**6. Mechanochemistry/solid-state method**

Grinding is an important operation that is used industrially for particle size reduction and production of large surface areas or liberating valuable things from any mineral. It comprises of different steps including material transport to grinding zone, grinding action, initiation and propagation of cracks, breakage of particle, or initiation of solid-state reactions within. Size reduction and intergranular breakage are significantly achieved by subjecting particles to mechanical pressure for a prolonged period. Generally, the breakage and fracturing process during grinding involves

rupturing of chemical bonds in order to create several reactive sites. The reactive sites when created are highly prone to undergo change and form some new chemical bonds with some other additive if present in the same reaction mixture [28]. This concept forms the basis of mechanochemical grinding reactions in dry state.

Mechanochemistry involves transformations supported by mechanical force in the form of milling or grinding [29–31]. The reactions proceed with grinding or milling are cleaner and efficient in terms of solvent, chemicals, materials, etc. [29]. It is known that the *mechanical activation* of aluminosilicate material, e.g. fly ash, results in enhanced reactivity. This is due to the combined effects of particle size reduction and physiochemical changes induced during high-energy milling of fly ash particles [32]. The *mechanochemical activation* on the other hand involves breakage of existing bonds and formation of new chemical bonds during high-energy milling process in the presence of any chemical agent in dry environment along with particle size reduction and increased amorphization. Solid-state chemical transformation occurs during mechanochemical grinding process of raw materials used for the advanced geopolymerization process.

The basic study for advanced geopolymerization was conducted by [27] in which grinding of fly ash along with NaOH in a ball mill exposed to mechanochemical forces that trench the internal bonding of fly ash and NaOH due to friction and impact with tumbling balls for prolonged durations. The amorphous reactive Si/ Al phase disperses uniformly throughout the grinding process and reacts with Na<sup>+</sup> ions to form three intermediate phases which are termed as *precursor phases* for advanced geopolymerization reaction. The solid powder obtained after mechanochemical grinding of fly ash and NaOH is therefore termed as *advanced geopolymeric precursors* [8, 9, 33, 34].

**Figure 4** is the pictorial presentation of the advanced geopolymerization technology which clearly shows that by just addition of only water to the advanced geopolymeric precursor phases, gelation occurred, and this gel essentially contain N▬A▬S▬H phase [sodium aluminium silicate hydrate-geopolymeric phase].

#### **Figure 4.**

*Mechanochemical grinding of raw materials and development of advanced geopolymeric precursor phases due to solid-state chemical transformations.*

**17**

**Figure 5.**

*mechanism [33].*

*Advanced Geopolymerization Technology DOI: http://dx.doi.org/10.5772/intechopen.87250*

understood under the following points:

from siloxane ▬Si▬O▬Si▬.

Later on, established by a number of experimental analyses, it can be said that advanced geopolymer possesses improved properties in terms of strength of the

**7. Plausible solid-state mechanism for advanced geopolymerization**

The solid-state mechanism involved in advanced geopolymerization reaction is different from that of conventional geopolymerization in the initial steps [33]. So the plausible chemical reaction mechanism for advanced geopolymerization can be

• The 8 hours of mechanochemical activation of glassy silica/alumina in fly ash led to the dissociation of bonds present in glassy Si/Al phase; hence unlike conventional geopolymerization, the first step in the solid-state mechanism is *dissociation*. This step led to the formation of unstable silanone species ▬Si═O

• This unstable Si═O is active in nature and rapidly transform into silanol even in the presence of minimum amount of water. So the next step is the associa-

• In the presence of water, silanols form ▬Si▬O▬Al▬ linkages, and geopolymeric gel is then formed which on drying produces advanced geopolymeric

• First dissociation, followed by association reaction for the formation of advanced geopolymer, confirms its *unimolecular nucleophilic substitution*

tion of intermediate with the water molecules to form silanol.

**8. Advantages of advanced process over conventional process**

There are numerous advantages of advanced geopolymerization over conventional process. As we know, alkaline solution [pH around 10–14] is hazardous in nature which can cause skin hazards when accidently comes in contact with people

*Illustration of formation of silanone and silanols for advanced geopolymerization via SN1 solid-state chemistry* 

(SN1) mechanism as also presented in **Figure 5**.

material with considerable enhanced properties.

material and excellent corrosion protection [8, 9, 33–35].

*Geopolymers and Other Geosynthetics*

*meric precursors* [8, 9, 33, 34].

rupturing of chemical bonds in order to create several reactive sites. The reactive sites when created are highly prone to undergo change and form some new chemical bonds with some other additive if present in the same reaction mixture [28]. This concept

Mechanochemistry involves transformations supported by mechanical force in the form of milling or grinding [29–31]. The reactions proceed with grinding or milling are cleaner and efficient in terms of solvent, chemicals, materials, etc. [29]. It is known that the *mechanical activation* of aluminosilicate material, e.g. fly ash, results in enhanced reactivity. This is due to the combined effects of particle size reduction and physiochemical changes induced during high-energy milling of fly ash particles [32]. The *mechanochemical activation* on the other hand involves breakage of existing bonds and formation of new chemical bonds during high-energy milling process in the presence of any chemical agent in dry environment along with particle size reduction and increased amorphization. Solid-state chemical transformation occurs during mechanochemical grinding process of raw

The basic study for advanced geopolymerization was conducted by [27] in which

grinding of fly ash along with NaOH in a ball mill exposed to mechanochemical forces that trench the internal bonding of fly ash and NaOH due to friction and impact with tumbling balls for prolonged durations. The amorphous reactive Si/ Al phase disperses uniformly throughout the grinding process and reacts with Na<sup>+</sup> ions to form three intermediate phases which are termed as *precursor phases* for advanced geopolymerization reaction. The solid powder obtained after mechanochemical grinding of fly ash and NaOH is therefore termed as *advanced geopoly-*

**Figure 4** is the pictorial presentation of the advanced geopolymerization technology which clearly shows that by just addition of only water to the advanced geopolymeric precursor phases, gelation occurred, and this gel essentially contain N▬A▬S▬H phase [sodium aluminium silicate hydrate-geopolymeric phase].

forms the basis of mechanochemical grinding reactions in dry state.

materials used for the advanced geopolymerization process.

**16**

**Figure 4.**

*to solid-state chemical transformations.*

*Mechanochemical grinding of raw materials and development of advanced geopolymeric precursor phases due* 

Later on, established by a number of experimental analyses, it can be said that advanced geopolymer possesses improved properties in terms of strength of the material and excellent corrosion protection [8, 9, 33–35].
