Slag glass

Some workers using small angle X-ray scattering and light and electron microscopy have found evidence of phase separation within the glass (S90.R34) but others have concluded that this does not occur (U16) slag glasses may vary in this respect. 

Tanaka et at. (T45) partially masked the surfaces of disks of slag glass with gold coatings the disks were then embedded in cement pastes for various periods, after which they were removed and examined by SEM. This showed that two layers of in situ product were formed. The innermost one had Si/Ca 0.64, Al/Ca 0.32 and Mg/Ca 0.34 the outer one had Si/Ca 0.61, Al/Ca 0.24, Mg/Ca 0.20. The product formed immediately outside the original boundary of the slag had Si/Ca 0.48, Al/Ca 0.09, Mg/Ca 0.17. The two layers of in situ product could have been mixtures in differing proportions of C-S-H. a hydrotalcite-type phase and possibly AFm phase. 

Clinker phases C-S-H Ca(OH)2 AFm AFt Slag HP FeHP Mg HP CaCOj Slag glass Slag res. Other Pores... 

Figure 11. The thermal conductivity of various slags, glasses and minerals O, MgO Al2O2 3Sl2O2 2SiO2 X, 2MgO SiO2 ...

Granulated blastfurnace slag can hydrate without activation too [2]. The calcinm hydroxide necessary to activate the reaction of slag glass is probably formed as a result of calcium sulphide hydrolysis ... 

Fig. 7.5 Compressive strength of mortars from slag glasses of composition given by the dashed area (+ 5 % MgO), activated with Ca(OH)j (according to [43])...

Another approach to the positive effect of the begiiming of crystallization of slag glass on the hydranlic activity can assmne the favorable changes of its chemical composition, which improve the reactivity with water. 

The alttminttm ion has a great irrrpact on the properties of slag glass. Because of its amphoteric properties it can play a role of glass-forming element, when it occtrrs in tetrahedral coordination, or as a modifier—in octahedral coordination respectively. Altrrrtirtitrm share in one of these coordination depends on the alkaline... 

The examination of chemical composition of slag glass surface at the early age of hydration has shown that it is modified immediately after the contact with the Uquid phase [6]. As the result of incongment dissolution of slag grains on their surface the l er of C-S-H is formed, with, however, lower C/S ratio than in the Portland cement paste. When the hydration of slag is activated by alkalis, this phase contains the Na+ orK+ ions. 

However, Fierens [9] has shown, that the hydroxylation of the slag glass surface layer, as a result of water molecules chemisorption, which is enhanced by the surface electron defects (trapped electrons), can be considered as a topochemical process. The topochemical processes became important also at later hydration stage, when the pozzolanic reaction of slag glass network, impoverishes of the majority of alkaline elements, with calcium ions is occtrrring, and calcium ions are chemisorbed on the active sites of solid phase. 

Fax (617) 630-5919 Email elisabeth.james.b bayer.com Website www.hcstarck.com SPINEL. MgO-AljOj or MgAl204. Mol. wt. 142.26 sp. gr. 3.6-3.9 m.p. 2135°C. A mineral found in small deposits. It is formed by solid-state reaction between MgO and AljOj and is an excellent refractory showing high resistance to attack by slags, glass, etc. 

Fredericci, C., E. D. Zanotto and E. C. Ziemath (2000). Crystallization mechanism and properties of a blast furnace slag glass . Journal of Non-Crystalline Solids 273 64-75. 

---