سرامیک­ های ابررسانا

Superconductive Ceramic
سرامیک­ های ابررسانا

ABSTRACT

Since the discovery of superconductivity in mercury in 1911 by kamerlingh Onnes superconductivity was found in many other metals and in an extremely large number of metallic alloys and compounds . The highest temperature of the transition to the superconducting state ( critical temperature T_c ) increased in steps whit year as shown in Figure 8.1.1 and had reached 23 K for Nb₃ Ge by 1973 . stable cooling to achieve  superconductivity for these so-called conven tional metallic superconductors is possible only by using liquid helium (4.2K) which makes the technology complex and costly . As a result superconductivity application was limited to special ones such as the generation of strong magnetic field which could not be attained by using conventional copper wire. In early 1986 Bednorz and Mueller made the amazing and unexpected discovery of high-temperature superconductivity at around 35K in La-Ba-Ca-Cu-O system .

سنتز صفحات زیرکونیوم براید از مخلوط پودر ZrCl4 و B فعال شده به صورت مکانیکی

Synthesis of zirconium diboride platelets from mechanically
activated ZrCl4 and B powder mixture

سنتز صفحات زیرکونیوم براید از مخلوط پودر ZrCl₄ و B فعال شده به صورت مکانیکی

 

ABSTRACT

In summary, the platelet-like ZrB2 particles were successfully prepared by the mechanochemical processing of a ZrCl4– B mixture and subsequent annealing from 1000 8C to 1200 8C. ZrO2 was identified as the possible intermediate reaction product. At 1000 8C, the ZrCl4–B mixture transformed to ZrB2 by a reaction between ZrO2 and B that accompanied the hydrolysis reaction of ZrCl4 following the dehydration of zirconium oxide halides to ZrO2 upon heating. Trace quantities of unreacted ZrO2 were detected at 1000 8C and 1100 8C. At1200 8C, the ZrCl4–B mixture completely converted to ZrB2 without the presence of any residual ZrO2. The resulting ZrB2 powder consisted of platelet-like particles with a diameter of ۰٫۱–۲٫۱ mm, a thickness of 40–۲۰۰ nm and traces of whiskers.Also, another study of the borothermal reduction of ZrO2 and B powder mixture showed that ZrB2 was prepared by the mechanochemical processing and subsequent annealing at 1100 8C instead of 1700–۲۰۰۰ ۸C without mechanical treatment [19]. The direct synthesis of ZrB2 at lower temperatures was mainly attributed to the increased chemical mixing as well as concentration of defects in the ZrO2 grains during milling. A similar explanation is favoured in this study because the ZrO2 obtained upon heating of ZrCl4 showed many defects.

 

تأثیر دما بر خوردگی Cu/HNO3 در حضور ممانعت کننده آلی

The Effect of Temperature on the Corrosion of Cu/HNO3 in the Presence of Organic Inhibitor

تأثیر دما بر خوردگی Cu/HNO₃ در حضور ممانعت کننده آلی

ABSTRACT

The effect of temperature on the corrosion behaviour of copper in 2M nitric acid solution in the presence and absence of 5-(2,6-dichlorobenzyl)-6-methylpyridazin-3(2H)-one (P3) has been investigated by weight loss method. The inhibitory effect increases with increasing inhibitors concentration and decreases with rise of temperature from 303 to 343K. Adsorption follows the Langmuir isotherm with negative values of free enthalpy suggesting a spontaneous adsorption process. Other thermodynamic parameters such as, equilibrium constant, adsorption heat and adsorption entropy were obtained. The various parameters of activation determining the kinetic data such as energy, enthalpy and entropy at different concentrations of the inhibitor were evaluated and discussed.Pure copper is a very soft, malleable metal. It is alloyed with small quantities of metals such as Be, Te, Ag, Cd, As, and Cr to modify the properties for particular applications, while retaining many of the characteristics of the pure metal. The reasons for this enormous consumption of copper plumbing tube are its excellent corrosion resistance, its ease of fabrication during installation, and hence low-installation costs, and additionally, its contribution to health and the maintenance of healthy water. Further, copper is seen as environmentally friendly due to its potential to be 100% recycled .

اثر کار مکانیکی اولیه بر ساختار و ظرفیت تغییرشکل

EFFECT OF PRIOR WORKING ON THE STRUCTURE AND DEFORMATION CAPACITY

اثر کار مکانیکی اولیه بر ساختار و ظرفیت تغییرشکل آلیاژ Mn-29.5%Al-0.5%C

ABSTRACT

Alloys based on the system Mn–AI–C relate to promising magnetically hard materials which in magnetic properties in an anisotropic state are close to barium ferrites, and in magnetic energy referred to density, they markedly surpass widely known alloys of the YuNDK type . The high magnetic properties of the system Mn–Al–C are obtained as a result of plastic deformation . Metastable r-phase, governing the ferromagnetic properties of these alloys, is stable up to 700-750°C, and therefore deformation treatment of them is not carried out at higher temperatures. It should be noted that alloys of the Mn–AI–C system have high brittleness, low ductility, and poor workability. For example, in order to obtain magnets of these alloys by extrusion at 700°C a stress of more than 800 N/mm2 is required , which leads to rapid wear of the die tool. A study was made in  of alloys containing lamellar T-phase of the martensitic type obtained after air cooling. The morphology of the r-phase may be altered by using special working methods, e.g., extrusion  or prior plastic deformation as a result of which it is possible to expect a considerable improvement in the working capacity of the alloy. It is of interest to study prior deformation of an alloy of the Mn–AI–C system in the temperature region for existence of high-temperature e-phase followed by cooling.

