Preconditioning of AISI 304 stainless steel surfaces in the presence of flavins—Part I: Effect on surface chemistry and corrosion behavior

Stainless steel AISI 304 surfaces were studied after a mild anodic polarization for oxide growth in the presence and absence of two derivatives of vitamin B2 (riboflavin and flavin mononucleotide) that can be secreted by metal-reducing bacteria and act as a chelating agent for iron species. The alterations in oxide chemistry were studied by means of surface-sensitive techniques such as X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analysis. The complementary electrochemical characterization revealed a preferential growth of an oxide/hydroxide iron-rich film that is responsible for an altered pit initiation and nucleation behavior. These findings suggest that as the corrosion behavior is determined by the interplay of the chemical and electronic properties, only a mild anodic polarization in the presence of redox-active molecules is able to alter the chemical and electronic structure of the passive film formed on stainless steel AISI 304. This helps to achieve a profound understanding of the mechanisms of microbially influenced corrosion (MIC) and especially the possible effects of the redox-active biomolecules, as they may play an important role in the corrosion susceptibility of stainless steel surfaces.     

A study on swelling behavior of poly(p‐chloro styrene) networks in some aromatic hydrocarbons and linear poly(p‐chloro styrene) solutions

Crosslinked networks (NPPCS) and linear polymers (LPPCS) of poly (p‐chloro styrene) were synthesized by free‐radical polymerization of p‐chloro styrene. NPPCS networks were swollen in four different molecular weights of LPPCS solutions in toluene at three different concentrations. The equilibrium swelling results were evaluated by means of Flory‐Rehner theory to obtain network–linear polymer interaction parameter, χ′₂₃ between NPPCS and LPPCS. It was concluded that the parameter χ′₂₃ decreased with molecular weight but increased with concentration of LPPCS in outer solution. The solvent independent interaction parameter between NPPCS and PPCS was estimated as 0.7 by extrapolation of the values of χ′₂₃ to zero value of the fraction ratio of solvent to linear polymer, ν₁/ν₃ inside the network. As well as, the binary interaction parameters, χ₁₂ of NPPCS with benzene, ethyl benzene, n‐propyl benzene and isopropyl benzene were obtained by means of Flory‐Rehner theory at temperatures between 25 and 55°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of nitrogen flow rate on TiBN coatings deposited on cold work tool steel

TiBN coatings have high hardness and high adhesion. Due to these excellent properties there has been increasing interest in TiBN coatings. In this study, TiBN coatings were deposited on AISI D2 cold work tool steel and silicon wafers by closed field unbalanced magnetron sputtering (CFUBMS). The structural, mechanical and adhesion properties of these coatings were analysed by X-ray diffraction, scanning electron microscopy, microhardness test, indentation test and scratch tests. TiBN coatings produced by magnetron sputtering exhibited a dense and columnar structure. These results indicate that TiB₂, TiN and h-BN exist in crystalline forms at all coatings. The highest hardness was obtained at the lowest nitrogen flow rate. Very few cracks were observed at the edge of the indentation marks at the highest nitrogen flow rate. The highest critical load obtained with scratch test was identified as 102?N.     

The Effect of Olive Leaf Addition on Antioxidant Content and Antioxidant Activity of “Memecik” Olive Oils at Two Maturity Stages

In this study, the effects of leaf addition, maturity stage and storage on the antioxidant content and activity of olive oils (cv. Memecik) were investigated in the 2008/09 and 2009/10 crop seasons. Olive fruits were harvested at two different maturity stages (early and late), and the leaves of the same cultivar were added at different rates (0, 1, and 3 %) prior to oil extraction. After extraction, the oil samples were stored for 18 months and total chlorophyll, α-tocopherol, total phenolic content and the antioxidant activity [DPPH^· (2,2-diphenyl-1-picrylhydrazyl) and ABTS^·+ (2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid) radical scavenging] were determined at 6 month-intervals. Olive leaf addition induced a significant increase in total chlorophyll, α-tocopherol, total phenolic content, and antioxidant activities in both years (P < 0.001). During the storage period antioxidant content and antioxidant activities in the oils significantly decreased in both years (P < 0.001). However, the oils to which leaf material was added had higher antioxidant contents and activities than those without leaf material addition at the end of the 18-month storage period. After storage, the antioxidant content and DPPH^· radical scavenging activity of control (0 %) samples were lower than those in the leaf added samples (3 %). The data obtained from this study suggested that the addition of olive leaf to oils allowed more functional olive oils with higher antioxidant contents.     

Overall equipment effectiveness when production speeds and stoppage durations are uncertain

Evaluation of manufacturing equipment performance has been very important in production-related functions such as planning, scheduling, and maintenance. Nevertheless, low accuracy of performance measurements can mislead decision makers. In this study, overall equipment effectiveness (OEE) is considered as a performance indicator of manufacturing equipment. In practice, components of OEE may consist of uncertainty due to manual or semi-automatic measurement systems. As a consequence, true performance of equipment may be masked by the uncertainty of measurements. In this study, two types of uncertainty are considered in production speed and stoppage duration measurements, which are used in calculating OEE components. When the measurements have uncertainty due to use of linguistic terms or some minor stoppages, idling, or speed losses being ignored, fuzzy arithmetic is used as a method to handle uncertainty. In some low accuracy cases, best guess interval estimates of operators may better reflect the state than just providing a point estimate. For such cases, interval arithmetic is used as a method to handle uncertainty. Implementation of the methods are illustrated using two real-world examples and a software is provided for practitioners. Proposed methods help making better informed decisions using OEE under measurement uncertainty of production speed and stoppage durations.     

Effects of minor Cu and Si additions on glass forming ability and mechanical properties of Co-Fe-Ta-B Bulk metallic glass

Effect of Cu and Si substitutions for Co and B on the glass forming ability (GFA) of Co_(43-x)Cu_xFe₂₀Ta_5.5B_(31.5-x)Si_y (x=0-1.5 and y=5-10) were systematically investigated by X-ray diffraction, optical microscopy, scanning electron microscopy, and differential scanning calorimetry. In order to evaluate the contribution of copper and silicon, appropriate amounts of copper and silicon were individually introduced to the base alloy composition. By using the effects of copper and silicon together, significant enhancement was obtained and the critical casting thickness (CCT) of the base alloy was increased three times from 2 mm to 6 mm. Moreover, mechanical properties of the alloys were examined by compression tests and Vickers hardness measurements. The compression test results revealed that the glassy alloys having enhanced GFA shows high strength of about 3500-4000 MPa. In addition, existence of (Co,Fe)₂B and (Co,Fe)_20.82Ta_2.18B₆ crystalline phases in glassy matrix influences the hardnesses of the alloys compared to monolitic glassy structure having hardness of about 1200 Hv.