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.