1- Which of these processes will lower the glass transition temperature of a glass?
Increase the cooling rate
Decrease the cooling rate
Increase amount of network modifier
Decrease amount of network modifier
Quench the glass to cool the surfaces quickly
Decrease the number of defects
2- Which of the following statements describes why ion exchange of 99% SiO2 - 1% B2O3 in a salt bath of molten postassium chloride (KCl) is not an effective way to increase the surface strength of the glass sample?
The ion exchange works correctly, however both air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.
The ion exchange works correctly, however both air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.
The ion exchange works correctly, however both air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.
The sample described above is composed of SiO2 and B2O3. Neither of these components are network modifiers, so ion exchange does not take place to strengthen the surface of the glass.
The surfaces of the glass sample are not cooled quickly enough to create a high internal strain energy that leads to strong surfaces.
3- In which of the following ways would you change the glass sample to make the ion exchange more efficient?
Change the composition of the glass to increase the proportion of B2O3.
Change the composition of the glass to add Na2O, Li2O, or MgO.
Change the composition of the glass to add CaO.
Change the composition of the salt bath (KCl) to an ion smaller than potassium, such as sodium chloride (NaCl).
Lower the temperature of the salt bath to cool the sample more quickly.
4-Please mark below all of the statments that correctly describe the physical properties of glass.
Glasses do not have slip systems.
Glasses consist of both covalent and ionic bonding.
Glasses are brittle at room temperature.
Glasses are amorphous and have no long range symmetry.
The volume of a sample of glass depends on its cooling rate.
Glasses must consist of network formers and modifiers.
5- You have a single crystal of 100% pure gold. Identify which of the following defects you would expect to be present at room temperature.
Free surface
Grain boundaries
Vacancies
Inclusions
Substitutional impurity atoms
Interstitial impurity atoms
6- At 10°C below the melting point of aluminum, 0.08% of the atom sites are vacant. At 484°C only 0.01% are vacant. Given this information, determine the energy of vacancy formation (ΔHv) for aluminum.
Energy of vacancy formation (in joules / vacancy)
X=.......
7- Determine the radius of the largest atom that can be accommodated in the interstices of BCC iron (Fe) without stress. (Hint: the center of the largest site is at ½, ¼, 0; draw a unit cell - it helps.)
Radius (in centimeters):......
8-An activationenergy of 2.0 eV is required to form a vacancy in a metal. At 800°C there is one vacancy for every 10-4 atoms. At what temperature will there be one vacancy for every 1000 atoms?
Temperature (in degrees Kelvin):......
1. Decrease the cooling rate, Increase amount of network modifier.
2. The sample described above is composed of SiO2 and B2O3. Neither of these components are network modifiers, so ion exchange does not take place to strengthen the surface of the glass.
3. Change the composition of the glass to add Na2O, Li2O, or MgO.
4. Glasses do not have slip systems , Glasses are amorphous and have no long range symmetry. , The volume of a sample of glass depends on its cooling rate.
5. free surface , vacancies
1- To lower the glass transition temperature of a glass, you can increase the cooling rate, increase the amount of network modifier, quench the glass to cool the surfaces quickly, or decrease the number of defects. These processes can destabilize the glass structure and lower the temperature at which the glass transitions from a solid to a supercooled liquid.
2- The correct statement is: The surfaces of the glass sample are not cooled quickly enough to create a high internal strain energy that leads to strong surfaces. Ion exchange of 99% SiO2 - 1% B2O3 in a salt bath of molten potassium chloride (KCl) is not an effective way to increase the surface strength of the glass sample because the surfaces of the glass sample are not cooled quickly enough to create a high internal strain energy. Air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.
3- To make the ion exchange more efficient, you can change the composition of the glass by adding network modifiers such as Na2O, Li2O, or MgO. This will increase the mobility of ions in the glass and enhance the ion exchange process. Changing the composition of the salt bath to an ion smaller than potassium, such as sodium chloride (NaCl), can also improve the efficiency of ion exchange. Lowering the temperature of the salt bath will cool the sample more quickly and increase the effectiveness of the ion exchange process.
4- The correct statements that describe the physical properties of glass are:
- Glasses are brittle at room temperature.
- Glasses are amorphous and have no long-range symmetry.
- The volume of a sample of glass depends on its cooling rate.
- Glasses must consist of network formers and modifiers.
5- In a single crystal of 100% pure gold at room temperature, you would expect to find the following defects:
- Free surface: Since the crystal has exposed surfaces, free surfaces are present.
- Grain boundaries: Since the crystal is a single crystal, there are no grain boundaries.
- Vacancies: Vacancies may be present as atomic sites that are unoccupied within the crystal lattice.
- Inclusions: In a pure gold crystal, there should be no inclusions.
- Substitutional impurity atoms: Since the gold crystal is 100% pure, there should be no impurity atoms.
- Interstitial impurity atoms: Since the gold crystal is 100% pure, there should be no interstitial impurity atoms.
6- To determine the energy of vacancy formation (ΔHv) for aluminum, we can use the equation ΔHv = (RT^2/v) ln(C/C0), where R is the gas constant, T is the temperature, v is the number of atomic volume, C is the concentration of vacancies, and C0 is the equilibrium concentration of vacancies. With the given information, the energy of vacancy formation can be calculated using the formula and the given concentrations of vacancies at different temperatures.
7- To determine the radius of the largest atom that can be accommodated in the interstices of BCC iron (Fe) without stress, we can use the simple cubic unit cell of BCC iron and consider the position of the largest interstitial site. The radius of the largest atom can be calculated using the distance between adjacent atoms in the BCC structure.
8- To determine the temperature at which there will be one vacancy for every 1000 atoms, we can use the equation ln(C0/C) = -(ΔHv/RT), where ΔHv is the energy of vacancy formation, R is the gas constant, T is the temperature, C0 is the equilibrium concentration of vacancies, and C is the concentration of vacancies. By rearranging the equation, we can solve for the temperature using the given values for ΔHv and C.