Phosphate-fluoride treatment

Modified phosphate-fluoride treatment As a result of questionable durability of the bonds made using the phosphate-fluoride process, a modified phosphate-fluoride process was introduced. In this process 0.75% sodium sulfate is added to the conversion coating solutions and this stabilizes the oxide formed. Even with this modification, the improvement over the phosphate-fluoride process is minimal. 

T. J. St. Clair (MASA Langley Re6eaAch CentoX) The PASA-JELL 107 method was used for cleaning all of adherends used in the presented work. The phosphate-fluoride treatment was studied in our lab and was found to give the same lap shear results at room temperature on the systems that were tested. 

More recent work with the PPQ in Eq. (3) has involved chromic acid and phosphoric acid anodized Ti surface treatments, which result in better moisture resistance but less thermal resistance than the surface from phosphate fluoride treatment. Chromic acid anodized Ti TSS provided strengths of 5000 psi at 25°C (cohesive failure), 2,000 psi at 232°C after 5,000 hours at 232°C in air (mixed failure) and low strengths at 232°C after 10,000 hours at 232°C in air (100% adhesive failure).An anodized Ti surface degrades when bonding temperatures approaching 370 C are employed. This may have been one of the factors which caused lower strengths at 232 C after aging. 

Chemical acid etch plus phosphate-fluoride treatment... 

The anodic oxidation of magnesium does not normally produce a film that has sufficient corrosion resistance to withstand exposure without further protection by painting, and the solutions used are complex mixtures containing phosphates, fluorides and chromates. In the case of aluminium, a relatively simple treatment produces a hard, compact, strongly adherent film of oxide, which affords considerably increased protection against corrosive attack . 

Contaminated water from the phosphate fertilizer subcategory A is collected in gypsum ponds and treated for pH adjustment and control of phosphorus and fluorides. Treatment is achieved by double liming or a two-stage neutralization procedure, in which phosphates and fluorides precipitate out [7]. The first treatment stage provides sufficient neutralization to raise the pH from 1 to 2 to a pH level of at least 8. The resultant effectiveness of the treatment depends on the... 

The general sequence of surface preparation for ferrous surfaces such as iron, steel, and stainless steel consists of the following methods degreasing, acid etch or alkaline clean, rinse, dry, chemical surface treatment, and priming. The chemical surface treatment step is not considered a standard procedure, but it is sometimes used when optimum quality joints are required. It consists of the formation of a corrosion-preventing film of controlled chemical composition and thickness. These films are a complex mixture of phosphates, fluorides, chromates, sulfates, nitrates, etc. The composition of the film may be the important factor that controls the strength of the bonded joint. 

Treatment. Aluminum sulfate, aluminum chloride, calcium aluminate, calcfum catboiv ate, and defluoridated phosphate are recommended to reduce absorption of fluoride. Treatment is ineffective once dental aixi skeletal lesions have developed. 

Antacids—The nonabsorbable types of these compounds, such as aluminum hydroxide, may form insoluble complexes in the intestine, which reduce the absorption of phosphate, fluoride, and other essential minerals. Also, it recently became apparent that certain patients with kidney diseases who had been put on diets low in phosphate and who were given regular dialysis treatments absorbed considerable amounts of aluminum from antacids, because they developed toxic deposits of the metal in the brain and the bones. ... 

The effect of a 3-day water boil on the strength of adhesive specimens of the PPQ in structure 4 is summarized in Table 6. The phosphate fluoride surface treatment is sensitive to moisture and this is reflected in low strengths after 3-day water boil. The anodized surface is significantly more resistant to moisture than the phosphate fluoride surface, but the PPQ apparently absorbed water after the 3-day water boil and became plasticized, exhibiting what appeared to be thermoplastic failure at 288 C. This was surprising since PPQs gen-... 

Beside the chemical treatment, anodizing is an effective treatment method too. The magnesium part is the anode in an electrochemical cell and dissolves into magnesium ions. Together with electrolyte, a defined oxide and hydroxide layer is formed on the magnesium surface. If phosphates, fluorides, sflicates, or chromates are present in the electrolyte they will be incorporated into the surface layer. 

Chromium Phosphate. Chromium phosphate treatment baths are strongly acidic and comprise sources of hexavalent chromium, phosphate, and fluoride ions. Conversion coating on aluminum precedes by the foUowing reactions (24) ... 

Although tetrafluorosilane can be readily produced by the action of hydrogen fluoride on sihca, its production is a by-product of HF production by the reaction of fluorospar and sulfuric acid and as a by-product from phosphate fertilizer production by the treatment of fluoroapatite with sulfuric acid (171). The most significant U.S. production is by IMC-Agrico at Uncle Sam, Louisiana. 

The SEM ester was used to protect a carboxyl group where DCC-mediated esterification caused destruction of the substrate. It was formed from the acid and SEM chloride (THF, 0°, 80% yield) and was removed solvolytically. The ease of removal in this case was attributed to anchimeric assistance by the phosphate group. Normally SEM groups are cleaved by treatment with fluoride ion. Note that in this case the SEM group is removed considerably faster than the phenyl groups from the phosphate. ... 

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

Acid treatments The principal acid processes were developed in the USA under the name Alodine, and are marketed in the UK as Alocrom and under other names. The original solutions were based on acid solutions containing phosphate, chromate and fluoride ions. Immersion for up to 5 min in the cold or warm solution leads to the deposition of a greenish film containing the phosphates of chromium and aluminium, and possibly some hexavalent chromate. The more recent Alocrom 1 200 process uses an acid solution containing chromate, fluoride and nitrate. Room-temperature immersion for 15 s to 3 min deposits golden-brown coatings which contain chromate as a major constituent. 

A large number of electrolytic treatments of magnesium, anodic or a.c., have been developed, in which adherent white or grey films consisting of fluoride, oxide, hydroxide, aluminate or basic carbonate are deposited from alkaline solutions containing caustic alkali, alkali carbonates, phosphates, pyrophosphates, cyanides, aluminates, oxalates, silicates, borates, etc. Some films are thin, and some are relatively thick. All are more or less absorbent and act as good bases for paint, though none contributes appreciable inhibition. All can, however, absorb chromates with consequent improvement of protective efficiency. 

The next major obstacle is the successful deprotection of the fully protected palytoxin carboxylic acid. With 42 protected functional groups and eight different protecting devices, this task is by no means trivial. After much experimentation, the following sequence and conditions proved successful in liberating palytoxin carboxylic acid 32 from its progenitor 31 (see Scheme 10) (a) treatment with excess 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in ie/t-butanol/methylene chloride/phosphate buffer pH 7.0 (1 8 1) under sonication conditions, followed by peracetylation (for convenience of isolation) (b) exposure to perchloric acid in aqueous tetrahydrofuran for eight days (c) reaction with dilute lithium hydroxide in H20-MeOH-THF (1 2 8) (d) treatment with tetra-n-butylammonium fluoride (TBAF) in tetrahydrofuran first, and then in THF-DMF and (e) exposure to dilute acetic acid in water (1 350) at 22 °C. The overall yield for the deprotection sequence (31 —>32) is ca. 35 %. 

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