Zinc-dust

Zinc dust offers corrosion protection to steel via four mechanisms  

Cathodic protection to the steel substrate (the zinc acts as a sacrificial anode). This takes place at the beginning of the coating s lifetime and naturally disappears with time [86]. 

Barrier action. As a result of the zinc sacrificially corroding, zinc ions are released into the coating. These ions can react with other species in the coating to form insoluble zinc salts. As they precipitate, these salts fill in the pores in the coating, reducing permeability of the film [84]. 

Slightly alkaline conditions are formed as the zinc corrodes [86]. For this reason, of course, only binders that tolerate some degree of alkalinity must be used. 

Of these four mechanisms, the first two depend on a high zinc content to work properly the last two are independent of zinc content. 

A trade name is Zinc Dust Ultra 25 and 35 (Lindgens Sohne, Germany). 

Property Zinc dust Ultra 25 Zinc dust Ultra 35 

Lead powder can be combined with many binders [5.165], [5.166], It does not affect the stability or viscosity of the paint. Binders that absorb only small amounts of water are particularly suitable (e.g., epoxy resins, chlorinated rubber). When formulating paints based on lead powder, care must be taken not to dilute it with other pigments and extenders by more than 5 vol%. 

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It is prepared commercially by treating benzene diazonium chloride with sodium sulphite and then reducing the mixture with zinc dust and ethanoic acid. It can also be prepared by reduction of benzene diazonium chloride with SnCl. ... 

If a solid sulphite is heated with zinc dust (or carbon) the sulphite is reduced to sulphide ... 

Because of its resistance to corrosion, zinc may be used to coat iron. This may be done by dipping the iron into molten zinc or by spraying zinc on the iron articles, for example iron sheets. This is known as galvanising. Smaller iron articles may be coated by heating with zinc dust, a process known as sherardising, or suspensions of zinc may be used in paints. 

Zinc oxide or zinc white is used in paints, but more preferable, because of its better covering power, is lithopone (a mixture of zinc sulphide and barium sulphate). Both paints have the advantage over white lead that they do not blacken in air (due to hydrogen sulphide). Zinc dust and also zinc chromate are constituents of... 

Required Hydrazobenzene, lo g. zinc dust, lo g. HYDRAZOBENZENE. The above preparation of benzidine... 

Add 10 g. of the crude hydrazobenzene to 80 ml. of ethanol contained in a flask fitted with a reflux water-condenser. Heat the mixture on a water-bath until the ethanol bolls, and then add 10 g. of zinc dust and 30 ml. of 30% aqueous sodium hydroxide solution. Remove the flask from the water-bath and shake the contents vigorously from time to time. After about 10 minutes, replace the flask on the water-bath and boil the contents for 3-5 minutes. Filter the mixture at the pump, transfer the filtrate to a beaker and cool in ice-water with stirring. The hydrazobenzene separates as colourless crystals, which are filtered off at the pump and drained. A portion when dried in a desiccator has m.p. 124°. 

Preparation of REAOENTS.t It is essential for this preparation that the zinc powder should be in an active condition. For this purpose, it is usually sufficient if a sample of ordinary technical zinc powder is vigorously shaken in a flask with pure ether, and then filtered off at the pump, washed once with ether, quickly drained and without delay transferred to a vacuum desiccator. If, however, an impure sample of zinc dust fails to respond to this treatment, it should be vigorously stirred in a beaker with 5% aqueous sodium hydroxide solution until an effervescence of hydrogen occurs, and then filtered at the pump, washed thoroughly with distilled water, and then rapidly with ethanol and ether, and dried as before in a vacuum desiccator. The ethyl bromoacetate (b.p. 159 ) and the benzaldehyde (b.p. 179 ) should be dried and distilled before use. 

Required Ethyl acetoacetate, 20 g. sodium nitrite, 5 4 g. zinc dust, 11 g. glacial acetic acid, 60 ml. 

After 3 hours, replace the separating-funnel by a reflux condenser, and the thermometer by a stopper. Add 11 g. of zinc dust in small portions by rapid removal of the stopper at such a rate that the liquid is first brought to the boil (usually about 2 portions of 2 g. each) and is then maintained gently boiling. A ooid too rapid addition of the zinc, otherwise the reaction will become too vigorous, and rapid immersion of the flask in ice-water will be necessary to control the effervescence. 

Preparation of the Reagent. Grind thoroughly together in a dry mortar 25 g. of pure anhydrous ( Analar ) sodium carbonate and 50 g. of the purest obtainable zinc dust. Preserve the reagent in a wide-necked stoppered bottle until required. 

Zinc dust of good quality usually contains only negligible quantities of halogen and sulphur, and is nitrogen-free. A blank for these elements should, however, be made with every fresh batch of reagent prepared if perceptible traces of halogen or sulphur are present, a blank or control test must be performed side by side with that on the organic compound, and the results compared. 

Pure aniline has a b.p. of 184°. When freshly distilled it is a colourless liquid, but becomes discoloured on standing, particularly when exposed to light owing to atmospheric oxidation. The colour may usually be removed by distillation from a little zinc dust. 

