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MEE 241 Prepared by- Md. Ferdous Alam, Lecturer, MEE, SUST
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MEE 241

Prepared by- Md. Ferdous Alam, Lecturer, MEE, SUST

Shape Memory Alloy

Smart coating- anti corrosion

CLASSIFICATION OF MATERIALS

• Metals

• Ceramics

• Polymers

This classification is based primarily on chemical makeup and atomic structure, and most materials fall into one distinct grouping or another.

Metals

• Materials in this group are composed of one or more metallic elements (e.g., iron, aluminum, copper, titanium, gold, and nickel), and often also nonmetallic elements (e.g., carbon, nitrogen, and oxygen) in relatively small amounts

• Atoms in metals and their alloys are arranged in a very orderly manner

• In comparison to the ceramics and polymers, metals are relatively dense

• Regarding to mechanical characteristics, these materials are relatively stiff and strong

• Metals are ductile (i.e., capable of large amounts of deformation without fracture), and are resistant to fracture

• Metallic materials have large numbers of nonlocalized electrons; that is, these electrons are not bound to particular atoms. Many properties of metals are directly attributable to these electrons. For example, metals are extremely good conductors of electricity and heat, and are not transparent to visible light; a polished metal surface has a lustrous appearance.

• Some of the metals (i.e., Fe, Co, and Ni) have desirable magnetic properties.

Ceramics • Ceramics are compounds between metallic and

nonmetallic elements; they are most frequently oxides, nitrides, and carbides

• For instance, common ceramic materials include aluminum oxide (or alumina, Al2O3), silicon dioxide (or silica, SiO2), silicon carbide (SiC), silicon nitride (Si3N4), and, in addition, what some refer to as the traditional ceramics—those composed of clay minerals (i.e., porcelain), as well as cement and glass.

• Regarding to mechanical behavior, ceramic materials are relatively stiff and strong—stiffnesses and strengths are comparable to those of the metals

• Typically ceramics are extremely brittle (lack of ductility) and are highly susceptible to fracture

• Newer ceramics are being engineered to have improved resistance to fracture; these materials are used for cookware, cutlery, and even automobile engine parts.

• Regard to optical characteristics, ceramics may be transparent, translucent, or opaque

• Ceramic materials are typically insulative to the passage of heat and electricity (i.e., have low electrical conductivities), and are more resistant to high temperatures and harsh environments than metals and polymers.

Who can answer?

• Why do metals have widespread use in structural applications?

• Why are metals extremely good conductors of electricity?

• Which type of materials are more resistant to high temperatures?

Polymers • Polymers include the familiar plastic and rubber

materials

• Many of them are organic compounds that are chemically based on carbon, hydrogen, and other nonmetallic elements (i.e., O, N, and Si).

• They have very large molecular structures, often chainlike in nature, that often have a backbone of carbon atoms.

• Some common and familiar polymers are polyethylene (PE), nylon, poly(vinyl chloride) (PVC), polycarbonate (PC), polystyrene (PS), and silicone rubber

• They have low densities

• Their mechanical characteristics are generally dissimilar to the metallic and ceramic materials—they are not as stiff nor asstrong as these other material types

• In addition, many of the polymers are extremely ductile and pliable (i.e., plastic), which means they are easily formed into complex shapes.

• Normally they are relatively inert chemically and unreactive in a large number of environments.

• polymers have the tendency to soften and/or decompose at modest temperatures

• They have low electrical conductivities

Carbonated Beverage Containers

• Provide a barrier to the passage of carbon dioxide, which is under pressure in the container

• Nontoxic, unreactive with the beverage, and, preferably, recyclable

• Relatively strong and capable of surviving a drop from a height of several feet when containing the beverage

• Inexpensive, including the cost to fabricate the final shape

• If optically transparent, retain its optical clarity;

• Capable of being produced in different colors and/or adorned with decorative labels.

So, Which of the material we discussed, would you choose?

• Aluminum – Metal

• Glass - Ceramic

• Plastic - Polymer

• Beverages in aluminum and glass containers retain their carbonization for several years, whereas those in two-liter plastic bottles “go flat” within a few months.

- Plastic is not as impervious to the passage of carbon dioxide as the aluminum and glass.

Next Class

Composite


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