**1.2.2.3 Corrosion potential test of the material in simulated physiological environment**

Corrosion potential was measured with DJS-292 potentiostat. The connecting diagram is as shown in figure 1-2.The reference cathode was saturated calomel electrode (SCE). The sample was connected with copper wire, its working area was 10mm×10mm, and non-working area coated with silica gel. The samples both before and after cathodic-electrodeposition were dipped into Hank's solution (PH7.45) and Fusayama solution (PH6.13) respectively, then recording the electrode potential and time, potential value recorded once every one minute, until the potential no changing basically. Finally a curve of corrosion potential changed with time could be charted. The experimental parameters were set as in table 1-1.

Fig. 1-2. Schematic plan corrosion potential test

Ti-O Film Cathodically-Electrodeposited on

PH1.2 respectively, and the electrolyte without NO-

**1.3 Experimental results and discussion** 

**1.3.1 Cathodic-electrodeposition of Ti-O film** 

TiNi SMA. Its producing process is as following:

**1.3.2 The composition analysis of Ti-O film** 

NO3-

2H2O + 2e → H2 + 2OH-

**electrodeposition** 

and 0.2M of NO-

investigated.

of PH value and NO-

the Surface of TiNi SMA and Its Bioactivity and Blood Compatibility 7

With the SZX-STAD2 type of OLYMPUS metallurgical microscope, observation of the Ti-O films obtained by cathodic-electrodeposition for 4min in the electrolytes of PH0.71 and

Depositing TiNi SMA setting in different bearings, making direction of air flow produced during the TiNi SMA deposition different directions, with the SZX-STAD2 type of OLYMPUS metallurgical microscope, the effect of air flow on Ti-O film morphology was

Under trielectrode system, in mixing well the self-prepared Ti(SO4)2 solution electrolyte, catodic-electrodeposition was carried out at a constant current density of 5mA/cm2 for 4min. Because NO3- and H2O on the surface of cathode sample obtained electrons to be reduced, making sample surface PH value get high, moreover Ti (IV) could be easily hydrolyzed, so that a layer of amorphousstate Ti-O film was deposited on the surface of

+ 6H2O + 8e → NH3 + 9OH-

Ti4+ + 4OH- → Ti(OH)4 (1.3)

Figure 1-3 shows the SEM topography (at different amplifications) of a Ti-O film cathodically-electrodeposited. It can be seen from the figure that under this experimental parameter, the Ti-O film obtained was well-distributedly deposited on TiNi SMA surface. This Ti-O film is closely composed of a lot of tiny particles, the particle's size is in about dozens of nanometers. This close bonding of the particles in nanometer class is conducive to strengthen the TiNi SMA surface properties, and to prevent Ni release from substrate.

Figure 1-4 shows an EDS analysis of the Ti-O film after cathodic-electrodeposition. It can be seen from the figure that this film mainly contains Ti element, as well as a small of amount of Ni element, and the ratio of Ti and Ni reachs 3:1. It illustrates that there is a lot of Ti element in the film. Because EDS might possibly puncture the Ti-O film, thus reflecting the substrate's element, so it could be preliminarily verified that by cathodic-elcetrodeposition, a layer of film

mainly including Ti element indeed has been deposited on the surface of TiNi SMA.

The Ti(SO4)2 gel reactively produced was deposited on the surface of the sample.

3 concentration on cathodic-electrodeposition.

3 adding in respectively, were carried out, in order to investigate the effect

3 added in and electrolyte with 0.02M

(1.1)

(1.2)

**1.2.2.8 Effect of electrolytes' PH values and NO3 concentration on cathodic-**

**1.2.2.9 Effect of air flow curtain on surface morphology of Ti-O film** 


Table 1-1. Parameters of dynamic polarization test
