Sodium oxide flux

Soda (composed of sodium oxide) and potash (composed of potassium oxide) are relatively easy to obtain or to make, work, and handle. Although they do not occur naturally, they could be quite easily prepared in the past by burning some plants (see Textbox 28). Both these oxides were used as fluxes for making early types of glass articles, particularly small vessels and decorative objects. 

Other oxides such as sodium oxide, potassium oxide, and lead oxide are fluxes. They lower the melting point of the silicon dioxide. 

Molten solutions can also be used for crystallization. Fluxes are selected that have a high solubility of the to-be crystallized material. Borate fluxes are used for some oxide systems, sodium sulfide fluxes are used for sulfide systems, and molten metal fluxes are used for carbide and nitride systems. In both the melt and flux systems, the solubility is highly temperature dependent. The solubility in flux systems is not particularly well known except for a few systems. The general solubility behavior is like that in liquid phase precipitation, which was discussed in Chapter 6. In melt solidification, the supersaturation, S, is given by... 

Crystals of Na4Mno.5Po.5O5, a mixed-metal Mn(VII)/P(V) oxide, were synthesized via a sodium hydroxide flux. ... 

Different fluxes can be used. Basic fluxes employed for the attack of acidic materials include carbonates, hydroxides, peroxides, and borates. Oyrosulfates can be used as acidic flux. If an oxidizing flux is required, sodium peroxide can be used. As an alternative, small quantities of alkali nitrates or chlorates can be mixed with sodium carbonate. Basic and acidic fluxes are dissolved in an acid or basic medium, respectively. 

When fluxing action is needed during melting, and glass with high thermal expansion is undesirable, boric oxide is added forming borosilicate glasses, which have lower thermal expansion and improved resistance to attack by aqueous solutions because of lower sodium oxide contents. 

Boron oxide Calcium fluoride Lead oxide, red Sodium nitrate flux, ceramic glazes Aluminum fluoride flux, ceramics Aluminum orthophosphate flux, copper soldering Triethylamine flux, enamels... 

Its principle is based on the use of a solid/liquid reaction between the oxidizing flux (Pb0-B202) and the sodium diluted in a metal (formation of an alloy with lead) which is inert to the oxidizing function. The violent nature of the oxidation reaction does not allow direct interaction between liquid sodium and the flux in the solid state. 

They readily dissolve metal oxides and are effective metal surface cleaners and fluxes (see Metal surface treatments). They also have bactericidal and fungicidal properties (74). However, the main commercial appHcation among monofluorophosphates is of sodium monofluorophosphate ia dentifrices. 

Scrap that is unsuitable for recycling into products by the primary aluminum producers is used in the secondary aluminum industry for castings that have modest property requirements. Oxide formation and dross buildup are encountered in the secondary aluminum industry, and fluxes are employed to assist in the collection of dross and removal of inclusions and gas. Such fluxes are usually mixtures of sodium and potassium chlorides. Fumes and residues from these fluxes and treatment of dross are problems of environmental and economic importance, and efforts are made to reclaim both flux and metal values in the dross. 

Another large appHcation is as an ingredient in the production of charcoal briquettes. The amount of sodium nitrate used in charcoal briquette manufacture depends on the type and amount of wood and coal used. Typically charcoal briquettes contain up to almost 3% sodium nitrate. Sodium nitrate is also used in the manufacture of enamels and porcelain as an oxidizing and fluxing agent. In porcelain—enamel frits used for metal coating, the amount of sodium nitrate in a batch varies with the various metal bases to be coated, typically from about 3.8 to 7.8 wt %. 

The fluorine industry is intimately related to aluminum production. Aluminum oxide, (AljOj) is electrolyzed to metallic aluminum with a flux of sodium fuoroaluminate (Na AlF,), called cryolite - a rare mineral found in commercial quantities only in Greenland with other uses glass, enamels, and as a filler for resin-bonded grinding wheels. 

Oxidation tests on Nimonic 90A, in which sodium chloride was introduced into the atmosphere, showed that this constituent produces a significant deterioration in the protective nature of the normally adherent film. Although under certain service conditions the presence of sodium chloride is likely, this is not always so, and thus the general applicability of the results of laboratory tests in sodium sulphate and mixtures involving sodium chloride may be questioned. Test procedures for hot-salt corrosion have been reviewed by Saunders and Nicholls who concluded that burner rig testing is the most appropriate procedure provided contaminant flux rates similar to those found in an operating turbine are used in the rig. 

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