Influence of thermal history on conversion of aluminate species in sodium aluminate solution

Ab Initio Molecular Dynamics Reveal Spectroscopic Siblings and Ion Pairing as New Challenges for Elucidating Prenucleation Aluminum Speciation

“…Turning to the IR spectra also illustrates fundamental uncertainties in speciation caused by the sensitivity of the energetic stability of the two dimers to ion pairing and overlap in IR bands for different ion-paired species, thereby revealing other spectroscopic siblings. While the experimental solution-phase spectrum presents a band at 550 cm –1 , there is no analogue in the simulated solution-phase IR spectrum of Al 2 O­(OH) 6 2– beyond a weak shoulder. The simulated band at 550 cm –1 from the IR spectrum of Al 2 (OH) 8 2– (Figure d) may explain the experimental findings; however, it is also possible that ion pairing may result in changes to the IR intensities.…”

“…Considering the T d AlO 4 core of Al­(OH) 4 – , the fully symmetric A 1 mode (R), 1E mode (R), and 2T 2 modes (IR and R) are expected. Previous Raman studies assigned (i) a highly polarized band at 620–625 cm –1 ,, to the A 1 (ν s Al–O); (ii) a depolarized band at 715–725 cm –1 ,, to the T 2 (ν αs Al–O), which is also present in the IR spectrum; and (iii) a depolarized band at ∼ 325 cm –1 , to another T 2 mode (ν as AlO 4 bend). A broad band at ∼950 cm –1 is assigned to δ Al–O–H , due to the observed changes upon deuteration; the aforementioned bands also feature a contribution from the Al–O–H bend .…”

“…(a) Experimental Raman spectra of a potassium aluminate solution in the 450–1200 cm –1 range: (b) through (d) AIMD Raman (R) and IR , spectra of Al­(OH) 4 – (b), Al 2 O­(OH) 6 2– (c), and Al 2 (OH) 8 2– (d) and Fourier transforms of the autocorrelation of the velocities projected on ν Al–O and δ Al–O–H internal coordinates. The vertical lines represent the positions of the experimental IR , and Raman (R) bands. The frequencies of the AIMD spectra were rescaled by 1.048.…”

“…Although dielectric relaxation spectroscopy has been able to observe the dimer in alkaline aluminate solutions, the dimer stoichiometry has not been determined . Instead, Raman (R) and infrared (IR) spectroscopies have been used in numerous studies of Al chemistry, where a combination of selection rules, symmetry-specific vibrational modes, and isotope effects permit in-depth analysis that can help elucidate speciation. ,− In dilute conditions ([Al] < 0.5 M), aluminate solutions only exhibit characteristic bands at ca. 620 and 720 cm –1 , corresponding to the symmetric (R) and antisymmetric (IR) Al–O stretch of the AlO 4 unit, respectively, of Al­(OH) 4(aq) – .…”

Compressed earth blocks stabilized with glass waste and fly ash activated with a recycled alkaline cleaning solution

“…Therefore, it is not surprising that ionic species of Al(OH) -4 aluminates in solution were identified in this same region. These aluminate species are predominant in pH values between 8-12, with vibrations of Al-OH type bonds (Li et al, 2014;MA et al, 2007). According to Ram (2001), the bands in the IR spectrum of the cleaning solution around 1019 and 1420 cm -1 could be considered as vibration signals of double bond stretching of Al=O of amorphous compounds.…”