Chemical conversion treatments

The use of certain chemical conversion treatments on a substrate prior to application of a bonded molybdenum disulphide film can give very considerable... 

Before the anode potential measurements, the anodes were initially conditioned by electrolysis (chemical conversion treatment) applying a 160 g/1 H2SO4 electrolyte at 40 C and a current density of 50 mA/cm for 24 h in order to prepare a Pb02 oxide layer at the anode surface. The distance between the anode and cathode in the chemical conversion treatment was 3 cm. After the chemical conversion treatment, the anode potential was measured in a 160 g/1 H2SO4 and 60 g/1 Zn electrolyte at a current density of 50 mA/cm for 1,0 h. The experiment temperature was 40° C and the anode-cathode distance was 3 cm. Another experiment with the same characteristics as above mentioned, but without Zn in the electrolyte and with no preliminary electrolysis, was performed for 20 days electrolysis time, the electrolyte being replaced every two days. The aluminum cathode used in the experiments had a surface area of... 

The materials required are the zinc plates to be treated and zinc phosphate (Zn3(P04)2), which is the reagent necessary for chemical conversion treatment, and these items are reflected in the input data section of the inventory analysis. The system boundary is then set, representing the assessment scope of the LCA, and is determined based on its objective. Eor example, it may be necessary to consider whether to include the manufacturing processes involved in making the zinc plates from the original raw material, which is zinc ore, in the scope. 

One of the principal methods of protection is to enhance the thickness and quality of the natural oxide by prefilming in hot water, which can thicken the surface oxide by about a factor of 10. The film can be thickened even more (to 1000 or more times the natural thickness) by anodizing in special acid (e.g., sulfuric or chromic) electrol3 es. Chemical conversion treatments also provide protection, but to a much lesser degree and are primarily used as a substrate for the subsequent application of organic films. A discussion of the effective use of organic coatings is beyond the scope of this chapter. 

Chemical conversion treatments form a thin, complex oxide layer which may reach 0.05-0.15 pm. The formation of these complex oxides may be obtained in acidic or alkaline phosphate or chromate baths [4]. As in the case of boehmite formation, the chromate treatment starts at grain boundaries [5]. 

In addition to the cleaning of the surface, a chemical conversion treatment or an anodizing process can be applied which offers more homogenous surface properties. The oxide layer is stabilized and the adhesion of the adhesive, the primer, or the paint is improved. Anodizing is commonly used to prepare aluminium for bonding in the aerospace industry. 

Finishes for aluminum products can be both decorative and useful. Processes in use include anodic oxidation, chemical conversion coating, electrochemical graining, electroplating (qv), thin film deposition, porcelain enameling, and painting. Some alloys respond better than others to such treatments. 

Surface preparation of the core foil was originally simple acid etching. As the importance of durable surface treatments became known, a more stable chemical conversion coating with an organic primer-like coating became standard. Still, water ingression into honeycomb structure continued to cause the occasional... 

For metal compounds, the calculation of the reportable concentration and treatment efficiency is based on the weight ot the parent metal, not on the weight of the metal compounds Metals are not destroyed, only physically removed or chemically converted from one form into another. The treatment efficiency reported represents only physical removal of the parent metal from the wastestream, not the percent chemical conversion of the metal compound. If a listed treatment method converts but does not remove a metal (e.g., chromium reduction), the method must be reported, but the treatment efficiency must be reported as zero. 

Protective measures range from chemical conversion coatings and anodising to the application of more substantial protective layers, e.g. enamels. For a more detailed treatment of the subject, the reader is advised to consult References 19, 20, 21 and 22. 

A chemist from the Federal Bureau of Narcotics and Dangerous Drugs, who was in Bolivia to observe clandestine cocaine operations, related the following step-by-step procedure for manufacturing cocaine. The method can be conveniently divided into three major steps (1) extraction of cocaine from the leaf and chemical conversion to the sulfate (2) treatment of cocaine sulfate with potassium permanganate and conversion to the free base (aka paste) and (3) conversion of the paste or free base to cocaine hydrochloride. In general, steps (1) and (2) are carried out in sulfate labs while step (3) is performed in crystal labs. 

Knowledge about chemical conversion processes which take place in aquatic and terrestic systems. Also the knowledge and experience of the chemical industry may be of interest in the development of new chemical treatment processes. 

Atom economy is high. As a reagent, no compounds are needed and consequently none are produced as the electron is immaterial. This results in a greater advantage of electrochemical reactions compared to chemical conversions, namely, an effective contribution to pollution control. The direct ET from the electrode to the substrate avoids the problem of separation and waste treatment of the, frequently, toxic end products of chemical reductions or oxidations. Furthermore, by electrodialysis, organic acids or bases can be regenerated from their salts without the use of, for example, sulfuric acid or... 

A cracking catalyst is subjected to two pretreatment steps. The first step effects vanadium removal the second, nickel removal, to prepare the metals on the catalyst for chemical conversion to compounds (chemical treatment step) that can... 

Phenylpyrimidine. On treatment of 4-phenylpyrimidine with potassium amide in liquid ammonia at 33°C for 70 hr in the presence of potassium nitrate, followed by quenching the reaction mixture by addition of ammonium chloride and workup, two products were isolated 2-amino-4-phenylpyrimidine (60%) and 6-amino-4-phenylpyrimidine (15%) (79JOC4677). When the reaction was carried out with labeled potassium amide in liquid ammonia and using the combined methodologies of chemical conversions and mass spectrometry as discussed previously (see Section II,C,l,a) it was found that in 6-amino-4-phenylpyrimidine (62/63), hardly any label was incorporated in the ring ( 5%), but that about... 

It was Henri who first proposed that enzyme catalysis depended on the formation of a transient complex of enzyme and substrate, followed by the breakdown i.e., chemical conversion) of bound substrate into product. Nonetheless, credit for derivation of the rate expression for the initial rate phase of one-substrate enzyme-catalyzed reactions is given to Michaelis and Menten. Both treatments gave the same general result ... 

Waste waters containing low concentrations of soluble organic lead in the presence of high concentrations of other diverse ions such as Cl pose a particularly difficult treatment problem. Generally, organic lead exists in solution as the tri- or dialkyl lead chloride species. These salts are not amenable to the conventional methods used to remove inorganic lead, viz., those of pH adjustment followed by settling. The technique of chemical conversion of the... 

Filter sludges Plating and chemical conversion Silica, silicides, carbides, ash, plating and other surface treatment bath consituents... 

Two principal conclusions are drawn from the experiments. The acid solubility of metals bonded in the CBI ceramic aggregate is very low, typically a few percent of the California TTLC and STLC limits and the physical properties of the CBI ceramic aggregate are very suitable for use as specialized construction materials. The CBI process is not merely a treatment or encapsulation of wastes it is a physical and chemical conversion which creates a product of genuine commercial value. 

Mordenite minerals vary in the ease with which they may be converted to the large port type by chemical treatment (20). The presence of Cmmm as in the Rome, Ore., mordenite should enhance the ease of the chemical conversion by providing greater access to the internal regions of the crystals. Sand (22, 28) reported that mordenite from Rome, Ore., can be easily converted to the large port variety by chemical treatment. Thus the... 

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