Sunday
April 20, 2014

Homework Help: Chemistry

Posted by youlifex on Tuesday, October 29, 2013 at 5:42pm.

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 10C below the melting point of aluminum, 0.08% of the atom sites are vacant. At 484C 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 , , 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 800C 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):......

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