Effect of H3PO4 content and processing temperature on the structure and mechanical properties of porous Si3N4

Open-porous silicon nitride ceramics have been fabricated via low-temperature processing at 1200 degrees C using phosphoric acid as an inorganic binder and pore-forming agent. A detailed study of the effect of phosphoric acid content on the microstructure development and an in-depth analysis of the influence of the porosity and pore morphology on compressive strength, flexural strength, and notch-root radius corrected fracture toughness has been performed. Further, the progressive evolution of porosity and the amount and type of crystalline phases as a function of processing temperature were studied by intermittent XRD analysis. For the first time, a detailed analysis of the pore structure evolution on the longitudinal elastic constant of the porous samples was studied using a non-destructive ultrasonic technique. The critical H3PO4 content of 40 vol% yielded a homogeneous nanoporous structure that resulted in the best mechanical properties - compressive strength >120 MPa, flexural strength >70 MPa, and a notch-root radius corrected K-IC similar to 1 MPa m(1/2). Despite the low fabrication temperature and economic processing route, the mechanical properties of the fabricated porous samples are comparable to the values for porous Si3N4 reported in the literature.

Automated summary

Open-porous silicon nitride ceramics were successfully fabricated via low-temperature processing using phosphoric acid as a binder and pore-forming agent. The detailed analysis showed that samples with a phosphoric acid content of 40% exhibited the best mechanical properties.