Chemical treatment

In wet chemical surface modification, a material is treated with liquid reagents to generate reactive functional groups on the surface. 

Many methods were described for the chemical modification of PET surfaces. Most of them concern chemical breaking of ester bonds by reaction with low molar mass compounds containing hydroxyl or amine groups thus incorporating corresponding functionalities onto the surface. These reactions increase the hydrophilicity of the polymer surface and create anchored functionalities (when difunctional compounds were used) available for subsequent reactions. 

The main problem of these treatments is to find optimal conditions that do not cause severe degradation and significant decrease of mechanical properties of the PET material (films or fibers). 

Normally a chemical treatment of Zerodur is carried out for one of the following purposes  

In the first case a chemical attack of the Zerodur material is desired. In the second case the chemical treatment should not attack the Zerodur material in a noticeable way, only the coating (normally an aluminum layer) is to be dissolved. 

Reduction/Removal of Surface Notch Tensions by Etching 

Hydrofluoric-acid/hydrochloric-acid etching baths are suitable for removing noticeable amounts of material from Zerodur in warrantable times. Microcracks are healed up or removed by this process. Due to the use of hydrochloric acid in the etching bath the formation of fluoride layers which are difficult to dissolve on the surface is not possible these fluoride layers would affect the etching process. 

The stock removal per surface and unit of time at a given temperature changes depending on the composition of the etching bath. The treatment 

Pretreatment of a membrane with certain chemicals can provide enhanced uniformity of the pore system formed during pyrolysis. Among the chemicals commonly used for chemical pretreatment are hydrazine, dimetltyl formamide (DMF), HCl andNH Cl [77]. 

During the manufacture of porous carbon membranes by Schindler and Maier [24], an acrylic precursor was subjected to a pretreatment with an aqueous solution of hydrazine. It was found that the pretreatment improved the dimensional stabihty of the membrane during the subsequent processing steps and, in particular, that the formation and clogging of the pores could be avoided during these steps. Very good results were obtained from the acrylic precmsor using a pretreatment with 80% hydrazine hydrate for 30 min at a solution temperature of 90°C. 

Dining the chemical pretreatment, the membrane is fully immersed in the appropriate solution. After that, the membrane is washed and dried before it is fed to the first treatment station. In certain cases, it has also been proven that it may be advantageous to evacuate the pores of the membrane by applying a low air pressure, and subsequently fill them with nitrogen gas at normal pressure prior to pretreatment with an aqueous solution. In this way, one can obtain membranes of carbon contents higher than those made from the precursors whose pores remained full of air during the pretreatment [24]. 

Another type of chemical pretreatment involves the use of catalysts including mineral acids and acidic salts, such as phosphoric acid and diammonium hydrogen phosphates, before carbonization. However, the preparation of carbon hollow fiber membranes with carbonization catalyst causes problems. In carbon hollow fibers. 

Another method of eatalytic carbonization involves application of a gaseous catalyst such as HCl, or NH Cl in a stream of inert gas. This method leads to two useful results [27]. 

The applicability of chemical treatment to wastes depends on the chmiical properties of the waste constituents, particularly acid-base, oxidation-reduction, precipitation, and complexation behaviors reactivity flammability/combustibility corrosivity and compatibility with other wastes. The chemical behavior of wastes translates to various unit operations for waste treatment that are based on chemical properties and reactions. 

Chemical precipitation is used in hazardous waste treatment primarily for the removal of heavy metal ions from water. The most widely used means of precipitating metal ions is by the addition of base (Ca(OH)2), NaOH, or Na2C03), leading to the formation of hydroxides such as chromium(III) hydroxide 

Coprecipitation, most commonly with iron(III) hydroxide, may be used to remove heavy metals from wastes. An example is removal of lead from lead battery industry wastewater with Fe(OH)3 to which a soluble Fe salt has been added. 

Chemical reduction is less frequently used for waste treatment but does find one important application in treatment of waste containing highly toxic Cr(vi). Commonly employed reducing agents include Fe(ll) salts and sodium metabisulfite (Na2S205). The reduced product, Cr(iii) has a lower toxicity and can be removed from basic solution by filtration. 

The removal of trace metals from effluent streams is common. Several techniques are employed in addition to the physical ones identified above, including precipitation as the sulfide, hydroxide or carbonate followed by filtration. 

In many cases the metal ion is complexed in solution electrochemical reduction is more difficult in these situations but still finds industrial use. Recovery of silver trom photographic fixing processes is of economic importance. In simple terms the waste stream can be described as a solution of complexed silver thiosulfate from which silver metal may be recovered according to Equation (2.3). 

The process must be carefully controlled since under certain conditions 

One of the major limitations of this basic cell is poor mass transfer, particularly at low ion concentrations. Many cell improvements have concentrated on improving mass transfer through, for example, injecting a fine stream of air across the surface of the cathode. 

