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NDT Materials and Processes > Physical and Chemical Properties > Flashcards

Physical and Chemical Properties Flashcards

1
Q

What are physical properties?

A

Properties that can be observed without changing the identity of the substance - e.g. color, density, hardness

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2
Q

What are chemical properties?

A

Properties that describe how a substance changes into a completely different substance - e.g. flammability and corrosion/oxidation resistance.

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3
Q

What is phase?

A

A physical property of matter & matter can exist in 4 phases - solid, liquid, gas and plasma.

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4
Q

What are phase transformation temperatures?

A

Transitions from solid to liquid, liquid to gas, gas to solid and visa versa are phase transformations and the temperatures that these processes occur are the phase transformation temperatures. E.g. melting point, boiling point, glass transition temperature.

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5
Q

What is glass transition temperature?

A

The temperature at which a solid, glassy material begins to soften and flow.

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6
Q

What is density?

A

The mass of a material per unit volume, how tightly packed the mass is in its volume.

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7
Q

What does density depend on?

A

The phase of the material and the temperature.

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8
Q

What is specific gravity?

A

The ratio of density of a substance to the density of fresh water at 4 degrees C (1g/ml).

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9
Q

Relation of an object floating in water to specific gravity?

A

If an object has a density less than the density of water it will float in water and if it has a density greater than the density of water it will sink.

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10
Q

What is thermal conductivity?

A

The intrinsic property of a material which relates its ability to conduct heat.

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11
Q

When does heat conduction take place?

A

When there is a temperature gradient in a solid or stationary fluid medium.

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12
Q

How is energy transferred in heat conduction?

A

Energy is transferred from the more energetic to the less energetic molecules when neighboring molecules collide.

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13
Q

What is the thermal conductivity equation?

A

Thermal Conductivity = heat x distance / (area x temperature gradient).

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14
Q

Describe thermal expansion in terms of atoms?

A

When heat is added to most materials, the average amplitude of the atoms’ vibrating within the material increases. This, in turn, increases the separation between the atoms causing the material to expand.

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15
Q

What is the linear coefficient of thermal expansion?

A

The linear coefficient of thermal expansion describes the relative change in length of a material per degree temperature change.

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16
Q

What is electricity?

A

The directional movement of electrons due to an electromotive force

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17
Q

What is electrical conductivity?

A

Electrical conductivity is a measure of how well a material accommodates the movement of an electric charge. It is the ratio of the current density to the electric field strength.

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18
Q

What is the SI unit of electrical conductivity?

A

Siemens per meter (S/m)

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19
Q

What is a common unit for reporting electrical conductivity?

A

percent IACS - IACS is an acronym for International Annealed Copper Standard. The conductivity of annealed copper (5.8001 x10^7 S/m) is defined to be 100% IACS at 20 degC.

20
Q

How to convert from S/m to % IACS?

A

multiply by 1.7241 x10^-6

21
Q

What examples are there of useful things electrical conductivity can be used for?

A

Measuring the purity of water, sorting materials, checking for proper heat treatment of metals, and inspecting for heat damage in some materials.

22
Q

What is electrical resistivity?

A

The reciprocal of conductivity, it is the opposition of a body or substance to the flow of electrical current through it, resulting in a change of electrical energy into heat, light or other forms of energy.

23
Q

What is the SI unit for electrical resistivity?

A

the Ohm meter.

24
Q

What typically happens to the conductivity and resistivity of most materials as the temperature increases?

A

Conductivity typically decreases as temperature increases and resistivity typically increases as temperature increases.

25
Q

Why does resistivity increase with increasing temperature?

A

Because at higher temperatures there is a larger number of imperfections in the atomic lattice structure so these hamper electron movement.

26
Q

What is magnetic permeability?

A

The ease with which a material can be magnetized. It is a constant of proportionality that exists between magnetic induction and magnetic field intensity.

27
Q

What are diamagnetic materials?

A

Materials that cause the lines of flux to move farther apart, resulting in a decrease in magnetic flux density compared with a vacuum.

28
Q

What are paramagnetic materials?

A

Materials that concentrate magnetic flux by a factor of more than one but less than or equal to ten.

29
Q

What are ferromagnetic materials?

A

Materials that concentrate the flux by a factor of more than ten.

30
Q

What is corrosion?

A

Corrosion involves the deterioration of a material as it reacts with its environment. Corrosion is the primary means by which metals deteriorate. Corrosion literally consumes the material reducing load carrying capability and causing stress concentrations.

31
Q

How is the corrosion properties of materials expressed?

A

Not in terms of a design property value like other properties but rather in more qualitative terms such as immune, resistant, susceptible or very susceptible to corrosion.

32
Q

Why does corrosion occur?

A

Because unstable materials, such as refined metals, want to return to a more stable compound.

33
Q

What are the two chemical processes involved in corrosion?

A

Oxidation - stripping electrons from an atom

Reduction - when an electrode is added to an atom

34
Q

Where does the oxidation process take place?

A

At an anode, where positively charged atoms leave the solid surface and enter into an electrolyte as ions.

35
Q

What happens at the anode?

A

Positively charged atoms leave the solid surface and enter into an electrolyte as ions. The ions leave their corresponding negative charge in the form of electrons in the metal which travel to the location of the cathode through a conductive path.

36
Q

What happens at the cathode?

A

The corresponding reduction reaction takes place and consumes free electrons. The electrical balance of the circuit is restored at the cathode when the electrons react with neutralizing positive ions in the electrolyte (such as hydrogen ions).

37
Q

What are the four essential components needed for a corrosion reaction?

A

An anode, a cathode, an electrolyte with oxidizing species and some direct electrical connection between the anode and the cathode.

38
Q

What are the 8 types of corrosion?

A 
Uniform or general
Localized
Intergranular
Galvanic
Environmental Cracking
Erosion Cracking
Fretting Corrosion
Dealloying
39
Q

What is uniform or general corrosion?

A

Corrosion that is distributed more or less uniformly over a surface

40
Q

What is localized corrosion?

A

Corrosion confined to a small area, often occurs due to a concentrated cell.

41
Q

What is intergranular corrosion?

A

Preferential corrosion at or along the grain boundaries of a metal.

42
Q

What is galvanic corrosion?

A

Corrosion associated with the electrical coupling of materials with significantly different electrochemical potentials.

43
Q

What is environmental cracking corrosion?

A

Brittle fracture of a normally ductile material that occurs partially due to the corrosive effect of an environment.

44
Q

What is erosion corrosion?

A

A corrosion reaction accelerated by the relative movement of a corrosive fluid and a metal surface.

45
Q

What is fretting corrosion?

A

Damage at the interface of two contacting surfaces under load but capable of some relative motion.

46
Q

What is dealloying corrosion?

A

The selective corrosion of one or more components of a solid solution alloy.

NDT Materials and Processes (3 decks)

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