(a) A schematic of TARXD setup to probe structural and chemical evolutions during rapidly propagating intermetallic reactions. The system employs intense monochromatic synchrotron x-rays, a 2D array detector (PILATUS) and a custom-designed diffraction chopper. (b) Plots of time-resolution (or x-ray exposure time) and recording time in each 2D detector frame as a function of chopper frequency (or rotation speed). The inset shows the slot opening of chopper (1.56°), which defines the x-ray exposure time.
(Left panel) A series of micro photographic images showing highly exothermic intermetallic reactions between Ni and Al nano-multilayers. The burn front speed gives the reaction propagation rate of 7.7 m/s. (Right panel) The optical signal measured by an optical fiber (a), which is used to generate a triggering signal (b) for the PILATUS detector as shown in (c) for a high time-resolution mode. Note that the detector is “off” for ∼3 ms between the frames (“On”) to read and store the data.
Time-resolved temperature changes during the initial stage of intermetallic reactions between Ni and Al nano-multilayers showing together with the raw PMT records of six optical channels set at different wavelengths in the lower inset and the gray body fits of the records at times noted as t 1, t 2, and t 3 in the upper inset. The time zero signifies the instant of trigger and the reaction starts with an induction period of ∼700 μs and reaches the peak temperature of 1680 K within ∼100 μs then cools down over the next 10 ms.
TARXD of Ni-Al nano-multilayers in static (a) and dynamic (b-f) conditions probing the intermetallic reaction yielding AlNi alloy. The record (b) was obtained in high time-resolution of 45 μs, whereas those of (c-f) were in low time-resolution of 280 μs. The red lines in (b) and (c) signify the onset of the reaction. The diffraction lines of Al, Ni, and AlNi are indexed for comparison. Note that broad diffraction lines of unreacted Al and Ni nano-layers and sharp lines of AlNi products which develop larger crystallites over ∼10 ms (c). Also, note that on a set of new diffraction lines from V and Ag3In appears in (d) and (f).
Caked images of TARXD images in Fig. 4, as plotted in the 2θ (Bragg angles) vs. azimuth angles (time). The vertical lines in (b) and (c) signify thermal expansion of the AlNi (110) lattice during the initial reaction period and thermal contraction during the later cooling period. This thermal cycle effects result in kinks in the diffraction lines as indicated by a red arrow in (c). The onset of the reaction is also marked by an arrow in (b). The diffraction lines for Al, Ni, and AlNi are indexed in (a) and (b) and those from V and Ag3In are marked in (d) and (f), as shown in Fig. 4.
ARXD patterns of reacting Ni-Al multilayers at discrete times obtained by integration of the caked images over a discrete time period. Also marked are the (hkl) indexes of different chemical species. The shift of the diffraction lines as indicated by the red lines indicates the lattice expansion and contraction of AlNi compound formed in the reaction.
The lattice parameters of Al, Ni, and AlNi (open symbols) plotted as a function of time. It shows the lattice changes during the exothermic intermetallic reaction and subsequent cooling. The lattice parameters at ambient conditions are also marked in solid symbols for comparison.
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