There are numerous chemical processes for the treatment of wastes that are used in conjunction with other methods. These methods include calcination, precipitation, catalysis, electrolysis, hydrolysis, neutralization, photolysis, cholrinolysis, oxidation, and reduction. 

Calcination. Calcination is a well-established single-step process for the treatment of complex wastes, containing organic and inorganic components in slurries, sludges, tar, and aqueous solutions, by heating at higher temperatures in the absence of air to remove volatiles. 

The real application of this process is the recalcination of lime sludges from water treatment plants, coking of heavy residues and tars from petroleum refinery operations, concentration and volume reduction of liquid, radioactive wastes, and treatment of refinery sludges containing hydrocarbons, phosphorus, and compounds of calcium, magnesium, iron, and aluminum. 

Electrolysis. Electrolysis is a process in which oxidation or reduction reactions take place at the surface of conductive electrodes immersed in an electrolyte under the influence of an applied potential. 

This process can also be applied to radioactive wastes that contain metals in ionic forms. The removal of collected ions from the electrodes is not difficult. These ions can be recycled and reused or can be disposed of. 

To obtain optimum adhesion onto a wide range of materials, chemical treatment of the surface is often recommended. The first action, as with the mechanical treatment, is to remove surface contamination such as grease with a clean solvent. The surface of the material is then modified to provide 

Cast iron Solvent and abrasion carbon nodules in SG cast iron is a problem 

Magnesium and its alloys Dilute silicate/phosphate rinse followed by chromium treatment 

Zinc and galvanized metals Dilute hydrochloric acid treatment 

These chemicals are dangerous, and full protective equipment must be used when carrying out the treatments. The appropriate MSDS must be consulted prior to use. 

Calcium Hypochlorite, also known as High Test Hypochlorite (HTH) is supplied in erystal form it is nearly 70% available chlorine. One produet, the Sanitizer (formally the Sierra Water Purifier) uses these erystals to superehlorinate the water to insure pathogens were killed off, then hydrogen peroxide is added to drive off 

Water treated with iodine can have any objectionable taste removed by treating the water with vitamin C (ascorbic acid), but it must be added after the water has stood for the correct treatment time. Flavored beverages containing vitamin C will 

Potassium permanganate is no longer commonly used in the developed world to kill pathogens. 

Most of the floeculation agent is removed with the floe, nevertheless, some question the safety of using alum due to the toxicity of the aluminum in it. There is little to no seientific evidence to back this up. Virtually all municipal plants in the US dose the water with alum. In bulk water treatment, the alum dose can be varied untU the idea dose is found. The needed dose varies with the pH of the water and the size of the particles. Increase turbidity makes the floes easier to produce not harder, due to the increased number of eollisions between partieles. 

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Primary or pretreatment of wastewater prior to biological treatment involves both physical and chemical treatment depending on the nature of the emission. 

The integral under the heat capacity curve is an energy (or enthalpy as the case may be) and is more or less independent of the details of the model. The quasi-chemical treatment improved the heat capacity curve, making it sharper and narrower than the mean-field result, but it still remained finite at the critical point. Further improvements were made by Bethe with a second approximation, and by Kirkwood (1938). Figure A2.5.21 compares the various theoretical calculations [6]. These modifications lead to somewhat lower values of the critical temperature, which could be related to a flattening of the coexistence curve. Moreover, and perhaps more important, they show that a short-range order persists to higher temperatures, as it must because of the preference for unlike pairs the excess heat capacity shows a discontinuity, but it does not drop to zero as mean-field theories predict. Unfortunately these improvements are still analytic and in the vicinity of the critical point still yield a parabolic coexistence curve and a finite heat capacity just as the mean-field treatments do. 

Hydrocarbons are divided into two mam classes aliphatic and aromatic This classifi cation dates from the nineteenth century when organic chemistry was devoted almost entirely to the study of materials from natural sources and terms were coined that reflected a substance s origin Two sources were fats and oils and the word aliphatic was derived from the Greek word aleiphar meaning ( fat ) Aromatic hydrocarbons irre spective of their own odor were typically obtained by chemical treatment of pleasant smelling plant extracts... 

Gua/aco/ is obtained by chemical treatment of lignum vitae the wood from a species of tree that grows in warm climates It is some times used as an expectorant to help relieve bronchial congestion... 

Although isotope-dilution analysis can be very accurate, a number of precautions need to be taken. Some of these are obvious ones that any analytical procedure demands. For example, analyte preparation for both spiked and unspiked sample must be as nearly identical as possible the spike also must be intimately mixed with the sample before analysis so there is no differential effect on the subsequent isotope ration measurements. The last requirement sometimes requires special chemical treatment to ensure that the spike element and the sample element are in the same chemical state before analysis. However, once procedures have been set in place, the highly sensitive isotope-dilution analysis gives excellent precision and accuracy for the estimation of several elements at the same time or just one element. 

