FTIR imaging in diffusion studies: CO2 and H2O in a synthetic sector-zoned beryl

Abstract

In this work we investigate the strongly inhomogeneous distribution of CO 2 and H 2 O in a synthetic beryl having a peculiar hourglass zoning of Cr due to the crystal growth. The sample was treated at 800 • C, 500 MPa, in a CO 2 -rich atmosphere. High-resolution FESEM images revealed that the hourglass boundary is not correlated to physical discontinuities, at least at the scale of tens of nanometers. Polarized FPA-FTIR imaging, on the other side, revealed that the chemical zoning acts as a fast pathway for carbon dioxide diffusion, a feature never observed so far in minerals. The hourglass zone boundary may be thus considered as a structural defect possibly due to the mismatch induced by the different growth rates of each sector. High-resolution synchrotron-light FTIR imaging, in addition, also allows enhancement of CO 2 diffusion along the hourglass boundary to be distinguished from diffusion along fractures in the grain. Therefore, FTIR imaging provides evidence that different diffusion mechanisms may locally combine, suggesting that the distribution of the target molecules needs to be carefully characterized in experimental studies. This piece of information is mandatory when the study is aimed at extracting diffusion coefficients from analytical profiles. Combination of TOF-SIMS and FPA data shows a significant depletion of type II H 2 O along the hourglass boundary, indicating that water diffusion could be controlled by the distribution of alkali cations within channels, coupled to a plug effect of CO 2 .

Activated Carbon Obtained from Bamboo: Synthesis, Morphological, Vibrational, and Electrical Properties and Possible Temperature Sensor

“…The spectrum of sample AC‐573 presents the peak at 2920 cm −1 , associated with the asymmetric and symmetric stretching vibration from the CH bond, indicating the presence of organic remnants from the precursor. The small band at 2362 cm −1 , present in almost all spectra, is characteristic of CO 2 from the environment . The peak at 1637 cm −1 shows the aromatic ring band or CC double bond, present in the hexagonal structure of the graphene individual layers, adjoined by Van der Waals force to form graphite domains, which is evidenced because when the carbonization temperature increases, the CC band intensifies.…”

Speciation and diffusion profiles of H2O in water-poor beryl: comparison with cordierite

“…4) show that the H 2 O content is maximum at both edges of the crystal or in fractures along the sample (Fig. 4a, see also Della Ventura et al 2015). Based on single-spot FTIR data, Fukuda et al (2009) inferred that the H 2 O diffusion in beryl proceeds exclusively along the structural channels parallel to the c-axis, implying that the H 2 O content must be maximum on the edge of the grain and then progressively decrease toward the crystal; this is what we actually observe using FPA imaging (Fig.…”

“…Experiments were carried out using synthetic H 2 O-and CO 2 -free beryls Perrey 1888, 1890;Bellatreccia et al 2008;Della Ventura et al 2015) as starting materials. Single crystals were packed into Pt tubes together with crushed Al 2 O 3 powder as inert, and silver carbonate as a CO 2 source, and treated at different PTt conditions.…”

“…2. The spectra show a sharp and very intense peak at 2360 cm −1 for E⊥c that is assigned to the antisymmetric stretching mode of CO 2 (Wood and Nassau 1968;Aines and Rossman 1984;Della Ventura et al 2015) and a group of sharp peaks in the H 2 O stretching region (3750-3500 cm −1 ).…”

Characterization of double-deformable-mirror adaptive optics for IR beam shaping in hyperspectral imaging

“…The multichannel recording capability of focal plane array (FPA) enables the extension of microspectroscopy to hyperspectral imaging and expedites the acquisition time, albeit at the expense of signal to noise ratio (SNR) and spatial resolution. 7 Synchrotron IR (SRIR) radiation, with three order of magnitude higher brilliance than thermal source, one order of magnitude larger spectral distribution than laser sources 8 and superior spectral stability to tunable lasers, is an ideal choice for FTIR microspectroscopy and imaging. In addition, the lowétendue of SRIR benefits FTIR such that the diffraction-limited resolution with high spectral quality can be achieved for both single detector 9 and FPA.…”