12 research outputs found
Pseudocubic Crystal Structure and Phase Transition in Doped Yeāelimite
Sodalites are tridimensional alumino-silicate
materials containing
cages where loosely bonded anions are located. Yeāelimite,
Ca<sub>4</sub>[Al<sub>6</sub>O<sub>12</sub>]ĀSO<sub>4</sub>, is outstanding
as an aluminate sodalite with a flexible framework accepting several
type of dopants with important structural consequences. Moreover,
yeāelimite is also important from an applied perspective as
it is the most relevant phase in calcium sulfoaluminate cements. The
crystal structure of stoichiometric yeāelimite has recently
been unraveled, but the structure of dopant-containing yeāelimite,
which is present in cements, is not well studied. Here, we report
the pseudocubic crystal structure of doped yeāelimite, Ca<sub>3.8</sub>Na<sub>0.2</sub>Al<sub>5.6</sub>ĀFe<sub>0.2</sub>Si<sub>0.2</sub>O<sub>12</sub>SO<sub>4</sub>, from high-resolution synchrotron
powder diffraction data. The powder pattern is indexed with a cubic
cell, and a structural model is reported based on the <i>I</i>4Ģ
3<i>m</i> space group. However, this compound displays
diffraction peak narrowing on heating. Furthermore, some high-angle
split peaks become a single peak on heating, and a phase transition
is measured at 525 Ā°C. Therefore, it is concluded that the crystal
structure at room temperature has a lower symmetry, although it can
be described as cubic. The structural study at 800 Ā°C suggests
a truly cubic structure, and we speculate that this phase transition,
on heating, is likely related to the dynamical disordering of the
sulfate anions. Finally it is concluded that the high temperature
cubic state was not quenchable to ambient, even when the tested chemical
substituents are introduced into the structure
In Situ Bragg Coherent Diffraction Imaging Study of a Cement Phase Microcrystal during Hydration
Results of Bragg coherent diffraction
imaging (BCDI) confirm that
ion migration and consumption occur during hydration of calcium monoaluminate
(CA). The chemical phase transformation promotes the hydration process
and the formation of new hydrates. There is a potential for the formation
of hydrates near where the active ions accumulate. BCDI has been used
to study the in situ hydration process of CA over a 3 day period.
The evolution of three-dimensional (3D) Bragg diffraction electron
density, the āBragg densityā, and strain fields present
on the nanoscale within the crystal was measured and visualized. Initial
Bragg densities and strains in CA crystal derived from sintering evolve
into various degrees during hydration. The variation of Bragg density
within the crystal is attributed to the change of the degree of crystal
ordering, which could occur through ion transfer during hydration.
The observed strain, coming from the interfacial mismatch effect between
high Bragg density and low Bragg density parts in the crystal, remained
throughout the experiment. The first Bragg density change during the
hydration process is due to a big loss of Bragg density as seen in
the image amplitude but not its phase. This work provides new evidence
supporting the through-solution reaction mechanism of CA
Hydration Reactions and Mechanical Strength Developments of Iron-Rich Sulfobelite Eco-cements
Belite calcium sulfoaluminate (BCSA)
cements are low-CO<sub>2</sub> building materials. However, their
hydration behavior and its effect
on mechanical properties have still to be clarified. Here, we report
a full multitechnique study of the hydration behavior up to 120 days
of nonactivated and activated BCSA laboratory-prepared clinkers, with
Ī²- or Ī±<sub>H</sub>-belite as main phase, respectively.
The effects of the amount of gypsum added were also studied. The hydration
and crystallization processes are reported and discussed in detail.
