Biomedical Engineering Reference
In-Depth Information
At the same time, the studied model should conform to the measurement techniques used in
materials science laboratories like electron microscopes, X-ray diffraction, tensile tests, and pin on
disk friction testing device. This dilemma was encountered in all the measurements reported here
and beyond. In fact, for most of the experiments done in the present laboratory, the time spent on
designing, constructing, and readapting the experimental models was by far the longest compared
to the data collection and analysis.
13.4.2
Coating process and tribological measurements
13.4.2.1
SS wires with IF-WS
2
impregnated in electroless nickel
phosphorous film
0.025 in.
2
rectangular SS) were coated by electroless
Orthodontic wires (Ormco, California 0.019
3
process with a uniform and smooth nickel
P) film using 100 mL solution
(ENPLATE Ni-425, Enthone Inc.)
[35]
. The orthodontic wires (or SS plate substrate) were inserted
into the electroless Ni
phosphorous (Ni
P bath (88
C, pH
5
4.8, magnetic stirring) for 30 min. The plating
resulted in a shiny smooth Ni
P layer. To another electroless solution, 200 mg of agglomerated
IF-WS
2
powder with average particle size of 120 nm was added together with a cationic surfactant
(cetyl-trimethylammoniumbromide: CTAB). A short (1 min) sonication (Sonifaier 150, Branson-30
Watts) was used to disperse the agglomerates and ensure the stability of the suspension. A special
procedure was developed to deposit a uniform and relatively smooth composite Ni
IF film
and secure its adequate adherence to the underlying archwire. Following hydorfluoric acid etching,
a pure Ni film was electron-beam deposited onto the substrate; then Ni
P
1
P film was deposited from
the electroless solution. Finally, a composite Ni
IF film was deposited. In several cases, the
coated samples were annealed in nitrogen gas atmosphere at 400
C.
P
1
13.4.2.2
SS wires with IF-WS
2
impregnated in electrocodeposition nickel film
The IF-WS
2
NP were dispersed in an aqueous solution of nickel salt (NiCl
2
3
6H
2
O) and plated on
0.025 in
2
and made of SS 110 mm in length (provided
by Ormco Corporation, Orange, CA)
[38]
. The coating was produced by the electrochemical
codeposition process with a direct current of 0.02 A and exposure of 20 min for every wire piece at
25
C. To minimize the agglomeration of the IF NP in the bath, a combination of ultrasonic treat-
ment and the CTAB surfactant was used.
a wire with a cross section of 0.019
3
13.4.2.3
Ni
Ti wires with cobalt and IF-WS
2
film by electroplating procedure
Ni
Ti (Nitinol) wires were supplied by the following companies: Orthonol (CO, USA); Ormco
(CA, USA), Nitinol Classic (CA, USA); Dentsply (NY, USA). Codeposition of cobalt and IF-WS
2
NP film was carried out from a cobalt chloride
IF solution buffered by boric acid and CTAB as
surfactant
[39]
. The film was deposited at 55
C by galvanostatic plating with a current density
of 15 mA/cm
2
. In order to assure proper adhesion of the film to the substrate, Ti (10 nm) and
Ni (20 nm) films were deposited onto the cleaned Ni
1
Ti wires by electron-beam evaporation prior
to the electrodeposition process. Uniformity of the coating was achieved by rotating the sample.
The effects of cobalt coatings of endodontic files with impregnated fullerene-like WS
2
NP on
file fatigue and failure were also examined. Dynamic X-ray diffraction (XRD), nanoindentation,
and torque measurements all indicate a significant improvement in the fatigue resistance and
consequently delay in the time to breakage of the coated files. This observation was attributed to
