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# MSE Ch 5

### Atomic and Ionic movements in materials.

Term | Definition |
---|---|

In diffusion, the magnitude of flux depends on ___ and ___. | the initial concentration, temperature |

Diffusing C into Fe from the surface is called ___ or ___. | carburizing, case hardening |

Case hardening with nitrogen is called ___. | nitriding |

Name the 2 ways diffusion occurs. | through interstitial sites or through defects |

Is diffusion more difficult through defects or interstitial spaces? | interstitial spaces |

When diffusion occurs at a grain boundary it can cause the boundary to ___. | move |

Diffusion through crystals is usually through defects because ___. | atoms are usually too large to fit in interstitial sites |

T or F? Vacancies are always moving. | True |

Name the 3 types of diffusion. | 1. volume, 2. grain boundary, 3. surface. |

Name the 3 subtypes of volume diffusion. | 1. interstitial, 2. vacancy, 3. dislocations. |

Increasing the number of grains ___(increases/decreases) the grain boundary area and thus ___(increases/decreases) the rate of diffusion. | increases, increases |

Of the 3 types of diffusion, ___ difffusion is the most easily achieved. | surface |

The energy required to begin diffusion is called ___ and is noted with ___. | activation energy, Q |

___ diffusion requires the most energy and ___ requires the least. | volume, surface |

The Arrhenius equation for jump rate of atoms is ___. | Jump rate = c_0*e^(-Q/RT) |

In c_0*e^(-Q/RT), c_0 = ___. | a constant for the material |

Q is in ___ per ___. | cal, mol |

The Arrhenius equation for diffusivity is ___. | D = D_0*e^(-Q/RT) |

In D = D_0*e^(-Q/RT), D_0 = ___. | a constant for the material |

Fick's first law is for ___ diffusion and describes the ___ of atoms. | steady state, flux |

Fick's first law is defined by the equation ___. | J = -D(∆c/∆x) |

In J = -D(∆c/∆x), J = ___. | flux of atoms |

In J = -D(∆c/∆x), (∆c/∆x) = ___ and is in ___ units. | the concentration gradient, (atoms/cm³∙cm) |

In J = -D(∆c/∆x), ∆c = ___. It will always be a ___ (-,+) number. | starting concentration minus ending concentration, (-) |

In J = -D(∆c/∆x), ∆x = ___. | the distance or depth of the desired concentration |

Steady state diffusion is ___(common/rare) in solids. | rare |

All else being equal, D is higher in ___(FCC/BCC) structures because ___. | BCC, there is more space |

As the temperature of Fe is INCREASED it changes phase from ___ Fe to ___ Fe at about ___°C or ___°K. | BCC, FCC, 912, 1185 |

Fick's second law describes ___, AKA ___. | transient diffusion, non-steady state |

Diffusion in solids is almost always ___. | transient |

One solution to Fick's second law when at the surface of a material is the equation ___. | (c_s - c_x)/(c_s - c_0) = erf[x/s√(Dt)] |

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_s = ___. | the constant concentration of diffusing atoms at the surface |

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_x = ___. | the concentration of diffusing atoms at point x below the surface |

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], c_0 = ___. | the starting concentration of diffusing atoms IN THE MATERIAL BEFORE diffusion occurs |

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], D = ___. | diffusivity |

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], t = ___. | seconds |

In (c_s - c_x)/(c_s - c_0) = erf[x/2√(Dt)], x/2√(Dt) = ___. | the argument of the error function |

erf can approach, but not reach or exceed ___. | 1 |

Using an error function table, to find a value between the given values we must use a process called ___. | linear interpolation |

T or F? Using an error function table, the left column is equal to x. | False. It is equal to x/2√(Dt). |

erf is equal to the ratio of ___ divided by ___. | (starting surface concentration of diffusing atoms) - (concentration at location x AFTER diffusion occurs), (starting surface concentration of diffusing atoms) - (concentration of diffusing atoms already at location x BEFORE diffusion) |

What are the units for erf? | None. |

What are the units for the argument of the erf? | None. |