Porous fracture strength, porosity dependence

Figure 8.22 Porosity dependence of fracture strength and fracture energy of porous silicon nitride with large fibrous grain alignment. Stress is applied parallel to the alignment direction. The vertical bars indicate standard deviations. Reprinted with permission from Ref [51] ...

Crystalline silicon is a strong but brittle material. The introduction of porosity often lowers hardness, stiffiiess, and fracture strength (see handbook chapter Mechanical Properties of Porous Silicon ), and if the stmcture becomes too weak, it cannot often survive common material processing techniques without alteration. Examples include air drying (see handbook chapter Drying Techniques Applied to Porous Silicon ), reduction of particle size via communition (see handbook chapter Milling of Porous Silicon Microparticles ), and oxidation of layers (see handbook chapter Oxidation of Mesoporous Silicon ). The properties of electrochemically etched layers can depend not only on etch parameters but how the material was dried. The properties of microparticles can be sensitive to how they were milled. 

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