Powder brittle fracture

All three grades of mannitol showed similar, relatively low BFI values. This low tendency for brittle fracture represents a very significant advantage of mannitol, particularly with direct compression formulations where material properties, and not powder processing, must be used alone to overcome deficiencies of the API and other ingredients. It should be remembered that low BFI is but one consideration of many when selecting excipients for direct compression formulations. 

Hilmas, G., Brady, A., and Halloran, J.W. (1995), SiC and Si3N4 fibrous monoliths non-brittle fracture from powder processed ceramics , Ceram. Trans., 51, 609-614. 

Generally, only powders that form hard compacts under an applied pressure without exhibiting any tendency to cap or chip can be considered as readily compactible. The compactibility of pharmaceutical powders can be characterized by its tensile strength and indentation hardness, which can be used to determine three dimensionless parameters strain index, bonding index, and brittle fracture index. 

Pharmaceutical compacts are complex structures that present difficult challenges when measuring their mechanical properties. Hiestand was a pioneer who quantified the compaction properties of pharmaceutical powders and (105-109) the result of his work are indices known as the Hiestand Tableting Indices. These indices are dimensionless numbers used to describe the mechanical properties and consolidation behavior of materials under compression and decompression. The three main Hiestand Tableting Indices are the bonding index, brittle fracture index BFl), and strain index. 

Hiestand Tableting Indices Likelihood of failure during decompression depends on the ability of the material to relieve elastic stress by plastic deformation without undergoing brittle fracture, and this is time-dependent. Those which relieve stress rapidly are less likely to cap or delaminate. Hiestand and Smith [Powder Technol., 38, 145 (1984)] developed three pharmaceutical tableting indices, which are applicable for gener characterization of powder com-pactiability. The strain index (SI) is a measure of the elastic recovery following plastic deformation, the bonding index (BI) is a measure of plastic deFormation at contacts and bond survival, and the brittle fracture index (BFI) is a measure of compact brittleness. 

Figure 11.7 The behaviour of powders subjected to a compaction force fa) brittle fracture and [b] plastic deformation.

Low temperature ashing in an oxygen plasma can be carried out in the same way as described for bone after finely powdering the soft tissue using the brittle fracture technique. 

Fig.S indicates that using nano-SiC as the matrix, the prepared C /SiC composite demonstrates the typically non-catastrophic fiacture behavior. With the increase in the particle size of SiC, the fracture toughness decreases correspondingly. As using SOOnm SiC powder, the fracture toughness is down to 7.S MPa-m , similar to that of brittle ceramics.

Shipway, P. H., and Hutchings, I. M., Attrition of Brittle Spheres by Fracture under Compression and Impact Loading, Powder Tech., 76 23 (1993)... 

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