Nowadays there is a strong demand to replace Ni-Cr steels used for biomedical applications such as brackets in orthodoncy with a new generation of more biocompatible austenitic, nickel-free alloys. The aim of this work is the assessment of the substances that leach from the steel and the investigation of the growth and stability of the surface film formed on DIN 1.4456 Ni-free stainless steel in artificial saliva (pH 7.9) at 37°C by electrochemistry and XPS surface analyses. So far the data available in the literature refer to tests carried out at ambient temperature. Previous works of this research group [1] have shown that Ni-free stainless steel immersed into 0.1M NaOH solution form a passive film that changes its composition with immersion time. These results are confirmed in the present investigation: the corrosion current values decrease from 1 to 24 hours exposure time (see Table) to the solution and the passive film becomes more protective and thick. XPS provides evidence that the surface film formed is mainly composed of oxides and hydroxides of Fe (III), Cr(III) and Mn (see figure). Fe (II) amount in the passive film decreases with immersion time in favor of Fe (III) oxide (Fe2O3) and hydroxide (FeOOH). Cr as well is first present as Cr2O3 and turns to Cr(OH)3 for longer contact time to artificial saliva. The results will be discussed in comparison with those obtained on at ambient temperature [ref]. References. 1. T. H. Huang, Am. J. Orthod. Dentofac. (2001), 120, 1 2. C.T. Kao, Eur. J. Orthod. (2010), 32, 555-560 3. B. Elsener, Elec. Acta (2011), 56,4489-4497
Surface chemistry of Ni-free stainless steel
FANTAUZZI, MARZIA;ELSENER, BERNHARD;ROSSI, ANTONELLA
2012-01-01
Abstract
Nowadays there is a strong demand to replace Ni-Cr steels used for biomedical applications such as brackets in orthodoncy with a new generation of more biocompatible austenitic, nickel-free alloys. The aim of this work is the assessment of the substances that leach from the steel and the investigation of the growth and stability of the surface film formed on DIN 1.4456 Ni-free stainless steel in artificial saliva (pH 7.9) at 37°C by electrochemistry and XPS surface analyses. So far the data available in the literature refer to tests carried out at ambient temperature. Previous works of this research group [1] have shown that Ni-free stainless steel immersed into 0.1M NaOH solution form a passive film that changes its composition with immersion time. These results are confirmed in the present investigation: the corrosion current values decrease from 1 to 24 hours exposure time (see Table) to the solution and the passive film becomes more protective and thick. XPS provides evidence that the surface film formed is mainly composed of oxides and hydroxides of Fe (III), Cr(III) and Mn (see figure). Fe (II) amount in the passive film decreases with immersion time in favor of Fe (III) oxide (Fe2O3) and hydroxide (FeOOH). Cr as well is first present as Cr2O3 and turns to Cr(OH)3 for longer contact time to artificial saliva. The results will be discussed in comparison with those obtained on at ambient temperature [ref]. References. 1. T. H. Huang, Am. J. Orthod. Dentofac. (2001), 120, 1 2. C.T. Kao, Eur. J. Orthod. (2010), 32, 555-560 3. B. Elsener, Elec. Acta (2011), 56,4489-4497
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