Interlaminar water

Vermiculite - The basic talc structure also typifies vermieulite, as illustrated in Figure 16. Vermiculite differs from talc primarily in its substitution of Al for tetrahedral Si" and the presence of two oriented layers of water between individual laminae. Limited substitution of octahedral by Fe and Al also occurs. The charge imbalance arising primarily from tetrahedral substiutions is compensated by cations, usually Mg, between interlaminar water layers. Because these cations are not structural components, they can be exchanged with other charge-balancing cations under the proper conditions. 

Unlike vermiculite, the smectite crystal structure accommodates additional interlaminar water layers, due at least in part to its lower counterion density. This allows for hydraulic delamination. On immersion in water, sodium smectites incorporate enough additional water layers to overcome weak... 

The formation of NiOOH starting from the common brucite modification j3-Ni(OH)2 involves no changes in the structural parameters. The a-Ni(0H)2 is a loosely hydrated species which can be electrochemically oxidized to yield y-NiOOH. This compound retains the octahedral position of the oxygen atoms with an interlaminar material consisting of disorderly arranged water... 

J R M D Almeida, Effects of distilled water and saline solntion on the interlaminar shear strength of an aramid/epoxy composite . Composites 1991 22 448-449. 

Figure 7.7 Normalized interlaminar shear strength versus absorbed water content. Least squares adjusted equation correlation coefficient, r = 0.988 , as fabricated O, distilled water , salt water. (Reproduced from d Almeida [40], p 449, with kind permission of the author and Elsevier Science)...

D Almeida [40] has reported interlaminar shear strength (ILSS) results for 65v/o Kevlar 49 fibres in DER 383 epoxy resin cured with 27phr DEH 50 aromatic polyamine with a void content below 0.5%. The ILSS values decreased as a function of immersion time, with specimens immersed in distilled water declining faster than those in saline solution, which is absorbed more slowly. When the results were normalized to water content the results were coincident, suggesting that the degradation mechanism was the same in both cases (Fig. 7.7). 

Davies et al. [64] studied the influence of water absorption on the interlaminar shear strength and end notch flexure (ENF mode II shear) fracture toughness of quasi-unidirectional (88% 0°, 12% 90°) E-glass fibres in DGEBA epoxy resin cured with an amine hardener. Laminates were immersed in (a) distilled water and (b) the Atlantic Ocean ( at Boca Raton, Florida) for up to 8 months at temperatures of 20°C, 50°C and 70°C. Sea water was more slowly absorbed than distilled water. This observation has frequently been made and it provides some reassurance that laboratory tests using distilled water are useful, if slightly cautious, estimates of behaviour in the ocean. 

Pre-accelerated, low viscosity fast wet-out, thixotropic, low styrene emission, orthophthalic resin, offering good interlaminar adhesion, high heat resistance, improved water resistance and low exotherm enabling thick sections to be fabricated by either hand-lay or spray/projec ion techniques colour change on cure. Approved for food contact applications, Lloyd s and Det Norske Veritas. 

Effects on interlaminar shear and flexural modulus because of water absorption... 

Hodzic A, Kim J K, Lowe A E and Stachurski Z H (2004) The effects of water aging on the interphase region and interlaminar fracture toughness in polymer-glass composites, Compos Sd Technol 64 2185-2195. 

Smectite clay - Like mica, smectite cl (commonly called bentonite) has either a pyrophyllite or talc structure. Montmorillonite, a common high-aliunimun smectite, can be characterized by die pyrophyllite crystal structure with a small amount of octahedral Al replaced by Mg. The resulting charge imbalance is compensated by exchangeable cations, usually Na or Ca, between the laminae. In addition to diese counterions, oriented water, similar to that in vermiculite, occupies the interlaminar space. When Ca is the exchangeable cation, there are two water l ers, as in vermiculite when Na is the counterion, there is usually just one water layer. Figure 18 shows the montmorillonite structure. 

Saponite, a high magnesium smectite, is similar in strueture to talc but with limited substitution of tetrahedral Sf by while heetorite has the talc structure but with limited substitution of Li for octahedral Mg and F for OH". As with montmorillonite, the resulting charge imbalanee is eompensated by Na or Ca residing with oriented water in the interlaminar spaces. Saponite and heetorite have swelling, ion exchange, and absorbent properties similar to those of montmorillonite. 

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