigated is emission infrared spectroscopy

Enhanced Presentation of Tomographic Data

X-ray tomography yields a very large amount of data in three dimensions. Effectively displaying this data to a broad audience is a challenge. Techniques are discussed to improve presentation of movies of both 2D and 3D tomographic data using commercially available softwares