tribochemical.pdf

Materials Science and Engineering C 23 (2003) 461–465

www.elsevier.com/locate/msec

Tribochemical structuring and coating of implant metal surfaces with

titanium oxide and hydroxyapatite layers

U. Gbureck a, * , A. Masten a , J. Probst b , R. Thull a

a Chair of functional Materials in Medicine and Dentistry, Universit¨tofW¨rzburg, Am Pleicherwall 2, D-97070 W¨rzburg, Germany

b Fraunhoferinstitut f¨r Silicatforschung, Neunerplatz 2, D-97070 W¨rzburg, Germany

Abstract

The sandblasting process with corundum is used for cleaning, roughening and activating of metal surfaces in dentistry and orthopaedics.

The high local energy transfer at the impact point originates the displacement of particles in the surface. In principle, this method can be used

for coating surfaces by sandblasting. In this work, we present a newly developed technique, which allows the coating of metal surfaces with

titanium dioxide (TiO 2 ) and hydroxyapatite (HA) using a sandblasting process. The blasting material is a composite ceramic consisting of an

alumina core (carrier material) covered with a porous shell of titanium dioxide or hydroxyapatite. The technique is applied to titanium

substrates; the surface roughness, morphology and composition of the samples are analysed. The procedure results in an averaged surface

roughness of 10–15 Am. Energy dispersive X-ray analysis (EDX) indicates the formation of a thin layer consisting of coating material on the

metal surface. Furthermore, the traces of corundum crystals, which are inevitable by using the common technique, i.e. sandblasting with

single-component grains, are clearly decreased. X-ray diffraction analysis (XRD) indicates mainly the existence of crystalline rutile and

hydroxyapatite/h-tricalcium phosphate (h-TCP) on the surface. Therefore, the presented method would be suitable for simultaneously

roughening, coating and optimizing the biocompatibility of metal implant surfaces in dentistry and endoprosthetics.

Keywords: Sandblasting; Titanium oxide; Hydroxyapatite; Tribochemical

1. Introduction

The impact not only affects the metal surface but addi-

tionally leads to the deformation and in some cases to the

total disintegration of the grain itself. Thereby the aluminum

oxide partly gets incorporated within the metal surface, i.e.

corundum sandblasted surfaces become Al 2 O 3 -contami-

nated [4–6] .

In our method, this contamination effect is utilised for

coating the metal surface during the sandblasting process.

The pure corundum grains are therefore replaced with

composite ceramics consisting of a massive core, the base

material, and a porous shell, i.e. a layered material. This

results in a tribochemical coating of the metal due to the

sandblasting procedure. Thus, simultaneous roughening,

activation and coating of the substrate becomes feasible.

In the field of dental prosthesis, this procedure is already in

use. Here the metal surfaces get conditioned with a silicon–

ceramic layer serving as a hydrolytic stable interface be-

tween metal and polymer [7] .

The main goal of the presented work was the development

of a reproducible method which allows the conditioning of

titanium and CoCr-alloys via sandblasting with titanium

dioxide or hydroxyapatite. Therefore, the surface treatment

Sandblasting with corundum is a common method for

cleaning, roughening and activating metal surfaces for

applications in dentistry and orthopaedics [1–3] . The

impact of a grain on the metal surface results in the transfer

of its momentum and kinetic energy, respectively. The

kinetic energy is partly absorbed by the crystal lattice

causing surface melting within a microscopic range. More-

over, a larger area of lattice defects is observed. The

dimensions of the melting zone and the lattice defect zone,

respectively, depend on the material properties of the metal

substrate and on the energy of the blasting grain. Local

changes of the metal surface structure initiated by the grain

impact are schematically shown in Fig. 1 . Note that the

particle momentum shown and the corresponding kinetic

energy are restricted to the surface area.

* Corresponding author. Tel.: +49-931-201-73550; fax: +49-931-201-

73500.

E-mail address: uwe.gbureck@fmz.uni-wuerzburg.de (U. Gbureck).

PII: S0928-4931(02)00322-3

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U. Gbureck et al. / Materials Science and Engineering C 23 (2003) 461–465

Fig. 1. Variations of a metal surface at the impact point of a grain during sandblasting process.

of metal implants, which will be in contact with bone tissue, is

scheduled to be the area of application. The generated

tribochemical layers are characterized with regards to surface

morphology, composition, roughness and adhesion.

avoid texture effects, measurements were performed on

rotating samples.

