Papers by Keyword: α-TCP

Abstract: The present report aims to fabricate biphasic calcium phosphate (BCP) biocomposite in order to study the effects of sintering temperature on the sintered BCP biocomposite characteristics (phase’s formation, porosity and hardness properties). These effects were quantified using design of experiment (DOE) to develop mathematical models. BCP biocomposite pellets (60 wt% HA) were fabricated using mixing, pressing and sintered at two different temperatures (1100°C and 1250°C). The experiment was run by following the run order suggested by DOE software (Minitab 16) through randomization stage. Results show that sintering temperature will affect the formation of α-tricalcium phosphate (α-TCP) and the porosity of the samples. The formation of α-TCP phases will reduce the hardness value of BCP biocomposite.

Abstract: Triphasic calcium phosphate, composed of a more stable phase hydroxyapatite (HA) and highly soluble tricalcium phosphates (α- and β-TCP) has been synthesized through hydrothermal method. In the present work, an in-situ method to disperse 1wt% multiwall carbon nanotubes (MWCNTs) within HA/TCP powder has been used in order to develop HA/TCP-CNTs composite. XRD results confirmed the formation of HA, α-TCP and β-TCP in both as-prepared powder and composite samples. The graphite peaks appeared in the composite samples as well. FTIR analysis of sintered compacted powder showed the formation of weak bands of PO₄^3- as the temperature was increased. The sintered compacts were mechanically tested by Vickers microhardness indentation method. HA/TCP-CNTs composite was found to have a significant of Vickers Hardness of 1.98 GPa after 1100°C sintering. The morphology analysis showed that in-situ deposition technique provides homogeneous dispersion of CNTs in the calcium phosphate matrix.

Abstract: Phase-pure α-TCP powder was milled using a high-energy planetary mill to obtain a partially X-ray amorphous material. Calcination at temperatures between 350 and 600 °C was employed to recrystallize the powder. The phase composition as a function of calcination time and temperature was determined in-situ using high-temperature XRD equipment. It was found that the amorphous fraction recrystallized mainly to α-TCP, with only small amounts of β-TCP formed. At low temperatures (≤ 450 °C), a stable composition with approximately 85 wt-% α-TCP was found once 100% crystallinity was reached. The time required to reach full crystallinity depended on the calcination temperature. For temperatures > 450 °C a slow transformation to β-TCP was observed. The transformation rate depended on the calcination temperature and on the milling intensity. A moderately milled powder recrystallized to α-TCP, followed by a slow transformation to β-TCP at 600 °C, whereas an intensely milled powder also recrystallized to α-TCP, followed by a fast transformation to β-TCP at the same temperature.

Abstract: Pure calcium phosphate and ZrO₂ doped calcium phosphate biomaterials were synthesized using an organic based phosphoric acid (DEHPA) as its starting material. The precipitated products obtained from the sol-gel reaction were then used to compare the phase transformation using in-situ XRD. The study shows that amongst the notable difference between these two samples is that the ZrO₂ doped calcium phosphate tends to form the β-Ca(PO₃)₂, β-TCP and HA phases at lower heating temperatures compared to the pure calcium phosphate. Another major different seen in the phase transformation of the ZrO₂ doped calcium phosphate is the transformation of β-TCP into HA before it leads to the formation of α-TCP at higher temperatures.

Abstract: In the present work, apatite powders were synthesized at pH 10, pH 11 and pH 12 in order to give rise to biphasic and triphasic bioceramics after sintering. A modified gelcasting process, including polyethylene wax spheres addition to the suspension, is proposed in comparison to the original gelcasting method. The aim of the addition is the creation of uniform, open and interconnected pores in the body of samples.

Abstract: X-ray amorphous tricalcium-phosphate nanoparticles (ATCP) produced by flame spray synthesis were heat-treated at temperatures between 500 and 1000 °C and analyzed in situ by X-ray powder diffraction. The main phase occurring after crystallisation at 525 °C was α-TCP, minor phases were identified as β-TCP and hydroxyapatite. More elevated temperatures induced crystallite growth and the transformation of α-TCP into β-TCP. Above 900 °C no α-TCP was traceable anymore. α’-TCP was not observed in the experiment. This study shows that nanoparticulate α-TCP can be obtained by thermal treatment of an amorphous TCP nanoparticle in a temperature range where sintering effects such as particle growth and densification are moderate or nearly negligible.

Abstract: HAp (Hydroxyapatite) and α-TCP (alpha tribasic calcium phosphate) are non-toxic to human cells and, thus, have been studied for applications as biomaterials. HAp is a bioactive material that is not readily absorbed by the body; it offers both high strength and better tissueadhesive properties than α-TCP. In contrast, α-TCP is highly bioabsorbable; it is quickly absorbed by the body, and, therefore, for example, disappears before bone is completely replaced. If porous beads could be fabricated that would take advantage of the useful properties of α-TCP and HAp, they could be used as excellent scaffolds for cultivating cells. In the present study, ceramic beads with α-TCP at the center were fabricated and coated with a functionally graded film of HAp. A scaffold based on this configuration would be expected to have the following characteristics: good cell adhesion; strong beads; and a rate of absorption into the body that would be easy to control. In addition, to accelerate the formation of porous structure, some acid solutions were used to dissolve the beads surface layer and to penetrate pores toward inside of the bead. HAp formation through hydrolytic reaction seemed to be promoted by these acid solutions.