Finally, shrinkage/expansion data are also given. The optimum amount
of gypsum was close to 10 wt %. Our study has demonstrated that Ī²-belite
reacts at a higher pace than Ī±ā²<sub>H</sub>-belite, irrespective
of the gypsum content. The hydration mechanism of belite determines
the development of the mechanical strengths. These are much higher
for activated BCSA cement, ā¼65 MPa at 120 days, against ā¼20
MPa for nonactivated BCSA cement, with the latter having larger amounts
of stratlingite
Chemistry and Mass Density of Aluminum Hydroxide Gel in Eco-Cements by Ptychographic Xāray Computed Tomography
Eco-cements are a
desirable alternative to ordinary Portland cements
because of their lower CO<sub>2</sub> footprints. Some yeāelimite-based
eco-cements are attracting a lot of interest. Understanding the reasons
for the mechanical performances requires the characterization of features
such as mass density of the hydrated component phases, including the
amorphous gel, on the submicrometer scale, which is challenging. Here
we use ptychographic X-ray computed tomography to provide 3D mass
density and attenuation coefficient distributions of eco-cement pastes
with an isotropic resolution close to 100 nm allowing to distinguish
between component phases with very similar contrast. In combination
with laboratory techniques such as the Rietveld method, <sup>27</sup>Al MAS NMR, and electron microscopies, we report compositions and
densities of key components. The ettringite and gel volume distributions
have been mapped out in the segmented tomograms. Moreover, we discriminate
between an aluminum hydroxide gel and calcium aluminum monosulfate,
which have close electron density values. Specifically, the composition
and mass density of two aluminum hydroxide gel agglomerates have been
determined: (CaO)<sub>0.04</sub>AlĀ(OH)<sub>3</sub>Ā·2.3H<sub>2</sub>O with 1.48(3) gĀ·cm<sup>ā3</sup> and (CaO)<sub>0.12</sub>AlĀ(OH)<sub>3</sub> with 2.05(3) gĀ·cm<sup>ā3</sup>, which
was a long-standing challenge
Structure, Atomistic Simulations, and Phase Transition of Stoichiometric Yeelimite
Yeelimite, Ca<sub>4</sub>[Al<sub>6</sub>O<sub>12</sub>]ĀSO<sub>4</sub>, is outstanding as an aluminate
sodalite, being the framework of
these type of materials flexible and dependent on ion sizes and anion
ordering/disordering. On the other hand, yeelimite is also important
from an applied perspective as it is the most important phase in calcium
sulfoaluminate cements. However, its crystal structure is not well
studied. Here, we characterize the room temperature crystal structure
of stoichiometric yeelimite through joint Rietveld refinement using
neutron and X-ray powder diffraction data coupled with chemical soft-constraints.
Our structural study shows that yeelimite has a lower symmetry than
that of the previously reported tetragonal system, which we establish
to likely be the acentric orthorhombic space group <i>Pcc</i>2, with a ā2a Ć ā2a Ć a superstructure based
on the cubic sodalite structure. Final unit cell values were <i>a</i> = 13.0356(7) Ć
, <i>b</i> = 13.0350(7) Ć
,
and <i>c</i> = 9.1677(2) Ć
. We determine several structures
using density functional theory calculations, with the lowest energy
structure being <i>Pcc</i>2 in agreement with our experimental
result. Yeelimite undergoes a reversible phase transition to a higher-symmetry
phase which has been characterized to occur at 470 Ā°C by thermodiffractometry.
The higher-symmetry phase is likely cubic or pseudocubic possessing
an incommensurate superstructure, as suggested by our theoretical
calculations which show a phase transition from an orthorhombic to
a tetragonal structure. Our theoretical study also predicts a pressure-induced
phase transition to a cubic structure of space group <i>I</i><u>4</u>3<i>m</i>. Finally, we show that
our reported crystal structure of yeelimite enables better mineralogical
phase analysis of commercial calcium sulfoaluminate cements, as shown
by R<sub>F</sub> values for this phase, 6.9% and 4.8% for the previously
published orthorhombic structure and for the one reported in this
study, respectively
High Proton Conductivity in a Flexible, Cross-Linked, Ultramicroporous Magnesium Tetraphosphonate Hybrid Framework
Multifunctional materials, especially those combining
two or more properties of interest, are attracting immense attention
due to their potential applications. MOFs, metal organic frameworks,
can be regarded as multifunctional materials if they show another
useful property in addition to the adsorption behavior. Here, we report
a new multifunctional light hybrid, MgH<sub>6</sub>ODTMPĀ·2H<sub>2</sub>OĀ(DMF)<sub>0.5</sub> (<b>1</b>), which has been synthesized
using the tetraphosphonic acid H<sub>8</sub>ODTMP, octamethylenediamine-<i>N</i>,<i>N</i>,<i>N</i>ā²,<i>N</i>ā²-tetrakisĀ(methylenephosphonic acid), by high-throughput
methodology. Its crystal structure, solved by Patterson-function direct
methods from synchrotron powder X-ray diffraction, was characterized
by a 3D pillared open framework containing cross-linked 1D channels
filled with water and DMF. Upon H<sub>2</sub>O and DMF removal and
subsequent rehydration, MgH<sub>6</sub>ODTMPĀ·2H<sub>2</sub>O
(<b>2</b>) and MgH<sub>6</sub>ODTMPĀ·6H<sub>2</sub>O (<b>3</b>) can be formed. These processes take place through crystallineāquasi-amorphousācrystalline
transformations, during which the integrity of the framework is maintained.
