Guglielmo Gottoli

Production of Ni3Ti-TiCx intermetallic-ceramic composites employing combustion synthesis reactions

Combustion synthesis (CS) of nickel, titanium, and carbon (graphite) reactant particles can result in NiTi-TiC (stoichiometric) or Ni3Ti-TiCx (nonstoichiometric) composites. Since NiTi exhibits both superelasticity and shape memory properties while Ni3Ti does not, it is important to understand the SHS reaction conditions under which each of these composite systems may be synthesized. The stoichiometry of TiCx, for which 0.3 ≤ x ≤ 0.5, has an important controlling effect on the formation of either Ni3Ti or NiTi; i.e., formation of TiC0.7 results in a depletion of titanium and formation of Ni3Ti. This deficiency should be considered when developing the SHS reaction. This article examines the SHS conditions under which Ni3Ti-TiCx composites are produced. Ignition, combustion, and microstructure characteristics of nickel, titanium, and carbon (graphite) particles were investigated as a function of initial relative density and thermophysical properties of the reactant mixture. Combination of the thermophysical properties and burning velocities controlled TiCx particle size, yielding a dependence of particle size on cooling rate. Theoretical calculations were performed and are in good agreement with the experimental data presented.

The Application of Energetic SHS Reactions in the Synthesis of Multi-functional Bone Tissue Engineering and Drug Delivery Systems

The term combustion synthesis, or self-propagating high temperature synthesis (SHS), refers to an exothermic chemical reaction process that utilizes heat generated within the reaction to ignite and sustain a propagating combustion wave through reactants to produce desired product(s). The products of combustion synthesis normally are extremely porous: typically 50 percent of theoretical density. Advantages of combustion synthesis over traditional processing routes, e.g., sintering, in the production of advanced materials such as ceramics, intermetallic compounds and composites include process economics, simplicity of operation, and low energy requirements. However, the high exothermicity and rapid combustion propagation rates necessitate a high degree of control of these reactions. One research area being conducted in the Institute for Space Resources (ISR) at the Colorado School of Mines (CSM) is the application of combustion synthesis (SHS) to synthesize advanced, engineered porous multiphase/heterogeneous calcium phosphate (HCaP), NiTi, NiTiTiC, TiB-Ti, TiC-Ti for bone tissue engineering and drug delivery systems. Such material systems require a complex combination of properties that can be truly classified as multifunctional materials. The range of properties includes: an overall porosity of 40-60% with a pore size of 200-500 µm; mechanical properties (compression strength and Young’s modulus) that match those of natural bone to avoid ‘stress shielding’; and a surface chemistry that is capable of facilitating bone growth and mineralization. The paper will discuss the synthesis of porous multiphase/heterogeneous calcium phosphate (HCaP), NiTi, NiTi-TiC, TiB-Ti, TiC-Ti for bone tissue engineering and drug delivery systems.