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.

پوشش های آلومینیمی : شرح و سنجش

Aluminum Coatings: Description and Testing 
پوشش های آلومینیمی : شرح و سنجش

ABSTRACT

Pure aluminum, the 3xxx, 5xxx, and most 6xxx series alloys, are sufficiently resistant to be used in industrial atmospheres and waters without any protective coatings. Coatings are recommended for the higher strength 6xxx alloys, such as alloy 6013, and for all 2xxx and 7xxx alloys. The thickness of the natural oxide passive film can be increased by a factor of 10 by prefilming in hot water and by a factor of 1000 or more by anodizing in sulfuric acid. Different options for mechanical and chemical surface preparation are available depending on choice of coating, appearance, and/or performance. Weak organic acids and their derivatives form insoluble salts and rely on the adsorption of the hydrophobic anions to provide a thin barrier layer. Chelating inhibitors create a thin tenacious passive layer (up to 20 nm). Aluminum alloys are protected by more active metals or by cathodic protection. Corrosion can be prevented or reduced by cladding. Some joint-sealing compounds that contain suitable soluble inhibitors are particularly recommended. Aluminum can be protected by electroless or conventional plating. Aluminum and aluminum alloys in the active state act as a sacrificial anode in the form of plate or as a powder coating. Conversion layers can be created through physical vapor deposition, cathodic magnetron sputtering, high-energy ion beams, and laser ablation. Electrochemical anodization, plasma ablation, and chromate conversion coatings are frequently considered. There are thermoplastic coatings and converted coatings that are applied during or after processing and include principally three types of paints: epoxy, polyurethane, and moisture coatings. Corrosion monitoring is currently carried out by electrochemical impedance spectroscopy methods and electrochemical noise measurements.

آلومینات­ ها Aluminates

Aluminates

آلومینات­ ها

ABSTRACT

Aluminates form in binary systems with alkali, alkaline earth or rare-earth oxides and share the high melting point and resistance to chemical attack of the pure Al2O3 end-member. This means that these ceramics have a variety of applications as cements, castable ceramics, bioceramics, and electroceramics. Calcium aluminate cements are used for example in specialist applications as diverse as lining sewers and as dental restoratives. Ceramics in aluminate systems are usually formed from cubic crystal systems and this includes spinel and garnet. Rare earth aluminate garnets include the phase YAG (yttrium aluminium garnet), which is an important laser host when doped with Nd(III) and more recently Yb(III). Associated applications include applications as scintillators and phosphors. Aluminate glasses are transparent in the infrared region and these too have specialist applications, although the glass-forming ability is poor. Recently, rare earth aluminate glasses have been developed commercially in optical applications as alternatives to sapphire for use in, for example, infrared windows. Aluminates are refractory materials and their synthesis often simply involves solidstate growth of mixtures of purified oxides. Alternative synthesis routes are also used in specialist applications, for example in production of materials with controlled porosity and these invariably involve sol–gel methods. For glasses, one notable, commercially important method of production is container-less synthesis, which is necessary because of the non-Arrhenius (fragile) viscosity of aluminate liquids.

آلومینا Alumina

Alumina

آلومینا

ABSTRACT

The uses, processing, structure, and properties of alumina are summarized in this article. Various polymorphs of alumina and its phase relations with other oxides are described. The following properties are discussed: mechanical, thermal, thermodynamic, electrical, diffusional, chemical, and optical. Quantitative values for these properties are given in tables. The usefulness of alumina results from its high strength, melting temperature, abrasion resistance, optical transparency, and electrical resistivity. Traditional uses of alumina because of these properties are furnace components, cutting tools, bearings, and gem stones; more recent applications include catalyst substrates, tubes for arc lamps, and laser hosts. Possible new uses of alumina are in electronic circuits, optical components, and biomaterials. Alumina fibers for composites and optics must be pure, defect free, and cheap.

مروری بر مزایا و محدودیت های HPT

Advantages and limitations of HPT: a review

مروری بر مزایا و محدودیت های HPT

ABSTRACT

The improvements in the design of the HPT tools lead to a well defined torsiondeformation and permits, therefore, a comparison with other SPD-techniques. The design of thetools, the advantages and disadvantages of HPT, as well as the limitation in the sample size are discussed.For a long time torsion has been frequently used to determine the stress strain behaviour at large strains. In free torsion, the geometrical changes are usually very small. The fracture strain is significantly larger than in tensile experiments due to the vanishing macroscopic hydrostatic tension component of the stress. By applying an additional hydrostatic compression stress, the fracture strain can be further enhanced and can be increased to infinity at very high hydrostatic compression stresses.High pressure torsion, HPT, is a realisation of such a torsion experiment [1-3]. One can distinguish between constrained and unconstrained version.

مطالعه ه­ای تئوری بر روی بازدارنده­ های خوردگی مس در اسید نیتریک

A theoretical study on the inhibition efficiencies of some quinoxalines as corrosion inhibitors of copper in nitric acid

مطالعه ه­ای تئوری بر روی بازده­ های بازدارندگی چند مورد از کوین­اگزالات­ ها به عنوان بازدارنده­ های خوردگی مس در اسید نیتریک

ABSTRACT

Quantum chemical calculations based on DFT method were performed on three quinoxalines compounds namely ethyl 2-(4-(2-ethoxy-2-oxoethyl)-2-p-tolylquinoxalin-1(4H)-yl)acetate (Q1), 1-[4-acetyl-2-(4-chlorophenyl)quinoxalin-1(4H)-yl]acetone (Q2) and 2-(4-methylphenyl)-1,4- dihydroquinoxaline (Q3), used as corrosion inhibitors for copper in nitric acid media to determine the relationship between the molecular structure of quinoxalines and inhibition efficiency. Quantum chemical parameters such as the highest occupied molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital energy (ELUMO), energy gap (DE), dipole moment (l), electronegativity (v), electron affinity (A), global hardness (g), softness (r), ionization potential (I), the fraction of electrons transferred (DN), and the total energy (TE), were calculated. The theoretically obtained results were found to be consistent with the experimental data reported.