Fig. 5 shows the measured electrochemical impedance spectra
of 316L stainless steel samples with and without Pd films in 20%
H2SO4 solution at open circuit potentials. It is seen that in 20%
H2SO4 solution at 102 C 316L stainless steel showed very small
impedance, indicating that the steel was in active dissolution
state. The palladium plated samples showed much higher impedance
values. The impedance values for both electroplated and
electroless plated samples increased by 3–4 orders of magnitude
compared with the sample without Pd films. It is an indication
that stable passivation was established on the surface of the samples.
The results are quite consistent with those obtained from
polarization tests. Palladium plating on stainless steel effectively
improved passive ability of the steel in strong reductive corrosive
environments.
The porosity tests showed that the electroless plated film has
lower porosity, but corrosion rate of the electroless plated samples
is a little higher than that of the electroplated film. This result indicates
that the increase of corrosion resistance by Pd plating on
stainless steel does not rely on the barrier effect of the films. The
standard oxidation/reduction potential of Pd/Pd2+ is +0.987 VSHE
or +0.743 VSCE, much higher than that of stainless steels. As a
cathodic film, the function of palladium film to improve corrosion
resistance of stainless steel is mainly due to its effect of promoting
passivation. In strong reductive corrosion mediums like boiling
sulfuric acid solutions, the passive film on 316L stainless steel is
not stable and active dissolution happens at open circuit potential.
However, the polarization curves in Fig. 4 show that passivation is
possible at higher potential range. With palladium films, the open
circuit potentials of stainless steel in boiling sulfuric acid solutions
were raised to higher potential range where passivation was again
established on the surface.
The measured corrosion potential may more or less reflect the
stability of passivation under the experimental conditions. The
samples with electroless plated Pd film showed more negative
corrosion potential and slightly higher corrosion rate than the
samples with electroplated Pd films, which should be attributed
to the presence of phosphorus and nitrogen in the film. The almost
pure palladium film without impurities by electroplating
may lead the stainless steel surface to higher open circuit potential
and relatively higher passive ability. Another advantage of
electroplating is the plating time needed for the same film
thickness is much shorter than electroless plating. Both of the palladium
plating techniques may be used to improve corrosion
resistance
316L不锈钢样品和无钯薄膜在20 ％
H2SO4溶液中的开路电位。它被看作是在20 ％
H2SO4溶液在102摄氏度316L不锈钢显示非常小
阻抗，表明钢积极解散
状态。 The palladium plated samples showed much higher impedance
价值观。阻抗值为电镀和
化学镀样品增加了3-4个数量级
相对於样品无钯薄膜。这是一个迹象
稳定的钝化成立表面的样本。
结果是相当符合这些从
偏振测试。钯电镀不锈钢有效
改善被动能力钢在还原性强腐蚀性
环境。
孔隙率测试结果表明，化学镀薄膜
低孔隙度，但腐蚀速率的化学镀样本
有点高於电镀电影。这一结果表明
所增加的耐腐蚀性能钯电镀
不锈钢不依赖於隔离墙影响的电影。那个
标准氧化/还原电位的Pd/Pd2 +是0.987 VSHE
或0.743 VSCE ，远远高於不锈钢。作为一个
阴极薄膜，功能的钯膜，以改善腐蚀
阻力不锈钢主要是由於其影响促进
钝化。在强腐蚀介质还原一样沸腾
硫酸的解决方案，钝化膜对316L不锈钢是
没有稳定的和积极的解体发生在开路电位。
然而，极化曲线图。 4表明，钝化
可能在更高的潜在范围。与钯薄膜，开放
电路电位不锈钢在硫酸沸腾的解决方案
提出了更高的潜在范围又在那里钝化
成立於表面。
腐蚀电位的测定可能或多或少地反映了
稳定的钝化在实验条件下。那个
样品镀钯薄膜显示更多的负面
腐蚀电位和腐蚀速率稍高比
样品电镀钯薄膜，这应归功於
在场的情况下，以磷，氮的电影。几乎
纯钯薄膜无杂质的电镀
可能导致不锈钢表面，以更高的开路电位
和相对较高的被动能力。另一个优点
电镀是电镀所需的时间相同的电影
厚度为短得多镀。两个钯
电镀技术可用於改善腐蚀
阻力
