Oxidation Resistance of Diffusion Silicide Coatings on Mo and TZM Alloy

Characterization of microstructure of pack cemented silicide coatings based on MoSi2phase was described in this article as well as a short term oxidation resistance of these types of coatings at temperature 1200oC. Silicide coatings were deposited on top surface of Mo and Mo alloys of TZM type by diffusional process of siliconizing in activated powders. Morphology of coatings was characterized by evaluation of chemical and phase’s composition of deposited coatings by EDS and XRD methods respectively. In the case of Mo sheet after diffusion process of siliconizing single layer of MoSi2type was obtained, but in the case of TZM alloy, in the same conditions of process, double layered coating was generated. Thick outer layer was build form MoSi2phase, but very thin internal layer consist Mo5Si3phase. The thicknesses of coatings were ca. 45μm, and were uniform. Morphology of coatings was free from inclusion and contaminations in their cores. The isolated cracks were observed, but their volume was very small. The oxidation test was performed at temperature 1200oC. The specimens were tested at 25, 500 and 100 hours of test. After each period of test characterization of coatings top surface was made. Total destruction of specimens was observed in range between 50 and 100 h of test.

Vectorial activation of smooth muscle myosin filaments and its modulation by telokin

Smooth muscle myosin copurifies with myosin light chain kinase (MLCK) and calmodulin (CaM) as well as with variable amounts of myosin phosphatase. Therefore, myosin filaments formed in vitro also contain relatively high levels of these enzymes. Thus these filaments may be considered to be native-like because they are similar to those expected to exist in vivo. These endogenous enzymes are present at high concentrations relative to myosin, sufficient for rapid phosphorylation and dephosphorylation of the filaments at rates comparable to those observed for contraction and relaxation in intact muscle strips. The phosphorylation by MLCK/CaM complex appears to exhibit some directionality and is not governed by a random diffusional process. For the mixtures of myosin filaments with and without the endogenous MLCK/CaM complex, the complex preferentially phosphorylates its own parent filament at a higher rate than the neighboring filaments. This selective or vectorial-like activation is lost or absent when myosin filaments are dissolved at high ionic strength. Similar vectorial-like activation is exhibited by the reconstituted filament suspensions, but the soluble systems composed of isolated regulatory light chain or soluble myosin head subfragments exhibit normal diffusional kinetic behavior. At physiological concentrations, kinase related protein (telokin) effectively modulates the activation process by reducing the phosphorylation rate of the filaments without affecting the overall phosphorylation level. This results from telokin-induced liberation of the active MLCK/CaM complex from the filaments, so that the latter can also activate the neighboring filaments via a slower diffusional process. When this complex is bound at insufficient levels, this actually results in acceleration of the initial phosphorylation rates. In short, I suggest that in smooth muscle, telokin plays a chaperone role for myosin and its filaments.Key words: smooth muscle, regulation, myosin filament, phosphorylation, activation mechanism, myosin kinase, phosphatase, telokin.

Effect of mechanical alloying on combustion synthesis of MoSi2

Characteristics of the combustion synthesis of MoSi2 using elemental Mo and Si powder mixtures prepared by mechanical alloying were investigated. The mechanical alloying resulted in powders of pseudolamellar structure and a partial conversion of the elemental powders to hexagonal MoSi2 phase. Combustion reaction of the mixture was ignited around 670 °C, which is much lower than that with the powder prepared by low-energy ball milling. A mathematical model was developed to demonstrate the possibility of the ignition of the combustion reaction of the lamellar structure via a solid-state diffusional process. On the basis of model, effects of mechanical alloying time on the ignition temperature and combustion temperature are discussed.