Assessment of stress corrosion crack initiation and propagation in AISI type 316 stainless steel by electrochemical noise technique

Electrochemical noise (EN) analyses, using time domain, frequency domain and statistical parameters, were carried out on the potential and current data obtained on AISI type 316 stainless steel during (i) pitting corrosion in deaerated 0.5 M sodium chloride (NaCl) solution, and during (ii) stress corrosion cracking (SCC) in boiling acidified NaCl solution. Visual records and statistical analysis of the current and potential data alongwith the spectral estimation using maximum entropy method (MEM) gave useful informations on differentiating between these corrosion processes and on the effect of stress in accelerating pitting corrosion. The results correlated well with the optical microscopic observations.     

Recursive exponentially weighted PLS and its applications to adaptive control and prediction

A new and fast recursive, exponentially weighted PLS algorithm which provides greatly improved parameter estimates in most process situations is presented. The potential of this algorithm is illustrated with two process examples: (i) adaptive control of a two by two simulated multivariable continuous stirred tank reactor; and (ii) updating of a prediction model for an industrial flotation circuit. The performance of the recursive PLS algorithm is shown to be much better than that of the recursive least squares algorithm. The main advantage of the recursive PLS algorithm is that it does not suffer from the problems associated with correlated variables and short data windows. During adaptive control, it provided satisfactory control when the recursive least squares algorithm experienced difficulties (i.e., ‘blew’ up) due to the ill-conditioned covariance matrix, (X^TX)_t. For the industrial soft sensor application, the new algorithm provided much improved estimates of all ten response variables.     

Effect of Solution Annealing on Susceptibility to Intercrystalline Corrosion of Stainless Steel with 20% Cr and 8% Ni

In general, as-received (AR) austenitic stainless steels (ASSs) contain complex carbide precipitates due to manufacturing operations, subsequent annealing treatment, or due to the fabrication processes such as welding. The presence of pre-existing carbides leads to cumulative sensitization and make the steel susceptible to intercrystalline corrosion (ICC)/intergranular corrosion (IGC) which causes premature failure during service. Solution annealing (SA) is one of the ways to deal with such situations. In this present investigation, the AR (hot rolled and mill annealed) chromium-nickel (Cr-Ni) ASS is compared with SA Cr-Ni ASS. The extent of ICC/IGC was evaluated qualitatively and quantitatively by various electrochemical tests including ASTM standard A-262 Practice A and Practice E, double loop electrochemical potentiokinetic reactivation and electrochemical impedance spectroscopy. The degree of sensitization for hot rolled mill annealed AR condition is found to be substantially higher (51.55%) than that of SA condition (26.9%) for thermally aged samples (at 700 °C). The chemical composition across the grain boundary was measured using electron probe micro-analyzer for both (AR and SA) conditions and confirms that the pre-sensitization effect was completely removed after SA treatment.     

Use of Electrochemical Noise (EN) Technique to Study the Effect of sulfate and Chloride Ions on Passivation and Pitting Corrosion Behavior of 316 Stainless Steel

In the present paper, studies were conducted on AISI Type 316 stainless steel (SS) in deaerated solutions of sodium sulfate as well as sodium chloride to establish the effect of sulfate and chloride ions on the electrochemical corrosion behavior of the material. The experiments were conducted in deaerated solutions of 0.5 M sodium sulfate as well as 0.5 M sodium chloride using electrochemical noise (EN) technique at open circuit potential (OCP) to collect the correlated current and potential signals. Visual records of the current and potential, analysis of data to arrive at the statistical parameters, spectral density estimation using the maximum entropy method (MEM) showed that sulfate ions were incorporated in the passive film to strengthen the same. However, the adsorption of chloride ions resulted in pitting corrosion thereby adversely affecting noise resistance (R _N). Distinct current and potential signals were observed for metastable pitting, stable pitting and passive film build-up. Distinct changes in the values of the statistical parameters like R _N and the spectral noise resistance at zero frequency (R°_SN) revealed adsorption and incorporation of sulfate and chloride ions on the passive film/solution interface.     

