بازدارندگی مس به وسیله 3،2،1، بنزوتریازول

Inhibition of copper corrosion by 1,2,3-benzotriazole

بازدارندگی مس به وسیله 3،2،1، بنزوتریازول

ABSTRACT

Benzotriazole (BTAH) has been known for more than sixty years to be a very effective inhibitor of corrosion for copper and its alloys. In spite of numerous studies devoted to the investigation of BTAH action, the mechanism of its action is still not completely understood. The aim of this review is to summarize important work in the field of BTAH as a copper corrosion inhibitor, from the early discoveries to the present time. Special attention is given to the BTAH surface structure. The disagreement between findings and mechanisms is discussed.

جوشکاری اصطکاکی لحظه ای (IFW) برای کاربردهای هوافضا

 Inertia friction welding (IFW) for aerospace applications

جوشکاری اصطکاکی لحظه ای  (IFW) برای کاربردهای هوافضا

ABSTRACT

The use of inertia welding in the aerospace industry has been steadily increasing owing to the signifi cant improvements it provides in joint quality, compared with the use of fusion welding. This chapter introduces the process, with respect to its operation, parameters, differences from other friction welding techniques and equipment. It also explains the application of the technique and the selection of the process parameters, and the different mathematical, analytical and numerical approaches that are used to model the thermal fi elds and residual stress development. Details of the microstructural, mechanical properties and residual stress development in inertia friction-welded Ni-based superalloys, titanium alloys, steels and other alloys are also discussed.

سنتز هیدروترمال و خواص نوری نانورنگدانه ­های CoAl2O4

 Hydrothermal synthesis and optical property of nano-sized CoAl2O4 pigment

سنتز هیدروترمال و خواص نوری نانورنگدانه ­های CoAl₂O₄

ABSTRACT

Nano-sized CoAl2O4 was synthesized by hydrothermal method. The powder was characterized by XRD, DTA–TG, TEM, BET, IR, XPS, and UV–Vis techniques. The particle size was ca. 70 nm, and the particle size distribution was narrow. The BET surface area was 29.22 m2 g
1. It was thermally stable. The maximum absorption was f600 nm. D 2002 Elsevier Science B.V. All rights reserved . CoAl2O4 is a double oxide with a normal spineltype structure. It is well known as Thenard’s blue for its impressive optical property and widely used in the ceramics, glass, paint industry, and color TV tubes as contrast-enhancing luminescent pigment.CoAl2O4 pigment is usually synthesized at high temperature at solid state from a mixture of the two oxide components . However, the reaction involves processing temperatures > 1000 jC for extended time periods, which influences the pigment tonalities. Recently, various solution chemical synthesis techniques  have been utilized to prepare the pigment. Among them, the sol–gel process has big advantages for coating; hydrothermal synthesis can prepare powders without calcination. Various oxides and complex oxides with narrow particle size distribution, single phase, and controlled particle morphology have been synthesized by hydrothermal technique. However, little attention has been paid to preparing spinel oxides. No literature precedence, to our knowledge, is available on the synthesis of CoAl2O4 by this method. In this letter, the hydrothermal method is introduced to synthesize CoAl2O4. The results illustrate the effectiveness of the technique in producing the nano-sized and narrow size distribution pigments.

خوردگی داغ مواد : مکانیزم جریان سیال ؟

  ?Hot corrosion of materials: a fluxing mechanism

خوردگی داغ مواد :  مکانیزم جریان سیال  ؟

ABSTRACT

Hot corrosion is the accelerated oxidation of a material at elevated temperature induced by a thin  film of fused salt deposit. Fused Na2 S04 , which is the dominant salt involved in hot corrosion, is an ionic conductor, so that the corrosion mechanism is certainly electrochemical in nature.  Further, the acid/base nature of this oxyanion salt offers the possibility for the disso- lution  (fluxing) of the normally protective oxide scale. Non-protective precipitated oxide par- ticles are  often observed in the corrosion products. In this paper, the status of knowledge for the  solubilities of oxides in fused Na2 S04 is reviewed, and the effects of various influences on a  fluxing mechanism are discussed. An evaluation of a negative solubility gradient as a cri- terion  for continuing hot corrosion is made. © 2001 Elsevier Science Ltd. All rights reserved.

مواد دما بالا برای توربین ها گازی

: High Temperature Materials for Gas Turbines
The Present and Future

مواد دما بالا برای توربین ها گازی:

حال و آینده

ABSTRACT

Increased operating temperatures and higher efficiency in gas turbines and jet engines can reduce CO2 emission, thus contributing to the prevention of global warming. To achieve this goal, it is essential to improve the properties of high temperature materials. Various Ni-base superalloys are used for high-temperature components, e.g., combustors and high-pressure turbine blades and vanes, that determine the power and efficiency of jet engines and industrial gas turbines. Among them, single crystal (SC) superalloys have the highest temperature capabilities. A third-generation SC alloy has been used practically in Jet engines and fourth-generation SC alloys with platinum group metals additions are being developed for the next generation Jet engines. In land-based gas turbines also SC superalloys have been introduced to increase their inlet gas temperatures, and thus thermal efficiencies. As for new materials, intermetallic alloys, refractory alloys, ceramics, etc., are also being developed as possible alternative materials. Some unique materials have recently been proposed in Japan and being evaluated.

