Chemical analysis for steel products requires its own specialized techniques and processes due to steel’s physical and chemical properties and the different types of chemical information manufacturers often need to test.
Innovatech most commonly uses Electron Spectroscopy for Chemical Analysis (ESCA) to conduct chemical analysis on the surfaces of steel products. ESCA is a type of surface analysis technique that is especially useful for chemical analysis for steel because it’s fast, highly accurate, and combines physical and chemical testing.
This is what you should know about ESCA, including how it works, how Innovatech uses it, and how it could help you.
What is Electron Spectroscopy for Chemical Analysis (ESCA)?
As its name implies, ESCA, also known as X-ray Photoelectron Spectroscopy (or XPS analysis for short), is a form of Scanning Electron Microscopy (SEM) that incorporates X-ray beams along with electron scanning in order to penetrate the topmost layers of a metal sample in order to understand its chemical composition.
Compared to conventional SEM, ESCA can determine even more chemical information about the surface of a sample, making it highly useful when chemical analysis and physical analysis are both required simultaneously.
ESCA works similarly to SEM, but with the addition of an x-ray beam. When this beam passes over the surface of the metal, the metal’s atoms absorb its photon energy in their core electrons. This “excites” the core electrons, forcing them to detach from the atom itself and emit onto the surface of the metallic sample, where they can be detected. The depth of analysis for ESCA is on the order of a few nanometers, whereas electron beams from SEM’s penetrate to depths of micrometers. This makes ESCA the prime tool for investigating chemistry at the surface.
The specific amount of photon energy a core electron will absorb before becoming excited and detaching from its atom is unique to every single element. By measuring how much energy each electron absorbs before emitting and becoming measurable via SEM, ESCA can determine the elements contained in the sample.
The binding energy required for a core electron to detach from its atom and emit is not determined by the atom’s element alone. It is also affected by the chemical environment of the sample material at the moment of emission (this is called “chemical shift”). Different chemical shifts affect emission requirements in unique, highly precise, and measurable ways.
By measuring how much the chemical environment of the material affected how much binding energy was required to get these core electrons to emit. ESCA can identify not only the elements present within the sample material but also the chemical environment each of these elements exists in within the metal. This is unique to ESCA compared to other x-ray and electron beam based techniques.
What kinds of chemical analysis for steel is ESCA used for?
In chemical analysis for steel, ESCA is primarily used for surface characterizations. ESCA has the ability to provide a great deal of information about the outermost 10 nanometers (or three atomic layers) of a wide range of metallic products.
Obtaining this kind of surface information as quickly and accurately as ESCA makes the process the gold standard for a wide range of quality assurance testing of metallic products. ESCA is frequently used to assess metal’s resistance to corrosion, its thickness and toughness, its electrical conductivity, and its susceptibility to different types of contamination.
Innovatech frequently uses ESCA for testing the passivation layer integrity of stainless steel and other metallic products, as well as to identify contaminants that may have been produced by pre-treatment techniques.
Stainless steel passivation testing
Stainless steel is rust-resistant because of a chromium oxide-rich passivation layer applied to its surface during the manufacturing process. ESCA is frequently used to ensure this passivation layer has been properly applied.
ESCA is particularly useful for this analysis because it can easily identify the chromium-to-iron ratio within the surface layers of a sample of the stainless steel product. In order for a stainless steel sample to be truly rust-resistant, its surface layers must possess a chromium-to-iron ratio of around 2.0.
Using ESCA, Innovatech’s analysts can create high-resolution scans of the chromium and iron quantities present in the surface layers of a stainless steel sample. This allows them to visually determine the ratio of chromium to iron and therefore conclude whether a stainless steel product can be considered truly rust resistant.
Physical and chemical purity testing of steel surfaces
Beyond passivation layers, ESCA is an ideal solution for determining how a wide variety of pre-treatments affect metals such as stainless steel, nitinol, and Ti. The analysis technique can find both physical and chemical impurities introduced into the topmost layers during these treatment processes. One unique aspect of ESCA compared to SEM is that the surfaces of non-conducting materials, like polymers, can be investigated without the charging inherent with electron beam systems.
Innovatech once used ESCA to help an electronics manufacturer figure out why a haze was left behind on their product following its manufacturing. ESCA testing was able to successfully confirm that the haze left behind on the polyamide film product was a chromium residue. This helped the electronics manufacturer determine that the chromium film used in the manufacturing of the product was not completely etched away by its current process. The manufacturer used this information to locate and correct the problematic steps in their process, ensuring the quality of their product going forward.
Our experts have years of experience providing each of these chemical analysis techniques. If you’re in need of chemical analysis for your steel products, Innovatech and Secat are ready to help. Get in touch with our experts today.