Retardation, chemical

By adding an oil-wetting surfactant to an acid, one can promote the temporary formation of a film on formation surfaces thus reducing the rate of rock dissolution. Acids containing these surfactants are known as chemically retarded acids. 

Chen, F., Burns, P. C. Ewing, R. C. 1999. 79Se geochemical and crystallo-chemical retardation mechanisms. Journal of Nuclear Materials, 275, 81-94. 

Longer processing times have commonly been obtained by the use of chemical retarders (77MI11504). These compounds not only delay the beginning of cure, but also affect the rate of cure once it has started. The use of a prevulcanization inhibitor (PVI), on the other hand, delays the onset of vulcanization with only minimal effects on the rate of cure and on the properties of the vulcanizate. The introduction of PVIs represents one of the major developments in the rubber industry in recent years (70USP3546185). 

Many investigators are seeking further improvements in the handling of fresh produce. Among methods receiving much attention are the use of postharvest chemicals, retardants of senescence, thermal treatment, controlled atmospheres, new packaging techniques, better temperature control in storage and transit, and irradiation. One method may work well with one fruit or a particular variety of fruit but not with another fruit. 

Church, J. M., Fundamental Studies of Chemical Retardants for the Fire-Resistant Treatment of Textiles, U. S. Q. M. C. Textile Series, Rept. 38. (1952). 

There is evidence, however, that wood treated with some chemical retardants at low retention levels will ignite (flame) or start glowing combustion at slightly lower temperatures or irradiance levels than does untreated wood (19,20), though sustained combustion is usually prevented or hindered. 

Some chemicals retard or suppress free-radical polymerization by reacting with primary radicals or macroradicals to yield radicals that are very stable to further reaction or yield nonradical products. These materials could be retarders or inhibitors. Retarders slow down the formation of polymer but inhibitors completely eliminate it. Oxygen is one of the most commonly known inhibitors for vinyl polymerization and good practice requires the removal of air from the reactor vessels before the reaction is started. It combines with active radicals to form unreactive peroxy radicals. 

In dynamic studies the chemical retardation is defined as the ratio of velocities of water (w) and of the species of interest (M) through a control volume. 

Chemical equilibrium problem, formulation, 586, 589 Chemical retardation, 335 Chlorite... 

Having a model that has a good theoretical basis, that has been validated in laboratory experiments, and that is consistent with field observations, it is advisable to make some predictions about particle deposition in systems of interest. An example is presented in Figure 3, adapted from the work of Tobiason (1987). The travel distance in an aquifer required to deposit 99% of the particles from a suspension is termed Lgg and is plotted as a function of the diameter of the suspended particles for two different values of a(p, c), specifically 1.0 (favorable deposition) and 0.001 (deposition with significant chemical retardation of the particle-collector interaction, termed unfavorable deposition ). Assumptions include U = 0.1 m day"1, T= 10°C, dc = 0.05cm, e = 0.40, pp= 1.05 gem"3, and H=10 2OJ. These results indicate the dependence of the kinetics of deposition on the size of the particles in suspension that has been predicted and observed in many systems. Small particles are transported primarily by convective Brownian diffusion, and large particles in this system are transported primarily by gravity forces. A suspended particle with a diameter of about 3 /im is most difficult to transport. Nevertheless, in the absence of chemical retardation, a travel distance of only about 5 cm is all that is needed to deposit 99% of such particles in a clean aquifer, that is, an aquifer that has not received and retained previous particles. 

Quite often, acid will form predominantly single wormholes from limited numbers of perforations, without significant branching. That is the case with strong acids, such as HCl. Weaker acids, such as carbox)dic acids (e.g., acetic add), and retarded acid systems tend to create more branching of wormholes, which is desirable but only to a certain extent. Retarded acid systems include viscosified acids (e.g., polymer- or surfactant-gelled acid, emulsified acid, and foamed acid) or chemically retarded (surfactant-retarded) acid. The nature of wormholes created depends on injection rate, temperature, and formation reaction characteristics as well. 

Viscous acid fracturing uses viscous acid systems such as gelled, emulsified, and foamed acid, or chemically retarded adds, to both create the fracture and differentially etch the fracture face. Treatments with viscous acid are applicable in heterogeneous carbonates such as dolomites or impure limestones. 

Addition of organic acids and/or reaction products to acid (chemical retardation)... 

The desorption of PHCs for example can give some insight into organic chemical retardation phenomena. The studies by Yaron (1989) of desorption of m-xylene, n-decane, t-butylbenzene... 

Retarded acid can be chemically retarded (surfactant retarded) slightly gelled or foamed... 

Note The following acid additives are required acid retardant (chemical retardant/surfactant), corrosion inhibitor, and friction reducer, Examples of chemically retarded acids include 20% HCI, 1.2% high-temperature corrosion inhibitor, 5,0% formic acid (corrosion inhibitor booster), acid-retarding surfactants, high-temperature iron controi agents, 2,5% methanoi, 0,2% fiuorosurfactant (flowback enhancement), 0,3 ga ton friction reducer,... 

Gelled to 40 pounds chemically retarded by addition of surfactant. 

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