Lec 1 Flashcards
Semiconductors
Semiconductors have electrical properties that are intermediate between those of electri- cal conductors and insulators
Impurity concentration varies, more conductive with higher temp
Structure
Structure of a material relates to the arrangement of its internal components
Nanomaterials
Nanomaterials are small materials with diameters bellow 100 nm (0,1,2,3 dimensions).
Large surface to volume ratio
Six different property classifications of materials determine their applicability
mechanical, electrical, thermal, magnetic, optical, and deteriorative.
Property
property is defined as a material trait that specifies the type and magnitude of response to a particular stimulus.
Typically, no dependence on material shape and size.
What can affect mechanical properties of a material eg.
Increasing carbon content increases hardness of steel
What can affect electrical properties of a material eg.
Copper
- Increasing temperature increases resistivity.
- Increasing impurity content (e.g., Ni) increases resistivity.
- Deformation increases resistivity.
What can affect thermal properties eg.
Increasing impurity content (e.g., Zn in Cu) decreases thermal conductivity (measure of a material’s ability to conduct heat)
Highly porous materials are _ conductors of heat
poor
Example of structure changing optical properties
Aluminum oxide single crystal (high degree of perfection)—is optically transparent
Aluminum oxide polycrystalline material
(having many small grains)—is optically translucent
Aluminum oxide polycrystalline material having some porosity—is optically opaque
For stress-corrosion cracking, how is rate of crack growth diminished
by heat treating, you avoid Small cracks formed in steel bar that was simultaneously stressed and immersed in sea water
- Form of stress-corrosion cracking
Processing
Materials processing involves a series of chemical, thermal, and physical processes that prepare a starting material, create a shape, retain that shape, and refine the structure and shape.
Goal of material processing
develop the structural features (e.g., crystal structure, microstructure, size, and shape) needed for the product to perform well in its intended application.
§ The result can be microstructural change that can directly affect the material properties of a material.
Metal def
composed of metallic elements like iron, aluminum, copper, titanium, gold, and nickel.
Metal characteristics
– Strong, ductile
– High thermal & electrical conductivities
– Opaque, reflective
- Orderly atoms, free electrons
- dense
Ceramics def
compounds formed between metallic and nonmetallic elements, often oxides, nitrides, and carbides.
Ceramics properties
– Hard, stiff Brittle
– Low thermal & electrical conductivities
– Opaque, translucent, or transparent
- Can be magnetic
Polymers def
encompass common materials like plastics and rubber, primarily consisting of organic compounds based on carbon, hydrogen, and other nonmetallic elements (O, N, Si).
Large, often chainlike molecular structures with carbon atom backbones
Polymers properties
Low density
Low stiffness and strength
Ductile
Chemically inert
Composites
Combine materials from metals, ceramics, and polymers to achieve unique properties. The goal is to integrate the best characteristics of each component material.
Synthetic or natural
eg. Carbon fiber-reinforced polymer, fiberglass
Semiconductor
A semiconductor is a material with electrical conductivity falling between that of a conductor (e.g., copper) and an insulator (e.g., glass).
Properties: when the temperature rises, the conductivity of the semiconductor will be better (as opposed to metal)
