مواد ابر رسانا

Superconducting Materials

مواد ابر رسانا

ABSTRACT

The phenomenon of superconductivity came to be known in 1911 by observing that a capillary column of mercury immersed in a liquid helium bath woud show an abrupt reduction in resistance and at 4.2 K it became impossible to measure the low resistance exhibited by the column with the then available measurement techniques . It was concluded that below a critical temperature (T_c) the mercury had passed into a new state . Subsequent studies on superconduction were pursued with tin and lead as candidate materials and it was discovered that a critical current density (J_c) is carried by a superconduction sample before it returns to its normal ( metallic ) state .

مقدمه الزامات مهندسی برای مواد کامپوزیتی صنعت هوافضا

Introduction: engineering
requirements for aerospace
composite materials

مقدمه الزامات مهندسی برای مواد کامپوزیتی صنعت هوافضا 

ABSTRACT

Composite materials have gained popularity (despite their generally high cost) in high performance products that need to be lightweight, yet strong enough to take high loads such as aerospace structures (tails, wings and fuselages), boat construction, bicycle frames and racing car bodies. Other uses include storage tanks and fishing rods. Natural composites (wood and fabrics) have found applications in aircraft from the first flight of the Wright Brothers’ Flyer 1, in North Carolina on December 17, 1903, to the plethora of uses now enjoyed by man-made (engineered) composite materials on both military and civil aircraft, in addition to more exotic applications on unmanned aerial vehicles (UAVs), space launchers and satellites. Their adoption as a major contribution to aircraft structures followed on from the discovery of carbon fibre at the Royal Aircraft Establishment at Farnborough, UK, in 1964.

وضعیت صنعت در کنترل آخال ها در طی ریخته گری شمش فولادی

State of the Art in the Control of Inclusions during Steel
Ingot Casting

وضعیت صنعت در کنترل آخال ها در طی ریخته گری شمش فولادی

ABSTRACT

This article extensively reviews published research on inclusions in ingot steel and defects on ingot products, methods to measure and detect inclusions in steel, the causes of exogenous inclusions, and the transport and entrapment of inclusions during fluid flow, segregation, and solidification of steel cast in ingot molds. Exogenous inclusions in ingots originate mainly from reoxidation of the molten steel, slag entrapment, and lining erosion, which are detailed in this article. The measures to prevent the formation of exogenous inclusions and improve their removal are provided, which are very useful for the clean steel production of ingot industries.

مواد فریتی

Ferrites Materials

مواد فریتی

ABSTRACT

Ferrites are mixed crystals of various metallic oxides and may be considered to consist of oxygen ions in a closed-packed structure with cations filling the interstices . They have a general formula : MOFe₂O₃ , xH₂O where M is a divalent metallic ion such as Mn²⁺ , Fe²⁺ , Co²⁺ , Ni²⁺ , Zn²⁺ , Mg²⁺ , and Cd²⁺ . In general , the magnetic satruration intensity to ferrites is lower than that of various metallic magnetic alloys , but the ferrites have very high resistivity and as such are insulator-like . Therefor , the power loss in ferrites is very small especially at high frequencies . Further , ferrites have a narrow hysteresis (BH) loop and can be made with square-loop characteristics .