Download or read book Determinations of the Kinetics and Mechanisms of Deboronization at 11350C written by Julian H. Cherubini and published by . This book was released on 1961 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Determinations of the Kinetics and Mechanisms of Deboronization at 1135 C written by Julian Henry Cherubini and published by . This book was released on 1961 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Determinations of the Kinetics and Mechanisms of Deboronization at 1135 C written by and published by . This book was released on 1961 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The mechanisms and kinetics of the loss of boron during heating at 1135 deg C under various dynamic environments were determined from powder compacts of 5 wt% elemental boron dispersed in matrices of Fe, Cr, Ni, Si, Fe/sub 2/O/sub 3/, Cr/sub 2/O/sub 3/, NiO, and SiO/sub 2/, compacts of austenitic stainless steel alloy powder containing 0.25 wt% boron, and wrought specimens of 0.13 wt% boron-- stainless steel alloy. The compacts containing 5 wt% boron were heat treated in vacuum, highpurity argon, wet helium, and hydrogen. With the exception of those heat treated in hydrogen, significant boron losses occurred only when a supply of oxygen, either from the sample itself or as a deliberate addition to the heat- treating environment, was available. Correspondingly, the loss mechanism is postulated to be the oxidation of boron to boron sesquioxide and its volatilization from the sample. The loss rate is controlled by the volatilization rate of the oxide which is directly influenced by structure of the compact and sintering environment. Independent of the chemical nature of the matrix, boron losses were incurred during heat treatment in hydrogen. Variations of the water content of the hydrogen from 7 to 460 ppm did not significantly influence the total boron loss observed. The synthesis of boron and hydrogen into a gaseous boron-hydrogen species is postulated as a predominating loss mechanism in a hydrogen environment. Compacts of austenitic stainless steel powder containing 0.25 wt% boron were heat treated at 1135 deg C from 1/4 to 16 hours in hydrogen atmospheres of 3 different water vapor levels, 1, 100, and 450 parts per million. The losses observed in each environment for the first few hours of heat treatment followed the relationship: DELTA B = 0.26t + C, where DELTA B is total boron loss in milligrams, t is total heat-treating time in hours, and C is a constant. However, the rate of boron loss of samples heated in the driest hydrogen decreased abruptly after two hours at temperature. Under the other environmental conditions, a similar decrease was observed after seven hours. The degree of sample sintering was found to be the predominating factor determining the boron loss rate. The rate of decrease of total sample surface area by sintering was observed to have a proportional effect in decreasing the rate of boron loss. However, the rate-controlling step in the deboronization of master alloy compacts was the rate of diffusion of gaseous reactant in and reaction products out of the sample. This in turn was controlled by the effective diameter, length, and number of channels permeating the compact and exposed to the sintering environment. Deboronization of wrought specimens was observed in both hydrogen (less than 15 parts per million H/sub 2/O) and helium (15,000 parts per million H/sub 2/O). (auth).