Method 2. In a 500 ml. round-bottomed flask, equipped with a reflux condenser, place 20 5 g. (20 ml.) of anUine, 21 5 g. (20 ml.) of acetic anhydride, 21 g. (20 ml.) of glacial acetic acid, and 01 g. of zinc dust (1), Boil the mixture gently for 30 minutes, and then pour the hot Uquid in a thin stream into a 1 Utre beaker containing 500 ml. of cold water whilst stirring continually. When cold (it is preferable to cool in ice), filter the crude product at the pump, wash with a Uttle cold water, drain well and dry upon filter paper in the air. The yield of acetaniUde, m.p. 113°, is 30 g. It may be recrystaUised as in Method 1 aflFording 21 g, of pure acetaniUde, m.p. 114°. 

When pyridine is treated with zinc dust and acetic anhydride, a type of reductive coupling occurs and the product is diacetyltetrahydrodipyridyl (I) this undergoes a curious change on heating yielding pyridine and a new diacetyl compound, 1 4 diacetyl 1 4-dihydropyridine (II). The latter is reduced by zinc and acetic acid to 4-ethylpyridine (III). 

Reduction of 3-Nitro-2-cholestene. - Zinc dust (dOOmg) was added in portions during 1 hr to a stirred warm (4(fC) suspension of 250 mg of 3-nitro-2-cholestene in 15mL of acetic acid and 0.5 ml of water. After 4 hr reflux, the mixture was Altered hot and the zinc washed well with hot HOAc. Addition of water and extraction with ether gave 116mg of product."... 

In the flask were succesively placed 0.10 mol of the sulfinate (note 2), 25 ml of dry, pure HMPT (note 3), 4 g of powdered sodium iodide, 40 g of zinc dust and some boiling stones. After swirling for a few seconds the flask was connected with the other parts of the distillation apparatus, the system was evacuated immediately by means of the water pump (note 4) and the flask was then heated cautiously (free flame). A vigorous reaction started suddenly and the cumulene and part of the HMPT passed over. When the distillation had stopped completely... 

Bromo-2-nitrophenylacetic acid (26 g, 0.10 mol) was dissolved in a mixture of 50% HjSO (400 ml) and ethanol (600 ml) and heated to 90°C. Over a period of 1 h, zinc dust (26.2 g, 0.40 mol) was added. slowly and then heating was continued for 2 h. The excess ethanol was removed by distillation. The solution was cooled and filtered. The filtrate was extracted with EtOAc. The filtered product and extract were combined, washed with 5% NaCOj and brine and then dried (MgSO ). The solvent was removed in vacuo and the residue recrystallized from methanol to give 20.5 g (97% yield) of the oxindole. 

Reduction of A-4-thiazoline-2-one by zinc dust gives low yields of the corresponding thiazoles (36, 231). The formation of thiochrome (95) results from an intramolecular nucleophilic attack (Scheme 47) (232). 

Mesalamine. Rowasa, Asacol, and Pentasa are trade names for mesalamine [89-57-6] (5-ASA, 5-amino-2-hydroxybenzoic acid). It is a white to pinkish crystalline substance that is slightly soluble in cold water and alcohol, more soluble in hot water, and soluble in hydrochloric acid. It may be prepared by the reduction of y -nitrobenzoic acid with zinc dust and HCl. 

Hydroxyisoquinolines. Hydroxy groups in the 5-, 6-, 7-, and 8-position show phenoHc reactions for example, the Bucherer reaction leads to the corresponding anainoisoquinolines. Other typical reactions include the Mannich condensation, azo-coupling reactions, and nitrosation. Both 0-methyl and /V-methyl derivatives are obtained from the methylation of 1-hydroxyisoquinoline, indicating that both tautomeric forms are present. Distillation of various hydroxy compounds, eg, 1- and 4-hydroxyisoquinoline, with zinc dust removes the oxygen. Treatment of 1-isoquinolinol with phosphoms tribromide yields 1-bromoisoquinoline [1532-71 -4] (178). 

The most significant chemical property of zinc is its high reduction potential. Zinc, which is above iron in the electromotive series, displaces iron ions from solution and prevents dissolution of the iron. For this reason, zinc is used extensively in coating steel, eg, by galvanizing and in zinc dust paints, and as a sacrificial anode in protecting pipelines, ship hulls, etc. 

Zinc hydrosulfite (zinc dithionite) is a powerhil reducing agent used in bleaching paper and textiles it is prepared from zinc dust and sulfur dioxide ... 

Copper sulfate, in small amounts, activates the zinc dust by forming zinc—copper couples. Arsenic(III) and antimony(TTT) oxides are used to remove cobalt and nickel they activate the zinc and form intermetaUic compounds such as CoAs (49). Antimony is less toxic than arsenic and its hydride, stibine, is less stable than arsine and does not form as readily. Hydrogen, formed in the purification tanks, may give these hydrides and venting and surveillance is mandatory. The reverse antimony procedure gives a good separation of cadmium and cobalt. 

Ref. 66. Zinc dust, gross weight waste and scrap, gross weight dross and skimmings = zinc content. ... 

Zinc dust, light metal alloys, desilvering lead, bronze and brass powders, zinc chemicals. 

Zinc Dust. 1 LJ.S. production and imports are given in Table 17 (65), distribution of consumption in Table 18 (2). The slight decline since 1970 ... 

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