Electrochemical concepts and techniques in the study of stainless steel ennoblement.

Electrochemical theory and technique used to investigate microbially influenced corrosion is discussed with a focus on methods used to demonstrate the manganic-oxide mechanism of stainless steel Ennoblement. The concept of mixed potential and its relationship to the current-voltage behavior of stainless steel is developed. This concept is used to interpret microbially induced changes in corrosion potential, polarization behavior, surface-oxide abundance, and the redox environment at submerged metal surfaces. Microelectrode, capacitance, and coulometric methods are described that can be used to discriminate electrochemical effects caused by changes in solution properties from those caused by mineral deposition at the metal surface. The variety of electrochemical, wet-chemical, microbiological, and surface analytical techniques used to demonstrate the effect of biomineralized manganese dioxide on the electrochemical behavior of stainless steel are summarized.

Ennoblement of Stainless Steel by the Manganese-Depositing Bacterium Leptothrix discophora.

The noble shift in open-circuit potential exhibited by microbially colonized stainless steel (ennoblement) was investigated by examining the relationship among surface colonization, manganese deposition, and open-circuit potential for stainless steel coupons exposed to batch cultures of the manganese-depositing bacterium Leptothrix discophora. Open-circuit potential shifted from -100 to +330 mV(infSCE) as a biofilm containing 75 nmol of MnO(infx) cm(sup-2) formed on the coupon surface but changed little further with continued MnO(infx) deposition up to 270 nmol cm(sup-2). Increased open-circuit potential corresponded to decreasing Mn(II) concentration in solution and to increased MnO(infx) accumulation and attached cell density on the coupon surfaces. MnO(infx) deposition was attributable to biological activity, and Mn(II) was observed to enhance cell attachment. The experimental results support a mechanism of ennoblement in which open-circuit potential is fixed near +350 mV(infSCE) by the cathodic activity of biomineralized MnO(infx).

Manganese biofouling and the corrosion behavior of stainless steel.

Manganese- and iron-oxidizing bacteria (MFOB) are widely implicated in microbially influenced corrosion, often in association with sulfate-reducing bacteria (SRB). Traditionally MFOB have been assigned a passive role in the corrosion process, promoting differential aeration cells, and providing oxygen depleted conditions conducive to the growth and corrosive attack of SRB. Recent work, summarized in this article, demonstrates that manganese biofouling alters the electrochemical behavior of stainless steel (SS), and suggests that MFOB are more active in localized corrosion than traditionally held. The paper discusses the chemistry and potentially corrosive impact of manganese and iron oxides on SS, explores the possible relationship between MFOB and SRB, and proposes a model to describe the synergistic influence these organisms may exert in the corrosion process.

Muscle strength testing following surgery for acetabular fractures.

A retrospective clinical analysis was performed on 30 patients who underwent surgery for acetabular fractures. In addition to clinical and radiographic evaluations, muscle strength was tested using an isokinetic dynamometer. Average follow-up time was 21 months. Joint surface and congruency were restored within 3 mm in 29 of 30 cases. The average hip score was 83. Eight patients had an unsatisfactory result. Only 14 patients had a normal gait, while seven patients had a Trendelenburg gait. The overall strength deficit was 27%. This mean strength deficit was highly correlated with the hip-rating score. The greatest loss of strength was in abduction, where the average deficit was 50%. The loss of abduction strength was significantly greater for patients operated on through posterior approaches. Among patients operated on through a Kocher-Langenbeck approach, those with transverse fractures had significantly larger losses of abduction strength than those with posterior wall fractures.