New calcium aluminate hydrates

Abstract

Several modifications of the ‘hexagonal’ tetracalcium and dicalcium aluminate hydrates have been obtained, some of which have not been described previously. Only a newly established 4CaO,Al2O3, 19H2O hydrate, and an α‐form and a hitherto undescribed β‐form of a 2CaO,Al2O3,8H2O hydrate have been found to occur in the aqueous system at 25°. Other modifications are produced on drying under various conditions. The 4CaO,Al2O3,19H2O hydrate, characterized in the X‐ray patterns by a longest basal spacing of 10·6Å, is dehydrated relatively easily to give a mixture of α‐and β‐forms of a 13H2O hydrate, characterized by longest basal spacings of 8·2Å and 7·9Å, respectively. There is little difference in stability between the two forms and it appears to be a matter of chance as to the relative amount of each which may be formed. Two other tetracalcium aluminate hydrates have been obtained with water contents of 11H2O and 7H2O, both of which give longest basal spacings of 7·4Å. The α‐ and β‐forms of 2CaO,Al2O3,8H2 are characterized by longest basal spacings of 10·7Å and 10·4Å respectively. The α‐form appears to be more stable than the β‐form. Three other states of hydration of the dicalcium compound exist, having water contents of 7·5H2O, 5H2O and 4H2O, and giving longest basal spacings of 10·6Å, 8·7Å, and 7·4Å, respectively. With various preparations of the compound 3CaO,Al2O3,CaSO4,aq., basal spacings of 10·3Å, 9·6Å, 8·9Å, 8·2Å, and 8·0Å have been observed, but these modifications await further study.

Hydration of calcium aluminates at 60°C – Development paths of C2AHx in dependence on the content of free water

“…During hydration of the CAC‐Ceramic‐Composite material after 6 hours the C 2 AH 7.5 content suddenly rises on the expense of C 2 AH 8.2 and C 2 AH 8 . It is reported that C 2 AH 7.5 is formed by drying C 2 AH 8 at 34% relative humidity . At the same time the CA 2 hydration stops (see Figure ).…”

“…(microcrystalline AH 3 ) . In this temperature range the H 2 O content of the C 2 AH 8 phase varies between 7.5 and 8.2 moles during the hydration of calcium aluminates . Scheller and Kuzel determined space groups and lattice parameters for the 8‐, 7.5‐, and 5‐hydrates.…”

Estudio por difracción de rayos X de la hidratación de mezclas de CaAl₂O₄ - Humo de silice

“…El aluminato de calcio hidratado formado depende de la temperatura y de la composición de la solución ya que la cantidad de agua interlaminar depende de la presión de vapor de agua y de la humedad de los hidratos que son fácilmente atacados por el CO 2 de la atmósfera (4)(5)(6) Simultáneamente tiene lugar una disminución de la intensidad del CaAl 2 O 4 , que indica otro hecho importante expuesto en la literatura, que podría estar asociado, a la ruptura de la capa hidroxílica formada principalmente por geles de AH x y pequeños cristalitos de hidratos que han crecido durante este intervalo de tiempo en la superficie de las partículas del CaAl 2 O 4 (25). La ruptura de esta capa, permite el acceso de agua al interior de los granos anhidros presentes en la pasta, para formar una nueva capa de productos amorfos, que se vuelve a romper a ~ 29 h, donde se observa de nuevo un aumento de la intensidad de la fase Ca 2 (27).…”

X-ray studies of lime-bentonite reaction products

“…Taylor (56) states that before 1957, the compound now described as C^AH^g was considered to be C4AH13. Roberts (51) found that dehydration of C^AH^g to give C^AH-^ occurs very easily, as soon as the solid has been separated from its mother liquor.…”

“…Roberts (51), Buttler, Classer and Taylor (10) and Aruja (4) have contributed in recent years to clarification of aluminate phases by x-ray and electron diffraction studies of single crystals.…”