Cement hydration inhibition and crosslinking in the guar-borate system
Barron, Andrew R.
Doctor of Philosophy
The hydration of cement and its individual mineral phases in the presence of different inhibitors has been investigated. The behavior of an exemplary oligo-phosphate, nitriltris(methylene)phosphonic acid (H6ntmp), is compared to the behavior of more traditional retarders. The reaction between H6ntmp and calcium hydroxide, tricalcium silicate, tricalcium aluminate, and cement have revealed that the calcium phosphonate complex, [Ca(H 4ntmp)]infinity, plays a role in inhibition with phosphonates. NMR and XPS data suggest that the presence of uncoordinated P-O bonds in calcium phosphonates lends phosphonates the unique ability to simultaneously complex calcium ions while adhering to hydrating aluminate surfaces, promoting heterogeneous nucleation of calcium phosphonates at the surface of aluminate minerals and blocking normal hydration reactions. Reactions with tartaric acid also forms a calcium complex on top of the aluminate phases. In contrast, sucrose, appears to act directly on the silicate phases actually accelerates the reactions of the aluminate phases. The reactions of borate ions with diols and monosaccharides have been used to model cross-linking in the guar-borate system. Specifically, the reactions of borate with alcohols were characterized by 11B NMR to determine which reactions are most favorable. It was found that the acidity of the hydroxyl groups plays an important role in the efficiency of cross-linking, and has a greater effect on the energy of the resulting borate-diol complexes than the conformation (i.e., cis versus trans) in reactions of borate with cyclohexanediols and monosaccharides. The role of Group 1 metal salts in the borate-diol reactions was also investigated by 11B NMR and by the synthesis of model compounds. It was found that the metal cations play an important role in stabilizing the borate-diol complexes in the solid state. In solution, it was found that cross-linking is enhanced by the presence of strongly coordinating cations, as opposed to more purely ionic cations, and cross-linking is decreased in the presence of non-coordinating ammonium cations.
Inorganic chemistry; Engineering; Materials science