Doping Procedure:
Silicate glass composites were strengthened in a salt bath containing KNO3. This is because most glasses contain a small alkali halide molecule such as Li2O or Na2O, with which we can perform the ion exchange process. By exchanging the Na+ ions with the K+ ions, we can increase the yield strength of the glass. The glass samples were doped for periods of 4, 5, 6, 7, and 8 hours.

Instron Testing:
Using a Universal Testing Machine (UTM), 3-Point Flexure tests were performed on the untreated and treated glass samples. This was done to find the fracture point, yield stress, and Young’s Modulus of the glass sample based on the number of hours the sample had been doped. This testing was done according to ASTM Guidelines C1161-18: Standard Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature.

Samples were placed carefully on the UTM, from which the loads at which fracture occurred were measured. As the number of hours the glass was doped increased, this point generally increased as well.

Qualitatively, the glass had more shattered fragments as the number of doping hours went up as well. This is likely because the ions form a compressive layer which resists cracks up until a point, when it shatters altogether.

Ion-Doping Effect on Young’s Modulus:
Figure 1 demonstrates the effect of doping at 375 degrees C for a certain number of hours on the Young’s Modulus of the glass sample. A sqrt(t) curve was approximately fit and theoretically work best with a constant source of diffusion because Fick’s Law relates the change in concentration using diffusion as a constant times sqrt(t).

This makes sense qualitatively, as when many K+ ions are inside the glass, and there is a balance between the solution ions and the number of ions in the glass, there is not as much room to insert more ions to further strengthen it. This fit demonstrates how there are diminishing returns on doping for a larger amount of time—at some point, the Young’s Modulus will not increase anymore.

Figure 1. Young’s Modulus of Glass Composites by Hours Doped

Ball-Drop Test Procedure:
To simulate a more everyday impact, such as that which smartphone screens endure, a ball-drop test was performed on a treated and untreated glass composite.

The treated sample was doped for 5 hours.

From varying heights, varying ball weights were dropped onto the composite to see if failure occurred. Whether or not the composite “passed” that round was measured.

Ball-Drop Test Results:
As expected, compared with the untreated sample, the treated sample was able to withstand drops of greater height and weight. These results are summarized in Table I. These results did match my 3- point flexure measurements, as the 5-hour doped glass was able to withstand a greater height and weight drop than the untreated glass. The ion-doped glass was able to survive the drop of the 6 g ball from 62.90 cm, whereas the untreated glass was unable to do so.

Table I. Ball-Drop Test Results on Treated and Untreated Samples

Key Takeaways: In this project, concepts of constant source solution concentration in diffusion and Fick’s First and Second Laws were demonstrated. In terms of fortifying glass, ion-doping remains a useful strategy. It both increases Young’s Modulus and helps the glass withstand impacts.

Constant source solution change in concentration as a function of time:

Ficks 1st and 2nd Laws: