خوردگی سرب و آلیاژهای سربی

Corrosion of Lead and Lead Alloys

خوردگی سرب و آلیاژهای سربی

ABSTRACT

LEAD has such a successful record of service in exposure to the atmosphere and to water that its resistance to corrosion by these media is often taken for granted. Underground, thousands of kilometers of lead-sheathed cable and lead pipe give reliable long-term performance all over the world. In the chemical industry, lead is used in the corrosion-resistant equipment necessary for handling many chemicals. Batteries account for the largest use of lead and are the source of most recycled lead. General information on compositions, properties, and applications can be found in the article “Lead and Lead Alloys” in Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, Volume 2 of ASM .The rate of corrosion is a function of the current flowing between the anodes and cathodes of the corrosion cell. Many factors and conditions can initiate or influence this flow of current. In the corrosion of a single metal, such as lead, local anodes and cathodes may be set up as a result of inclusions, inhomogeneities, stress variations, and differences in temperature. In galvanic corrosion, the anodic and cathodic sites are ondifferent metals, with the less noble metal (anode) corroding in preference to the more noble metal (cathode).

ممانعت کننده های خوردگی مس Copper Corrosion Inhibitors

Copper Corrosion Inhibitors

ممانعت کننده های خوردگی مس

ABSTRACT

Copper is metal that has a wide range of applications due to its good properties. It is used in electronics, for production of wires, sheets, tubes, and also to form alloys. Copper is resistant toward the influence of atmosphere and many chemicals, however, it is known that in aggressive media it is susceptible to corrosion. The use of copper corrosion inhibitors in such conditions is necessary since no protective passive layer can be expected. The possibility of the copper corrosion prevention has attracted many researchers so until now numerous possible inhibitors have been investigated. Amongst them there are inorganic inhibitors [1], but in much greater numbers there are organic compounds and their derivatives such as azoles [2-49], amines [50-56], amino acids [57, 58] and many others.

ممانعت از خوردگی مس در محلول H2SO4 اشباع از O2

Copper corrosion inhibition in O2-saturated H2SO4 solutions

ممانعت از خوردگی مس در محلول H₂SO₄ اشباع از O₂

ABSTRACT

Corrosion inhibition of copper in O2-saturated 0.50 M H2SO4 solutions by four selected amino acids, namely glycine (Gly), alanine (Ala), valine (Val), or tyrosine (Tyr), was studied using Tafel polarization, linear polarization, impedance, and electrochemical frequency modulation (EFM) at 30 C. Protection efficiencies of almost 98% and 91% were obtained with 50 mM Tyr and Gly, respectively. On the other hand, Ala and Val reached only about 75%. Corrosion rates determined by the Tafel extrapolation method were in good agreement with those obtained by EFM and an independent chemical (i.e., non-electrochemical) method. The chemical method of confirmation of the corrosion rates involved determination of the dissolved Cu2+, using ICP-AES (inductively coupled plasma atomic emission spectrometry) method of chemical analysis. Nyquist plots exhibited a high frequency depressed semicircle followed by a straight line portion (Warburg diffusion tail) in the low-frequency region. The impedance data were interpreted according to two suitable equivalent circuits. The kinetics of dissolved O2 reduction and hydrogen evolution reactions on copper surface were also studied in O2-saturated 0.50 M H2SO4 solutions using polarization measurements combined with the rotating disc electrode (RDE). The Koutecky–Levich plot indicated that the dissolved O2 reduction at the copper electrode was an apparent 4-electron process.

سیمان و بتن

Concrete and Cement

سیمان و بتن

ABSTRACT

Inorganic concretes are reviewed, emphasizing two major areas: construction concretes and high temperature (refractory) concretes. Although such materials are intended for completely different applications and markets, they have in common that they are made from inorganic ceramic oxides and both materials are used for structural purposes. Current applications and research topics representing new challenges are summarized.Concrete usually indicates a construction material made from Portland cement, aggregates (for instance, gravel and sand), water, and additives to improve mixing or specific properties of the final material. Refractory concretes (monolithic refractories) refer to high-temperature materials for the manufacture of shaped refractories. Most concrete refractories are based on calcium aluminates, although some applications require the use of other high-temperature ceramic materials, such as magnesium oxide. The distinguishable feature of these concretes is that the method of preparation does not involve forming or firing at the manufacturing plant as in the fabrication of refractory bricks. This compilation includes only concretes for construction and refractory applications.

مواد کامپوزیت دی الکتریک

Composite Dielectric Materials

مواد کامپوزیت دی الکتریک

ABSTRACT

Composite dielectrics represent, in general, a heterogeneous system of multiconstituent materials. Typically, a two-phase composite dielectric is constituted by a host material with an inclusion of another material. This host-inclusion system could be formed by a combination (or a mixture) of dielectric-dielectric, dielectric-conductor, and/or dielectric-semiconductor phases. The constituent phases may form structurally an embedment system consisting of multi-layer "layups" or random dispersion of the inclusions across the host medium; or there could be a structured matrix of specific type to yield certain desirable dielectric properties. Generically, a composite dielectric can be treated as as a mixture-medium, largely heterogeneous and could be anisotropic and nonlinear, as well.

