Calcium phosphate cleaning

When freshly mixed, the carboxyHc acid groups convert to carboxjiates, which seems to signify chemical adhesion mainly via the calcium of the hydroxyapatite phase of tooth stmcture (32,34—39). The adhesion to dentin is reduced because there is less mineral available in this substrate, but bonding can be enhanced by the use of minerali2ing solutions (35—38). Polycarboxylate cement also adheres to stainless steel and clean alloys based on multivalent metals, but not to dental porcelain, resin-based materials, or gold alloys (28,40). It has been shown that basic calcium phosphate powders, eg, tetracalcium phosphate [1306-01-0], Ca4(P0 20, can be substituted for 2inc oxide to form strong, hydrolytically stable cements from aqueous solution of polyacids (41,42). 

Crucibles fitted with permanent porous plates are cleaned by shaking out as much of the solid as possible, and then dissolving out the remainder of the solid with a suitable solvent. A hot 0.1 M solution of the tetrasodium salt of the ethylenediaminetetra-acetic acid is an excellent solvent for many of the precipitates [except metallic sulphides and hexacyanoferrates(III)] encountered in analysis. These include barium sulphate, calcium oxalate, calcium phosphate, calcium oxide, lead carbonate, lead iodate, lead oxalate, and ammonium magnesium phosphate. The crucible may either be completely immersed in the hot reagent or the latter may be drawn by suction through the crucible. 

Sample preparation is rather involved. A sample of urine or fecal matter is obtained and treated with calcium phosphate to precipitate the plutonium from solution. This mixture is then centrifuged, and the solids that separate are dissolved in 8 M nitric acid and heated to convert the plutonium to the +4 oxidation state. This nitric acid solution is passed through an anion exchange column, and the plutonium is eluted from the column with a hydrochloric-hydroiodic acid solution. The solution is evaporated to dryness, and the sample is redissolved in a sodium sulfate solution and electroplated onto a stainless steel planchette. The alpha particles emitted from this electroplated material are measured by the alpha spectroscopy system, and the quantity of radioactive plutonium ingested is calculated. Approximately 2000 samples per year are prepared for alpha spectroscopy analysis. The work is performed in a clean room environment like that described in Workplace Scene 1.2. 

In-Service Cleaning Involving the Removal of Calcium Phosphate, Calcium Sulfate, or Silica... 

Column cleaning is performed with high concentrations of phosphate buffer, with nonionic detergents, urea, and sodium hydroxide to restore the complex structure of calcium phosphate. 

Many remineralisation models mimic the situation found on smooth enamel surfaces in the mouth, i.e. appropriate salivary calcium, phosphate and fluoride concentrations and a clean enamel surface with no plaque analogue. Remineralisation of enamel lesions typically occurs during exposure to experimental solutions at neutral pH, whereas demineralisation occurs during exposure to acidic buffers. However, when good oral hygiene is maintained and with the use of fluoride toothpastes, caries is prevalent not on the smooth surfaces of the teeth but on those sites which are difficult to clean and where plaque tends to accumulate i.e. occlusal fissures and approximal surfaces [36], Here, caries is initiated and progresses not on a clean, smooth surface exposed to saliva, but... 

Virtually all dentifrice formulations contain abrasive particles, typically composed of amorphous silica, calcium carbonate, alumina or calcium phosphate. The mechanism by which the toothbrush and dentifrice interact to clean the teeth is one of abrasive cleaning. Toothpaste manufacturers thus aim to provide formulations with effective cleaning power, whilst minimising any wear to the underlying substrate. However, in such a system it is inevitable that some degree of abrasivity will be present, as toothpastes without abrasive particles are unable to prevent the build-up of extrinsic stain [12], It is, therefore, important to understand any abrasion a dentifrice product may cause to the hard tissues in the mouth. 

Normal human serum actually contains two chromatographically distinct forms of ceruloplasmin. A calcium phosphate column cleanly separates major (I) and minor (II) components, the latter being approximately 15% of the total ceruloplasmin present in the serum (109—111). Ryden (112, 113) has shown that the two forms though identical in amino acid composition and Cu binding capacity, differ in the degree to which carbohydrate components have been affixed to the protein during biosynthesis. Most of the presently accepted physical properties of human ceruloplasmin are presented in Table 2. 

About 264,000 metric tons of elemental capacity is available in North America, plus another 79,000 t (P equivalent) of purified wet phosphoric acid (14). About 85% of the elemental P is burned to P2 5 hydrated to phosphoric acid. Part of the acid (ca 21%) is used direcdy, but the biggest part is converted to phosphate compounds. Sodium phosphates account for 47% calcium, potassium, and ammonium phosphates account for 17%. Pinal apphcations include home laundry and automatic dishwasher detergents, industrial and institutional cleaners, food and beverages, metal cleaning and treatment, potable water and wastewater treatment, antifree2e, and electronics. The purified wet acid serves the same markets. 

NOTE If the BW contains phosphate, the preferred reaction is for calcium to precipitate as hydroxyapatite, rather than to chelate with EDTA or NTA (a further competing anion effect). Consequently, there would seem to be no valid reason to produce combined phosphate-chelant programs, with the chelant acting as a reserve against unforeseen hardness incursions caused by a softener leakage, or other source. In practice, the chelant acts to solubilize existing deposits, producing a very clean boiler. 

Traditional methods for in-service cleaning of calcium salts such as phosphate and sulfate (which are not particularly amenable to simple acid-cleaning procedures) have often employed EDTA or NTA chelant-based formulations, together with ingredients such as phosphonate and polyacrylate. 

Calcination. Phosphate rock normally is used as a dry rock or in slurry form. However, in some cases, particularly where the raw phosphate is high in carbonaceous matter or it is desirable to have a clean acid, the rock is calcined. Also, in a few cases, the phosphate rock is calcined, the product slaked, and free lime separated as a beneficiation step. Calcination is energy intensive and produces a less reactive rock and, in some cases, a less filterable gypsum. Therefore, the use of calcination is diminishing, and is being replaced by a wet oxidation step to produce green acid.16 In separating calcium carbonate, flotation, where it is successful, is favored over calcination because of its lower cost. 

Citric acid is used in soft drinks, candies, wines, desserts, jellies, jams, as an antioxidant in frozen fruits and vegetables, and as an emulsifier in cheese. As the most versatile food acidulant, citric acid accounts for about 70 percent of the total food acidulant market. It provides effervescence by combining the citric acid with a biocarbonate/carbonate source to form carbon dioxide. Citric acid and its salts are also used in blood anticoagulants to chelate calcium, block blood clotting, and buffer the blood. Citric acid is contained in various cosmetic products such as hair shampoos, rinses, lotions, creams, and toothpastes. More recently, citric acid has been used for metal cleaning, substituted for phosphate in detergents, for secondary oil recovery, and as a buffer/absorber in stack gas desulfurization. The use of sodium citrate in heavy-duty liquid laundry detergent formulations has resulted in a rapid increase in the use of citric acid. 

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