Normal vanadium

Fig. 3.5. Specific heat of vanadium. Data from [26]. The solid line represents data taken at H = 0 and illustrates the second-order transition. The dashed curve for normal vanadium was obtained by applying a magnetic field... 

After intrauterine vanadium depletion, the post-natal development of both sexes was significantly reduced. Kids with a normal vanadium supply during intrauterine development grew normally (Illing-Giinther et al. 1995). 

Carbon content is usually about 0.15% but may be higher in bolting steels and hot-work die steels. Molybdenum content is usually between 0.5 and 1.5% it increases creep—mpture strength and prevents temper embrittlement at the higher chromium contents. In the modified steels, siUcon is added to improve oxidation resistance, titanium and vanadium to stabilize the carbides to higher temperatures, and nickel to reduce notch sensitivity. Most of the chromium—molybdenum steels are used in the aimealed or in the normalized and tempered condition some of the modified grades have better properties in the quench and tempered condition. 

Depending on the peroxide class, the rates of decomposition of organic peroxides can be enhanced by specific promoters or activators, which significantly decrease the energy necessary to break the oxygen—oxygen bond. Such accelerated decompositions occur well below the peroxides normal appHcation temperatures and usually result in generation of only one usehil radical, instead of two. An example is the decomposition of hydroperoxides with multivalent metals (M), commonly iron, cobalt, or vanadium ... 

The adopted values for TWAs for airborne vanadium, including oxide and metal dusts of vanadium, is 0.5 mg/m the values for fumes of vanadium compounds is 0.05 mg/m. These limits are for normal 8-h workday and 40-h work-week exposures. The short-term exposure limit (STEL) is 1.5 mg/m for dusts (25). A description of health ha2ards, including symptoms, first aid, and organ involvement, personal protection, and respirator use has beenpubhshed (26). 

Catalytic Pyrolysis. This should not be confused with fluid catalytic cracking, which is used in petroleum refining (see Catalysts, regeneration). Catalytic pyrolysis is aimed at producing primarily ethylene. There are many patents and research articles covering the last 20 years (84—89). Catalytic research until 1988 has been summarized (86). Almost all catalysts produce higher amounts of CO and CO2 than normally obtained with conventional pyrolysis. This indicates that the water gas reaction is also very active with these catalysts, and usually this leads to some deterioration of the olefin yield. Significant amounts of coke have been found in these catalysts, and thus there is a further reduction in olefin yield with on-stream time. Most of these catalysts are based on low surface area alumina catalysts (86). A notable exception is the catalyst developed in the former USSR (89). This catalyst primarily contains vanadium as the active material on pumice (89), and is claimed to produce low levels of carbon oxides. 

Molybdenum tends to be protected by vanadium in aerated 7 1 % hydrochloric acid and it receives a high degree of protection when coupled with copper in this medium. Molybdenum corrodes somewhat faster than normal in 3 1 % nitric acid when coupled with tungsten. It is not affected by contact with titanium in 3-1% nitric acid. It is protected by aluminium and copper in aerated 10% formic acid and by aluminium in air-aerated 9% oxalic acid. In the latter solution, copper had only a slight protective effect when coupled with molybdenum. 

One of the most important impurities, found particularly in the residual oils, is vanadium, occurring in the resultant ash as vanadium pentoxide. The fluxing action of the ash with which corrosion is normally associated and the marked difference in severity of attack at temperatures above and below the melting point of the ash again suggest molten salt induced attack. 

Vanadium atom depositions were further studied in alkane matrices 109) in an effort to observe the influence of other low-temperature, matrix environments on the optical spectra and clustering properties of metal atoms. Thus, vanadium atoms were deposited with a series of normal, branched, and cyclic alkanes over a wide range of temperature. The atomic spectra were somewhat broadened compared to those in argon, but the matrix-induced, frequency shifts from gas-phase values were smaller. As shown in Fig. 3, these shifts decrease with in-... 

Figure 3. Arrhenius plots for the formation of formaldehyde or acetaldehyde from methanol or ethanol, normalized by the number of vanadiums (open symbols) and by the amount of oxygen uptake measured at 625 K (filled symbols). Lines on the right panel are calculated from the data reported by Oyama and Somorjai [11].

Neither the oxidation of methanol to make formaldehyde nor that of ethanol to make acetaldehyde is sensitive to the adjacency of redox sites in the catalysts the number of exposed vanadium serves well to normalize the reaction rate in both cases. This conclusion does not contradict a statement by other authors [23-25] that the selectivity of alcohol... 

Vanadium forms numerous oxides, the most important of which are vanadium monoxide, vanadium sesquioxide, vanadium dioxide and vanadium pentoxide. In the earlier examples (e.g., oxides of chromium and of niobium) the enthalpy values for the aluminothermic reduction of each of the oxides was given for the purpose of illustration. Normally, the consideration can be restricted to only those oxides which are readily obtained and which can be handled freely without any special or cumbersome precautions. In the case of vanadium for example, it is sufficient to consider the reduction of the sesquioxide (V203) and the pentoxide (V2Os). The pertinent reactions are ... 

Figure 3. Logarithm of the reactivities of niobium and vanadium clusters. The Exxon data (circles) are scaled relative to the Argonne Fe o reactivity, and the Rice data (crosses) are normalized to Nbg.

Insulin binding to the extracellular side of cell membranes initiates the insulin cascade , a series of phosphorylation/dephosphorylation steps. A postulated mechanism for vanadium is substitution of vanadate for phosphate in the transition state structure of protein tyrosine phosphatases (PTP).267,268 In normal physiological conditions, the attainable oxidation states of vanadium are V111, Viv and Vv. Relevant species in solution are vanadate, (a mixture of HV042-/ H2VOO and vanadyl V02+. Vanadyl is not a strong inhibitor of PTPs, suggesting other potential mechanisms for insulin mimesis for this cation. 

It has been suggested that an increase in the coordination number of vanadium from 4 to 5 already takes place in the second protonation step, i.e. when [H2V04] is formed (21). For reactions (1) and (2), however, the protonation constants and thermodynamic parameters are comparable with those reported for P04 and As04 , providing firm evidence that reaction (2) is not accompanied by incorporation of water in the vanadate ion (15, 17). Further, the estimated thermodynamic quantities for reaction (6), AH° = -39 kJ/mol and AS0 = —51 J/(mol K), obtained by extrapolation from the experimental values for reactions (1) and (2) and those for the three protonation steps of P04 and As04 , are not typical of a simple protonation reaction (17). For such a reaction the entropy change is normally a positive quantity often amounting to 100 50 J/(mol K) and the enthalpy... 

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