Cerium iron effects

The most common accelerators for methyl ethyl ketone peroxide and cyclohexanone peroxide are salts of metals which exhibit more than one valency. The most widely used metal of this kind is cobalt, although salts of cerium, iron, manganese, tin and vanadium also find some application. In order to be effective as an accelerator a metal salt must be soluble in the polyester resin. The most commonly used salts are naphthenates, which are readily soluble octoates also may be used. (Naphthenic add is extracted from the gas oil and kerosene fractions of petroleum and consists of a complex mixture of carboxylic acids of substituted cyclopentanes and cyclohexanes. ) The decomposition of a hydroperoxide (ROOH) by a metal salt such as cobalt naphthenate to give free radicals proceeds according to the following chain reaction ... 

Iron and cerium driers effectively catalyze polymerization and through-drying at elevated temperatures and therefore are used in baking enamels. Iron driers have the limitation of dark color, and hence cerium based driers are often preferred where color retention is important. 

During the addition of the cerium(IV) solution up to the equivalence point, its only effect will be to oxidise the iron(II) (since K is large) and consequently change the ratio [Fe3+]/[Fe2 + ], When lOmL of the oxidising agent have been added, [Fe3+]/[Fe2 + ] = 10/90 (approx.) and... 

With the exception of iron(II) and uranium(IV), the reduced solutions are extremely unstable and readily re-oxidise upon exposure to air. They are best stabilised in a five-fold excess of a solution of 150g of ammonium iron(III) sulphate and 150 mL of concentrated sulphuric acid per litre [approximately 0.3M with respect to iron] contained in the filter flask. The iron(II) formed is then titrated with a standard solution of a suitable oxidising agent. Titanium and chromium are completely oxidised and produce an equivalent amount of iron(II) sulphate molybdenum is re-oxidised to the Mo(V) (red) stage, which is fairly stable in air, and complete oxidation is effected by the permanganate, but the net result is the same, viz. Mo(III)- Mo(VI) vanadium is re-oxidised to the V(IV), condition, which is stable in air, and the final oxidation is completed by slow titration with potassium permanganate solution or with cerium(IV) sulphate solution. 

A detailed study of the dehydrogenation of 10.1 l-dihydro-5//-benz[6,/]azcpinc (47) over metal oxides at 550 C revealed that cobalt(II) oxide, iron(III) oxide and manganese(III) oxide are effective catalysts (yields 30-40%), but formation of 5//-dibenz[7),/]azepinc (48) is accompanied by ring contraction of the dihydro compound to 9-methylacridine and acridine in 3-20 % yield.111 In contrast, tin(IV) oxide, zinc(II) oxide. chromium(III) oxide, cerium(IV) oxide and magnesium oxide arc less-effective catalysts (7-14% yield) but provide pure 5H-dibenz[b,/]azepine. On the basis of these results, optimum conditions (83 88% selectivity 94-98 % yield) for the formation of the dibenzazepine are proposed which employ a K2CO,/ Mn203/Sn02/Mg0 catalyst (1 7 3 10) at 550 C. 

The degradation of the B02 was conducted by using iron oxide catalyst supported on cerium oxide as a heterogeneous Fenton catalyst in the presenee of H2O2. The effect of the... 

The various rare earths are used in the foundry industry as rare earth silicides, in which the rare earth content is about 30%. Other alloys are used in which the level of rare earths is about 10% (10% cerium, 2% other rare earths) with silicon and iron comprising the bulk of the remaining elements. In the magnesium-ferrosilicon alloys, the rare earths are present in amounts from about 0.1% to 1.0%. These alloys are used differently by the various consumers. However, the effects of the rare earth elements, introduced by whatever means, are the same. 

These same researchers also explored the efficacy of the individual rare earths as nodulizers (17). They concluded, by their ability to produce nodular iron having adequate physical properties without excessive iron carbides present, that cerium was the most effective of the four rare earth elements (lanthanum-neodymium) evaluated as nodulizers. They reported that it required 1.5 times as much neodymiun or praseodymium and three times as much lanthanum as cerium to yield equivalent results. 

