1.What are the measurement principles, advantages, and disadvantages of glow discharge spectrometers?
Principle: This is the most commonly used and authoritative method. It utilizes glow discharge to bombard the sample surface with ions, sputtering material layer by layer, while simultaneously analyzing the elemental spectral signals of the sputtered material. By analyzing the changes in these signals over time, an elemental depth distribution map from the surface to the substrate can be directly obtained.
Advantages:
It can directly, quickly, and accurately measure the thickness and composition of the oxide layer.
It can simultaneously analyze the structure and thickness of the entire coating (including pure zinc layers, alloy layers, etc.).
Disadvantages:
The equipment is expensive and requires professional operation.
It is a destructive test, leaving a small pit on the sample.
2.What are the principles, advantages, and disadvantages of X-ray photoelectron spectroscopy?
Principle: By irradiating the sample with X-rays and measuring the energy of the excited electrons, the chemical elemental state of an extremely thin surface region (a few nanometers) can be precisely analyzed (e.g., distinguishing between metallic zinc (Zn) and zinc oxide (ZnO)).
Advantages:
Extremely sensitive to the outermost oxide layer (a few nanometers thick), providing chemical state information.
Disadvantages:
Very shallow analysis depth, primarily targeting the outermost layer.
The equipment is very expensive, and the analysis speed is relatively slow.
3.What are the principles, advantages, and disadvantages of scanning electron microscopy/transmission electron microscopy?
Principle: A cross-section of the sample is prepared, and the thickness of the oxide film is directly observed and measured under an electron microscope. This is the most intuitive method.
Advantages: The results are very intuitive, showing the morphology of the oxide film.
Disadvantages: Sample preparation is complex and time-consuming, the equipment is expensive, and only a local area can be observed.
4.What are the principles, advantages, and disadvantages of using a magnetic thickness gauge combined with the peeling method?
Principle:
First, measure the total thickness of the galvanized coil (including the oxide film) using a standard magnetic thickness gauge.
Then, gently scrub a small area with a very mild acidic solution (such as diluted acetic acid or a specialized oxide film remover) to remove only the surface oxide film without damaging the underlying zinc layer.
Measure the thickness of the same area again using the magnetic thickness gauge.
The difference between the two measurements is the thickness of the oxide film.
Advantages:
Simple equipment (only a common coating thickness gauge and chemical reagents are needed).
Relatively fast and can be performed on-site.
Minimally damaging to the sample (only a tiny wiping point).
Disadvantages:
The key lies in "selective corrosion." Operation requires experience; otherwise, the pure zinc layer may be etched through, leading to inaccurate results.
It is an indirect measurement, with lower accuracy than laboratory methods.
5.What are the principles, advantages, and disadvantages of electrochemical methods?
Principle: By measuring electrochemical parameters such as open-circuit potential and polarization curves of a sample in a specific electrolyte, the density and protective properties of the surface oxide film can be indirectly reflected. Thicker, more complete oxide films exhibit a more positive potential and higher impedance.
Advantages: Can evaluate the functional properties (corrosion resistance) of oxide films.
Disadvantages: Requires electrochemical equipment and expertise; results are affected by various factors and cannot directly provide physical thickness.