A water adsorption study, at constant temperature, showed that this
magnesium tetraphosphonate hybrid reversibly equilibrates its lattice
water content as a function of the water partial pressure. Combination
of the structural study and gas adsorption characterization (N<sub>2</sub>, CO<sub>2</sub>, and CH<sub>4</sub>) indicates an ultramicroporous
framework. High-pressure CO<sub>2</sub> adsorption data are also reported.
Finally, impedance data indicates that <b>3</b> has high proton
conductivity Ļ = 1.6 Ć 10<sup>ā3</sup> S cm<sup>ā1</sup> at <i>T</i> = 292 K at ā¼100% relative
humidity with an activation energy of 0.31 eV
High Proton Conductivity in a Flexible, Cross-Linked, Ultramicroporous Magnesium Tetraphosphonate Hybrid Framework
Multifunctional materials, especially those combining
two or more properties of interest, are attracting immense attention
due to their potential applications. MOFs, metal organic frameworks,
can be regarded as multifunctional materials if they show another
useful property in addition to the adsorption behavior. Here, we report
a new multifunctional light hybrid, MgH<sub>6</sub>ODTMPĀ·2H<sub>2</sub>OĀ(DMF)<sub>0.5</sub> (<b>1</b>), which has been synthesized
using the tetraphosphonic acid H<sub>8</sub>ODTMP, octamethylenediamine-<i>N</i>,<i>N</i>,<i>N</i>ā²,<i>N</i>ā²-tetrakisĀ(methylenephosphonic acid), by high-throughput
methodology. Its crystal structure, solved by Patterson-function direct
methods from synchrotron powder X-ray diffraction, was characterized
by a 3D pillared open framework containing cross-linked 1D channels
filled with water and DMF. Upon H<sub>2</sub>O and DMF removal and
subsequent rehydration, MgH<sub>6</sub>ODTMPĀ·2H<sub>2</sub>O
(<b>2</b>) and MgH<sub>6</sub>ODTMPĀ·6H<sub>2</sub>O (<b>3</b>) can be formed. These processes take place through crystallineāquasi-amorphousācrystalline
transformations, during which the integrity of the framework is maintained.
A water adsorption study, at constant temperature, showed that this
magnesium tetraphosphonate hybrid reversibly equilibrates its lattice
water content as a function of the water partial pressure. Combination
of the structural study and gas adsorption characterization (N<sub>2</sub>, CO<sub>2</sub>, and CH<sub>4</sub>) indicates an ultramicroporous
framework. High-pressure CO<sub>2</sub> adsorption data are also reported.
Finally, impedance data indicates that <b>3</b> has high proton
conductivity Ļ = 1.6 Ć 10<sup>ā3</sup> S cm<sup>ā1</sup> at <i>T</i> = 292 K at ā¼100% relative
humidity with an activation energy of 0.31 eV
Structural Variability in Multifunctional Metal Xylenediaminetetraphosphonate Hybrids
Two new families of divalent metal
hybrid derivatives from the aromatic tetraphosphonic acids 1,4- and
1,3-<i>bis</i>(aminomethyl)Ābenzene-<i>N</i>,<i>N</i>ā²-<i>bis</i>(methylenephosphonic acid),
(H<sub>2</sub>O<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>āNāCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>āNĀ(CH<sub>2</sub>PO<sub>3</sub>H<sub>2</sub>)<sub>2</sub> (designated herein as <b><i>p</i>-H<sub>8</sub>L</b> and <b><i>m</i>-H<sub>8</sub>L</b>) have been synthesized by crystallization
at room temperature and hydrothermal conditions. The crystal structures
of MĀ[(HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>NĀ(H)Ā(CH<sub>2</sub>PO<sub>3</sub>H)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]Ā·2H<sub>2</sub>O (M = Mg, Co, and Zn), <b>Mā(<i>p</i>-H<sub>6</sub>L)</b>, and MĀ[(HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>NĀ(H)Ā(CH<sub>2</sub>PO<sub>3</sub>H)<sub>2</sub>]Ā·<i>n</i>H<sub>2</sub>O (M = Ca, Mg, Co, and Zn and <i>n</i> = 1ā1.5), <b><b>Mā(<i>m</i>-H<sub>6</sub>L)</b></b>,
were solved ab initio by synchrotron powder diffraction data using
the direct methods and subsequently refined using the Rietveld method.
