Slow set

Zinc Oxide—Eugenol Cements. Zinc oxide—eugenol cements have many uses in dentistry. The admixture of powdered zinc oxide [1314-13-2] and Hquid eugenol [97-33-OJ, fotins a bland, easily mixed paste having exceUent working time but slow-setting characteristics. 

Non-setting Slow setting Moderate setting Fast setting Fast setting crystalline mass Ultra-fast setting... 

Post-operative sensitivity has occasionally been reported when the glass-ionomer cement has been used as a luting agent. This observation is more than anecdotal, but the reason for it is unknown. It is not connected with pulpal irritation but may be related to hydraulic pressures (Pameijer Stanley, 1988). The indication is that sensitivity is related to clinical technique and is exacerbated if certain slow-setting glass-ionomer cements are used, especially if they are mixed too thinly. 

After heat shocking, remove the rinse samples and place in cool water. After cooling, shake container on mechanical shaker at slow setting for 30 minutes. Sonicate for 2 minutes just prior to testing. Transfer the samples to a laminar flow hood. 

Calculate the overall Ca and Si contents (expressed as CaO and Si02) of a Portland cement clinker that has 55% alite, 30% belite, 5% alumi-nate phase, and 10% ferrite (assume ideal compositions for the latter two). Would you expect this to behave as a fast or a slow setting cement ... 

This indicates that no synergist effects occur with regard to the pseudo-limiting-current of the prewave of hydrogen peroxide. To verify that the wrong conclusions had not been drawn because of slow setting in adsorption equilibria, the experiment was repeated, adding both additives in reverse direction. Flence, in a second experiment, of which the results are also presented in Fig.5.4, first Defindol E was added and subsequently... 

The colours, flavours and remaining acid are added. Once this acid has been added the product can set. A slow set pectin is used otherwise the product could pre-set with disastrous consequences. 

Set-off can be avoided by the use of anti-set-off compoimds. These are spray powders that reduce the frictional contact between the sheets. Materials like silica and starch, which have a particle diameter slightly greater than the printed ink film thickness, can be used. Slow setting problems may be reduced by the use of less solvent or by a higher ratio of resin to oil. Varnishing with a formula that utilises polymerisation induced by radiation is another way to avoid set-off. The varnish covers the printed surface and direct contact between the layer of print and the iimer food contact surface of the substrate is avoided. 

When radical anions and dianions leads to very slow SET, their nucleophilic properties have to be taken into account. Reactions of electrogenerated species toward CO2, acetic anhydride, acetic chloride, and some classic RX compounds as electrophiles can be explained on the basis of nucleophilic substitutions, but extreme cares have to be taken on the intrinsic nature of the mechanism (Sn vs. radical coupling). Thus reactions involving azo and diazo compounds in the presence of CO2 could be explained by nucleophilic addition (formation of A-functionalized azine and diazines [13]). Several reactions [15,215,229] implying CO2 and acetic anhydride [230] were described. 

Polystyrene Although polystyrene is usually bonded by solvent cementing, it can be bonded with vinyl acetate/vinyl chloride solution adhesives, acrylics, polyurethanes, unsaturated polyesters, epoxies, urea-formaldehyde, rubber-base adhesives, polyamide (Versamid-base), polymethylmethacrylate, and cyanoacrylates. The adhesives should be medium-to-heavy viscosity and room-temperature and contact-pressure curing. An excellent source is a Monsanto Company technical information bulletin which recommends particular commercial adhesives for bonding polystyrene to a number of different surfaces. Adhesives are recommended in the fast-, medium-, and slow-setting ranges (10). 

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