Fast X-ray microdiffraction techniques for studying irreversible transformations in materials

Abstract

A pair of techniques have been developed for performing time-resolved X-ray microdiffraction on irreversible phase transformations. In one technique capillary optics are used to focus a high-flux broad-spectrum X-ray beam to a 60 mm spot size and a fast pixel array detector is used to achieve temporal resolution of 55 ms. In the second technique the X-rays are focused with Kirkpatrick-Baez mirrors to achieve a spatial resolution better than 10 mm and a fast shutter is used to provide temporal resolution better than 20 ms while recording the diffraction pattern on a (relatively slow) X-ray CCD camera. Example data from experiments are presented where these techniques are used to study self-propagating high-temperature synthesis reactions in metal laminate foils.

Self-propagating reactions in Al/Zr multilayers: Anomalous dependence of reaction velocity on bilayer thickness

“…41 Though the 1 Al:1 Zr foils have similarly been shown to form a Zr-rich oxide following the intermetallic formation reaction in air, 42 during these x-ray phase contrast experiments the oxidation reaction was quenched by heat losses to the stainless steel sample holder (see Ref. 20 for a schematic of the holder) and no oxide phases were found during post-reaction characterization. The 3 Al:1 Zr foils also do not reveal any oxide phases following the self-propagating reaction in air, likely because they have insufficient Zr content to selfsustain oxidation.…”

“…At JHU, the reaction temperature was measured by a two-color ratio pyrometer. 20 For this measurement, light was collected in a 200 lm diameter optical fiber (NA ¼ 0.22), positioned within 0.5-2 mm of the foil, for an effective spot size of 0.6-1.1 mm. The light was split at a dichroic mirror and filtered to 1395 6 15 nm and 1600 6 15 nm which were sent to separate photodiodes.…”

“…The foils were deposited at JHU in two dedicated runs to obtain enough nominally identical samples of sufficient thickness for a strong diffraction signal. The details of this experimental setup are presented elsewhere 20 and are described only briefly here. A high flux (10 14 photons/s) beam of 12 keV (2% bandwidth) x-rays was focused to a 10 lm 6 2 lm  10 lm 6 2 lm spot size and chopped to produce pulses of 15-75 ls duration.…”

Time-resolved x-ray diffraction techniques for bulk polycrystalline materials under dynamic loading

“…A similar pulsed technique has been used by us and others for studies of irreversible transformations in materials. [18][19][20] We conducted these experiments at beamline 1-ID of the Advanced Photon Source (APS) using a monochromatic 86 keV x-ray beam vertically focused to a spot size of ∼30 μm × 1 mm together with a large-format amorphous silicon detector centered on the transmitted beam ( Fig. 6(a)).…”

High-speed imaging at high x-ray energy: CdTe sensors coupled to charge-integrating pixel array detectors

“…The Keck PAD [2,3,4], shown as a simplified schematic in Figure 1b, shares operating principles with past detectors [1,5] like the analog integrating approach with in-pixel storage, which in turn inspired current day burst mode imagers like the AGIPD [6,7]. Burst imaging at the 10 MHz level is possible (100 ns pulse separation) and the front-end conversion gain is set by the configuration of switches F1-F4, making it adjustable by a factor of up to 6.5.…”