This review examines the detailed chemical insights that have been generated through 150 years of work worldwide on magnesium-based inorganic cements, with a focus on both scientific and patent literature. Magnesium carbonate, phosphate, silicate-hydrate, and oxysalt (both chloride and sulfate) cements are all assessed. Many such cements are ideally suited to specialist applications in precast construction, road repair, and other fields including nuclear waste immobilization. The majority of MgO-based cements are more costly to produce than Portland cement because of the relatively high cost of reactive sources of MgO and do not have a sufficiently high internal pH to passivate mild steel reinforcing bars. This precludes MgO-based cements from providing a large-scale replacement for Portland cement in the production of steel-reinforced concretes for civil engineering applications, despite the potential for CO2 emissions reductions offered by some such systems. Nonetheless, in uses that do not require steel reinforcement, and in locations where the MgO can be sourced at a competitive price, a detailed understanding of these systems enables their specification, design, and selection as advanced engineering materials with a strongly defined chemical basis.

Magnesia-Based Cements: A Journey of 150 Years, and Cements for the Future?

Infrared Spectroscopy of Minerals and Related Compounds

SO42- ions direct the one-dimensional growth of 5Mg(OH)2 · MgSO4 · 2H2O

A new magnesium oxysulfate hydrate phase, 5Mg(OH)2·MgSO4·7H2O was synthesized and structurally characterized. The new phase crystallizes in the form of microsized needles and its crystal structure was solved using X-ray powder diffraction. The crystal packing is made of infinite triple MgO6 chains, intercalated with sulfate groups, water molecules, and hydroxide anions. Using vibrational spectroscopy [infrared (IR) and Raman] and Rietveld refinement, the arrangement of water molecules and hydroxide anions were observed to be statistically distributed and dynamically disordered. The high-temperature behavior and decomposition were studied by thermal analyses and in situ X-ray powder diffraction. The high-temperature measurements reveal the presence of five decomposition stages from the new phase to the production of MgO. After the reactions with atmospheric carbon dioxide were analyzed using micro-Raman spectroscopy, two new carbonate phases were detected on the surface of the material.

Structural Characterization of a New Magnesium Oxysulfate Hydrate Cement Phase and Its Surface Reactions with Atmospheric Carbon Dioxide

The crystal chemical analysis of the class of borates has been carried out using the extended Dornberger-Schiff order–disorder (OD) theory based on the recognition of building blocks of various dimensions. All of the borate structures are built from several fundamental building blocks typical for every group of hexa-, penta-, tetra-, tri-, diborates; polyborates contain combinations of these different units. Zero dimensional periodic blocks and the fundamental building blocks in the Christ, Clark, and Strunz systems are in fact the same. Every block possesses its own topology and local symmetry. Consecutive condensation of blocks to rods, layers and frameworks is governed by symmetry laws, that is together with the local symmetry of units the subject of OD-analysis. For all borate groups considered, symmetry groupoids of various ranks have been proposed for different condensation units. Structural-generic branches for borates have been distinguished, hypothetical structural variants predicted, and the pos...

Zhu Lixia

Papers

Crystal growth and crystal structure of magnesium oxysulfate 2MgSO4·Mg(OH)2·2H2O

Crystal structure and characterization of Rb2Ca[B4O5(OH)4]2·8H2O

Thermochemistry of hydrated rubidium tetraborate

Crystal structure and thermal behavior of Rb2Co[B6O7(OH)6]2·4H2O

Thermochemistry of hydrated lithium monoborates