Here’s a recommended approach based on typical practices in ceramic processing:

1. Initial Ball Milling of Raw Powders

• Start with the silicon nitride powders and any sintering additives, such as rare-earth (RE) oxides or other oxide additives.

• Add the dispersant at this stage to promote homogeneous dispersion of the powders in the ethanol solvent. Dispersants help to prevent agglomeration and ensure even particle distribution.

• Perform ball milling to achieve the desired particle size and uniform distribution. This step ensures that the raw powder mixture is well-prepared for subsequent processing.

2. Incorporation of Binders

• After sufficient ball milling of the raw powders, introduce the binder (e.g., polyvinyl butyral, PVB) into the pre-milled slurry.

• Binders are typically added after the initial ball milling to prevent excessive wear of the milling media and to avoid binder degradation during prolonged milling. The binder ensures the green body has adequate strength after drying.

3. Addition of Plasticizers

• Add the plasticizer (e.g., polyethylene glycol [PEG], dioctyl phthalate [DOP], dibutyl phthalate [DBP]) at the same time as or after the binder. Plasticizers enhance the flexibility and handleability of the granules and reduce the risk of cracking during pressing.

• Mix the binder and plasticizer thoroughly into the slurry to ensure homogeneity. Gentle stirring is often sufficient, as excessive mechanical action may degrade the binder or plasticizer.

4. Incorporation of Lubricants

• If you are using lubricants (e.g., stearic acid or waxes), add them after the binder and plasticizer. Lubricants help reduce friction during the pressing process and prevent sticking to the die walls.

• This can also be done during the drying process or after spray-drying, depending on the specific system used.

5. Final Mixing and Drying

• Ensure the slurry is homogeneously mixed after all additives are incorporated.

• Dry the slurry carefully (e.g., using spray drying) to form free-flowing RTP granules with uniform composition and suitable particle size for pressing.

Here are the key considerations:

• Sequence Matters: Adding the binder and plasticizer too early (during initial milling) can lead to degradation, uneven mixing, and contamination of the milling media.

• Dispersant First: Always add dispersants before or during the initial milling of powders to achieve optimal dispersion.

• Homogeneity: Ensure every additive is evenly distributed within the slurry before drying, as this greatly influences the strength and uniformity of the green body.

• Drying Method: Spray drying is often preferred for forming RTP granules, as it provides consistent granule size and flowability for pressing.

I hope this helps?

Hi Jian Yang, little tip to add for your consideration along green-body preparation.

Pls take note on the distribution-ratio of the particle sizes.

In some case, when you find a correct ratio that, would attribute to achieve Uniformity of Si-Nitride in green-body.

Good luck !