Catalytic converters in cars reduce hazardous emissions, like carbon monoxide, hydrocarbons and nitrogen oxides. These harmful substances are converted into neutral carbon dioxide, water and nitrogen by catalytic chemical reactions accelerated by three platinum group metals (PGM): platinum, palladium, and rhodium.
Due to a significant number of car catalyst types, an amount of PGM’s varies significantly. A fast and accurate testing method is required for the PGM’s content evaluation. Olympus XRF analyzer provides precise and fast catalytic converters analysis for simple sorting and price evaluation. Usually, a concentration of PGM’s in a car catalyst is much higher than in ores.
With Vanta Handheld XRF Analyzer, it takes just seconds to give the result instead of hours or days through traditional means. Simple operation training and easy sample preparation are ideal for the daily business for quality control and price evaluation during catalysts buying and selling.
Some of the essential benefits of the Vanta handheld XRF analyzer are as follows:
- Cost-Efficient – Car catalytic converters account for more than half the demand for platinum and palladium and the bulk of rhodium demand. Knowing the PGM content of catalyst material is vital for recyclers to price their material correctly. Catalyst converters’ internal ceramic honeycomb structures are coated with a washcoat that contains Pt, Pd, and Rh. Other elements may also be present to benefit the catalytic converter. The Vanta analyzer’s element suite covers several other elements commonly added to wash coats along with the accurate measurement of Pt, Pd, and Rh concentrations. To help protect against fraud, Olympus has also included elements that individuals can add to catalyst materials to boost precious metals values falsely.
- Product Reliability – The reference standard samples tested have been crushed, dried, and sieved to a constant size, homogenized, and presented to the analyzer in cups with a four μm Prolene® film. For accurate and representative results, sample preparation is required. Trying to analyze the surface of a ceramic honeycomb can produce misleading results. Thirty samples were tested for 60 seconds per test for Vanta models VLW, VCW, and VCA. Excellent correlation was achieved for all models. The correlation was maintained even though the samples consisted of various matrices with a wide range of other elements. VLW results are presented below.
- Precision – The most significant difference among the models is the uncertainty value, or the accuracy, for each reading. The VLW model has a cost-effective Si-PiN detector and a lower count rate than the two C series models. The result is a correspondingly larger uncertainty (+/-) value. The silicon drift detector (SDD) detector in the VCW and VCA models have higher count rates and lower uncertainties. The results also indicate that the VCW outperforms the VCA. This is attributed to the tungsten anode of the VCW model having superior excitation to the VCA model’s silver anode.
Principles of XRF:
An HHXRF instrument can be broken down into three main parts: an X-ray source, a detector, and a processor. First, a tube source emits X-rays toward a target sample. The sample then emits a characteristic wavelength as photons that enter the analyzer and are read by the detector. X-ray energies are specific to an element, so the processor uses it and interprets the data into the chemistry that a user can read. HHXRF has methods that cater to different applications and different elements of interest. X-ray analysis depth is dependent on the physical properties of the sample and that information reaching the detector.
Generally, the greater the source’s excitation energy, the further the distance an X-ray travels into the sample. Due to this, heavier elements are more easily excited with greater energies (40 kV). Still, these energies can cause lighter elements to scatter because too much energy is being thrown at them. To target lighter elements, a lower energy beam is used for better accuracy (10 kV). HHXRF analyzers are also optimized with an element suite to account for all the matrix effects possible and/or the elemental overlaps. For example, selenium and tantalum are used interchangeably to increase platinum values falsely. This is done with the foreknowledge that XRF concentration values could be tricked because the elements’ characteristic energies overlap with one another. However, there are algorithms to distinguish one from the other and void this kind of trickery.
To obtain maximum accuracy with HHXRF, the powder being analyzed needs to be dry, homogenized, and finely ground. If the sample is not ground finely enough, the difference in particle sizes may undergo a sifting effect where the sample is not well mixed. This would result in a granular effect where elements of a larger size gravitate toward the top, and those of a smaller size fall in between this spacing toward the bottom of a sample cup. For catalytic converters, the monoliths must be ground before HHXRF testing. Some users desire in situ testing without sample preparation. For this to work effectively, user-defined software values need to be applied to account for the differences in the sample’s physical state.
Five samples were tested with an Olympus VantaTM handheld XRF analyzer to assess accuracy. The results (below) are ordered from the highest to lowest concentrations. For testing conditions, each sample was kept in place for all five repeats. The test times for the 40 kV beam varied from 10, 20, and 30 seconds, and the test time for the 10 kV beam was 30 seconds for all tests.
We tested precision using the same parameters described above for the accuracy tests, and the results are shown below for Pt, Pd, and Rh. For each sample, the 1-sigma error decreases as time increases. In other words, as test times increase, precision also increases. At a certain point, longer test times diminish returns, so it is not helpful to increase test times any further.
Lastly, the relative standard deviation is shown below for each of the five samples, arranged from highest to lowest concentrations. The same test parameters were used as described above. The results for Pt, Pd, and Rh show that, overall, the relative standard deviation decreases as time increases. This is most pronounced in PTAT low concentrations (standards 3,4,5 assayed to 1200, 700, and 300 ppm, respectively). Catalysts, in general, do not exceed 10000 ppm concentration levels for any of these three elements.
HHXRF can provide accurate, precise, fast, and nondestructive analysis of finely ground car catalyst material. The low PGM concentrations obtained from 40-, 50-, and 60-second tests provided repeatable results. Precision also improved as test time increased, however at the longer test time of 30 seconds, the return on accuracy diminished, and it was not as valuable to continue growing test times. The relative standard deviation also improved overall at longer test times.