3. Results

2. Materials and methods

3.1. Composite blasting material

Composite ceramics for sandblasting were synthesized

by sintering aqueous titanium dioxide (TiO 2 ) or hydroxya-

patite (HA) suspensions on corundum (110 Am medium

particle size) at a mass ratio of 1:5. Typically 200 g of fine

powdered coating material was suspended in 300 ml of

water and stirred for 1 h. Afterwards, 1000 g of corundum

were added to the suspension. After drying the suspension at

100 jC, the materials were sintered at a temperature of 1250

jC for 1 h and subsequently sieved. In order to achieve an

optimized covering of the corundum grains with TiO 2 or

HA, the coating procedure was repeated. The sandblasting

of commercial pure (cp) titanium plates (d = 16 mm) was

performed by using a sandblaster Topstar 3 (Bego, Bremen,

Germany) at a blasting pressure of 0.4 MPa for 20 s/cm 2 .

The surface roughness was measured with a profilometer

Surftest 211 (Mitutoyo, Japan); five measurements were

carried out at various positions on the surface; the average

and the deviation were calculated.

SEM-analyses were performed with a DSM 940 (Zeiss,

Oberkochen, Germany). Energy dispersive X-ray analysis

(EDX) of the sandblasted surfaces were recorded with a

QX2000 system (Link, England) at a working distance of 25

mm, an acceleration voltage of 10 kV. To determine the

adhesion of the coatings, the samples were cleaned accord-

ing to custom [8,9] ultrasonically for 15 min in deionised

water and once more characterized by EDX.

The phase composition of the coatings was investigated

with an X-ray diffraction system D5005 (Siemens, Karls-

ruhe, Germany) in the range of 2Theta = 20–50j. In order to

Twofold sintering of aqueous TiO 2 or HA suspensions

onto corundum in a mass ratio of 1:5 revealed as a proper

method to synthesize the composite ceramics. After the

coating procedure, the surface of the corundum grains is

covered by a porous shell of coating material. It was proved

by X-ray diffraction analyses that no aluminium titanate or

calcium aluminate was formed at the sintering temperature

of 1250 jC.

Fig. 2. SEM-micrograph of a titanium surface sandblasted with a TiO 2 /

corundum composite ceramic.

U. Gbureck et al. / Materials Science and Engineering C 23 (2003) 461–465

463

Fig. 3. SEM-micrograph of a titanium surface sandblasted with a TiO 2 /

corundum composite ceramic; ultrasonically cleaned in deionised water for

15 min.

3.2. Surface morphology

In a macroscopic scale, the metal surface shows a dark

grey colour after the sandblasting process with the compo-

site ceramics. In contrast, sandblasting with pure corundum

normally retains the colour of the untreated metal surface.

Figs. 2 and 3 show SEM micrographs of tribochemical

coated titanium, sandblasted with the TiO 2 composite

ceramic.

The coating appears to be strongly adhesive to the metal

substrate. After the ultrasonic cleaning procedure, the sur-

face morphology remained unchanged (Fig. 3) .

The results of the surface roughness measurements are

listed in Table 1 . The average roughness is in the range of

10–15 Am. Compared to pure corundum, the surface rough-

ness is slightly increased for the composite ceramics. This

may be due to the larger average grain mass.

Fig. 4. EDX-analysis of tribochemically coated titanium surfaces; surface

sandblasted with (A) corundum, (B) TiO 2 composite ceramic, (C) TiO 2

composite ceramic (ultrasonically cleaned), (D) hydroxyapatite composite

ceramic and (E) hydroxyapatite composite ceramic (ultrasonically cleaned).

corundum, the use of composite ceramics yields to a

significantly decreased alumina embedding within the sur-

face. The titanium dioxide and hydroxyapatite layers are

mostly resistant against further surface cleaning. The result

is a strong adherence of the coatings. Element distribution

micrographs also indicate a homogeneous coating of the

metal surface (Fig. 5) .

3.3. EDX analysis

The EDX analyses of a titanium surface sandblasted with

corundum and TiO 2 or hydroxyapatite blasting materials

before and after the ultrasonic cleaning procedure are shown

in Fig. 4 . Compared to the sandblasting procedure with pure

Table 1

Surface roughness of titanium sandblasted with various blasting materials

Blasting material

Average surface

roughness r z (Am)

Maximum surface

roughness r max (Am)

Corundum, 110 Am 8.54F0.8

9.68F0.8

TiO 2 /corundum

composite ceramic

12.3F0.7

14.8F2.5

HA/corundum

composite ceramic

13.3F1.2

15.3F2.2

Fig. 5. Calcium and phosphate element distribution of a titanium surface

sandblasted with a hydroxyapatite/corundum composite ceramic.

