Tsung-Shune Chin

FTIR, XRD, SEM and solid state NMR investigations of carbonate-containing hydroxyapatite nano-particles synthesized by hydroxide-gel technique

Abstract Nano-crystalline hydroxyapatite (HA), Ca 10 (PO 4 ) 6 (OH) 2 has been synthesized by a precipitate conversion technique using hydroxide gel at lower temperatures, e.g. 80xa0°C. HA crystallizes in hexagonal structure (space group: P 6 3 / m ) having lattice parameters: a=9.347 A and c=6.862 A and around 17xa0nm in crystallite-size for the 80xa0°C-heated sample. SEM micrographs show hexagonal crystallites of average particle dimensions approximately 50×20xa0nm for 80xa0°C heated sample. The structure analysis by XRD, FTIR, 1 H and 31 P MAS NMR show the existence of structural disorder at the particle surface that either does not form hydrogen bonding due to lack of adequate bonding parameters or forms a very weak dipolar bonding. The structural disorder has been explained as a result of chemical interactions between the phosphate groups either with the surface adsorbed water or the hydroxyl groups at the surface of the nano-particles.

Hydroxyapatite coating on Ti6Al4V alloy using a sol-gel derived precursor

A simple rapid-heating method was successfully developed for calcium phosphate coatings on Ti6Al4V substrates deposited by using a sol–gel derived precursor. After five repetitions of coating procedures and heat treatment at 600 ◦ C, the formation of hydroxyapatite (HA) has been confirmed by X-ray diffractometry (XRD) analyses and the substrate material was found to be slightly oxidized. The residual organics, as revealed by X-ray photoelectron spectroscopy (XPS) spectra of a coating calcined at 400 ◦ C, might retard the formation of calcium phosphate phase, thus only small amount of calcium phosphate phase is present. After calcining at 600 ◦ C, calcium phosphate phase is the only one identifiable by XPS spectra. The adhesive strength of the five-coating layer on the substrate is around 60 MPa. The surface morphology of the thick HA film, calcined at 400 ◦ C and then consolidated at 600 ◦ C, displays porous structure arisen from rapid-heating of the bulk precursor.

Phase purity of sol–gel-derived hydroxyapatite ceramic

Calcium oxide was reported in the sol-gel-derived hydroxyapatite (HA) as an unavoidable major impurity. In this study phase purity of HA synthesized by sol-gel route was explored using precursors of calcium nitrate tetrahydrate and triethyl phosphate. Two different drying methods, the fast drying of as-prepared precursors and the slow drying of aged precursors were adopted as major processing variables. The dried gels were subsequently calcined up to 600 degrees C. In the calcined powder from fast-dried gel, X-ray diffraction (XRD) patterns revealed an intense CaO peak. For the slow-dried gel, thermogravimetric analysis revealed a 2-step weight-loss behavior during heating. XRD analysis of the calcined powder, corresponding to the second weight-loss step, showed major peaks of hydroxyapatite and a very weak CaO peak. P-31 NMR analysis indicated formation of calcium phosphate complex during aging. Complete incorporation of Ca(NO3)2 into the complex due to proper aging therefore diminishes CaO formation. It was also found that the minor CaO derived in the slow drying method can be easily and completely washed out just by distilled water.

Hydroxyapatite layers deposited from aqueous solutions on hydrophilic silicon substrate

Abstract Devices of micro-electro-mechanical systems or biochips for diagnosis to be implanted into human body require a biocompatible and protective coating to avoid inflammatory effects. We have developed a method to deposit a bioactive hydroxyapatite (HA) layer onto pretreated hydrophilic Si(1xa01xa01) from supersaturated solutions containing Ca 2+ and PO 4 3− ions with an initial pH value of 7.40±0.05 at 298 K. The deposition starts with an initial uniform deposit at a low rate approximately 25 nm/h. Growth then takes place predominantly along the direction normal to the substrate through in-plane nucleation of multiple embryos at a high rate approximately 325 nm/h. The deposition rate increases with increasing time duration, attaining a maximum at a thickness approximately 8 μm, and then decreases. X-ray photoelectron spectroscopy (XPS) indicates typical chemical states of HA phase. X-ray diffraction pattern of a 4-day deposit shows the direct formation of crystalline HA corroborating with the XPS results. XPS results indicate the possible incorporation of carbonate.

X-Ray Diffractometry and X-Ray Photoelectron Spectroscopy Investigations of Nanocrytalline Hydroxyapatite Synthesized by a Hydroxide Gel Technique

Nanocrystalline hydroxyapatite (HA), Ca10(PO4)6(OH)2, has been synthesized by a precipitate-conversion technique using hydroxide gel. Hydroxyapatite crystallizes in a hexagonal structure (space group; P63/m) having lattice parameters; a=9.407 A and c=6.883 A, and around 37 nm in size for the 800°C-annealed sample. Substantial crystalline characteristics are observed for the material heat-treated at 80°C. With the increase of air-annealing temperature, from 80°C to 800°C, lattice expansion along all crystallographic axes occurs indicating a structural change in the HA lattice. These results have been attributed to (1) the formation of a relative Ca2+ deficiency in HA that incorporates various chemical species in the anionic sites compared to their lower temperature air-annealed counterparts, and (2) the precipitation of CaO with increasing air-annealing temperature. The X-ray photoelectron spectroscopy studies indicate a distorted anionic structure and two electronic states for the O1 s, corroborating the observed X-ray diffraction results.

Formation Mechanisms of Sol-Gel-Derived Hydroxyapatite Using Different Thermal Processings

Sol-gel-derived hydroxyapatite (HA) precursors were calcined by two thermal processings, a rapid-thermal-calcine (RTC) heating at 100–600°C/min and a conventional-furnace-calcine (CFC) heating at 1.67°C/min, respectively. X-ray diffraction patterns revealed that the onset temperature of HA crystallization is lower in RTC, 350°C, as compared to 600°C in CFC. Pyrolytic-GC/MS programs showed that the evolved gases out of a sample subjected to RTC are mainly H2O, N2O and ethylamine, while those of a sample subjected to CFC are CO2 and small organic molecules. The results leads to models that RTC can quickly remove organic portion of the gel networks, leading to a porous surface morphology and a collapse of gel networks at local areas, so that HA crystallite nucleation is facilitated due to intimate contacts among inorganic species at lower temperatures. On the other hand, slow evolution of organics during CFC leads to carbonaceous residues that isolate the inorganic species and inhibit nucleation of HA crystallites until at a higher temperature.

The electrochemical behavior of Bi(Pb)SrCaCuO superconductors in aqueous solutions

Abstract Electrochemical behavior of Bi(Pb)SrCaCuO superconductors was studied by potentiodynamic scanning in different aqueous solutions with a concentration of 0.1 M. The electrochemical stability, which is dependent on the passivation region and pH value of the aqueous solution, of the Bi2Sr2CaCu2Ox (2212) phase is superior in H2SO3(aq) and H3PO4(aq), while that of the Bi2Sr2Ca2Cu3Oy (2223) phase is superior in NH4OH(aq), KCl(aq) and H2SO4(aq). Passivation was observed in H2SO4(aq) and H3PO4(aq) for both phases. These solutions are thus possible etchants in lithography for these superconductors. The phase on the etched surface of the 2212 or 2223 BiSrCaCuO superconductor remained unchanged after potentiodynamic study in KCl(aq) and H2SO3(aq).