Hydration retarded

Oil well cements are manufactured similarly to ordinary Portland cements except that the goal is usually sluggish reactivity. Eor this reason, levels of C A, C S, and alkafl sulfates are kept low. Hydration-retarding additives are also employed. 

The self-diffusion of water itself provided proof of the above hypothesis, because ions due to hydration retarded it, but structure breakers could accelerate it. The plot of the self-diffusion parameter as a function of transition concentration fully confirmed the above-mentioned assumption. The transition concentration thus corresponded with that at which the maximum hydration occured. 

SPECIAL CELLULOSIC THICKENERS 4.1 Hydration Retarded Cellulosics... 

Unsaturated Polyesters. There are two approaches used to provide flame retardancy to unsaturated polyesters. These materials can be made flame resistant by incorporating halogen when made, or by adding some organic halogen compound when cured. In either case a synergist is needed. The second approach involves the addition of a hydrated filler. At least an equal amount of filler is used. 

Olefin Polymers. The flame resistance of polyethylene can be increased by the addition of either a halogen synergist system or hydrated fillers. Similar flame-retarder packages are used for polypropylene (see Olefin polymers). Typical formulations of the halogen synergist type are shown in Table 15 the fiUer-type formulations are in Table 16. 

Flame and Smoke Retardants. Molybdenum compounds are used extensively as flame retardants (qv) (93,94) in the formulation of halogenated polymers such as PVC, polyolefins, and other plastics elastomers and fabrics. An incentive for the use of molybdenum oxide and other molybdenum smoke and flame retardants is the elimination of the use of arsenic trioxide. Although hydrated inorganics are often used as flame retardants, and thought to work by releasing water of crystallization, anhydrous molybdenum oxides are effective. Presumably the molybdenum oxides rapidly form... 

Flame retardants (qv) are incorporated into the formulations in amounts necessary to satisfy existing requirements. Reactive-type diols, such as A/ A/-bis(2-hydroxyethyl)aminomethylphosphonate (Fyrol 6), are preferred, but nonreactive phosphates (Fyrol CEF, Fyrol PCF) are also used. Often, the necessary results are achieved using mineral fillers, such as alumina trihydrate or melamine. Melamine melts away from the flame and forms both a nonflammable gaseous environment and a molten barrier that helps to isolate the combustible polyurethane foam from the flame. Alumina trihydrate releases water of hydration to cool the flame, forming a noncombustible inorganic protective char at the flame front. Flame-resistant upholstery fabric or liners are also used (27). 

Zinc Borates. A series of hydrated 2inc borates have been developed for use as fire-retardant additives in coatings and polymers (59,153). Worldwide consumption of these 2inc salts is several thousand metric tons per year. A substantial portion of this total is used in vinyl plastics where 2inc borates ate added alone or in combination with other fire retardants such as antimony oxide or alurnina trihydrate. 

Concrete, Mortar, and Plaster. Citric acid and citrate salts are used as admixtures in concrete, mortar, and plaster formulations to retard setting times and reduce the amount of water requited to make a workable mixture (172—180). The citrate ion slows the hydration of Portland cement and acts as a dispersant, reducing the viscosity of the system (181). At levels below 0.1%, citrates accelerate the setting rate while at 0.2—0.4% the set rate is retarded. High early strength and improved frost resistance have been reported when adding citrate to concrete, mortar, and plaster. 

A large number of materials, generally inorganic in nature, have been used as additive-type flame retardants, of which hydrated alumina and antimony oxide are among the most important. 

After formulation with a flame retardant filler such as alumina trihydrate Al203 3H20, hydrated silica or calcium carbonate, a peroxide curing agent and... 

Typical non-enolising aldehydes are formaldehyde and benzaldehyde, which are oxidised by Co(III) Ce(IV) perchlorate and sulphate , and Mn(III) . The main kinetic features and the primary kinetic isotope effects are the same as for the analogous cyclohexanol oxidations (section 4.3.5) and it is highly probable that the same general mechanism operates. kif olko20 for Co(III) oxidation of formaldehyde is 1.81 (ref. 141), a value in agreement with the observed acid-retardation, i.e. not in accordance with abstraction of a hydroxylic hydrogen atom from H2C(OH)2-The V(V) perchlorate oxidations of formaldehyde and chloral hydrate display an unusual rate expression, viz. 

Lucchi , who studied the oxidation of substituted benzaldehyde derivatives found that chlorine atoms in the meta and para position accelerate the reaction and alkyl groups retard the oxidation. A Hammett plot of Lucchi s data yields a good straight line with the slope p = 1.06. These data suggest that the reaction proceeds by way of the chromic ester of hydrated benzaldehyde as intermediate, viz. 

The addition of STPP (1-7%) acted as a retarder and increased compressive strength (mortar II). Less heat and ammonia were evolved and the cement set more slowly in 10 minutes. The paste hardened in 30 to 60 minutes. Traces of ADP persisted for 30 minutes but no STPP was detected in the reaction products. Struvite, the main hydration product, schertelite and dittmarite all appeared within 5 minutes. Struvite continued to increase in amount as the cement aged schertelite disappeared after 3 hours and dittmarite after a week. Stercorite was found only during the first 7 hours. 

The phenomenon of pseudopolymorphism is also observed, i.e., compounds can crystallize with one or more molecules of solvent in the crystal lattice. Conversion from solvated to nonsolvated, or hydrate to anhydrous, and vice versa, can lead to changes in solid-state properties. For example, a moisture-mediated phase transformation of carbamazepine to the dihydrate has been reported to be responsible for whisker growth on the surface of tablets. The effect can be retarded by the inclusion of Polyoxamer 184 in the tablet formulation [61]. 

O. J. Samoilov proposed a statistical approach to hydration. Ions in solution affect the thermal, particularly translational, motion of the solvent molecules in the immediate vicinity of the ion. This translational motion can be identified with the exchange of the solvent molecules in the neighbourhood of the ion. Retardation of this exchange is thus a measure of the ion solvation. 

Flame retardants Antimony trioxide with chlorinated or brominated organics, hydrated alumina... 

Hydrated or slaked lime Ca(OH)2 is an inorganic accelerator used in the curing of fluoroelastomers. In conventional sulphur cured polymers it counteracts the retardation of cure due to the presence of acidic substances in a rubber compound. Quicklime (CaO) dispersed in mineral oil or in wax/oil is used as a dessicant to reduce porosity in vulcanisates, particularly in fluid bed curing. 

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