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U. Gbureck et al. / Materials Science and Engineering C 23 (2003) 461–465

Fig. 6. X-ray diffraction-analysis of tribochemically coated titanium

surfaces; surface sandblasted with (A) hydroxyapatite composite ceramic,

(B) TiO 2 composite ceramic and (C) corundum.

As deduced from EDX analyses and SEM micrographs,

the coatings show a strong adherence to the metal surface

and are almost resistant against ultrasonic cleaning. There

are three adhesion mechanisms, which can be considered:

physical bonding, incorporation of the coating material

within the surface and thermochemical reactions among

substrate and deposited material. An indication for a chem-

ical reaction could be the formation of aluminium or

calcium titanates. Such compounds were not detected,

maybe due to the detection limit of 1–2 wt.% of XRD

surface analyses. The most likely adhesion mechanism is

considered to be a strongly enhanced interdiffusion at the

impact point of a grain due to local surface melting. A

similar mechanism was already discussed by Ishikawa et al.

[10] who observed a sintering of fine hydroxyapatite grains

with titanium and among themselves during the sandblast-

ing process.

The methods used in this work (EDX and XRD) give

information about element and phase composition of the

surface with an analytical depth of about 2–20 Am. The

bone implant interaction is mostly affected by the properties

of the implant material near the interface. Previous studies

on tribochemical TiO 2 and SiO 2 coatings deposited on

stainless steel by means of electron spectroscopy for chem-

ical analysis (ESCA) showed a TiO 2 content on top of the

surface of 65% which decreased to about 48% in 1.1 Am

analytical depth. The thickness of the layer was calculated to

be 5–6 Am. No sharp interface between coating and metal

surface is expected, but a gradient-like composition [11] .

Therefore, future works will present XPS analyses of the

here considered TiO 2 and HA coatings. This method can

give additional informations about the composition of the

surface layer with an analytical depth of a few nanometers.

As mentioned before, the tribochemical TiO 2 and

hydroxyapatite coatings are of great interest with regard to

the required modifications of dental and orthopaedic implant

surfaces. State of the art is sandblasting with pure corun-

dum. Using this method, our investigations show a content

of about 30–35% corundum within the surface which is not

removable by ultrasonic cleaning neither in aqueous nor in

alcoholic solutions. Instead of this, our presented novel

tribochemical coating technique emerged as a proper as

well as a simple method in order to reduce the contami-

nation with corundum and to reinforce the native oxide layer

of titanium. Furthermore, the surface modification with

hydroxyapatite promotes bone ingrowth. The method

should also be applicable to other materials, e.g. stainless

steel or CoCr-alloys. Future works should be engaged in the

optimization of the composite ceramics with respect to the

resulting TiO 2 or HA covering and the achievable roughness

of the sandblasted surface. Variations of the grain size as

well as the TiO 2 (HA)/corundum ratio appear to be promis-

ing. In order to avoid any corundum contamination, TiO 2

could be used as core material of the composite ceramic

grains, but note that a biphasic grain composition is still

required to achieve a homogenous surface coating. Single

3.4. X-ray diffraction analysis

The X-ray diffraction analysis (XRD) patterns of tita-

nium after sandblasting with corundum, TiO 2 or HA-coated

corundum are shown in Fig. 6 . The peaks observed corre-

spond to titanium, corundum, rutile and hydroxyapatite/h-

tricalcium phosphate (h-TCP). The existence of the h-TCP

phase is traced back to a slight impureness of the hydrox-

yapatite raw material. Other phases as titanium aluminate or

calcium titanate, which would point at mechanochemical

reactions between blasting material and titanium substrate,

are not detected.

4. Discussion and conclusions

In this work was shown that a novel sandblasting

technique with composite ceramics makes the coating of

cp titanium with TiO 2 or HA possible. As observed for

corundum blasted surfaces, the result is a micro-mechanical

structured and activated implant surface with an average

surface roughness of 10–15 Am. The advantages of the

novel technique are the reduction of corundum contamina-

tion as well as the deposition of thin biocompatible TiO 2 or

calcium phosphate layers, which was shown via EDX and

XRD analyses.

U. Gbureck et al. / Materials Science and Engineering C 23 (2003) 461–465

465

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