Noble, Mark

The chemical reactivity of boron itself obviously depends markedly on the purity, crystallinity, state of subdivision and temperature. Boron reacts with F2 at room temperature and is superficially attacked by O2 but is otherwise inert. At higher temperatures boron reacts directly with all the non-metals except H, Ge, Te and the noble gases. It also reacts readily and directly with almost all metals at elevated temperatures, the few exceptions being the heavier members of groups 11-15 (Ag, Au Cd, Hg Ga, In, Tl Sn, Pb Sb, Bi). 

Fig. 1.71 How alloying with a noble metal produces a passive mixed potential and a marked reduction in corrosion rate (after Stern and Wissenberg )...

Similar curves determined in 50 Vo sodium hydroxide solution at 60°C show (Fig. 3.46) that the austenitic irons exhibit more noble active dissolution and also lower current densities in the active and passive regions than the ferritic irons the current densities in both regions decrease markedly with increasing nickel content (Fig. 3.47). 

One of the outstanding properties of the austenitic irons is their resistance to graphitic corrosion or graphitisation . In some environments ferritic cast irons corrode in such a manner that the surface becomes covered with a layer of graphite. This compact graphite layer, being more noble than the matrix, markedly increases the rate of attack. The austenitic irons rarely form this... 

Consequently, in the early 1990s, interest in the direct processes decreased markedly, and the emphasis in research on CH4 conversion returned to the indirect processes giving synthesis gas (13). In 1990, Ashcroft et al. (13) reported some effective noble metal catalysts for the reaction about 90% conversion of methane and more than 90% selectivity to CO and H2 were achieved with a lanthanide ruthenium oxide catalyst (L2Ru207, where L = Pr, Eu, Gd, Dy, Yb or Lu) at a temperature of about 1048 K, atmospheric pressure, and a GHSV of 4 X 104 mL (mL catalyst)-1 h-1. This space velocity is much higher than that employed by Prettre et al. (3). Schmidt et al. (14-16) and Choudhary et al. (17) used even higher space velocities (with reactor residence times close to 10-3 s). 

Table III gives values of the changes in Gibbs energy, enthalpy, entropy, and heat capacity of the solution process as calculated from the equations of Table I. Figure 1 shows the recommended noble gas mole fraction solubilities at unit gas partial pressure (atm) as a function of temperature. The temperature of minimum solubility is marked.

Daryl C. Drummond Mark E. Hayes, Charles O. Noble IV, and Dmitri B. Kirpotin... 

The solubility of noble gases in silicate melts obeys Henry s law but varies markedly with the chemistry and physical properties of the melt it increases with the... 

When Robert Noble carried out his studies on the periwinkle leaves, he found that they had no effect on blood sugar levels. However, they did appear to signihcantly reduce a subject s white blood cell count. Perhaps, Dr. Noble reasoned, the product could be used to treat diseases characterized by abnormally high white blood cell counts, such as leukemia. He was successful in isolating two chemicals from the periwinkle leaves, which he named vinblastine and vincristine, that markedly decreased white blood cell counts in patients with certain forms of cancer. The two chemicals were the first anticancer agents derived from natural sources to be approved for use with human patients. 

The author of The New Chemical Light (17th century) says "Simplicity is the seal of truth. Nature is wonderfully simple, and the characteristic mark of a childlike simplicity is stamped upon all that is true and noble in Nature." In another place the same author... 

It will be noted that with the exception of the organic cations and anions the more mobile hydrogen and hydroxyl ions are most readily adsorbed, whilst in the case of the metallic ions the influence primarily of the valency of the ion and both the position of the metal in the eleotrolytic potential series as well as the ionic mobility is most marked, the higher the valency and the more noble the element the more readily it is adsorbed. 

My thanks go also to other colleagues who took time to read and comment on the penultimate draft Mary Hartog, Anna-belle Mark, Stephen Hearnden and also Angela Hills, a Manager with Noble Lowndes. Their comments too have been gratefully heeded. 

In line with general indications on the reactivity order over both mixed oxide and noble metal catalysts, CO and H2 were found to be much more reactive than CH4 over all the investigated hexaaluminate catalysts. Specifically, the following reactivity order was determined over Mn-substituted samples CO>H2 CH4. Tio% values of 230 °C and 320 °C were obtained over BaMnAlnOj9 for CO and H2 respectively, to be compared with 540 °C required by CH4 combustion under similar experimental conditions. Apparent activation energies for CO and H2 combustion were calculated to be 10 kcal/mol lower than that of CH4 combustion (13-15 kcal/mol vs. 21-23 kcal mol), in line with the marked activity differences. 

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