The crystal structure of the isostructural <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> is constituted by organicāinorganic
monodimensional chains where the phosphonate moiety acts as a bidentate
chelating ligand bridging two metal octahedra. <b><b>Mā(<i>m</i>-H<sub>6</sub>L)</b></b> compounds exhibit a 3D pillared
open-framework with small 1D channels filled with water molecules.
These channels are formed by the pillaring action of the organic ligand
connecting adjacent layers through the phosphonate oxygens. Thermogravimetric
and X-ray thermodiffraction analyses of <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> showed that the integrity
of their crystalline structures is maintained up to 470 K, without
significant reduction of water content, while thermal decomposition
takes place above 580 K. The utility of <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> (M = Mg and Zn) hybrid materials
in corrosion protection was investigated in acidic aqueous solutions.
In addition, the impedance data indicate both families of compounds
display similar proton conductivities (Ļ ā¼ 9.4 Ć
10<sup>ā5</sup> SĀ·cm<sup>ā1</sup>, at 98% RH and
297 K), although different proton transfer mechanisms are involved
Structural Variability in Multifunctional Metal Xylenediaminetetraphosphonate Hybrids
Two new families of divalent metal
hybrid derivatives from the aromatic tetraphosphonic acids 1,4- and
1,3-<i>bis</i>(aminomethyl)Ābenzene-<i>N</i>,<i>N</i>ā²-<i>bis</i>(methylenephosphonic acid),
(H<sub>2</sub>O<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>āNāCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>āNĀ(CH<sub>2</sub>PO<sub>3</sub>H<sub>2</sub>)<sub>2</sub> (designated herein as <b><i>p</i>-H<sub>8</sub>L</b> and <b><i>m</i>-H<sub>8</sub>L</b>) have been synthesized by crystallization
at room temperature and hydrothermal conditions. The crystal structures
of MĀ[(HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>NĀ(H)Ā(CH<sub>2</sub>PO<sub>3</sub>H)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]Ā·2H<sub>2</sub>O (M = Mg, Co, and Zn), <b>Mā(<i>p</i>-H<sub>6</sub>L)</b>, and MĀ[(HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>NĀ(H)Ā(CH<sub>2</sub>PO<sub>3</sub>H)<sub>2</sub>]Ā·<i>n</i>H<sub>2</sub>O (M = Ca, Mg, Co, and Zn and <i>n</i> = 1ā1.5), <b><b>Mā(<i>m</i>-H<sub>6</sub>L)</b></b>,
were solved ab initio by synchrotron powder diffraction data using
the direct methods and subsequently refined using the Rietveld method.
The crystal structure of the isostructural <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> is constituted by organicāinorganic
monodimensional chains where the phosphonate moiety acts as a bidentate
chelating ligand bridging two metal octahedra. <b><b>Mā(<i>m</i>-H<sub>6</sub>L)</b></b> compounds exhibit a 3D pillared
open-framework with small 1D channels filled with water molecules.
These channels are formed by the pillaring action of the organic ligand
connecting adjacent layers through the phosphonate oxygens. Thermogravimetric
and X-ray thermodiffraction analyses of <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> showed that the integrity
of their crystalline structures is maintained up to 470 K, without
significant reduction of water content, while thermal decomposition
takes place above 580 K. The utility of <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> (M = Mg and Zn) hybrid materials
in corrosion protection was investigated in acidic aqueous solutions.
