Experiment I part A

Ready-Beam-Fire

Clay Labs

Objective:

To compare mechanical and thermal properties of fired and unfired beams made from art clay and clay suspensions (slip).

Review of Scientific Principles:

Clay was the first ceramic material used by humans, and it continues to be useful in modern times. Clays used for pottery are composed mainly of hydrated silica (SiO2) and alumina (Al2O3). Small amounts of other minerals (Fe2O3, MgO, etc.) are typically present.

Clay is somewhat unique in its ability to be plastically formed (shaped) when wet. This plasticity depends on the amount of water, the size and shape of the particles, ionic content, and temperature.

Clay slip is made by mixing clay with water to make a mixture that can be poured into a mold. This method, called slip casting, is used to make thin, detailed products. Plaster of Paris is commonly used to make the molds because it is inexpensive, easy to work with, and highly porous (easily absorbing water from the cast slip).

Clay objects must be allowed to dry before firing to eliminate most of the pore water. The remaining pore water is eliminated during the initial stage of firing at around 100˚C.

Firing and sintering change the properties of the object significantly. At about 350˚C the water of hydration is driven off. As the temperature increases into the sintering stage, the porosity changes from an open to closed network; and the object shrinks as porosity is eliminated. This leads to increased density and improved mechanical strength. The fired product is hard, dense, more durable, impermeable to liquids, and brittle. This activity investigates the relationships between mechanical strength, density (porosity), and thermal conductivity of unfired and fired clay objects.

Applications:

The slip casting method is used to make a variety of ceramic objects (e.g., clay-based dishes, kitchen and bath fixtures, as well as silicon nitride (Si3N4) turbocharger rotor blades). It is useful for three-dimensional complex objects with uniform wall thicknesses less than two centimeters.

Time:

This lab takes several days (6) to go from preparation to testing.

Part A (make molds): 1/2 hour first day

Part B (make beams and fire): 1/2 hour second day to make a set of beams of each type, 3 days for clay slip to air dry before firing

Firing time varies

Part C (Test beams): Testing four beams requires about 20 minutes for each test

Materials and Supplies:

Part A	Part B	Part C
Plaster of Paris	soft clay	3-point test apparatus
form (container) for plaster	clay slip	2 beams (green and fired)
block form for beam	waste bucket	candle
spoon	ruler	iron ring
waste bucket	balance	nails (4)
spoon	kiln	ring stand
knife		gas burner
All parts: safety glasses and apron		weights

General Safety Guidelines:

• Plaster of Paris, clay, and clay slip are very safe to use.

• Do not wash any of these down the sink! They can solidify and clog the sink. Use

a wash/waste bucket that can be dumped outside.

• Be aware of the high temperature of the kiln and the possibility of burns from that source.

Procedure:

Part A: Preparation

1. Mix Plaster of Paris and water in the specified container, making enough to

partially fill the form to a depth of 3-5 cm with a mixture that has the consistency

of pudding or yogurt. Smooth out the top surface of the Plaster of Paris mixture

by tapping the mixture on the table. Work quickly. You have less than five

minutes after adding the water before solidification sets in.

2. Push the block form down into the plaster to a depth of about 1 cm. Hold the

block in place for a few minutes until the plaster begins to harden. (Note the

change in temperature as the plaster hardens.)

3. After the plaster has set, remove the block form from the mold and let dry

overnight.

Mold Diagram

Part B: Making Beams

4. From the art clay, make a beam identical in size to the one that will be made in

the plaster of paris mold.

5. Measure the beam‘s mass, length, width, and thickness. Record.

6. Pour clay slip into the mold to a depth of 1 cm. Let stand until it is hard enough

to remove from the mold.

7. Remove the beam from the mold. Measure its mass, length, width, and

thickness. Record. Calculate the beam’s density.

8. Allow the beams to dry for at least three days before firing. Before the firing is

done, measure the mass and dimensions of the beam. Calculate the density of

the beam.

will explain how the firing will be done.

Part C. Testing Of Beams

10. Before testing, measure the mass and dimensions of each beam. Calculate the

10. Before testing, measure the mass and dimensions of each beam. Calculate the

density of the beam.

11. To test for the thermal properties of your beam, use a lit candle to drip wax on the beam. Attach four nails equally distributed along the side of the beam. Set the beam on a ring stand. Heat one end of a beam with a gas burner. Time how fast the heat travels down the beam by watching the objects fall when the heat reaches them. Record the times.

12. To test mechanical properties, place the beam to be tested across the supports. Attach any equipment needed for the testing apparatus.

13. Attach a container and add mass until the beam gives way.

14. Measure the added weight . Calculate the force that broke the beam.

15. Clean up as directed by instructor.

Data and Analysis:

Measurement	Green clay beam	Fired clay beam	Green slip beam	Fired slip beam
date formed
date fired
mass 1
mass 2
mass 3
dimension 1
dimension 2
dimension 3
volume
density 1
density 2
density 3
times
nail 1
nail 2
nail 3
nail 4
added mass
force applied

Questions:

1. What is accomplished by firing that is not accomplished by simple drying?

2. What might happen if the beam were fired before it dried?

3. How is strength different from hardness?

4. Summarize the differences in density, mechanical and thermal properties between

the fired and unfired beams as observed in this lab.

5. Palette, the art teacher, fires an assortment of ceramics. What might happen if the

firing temperature was too low? What if it was too high ?