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Mechanisms and Modes of Action in Flame Retardancy of Polymers
Published in Yuan Hu, Xin Wang, Flame Retardant Polymeric Materials, 2019
A substantial class of important polymers, such as polyesters and polyamides, containing oxygen and/or nitrogen, char poorly in the pure form, but can be induced to char by appropriate additives, most commonly, acid-generating additives. Additives that generate volatile acids such as hydrochloric are not especially effective because the acid is immediately volatilized. Less volatile is sulfuric acid, but it too is partially lost by volatilization. Sulfuric acid and its thermally decomposed derivatives such as ammonium sulfate or ammonium sulfamate are effective in polymers that char rapidly, such as cellulose, but are lost too soon in slow-charring polymers. The ideal acid for catalyzing char in burning oxygen- or nitrogen-containing polymers are phosphoric acids or polyphosphoric acids, which are substantially non-volatile. Since the acids are usually not suitable as polymer additives, thermally decomposable salts and esters of phosphorus acids are used. These represent one of the leading classes of flame retardants, used in a wide variety of charrable polymers. Further on, we will discuss how these same phosphorus compounds can be used in non-charrable or poorly charrable polymers. The leading char-inducing phosphorus compounds are ammonium phosphates (water soluble), ammonium polyphosphates (both water soluble and insoluble types), melamine phosphate, melamine pyrophosphate, melamine polyphosphate, ethylenediamine phosphate, piperazine pyrophosphate (insoluble polymer), and a wide variety of phosphate and phosphonate esters, which are discussed in other chapters.
Flame Retardance of Fabrics
Published in Menachem Lewin, Stephen B. Sello, Handbook of Fiber Science and Technology: Chemical Processing of Fibers and Fabrics, 2018
Sulfation-Phosphorylation: Sulfation of cellulose with ammonium sulfamate (AS) in the presence of urea or urea-based cross-linking agents imparts to cellulose an excellent flame resistance that is durable to over 50 alkaline soft- and hard-water launderings [206, 207, 207a]. A weight gain of ~10% corresponding to 3% bound sulfur was found necessary to obtain this effect. When bis(methoxymethyl)uron was used as cross-linking agent together with AS, the wash-and-wear rating increased from 1 to 2.5–3.0 after 25 launderings. The sulfated fabrics exhibited a high degree of afterglow, e.g., 60 sec before laundering and 300 sec after 10 launderings [207]. It was shown that this severe afterglowing could be overcome by the addition of phosphorus either by aftertreatment with DAP, which is not durable, or by a combined and simultaneous sulfation and phosphorylation treatment with ammonium sulfamate and phosphorus triamide. A ratio of P:S of 1.1:1 was needed to suppress the afterglow to less than 30 sec after 50 launderings in water with high Ca or high Na content, whereas a ratio of 1.3:1 was needed to eliminate afterglow completely, in both cases with full flame resistance (LOI 29–32) retained (see Fig. 1.25). PA reacts much more rapidly with cellulose than AS, as can be seen in Fig. 1.27. Phosphorus in the celluloses treated in this manner serves only for glow prevention. Its glow prevention effect is not changed, but the FR effect is lost by ion exchange, whereas the FR is maintained by the combined sulfur.
Product: Alfa-Tox
Published in Charles R. Foden, Jack L. Weddell, First Responder’s Guide to Agricultural Chemical Accidents, 2018
Charles R. Foden, Jack L. Weddell
FIRST AID Eye ExposureIf ammonium sulfamate gets into the eyes, flush with water for at least fifteen minutes. Lift the lower and upper lids occasionally. Contact lens should not be worn when working with this chemical. If irritation persists get medical attention.Skin ExposureIf ammonium sulfamate gets onto the skin, flush area with water. If irritation appears get medical advice.BreathingIf ammonium sulfamate dust is liberated into the air, move victims from area to fresh air.SwallowingIf ammonium sulfamate is ingested give person large amounts of water and get medical attention.
The Direct Leaching of Nickel Sulfide Flotation Concentrates – A Historic and State-of-the-Art Review Part I: Piloted Processes and Commercial Operations
Published in Mineral Processing and Extractive Metallurgy Review, 2023
Nebeal Faris, Mark I. Pownceby, Warren J. Bruckard, Miao Chen
In the Sherritt-Gordon Process, base metals are dissolved from the sulfide mineral particles by reaction with oxygen, water and ammonia; ferrous iron is oxidized and precipitated as hydrous ferric oxide (Forward 1953; Forward and Mackiw 1955). Sulfidic sulfur (S2-) is oxidized to thiosulfate (S2O32-) which then undergoes further oxidation by dissolved oxygen in solution to ultimately form sulfate (SO42-) and sulfamate (NH2SO32-) via a series of sequential reactions involving intermediates such as trithionate (S3O62-) (Forward 1953; Forward and Mackiw 1955). Dissolved copper in solution is believed to play a catalytic role in oxidation of thiosulfate to trithionate, sulfate and sulfamate (Forward 1953). Batch leaching tests by Forward (1953) showed that the nickel dissolution rate was influenced by factors such as temperature, oxygen partial pressure and free ammonia concentration; 95% of Ni could be extracted in under an hour by leaching at 220°F (104.4°C). Higher leaching temperatures and oxygen partial pressures, and longer retention times favor the oxidation of thiosulfate and trithionate to sulfate and sulfamate, however, a key aspect of the Sherritt-Gordon process is the retention of a portion of the unsaturated sulfur containing ions in solution for subsequent copper removal (Forward 1953; Forward and Mackiw 1955). Copper removal is achieved by boiling the solution (termed “copper boil”), where Cu(II) ions react with thiosulfate and trithionate in solution, precipitating copper as covellite (CuS) and chalcocite (Cu2S) (Forward 1953; Forward and Mackiw 1955). Precious and platinum group metals present in nickel matte are reported to be partially extracted during ammoniacal pressure leaching and are subsequently precipitated during the “copper boil” stage, reporting to the copper sulfide precipitate (Wishaw 1993). The copper-free solution produced from the ‘copper boil’ is treated in an autoclave at 245°C and air pressure of 4100 kPa to destroy residual unsaturated sulfur compounds and ammonium sulfamate present in solution (termed oxydrolysis) prior to metallic nickel recovery by pressure hydrogen reduction (Forward 1953; Wishaw 1993). The oxydrolysis step is necessary to prevent sulfur contamination in the final nickel product and to remove sulfamate, which is a herbicide and would not be permissible in the final ammonium sulfate by-product if used as a fertilizer (Wishaw 1993). The final products from the Sherritt-Gordon process are metallic nickel powder or briquettes, cobalt metal powder, briquette or sulfide precipitate, and ammonium sulfate (Forward 1953; Wishaw 1993).