The core method for determining if magnesium oxide is completely sintered is through metallographic analysis to observe whether the grains have recrystallized, combined with hot-state testing and X-ray detection for comprehensive evaluation. The hallmark of complete sintering is significantly grown grains, densely arranged, forming a continuous ceramic structure.
1. Metallographic Analysis (The Most Direct Judgment Basis)
Qualified Characteristics:
Significantly grown grains with clear boundaries, exhibiting recrystallization characteristics; Dense structure, without obvious micropores or loose powder areas; Sintering temperature must reach 800–1000℃, with a holding time ≥1 hour.
Unqualified Characteristics:
Fine, loose grains, resembling raw powder; Numerous micropores and discontinuous interfaces are visible under a microscope, indicating insufficient sintering temperature or too short a holding time.
Metallographic analysis is the gold standard for determining "true sintering," directly reflecting the internal structural state of the material.
2. Hot-State Testing Verification (Functional Testing)
Test Conditions: After 30 minutes of power-on operation until thermal equilibrium, measure the insulation resistance within 2 seconds of power-off.
Pass/Fail Standard: ≥200 MΩ (500V DC);
Abnormality Warning: If the cold-state test is passable (≥500 MΩ) but the hot-state test shows a sudden drop in resistance, it indicates incomplete sintering leading to micropore enlargement and leakage path formation at high temperatures.
This is an indirect but crucial operational verification method, especially suitable for pre-packaged finished products.
3. X-ray Inspection (Non-Destructive Structural Screening)
Key Inspection Points: Detection of defects such as voids, off-center cores, and uneven density in the filled area.
Resolution Requirement: ≥5μm, capable of identifying micron-level structural anomalies.
Judgment Criteria: If localized looseness or high porosity is found, it indicates inadequate filling before sintering or failure to activate densification during the sintering process.
This can complement metallographic analysis for non-destructive preliminary screening.
Comprehensive Judgment Logic
Test Items: Complete Sintering / Incomplete Sintering
Metallographic Analysis: Grain growth, dense and continuous / Loose powder, no recrystallization
Hot Insulation Resistance: ≥200 MΩ / <200 MΩ, even approaching 0
X-ray Inspection: Uniform filling, no voids / Localized looseness or porosity exists
Rework Recommendation: No need for resintering / Must be re-sintered
In practice, the combination of metallographic analysis and hot testing can accurately determine the sintering state with over 95% accuracy.
