3346 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
phase transitions were detected during DSC analyses. In
previous INS experiments, the behavior of both water mol-
ecules and OH groups from the double layer of the LDH
structure was examined. For Al2O3 – LDH, we reported
that the respective bands were broad and smooth, indicat-
ing that the water molecules and hydroxyl groups are disor-
dered. For Al(OH)3 – LDH and Fe-LDH, the peaks from
water and hydroxyl groups were found to be sharp, indicat-
ing that the water molecules form an ordered layer in the
crystals. [Wu 2019]
Quasielastic neutron scattering (QENS) focuses on the
broadening of the elastic peak, which can be observed when
diffusive motions take place in the sample. Hydrogen pos-
sesses a large incoherent neutron scattering cross-section
of about 80 barns, one or two orders of magnitude larger
compared to most other common elements. Therefore,
when hydrogen is present in the sample, the QENS signal
tends to dominate by the contribution arising from diffu-
sion of hydrogen (or any species containing hydrogen, e.g.,
OH, H2O). The data is modelled with elastic peak (delta
function), one or more QE components (Lorentzian func-
tions), and a lineal background term. The elastic peak, as
well as the Lorentzian functions are convoluted numeri-
cally with the experimentally determined resolution func-
tion (low temperature measurement of each sample for the
experiment). Figure 2 displays the elastic intensity scans
for Al(OH)3 and Al2O3 LDH where the sums over all the
assessed Q-values (from 0.3 to 1.9 Å–1) and normalized by
the samples’ masses. In the figure, the orange dots depict
the elastic intensities extracted from the full QENS spectra
collected at the selected temperatures, as shown in Figure 1.
For Al(OH)3 – LDH, Figure 2(a), the first scan, collected
upon cooling, presents a deviation from the monotonic
behavior in the elastic intensity slightly below 250K. Note
that this scan is in very good agreement with the orange
dots that were obtained upon heating. At higher tempera-
tures, one can observe a considerable gap between Scans 1
and 2, and a small gap between Scans 3 and 4. These gaps
are consistent with the temperatures in which the elimina-
tion of water was observed by previous DSC-TGA analyses.
[Wu 2019] Additionally, in Scan 2, an abrupt transition
is detected around 520K, but this process is not present
in Scan 4, suggesting an additional elimination of water
from the sample. Finally, the last data points in Scan 4 are
very discrepant from the data points collected at compa-
rable temperatures in Scans 1 and 2, which corroborates the
claim of elimination of water from the sample during the
experiment. In Figure 2(b) Al2O3 – LDH, the elastic inten-
sity scan was collected upon cooling and a deviation from
the monotonic behavior of the elastic intensity was detected
around 120K (the main figure is presented at the same scale
as Figure 2(a) but the activation of the dynamic processes at
120K can be better observed in the inset). From the orange
data points, it is also possible that additional activations
of dynamic processes of phase transitions occur at ~300K
and ~500K. For this sample, the elimination of water, as
indicated by the DSC-TGA analyses, occurs around 613K,
[Wu 2019] which is higher than the temperatures assessed
by the experiments at BASIS.
In Figure 3, the evolution of the QENS spectra (nor-
malized to unity) at different temperatures for each sample
is presented at Q =0.7Å–1. In Figure 3(a), the results from
Al(OH)3 – LDH indicate a somewhat complex scenario, as
the elastic intensity scans suggested. Namely, from 20K to
250K, an expected increase in the dynamic signal formed by
both the QENS signal and the background occurs. Then,
Figure 2. Elastic intensity scans collected for (a) Al(OH)
3 – LDH and (b) Al
2 O
3 – LDH samples
phase transitions were detected during DSC analyses. In
previous INS experiments, the behavior of both water mol-
ecules and OH groups from the double layer of the LDH
structure was examined. For Al2O3 – LDH, we reported
that the respective bands were broad and smooth, indicat-
ing that the water molecules and hydroxyl groups are disor-
dered. For Al(OH)3 – LDH and Fe-LDH, the peaks from
water and hydroxyl groups were found to be sharp, indicat-
ing that the water molecules form an ordered layer in the
crystals. [Wu 2019]
Quasielastic neutron scattering (QENS) focuses on the
broadening of the elastic peak, which can be observed when
diffusive motions take place in the sample. Hydrogen pos-
sesses a large incoherent neutron scattering cross-section
of about 80 barns, one or two orders of magnitude larger
compared to most other common elements. Therefore,
when hydrogen is present in the sample, the QENS signal
tends to dominate by the contribution arising from diffu-
sion of hydrogen (or any species containing hydrogen, e.g.,
OH, H2O). The data is modelled with elastic peak (delta
function), one or more QE components (Lorentzian func-
tions), and a lineal background term. The elastic peak, as
well as the Lorentzian functions are convoluted numeri-
cally with the experimentally determined resolution func-
tion (low temperature measurement of each sample for the
experiment). Figure 2 displays the elastic intensity scans
for Al(OH)3 and Al2O3 LDH where the sums over all the
assessed Q-values (from 0.3 to 1.9 Å–1) and normalized by
the samples’ masses. In the figure, the orange dots depict
the elastic intensities extracted from the full QENS spectra
collected at the selected temperatures, as shown in Figure 1.
For Al(OH)3 – LDH, Figure 2(a), the first scan, collected
upon cooling, presents a deviation from the monotonic
behavior in the elastic intensity slightly below 250K. Note
that this scan is in very good agreement with the orange
dots that were obtained upon heating. At higher tempera-
tures, one can observe a considerable gap between Scans 1
and 2, and a small gap between Scans 3 and 4. These gaps
are consistent with the temperatures in which the elimina-
tion of water was observed by previous DSC-TGA analyses.
[Wu 2019] Additionally, in Scan 2, an abrupt transition
is detected around 520K, but this process is not present
in Scan 4, suggesting an additional elimination of water
from the sample. Finally, the last data points in Scan 4 are
very discrepant from the data points collected at compa-
rable temperatures in Scans 1 and 2, which corroborates the
claim of elimination of water from the sample during the
experiment. In Figure 2(b) Al2O3 – LDH, the elastic inten-
sity scan was collected upon cooling and a deviation from
the monotonic behavior of the elastic intensity was detected
around 120K (the main figure is presented at the same scale
as Figure 2(a) but the activation of the dynamic processes at
120K can be better observed in the inset). From the orange
data points, it is also possible that additional activations
of dynamic processes of phase transitions occur at ~300K
and ~500K. For this sample, the elimination of water, as
indicated by the DSC-TGA analyses, occurs around 613K,
[Wu 2019] which is higher than the temperatures assessed
by the experiments at BASIS.
In Figure 3, the evolution of the QENS spectra (nor-
malized to unity) at different temperatures for each sample
is presented at Q =0.7Å–1. In Figure 3(a), the results from
Al(OH)3 – LDH indicate a somewhat complex scenario, as
the elastic intensity scans suggested. Namely, from 20K to
250K, an expected increase in the dynamic signal formed by
both the QENS signal and the background occurs. Then,
Figure 2. Elastic intensity scans collected for (a) Al(OH)
3 – LDH and (b) Al
2 O
3 – LDH samples