تولید رنگدانه قرمز از ساختار پروسکایت Y(Al,Cr)O3

Colour development of red perovskite pigment Y(Al,Cr)O3 in various ceramic applications

تولید رنگدانه قرمز از ساختار پروسکایت Y(Al,Cr)O₃ مورد مصرف در کاربردهای مختلف صنایع سرامیک

ABSTRACT

Ceramic pigments based on the perovskite structure develop a promising red hue and furthermore present no environmental or health care problems. Pigment colouring efficiency was tested in different ceramic applications, both through-body and glazes. Final products, fired varying both the maximum temperature and soaking time, were characterized by the colourimetric point of view. Research efforts were focused both on the factors and on the mechanism mainly influencing perovskite dissolution by calculating the phase composition of different ceramic matrices and by observing the pigment microstructure. Furthermore, pigment powders were characterized by a structural and spectroscopic point of view. The pigment dissolution is slightly affected by the firing cycle and mostly governed by amount and chemical composition of the liquid phase. In particular, the larger the content of chemically aggressive components - such as calcium, magnesium, zinc and lead oxides - the strongest and faster the pigment dissolution.

روش های پوشش دهی با استفاده از فلزات پلاتینی

Coating Methods for Use with the Platinum Metals

روش های پوشش دهی با استفاده از فلزات پلاتینی

ABSTRACT

There is now a wide variety of methods that can be employed to form coatings of the platinum group metals. The choice of materials and methods to be used can best be made after the manufacturer and the user of the product have considered the required properties and related factors such as the thickness and physical properties of the coating, the properties of suitable substrates, and the cost of alternative processes. This review describes processes which can be used to deposit a coating of a platinum group metal on to a substrate. The properties of the coating and the type of substrate to which the various methods are applicable, and the thickness normally to be obtained, are also discussed.

رس ها

Clays

رس ­هـا

ABSTRACT

Clays are ubiquitous constituents of the Earth’s crust that serve as raw materials for traditional ceramics. Mineralogically, clays are phyllosilicates or layered aluminosilicates. Bonding is strong within layers, but weak between layers, allowing clays to break into micrometer-sized particles. When mixed with water, clays develop plasticity and can be shaped easily and reproducibly. When heated, clays undergo a series of reactions that ultimately produce crystalline mullite and a silica-rich amorphous phase. Beyond the structure and properties of clays, the science that developed to understand traditional ceramics continues to serve as the framework for the study of advanced ceramics.

بنزوتریازول: یک ممانعت کننده مؤثر خوردگی برای آلیاژهای مس

Benzotriazole:An effective corrosion inhibitorfor copper alloys 
بنزوتریازول: یک ممانعت کننده مؤثر خوردگی برای آلیاژهای مس

ABSTRACT

Copper is the only engineering metal that is noble metal. It resists many corrosive environments. But copper tarnish or corrodes under some circumstances. In recent years, investigators have shown that a system of tarnish or corrosion control for copper, brass and bronze can be built around the organic compound, 1, 2, 3, benzotriazole. Benzotriazole forms a strongly bonded chemisorbed two-dimensional barrier fi lm less than 50 angstroms thick. This insoluble fi lm, which may be a monomolecular layer, protects copper and its alloys in aqueous media, various atmospheres, lubricants, and hydraulic fl uids. Benzotriazole also forms insoluble precipitates with copper ions in solution (that is, it chelates these ion), thereby preventing the corrosion of aluminum and steel in other parts of a water system.
J. B. Cotton. Imperial Metal Industries Ltd., Birmingham, England, has studied the tarnishing of copper and copper alloys exposed to humid environments, and the possibility of the prevention of staining by reaction with triazole type compounds. At the Second International Congress on Metal Corrosion, New York, 1963, he summarized the properties of commercially available benzotriazole and the reaction of this class of compound with copper ions. His report, “Control of Surface Reaction on Copper by Means of Organic Reagents”, points out that the nitrogen-hydrogen group, and at least one of the other nitrogens in the ring, is involved in the complex bonding arrangements to copper. The polymeric chains or monomolecular plate-like complexes completely cover a clean metal surface, affording excellent protection. In the more typical case, benzotriazole probably plugs holes and defects in the copper oxide surfaces fi lm. Use of benzotriazole, and other protective chemicals such as tolutriazole, constitutes a signifi cant advance in the quest for corrosion inhibitors. It demonstrates that effective inhibition can function through the formation of true chemicalbonds.

روشی برای مسطح سازی جبهه انجمادی در فن آوری انجماد جهت دار

A method for flattening the solidification fron tindirectional solidification technology

روشی برای مسطح سازی جبهه انجمادی در فن آوری انجماد جهت دار

ABSTRACT

Nonplanar solidification front causes defects in directional solidification process.The transverse temperature gradient,which can bedivided into radial temperature gradient and circumferential temperature gradient,is one of the reason scausing the nonplanar solidification front . This paper presents a method by varying the wall thickness of the mould to decrease the circumferential temperature gradient and hence flatten the solidification front.The equations for calculating the wall thickness were deduced by heat transfer analysis.The optimized mould contour was obtained by solving the equations numerically.It was proved by simulation that the circumferential temperature gradient can be almost reduced by 40%.Furthermore,the starting time difference of solidification at one cross section along the circumferential direction almost reduces by half.Additionally,this paper also researches the influences of parameters of the mould and the furnace etc. on the shape of the mould and the circumferential temperature gradient.The circumferential temperature gradient decreases as the thermal conductivity and the emissivity of the mould increase. And the temperature of the cooling ring impacts little on the circumferential temperature gradient. According to the development trend of the blade manufacturing, this method may be applied widely.