In addition, the impedance data indicate both families of compounds
display similar proton conductivities (Ļ ā¼ 9.4 Ć
10<sup>ā5</sup> SĀ·cm<sup>ā1</sup>, at 98% RH and
297 K), although different proton transfer mechanisms are involved
Guest Molecule-Responsive Functional Calcium Phosphonate Frameworks for Tuned Proton Conductivity
We report the synthesis, structural
characterization, and functionality (framework interconversions together
with proton conductivity) of an open-framework hybrid that combines
Ca<sup>2+</sup> ions and the rigid polyfunctional ligand 5-(dihydroxyphosphoryl)Āisophthalic
acid (<b>PiPhtA</b>). Ca<sub>2</sub>[(HO<sub>3</sub>PC<sub>6</sub>H<sub>3</sub>COOH)<sub>2</sub>]<sub>2</sub>[(HO<sub>3</sub>PC<sub>6</sub>H<sub>3</sub>(COO)<sub>2</sub>H)Ā(H<sub>2</sub>O)<sub>2</sub>]Ā·5H<sub>2</sub>O (<b>Ca-PiPhtA-I</b>) is obtained by
slow crystallization at ambient conditions from acidic (pH ā
3) aqueous solutions. It possesses a high water content (both Ca coordinated
and in the lattice), and importantly, it exhibits water-filled 1D
channels. At 75 Ā°C, <b>Ca-PiPhtA-I</b> is partially dehydrated
and exhibits a crystalline diffraction pattern that can be indexed
in a monoclinic cell with parameters close to the pristine phase.
Rietveld refinement was carried out for the sample heated at 75 Ā°C, <b>Ca-PiPhtA-II</b>, using synchrotron powder X-ray diffraction data,
which revealed the molecular formula Ca<sub>2</sub>[(HO<sub>3</sub>PC<sub>6</sub>H<sub>3</sub>COOH)<sub>2</sub>]<sub>2</sub>[(HO<sub>3</sub>PC<sub>6</sub>H<sub>3</sub>(COO)<sub>2</sub>H)Ā(H<sub>2</sub>O)<sub>2</sub>]. All connectivity modes of the āparentā <b>Ca-PiPhtA-I</b> framework are retained in <b>Ca-PiPhtA-II</b>. Upon <b>Ca-PiPhtA-I</b> exposure to ammonia vapors (28% aqueous
NH<sub>3</sub>) a new derivative is obtained (<b>Ca-PiPhtA-NH</b><sub><b>3</b></sub>) containing 7 NH<sub>3</sub> and 16 H<sub>2</sub>O molecules according to elemental and thermal analyses. <b>Ca-PiPhtA-NH</b><sub><b>3</b></sub> exhibits a complex X-ray
diffraction pattern with peaks at 15.3 and 13.0 Ć
that suggest
partial breaking and transformation of the parent pillared structure.
Although detailed structural identification of <b>Ca-PiPhtA-NH</b><sub><b>3</b></sub> was not possible, due in part to nonequilibrium
adsorption conditions and the lack of crystallinity, FT-IR spectra
and DTA-TG analysis indicate profound structural changes compared
to the pristine <b>Ca-PiPhtA-I</b>. At 98% RH and <i>T</i> = 24 Ā°C, proton conductivity, Ļ, for <b>Ca-PiPhtA-I</b> is 5.7 Ć 10<sup>ā4</sup> SĀ·cm<sup>ā1</sup>. It increases to 1.3 Ć 10<sup>ā3</sup> SĀ·cm<sup>ā1</sup> upon activation by preheating the sample at 40 Ā°C
for 2 h followed by water equilibration at room temperature under
controlled conditions. <b>Ca-PiPhtA-NH</b><sub><b>3</b></sub> exhibits the highest proton conductivity, 6.6 Ć 10<sup>ā3</sup> SĀ·cm<sup>ā1</sup>, measured at 98% RH
and <i>T</i> = 24 Ā°C. Activation energies (<i>E</i><sub>a</sub>) for proton transfer in the above-mentioned
frameworks range between 0.23 and 0.4 eV, typical of a Grothuss mechanism
of proton conduction. These results underline the importance of internal
H-bonding networks that, in turn, determine conductivity properties
of hybrid materials. It is highlighted that new proton transfer pathways
may be created by means of cavity āderivatizationā with
selected guest molecules resulting in improved proton conductivity