Binders sodium silicate

As of the mid-1990s, soluble sihcates are used primarily as sources of reactive siUca (57%), in detergency (qv) (23%), in pulp (qv) and paper (qv) production (7%), for adhesives and binders (5%), and in other appHcations (8%). The stmcture and chemistry of solutions containing polymeric siHcate species have been characterized using modem analytical techniques. This improved understanding of siHcate speciation contributes to the development of new markets. Thus, the sodium silicates constitute a versatile, stable, and growing commodity and are ranked among the top 50 commodity chemicals. 

Carbon dioxide-silica process. Sand is mixed with sodium silicate (3.0 to 3.5% of sand volume), and the mixture is blown or hand-rammed into a core box or around a pattern. Carbon dioxide gas is passed through the compacted sand to harden the binder. The bonding strength eliminates the need for drying or baking the mold and metal can be poured into the mold immediately. Over-gassing should be avoided because it makes the mixture friable. 

The cyclic alkylene carbonates have also been applied as the cure-accelerators of phenol-formaldehyde (PF) [262-266] and sodium silicate [267] resin systems, which are widely used in foundry sand and wood binder applications. 

Fe203 and 55 weight % silica, as support, with 1% sodium silicate as a binder. In the preliminary work fly ash was considered as a support material but the maximum amount of iron oxide which could be incorporated with it was 25 weight % Based on this and the other criteria discussed above, the iron oxide-silica composition was found to be the most suitable sorbent for bulk H2S removal,... 

Starch can be enzymically converted in the presence of pigment. The conversion follows a similar time-temperature cycle as in neat starch conversion. The pigment will adsorb a portion of the enzyme adsorption can be minimized by the addition of sodium silicate to the mixture prior to the addition of the enzyme (Vanderbilt process). Even with silicate treatment, a higher quantity of enzyme will be required to reach a specific viscosity target. Other coating components, such as latex and lubricants, have to be added after the conversion. The Vanderbilt process is now rarely used for the preparation of coating binder. 

Wood Plastic Composites (WPC) In WPC applications, it was claimed that the addition of organic phosphate, zinc borate/boric acid, sodium silicate, or ATH to milled rice straw with a resin binder can produce a fire-resistant board.65... 

Other salts which have been used successfully as water-soluble binders are potassium silicate, sodium phosphate, sodium borate and aluminium phosphate , the last two being the only ones apart from sodium silicate which have apparently been widely used. Their application techniques are similar to those described for sodium silicate. The concentration of molybdenum disulphide in inorganic salt binders is usually between about 20 and 75%. 

It is less clear why there has been very little use of other types of inorganic matrices. Some inorganic solids would seem to have useful properties for this purpose, but the only one which has been described in any detail is sodium silicate. This was the binder for the bonded coating developed by the US Naval Aircraft Materials Laboratory which was described in Chapter 11, but the same material was used ° as a bulk composite in certain components in a dry-lubricated engine. It was used to provide transfer lubrication, and presumably it was not capable of use in load-bearing situations. 

In binding thermite with sodium silicate, it is very essential that all the water be driven out, and, because of the difficulty of completely drying the silicate-bound thermite, a number of other binders w ere tried. Sulfur W as highly recommended as a binder, since a unit of weight of mixture made up according to the equation... 

Other organic and inorganic binders have also been tested. Polymerization of styrene or methyl methacrylate in cancrinite-monomer mixtures produces hard, rugged products. Sodium silicate solution mixed with powdered silica also appears to be an effective binder for the cancrinite. 

Silica sol which is a stable sol of monodispersed particles is made by the decomposition of sodium silicate at low concentration under controlled pH and surface treatment and then evaporation of water. A stable floccular aggregates of silica particles are made by the peptization of dilute hydrogels under controlled pH. The former material is used as fiber and paper sizing, binder and the latter is used for water treatment. 

A process has been developed at Ford Motor Company that uses dehydrated sodium silicate as a core binder for aluminum casting Silicate sand binders are attractive for their environmental qualitiesy such as the lack of organic emissions and odory and for other properties beneficial to the casting process O). 

Above a certain concentration which decreases with increasing silica-soda ratio as explained above, sodium silicate aqueous solutions become very viscous and are stable for only a limited period of time. Stability in this case means resistance to gelling. More stable solutions can be made at lower sodium silicate concentrations but this may become impractical in a foundry binder. The high water content of very high ratio (more than 4 to 5) sodium silicate solutions at practical viscosities prevent their extended use as a foundry binder in the present invention. Excessively high water content in a foundry binder means unacceptably weak sand molds or cores and detrimental quantities of steam evolving when the molten metal is poured into the sand mold-core assembly. 

A practical way of using high ratio silicate as binders for foundry sands is to mix concentrated silica aquasols and concentrated sodium silicate aqueous solutions in situ, that is on the surface of the sand grains, thus forming the high ratio silicate on the sand surface. 

However, 1 have discovered that effective mixing and binding effect is obtained with sand if the concentrated silica sol is mixed first with the sand to form a uniform and continuous film on the surface of the sand grains. The concentrated sodium silicate solution is then added to the sand mass in a second, separate step and the sodium silicate then mixed with the colloidal silica film on the surface of the sand, gelling in situ to form an intimately and uniformly mixed binder within the sand mass. The sand mix thus formed in the mixer can be molded by any of the various processes available in foundry practice and hardened to form strong molds or cores. 

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