Effect of Heat Treatment on High Pressure Plasma Sprayed Hydroxyapatite Coatings

Abstract

T his paper reports the characteristics and properties used to characterise these coatings. Scanning electron microscopy ( SEM) was used to observe surface and of two diVerent sets of hydroxyapatite ( H A) coatings cross-section morphology of both powder and sprayed obtained by thermal spraying two diVerent H A powders, coatings. T he phase and chemical characteristics of the spray dried H A ( SDH A) and spheroidisided H A samples were evaluated by X -ray diVraction ( X R D) ( SH A) , at various chamber pressures. T he evaluation and Fourier transform infrared spectrometry ( FT IR) . of the coatings following post-spray treatment at 800°C Finally, in order to have a qualitative measure of the is also included. Comparisons to the results from the integrity of the coatings, V ickers hardness testing was as sprayed coatings were made to show the eVects of performed on polished cross-sections of the coatings. post-spray heat treatment. T he median particle sizes SE/S230 for SDH A and SH A were 35 and 47 mm, respectively. T he main diVerence between the powders is their Dr Espanol ( P43690802W@ntu.edu.sg) and Dr K hor density and morphology. T he SH A powder provides are at the Nanyang T echnological University, School higher density and spherical morphology, and a more of Mechanical and Production Engineering, Nanyang porous and rough surface is present in the SDH A Avenue, Singapore 639798, Singapore. Dr Guipont and powders. T hese two powders were sprayed using a Dr Jeandin are at the Ecole Nationale Supérieure des controlled atmosphere plasma spraying ( CAPS) system Mines de Paris/C2P, Center for Plasma Processing, in the inert plasma spray ( IPS) and high pressure BP87, 91003 Evry cedex, France, and Dr Llorca-Isern plasma spray ( HPPS) modes. Four diVerent pressures is at the Universitat De Barcelona, Metallurgical and of 100, 150, 200, and 250 kPa were applied in an argon Chemical Engineering Department, Marti i Franques atmosphere. Post-spray heat treatment was performed 1, 08028 Barcelona, Spain. Manuscript received 12 to increase the crystallinity of the coatings, to homogDecember 2001; accepted 27 A pril 2002. enise their structure, and to convert other calcium phosphate phases to H A . DiVerent techniques were

Production and characterization of plasma-sprayed TiO2–hydroxyapatite functionally graded coatings

“…In fact, it is known from the literature that plasma spraying usually induces a thermal decomposition of HAp, decreasing its crystallinity and giving place to various decomposition products. 4,20,26 As regards the HAp crystallinity, though it is usually acknowledged that a small amount of amorphous HAp may be advantageous at the coating surface, because it may promote profitable physiological activities, a high degree of crystallinity is generally preferable, 27,28 because highly crystalline HAp may create a direct bond with bone in vivo and show low dissolution rates. On the other hand, as regards the CaO, since its content in the feedstock HAp powder was negligible, its presence in the sprayed coatings could be considered as representative of the development of byproducts.…”

“…Moreover, the content of calcium oxide should be minimized because CaO is extremely reactive with water and undesired in biomedical implants 28 and, if its content is excessive, it cannot completely transform into HAp during post-deposition heat treatments. 26,28 These values of torch power (40 kW) and H 2 flux (5 slpm) were used to deposit the graded coating, according to the approach previously described. The microstructure of the graded coating is presented in Fig.…”

Effect of Heat Treatment on Characteristics of Plasma Sprayed Hydroxyapatite Coatings

“…On the contrary, when crystallization and phase transformations occur, the stresses caused by the associated volume change orinigating from the transformation of various nonapatite phases to apatite is superimposed on the residual stresses already present, which can induce cracking inside the deposit. 21,44) Many studies claimed that the coatings adjacent to substrate have more amorphous phase. 8,35) When heattreated at higher temperature such as 700 C, the regions near the substrate may result in a larger amount of cracks caused by the large volume shrinkage during the crystallization and phase transformation, in turn, detrimental to the bonding strength of the coating, although possessing a higher crystallinity.…”

In vitro characterisation of plasma-sprayed apatite/wollastonite glass–ceramic biocoatings on titanium alloys

“…21,22 One of the most accepted and commercialised bioactive coating is the plasmasprayed hydroxyapatite (HA) coating. [23][24][25][26][27][28] The advantages of the plasma-spray technique are the high deposition rate and the high bonding rate between the plasma-sprayed biocoatings and human tissues. The HA-coated implants still have some serious drawbacks resulting in significant challenges in their expanded utilisation.…”