Rapid hardening

Cast lead—calcium—tin alloys usually contain 0.06—0.11 wt % calcium and 0.3 wt % tin. These have excellent fluidity, harden rapidly, have a fine grain stmcture, and are resistant to corrosion. Table 4 Hsts the mechanical properties of cast lead—calcium—tin alloys and other alloys. 

The properties of cured Pordand cement are affected by these four constituents of the manufactured Pordand cement. Tricalcium siHcate hydrates and hardens rapidly, giving rise to the initial set and eady strength. Increased concentrations of tricalcium siHcate causes an increase in the eady strength of Pordand cement concretes. Dicalcium siHcate hydrates and hardens more slowly, giving the cured concrete its strength increases beyond one week. 

Dry ice is used to chill aluminum rivets. These harden rapidly at room temperature, but remain soft if kept cold with dry ice. It has found numerous uses in laboratories, hospitals, and airplanes as a convenient and readily available low temperature coolant. 

Another common problem on moulding is voids. These occur when a moulding or extrudate cools and hardens rapidly on the surface. On further cooling the moulding or extrudate cannot shrink inward because the outside dimensions are fixed and therefore the molecules are pulled towards the surface of the product, generating internal voids. At the same time molecules in the inner... 

The zinc polycarboxylate cement sets within a few minutes of mixing and hardens rapidly. Strength is substantially developed within an hour. However, even when fully hardened the cement exhibits marked plastic behaviour. Its most important property is its ability to bond permanently to untreated dentine and enamel. 

Acid Hardening Rapid Fixer (Donald B.Alnutt)... 

Barnacles secrete an adhesive to attach themselves to rocks, ships, and other objects. This adhesive hardens rapidly, even in seawater. This adhesive, which is predominately calcium carbonate in a proteinaceous matrix, contains chitin (55), Eggs of lice are attached to the bristles of hogs by a very hydrolysis-resistant adhesive that contains chitin and p-benzoquinone (56),... 

Calcium aluminate cements harden rapidly as soon as the massive precipitation of hydrates begins. This may be attributed to the fact that, unlike those of Portland cement, the major hydration products are crystalline. Relatively high proportions of water are taken up in the hydration reactions, the theoretical w/c ratios needed for complete hydration of CA being 1.14, 0.63 and 0.46 for the formation of CAHj, CjAHg -F AHj and CjAH -F 2AHj, respectively. For this reason, and also because of the rapid heat... 

Various methods have been used to obtain cements that set and harden rapidly. They include the use of Portland cement with admixtures and of mixtures containing both Portland and calcium aluminate cements, described in Sections 11.5 and lO.I.IO, respectively. Another approach has been the manufacture of clinkers containing either CuAy CaF, or C 4A, S. both of which hydrate rapidly under appropriate conditions with the formation of ettringite. 

To pump cement slurry into a well and place it in the annulus between the casing and the formation, or at the desired depth, at least 3 h is required. Depending on the depth, even additional time may be needed. Therefore, the slurry should remain as low-viscosity fluid during that time and should harden rapidly when placed in the borehole. Operations on oil well platforms are expensive, and failures can be costly. For this reason, every cement composition is pretested in a laboratory before its use in the field to ensure its reliability. 

CBPCs may be placed as a paste or can be injected at the right place in a human body. It will harden rapidly after its delivery. It will attach itself to the adjacent surfaces and form a firm bond. The process is less intrusive as compared to hardened ceramics that need to be implanted surgically. 

Corrosive sublimate (HgCla) in 0.2 per cent, aqueous or alcoholic solution penetrates and hardens rapidly but doesn t give as sharp optical differentiation as the others considered,... 

CACs were developed in response to the need for cements resistant to groundwater and seawater attack and are the only cements, other than Portland cement, that are in continuous long-term production [2], The property of CAC that was most important in their commercial development is the resistance to sulfate attack, which contrasted with the poor-sulfate resistance of contemporary Portland cements [2], and CAC was first patented in 1908 [2], Most early applications, in construction projects following the First World War, were in structures exposed to seawater, such as harbor pilings. Because CAC hardens rapidly, it was adopted for prestressed concrete beams in the post World War II construction boom, with some unfortunate results. Poor understanding of the material properties of CAC and incorrect water to cement ratios led to the collapse of several buildings, and the use of Portland cements, which are cheaper, has replaced CAC in prestressed concrete beams[2]. 

For many years, alloys with V values above 9 1 were not utilized for VRLA batteries. Large battery grids and tubular grids required alloys which would harden rapidly. Alloys of 0.08-0.12wt.% Ca and 0.3. 6wt.% Sn were most commonly utilized for VRLA batteries for standby and telecommunications service. These alloys harden rapidly and the alloys can be handled and pasted after a short ageing time at room temperature compared with weeks for materials with high r values. 

The early strength of concrete is the result of hydration of tricalcium silicate C jS) and tricalcium aluminate (C.,A) phases of Portland cement. When mixed with water C.-,S hardens rapidly and both C.,S and C..,A release heat. 

This type of finish is an extension of the one-pack moisture-curing type. It is virtually the same finish, to which a small quantity of catalyst is added just before use. Tertiary amines, such as N,N-dimethylethanolamine [HO CH2 CH2 N(CH3)2], are most frequently used as catalysts. Even if the moisture content of the air is low, the finish will harden rapidly, but the more reliable drying performance is obtained at the expense of a limited pot-life. Unfortunately, the activator is non-polymeric and so cannot be used for pigment dispersion. Pigments are dispersed in pre-polymer and must be free from moisture, as in the one-pack composition. The uncatalysed finish is water-sensitive, presenting a shelf-life storage problem as before. 

Rapid hardening Rapid hardening Normal Slow hardening Slow hardening... 

In contrast to the low crystallinity required for mbber products, crystallization is a great benefit for adhesives. In solution, crystallization doesn t occur but, after drying, the adhesive film hardens rapidly due to crystallization. 

USS Tenelon was found to strain harden rapidly even though there was little accompanying transformation to martensite. 

A preaccelerated, low viscosity, rapid hardening, rapid wet-out, thixotropic orthophthalic, suitable for resin concrete applications. 

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