Aggregate reactive

Hogan, F.J., The effect of blast furnace slag cement on alkali aggregate reactivity a literature review, Cement Concrete and Aggregates, 7, 2, 1985. 

The formylated peptide fMet-Leu-Phe is probably the most commonly-used activator of neutrophils in vitro. It is used as a model agonist to study receptor-mediated processes, generating intracellular signalling molecules that then activate cell functions. This compound can, depending upon the concentration used, activate many varied functions, such as chemotaxis, aggregation, reactive oxidant production, cytoskeletal changes and (particularly in combination with cytochalasin B) degranulation. 

Durand, B. and Chen, H. (1991). Petrography and Alkali-Aggregate Reactivity, Course Manual, Ottawa, March 12-14, 399-489. 

Prevention. In conclusion, to prevent ASR it is preferable to use non-reactive aggregate, low alkali Portland cement or blended cements with sufficient amounts of fly ash or slag, such as GEM II/B-V (> 25 % fly ash), GEM III/B or GEM III/A with >50% slag [23]. However, it should be noted that it is not always possible to avoid using reactive aggregates, because of the limits of local availability. In addition, methods for the evaluation of aggregate reactivity are sometimes difficult because... 

Fig. 6.33 Assessment of the aggregate reactivity based on the accelerated chemical method.

A variety of rocks may cause expansion and crack formation in concrete if used as aggregate in combination with Portland cement that contains amounts of alkalis considered acceptable for normal use. Such alkali-aggregate reactivity occurs in two forms as alkali-silica or alkali-silicate reactivity, and as alkah-carbonate reactivity, of which the former is much more common. 

In aprotic solvents, no hydrogen atoms capable of hydrogen bonding are present, and this type of solvation cannot occur. As a result, the electrons of the anion are more easily available for reaction. The polarity of the aprotic solvent involved is important, because if the solvent has a low dielectric constant, dissolved ionic compounds are likely to be present as ion pairs or ion aggregates. Reactivity in this case is greatly... 

This collection of different, partly contradictory answers to the question of the reactive species in an ensemble of enolate and enolate aggregates may reflect the difficulties mechanistic interpretations of enolate reactions encounter clearly there is much we do not understand about lithium reagent aggregate reactivities [33]. 

Clusters are intennediates bridging the properties of the atoms and the bulk. They can be viewed as novel molecules, but different from ordinary molecules, in that they can have various compositions and multiple shapes. Bare clusters are usually quite reactive and unstable against aggregation and have to be studied in vacuum or inert matrices. Interest in clusters comes from a wide range of fields. Clusters are used as models to investigate surface and bulk properties [2]. Since most catalysts are dispersed metal particles [3], isolated clusters provide ideal systems to understand catalytic mechanisms. The versatility of their shapes and compositions make clusters novel molecular systems to extend our concept of chemical bonding, stmcture and dynamics. Stable clusters or passivated clusters can be used as building blocks for new materials or new electronic devices [4] and this aspect has now led to a whole new direction of research into nanoparticles and quantum dots (see chapter C2.17). As the size of electronic devices approaches ever smaller dimensions [5], the new chemical and physical properties of clusters will be relevant to the future of the electronics industry. 

Raw ] Ia.teria.ls. Most of the raw materials are oxides (PbO, Ti02, Zr02) or carbonates (BaCO, SrCO, CaCO ). The levels of certain impurities and particle size are specified by the chemical suppHer. However, particle size and degree of aggregation are more difficult to specify. Because reactivity depends on particle size and the perfection of the crystals comprising the particles, the more detailed the specification, the more expensive the material. Thus raw materials are usually selected to meet appHcation-dependent requirements. 

Lithium hydroxide can be used for preparation of numerous lithium salts. The dominant use is the preparation of lithium stearate [4485-12-5], which is added to lubricating greases in amounts up to about 10% by weight. This salt has very low water solubiHty and extends the acceptable viscosity for the grease to both low and high temperatures (see Lubrication and lubricants). Lithium hydroxide is also used in production of dyes (62) and has been proposed as a source of lithium ion for inhibition of alkaH-aggregate expansive reactivity in concrete (63). 

Jiir-entraining cements produce concretes that protect the concrete from frost damage. They are commonly used for concrete pavements subjected to wet and freezing conditions. Cement of low alkah content may be used with certain concrete aggregates containing reactive siUca to prevent deleterious expansions. 

Once the particle-reactive species have been scavenged, subsequent packaging and/or aggregation can result in the flux of particles and particle-reactive species from the water column. Thorium provides a unique way to study the environmental pathways and the biogeochemical processes that affect particle-reactive species. The four useful thorium isotopes are Th = A x yx), °Th... 

In solutions of n-propyllithium in cyclopropane at 0°C, the hexamer is the main species, but higher aggregates are present at lower temperatures. The reactivity of the organo-... 

One of the general features of the reactivity of enolate anions is the sensitivity of both the reaction rate and the ratio of C- versus O-alkylation to the degree of aggregation of the enolate. For example, addition of HMPA fiequently increases the rate of enolate alkylation... 

The order of enolate reactivity also depends on the metal cation which is present. The general order is BrMg < Li < Na < K. This order, too, is in the order of greater dissociation of the enolate-cation ion pairs and ion aggregates. Carbon-13 chemical shift data provide an indication of electron density at the nucleophilic caibon in enolates. These shifts have been found to be both cation-dependent and solvent-dependent. Apparent electron density increases in the order > Na > Li and THF/HMPA > DME > THF >ether. There is a good correlation with observed reactivity under the corresponding conditions. 

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