Chemical Composition Of Substrate Research Articles

Antimicrobial action of exogenous chitosan.

The objective of this chapter is to present fundamental factors (e.g. intrinsic and extrinsic) influencing chitosan as antimicrobial agent, for effective practical application. The antimicrobial activity of chitosan is well observed on a wide variety of micro-organisms including fungi, algae and some bacteria. However, the antimicrobial action is influenced by intrinsic and extrinsic factors such as the type of chitosan (e.g. plain or derivative); degree of chitosan polymerization; host natural nutrient constituency; substrate chemical and/or nutrient composition; and environmental conditions (e.g. substrate water activity (Aw) and/or moisture). Although both plain and derivative chitosans are effective as antimicrobial agents, there is a differential effect between them. Their differential antimicrobial effect is mainly exhibited in live host plants; thus the antifungal effect of N-carboxymethyl chitosan (NCMC) is different in vegetable as compared with graminea host. At the same time, pentamer and heptamer chitosan units seem to have better antifungal action than larger units. Chitosan antimicrobial action is more immediate on fungi and algae, followed by bacteria; the chitosan site of action is at the microbial cell wall.

Microstructure and Electrical Characteristics of La1−xSrxMnO3 (0.19≤x≤0.31) Thin Films Prepared by Sputter Techniques

AbstractLa1−x SrxMnO3(0.19≤x≤0.31) thin films were prepared on silicon wafers by sputter techniques. The effect of substrate temperature, chemical composition and post-deposition heat-treatment on the crystalline structure and electrical characteristics of the films was investigated. The films grown at a substrate temperature of 500°C were found to be of the pseudo-tetragonal system (0.97≤a/c≤1) and exhibited a strong tendency of {001} planes to lie parallel to substrate surface. With the increase of x, the electrical resistivity of the films decreased and the transition temperature between the metallic and semiconducting electrical transport behaviors shifted to high temperature. With a magnetic field of 0.18 Tesla, the maximum magneto-resistance ratio (MR%) of La0.69Sr0.31MnO3 polycrystalline thin films was about 390%.

Study of Aluminium Filiform Corrosion by Using Electrochemical Techniques

Filiform corrosion of aluminium alloys has increased drastically in the last 10 years, in particular when manufactured articles are working in marine or industrial environments. This type of corrosive attack usually starts at coating defects or at cut edges following anodic undermining or cathodic delamination as corrosion mechanisms. As described in the literature, main controlling parameters are: water permeability and elasticity of the coating, oxygen diffusion paths, presence of salts, substrate chemical composition. In particular the metal coating interface is the critical point. It is well know that aluminium paint bonding is enhanced by treating the metal surface in chromate or chromate-phosphate baths and this kind of conversion coatings have also a beneficial effect in preventing filiform corrosion. Aim of this work is to study the filiform corrosion behaviour of aluminium samples treated using environmentally friendly pretreatment baths and to compare these results with that of chromate treated samples. In the same time together with the use of traditional testing procedure of the filiform corrosion we tried to develop and use a new testing method based on Electrochemical Impedance Spectroscopy with the aim to obtain more quantitative data in a shorter testing time. Under the experimental conditions used in our tests, Electrochemical Impedance Spectroscopy showed to be useful and allowed to obtain the same results obtained following the DIN 65472 standard. The resistance to filiform corrosion was greatly influenced by wet adhesion, when it is poor the filament grows rapidly producing also a lateral detachment.

Fracture toughness of boride formed on low-alloy steels

In this study, we investigated the fracture toughness of boride layers formed on steel surfaces. The samples used for this study were prepared from low-alloy and low-carbon steels essentially containing Cr and/or Mn as the major elements. Boronizing was done in a salt bath consisting of borax, boric acid, and ferro-silicon. The temperature of the bath was 940 °C and the boronizing was conducted at an atmospheric pressure for 5–7 h. The presence of borides, e.g. Fe 2B, was revealed by X-ray h diffractometry, SEM, and optical microscopy. The fracture toughness of borided surfaces was measured via Vickers indenters with a load of 2 N. It was found that the fracture toughness of the borides ranged from 4 to 6 MPa 1/2. The fracture toughness of the borides depends strongly on chemical composition of substrate and boronizing time. Mn as an alloying element has a beneficial effect on fracture toughness, and the longer boronizing time results in higher fracture toughness.

Factors influencing the adhesion of diamond coatings on cutting tools

CVD diamond coatings can greatly extend the tool life of cemented carbide cutting tools when machining abrasive non-ferrous materials. However, reliable tool performance is difficult to obtain due to the problem of controlling coating adhesion. In this work, diamond coatings have been deposited on cemented carbide tool inserts with variation of substrate chemical composition and surface pre-treatment. The coatings have been characterized with respect to nucleation density, crystallinity, non-diamond material content and residual stresses. The adhesion and wear resistance of the coatings were investigated by machining tests in Al-18%Si alloy. The diamond deposition process and the resulting coating adhesion are both strongly influenced by the surface characteristics of the substrate surface. Formation of voids and non-diamond material at the coating-substrate interface in combination with high compressive stresses in the coating are believed to be the main reasons for poor adhesion.

Behavior of perpendicular recording materials in Cl and S containing atmospheres

The corrosion behavior of Co-Cr and Ni-Fe alloys is reported after exposure to Cl 2 , SO 2 , and O 2 containing test atmospheres at various relative (RH) humidities. Surface Chemistry, physical features, and magnetic properties were characterized. The Ni-Fe alloys exhibited excellent corrosion resistance in elevated RH atmospheres. Co-Cr alloys showed little change in magnetic properties even when significant chemical penetration of the film occurred. Substrate chemical composition proved to be an important factor in sputtered film corrosion behavior.

Effect of substrate on the freezing potential

Abstract The magnitude of the freezing potential (Workman-Reynolds' effect) has been shown to depend on the nature of the substrate used to initiate freezing. The freezing potential was unrelated to the initial charge excess (with respect to potential of zero charge) at a mercury—electrolyte interface. Substrate chemical composition strongly affected the freezing potential even as ice growth proceeded remote from the starting surface.