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Sandwich Structured Composites

Sandwich composites are a special class of composite materials which are widely used because of their high specific strength and bending stiffness. Lower density of these materials makes them well suited for marine and aerospace applications. Developments in aviation posed requirements of lightweight, high strength and highly damage tolerant materials. Sandwich structured composites, fulfilling these requirements became the first choice for many applications including structural components for ground transport and marine vessels. The use of cores such as closed cell structured foam in sandwich structures gives some distinct advantages over open cell structured foams and cores. The specific compressive strength of close cell structured foams is much higher and absorbs less moisture than open cell structured foam.

(E.E. Gdoutos, Experimental Analysis of Nano And Engineering Materials and Structres,p.761)

Ferromagnetism

Ferromagnetism refers to solids that are magnetized without an applied magnetic field. These solids are said to be spontaneously magnetized.  Ferromagnetism occurs when paramagnetic ions in a solid “lock” together in such a way that their magnetic moments all point (on the average) in the same direction. At high enought temperatures, this “locking” breaks down and ferromagnetic materials become paramagnetic. The temperature at which this transition occurs is called the Curie Temperature.

There are two aspects of Ferromagnetism. One of these is the description of what goes on inside a single magnetized domain( where the magnetic moments are all aligned). The other is the description of how domains interact to produce the observed magnetic effects such as hysteresis.

(James D. Patterson, Bernard C. Bailey, Solid-State Physics: Introduction to the Theory, p. 360)


Ferrimagnetism

Ferrimagnetic substances exhibit a substantial spontaneous magnetization at room temperature, just like ferromagnetics, and this fact alone makes them industrially important. Like ferromagnetics, they consist of magnetically saturated domains, and they exhibit the phenomena of magnetics saturation and hysteresis. Theri spontaneous magnetization disappears above a certain critical temperature Tc, also called the Curie temperature, and then they become paramagnetic. Ferrimagnetics were not recognized as forming a distinct magnetic class until 1948. In practical importance they are second only to ferromagnetics and are essential materials in some applications.

The most important ferrimagnetic substances are certain double oxides of iron and another metal, called ferrites(although not all oxide ferrites are ferrimagnetic). This mineralogical term is not to be confused with the same word applied by metallurgists to bodycentered cubic iron. The ferrites were develop into commercially useful magnetic materials, chiefly during the years 1933-1945, by Snoek and his associated at the Philips Research Laboratories in the Netherlands.

(Bernard Dennis Cullity, Chad D. Graham, Introduction to magnetic materials, p.175)


Electroplanting 

1)Theory

The article to be electroplated is first cleaned thoroughly. A suitable electrolyte is taken in a tank made up of insulating material( cement, rubber, glass etc.). Suppose anode is made up of coating metal (M). During electrolysis the concentration of electrolytic solution remains unaltered since the metal ion deposited from the solution are replenished continuolusly by the reaction of free anions with anode metal. IfCuSO solution is used as ana electrloyte, then it ionizes as;

CuSO → Cu(+)  + SO (-)  Ionization

On passing current Cu ions move to cathoed and get deposited there

Cu(+) + 2e(-) → Cu ( At Cathode)

The free SO(-) thus formed is dissolved in the electrolyte. So there is complete replenishment of electrolytic salt during electrolysis.

2) Aim of Electroplanting

1. To increase the resistance to corrosion of plated metal.

2. To improve the surface properties.

3. To improve physical appearance and hardness

4. To improve the resistance to chemical attack and wear resistance

5. To increase the decorative and commercial value of the metal

3)Characteristics of Electroplating

1. Thickness

2. Hardness

3. Protective Values

5. Temperature

6. Current Density

7. Agitation of Bath

8. Throwing Power

9. Cleaning of Article to be plated

10. Choke of solvent

11. Concentration of metal ions in the bath

(D Singh, Balraj Deshwal, Satish Kumar Vats, Comprehensive Engineering Chemistry, p. 151-152)