To determine whether the molybdenum crucible contaminates the sample, a comprehensive evaluation is required from multiple dimensions such as component analysis, physical characterization, and experimental comparison. The following are the specific methods and steps:
- Composition analysis: Direct detection of molybdenum in samples
Spectroscopic analysis
Tools: Inductively coupled plasma optical emission spectrometer (ICP -OES) or inductively coupled plasma mass spectrometer (ICP -MS).
standard:
molybdenum content in the sample exceeds the background value (such as 0.01%), contamination may exist.
molybdenum content in a pure aluminum sample should not exceed 0.005%. If 0.02% is detected, it is considered contamination.
X-ray fluorescence spectroscopy (XRF)
Advantages: fast and non-destructive testing.
Application: Suitable for initial screening of large quantities of samples.
- Physical characterization: Observe sample surface and structural abnormalities
Surface morphology analysis
Tools: Scanning electron microscope (SEM) or transmission electron microscope (TEM).
Judgment basis:
Needle-shaped, granular or layered heterogeneous phases appear on the surface of the sample, which may be molybdenum or molybdenum oxides.
Example: In a metal melt, molybdenum contamination may form Carbide particles such as Mo₂C and MoC.
Lattice structure analysis
Tool: X-ray diffractometer (XRD).
standard:
If detected in the sample If the characteristic peaks of molybdenum or molybdenum compounds (such as the (110) crystal plane peak of MoO₂) are detected, it is judged as contamination.
- Experimental comparison: blank experiment and control experiment
Blank experiment
Operation: Without adding samples, use only molybdenum crucibles for the same process (such as melting, sintering).
Judgment basis:
molybdenum is detected in the blank experiment product, it means that the crucible itself is at risk of contamination.
Control experiment
operate:
The same experiment was carried out using a graphite crucible or a quartz crucible to compare the molybdenum content in the samples.
Judgment basis:
If the molybdenum content of the sample in the molybdenum crucible experiment is significantly higher than that in the control experiment, it is judged to be contaminated.
- Process Analysis: Tracing the Source of Pollution
Crucible use conditions
High temperature oxidation: If the crucible is used for a long time at > 800°C, MoO₃ may be generated and volatilize and contaminate the sample.
Reactive melts: Melts that are highly reactive with molybdenum (such as aluminum and titanium) are more likely to cause contamination.
Crucible surface condition
Oxide layer thickness: If the oxide layer on the crucible surface is > 0.1mm, the risk of contamination increases significantly.
Surface cracks: Cracks may become channels for the leakage of molybdenum.
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