Papers by Author: N. Ehsani

Abstract: The goal of this study was to produce hydroxyapatite (HAp), a bioactive biomaterial, in a decomposition-free form with fracture toughness comparable to bone by metal fibre-reinforcement. This goal was ultimately achieved. Glass encapsulation of FeCralloy^®-reinforced HAp was an unsuccessful technique due to the excessive low-temperature volatilisation, which aerated the glass. Therefore a graphite/stainless steel encapsulation system was used in the present study. Hot isostatic pressing enabled the production of fully dense decomposition-free HAp with toughness improvements of 14 times (FeCralloy^® fibres, optimally 15 vol%), comparable to cortical bone. Further, it was found that the HAp decomposition temperature was higher at 100 MPa (the HIPing pressure) than for pressureless sintering. Addition of the FeCralloy^® fibre additive induced significant plastic deformation and ductile fracture of the hydroxyapatite.

Abstract: The Aim of the Project Was to Enhance the Fracture Toughness of Hydroxyapatite to a Level Comparable to that of Natural Bone for in Vivo Applications. to this Aim, the Effect of Various Parameters, Were Studied. Fully Dense Decomposition-Free Hap Matrix Composite Was Produced Using Hot Isostatic Pressing Technique. A Graphite/stainless Steel Encapsulation System Was Found to Be an Appropriate Method. Glass Encapsulation Was Unsuccessful Technique due to the Excessive Low-Temperature Volatilisation, which Aerated the Glass. Toughness Improvement Was 2.7 Times for PSZ Fibres, and 2.4 Times for PSZ Powder. the Optimal Addition Level of PSZ Fibre and PSZ Powder Was 20 Vol% and ~30 Vol% Respectively. Further, it Was Found that the Hap Decomposition Temperature Was Higher at 100 Mpa (the Hiping Pressure) than for Pressureless Sintering. the Toughening Effect of the Additives Induced Plastic Deformation and Ductile Fracture.

Abstract: Fracture Toughness Improvement of the Hydroxyapatite Matrix Composite, to a Level Comparable to that of Natural Bone for in Vivo Applications, Was the Aim of the Present Work. Hot Isostatic Press Using a Graphite/stainless Steel Encapsulation System Enabled the Production of Fully Dense Decomposition-Free Hap with Toughness Improvements of: 2.4 Times (Al2O3 Fibres, Optimally 20 Vol%). Glass Encapsulation of Fibre-Reinforced Hap Resulted in Aeration from Sample Volatilization. Further, it Was Found that the Hap Decomposition Temperature Was Higher at 100 Mpa (the Hiping Pressure) than for Pressureless Sintering. the Toughening Effect of the Al2o3 Fibre Additive Induced Plastic Deformation and Ductile Fracture.

Abstract: PSZ (ZrO₂ Fiber)-reinforced HAp was sintered using conventional and microwave hybrid heating. Microwave heating cycles were ~50 times faster than conventional sintering cycles and enabled the use of reduced densification temperatures and soak times by as much as ~100°C and 55 min, respectively. However, although there was a significant improvement in densification levels attainable before decomposition, the improvements were insufficient to produce near-fully or fully dense samples. However, the promising gains made suggest that microwave hot pressing would be a suitable area for future work. Keywords: Hydroxyapatite, microwave sintering, fibre-reinforced ceramics, bioceramics, zirconia fibre

Abstract: Al₂O₃ Fiber-reinforced HAp was sintered using microwave and conventional heating. Microwave heating cycles were ~50 times faster than conventional sintering cycles and enabled the use of reduced densification temperatures and soak times by as much as ~100°C and 55 min, respectively. However, although there was a significant improvement in densification levels attainable before decomposition, the improvements were insufficient to produce near-fully or fully dense samples.

Abstract: Nanostructured CuO powders have been synthesized using chemical methods in the current study. Ammonium oxalate and copper nitrate were used as the precursor materials. The weight ratios of the raw materials (ammonium oxalate/copper nitrate) were 1.1, 1.2, 1.3, and 1.4. As a result of chemical reaction (between them), copper oxalate was synthesized. Produced samples were analyzed by XRD and SEM. The results show that the best ratio (for ammonium oxalate/copper nitrate) is 1.2. Produced copper oxalate powder was heated at 600, 700 and 800oC. The final product was CuO nanopowder. XRD studies indicate that the highest ratio of Cu2O to CuO was observed in the specimen heated at 700oC.