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.
Highlights
Liquid alkali silicates, known as waterglasses, have been widely used in many industrial applications, for example, in the production of detergents, paints, and adhesives
In order to characterize the interactions between the liquid alkali silicates and phosphate hardeners during the setting process, waterglass–phosphate mixes were investigated by means of dynamic mechanical analysis (DMA)
Structural information was obtained by nuclear magnetic resonance spectroscopy (NMR) experiments using thoroughly hardened samples
Summary
Known as waterglasses, have been widely used in many industrial applications, for example, in the production of detergents, paints, and adhesives. A large field of application has been found in their use as chemical binders for different groups of materials, such as types of cement, grouts, and refractories [1,2]. In the case of waterglass binders, the duration of the setting process has become of particular interest, due to their use in cold-setting applications. In the present work, an extensive investigation was carried out on the setting process of chemically hardened waterglasses. The research focuses both on the influences of different factors (i.e., the chemistry of the chemical hardener, the hardener portion, and temperature) on the mechanisms of the setting process and the resulting network structures, which lead to the binding effect
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