Setting chemistry

There have been a number of studies aimed at understanding the chemistry of the curing and setting of magnesium oxychloride cements and at identifying the phases that are present in the final material. Investigations in the first half of the twentieth century revealed that cement formation in the MgO-MgCla-HaO system involves gel formation and crystallization of 

Above 100 °C, a different set of phases was stable in the simple magnesium oxychloride system (Demediuk, Cole Hueber, 1955 Cole Demediuk, 1955) a 2-form 2Mg(OH)2.MgCl2.4H20 and a 9-form 9Mg(OH)2.5H2O were found to occur. Apart from identifying these phases, these workers were not able to give details on the structures. 

Of all the studies on this system, that by Sorrell Armstrong (1976) has provided the most useful information, both on the phase relationships and on the kinetics of interconversion. They used three different grades of 

produced by different but well-defined routes and having different reactivities towards aqueous MgCl in this way, it was possible to study the cementation reactions in some detail and to ensure a reasonably close approach to equilibrium. 

To study reaction kinetics, cement batches of total mass 300 g were prepared using ingredients measured to the nearest 0-1 g. Mixing was carried out for 10 minutes using a kitchen blender, after which specimens were cast in slabs 10 x 10 x 1-2-1-5 cm in polyethylene moulds. When the setting reaction had proceeded to a sufficient extent and viscosity had risen to give a reasonably stiff paste, a small portion was removed, placed on a glass microscope slide and immediately examined by X-ray diffraction. The remainder of the sample was allowed to set. 

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The setting chemistry of resole resins is complex, and experimentally difficult to study, mainly because the cured product, being insoluble, is not amenable to ready chemical investigation. Part of the information on these materials has come from studies of model systems such as mononuclear methylphenols, which give soluble products. These products present fewer difficulties in chemical analysis. 

Wasson, E. A. Nicholson, J. W. (1990). A study of the relationship between setting chemistry and properties of modified glass-poly(alkenoate) cements. British Polymer Journal, 23, 179-83. 

In addition to spectrosopic studies of the setting chemistry of AB cements, numerous mechanical tests have been used to measure properties of the set materials. This latter group has included determination of compressive and flexural strengths, translucency, electrical conductivity and permittivity. The present chapter describes each of these techniques in outline, and shows how they have been applied. Results obtained using these techniques are described in earlier chapters which deal more thoroughly with each individual type of AB cement. 

Changes in electrical conductivity have occasionally been used to study the setting chemistry of AB cements. Conductivity has been particularly used in the study of dental cements, notably the dental silicate (Wilson Kent, 1968), the zinc polycarboxylate (Cook, 1982), the glass-ionomer cement (Cook, 1982) and the ZOE cement (Crisp, Ambersley Wilson, 1980). 

The technique is not optimal the instrument response (Y) is a predictor of analyte values (X). The limitation for modeling is in the representation of calibration set chemistry, sample presentation, and unknown variations of instrument and operator during measurement. 

The New Chemistry is a set of six hooks intended to provide an overview of some areas of research not typically included in the beginning middle or high school curriculum in chemistry. The six hooks in the set—Chemistry of Drugs, Chemistry of New Materials, Forensic Chemistry, Chemistry of the Environment, Food Chemistry, and Chemistry of Space—are designed to provide a broad, general introduction to some helds of chemistry that are less commonly mentioned in standard introductory chemistry courses. They cover topics ranging from the most fundamental helds of chemistry, such as the origins of matter and of the universe, to those with important applications to everyday life, such as the composition of foods... 

A wide variety of soils and sludge have now been treated. Soil characteristics that can impact the SET chemistry include the general soil type, which is treated (loam, sand, silt, and clay), the presence of humic material, the pH value, the soil s cation exchange capacity, its particle size, the amount of water present, and the iron content. Processes have been engineered to accommodate this wide range of variables [7,8,34]. Some soils can be treated... 

In England in 1660 Charles II helped inaugurate just such a scientific group by founding the Royal Society of London. One of its first members, Robert Boyle, was instrumental in setting chemistry on its feet as a science in its own right, freeing it both... 

Extensive research by Dimmel and coworkers has shown that another mechanism is also possible between AHQ and QMs. They propose that single electron transfer (SET) chemistry promotes the delignification of wood [52]. As is the case for the adduct mechanism, this proposed chemistry is based solely on model compound studies and can account for coniferyl alcohol-type prodncts. Evidence for SET chemistry comes from a combination of studies involving electrochemistry... 

Reterence Tables tor Physical Setting/Chemistry Reterence Tables tor Physical Setting/Chemistry... 

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