Inert atmosphere processing of hydroxyapatite in the presence of lithium iron phosphate

Abstract

The present study describes sintering behaviour of hydroxyapatite (HAp) upon addition of lithium iron phosphate (LFP) (1-10 wt. %) system in inert (Ar) atmosphere. The interaction between materials and melting of LFP influenced early and intermediate stages of HAp sintering, shifting the densification curves towards low-temperature side. Analysis of densification process indicated significant differences upon LFP addition. The reaction mechanism that assumes the initial interaction between phosphates from LFP and calcium from HAp was proposed, generating calcium vacancies and contributing to HAp densification. Cross-sections of sintered samples showed changes in microstructural properties, with uniform atomic distribution and presence of Li 2 Fe 3 O 4 spherical inclusions (200 nm) located at grain boundaries of calcium phosphate matrix. The Rietveld refinement analysis indicated changes in structural and microstructural parameters like crystallite size, anisotropy and microstructural strain of HAp upon LFP addition. Mechanical characterisation indicated improvements in fracture behaviour upon LFP addition.

Fiber-Templated 3D Calcium-Phosphate Scaffolds for Biomedical Applications: The Role of the Thermal Treatment Ambient on Physico-Chemical Properties

“…Concurrently, up to 1200 °C, HA was found to gradually decompose into β-TCP or a mixture of β-TCP and α-TCP [ 19 , 60 ]. The high temperature de-hydroxylation of HA (with the intermediate formation of oxyapatite, regardless of the sintering ambient [ 51 , 52 ]) is known to be the main promoter of its conversion to β-TCP [ 53 , 61 , 62 ]. Thereby, the presence of the minor oxyapatite phase for the air sintered specimens ( Figure 1 a,b) could be interpreted as an indication that the de-hydroxylation process of HA already began, suggesting that its decomposition can be expected at temperatures in excess of 1200 °C.…”

“…The dissimilarity in crystalline phase composition of the samples sintered in air ambient ( Figure 1 a,b), with respect to those processed in nitrogen (regardless of their compactness) ( Figure 1 c,d), is undoubtedly enabled by the sintering environment. This was to be expected since scientific literature evidence advocates that a less-reactive ambient alone, such as nitrogen, favors an accentuated de-hydroxylation of the HA and, hence, a diminished structural stability at high temperatures (i.e., 1200 °C), shifting the equilibrium to both β- and α-TCP phases [ 12 , 52 ].…”

“…This is markedly evident for the CP-type specimens ( Figure 2 a), composed of closely packed ceramic particles admixed with Gr. This phenomenon can be ascribed to the generation of a higher thermal gradient (as Gr has a significantly higher thermal conductivity (3000 W/m·K) with respect to CaPs (1.1–1.25 W/m·K) [ 10 , 25 , 64 ]), which in turn, can foster an accelerated phase transformation [ 25 , 52 ].…”

“…Adequate spatial porosity and mechanical resistance properties can be attained by sintering processing in various ambient environments via diffusion, evaporation, and condensation mechanisms [ 28 , 29 , 48 ]. Several studies outlined the typical behavior and phase transition of CaPs (i.e., HA, DCPD) with/without graphene materials, in oxidative, reductive, or inert ambient environments [ 2 , 27 , 44 , 45 , 49 , 50 , 51 , 52 , 53 ]. However, the benefits of the sintering ambient on the overall features of HA and DCPD-composite assemblies with Luffa fibers remains, to the best of our knowledge, an untouched area of research.…”

Li-Doped Bioactive Ceramics: Promising Biomaterials for Tissue Engineering and Regenerative Medicine

“…Although adding Li to HA did not affect the degradation rate, doping Li into HA scaffolds increased new bone formation by decreasing GSK- 3β and β-catenin mechanisms, but did not have a significant angiogenic effect [ 240 ]. The incorporation of Li in HA causes densification [ 241 ], with greater crystallinity for Li-doped HA than undoped HA. Li also reduces the dielectric constant, which is good for dental and orthopedic applications [ 242 ].…”