Isothermal calorimetric investigation of a reversible reaction in rapidly solidified Fe/sub 40/Fi/sub 40/B/sub 20/ Page: 4 of 7
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MeU-spun .Tietallic glass ailoy w,tn nominal composition Fe40 Nil0 B,0 was suppliea as 6
mm-wide riboon of roughiy 25 4m thickness compliments of Allied Chem.cal. Calorimetri"
measurments were made on a single disc-shaped sample roughly 3 mm .n diameter. Before
measurement the sample was given a pre-anneal for 60 minutes at 360°C which caused
crystallization as indicated by x-ray measurements. Diffraction lines were observed which
wmch were consistent both with the phases (Fe/'Ni),, B, and y-Fe Ni reported for this alloy
by Oerling and Wagner  and with (Fe/Ni),B reported for the crystallized glass Fe,0 NiJ#
B10 by Walter et al [3|. .
Calorimetric measurements were made with a Perkin-Elmer DSC-2 differential scanning
calorimeter equipped with an intercooler attachment to give optimal baseline stability for
isothermal operation. The analog signal of heat flow rate versus time was monitored with a
chart recorder. Measurements were made according to the following temperature schedule:
After the pre-anneal the sample was cycled between two temperatures, a holding or annealing
temperature of either 250°C or 300°C. and a measuring temperature of 360aC. At the former
temperature the sample was held for a variable hold time. thdld, ranging from less than one
minute to more than 12 hours. During annealing at this holding temperature, the reaction
approaches its equilibrium value to an extent depending upon ^h01d: however, the heat release
rate at this ten perature was only just measurable and then only during the i.iitial time of the
reaction. Thus no attempt was made to study the heat release during tS0ld. After each anneal
at the holding temperature the sample was rapidly heated to the measuring temperature. (All
temperature changes were made at the maximum heating rate of the calorimeter,
320°C/minute.) At the measuring temperature of 3C0°C it was determined that the new
equilibrium was established relarvely rapidly (£ 60 minutes) and importantly, the rate of
heat absorption was of sufficient magnitude so that it could be measured during this period
and subsequently integrated to obtain the magnitude of the heat. ^H. Thus the net result of
this measurement procedure was that after each measurement at 360°C the sample was
returned to the same initial state so that a later anneal at Tldld and measurement at 360°C
gave a point on the plot of AH(t) vs time. This allowed the enthalpy changes associated with
the reaction to be followed.
Fig. I shows a plot of the rate of heat absorption. dH/dt versus time at the measuring
temperature of 360°C for the sample held at TiBld ■ 300° fur four different hold times. To
correct for instrumental transients, each of these curves has had a zero hold-time curve
(obtained by cooling to 300°C followed by immediately heating to 360*C) eubtracted frem it.
Thle relatively small correction wae partcularly important for the heat ebaorptlon measure-
ments after short hold-t mes. a.g., the curve for i>Bld - 1C minutes. It is clear that this heat
absorbed at the measuring temperature is due to heat being released it the holding
temperature ae the specimen approaches the equilibrium state associated with lower
temperature. It may be observed in Pig. 1 that the rate of heat absorption at J60aC deeaye
roughly exponentially with time 'o agreement with Bq. I. Also, there la measurable heat
absorption for hold times as low as 10 minutes, indicating that at the 300*C hold temperature
tome of the reaction toward the new equilibrium was taking olaoe even for relatively short
times. The maximum value for the heat absorption rate in Pig. 1 of roughly 0.02 meal/s
represents roughiy 20H of full scale on the chart recorder with the calorimeter at Its optimal
sensitivity. Since this signal had noise which was roughly 2H of full scale, theia is
appreciable uncertainty in the results shown in Pig. I.
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Cost, J.R.; Elliott, R.O. & Stanley, J.T. Isothermal calorimetric investigation of a reversible reaction in rapidly solidified Fe/sub 40/Fi/sub 40/B/sub 20/, article, January 1, 1983; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1069992/m1/4/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.