Why Add Cold Isostatic Pressing (Cip) After Mold Pressing For Mgti2O5/Mgtio3? Enhance Density And Prevent Cracking

The addition of a Cold Isostatic Press (CIP) step is a critical quality assurance measure in the fabrication of MgTi2O5/MgTiO3 green bodies. While initial mold pressing defines the geometry, CIP applies ultra-high, isotropic pressure (typically around 200 MPa) via a liquid medium to eliminate internal density gradients, ensuring the component does not crack or deform during high-temperature sintering.

The Core Takeaway Initial mold pressing shapes the part but creates uneven internal stress; CIP fixes this by applying pressure from every direction simultaneously. This "secondary compaction" homogenizes the density of the green body, ensuring uniform shrinkage and mechanical reliability during the firing process.

The Problem: Limitations of Uniaxial Pressing

The Creation of Density Gradients

When you form a green body using standard mold pressing (uniaxial pressing), pressure is applied from only one or two directions. Friction between the powder and the die walls creates density gradients, where some areas of the part are packed tightly while others remain loosely compacted.

Internal Stress Concentrations

These gradients result in "stored" internal stress within the green body. If left untreated, these stresses act as weak points that can lead to catastrophic failure once the material is subjected to heat.

The Solution: Mechanics of Cold Isostatic Pressing

Isotropic Pressure Application

CIP submerges the pre-formed green body in a liquid medium to transmit pressure. Unlike a rigid die, the liquid applies pressure equally from all directions (isotropically) to the entire surface of the object.

Particle Rearrangement

Under ultra-high pressure (e.g., 200 MPa), the powder particles are forced to rearrange themselves. This eliminates large pores and voids that were "bridged" over during the initial molding process, resulting in a tighter particle arrangement.

Reduced Reliance on Binders

The primary reference notes a specific advantage: CIP ensures tight contact between powder particles without the need for binders. By relying on mechanical interlocking driven by high pressure rather than chemical adhesion, the purity and integrity of the ceramic composition are maintained.

Impact on Sintering and Reliability

Ensuring Uniform Shrinkage

The ultimate goal of adding CIP is to survive the high-temperature sintering process. Because the density is now uniform throughout the body, the material shrinks at a consistent rate in all directions.

Prevention of Deformation and Cracking

When density is uneven, parts warp or crack as they shrink differentially. By eliminating the density gradients beforehand, CIP effectively prevents deformation and cracking, guaranteeing the mechanical reliability of the final structure, whether it is intended to be a dense solid or a porous ceramic.

Understanding the Trade-offs

CIP is Not a Shaping Process

It is important to understand that CIP is strictly a densification process, not a shaping process. It cannot create complex geometries or sharp features on its own; it merely uniformly shrinks the shape provided by the initial mold pressing.

The Two-Step Necessity

You cannot simply skip the mold pressing and go straight to CIP for complex parts. CIP requires a pre-formed "green" shape to act upon. Therefore, this is an additive process step that increases total cycle time but is necessary for parts where structural integrity is non-negotiable.

Making the Right Choice for Your Goal

When deciding how to configure your forming process for MgTi2O5/MgTiO3, consider your specific performance requirements:

If your primary focus is Geometric Complexity: Invest heavily in the initial mold design, but understand that without CIP, complex features are highly prone to warping during firing.
If your primary focus is Mechanical Reliability: You must include a CIP step (200 MPa) to eliminate the internal density gradients that cause structural defects.
If your primary focus is Binder-Free Purity: Utilize CIP to achieve high green strength through particle interlocking, minimizing the need for organic binders that must be burned out later.

By equalizing internal pressure, CIP transforms a fragile, uneven green body into a robust structure ready for successful sintering.

Summary Table:

Feature	Uniaxial Mold Pressing	Cold Isostatic Pressing (CIP)
Pressure Direction	One or two directions (Uniaxial)	Isotropic (Equal from all sides)
Density Profile	Creates density gradients/unevenness	Homogenizes density and eliminates voids
Primary Function	Shapes the geometry of the part	Densifies and stabilizes the green body
Internal Stress	Higher risk of stress concentrations	Relieves stress through uniform compaction
Sintering Result	Prone to warping and cracking	Ensures uniform shrinkage and reliability

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References

Yoshikazu Suzuki, Masafumi Morimoto. Porous MgTi2O5/MgTiO3 composites with narrow pore-size distribution: in situ processing and pore structure analysis. DOI: 10.2109/jcersj2.118.819

This article is also based on technical information from Kintek Press Knowledge Base .