Week 8 - Material Properties 2 Flashcards
What is specific heat (Cp)
the heart energy required to increase the temperature of a unit volume by 1 degrees
What is thermal conductivity (K)
the rate of transportation of heat (cal or J) through material per unit temperature gradient
What is thermal diffusivity (h)
the rate at which heat spreads through a material. It indicates how quickly a material can conduct thermal energy relative to how much it can store. In other words, thermal diffusivity reflects how fast temperature changes in a material when it is subjected to a thermal gradient.
What temperature can cause tooth pulp damage
increasing tooth pulp temperature 5.5 degrees or more
What is coefficient of thermal expansion
the fractional increase in the dimension of a body as a function of increased temperature. = the extent to which a material expands or contracts when its temperature changes. It describes how much of a material size will change per degree change in temperature.
the expansion and contraction of dental materials is a function of what
- thermal diffusivity
- coefficient of thermal expansion
what type of degradation occurs in metals
- tarnish
- Corrosion
What type of degradation occurs in polymers
- Chain scission
- Absorption/adsorption
- dissolution
What type of degradation occurs in ceramics
- hydrolytic attack
- Dissolution
What is tarnish
the surface discolouration due to the formation of soft and hard surface deposits. E.g. sulphides and chlorides
- when a thin layer of corrosion forms on the surface of a metal due to a chemical reaction with environmental elements, such as oxygen, sulfur or other compounds.
What is corrosion
a deterioration of a material by chemical reaction with its environment
what does corrosion of material properties lead to (3)
- structural breakdown
- leaching out cytotoxic or allergic elements
- tissue discolouration
What are the different types of corrosion
- chemical corrosion
a. dry corrosion
b. wet corrosion
- Stress corrosion (chemical + mechanical)
- Galvanic corrosion
- Concentration cell corrosion (surface roughness or deep pit and fissures)
What is dry corrosion
Dry corrosion is a type of corrosion that occurs in the absence of moisture, typically when metals react directly with gases in the environment (such as oxygen) at elevated temperatures.
What is an example of dry corrosion
The reaction where iron reacts with oxygen at high temperature to form iron oxide (Fe2O3) is a common example (rusting)
This process forms an unstable oxide surface which will flake off and corrosion will continue. however this process is self limiting in some metals where a stable surface oxide forms e.g. chromium oxide on stainless steel.
Where does corrosion occur
Corrosion occurs in the Anode where an electro negative metals are placed in an electrolyte
What is galvanic corrosion
galvanic corrosion occurs when two dissimilar metals are connected by an electrolyte, leading to the accelerated corrosion of one metal (the more anodic) while the other metal (the more cathodic) is protected.
What is an example of galvanic corrosion
Pt and An
what is crevice corrosion
Crevice corrosion is a localized form of corrosion that occurs in a sharp crack or fluid filled space . the confined nature of the space allows corrosive agents (such as moisture or salt) to become trapped and concentrate, leading to accelerated corrosion in these areas.
