Influence of Aluminium and Boron Orthophosphate on the Setting and the Resulting Structure of Alkali Silicate Binders for Refractory Application

Abstract

Liquid alkali silicates (waterglasses) are used as chemical binders for a wide range of refractory applications, the setting of which can be initiated by the addition of phosphate hardeners. The duration of the setting process is of special interest for an economic lining with short aggregate downtimes. Therefore, in the present work, the influences of two different types of phosphate (aluminium orthophosphate and boron orthophosphate) on the hardening mechanisms of waterglasses are investigated. Time-dependent measurements by dynamic mechanical analysis (DMA) are carried out to observe the setting process. Structural information of the hardened amorphous samples is obtained by means of nuclear magnetic resonance (NMR) spectroscopy. It is shown that the use of different phosphates leads to differences in the setting rate, caused by different modes of network formation. The resultant silicate networks incorporate the aluminium or boron species but differ in the connectivity of those units. In addition, the distribution following the well-known Qn notation of the silicate units is directly influenced by the phosphate type.

Structure–Property Functions of Inorganic Chemical Binders for Refractories

“…Dynamic Mechanical Analysis investigations of a sol-gel-based pure binder system consisting of a sodium water glass hardened by either aluminum or boron orthophosphate were carried out with the aim to determine the influence of the attendant cation thus leading to a better understanding of the setting process of the alkali silicate systems [ 19 ]. The results of the DMA as shown in Figure 6 exhibit the overall setting of the water glass to be much faster when using boron orthophosphate as hardening agent instead of aluminum orthophosphate.…”