DIATOMITE FOR NON FILTERAID USES
The versatility of diatomite products is exhibited to a remarkable degree in the non-filteraid uses. A comprehensive review of these applications would fill a book —hence, only a few highlights here. CHEMICAL PROPERTIES. In many of its applications as a filler, diatomite is chosen because of its inertness. The calcined and flux calcined grades are outstanding in this respect. In most compositions these grades exhibit no solubility or adsorption whatsoever. On the other hand, non-calcined (natural) diatomite is extremely reactive, particularly to alkalis. While no fundamental studies on specific reaction rates have been reported in the -literature, considerable work has been conducted in industrial laboratories. These experiments have shown that natural diatomite is intermediate in reactivity between crystalline forms of silica and silica g e l . . . this follows, of course, from the fact that natural diatomite is hydrous silica. Natural diatomite has tremendous surface area in proportion to weight; that from certain deposits has nitrogen adsorption surface areas exceeding 35 square meters per gram. Thus, the diatomite industry provides a naturally-occurring mineral, in a variety of carefully controlled grades, priced in the range of other non-metallic minerals, which has the characteristics of manufactured products, such as silica gel, which cost several times as much. Several uses have been made of this property of natural diatomite. For example, the high reactivity of diatomite to alkali has been used to control deleterious effects occurring when high alkali Portland cements are combined with reactive aggregates. No known naturally-occurring material reacts more rapidly with free alkali in cement slurries than does diatomite. The insulation industry uses a large tonnage of diatomite to produce precast and other forms of thermal insulation by the reaction of hydrated lime and diatomite. This reaction, suitably catalyzed, is so fast that solid gels may be formed by heating to 175° F. for one minute. This permits rapid stripping from the molds to hold production costs in line. Such fast reaction presents profitable possibilities in the production of other lightweight products in the range of 5-25 pounds per cubic foot. (ADVERTISEMENT)
Paul W. Leppla Technical Director
4 CALCINED
/Shite ot 1 * * ·
dteC
Since Dicalite is essentially hydrated amorphous silica, it is i n e r t . . . we've stressed the point for years. But it might be noted that there is an exception. The natural grades of Dicalite (meaning not calcined or flux-calcined) are extremely reactive with alkalis, a property made use of in the cement and insulating fields, and one which should be of value if you are concerned with certain types of lightweight materials, or processes requiring solid gels. In the vast majority of applications, though, Dicalite 'filler' materials are completely inert, for all practical purposes. Furthermore, the unique characteristics given by the shape and structure of the diatomite particles provide several other desirable properties . . . great bulk in relation to weight, which gives bulking without significant increase in weight... tremendous surface area in relation to weight... extreme porosity, making Dicalite highly absorptive and also lending both heat-and-electrical resistance. These are the principal values of Dicalite filler materials; there are others. Dicalite's engineering service will be glad to advise with you on your particular problem, or you may obtain additional information by writing :
icalite
Dependable
®
GLC GREAT
LAKES
DIATOMACEOUS
MATERIALS
DICALITE DIVISION/GREAT LAKES CARBON CORP./612 S. FLOWER ST./LOS ANGELES I T
For further information, circle number 31 A on Readers' Service Card, page 129 A
VOL. 49, NO. 4
·
APRIL 1957
31 A