Chemicals from brine Chemical shift reagents Chemical shifts Chemicals in war Chemical treatments... 

Optional chemical treatments include potassium thiocyanate [333-20-0] for FIX and acid/enzyme treatment for IgG (iv). 

Other treatments fall into the three groups (1) summari2ed in Table 5. There are chemical treatments and impregnations which penetrate below the surface of the gemstone. Then there are surface coatings of various types. Finally, there are composite stones. 

Drilling diamonds using a focused laser beam to bum out dark inclusions or make the inclusions accessible to a chemical treatment is a frequent enhancement. In a potential deception, a cubic zirconia diamond imitation was laser drilled to make it more convincing (15). 

The sweet water from continuous and batch autoclave processes for splitting fats contains tittle or no mineral acids and salts and requires very tittle in the way of purification, as compared to spent lye from kettle soapmaking (9). The sweet water should be processed promptly after splitting to avoid degradation and loss of glycerol by fermentation. Any fatty acids that rise to the top of the sweet water are skimmed. A small amount of alkali is added to precipitate the dissolved fatty acids and neutralize the liquor. The alkaline liquor is then filtered and evaporated to an 88% cmde glycerol. Sweet water from modem noncatalytic, continuous hydrolysis may be evaporated to ca 88% without chemical treatment. 

A wide range and a number of purification steps are required to make available hydrogen/synthesis gas having the desired purity that depends on use. Technology is available in many forms and combinations for specific hydrogen purification requirements. Methods include physical and chemical treatments (solvent scmbbing) low temperature (cryogenic) systems adsorption on soHds, such as active carbon, metal oxides, and molecular sieves, and various membrane systems. Composition of the raw gas and the amount of impurities that can be tolerated in the product determine the selection of the most suitable process. 

The lead—copper phase diagram (1) is shown in Figure 9. Copper is an alloying element as well as an impurity in lead. The lead—copper system has a eutectic point at 0.06% copper and 326°C. In lead refining, the copper content can thus be reduced to about 0.08% merely by cooling. Further refining requites chemical treatment. The solubiUty of copper in lead decreases to about 0.005% at 0°C. 

R. W. Murray and J. E. HiUis, "Magnesium Finishing Chemical Treatment and Coating Practices," Society of Automotive Engineers International Congress and Exposition, Paper 900791, Detroit, Mich., 1990. 

However, since the naphthalene produced from petroleum is of high purity and quaUty, the production of refined naphthalene by such chemical treatments essentially has ceased in the United States. Not only are such treatments expensive, but they also generate a significant amount of waste sludge, which creates additional costs for appropriate waste-disposal faciUties. 

Special chemical treatment can isolate the nuchdes of intermediate half-life, ie, cesium-137 and strontium-90 [10098-97-2] Sr, 39 yr (15). These... 

A number of other valuable aroma chemicals can be isolated from essential oils, eg, eugenol from clove leaf oil, which can also, on treatment with strong caustic, be isomerked to isoeugenol, which on further chemical treatment can be converted to vanillin (qv). Sometimes the naturally occurring component does not requke prior isolation or concentration, as in the case of cinnamaldehyde in cassia oil which, on dkect treatment of the oil by a retro-aldol reaction, yields natural ben2aldehyde (qv). This product is purified by physical means. 

Chemical treatments commonly appHed to cormgated paperboard packaging materials include additives that impart various degrees of water resistance, humidity resistance, oil and grease resistance, product abrasion resistance, product corrosion resistance, adhesion release properties, flame-retardant properties, nonskid properties, and static electricity control properties to the finished package (1,2). 

Certain chemical treatments can be employed during the TMP process to achieve improved strength. Sodium sulfite and hydrogen peroxide have been used either for chip pre- or post-treatment of the TMP pulp such pulp is called chemithermomechanical pulp (CTMP). The strength improvements, which may be 50%, are obtained at some sacrifice to yield and opacity. The yields of mechanical pulps are 90—95% the lower yields are associated with chemical treatment. No principal commercial pulps are produced in the next lower yield range, ie, 80—90%. 

Fusel Oils. The original source of amyl alcohols was from fusel oil which is a by-product of the ethyl alcohol fermentation industry. Refined amyl alcohol from this source, after chemical treatment and distillation, contains about 85% 3-methyl-1-butanol and about 15% 2-methyl-1-butanol, both primary amyl alcohols. Only minor quantities of amyl alcohol are suppHed from this source today. A German patent discloses a distillative separation process for recovering 3-methyl-1-butanol from fusel oil (93). 

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