Effects of the addition of boron – nitride nanoplatelets to hydroxyapatite: processing, testing, and characterization
Date
2017
Authors
Aguirre, Trevor G., author
Holland, Troy B., advisor
Radford, Donald W., committee member
Neilson, James R., committee member
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Abstract
Bioceramics range in biocompatibility from inert oxides that do not react with the body to the other extreme of materials that completely absorbed by the human body, but are prone to failure by fracture. Limited fracture toughness (KIC) and flexural strength (σFS) are major factors limiting wider scale application as structural implant materials. KIC and σFS of ceramics can be improved through grain size refinement and through the addition of various reinforcement materials. The bioceramic hydroxyapatite (HA), the primary inorganic component of bone, has excellent osteoconductivity which offers a suitable surface for new bone growth and integration but suffers from low KIC. To improve the KIC of HA we used boron nitride nanoplatelets (BNNPs), a strong and biocompatible material, making them excellent candidate for use in the human body. However, these materials have been shown to cause embrittlement of the material they are incorporated in; thus, it becomes important to understand the effect of BNNPs through analysis of the failure statistics of tested samples. Using spark plasma sintering to create these materials HA – BNNP composites with 0.5, 1.0 and 2.0 wt% BNNPs were fabricated. Sample grain sizes were measured to evaluate the effect the BNNPs had on the microstructure and the flexural strength, fracture toughness, and hardness were tested to observe the effect BNNP had on the mechanical properties of HA and as well as the failure statistics. To analyze the failure statistics of the HA BNNP composites the Weibull Distribution was used because studies have shown that the Normal Distribution does not accurately report the failure statistics of brittle materials. This work summarizes the effect of the addition of BNNPs to spark plasma sintered HA. The results of this study show that BNNPs are capable of increasing flexural strength and fracture toughness through grain size refinement but BNNPs lead to a measurable decrease in the reliability of the material, which is indicative of the predictability of measured material property value and yields information about the flaw distributions in these materials.
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Subject
boron nitride
fracture toughness
Weibull statistics
ceramic matrix composites
bioceramics
hydroxyapatite