Metallic surgical implants have been widely used in orthopedics and dentistry. This paper reviews the biodegradation of metallic implants and its local and systemic effects on patients. The review discusses typical damage of 316L stainless steel, Co-Cr alloy, commercially pure Ti, and Ti-based alloy implants due to corrosion and wear and factors affecting the biodegradation of these implants. Macrophage mediation of cellular and humoral regulatory pathways in inflammatory and immune responses to metallic ions and wear debris released from the implant is summarized. Implant-related factors influencing the susceptibility to local infection are also discussed.
The crack growth rate, C, for Type 304 stainless steel was measured in-situ in 0.5M H2SO4+0.5M NaCl solutions at 25, 40 and 80°C. In this solution the steel suffers SCC thus C can be measured even at temperatures lower than the critical temperature for SCC, Tc, at and below which the steel will not suffer from SCC in the neutral chloride solutions. The crack growth rate, C, of SCC was determined in a certain range of potentials near Ecorr where the observed cracking rate, Cob, remained steady. This rate was found to be equal to the cracking rate measured in the neutral chloride solutions and is therefore applicable for use as the crack growth rate in the competition concept which states that SCC will not occur when dissolution rate exceeds cracking rate. Based on the competition concept the estimated Tc for Type 304 steel was 40-55°C which was nearly equal to 50°C measured in the previous work.
The detrimental effect of active carbon on dew point corrosion by carbon-containing sulfuric acids was investigated using Ni-Cr-Mo alloys in 60 and 80% H2SO4 with and without active carbon at 120°C. The addition of active carbon leads to an increase in the dissolution rate of the alloys over a wide potential rage from -900 to 1200mV vs. SCE, along with an increase in current densities of both anodic and cathodic reactions. Active carbon decomposes adsorbed molecular sulfuric acid into active oxygen and sulfur dioxide, the latter of which is identified by gas chromatography. The reaction of active carbon with sulfuric acid also forms sulfonic acids. These reactions lead to a decrease in the intrinsic concentration of sulfuric acid and an increase in the corrosiveness in addition to acceleration of cathodic reaction. Spontaneous passivation in carbon-containing 80% H2SO4 occurs by the formation of a remarkably chromium-enriched passive film containing about 20 cationic % of molybdenum.
In order to study the cathodic protection of type 304 stainless steel (type 304 SS) by sol-gel derived TiO2 coating under illumination of light, the photoelectrochemical behavior of TiO2/type 304 SS system was investigated. During both the dipping and subsequent heat treatment procedures, the compositional elements of type 304 SS were found to be included into the TiO2 coating, especially Fe involvement being much more intense than the other elements, which greatly decreased the photoeffect of TiO2 coating. To avoid Fe involvement, a passivation treatment with HNO3 solution was performed before TiO2 coating, resulting in the formation of a Cr enriched passive film on the type 304 SS. This Cr enrichment in the passive film retarded the Fe involvement during the TiO2 coating process, and enabled the TiO2/type 304 SS specimens to exhibit remarkably less noble photopotentials when the heating temperature was 400°C. Under the optimum conditions for the HNO3-treatment and TiO2 coating, the feasibility of cathodic protection for type 304 SS by TiO2 coating under illumination was clearly demonstrated, as the photopotentials of TiO2/type 304 SS in neutral chloride solutions were much less noble than the critical repassivation potential for crevice corrosion of type 304 SS.
In outdoor or indoor atmosphere, metallic corrosion proceeds electrochemically through thin water film on metal surfaces. The reaction rate, in this case, is expected to be larger than that in bulk solution because of accelerated mass transfer or diffusion. Yet little information has been available on the mass-transfer, current flow and electrode potential in water film corrosion because of experimental difficulties. For the measurement of electrode potential of metals covered with thin water film, the Kelvin technique was applied, in which a gold wire of 0.5mm diameter was used as the Kelvin probe for potential detection. The gold probe placed in air was oscillated sinusoidally with respect to metal surface using a piezo-actuator so that it generates AC current proportional to electrostatic potential difference between the probe and metal surfaces. It is thus possible to measure relative electrode potential without touching the electrolyte. A galvanic couple model comprising of iron and zinc was used for demonstrating potential transition at the interface. Experiments were carried out under dry and wet condition with variety of water film thickness ranging 100-3000μm, and either pure water or 5%NaCl solution. Under the pure water film of 100μm thick, potential on zinc was about -1.1V while that on iron was about -0.6V. The zone of potential transition was 3.0mm wide from the boundary into Fe surface. The width of potential transition was influenced by both water film thickness and salt concentration. The width of potential transition zone under the film of the NaCl solution was larger than that under pure water. This indicates that galvanic effect reaches further into Fe surface in salt solutions. Potential distribution at Zn/Fe boundary was explained in terms of “transmission line model”.
By using an electrochemical method, ICP (Inductive Coupled Plasma) atomic emission spectrometry and AES (Auger Electron Spectroscopy), the dissolution behavior and film compositions of pure copper, Cu-Ni alloys (10%Ni, 30%Ni and 42%Ni), and pure nickel under one-hour oxidation condition have been investigated in 0.5kmol/m3 ammonium acetate solution of pH 7.11 at room temperature. The compositions of dissolved metal ions estimated from the amounts of dissolved ions show that the preferential dissolution of Ni takes place at the active region over the whole Ni content. In the passive and transpassive regions, the preferential dissolution of Cu occurs at the lower Ni content (10%Ni), whereas that of Ni occurs at the higher Ni content. The film formed on Cu-10%Ni alloy has the enrichment of Ni in the active and passive regions. The behavior of the preferential dissolution may be explained in terms of a composition and property of a film formed on the surface.
One type of localized corrosion, known as “ant's nest corrosion”, in copper tubes is caused by decomposition products from chlorinated organic solvent and some types of lubricant oil. The decomposition products include carboxylic acids, acetates, formates and chlorides. Vinegar is mainly composed of acetic acid, which is one of the potential corrosive substances that cause this type of corrosion. 1-month and 3-months exposure tests were conducted in test tubes containing volatile acids, aldehydes and seven different vinegar-containing commercial seasonings. The severity and morphological features of this type of corrosion in copper tubes differed between types of corrosive substances and commercial vinegar-containing seasonings. The penetration depth and density of the localized corrosion in copper tubes exposed to commercial scasonings were not as great as those in copper tubes exposed to volatile acids and aldehydes.
High temperature corrosion of MgO-stabilized ZrO2, MgO, Alumina, and Mullite on the market in chlorine and hydrogen chloride gases at 1273K has been investigated. MgO is converted into chlorides and the products volatilized, which leads to the weight loss of specimen. In the case of MgO-stabilied ZrO2, the depletion of MgO in the outer surface region of specimen leads to an increase in the amount of monoclinic ZrO2. Because the purity of alumina and mullite on the market is high enough, the corrosion resistance is quite excellent.