Effect of wood species on corrosion behavior of carbon steel and stainless steels in black liquors

Black liquors produced by pulping different wood species can have different corrosivity towards carbon steel equipment in pulp mills. Inorganic constituents of black liquor alone do not correlate well with the corrosivity of different black liquors. Organic constituents of the black liquor have significant effect on determining its corrosivity. However, understanding of the role of individual organic constituents or group of constituents of black liquors in overall black liquor corrosivity is generally lacking. The objective of this study was to determine the effect selected wood species on the corrosivity of their black liquors which contained similar inorganic constituents. The role of black liquor constituent, pyrocatechols, whose presence in the black liquor has been associated with an increase in corrosion of carbon steel, was also studied. Results from electrochemical tests point to the mechanisms by which the catechols may participate in the accelerated corrosion of carbon steels. This study demonstrates the role of organic constituents of the black liquor in determining its corrosivity.     

Durability of aminosilane-silica hybrid gas-barrier coatings on polymers

Aminosilane solutions with pH equal to 8 and to 11 were applied and cured on SiO₂-coated poly(ethylene terephthalate) (PET) films. The permeability of the silane-silica hybrid coating on PET was reduced twofold compared to that of the SiO₂/PET film, at solution concentrations as low as 1 wt.%, irrespective of the pH. This concentration level led to a dense silane monolayer crosslinked to the silica surface. The oxygen transport mechanisms in the hybrid coatings were determined based on the thermally activated rate theory. Permeation experiments were also performed under tensile loading, and the critical strain for loss of barrier performance was found to be improved by a factor of two, only in case of basic pH. The defect population and morphology of the hybrid coating subjected to hydrothermal aging were analyzed using a reactive ion etching method and atomic force microscopy, respectively. These experiments confirmed the defect healing action of the aminosilane at low concentrations in solution, through the formation of a densely crosslinked polysiloxane layer at the silane-silica interface for both pH8 and pH11. The influence of the silane treatment was emphasized in case of basic pH due to the dissolution of superficial oxide layers.     

Benzoylation of benzene to benzophenone over zeolite catalysts

The liquid phase benzoylation of benzene with benzoyl chloride (BOC) to benzophenone is catalyzed by various zeolites at 353 K. Zeolite H-beta is found to be more active than the other zeolites. The conversion of benzoyl chloride to benzophenone over H-beta increases significantly with increase in the reaction time, temperature, catalyst/BOC (wt/wt) and benzene/BOC (mole) ratios. The yield of benzophenone decreases with increase in SiO₂/Al₂O₃ ratio and isomorphous substitution of Al-by Ga- and Fe-in zeolite H-Al-beta in the following order: Al-> Ga-> Fe-H-beta suggesting that high density of acidic centers along with strong acid sites are required for the reaction.     

Effects of Postdeposition Treatments on the Mechanical Properties of a Chemical-Vapor-Deposited Silicon Carbide

The influence of different postdeposition treatments such as water quench and thermal heating in air, nitrogen, and vacuum on mechanical properties of chemical-vapor-deposited (CVD) silicon carbide was investigated. The results showed that these postdeposition treatments increased the flexural strength by as much as 60% but did not significantly change other properties such as hardness and fracture toughness. The strength increase was achieved by treatments performed in both the oxidizing and nonoxidizing environments. Compressive residual stresses in CVD SiC increased because of these treatments, but this increase was not large enough to explain fully the observed increase in the flexural strength. It is proposed that these thermal treatments led to strength increase via healing of surface machining flaws. Thermal treatments in nonoxodizing environments reduced or blunted the flaws through the rearrangement of atoms and restoration of damaged crystal structure in SiC, while in oxidizing environments, passive oxidation may have served as an additional flaw healing mechanism.     

Oxime-Modified Aluminum(III) Isopropoxide: A Promising Sol–Gel Precursor for Corrosion Resistive Nano-Alumina Coating on an Aluminum Alloy

Protection of Metals and Physical Chemistry of Surfaces - Dense alumina coatings were fabricated over aluminum alloy via dip coating method using oxime-modified aluminum(III) isopropoxide as a...     