توزیع ناهمگن نانوکریستال­ های فلزی در لعاب­ کاری سفالینه­ ها

Heterogeneous distribution of metal nanocrystals in glazes of historical pottery

توزیع ناهمگن نانوکریستال­ های فلزی در لعاب­ کاری سفالینه­ های باستانی

ABSTRACT

It has been recently shown that lustre decoration of medieval and renaissance pottery consists of silver and copper nanocrystals, dispersed within the glassy matrix of the ceramic glaze. Lustre surfaces show peculiar optical effects such as metallic reflection and iridescence. In many cases, lustre appears overlapped to colored drawings. Here we report the findings of a study on glazes, pigments and lustre of several shards belonging to Deruta and Gubbio pottery of XVI century. The components of glazes and pigments have been identified. Lustre is confirmed to be characterised by silver and copper metal nanocrystals inhomogeneously dispersed in the glassy matrix of the glaze. In the case of lustre overlapped to colored decorations, we found two contradictory cases. The first consists of a lustre surface successfully applied over a blue smalt geometrical drawing. The second consists of a lustre surface, unsuccessfully applied over a yellow lead-antimonate pigment. The yellow pigment hinders the formation of lustre and removes crystals of tin dioxide, normally present in the glaze as opacifier. # 2002 Elsevier Science B.V. All rights reserved.

درصد گاز در ریخته­ گری دایکاست فشار بالا

Gas content in high pressure die castings

درصد گاز در ریخته­ گری دایکاست فشار بالا

ABSTRACT

This paper presents the results of a quantitative study of the gas level in various types of castings from the high pressure die casting (HPDC) process using a vacuum fusion method. It was found that the major part of the gas was from the air entrapment during cavity filling. Other sources such as air entrapment during ladling, residual die lubricant and quenching water were also noticeable. Measurements of a large casting and castings from a multi-cavity die showed that the gas content was unevenly distributed. The modified vacuum fusion method has been proved to be a valuable tool for evaluating and quantifying the level of gas in castings as well as for an assessment of the influence of different process parameters on gas evolution in castings.

تغییر فاز در فولادهای میکرو آلیاژ کم آلیاژ استحکام بالا (HSLA)

Phase transformations in microalloyed high strength low alloy (HSLA) steels

تغییر فاز در فولادهای میکرو آلیاژ کم آلیاژ استحکام بالا (HSLA)

ABSTRACT

The addition of small amounts of Nb, Ti or V singly or in combination has been the key to  producing high strength low alloy (HSLA) steels with greatly improved mechanical properties. Such  microalloyed HSLA steels are now commonplace in a huge variety of applications. The combinations of  strength, toughness and formability that are possible are directly related to the way in which the steel is processed from the as- cast slab (usually) to the final plate or strip dimensions. The effects of microalloying result principally from three main effects on the austenite to ferrite  transformation. Firstly, the microalloying additions form precipitates in both austenite and ferrite; this factor alone can be exploited in various ways to control the microstructure, hence  mechanical properties, of the steel. Secondly, although present in relatively small quantities,there are discernible effects on ferrite transformations in terms of the hardenability of the steel. Finally, there are interactions between the various deformation sequences used in  steel production and the presence of microalloying elements as solutes or precipitates which can be  exploited to control microstructure. The interactions between processing, microstructural  development and the effect of microalloying additions on the austenite­ ferrite transformations are  the topic of this chapter. A brief history of the use of microalloying is also given as is some  indication of the range of mechanical properties that result from the current understanding of the role of microalloying additions.

مواد عایق برق Electrical insulating materials

Electrical insulating materials

مواد عایق برق

ABSTRACT

Electrical insulating materials ensure the integrity of desired paths of electromagnetic power flow in electrical systems and equipment . They are materials at very high resistivity and can thus be used as isolators or separator between conductors having different potential (voltage) levels . In its use such as in isolators an insulating materials has the basic function of confining the current flow within the conductive circuit of a given device or part of equipment thus protecting the latter from short circuit current leakage and similar undesirable malfunctions . insulating materials may be solid liquid or gaseous substances , they may be monolithic ( discrete ) materials or may be constituted by physically cohesive composites structured with multiple constituents . Based on the primary functions electric insulation can be categorized as follows :

• Separation-type insulation
• Barrier insulation
• Creepege insulation

چقرمگی شکست اپوکسی اصلاح شده با لاستیک هیبریدی

Fracture Toughness of a Hybrid Rubber Modified
Epoxy. II. Effect of Loading Rate

چقرمگی شکست اپوکسی اصلاح شده با لاستیک هیبریدی.

II. اثر نرخ بارگذاری

ABSTRACT

Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1–1000 mm/ min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1–10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10–1000), the fracture toughness of hybrid system decreased gradually to the level lower than that of ATBN-modified epoxy. Fractography of the damage zones showed the toughening mechanisms of ATBN-modified system was less affected by increasing the loading rate compared to that of hybrid system.