Study of Surface Morphology in Welds of Ti-5Ta-1.8Nb Alloy Exposed to 11.5 M Boiling Nitric Acid

This article presents the study on corrosion behavior of welds of a Ti-5%Ta-1.8%Nb alloy—a candidate material for reprocessing plant, where it is exposed to highly concentrated (11.5 M) and boiling nitric acid. The corrosion rates of Ti-Ta-Nb alloy in wrought condition have been established earlier to be low (0.26 mpy in liquid). The successful use of this material crucially depends on the behavior of its welds. Evaluation of corrosion rates of the welds in boiling nitric acid in the liquid, vapor, and condensate phases showed that the rates were low, <1 mpy and were comparable or less than those of the base metal. Since microstructure plays an important role in governing the corrosion rate, the microstructures in as-welded and nitric acid exposed conditions were studied. The alloy in “as-welded” state has a martensitic structure, which is microstructurally and microchemically homogeneous. Examination of the corroded surface showed the formation of a protective film, which acts as a barrier to dissolution of Ti after the initial high dissolution. The film was found to be ruptured at regions where Si-rich particles were embedded during surface preparation. The present studies have shown that the Ti-Ta-Nb welds show good corrosion resistance in all three phases of nitric acid and the alloy can be employed in highly oxidizing medium.     

Soluble iron modulates iron oxide particle-induced inflammatory responses via prostaglandin E2 synthesis: In vitro and in vivo studies

Background  

Ambient particulate matter (PM)-associated metals have been shown to play an important role in cardiopulmonary health outcomes. To study the modulation of PM-induced inflammation by leached off metals, we investigated intracellular solubility of radio-labeled iron oxide (⁵⁹Fe₂O₃) particles of 0.5 and 1.5 μm geometric mean diameter. Fe₂O₃ particles were examined for the induction of the release of interleukin 6 (IL-6) as pro-inflammatory and prostaglandin E₂ (PGE₂) as anti-inflammatory markers in cultured alveolar macrophages (AM) from Wistar Kyoto (WKY) rats. In addition, we exposed male WKY rats to monodispersed Fe₂O₃ particles by intratracheal instillation (1.3 or 4.0 mg/kg body weight) to examine in vivo inflammation.     

Transition from dislocation controlled plasticity to grain boundary mediated shear in nanolayered aluminum/palladium thin films

Nanolayered materials consisting of alternate layers of two different metals offer enhanced mechanical properties such as hardness but the strengthening mechanism is not well understood when the bilayer thickness approaches a few nanometers. Here, we report on the uniaxial compression of aluminum/palladium pillars (900 nm diameter) with bilayer thickness = 2, 20 and 80 nm. We observe that the deformation behavior of these pillars depends on the value of bilayer thickness, changing from dislocation driven plasticity at large bilayer thickness to shear due to grain rotation via grain boundary sliding at small bilayer thickness. The transition occurs at about a bilayer thickness of 20 nm where a mixture of the two mechanisms is apparent.     

Sensitization control in AISI 316L(N) austenitic stainless steel: Defining the role of the nature of grain boundary

Two grades of AISI 316L(N) austenitic stainless steels differing only in copper content (0.083 and 0.521 wt.%), showed remarkable difference in resistance to sensitization and susceptibility to intergranular corrosion. Different thermal treatments were carried out with an overall objective of altering the nature of the grain boundary. An attempt was made to correlate the degree of sensitization (DOS) with various microstructural parameters such as grain size and grain boundary nature. No clear trend could be established between the individual parameters and DOS. Effective grain boundary energy (EGBE), which is a combined parameter showed clear trend with DOS. The presence of 0.521 wt.% of copper brings down EGBE remarkably leading to improved resistance to sensitization.     

On the updatability of network views—extending relational view theory to the network model

This paper studies the problem of supporting network views. First, an abstraction of the existing network data models is introduced. A non-procedural calculus-based language for data manipulation and view definition in the network model is described. Then, a functor that transforms network schema and view extensions, operations and constraints into equivalent relational ones is defined. This serves as a vehicle for transporting the theory of view update translation in the relational model to views in the network model.     

Thermal aware workload placement with task-temperature profiles in a data center

Data centers now play an important role in modern IT infrastructures. Related research shows that the energy consumption for data center cooling systems has recently increased significantly. There is also strong evidence to show that high temperatures in a data center will lead to higher hardware failure rates, and thus an increase in maintenance costs. This paper devotes itself in the field of thermal aware workload placement for data centers. In this paper, we propose an analytical model, which describes data center resources with heat transfer properties and workloads with thermal features. Then two thermal aware task scheduling algorithms, TASA and TASA-B, are presented which aim to reduce temperatures and cooling system power consumption in a data center. A simulation study is carried out to evaluate the performance of the proposed algorithms. Simulation results show that our algorithms can significantly reduce temperatures in data centers by introducing endurable decline in system performance.