- Author
-
Carlson, E. T.
- Title
- Some Properties of the Calcium Aluminoferrite Hydrates.
- Coporate
- National Bureau of Standards, Washington, DC
- Report
-
NBS BSS 006,
June 1, 1966,
13 p.
- Keywords
-
calcium
|
hydration
|
differential thermal analysis
|
x ray diffraction
|
thermal analysis
- Identifiers
- calcium aluminoferrite hydrates; calcium sulfate reaction; DTA of calcium aluminoferrite hydrates
- Abstract
- Calcium aluminoferrite hydrates in two series, 4CaO-(Al2O3,Fe2O3)- n H2O (hexagonal plates) and 3CaO-(Al2Oc,Fe2O3)-6H2O (isometric), were prepared from the anhydrous aluminoferrites by hydration in the presence of Ca(OH)2. The hexagonal phase was stable below 15 deg C, the isometric above 35 deg C, in contact with solution. To end member, 2 CaO-Fe2O3, did not produce an isometric hydrate, however, x-ray diffraction patterns of the hexagonal series in the 19 H2O stage of hydration were indistinguishable from patterns of 4 CaO-Al2O3-19 H2O. After drying to the 13-hydrate stage, slight differences in the patterns were observed. The isometric series shows a definite shift in x-ray pattern with change in Fe2O3/Al2O3 ratio, the unit-cell edge increasing from 12.573 for 3 CaO-Al2O3-6 H2O to 12.716 for the member having Fe2O3/Al2O close to 5. DTA traces show endotherms near 100 and 200 deg C corresponding to dehydration stages of the hexagonal series and one near 300 deg C representing the first dehydration stage of the isometric phase. The hexagonal hydrates are converted to the isometric during the course of the DTA run. The peak attributed to the isometric phase shifts from 323 to 290 deg C going from the pure aluminate to the member richest in Fe2O3. All the aluminoferrite hydrates, both hexagonal and isometric, reacted with CaSO4 solution to give products of the monosulfate and trisulfate (ettringite) types, the latter predominating at later stages. The rate of reaction decreased with increasing Fe2O3 content.