Fabrication of Alumina/ Alkali Zinc Phosphate (AZP) Glass Laminates

1. Fabrication of Alumina/ Alkali Zinc Phosphate (AZP) Glass Laminates MSE REU Summer 2002 Presented by: Yeon Kim Advisor: Prof. Trice

2. Al2O3 AZP Al2O3 AZP Al2O3 My Goals for Summer • Develop a model material • Ceramic • Has both elastic and viscous properties • Elastic substance – Alumina • Viscous substance – AZP glass • Why these particular materials? • Alumina is relatively inexpensive and easy to buy in sheet form. • AZP glass is also relatively easy to process and has a low Tg (Laminate to be Made)

3. Possible Applications • May be possible to design an all ceramic system capable of absorbing a lot of energy – I.e. ballistic applications. • Why not just use metals? Ceramics are much less dense. • Most high temperature ceramic materials have a glassy phase – developing this model material would make it easier to observe and study behavior between elastic/ viscous materials.

4. Glass Properties: Highly sensitive to temperature No melting point but a glass transition temperature AZP Glass has a much lower Tg than the melting point of the alumina Experimental Approach Liquid Supercooled liquid Specific Volume Viscous region Solid Elastic Region Tg Temperature

5. Initial Approach • Find a good working temperature of the glass: • Cut pre-made sheets of Alumina (elastic material). • AZP glass powder is dispersed in isopropanol (using 1 gram of glass powder for every 10 mL isopropanol). • Spray AZP/isopropanol mixture onto Alumina using a hobby gun. • Heat in a vacuum furnace at varying temperatures and dwell times. Heat Vacuum Goal: Melt glass powder and remove air bubbles.

6. Initial Findings • Many bubbles in the glass layer. • Increasing processing T decreases the amount of pores. • Too much heat or long durations in the furnace crystallize the glass.

7. Revised Approach Heat (450oC) Heat (590oC) Vacuum • Melting the glass to just below its Tg makes the glass viscous enough to allow air to flow better than it would in the glass’s powder form. Temp. 590oC 450oC Time (hr)

8. Thinner layer produced less air bubbles. 15 Sprays 30 Sprays

9. Successful Method • Negligible pores: • Use a 1:20 ratio of AZP glass powder to isopropanol • Pre-melt at 450oC • Hold in vacuum furnace for 17 hours • Melt glass (590oC @ 1 hour)

10. Making a Two Layer Laminate AZP AZP Al2O3 Al2O3 Al2O3 AZP AZP Al2O3 Weight Setter Al2O3 AZP AZP Al2O3 Setter

11. I II Heat (450oC) Heat (590oC) Vacuum Vacuum Weight Setter Al2O3 AZP AZP Al2O3

12. Problem • Gaps found in the glass layer Air Gap Glass Layer

13. Processing Variables • Melt glass on one piece of alumina and layer, or melt glass on both pieces of alumina • Vary thickness of glass layer • Vary rate of temperature increase Al2O3 Al2O3 AZP AZP AZP Al2O3 Al2O3

14. Results • Laminate made with only one side melted with glass tends to fall apart more readily than laminates made with both sides • Thicker layer of glass produce less gaps than thinner layer • Increasing T at a slower rate produced laminates that fell apart more readily

15. Conclusions/Future Work • Laminates don’t seem to have enough glass • Readily falls apart • Glass layer has large gaps in between • Coefficient of Thermal Expansion • Alumina: ~ 9e-6 1/oC • AZP Glass: ~ 20e-6 1/oC • Sandblast the Alumina • Choose a different substrate