To confirm whether a powder sold as "SiC granules" is really a spherical granule for press forming, you need measurement data, not a photo or a sales description. The bottom line: cross-verifying SEM (morphology), EDS (composition), PSA (particle size), and XRD (crystal phase), then applying a double gate of a per-lot certificate (COA) and a third-party report, is the reliable verification method. When samples distributed as "granules" are actually run through this protocol, the variation in morphology, purity, and particle size can be substantial.
The Problem: Name Does Not Match the Material
When products sold as "SiC granules" are compared using SEM/EDS, PSA, and XRD, you sometimes find materials with very different morphology, purity, and particle size mixed under the same label. A buyer expecting a porous spherical granule for press-sinter forming can end up with something closer to abrasive-grade crushed angular powder. The grading of SiC powder itself is covered in Two faces of round SiC powder: granule vs spheroidized; this article focuses on how to verify that grading with actual measurements.
Real Case (Anonymized): Distributed as Granules, but Angular
In a case comparing several market samples, one sample distributed as "granules" showed the following characteristics on measurement.
Taken together, this sample is not a porous spherical granule but crushed angular particles, with a wide size distribution and residual free silicon and carbon — leading to the conclusion that it is unsuitable for press forming. Feeding such material into a press-sinter line leads to uneven die filling and green-body density variation.
Example Acceptance Criteria
If the intended use is a spherical granule for press sintering, the following criteria can serve as a rough reference. Actual specs are adjusted to the sintering process and final property requirements.
- Morphology: porous spherical granule (dimples visible under SEM)
- Particle size: D50 60–90µm
- Free Si: ≤ 0.2%
- Moisture: ≤ 0.5%
- SiC content: ≥ 98.5%
One caveat: a carbon-rich EDS result and detection of B₄C are not defect signals. They are the normal signature of a deliberately added sintering aid for pressureless sintering. In other words, composition data should be read not as "what was detected" but as "is this the right formulation for the application."
Verification Protocol: Four Measurements + Double Gate
Step 1: Four Measurements
Each measurement looks at a different axis. Any single one is incomplete for identification, so cross-verification is needed.
Two further lines do not identify the powder but decide whether it performs, and belong on the same certificate: BET surface area, the practical proxy for sintering activity, and trace metals by ICP reported as elements with the analytical detection limit stated. The ICP line, together with a per-lot magnetic-content check, is in the verification list on our green SiC micro powder page; BET is not carried there as a catalogue line and is agreed per order, since the surface area that matters is the one that co-fires against your process.
Step 2: Double Gate
Do not stop at measurement — apply a double document gate.
- First gate — per-lot COA: verify particle size, free Si, moisture, and SiC content using the certificate the supplier provides for each lot.
- Second gate — third-party report: validate the supplier's own data with a report from an independent lab such as SGS, KTR, or KICET. This is especially valuable for new suppliers and high-value, small-quantity lots.
This double gate reduces the risk of relying on supplier data alone. Combined with a vendor process audit (such as whether a spray dryer is owned), it raises the confidence of identification.
Frequently Asked Questions
Can I tell granules from angular powder by photo alone?
It is difficult. Low-magnification photos or sales descriptions alone cannot reliably distinguish morphology, particle size, and composition. Reliable identification requires SEM for morphology (dimples), PSA for size distribution, and EDS/XRD for composition and crystal phase together.
Why is free Si a problem?
Excess unreacted free silicon can adversely affect sintering behavior and final properties. If EDS shows a silicon excess and XRD shows free Si peaks together, suspect residual unreacted phases. The example acceptance criterion for press forming is free Si ≤ 0.2%.
If EDS shows carbon and B₄C, is that a defect?
No. It is a normal signal of a deliberately added sintering aid for pressureless sintering. Composition data should be interpreted by whether the formulation fits the application, not by mere detection.
When is a third-party report essential?
Especially for new suppliers, high-value small-quantity lots, or cases with high spec-variance risk. Cross-verifying the supplier COA with a report from an independent lab such as SGS, KTR, or KICET raises identification confidence.
References (Public Sources)
- Standard procedures for SEM/EDS, PSA, and XRD particle characterization
- General practice for ceramic raw material COAs and third-party testing (SGS/KTR/KICET)
A powder is only what its measurements say it is, and the label on the drum is not one of the measurements. Nami Tech Solutions (NTS) reads every mill COA line by line against the agreed specification — trace metals as elements with the detection limit stated, the full particle-size distribution rather than a single median value — arranges independent third-party testing when it is agreed for the order, and if a lot fails your incoming inspection takes the retained sample and the COA trail back to the mill under the rejection clause.