Modeling and Simulation of Variable-Reluctance Step Motors with Application to a High-Performance Printer System

Basic information on modeling and digital computer simulation of variable-reluctance (VR) step motors is provided. The nonlinear equations of the system are derived, and a method for implementing them on a digital computer is presented. As an example, a typical printer with a step motor is designed with this approach. The problem is defined by giving the desired system performance criteria and the step motor parameters and characteristics. The specification of the control schemes determined the design. Computer simulation runs are made to determine the optimal control parameters of the system. The case study demonstrates the advantages of the computer-aided design, before the physical construction of the experimental system.     

The influence of chromium on mechanical properties of austempered ductile cast iron

An investigation was carried out to examine the influence of microstructure and chromium on the tensile properties and plane strain fracture toughness of austempered ductile cast iron (ADI). The investigation also examined the growth kinetics of ferrite in these alloys. Compact tension and round cylindrical tensile specimens were prepared from ductile cast iron with Cr as well as without Cr. These specimens were then given four different heat treatments to produce four different microstructures. Tensile tests and fracture toughness tests were carried out as per ASTM standards E-8 and E-399. The crack growth mechanism during fracture toughness tests was also determined. The test results indicate that yield strength, tensile strength, and fracture toughness of ADI increases with an increase in the volume fractions of ferrite, and the fracture toughness reaches a peak when the volume fractions of the ferrite are approximately 60% in these alloys. The Cr addition was found to reduce the fracture toughness of ADI at lower hardness levels (<40 HRC); at higher hardness levels (≥40 HRC), the effect of chromium on the fracture toughness was negligible. The crack growth mechanism was found to be a combination of quasi-cleavage and microvoid coalescences, and the crack trajectories connect the graphite nodules along the way.     

The manganese-niobium-nickel system

The Mn-Nb-Ni system was investigated in a limited composition range of <33 at.% Nb and <70 at. % Mn. The solubility of Nb in the fcc γ phase is small, and it decreases with increase in Mn content. The C14-type Mn₂Nb Laves phase, ε, extends far into the ternary. The NbNi₃ phase, β, extends into the ternary only to a limited extent. At higher Nb contents, the Nb₇Ni₆ μ phase possibly extends into the ternary.     

Efficacy of essential oil extracts in inhibiting mould growth on panel products

The aim of this research was to exploit the chemical properties of natural products to control the incidence and extent of mould growth in houses. The screening of antimould activities of seven essential oil extracts showed that most of the extracts completely inhibited the growth of all three test mould at the concentration of 1% w/v on nutrient medium, whereas, different fractions of manuka oil showed varied activity. Subsequently, using both mycological and scanning electron microscopy, the testing of selected extracts on two different types of gypsum board finished with either paint or wall-paper, confirmed the antimould activity of eugenol, thymol and cinnamaldehyde against Penicillium corylophilum. This study identified certain essential oil extract as a potential mould inhibitor for panel products which is one of the most common mould habitats in the building environment. Mould growth in residential houses is a major concern and chemical fungicides commonly used to control the growth of mould are not often appropriate for indoor applications. Natural alternatives such as essential oils are desirable for this application. Knowledge gained through this research should lead to new niche panel product development to create healthier housing.     

Convective heat transfer enhancement techniques of heat exchanger tubes: a review

Heat exchangers are widely used in almost all industrial activities. Turbulent promoters used in heat exchanger tubes are an effective way of enhancing the performance. This paper summarises various investigations using twisted tapes, wire coil ribs, baffles, and swirl flow generators. The main objective of this paper is to review various studies, in which different obstacle roughness elements are used to enhance the rate of heat transfer in the heat exchanger tubes. It has been found that a lot of experimental and analytical studies reported in the literature. On the basis of correlations developed by various investigators an attempt has been made to compare the thermal hydraulic performance of obstacles in heat exchanger tubes. In this work, a comparative study is also carried out to select the best obstacle roughness shapes for higher heat transfer rate and low pressure drop losses.