High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

The overall goal of this materials processing method is to create and preserve nanostructured ceramics at typical centering temperatures by carbon templating hybrid materials in situ. This method can help answer key questions in the materials engineering, and processing fields, such as how to control ceramic nanostructures at conditions far from equilibrium. The main advantage of this technique is that it generates ceramic materials with 80 times more surface area than traditional techniques.

Though this method can provide insight into Yttria stabilized Zirconia nanostructures, it can also be applied to essentially any mixed metal oxide material. First, add a 25 millimeter magnetic stir bar and 113 milliliters of deionized water to a 500 milliliter beaker. Stir the deionized water at the highest rate that does not form a vortex.

Slowly add 13.05 grams of anhydrous Zirconium Chloride to the deionized water in small increments. After all of the Zirconium Chloride has dissolved, add 53.29 grams of glucose to the solution. After all of the glucose has dissolved, add 3.73 grams of Yttrium nitrate hexahydrate to the solution.

Increase the rate of stirring to approximately 700 RPM and wait for all of the solid to dissolve in solution. Following this, add 42 milliliters of propylene oxide to the solution. Once the solution is sufficiently mixed, decrease the stirring to approximately 150 RPM.

Continue stirring until the magnetic stir bar has stopped moving due to gel formation. Then tightly cover the beaker containing the gel with parafilm. After allowing the gel to age for 24 hours, remove the parafilm from the beaker and decant the liquid on top of the gel.

Next, add 300 milliliters of absolute ethanol to the beaker containing the gel. Tightly cover the beaker with parafilm and leave the covered beaker at room temperature for 24 hours. After repeating the previous step twice, remove the gel from the beaker and place it in a two liter porcelain evaporating dish using a laboratory spatula.

Break the gel into pieces with the spatula and spread the pieces over the surface of the evaporating dish. After allowing the gel pieces to dry under ambient conditions, grind the resulting xerogel into a fine powder with an agate mortar and pestle. Now, place one gram of xerogel powder into a 13 millimeter cylindrical pellet press die.

Using a hydraulic press, apply 22 kilo Newtons of force for 90 seconds to press the xerogel gel into a pellet. Slowly release the force applied by the press. Then, carefully remove the pellet out of the pellet die.

Place the xerogel pellet onto a YSZ plate and load the plate into the center of a tube furnace. Blow Argon at a rate of one third the volume of the working tube per minute for at least 15 minutes, venting the gas outlet to a fume hood. While continuously flowing Argon at a constant rate, program the tube furnace temperature controller to the appropriate heating schedule.

Start the program and double check that the tube furnace is heating up following the schedule. After the heating program has completed, remove the pellet from the tube furnace. Using a utility knife, cut a 50 milligram piece out of the centered xerogel pellet.

Then grind the xerogel into a fine powder with an agate mortar and pestle. Place approximately 50 milligrams of the fine powder into an Alumina sample cup for thermal gravimetric analysis. Using a thermo gravimetric analyzer, heat the sample at a rate of 10 degrees Celsius per minute from ambient temperature to 1200 degrees Celsius while flowing air over the sample at a rate of 100 milliliters per minute.

Calculate the percent change in weight that occurs between 350 and 700 degrees Celsius which corresponds to the total carbon content in the sample. At this point, place the centered xerogel pellet in an Alumina crucible. Place the crucible into a box furnace at 700 degrees Celsius for two hours.

Carefully remove the hot crucible from the box furnace with stainless steel crucible tongs. After cooling to room temperature for one hour, remove the porous white YSZ scaffold from the crucible. YSZ scaffold specific surface area as a function of carbon template concentration is shown here.

The carbon template concentration and specific surface area systematically increase with increasing glucose concentration and increasing glucose metals molar ratio respectively. The carbon template concentration as quantified by thermo gravimetric analysis was four weight percent and 64 weight percent of total solids for the glucose metals molar ratios of zero to one and 4.5 to one respectively. SEM images show that the particles of YSZ xerogel with glucose additive are several times smaller than those without glucose additive.

The formation of smaller particles by adding glucose to the gel in consistent with their high carbon content and surface area. XRD patterns of the strongest YSZ peak for YSZ scaffold as a function of glucose metals molar ratio is shown here. The crystallite size decreased as the molar ratio increased and the crystallite size progression is consistent with the observed increase in surface area with increasing molar ratio.

The YSZ scaffold pore size distribution as a function of glucose metals molar ratio shows both the number and size of pores increase with an increase in molar ratio. While attempting this procedure, it's important to remember to maintain a leak tight flow of inert gas through the tube furnace. Following this procedure, other ceramic structures can be created such as here our structures prepared by infiltration of hybrids into traditional progress scaffolds.

After watching this video, you should have a good understanding of how to create, preserve, and control ceramic nano morphology at high temperatures.