Alkaline activation

Activators. Activators are often added to removers to make them more efficient. Acids such as phenol [108-95-2] phosphoric acid [7664-38-2] acetic acid [64-19-7] formic acid [64-18-6]., and citric acid [5949-29-1] are used to increase the cutting abiHty on epoxide-type paints and other modem finishes. Strongly alkaline activators are effective on enamel andlatex paints. Other activators include ammonia [7664-41-7] monoethyl amine [75-04-7], and /V-phenyIdiethan ol amines. Acid and base activators shorten the shelf life of some removers. 

A ceUulose ether thickener such as hydroxypropyl methylceUulose can be added to thicken a methylene chloride remover. Removers that are acid or alkaline activated requite thickeners that wid not be hydroly2ed by the acid or the base. 

QuaHty control in the production of organic solvent finish removers may be done by gas—Hquid chromatography, which allows the manufacturer to determine the actual ratio of volatile solvent present in the finished product. If the product does not meet specifications, solvents can be added to bring the product to an acceptable composition. A less expensive approach is to use a hydrometer to determine the specific gravity of the product. The specific gravity indicates if the proper blend has been reached. Nonaqueous acid—base titration may be used to determine the amount of acid or alkaline activator present in a remover. 

The first instant color photography system, introduced by the Polaroid Corp. in 1963 as Polacolor, used the transfer of subtractive dyes to a receiver sheet to produce a positive image. The incorporated dye-developers, containing a hydroquinone moiety, are soluble in the alkaline activator solution, except where silver development occurs, when they are immobilized as the quinone form. 

Materials are now available which allow rapid access to positive colour reflection prints. This is achieved by incorporating, at the time of manufacture, into special picture-making units, all the chemicals required for the subsequent processing of the units. Thus, a viscous alkaline activator solution is contained in a pod and layers which cause the lowering of pH, after development of the unit has taken place, are included (B-77MI11403, B-79MI11400). 

Only one of the three FDPases was found to be sensitive to inhibition by AMP this was the neutral FDPase present in ungerminated castor beans. During germination a second activity appeared which was also active with RuDP. The alkaline activity was present in mature photo-synthesizing leaves, and its properties resembled those of the enzyme isolated from spinach leaves by Racker and Schroeder (55). All of the enzymes from the castor bean plant were found to require either Mg2+ or Mn2+. 

The predominance in central Italy of ultrapotassic rocks, possibly associated with carbonatites, and the absence of calc-alkaline activity. A similar association occurs in the Toro-Ankole igneous province (western branch of the East Africa Rift Bailey and Collier 2000), classically believed to have developed above mantle plumes. 

Various techniques, including Si MAS NMR, have been used to follow the reactive evolution of the alkaline activated slag cements. ... 

However, Kondo [3 ] is of the opinion that the hydrolysis of the glass in water occurs and the calcium ions are released initially to the liquid phase. Simultaneously on the surface of slag grains an acid, colloidal shell of silica-alumina gel is formed. This shell has low permeability and hence the further slag reaction with water is hindered. In the presence of Ca(OH)2, added as alkaline activator, the siUcon and aluminum from the shell are released to the solution (Fig. 8.2). The solubiUty of aluminum compounds becomes considerably increased in the solution of pH higher than 12.5 because in this condition the Al(OH) ions are formed [4]. The concentration of aluminum in the liquid phase is increasing because the calcium aluminates crystallize a httle later, primarily the C-S-H (1) is formed. Simultaneously the solubility of hydrates formed in this condition is reduced. 

Another activator is calcinm snlfate, which acts as a sink for Ca " and Al(OH)" ions released from the slag, yielding ettringite as the product of reaction. This sulfatic activator is not very effective at lower pH, but its effectiveness increases significantiy in combination with an alkaline activator. 

Alkali-activated slag cements (called also AAS cements) consist of ground granulated blast furnace slag and an alkaline activator whose role is to activate the Itydration of the... 

The alkaline activator causes the breaking of bonds between interlinked SiO and AlO tetrahedra constituting the three-dimensional network of the glass phase existing in the slag ... 

F-cement is a product developed and marketed in Finland. It consists of a finely ground granulated blast furnace slag, an alkaline activator, and a superplastcizer. It is used in the precast industry. 

In alkali-activated fly ash binders a fly ash is eombined with an alkali metal eompound, preferably sodium silieate, which will secure a high alka-linity (pH=13-14) of the liquid phase. The alkaline activator may be blended with the ash prior to mixing with water, or— preferably—dissolved in the mixing water before mixing with the ash. 

A variety of powdered natural materials and industrial by-products rich in Si02 and AI2O3 may be activated with suitable alkaline activators to yield a cementitious system that sets and hardens if mixed with appropriate amounts of water. 

The alkaline activators include sodium or potassium hydroxide, silicate, and carbonate. The rate of setting and hardening of alkali-activated binders and the quality and quantity of the resulting reaction products depend on a variety of factors, including the quality of the starting aluminosilicate, the quality and amount of alkaline activator, and the temperature of reaction. 

Cellulose ether esters can be s mthesizedby the reaction of alkylene oxides with alkaline-activated cellulose and further by grafting of the cellulose ether with lactones (36). 

The aluminum atom in this coordination is negatively charged and charge compensated by cations from the alkaline activation solution, such as Na, K, or by artificially introduced cations such as Li ", Ca, Ba ", NH4, or H30 [9,10]. According to the original nomenclature [3], the amorphous to semicrystaUine structure of geopolymers further consists of poly(sialate) (-Si-O-Al-O- PS), poly(sialate-siloxo) (-Si-O-Al-O-Si-0- PSS), and poly(sialate-disiloxo) (-Si-O-Al-O-Si-O-Si-O- PSDS) building blocks (Fig. 2). 

A. Fernandez-Jimenez, A. Palomo, I. Sobrados,J. Sanz, The role played by the reactive alumina content in the alkaline activation of Fly ashes, Microporous Mesoporous Mater. 91 (2006) 111-119. 

C. Ruiz-Santaquiteria, J. Skibsted, A. Fernandez-Jimenez, A. Palomo, Alkaline solution/binder ratio as a determining factor in the alkaline activation of aluminosilicates, Cem. Concr. Res. 42 (2012) 1242-1251. 

Several researchers have reported the sensitivity of alkali-sulphate activated slag mixtures to imprecise dosages of alkaline activators [28, 29]. The results presented in section 5.1,2 also showed that the compressive strength fell as the CKD/BPD content of the binary and temaiy paste mixtures increased. The lower strength due to a high alkali metal content in the pore solution can be attributed to the location of the ettringite precipitation [30],... 

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