prov:value
| - The porous structure may also contain other elements such as boron, alkali metals or alkaline-earth metals of the type Ca, Sr, Na, K, Ba, the total summed amount of said elements present preferably being less than 10% by weight, for example less than 5%, or 4%, or 3% by weight on the basis of the corresponding oxides B2O3, CaO, SrO, Na2O, K2O, BaO, in addition to the contents by weight of all the
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