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

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 T g Al 2 O 3 AZP (Laminate to be Made)

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.

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

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. Vacuum Goal: Melt glass powder and remove air bubbles. Heat

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.

Revised Approach Heat (590 o C) Vacuum Heat (450 o C) Melting the glass to just below its T g makes the glass viscous enough to allow air to flow better than it would in the glass’s powder form. Time (hr) Temp. 450 o C 590 o C

15 Sprays 30 Sprays Thinner layer produced less air bubbles.

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

Making a Two Layer Laminate Al 2 O 3 AZP Al 2 O 3 AZP Al 2 O 3 AZP Al 2 O 3 AZP Al 2 O 3 AZP Weight Setter

Al 2 O 3 AZP Al 2 O 3 AZP Weight Setter Vacuum Heat (450 o C) Vacuum I II Heat (590 o C)

Problem Gaps found in the glass layer Air Gap Glass Layer

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 Al 2 O 3 AZP Al 2 O 3 AZP Al 2 O 3 AZP

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

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/ o C AZP Glass: ~ 20e-6 1/ o C Sandblast the Alumina Choose a different substrate