Dr. Shangshang Mu, Applications Engineer, EDAX

Collecting die-cast toy cars is a childhood hobby that I picked up again twelve years ago. As kids play with Hot Wheels in the United States, you are sure to remember Matchbox toy cars if you were a kid in the 1980s and 1990s in China, like me. The brand originated in the United Kingdom and was given its name because the original die-cast toy cars were sold in boxes similar to those in which matches came in. I stepped into this mini world at the age of four when my father bought me my first Matchbox toy car. During my adolescence, I enjoyed exploring my gradually growing collection. Many years later, when I was in graduate school, these toy cars captured my attention again while I was shopping for groceries. I ran into a small section with some Hot Wheels and Matchbox cars hanging on the pegs. I was so excited to see that my favorite childhood toy brand was still alive and immediately reconnected with my old hobby.

Besides collecting toy cars released in the current year, I started to search on the internet to re-collect the same un-opened models that became worn and even destroyed in my childhood. Soon, I expanded my collection to include toy cars made in the 1970s and even 1960s and started to collect detailed scale model cars that are about the same size. Although collecting Matchbox or Hot Wheels cars is a hobby that attracts a lot of adult fans around the world, these cars are toys that do not have small parts, and all the vehicle types are about three inches in length, regardless if it is a passenger car or a truck (Figure 1). On the other hand, matchbox-sized detailed model cars are classified as 1/64 the size of the actual automobile, with many small parts that are only suitable for ages fourteen and up. 1/64 scale models bring back memories in another way because I am collecting models of classic cars and trucks from the era in which I grew up. Figure 2 shows some impressive cars from my childhood and a fire engine from my neighborhood in Boston.

Figure 1. A vintage railway playset from 1979 that my daughter likes to play with, and some toy cars ranging from the 1970s to 2010s.

Figure 2. Some matchbox-sized detailed models (1/64 scale) of the cars and trucks that I grew up with.

Sometimes my five-year-old daughter rolls my toy cars on racetracks to figure out which one is the fastest. She also likes playing with my vintage railway playset. As a parent, my daughter’s interest made me a little concerned about lead paint since some of the toy cars she plays with were manufactured decades ago. For example, the railway playset dates back to 1979. Safety standards have been changed and revised over time, so I decided to figure out if these toys are lead-free. As an Applications Engineer at EDAX, I had more than one choice of material characterization technique. The Orbis Micro-XRF Analyzer can do non-destructive elemental analysis with the flexibility to work across a wide range of sample types and shapes, meaning I could put the toy cars directly into the analyzer to get the results. At that time, I was in the middle of testing new features in our new APEX™ 2.0 Software for EDS, so I decided to go with Energy Dispersive Spectroscopy (EDS) to give the new Batch Mode feature a try. With the benefits of EDS analysis and the Batch Mode feature in the APEX 2.0 Software, I was able to load all the paint samples into the SEM chamber and run them all at once using an Octane Elite Silicon Drift Detector. I scratched a tiny paint chip from each toy car and stuck it on a 25 mm adhesive carbon tab. Overall, I got 28 samples to analyze, ranging from the 1960s to the 2010s. They were mostly Matchbox, including the cars my daughter plays with, but some were also from other major toy car brands sold in the United States (Figure 3).

Figure 3. A 25 mm adhesive carbon tab with paint samples from my toy cars

The Batch Mode operation allows you to collect data sets at different stage positions as a batch operation. Since the paint samples were hand stuck on the tab, the distance between adjacent samples was relatively large, and a single field of view was only able to show one sample. The Batch Mode feature’s automated stage movement was extremely useful in covering the paint samples all over the carbon tab in one operation batch. I was able to store all the paint samples in a batch list, set up collection parameters (Figure 4), and click on the Collect button to wait for all the samples’ results. Fortunately, the results show that all the samples I analyzed do not contain lead. The identified characteristic peaks were correlated to the paint samples’ colors; titanium dioxide and zinc oxide were white, carbon was black, and sulfur-containing sodium silicate was blue (Figure 5).

Figure 4. The growing batch list of the paint samples.

Figure 5. Selected SEM images and spectra overlay of the paint samples. The arrow indicates that no Pb L peak (10.55 keV) is present.

On a side note, it was relatively easy to identify a single element from a bunch of spectra that the energy region around the lead peak was pretty clean without any overlapping peaks. I simply had to overlay all the spectra together and see if the lead peak stuck up from the background. If you need to identify multiple compounds of contaminants from various samples, examining every spectrum or doing quantification analysis and comparing how close these numbers are over and over again is very time-consuming. An easy solution is to use the Spectrum Matching feature provided by the APEX 2.0 Software. You can collect spectra from those contaminants to build a library for them first, and then you can run Spectrum Matching to compare the unknown samples to the library. If Spectrum Matching finds more than three matches for an unknown sample, it will display the top three matches with numerical values of fit% for each unknown sample. This feature provides a remarkable benefit in improving the efficiency of your experimental work.

Now, I can stop worrying about the toxic component and let my daughter play with the vintage toy cars as she likes. My only concern is that some are hard to find now, so be careful and don’t break my vintage toy cars!