Production of mesophase carbon by PIM — Tailoring gel strength of agar binder

This paper reports the results of a study on a water based binder with agar as a backbone for the production of carbon parts by powder injection moulding of carbon mesophase. The binder strength or gel strength of agar-binder is directly depended on the agar concentration in water and can be increased drastically by adding potassium tetraborate-4-hydrate. As the drying shrinkage of powder injection moulded samples is depending on the binder strength, brown and sinter density also increases with increasing agar and additive content. The packing density of samples increases from 60% (green) up to 83% (brown) during drying. By adding gel strengthening additives the agar content can be decreased and as this reduces the elusion of gaseous degradation products during thermal treatment debinding and sintering defects are eliminated. In this way stiffness of carbon material was increased from 7 MPa to 16 GPa.

Agar binder in PIM-samples shrinks uniformly during drying and leads to a dense packing in the dried or brown state. Gel strength is crucial for this behavior and can be increased by adding more agar and additive leading to higher brown density and in that way higher density and stiffness of sintered samples.Figure optionsDownload as PowerPoint slideHighlights
► Agar binder shrinks during drying causing an increase in packing density.
► Gel strength is crucial for this behavior and can be modified.
► Higher agar and additive content increases density and stiffness of sintered sample.
► Carbon produced with agar has superior properties compared to using polymer binders.
► Agar helps to process powders with poor sinterability.