ترکیبات حاوی سرب Lead Compounds

Lead Compounds

ترکیبات حاوی سرب

ABSTRACT

Lead compounds include over forty naturally occurring minerals from which five lead oxides can be derived. The lead oxides, as well as some lead silicates, are used as raw materials in lead-containing glasses and crystalline electronic ceramics. The presence of lead in glass increases the refractive index, decreases the viscosity, increases the electrical resistivity, and increases the X-ray absorption capability of the glass. The lead in electronic ceramics increases the Curie temperature and modifies various electrical and optical properties. The refinement of metallic lead from minerals and recycled goods such as lead acid batteries and cathode ray tubes is a multistep process, supplemented by oxidation steps to produce lead oxides. Lead compounds are known to be toxic and are therefore highly regulated.

 

تهیه پودر ZrB2با اندازه نانو بوسیله سنتز خود انتشار دما بالا

Preparation of nano-size ZrB2 powder by self-propagating

high-temperature synthesis

تهیه پودر ZrB₂با اندازه نانو بوسیله سنتز خود انتشار دما بالا

ABSTRACT

Preparation of nano-size ZrB2 powder via SHS was demonstrated by adding 10–۵۰ wt.% NaCl into Zr–B elemental starting powder. Reactions took place completely even with high NaCl content. Adiabatic temperature of reactions, reaction wave velocity, average crystallite size and particle size of the formed ZrB2 decreased significantly with increasing NaCl content. ۳۰ wt.% NaCl addition was found to be the optimum and obtained ZrB2 particles were mostly finer than 200 nm. Hindrance of mass transport among ZrB2 crystals is believed to be  the basis of grain refinement effect of NaCl. Obtaining nano-sized powder was considered very difficult in SHS due to inevitable high temperatures. Owing to the introduction of NaCl into SHS, process control and preparation of ceramic powder having nano-sized particles were rendered possible. The development has the potential to enrich the spectrum and the properties of materials that could be produced via SHS.

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.

 

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 .

معرفی و بررسی شکست

Introduction and fracture over view

معرفی و بررسی شکست

ABSTRACT

In this chapter ، a fundamental approach to fracture will be followed in order to develop a few central ideas about why any given material is ductile or brittle ، and how the basic lattic defects of the material cooperate to give rise to these two general classes of behavior . The analytical discussion will tend to focus on relatively brittle phenomena ، partly because any idealization of  fracture – leads one first to the consideration of brittle fracture and partly because the analysis for brittle fracture is better understood and therefor more accessible .

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.