مواد کامپوزیت دی الکتریک با یک فاز رسانای گسسته

composite dielectric materials with a Discrete conducting phase 

مواد کامپوزیت دی الکتریک با یک فاز رسانای گسسته

 

ABSTRACT

A class of composite dielectric  materials refers to a two-phase refer ، host inclusion system in which the inclusion is a discrete- phase of conducting medium ( such as metals ، semiconductors ، or solid electrolytes ) dispersed randomly or textured as an orderly embedment in the host medium which forms a dielectric  receptacle . such composite are essentially dielectric – conductor mixtures and have Unique ( effective )  dielectric properties due to the fact that the constituent phases have extremely opposite characteristics as regards their electrical susceptance and the associated conduction phenomena .

تولید زیرکنیای تثبت شده با ایتریا به کمک تفجوشی مایکروویو

Microwave synthesis of yttria stabilized zirconia

تولید زیرکنیای تثبت شده با ایتریا به کمک تفجوشی مایکروویو

 

ABSTRACT

Yttria stabilised zirconia (YSZ) nanocrystals, with a mean size between 5 and 10 nm, were prepared by microwave flash synthesis. Flash synthesis was performed in alcoholic solutions of yttrium, zirconium chloride and sodium ethoxide (EtONa) using a microwave autoclave (RAMO system) specially designed by authors. Energydispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), BET adsorption technique, photon correlation spectroscopy (PCS) transmission and scanning electron microscopy (TEM and SEM) are used to characterized these nanoparticles. Compared with conventional synthesis, nanopowders can be produced in a short period (e.g. 10 s), both high purity and stoechiometric control are obtained. Nevertheless, this mean of production is more cheaper and much faster than the ones commonly used to produce yttria stabilized zirconia (YSZ) by conventional sol–gel techniques.

مشخصه یابی ریزساختاری آلیاژ Al-8Fe-1.4V-8Si تحت ریخته گری

Microstructural characterization of squeeze-cast Al–8Fe–1.4V–8Si

مشخصه یابی ریزساختاری آلیاژ  Al-8Fe-1.4V-8Si تحت فرایند ریخته گری فشاری

 

ABSTRACT

This paper investigates the effect of vanadium on the composition and morphology of intermetallics formed during the squeeze casting of Mgmodified Al–8Fe–1.4V–8Si alloy in both monolithic form and as-reinforced with 7.58, 10.52 and 15.68 wt.% SiC particles (SiCp). Iron intermetallics of -Al7(Fe,V)3Si and -Al18Fe11Si phases were predominantly observed in the alloy and composite. SEM studies and the EDX analyses revealed that refinement of Fe-intermetallics and modification of -phases to less deleterious morphologies of -phases has been achieved by vanadium addition of 1.4%. Also, heat treatment enhances V diffusion and SiC particles act as nucleation sites for the formation of finer -intermetallics. Fractographs exhibited cracking of long -phases and partial decohesion of SiCp from the matrix.

اصول پیش بینی عمر سرویس دهی سیستم های پوششی

Methodologies for Predicting the Service Lives of Coating Systems

اصول پیش بینی عمر سرویس دهی سیستم های پوششی

 

ABSTRACT

Over the last two decades the organic coatings industry has undergone rapid technological and structural changes. these  changes has been induced by legislative actions such as restriction pertatining to hazardous chemicals toxic effluents and volatile organic compounds . Further changes have been induced by competitive and consumer pressures to produce environmentally and user friendly coating without sacrificing ease of application initial appearance or most importantly without significantly reducing the expected service life of the coating systems .

سیلان مواد در طول جوشکاری اصطکاکی اغتشاشی Ti-6Al-V

Material Flow During Friction Stir Welding of Ti-6Al-4V

سیلان مواد در طول جوشکاری اصطکاکی اغتشاشی Ti-6Al-V

ABSTRACT

6 mm thick Ti-6Al-4V butt joints were produced with a tracer material embedded in the joint under a variety of process conditions, namely rotational speed and traversing speed, in an attempt to relate the welding process parameters to the material flow behavior via post weld radiographic and metallographic evaluations. It was found that by embedding refractory alloy powder into the joint line, welding through it, and subsequently x-raying the joint, the material flow patterns could be examined. The tracer material was distributed over a wider area in the weld zone relative to its starting position, implying a fair amount of mixing occurred even though little vertical movement of the tracer material was observed. There was minimal effect of material flow patterns as a function of welding parameters observed using the tracer material and radiographic examination, but defect formation in the root, where there was no tracer material, examined by cross sectional metallographic evaluations were found to be dependent on the rotational speed and traversing speed conditions. Lack of penetration defects were generally associated with relatively “cold” welding conditions (low rotational speed/high traversing speeds) and voids with “hot” conditions (high rotational speed/low traversing speeds).

اتصال با استفاده از تغییرشکل پلاستیک

Joining by plastic deformation

اتصال با استفاده از تغییرشکل پلاستیک

ABSTRACT

Vehicles such as aircraft and cars comprise a large number of mechanical parts produced by a variety of manufacturing processes. Cars generally consist of 10,000–30,000 parts, and the number of parts in aircraft is counted in millions. A trend in manufacturing such products is that both the number of parts and their complexity are increasing, including new combinations of dissimilar materials. Welding, adhesive bonding and mechanical fastening are typically used to join components during product assembly. In fusion welding, workpieces are joined by the application of an external heat source which melts material around the interface. Although the use of welding is widespread, the high temperatures required may reduce the quality, accuracy and reliability of joined parts. The strength of adhesively bonded and mechanically fastened joints is almost always lower than that achieved by welding. Commercial requirements for higher performance, higher productivity and lower cost in joining operations are becoming more demanding. In addition, strong joining of dissimilar materials is increasingly required. For example, high strength steel and aluminium sheets must be joined in some current car models, to allow weight reduction. There is therefore a need to identify new joining methods for new applications and materials.