The surface and cross-sectional morphologies of powder metallurgy (PM) Rene95 nickel-based superalloy after 100 h oxidation in the temperature range of 700-1100 °C were investigated. It is shown that oxides nucleate first on the surface of the alloy and form an oxides scale. Afterwards, oxides scale endures decohesion, rumpling, cracking and finally spalling owing to the weak cohesive strength of the scale/alloy interface. The XRD and EDS analyses confirmed that the oxides scale of PM Rene95 superalloy is mainly composed by Cr2O3 at 800 °C and NiCr2O4 is the main spinel at 1100 °C. The subsequent analysis of internal stress verified that cracking and spalling are caused by growth stress and promoted by thermal stress. On these bases, improvement of the cohesive strength of the scale/alloy interface is considered to be the main way to increase the oxidation resistance of PM Rene95 superalloy. 相似文献
Selective lipase-catalyzed acylation of 41-desmethoxyrapamycin has been achieved with a quaternary carboxylic acid avoiding the use of vinyl ester activation. Among the acyl donors investigated, the novel butanedione-monooxime and the N-acetylhydroxamate ester proved to be the most efficient donors, comparable in reactivity to the undesired vinyl ester and allowing selective, preparative acylation on gram scale in excellent yields. These new donors are proposed as sustainable and process-friendly alternatives to the widely used vinyl ester substrate activation in lipase-catalyzed acylations of secondary alcohols. 相似文献
Rotary biofilm contactor (RBC) is a reactor consisting of plastic discs that act as supports for micro-organisms. The discs are mounted on a horizontal shaft and placed in a medium-containing vessel. During nitrogen-rich growth phase, mycelia ofRhizopus oryzae ATCC 20344 grew on and around the discs and formed the “biofilm” of self-immobilized cells on the surface of the plastic discs. During the fermentation phase, the discs are slowly rotated, and the biofilms are exposed to the medium and the air space, alternately. With RBC, in the presence of CaCO3,Rhizopus biofilm consumes glucose and produces fumaric acid with a volumetric productivity of 3.78 g/L/h within 24 h. The volumetric productivity is about threefolds higher with RBC than with a stirred-tank fermenter with CaCO3. Furthermore, the duration of fermentation is one-third of the stirred-tank system. The immobilized biofilm is active for over a 2-wk period with repetitive use without loss of activity.