سیلیس و کوارتز

Quartz and Silicas

سیلیس و کوارتز

ABSTRACT

Silica is the most ubiquitous mineral in the earth’s crust, existing in a wide variety of crystalline and noncrystalline forms due to the flexibility of the linkage among SiO4 tetrahedra. The thermodynamically stable, room temperature form of silica is quartz, which is itself a widely available mineral and ingredient in many commercial ceramics and glasses. In addition to historically abundant raw material sources, crystalline and noncrystalline silicas can be produced by a wide range of synthetic routes. For example, synthetic quartz can be produced by hydrothermal growth in an autoclave, and synthetic vitreous silica can be produced from silicon tetrachloride by oxidation or hydrolysis in a methane–oxygen flame. Pure silicas serve as model systems in the study of ceramics and glasses, but at the same time, are used in a wide and steadily increasing variety of sophisticated technological applications, from piezoelectric crystals to optical fibers to waveguides in femtosecond lasers. Increased understanding of these ubiquitous materials is aided by improved experimental tools such as new neutron scattering facilities and increasingly sophisticated computer simulation methods.

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.

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.