آماده سازی سرامیک های دی براید زیرکونیوم

Preparation of zirconium diboride ceramics by reactive spark
plasma sintering of zirconium hydride–boron powders

آماده سازی سرامیک های دی براید زیرکونیوم به کمک واکنش سینتر کردن پلاسمای جرقه ایِ  پودرهای هیدرید زیرکونیوم-بور

ABSTRACT

Monolithic ZrB2 ceramics were prepared by reactive spark plasma sintering of a ZrH2–B mixture at 1650–۱۸۰۰ C. The microstructure of the resulting ZrB2 ceramics were characterized by X-ray diffractometry and scanning electron microscopy. The ZrH2–B mixture converted completely into ZrB2 without trace quantities of residual ZrH2 and B. Highly dense ZrB2 was obtained at 1750 C or above. The elastic moduli, flexural strength, thermal and electrical conductivities were comparable with those of ZrB2 ceramics obtained by sintering conventional ZrB2 powders

ابزار جوشکاری اصطکاکی اغتشاشی friction stir welding tools

friction stir welding tools

ابزار جوشکاری اصطکاکی اغتشاشی

ABSTRACT

Friction stir welding (FSW) is a widely used solid state joining process for soft materials such as aluminium alloys because it avoids many of the common problems of fusion welding. Commercial feasibility of the FSW process for harder alloys such as steels and titanium alloys awaits the development of cost effective and durable tools which lead to structurally sound welds consistently. Material selection and design profoundly affect the performance of tools, weld quality and cost. Here we review and critically examine several important aspects of FSW tools such as tool material selection, geometry and load bearing ability, mechanisms of tool degradation and process economics.

 

نورد و پوشش دهی سطحی فولاد

ROLLING AND SURFACE COATING OF STEEL

نورد و پوشش دهی سطحی فولاد

ABSTRACT

Steel, an alloy of carbon and iron, is a material which is both inexpensive and has great  mechanical strength. However, it is initially produced as steel slabs which are too thick and  heavy to be used. To convert the steel into useful products it must first be rolled into thin  sheets and coiled onto spools. This steel is more useful, but it is still prone to rusting and will  have its useful lifespan seriously shortened if it is used in a damp environment.  To prevent corrosion, the steel is coated with zinc in a process known as galvanising. Zinc is  found above iron in the electrochemical series, which means that in galvanised steel the zinc  is oxidised instead of the steel itself, thus lengthening the useful lifespan of the steel. Zinc is  chosen for this purpose because it is the least expensive of the metals above iron in the  electrochemical reactivity series and it can satisfactorily be coated on steel. If a suitable  paint coating is applied on the galvanised steel surface, the protection effect can be further  enhanced. The common uses of galvanised sheets and coils are the manufacture of roofing material, steel wall cladding and the steel bodies of home appliances.

 

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.