Effects of Changes in Structural Hydration of Multiphasic Heterogeneous Calcium Phosphate Powders Created via Auto-Ignit
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Effects of Changes in Structural Hydration of Multiphasic Heterogeneous Calcium Phosphate Powders Created via Auto-Ignition Combustion Synthesis Nina Vollmer1, Douglas Burkes2, John Moore1, and Reed Ayers1 1 Metallurgy and Materials Engineering, Colorado School of Mines, Golden, CO, 80401 2 Idaho National Laboratory, Idaho Falls, ID, 83415 Calcium phosphate (CaP) materials are commonly used in bone tissue engineering applications since they closely resemble the chemical structure of bone and teeth. In order to achieve functionality as an implant material, CaP materials should mimic the chemical, mechanical and morphological properties of naturally produced CaP. [1-5] The inorganic component of mineralized bone tissue is multiphasic in nature; thus to better replicate bony tissue, CaP materials should also be multiphasic. [3-4] Upon interaction with the human body, an appropriately engineered CaP implant with biomimitic properties can lead to minimal immune and inflammatory responses, reducing healing time and increasing tissue integration. Auto-Ignition Combustion Synthesis (AICS) is a self-propagating high temperature synthesis (SHS) process that converts the heat generated by the exothermic chemical reaction of the reactant species into an ignition and fuel source for the propagation of a combustion wave throughout the reactants. [7-10] AICS is economically advantageous as it is a very simple synthesis process; equipment set-up is very simple; uses low energy inputs over a relatively short time period and can be used to create versatile materials. [9-12] CaP AICS reactions are consistently less than 15 seconds from initiation to completion. Physiochemical properties of CaP created via AICS can be controlled by, but are not limited to, reactant stoichiometry, reaction atmosphere, combustion temperature and product cooling rate. [3] The purpose of this research is to study the effects of variations in the amounts of structural hydration in multiphasic heterogeneous (HCaP) powders via changes in fuel ratios and post-synthesis heat treatment. It is believed that structural water plays a large role in the synthesis of calcium phosphate product. [1-2,13-16] There is possibly a correlation between the structural water ratio (amount of urea in the reaction to the amount of water within the products) in the reactants to the specific phases of synthesized HCaP and their crystallinity. Fuel ratio dictates the actual molar mass of water in the reactants and final HCaP product. Whereas postsynthesis calcining dictates the molar mass of water in the products and released gaseous products. [16] Controlling reactant ratios may provide a reliable, simple process to synthesize biomimitic multiphasic HCaP powder for use in bone tissue engineering. Materials and Methods The theoretical reaction equation for this specific system is given below. X [Ca ( NO 3 ) 2 ⋅ 4 H 2O ] + Y [( NH 4 ) 2 HPO 4 ] + Z [CO ( NH 2 ) 2 ] = Ca X ( PO 4 )Y + f XYZ ( H 2O + N 2 + CO 2 + O2 )
Salts of calcium nitrate [ Ca (NO3 ) 2 ] and ammonium
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