CH(4) is known to be generated during the most active phase of composting, even in well-managed composting piles. In this manuscript, we studied the influence of biochar on the CH(4) metabolism during composting of cattle manure and local organic wastes. We evaluated the presence of methanogens and methanotrophs in the composting piles quantified by the level of mcrA encoding methyl coenzyme M reductase alpha subunit and pmoA encoding particulate methane monooxygenase. A decrease of methanogens (mcrA) and an increase of methanotrophs (pmoA) were measured in the composting mixture containing biochar during the most active phase of composting. During the thermophilic phase, the mcrA/pmoA ratios obtained in the composting piles with biochar were twofold lower than in the pile without biochar.
Synopsis:The tensile, Charpy impact bending, rotating bending fatigue, and impact bending fatigue tests on some carburized steels were performed in order to investigate the effect of chemical composition in steel and of heat treatment after carburizing on mechanical properties.The results obtained are summarized as follows:(1) The steel with re-quenching after direct quenching (specimen B) had superior properties of strength and ductility to the steel with direct quenching only (specimen A) in both tensile and Charpy impact tests. On the other hand, the fatigue strength of specimen A was higher than that of specimen B under both impact bending fatigue and rotating bending fatigue.(2) For these fatigue tests, the highest fatigue strength was obtained in the steel containing about 0.25% carbon. It was also found that these strength were improved by addition of Cr, Mo, and Ni.(3) In the impact fatigue tests, there was no clear difference in the number of blows to crack initiation for both specimen A and B. For each carburized steels, the crack propagation rate was decreased with the growth of crack at first, and then the rate was increased gradually with increasing number of blows and, finally, the specimen was led to the rupture with higher propagation rate of crack, that is, the three different stages were distinguished in the process of crack propagation. The crack propagation rate of specimen A was lower than that of specimen B for every stage to the rupture.
A study was made on the effect of hardness on fatigue properties of high strength steels. Rotating bending fatigue tests were carried out on four different carbon steels tempered at four temperatures.The results are summarized as follows;(1) Origin and location of fatigue fracture could be classified by hardness.(2) Even for high hardness steel showing fish eye fracture, fatigue limit was proportional to hardness under the same tempering condition. (3) Fatigue limit could be estimated as a function of hardness and tempering temperature.
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