Zinc oxide thickener

Below about 200°C, the film grows very slowly and is invisible and very adherent. It is often said that the first layer formed governs the corrosion resistance of the zinc throughout its life. If the film becomes too thick, it is liable to break away or become porous, when, of course, it ceeises to provide protection. Moreover, zinc oxide occupies a larger volume than the zinc from which it originated and, as the layer thickens, strains are set up which lead to the production of fissures. 

In its resistance to liquid metals, titanium shows variable behaviour, the rate of attack often depending upon temperature and increasing with rise in temperature. By thickening the surface film of oxide, resistance to attack is enhanced, and, for example, repeated repair of the surface film renders titanium resistant, on a limited-time basis, to molten zinc in galvanising baths. A surface-oxide thickening technique also enables titanium to be employed in contact with molten aluminium. Titanium equipment is also used in applications involving lead-tin solders, and it is resistant to mercury, at least up to 150 C. 

A mixture of 15 gms. of phthalic anhydride and 22 gins, of resorcinol is ground in a mortar. It is then transferred to a nickel or cast-iron vessel, and heated in an oil bath to 180°. At this temperature 7 gms. of powdered fused zinc chloride (see p. 509) are added, with stirring, during the course of 10 minutes. The temperature is raised to 210°, and maintained at this point until the liquid, which gradually thickens, becomes solid, for which 1—2 hours are required. The cold melt is removed from the vessel with a knife or chisel, powdered, and boiled 10 minutes with 200 c.cs. of water and 10 c.cs. of cone, hydrochloric acid. This treatment eauses the solution of zinc oxide and basic zinc chloride. The fluorescein is filtered off, washed with water until the filtrate no longer shows an acid reaction it is dried on a water bath. 

Subacute EmoElients are the mainstay of treatment. Zinc oxide cream or paste, with mild keratolytic if skin thickening present (salicylic add or coal tar added) topical corticosteroid ointment. Gamolenic acid (Epogam, evening primrose oil) is of unproven benefic. 

The first liquid foundations were known as neck and arm whiteners. They were developed for use in the theater and were early attempts to improve the characteristics of applied face powder. Early pharmaceutical methods used to develop improved foundations included combinations of calamine lotion, zinc oxide, glycerin, and water. Until the 1940s, foundations were in the form of nonflowing and very greasy pastes and creams (often called grease paint ). The cosmetic industry soon thereafter used different types of emulsifiers and thickeners combined with... 

This chapter describes ionic cross-linldng of the HASE thickener with zinc oxide or zinc ammonium complexes to improve early blister resistance. Zinc ammonium complexes have been used in ammonia-removable latex floor polishes for decades. Paint formulations containing zinc oxide have benefits but are prone to sporadic viscosity instability, which sometimes cannot be predicted by standard laboratory tests. However, many paint manufacturers have learned how to successfully stabilize these zinc oxide-containing latex paints. 

A typical exterior acrylic paint formulation see Appendix A) was thickened with a commercial HASE thickener that contained 5.23 meq/g of carboxylic acid functionality (4). This thickener was modified with 1 to 25 lb (1 lb = 0.4536 kg) of zinc oxide (French process) in the mill base in one set of paints and with post-added zinc ammonium complex such as acetate, carbonate, bicarbonate, or glycinate in another set of paints. 

Zinc Oxide. We found that as little as 5 lb of zinc oxide per 100 gal (1 gal = 3.785 L) of paint was sufiBcient to impart acceptable early blister resistance to the paint when tested in the rain or in the tap water fog box (Table I). Higher zinc oxide levels showed no further blister-resistance improvement in this paint. Blistering in the deionized water fog box was so severe that even the HEC-thickened control had a blister rating of 4D. (The note to Table I explains the rating method used.) However, a noticeable effect occurred at zinc oxide levels of 5 lb/100 gal of paint and higher. The zinc oxide combined with the ammonia in the paint and formed a zinc ammonium complex that may ionically cross-link the carboxyl groups in the HASE thickener and other paint constituents, and thereby reduce the overall water sensitivity of the paint. 

Zinc Ammonium Complexes. The zinc ammonium complexes were tested on a different chalky latex panel than the zinc oxide paints, and the entire series showed less blistering in the same deionized water fog box (Table II). The HEC-thickened control did not blister on this board. The HEUR control showed 7M blisters on this board vs. 2MD (Table I). Addition of the zinc ammonium complexes resulted in much-improved early blister resistance. Blister-resistance effectiveness differed depending on which complex was used. The four zinc ammonium complexes evaluated in the HASE-... 

Table II compares the zinc oxide paint results from all three sources of water. The more stringent deionized water fog box showed that even the HEC-thickened paint blisters badly, as does the HEUR paint, which shows no blistering on exterior exposures. The zinc cross-linked HASE-thickened paints blistered much more in the deionized water fog box than they did in the tap water fog box or in the rain. No significant differences were noted between 5 and 25 lb of zinc oxide per 100 gal of paint.

Ionic cross-linking of the water-sensitive carboxyl groups in the HASE thickeners (and probably other carboxyl groups in the paint) with either low levels of zinc oxide in the mill base or post-added zinc ammonium complexes can be effective in improving the early blister resistance of HASE-thickened latex paints over heavily chalked latex paint surfaces. Of the zinc ammonium complexes evaluated, the zinc ammonium carbonate and bicarbonate ap-... 

Table III. Viscosity Stability of Zinc Oxide-Modified Paints with HASE Thickener...

The viscosity of the zinc oxide cutaneous paste depicted in Table 12.40 is increased by zinc oleate that is formed from zinc ions with free fatty acids from the fatty oil. The preparation may be considered as a cutaneous oleogel of zinc oleate in arachis oil in which the excess zinc oxide is suspended. During preparation the product is stUl fluid. During storage more zinc oleate is created and the product thickens into a semisolid preparation that may be called a weak paste. This paste is used in subacute and chronic eczemas and in intertrigines. 

Clean metallic aluminum is extremely reactive. Even exposure to air at ordinary temperatures is sufficient to promote immediate oxidation. This reactivity is self-inhibiting, however, which determines the general corrosion behavior of aluminum and its alloys due to the formation of a thin, inert, adherent oxide film. In view of the great importance of the surface film, it can be thickened by anodizing in a bath of 15% sulfuric acid (H2SO4) solution or by cladding with a thin layer of an aluminum alloy containing 1 % zinc. 

The mechanism of inhibition by the salts of the long chain fatty acids has been examined . It was concluded that, in the case of the lead salts, metallic lead was first deposited at certain points and that at these points oxygen reduction proceeded more easily, consequently the current density was kept sufficiently high to maintain ferric film formation in addition, any hydrogen peroxide present may assist in keeping the iron ions in the oxide film in the ferric condition, consequently the air-formed film is thickened until it becomes impervious to iron ions. The zinc, calcium and sodium salts are not as efficient inhibitors as the lead salts and recent work has indicated that inhibition is due to the formation of ferric azelate, which repairs weak spots in the air-formed film. This conclusion has been confirmed by the use of C labelled azelaic acid, which was found to be distributed over the surface of the mild steel in a very heterogeneous manner. ... 

A paste of zinc powder and carbon tetrachloride (with kieselguhr as thickener) will readily burn after ignition by a high-temperature primer [1]. Intimate mixtures of chlorinated rubber with powdered zinc (or its oxide) in presence or absence of hydrocarbon or halocarbon solvents react violently or explosively at about 216°C... 

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