Figure 9. The effect of cerium, introduced as mischmetal along with the treatment alloy, as a junction of the cerium content of the alloy (21). Compositions of the irons were 3.4-3.7% C, 2.3-2.6% Si, 0.6% Mn, 0.01-0.02% S, 0.036-...

Further, it was demonstrated that the introduction of cerium, as mischmetal, in proper amounts was effective in eliminating iron carbides which cause deterioration in physical properties (21). The elimination of iron carbides in thin sections by proper use of the rare earths represents a major contribution to the industry. Different researchers have agreed that there is an optimum percentage for this rare earths addition, which they reported as cerium only, from 0.01% to 0.02% cerium (from about 0.02% to 0.04% total rare earths) that provides this increase in nodule count and control of iron carbides when used in conjunction with magnesium nodulizers (see Figure 9). 

Similar deleterious effects of small concentrations (that is, 0.001% to 0.005%) have been well documented for bismuth and antimony. Similarly, these effects were overcome by additions of small amounts of the rare earth elements. In the industry, it is accepted that roughly 0.01% cerium (once again as mischmetal that contains 50% cerium and approximately 50% lanthanum, neodymium and praseodymium) will neutralize the effects of the deleterious elements. The result is the production of high quality nodular iron, while still allowing for the use of commercially available steel scrap as a raw material. 

Having debated the mechanism of charge transport within the polymer film, it is now useful to consider a few examples of chemical applications of polymer modified electrodes. Electrodes coated with [Ru(bipy)2Cl(PVP)]Cl or [Ru(bipy)2(py)(PVP)]Cl2 show strong catalytic effects for the reduction of cerium(IV) and the oxidation of iron(II).52... 

Should any iron(II) reach the anode, it also would be oxidized and thus not require the chemical reaction of Eq. (4.13) to bring about oxidation, but this would not in any way cause an error in the titration. This method is equivalent to the constant-rate addition of titrants from a burette. However, in place of a burette the titrant is electrochemically generated in the solution at a constant rate that is directly proportional to the constant current. For accurate results to be obtained the electrode reaction must occur with 100% current efficiency (i.e., without any side reactions that involve solvent or other materials that would not be effective in the secondary reaction). In the method of coulometric titrations the material that chemically reacts with the sample system is referred to as an electrochemical intermediate [the cerium(III)/cerium(IV) couple is the electrochemical intermediate for the titration of iron(II)]. Because one faraday of electrolysis current is equivalent to one gram-equivalent (g-equiv) of titrant, the coulometric titration method is extremely sensitive relative to conventional titration procedures. This becomes obvious when it is recognized that there are 96,485 coulombs (C) per faraday. Thus, 1 mA of current flowing for 1 second represents approximately 10-8 g-equiv of titrant. 

The oxides of iron, bismuth, copper, cerium, and magnesium are capable of exerting an appreciable influence on the rate of decomposition,7 but much depends on the physical condition of the solid, freshly precipitated iron oxide, for example, being more effective than the ignited substance 8 aluminium hydroxide is rather exceptional in behaving as a negative catalyst and retarding the decomposition. 

Oxidation of iron(II) ions to iron (III) oxidation occurs slowly upon exposure to air. Rapid oxidation is effected by concentrated nitric acid, hydrogen peroxide, concentrated hydrochloric acid with potassium chlorate, aqua regia, potassium permanganate, potassium dichronate, and cerium(IV) sulphate in acid solution. 

Cerium dioxide is preferred over other oxides because platinum is expensive and vanadium and iron oxides are poisons for FCC catalysts. Usually an aqueous solution of a cerium salt is used to impregnate a spinel base which is then calcined to obtain the Ce02 active form. We have found that a 10 to 12% Ce02 is sufficient for effective S02 oxidation(1). 

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