Scope
This method is used for the determination of total ash of investment casting waxes, wax blends, and similar
material using microwave ash unit.
Definition
Total ash is the percentage of residue left after complete combustion of wax sample.
Equipment and Materials
- a. Crucibles: High form quartz crucible (Figure 1) or Coors High Form Porcelain Crucible 100-120 ml capacity
- b. Analytical Balance - Any suitable balance having a sensitivity of O.1 mg
- c. Crucible Tongs
- d. Desiccator with suitable desiccant
- e. Microwave furnace with ASTM, USP, ISO methods pre-loaded built in and built in exhaust system
Figure 1 - High Form Quartz Crucible
Safety
This test requires extreme care due to the use of open flame burners and a high temperature muffle
furnace. Proper PPE is required (heat resistant gloves, eye protection and protective clothing when
handling hot crucibles, and molten wax). Use proper ventilation. Have a properly rated fire extinguisher
nearby.
Procedure
Constant Weight of Crucible
- Heat the crucible in Microwave Ash Furnace, for 20 minutes when the unit reached 1800°F
- Using crucible tongs, remove the crucible from the furnace in a cradling manner and hold the crucible for 1 minute. Transfer the crucible to desiccator and let it cool to room temperature.
- Weigh the crucible on analytical balance to the nearest 0.1mg.
- Repeat steps 1-3 above until two consecutive weighing are within 0.1 mg. Record the constant weight. (CW1) Heating the crucible once at 1800°F, cooling and weighing does not satisfy the requirements in determining the constant weight of crucible as outlined above.
Procedure(Continued)
Analysis
- 5. Place 20.0 grams of a thoroughly representative wax sample in tared crucible. Record the weight of the sample to 0.1 mg using analytical balance. (WS) (Figure 2)
- 6. Place the crucible with wax sample in Microwave Ash Furnace that has been preset to 1800°F. (Figure 3)
- 7. After the furnace reached 1800°F, continue to leave the crucible inside the furnace for 20-30 minutes.
- 8. After ignition is complete, in a cradling manner using crucible tongs, remove the crucible from the furnace and transfer to the desiccator. Allow it to cool at room temperature. Record the final weight to the nearest 0.1 mg. (CW2)
Figure 2 - 20.0 Gram Wax Sample in Tared Crucible
Figure 3 - Crucible with wax sample in Microwave Ash Furnace
Calculation
Percent Total Ash = (CW2-CW1) / WS x 100%
WS = Weight of Sample
CW1 = Tare Weight of Crucible
CW2 = Weight of Crucible + Ash
CW1 = Tare Weight of Crucible
CW2 = Weight of Crucible + Ash
