3. Reagents
- calcium carbonate for analysis
- distilled water without CO2. Prepare the water by passing it over an ion exchange resin.
Use this water for all reactions.
- Saccharose for analysis
- Hydrochloric acid (decinormal)
- Indicator solution: 0,1 % phenolphthalein in 50% alcohol solution
4. Working method
- the apparatus id regulated to a temperature of 90°C
- weigh exactly 1 g of metakaolin in powder form into the dry clean Erlenmeyer
- use a calibrated pipette to add 250 ml of the above water
- add about 2 g of CaO exactly weighed
- prepare the CaO the following way:
o weigh 3,6 g of CaCO3 in a platinum crucible with known tare
o calcine for about 30 minutes at 1000°C
o weigh and verify that the LOI (loss on ignition) be 44%
- place the stirrer in the Erlenmeyer
- place the tap with the thermometer and the cooling column and homogenise the content of the Erlenmeyer
- place the apparatus on the heated stirrer and start heating
- verify that the temperature gets to 85°C±5
- stir and heat for 16 hours
- cool to room temperature
- add to the Erlenmeyer 250 ml saccharose solution freshly prepared (60 g saccharose dissolved in
water give exactly 250 ml solution)
- stir for 30 minutes on the magnetic stirrer. Filter about 200 ml take out 25 ml with a calibrated pipette.
- Make the same proceeding without metakaolin
4.1. Titrating the solution
- titrate with a burette using the HCl 0,1N solution using the phenolphthalein as indicator
5. Calculations
Definition:
- V1 (ml) is the volume of 0,1N HCl necessary for the 25 ml of solution obtained by the blank sample
- V2 (ml) is the volume of 0,1N HCl necessary for the 25 ml of solution obtained by the reaction of
the metakaolin
The titration reaction is:
CaO + 2HCl → CaCl2 + H2O
Ca(OH)2 + 2 HCl → CaCl2 + H2O
Check of the blank reaction
56 ⁄ 2 x V1 must be under 1000
Trial with metakaolin:
Mg of Ca(OH)2 fixed = 2 x V1 - V2 x 74 x 1000
V1 56
6. Results
The results are expressed in mg Ca(OH)2 fixed by the metakaolin
7. Precision
The results should have a variation of 10%.