材料概论课件

Lucalox lamps – introducing Ceramics
1 . refractory
Difficult to melt or work; resistant to heat. High-temperature-resistant material, such as many of the common ceramic oxides
Percent elongation at failure is a quantitative measure
Third , a freshly cut steel surface has a characteristic metallic luster , and fourth , a steel bar shares a fundamental characteristic with other metals : it is a good conductor of electrical current .
Silicon dioxide. One of Al2O3 various stable crystal magnesium oxide structures. MgO silica SiO2 silicates Si3N4 Ceramic compound with SiO2 as a major constituent.
The Different Colors of Corundum
Ruby
Sapphire
Aluminum oxide has two principal advantages over metallic Al .
First , Al2O3 is chemically stable in a wide variety of severe environments , whereas metallic aluminum would be oxidized . In fact , a common reaction product in the chemical degradation of aluminum is the more chemically stable oxide .
Cylinders of transparent Al2O3 became the heart of the design of high-temperature (10000C) sodium vapor lamps , which provide substantially higher illumination than do conventional lightbulbs .
3、One metallic element plus one of five
nonmetallic elements (C, N, O, P, or S)
structure leads to properties
To understand the properties or observable characteristics of engineering materials, it is necessary to understand their structure . Virtually every major property of the six materials categories outlined in this chapter will be shown to result directly from mechanisms occurring on a small scale (usually either the atomic or the microscopic level) .
brittleness
transparent ceramics To make traditionally opaque ceramics, such as aluminum oxide , into optically transparent materials required a fundamental change in manufacturing technology .
The Golden Gate Bridge
For many years, the Golden Gate held the title of „longest suspension bridge‟ in the world (2,737 meters). „symphony in steel‟
The elimination of porosity provided by the Lucalox patent (adding 0.1 wt % MgO ) produced a pore-free microstructure and a nearly transparent material with an important additional property--excellent resistance to chemical attack by high-temperature sodium vapor .
Second ,
higher melting point (20200C) Al (6600C ) Refractory use in industrial furnace construction .
Why isn‟t Al2O3 used for applications such as automotive engines in place of metallic aluminum? The most limiting property of ceramics
The dramatic effect that fine-scale structure has on large-scale properties is well illustrated by the development of transparent ceramics, just discussed in the introduction to ceramic materials .
The sundial bridge in Redding
the famous Spanish architect Santiago Calatrava.
Structural steel
characteristics : strong and readily formed Ductile metallic luster Electric conductor no brittleness Bridge alloy
2 . solution
A homogeneous mixture of two or more substances, which may be solids, liquids, gases, or a combination of these.
3. nonmetallic
Material such as a ceramic or polymer that is not metallic in nature.
1.3 six materials that changed your world
What materials are available to me ? Six categories
a . Metals b . Ceramics c . Glasses d . Polymers e . Composites f . Semiconductors
Traditional ceramics made in this way contained a substantial amount of residual porosity , corresponding to the open space between the original powder particles prior to high-temperature processing . A significant reduction in porosity resulted from a relatively simple invention that involved adding a small amount of impurity (0.1 wt % MgO ), which caused the high-temperature densification process for the Al2O3 power to go to completion .
This versatile construction material has several properties that we consider metallic : First , it is strong and can be readily formed into practical shapes . Material extensive , permanent Second , its having various properties deformability, or ductility , electrical such as ductility and is an important asset in permitting small amounts metals conductivity characteristic of of yielding to sudden and severe loads .
The microscopic-scale residual porosity in a traditional aluminum oxide , leads to loss of visible light transmission by providing a light-scattering mechanism .