Solid state 27Al NMR and X-ray diffraction study of alumina–carbon composites

Lopes, Thierry R.; Gonçalves, Gustavo R.; Barcellos, Ewerton de; Schettino, Miguel A.; Cunha, Ana Cristina Barros da; Emmerich, Francisco G.; Freitas, Jair C. C.

doi:10.1016/j.carbon.2015.06.001

Cited by 16 publications

(6 citation statements)

References 36 publications

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“…The cellulose displays a broad diffraction with 2h ranging from 5°to 35°, suggesting the amorphous structure of the polymeric scaffold (Oun and Rhim 2015). Besides the broad diffraction ascribed to the polymeric scaffold, the diffraction pattern for pristine MCC shows an intense peak at 15°, 16°, 22°, 23°and 26°that are the characteristic peaks of microcrystalline cellulose fibers, which coincides with reported literature values (Lopes et al 2015;RibeiroSoares et al 2015). Figure 7 presents the XRD patterns of GO.…”

Section: Raman Analysissupporting

confidence: 89%

Absorption of calcium ions on oxidized graphene sheets and study its dynamic behavior by kinetic and isothermal models

et al. 2016

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Sorption of calcium ion from the hard underground water using novel oxidized graphene (GO) sheets was studied in this paper. Physicochemical properties and microstructure of graphene sheets were investigated using Raman spectrometer, thermogravimetry analyzer, transmission electron microscope, scanning electron microscope. The kinetics adsorption of calcium on graphene oxide sheets was examined using Lagergren first and second orders. The results show that the Lagergren secondorder was the best-fit model that suggests the conception process of calcium ion adsorption on the Go sheets. For isothermal studies, the Langmuir and Freundlich isotherm models were used at temperatures ranging between 283 and 313 K. Thermodynamic parameters resolved at 283, 298 and 313 K indicating that the GO adsorption was exothermic spontaneous process. Finally, the graphene sheets show high partiality toward calcium particles and it will be useful in softening and treatment of hard water.

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Section: Raman Analysissupporting

confidence: 89%

Absorption of calcium ions on oxidized graphene sheets and study its dynamic behavior by kinetic and isothermal models

et al. 2016

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“…) clearly supports the disappearance of aluminum tetra‐ and hexa‐coordinated species after 900°C heat treatment (Table ). The contribution of different species was determined based on spectra deconvolution, as illustrated for 800°C treated sample (Fig. ).…”

Section: Resultsmentioning

confidence: 99%

High Fraction of Penta‐Coordinated Aluminum and Gallium in Lanthanum–Aluminum–Gallium Borates

et al. 2016

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This study is focused on structural changes induced by increasing treatment temperature of sol-gel-derived 4 , and AlO 6 , and starting with 800°C treatment also of BO 4 and AlO 5 structural units, but more detailed information related to boron, aluminum, and gallium environments is obtained from the analysis of MAS-NMR data. These data evidenced in both amorphous xerogels and in crystallized samples a high fraction of penta-coordinated aluminum and gallium.

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“…The spectra of calcined samples also consist of broad and small resonance at ca. 62 ppm (inset figure) in the region characteristic of tetrahedrally coordinated aluminum (40-80 ppm) [27,53,55,56] formed initially at temperatures below 600 • C. The appearance of tetrahedral Al in the fully dehydrated/dehydroxylated samples and its decreasing behavior with increasing calcination temperature from 600 to 1100 • C (Figure 8b,d) seems to have three overlapping reasons; one being the conversion of several possible metastable (transition) aluminas polymorphs (probably γ-Al 2 O 3 or transition alumina-type structure [27,28,54,[56][57][58][59][60] considered also as a mixed tetrahedral-octahedral Al 2 O 3 phase [61] formed initially below 600 • C to the most stable (six-coordinated) corundum phase [59], the second being the migration of Al 3+ ions from the periclase structure probably containing Al 3+ in solid solution (unstable MgO-like phase or periclase Mg(Al)O) [54,[62][63][64][65] or the other being the secondary spinel formation via reaction of a high surface area MgO-Al 2 O 3 mixed oxides [30,47,54,66,67] (or an amorphous mixed-phase oxide of nominal composition MgAlO x [62]) derived from hydrotalcite, in addition to the primary spinel derived from hydrotalcite. Note also that all the transition aluminas contain Al 3+ in both tetrahedral and octahedral sites [68], whereas Al 3+ in the periclase structure can be tetrahedrally [27,65,67,[69][70][71] or octahedrally [54,56,…”

Section: Ex-situ Lt-xrd Ft-ir and Nmr Investigationsmentioning

confidence: 98%

In Situ Spinel Formation in a Smart Nano-Structured Matrix for No-Cement Refractory Castables

Madej

Tyrała

2020

Materials

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The hydration of an equimolar mixture of MgO and Al 2 O 3 nano-powders has been proven to be an effective way to synthesize Mg 6 Al 2 CO 3 (OH) 16 ·4H 2 O as a component of a nano-structured matrix and magnesia-alumina spinel precursor for high-performance cement-free corundum-spinel refractory castables. (Mg 3 )-OH-brucite sites (417 • C) formed initially within the magnesia-alumina hydrating blended paste were replaced with (Mg 2 Al)-OH and (Mg 3 )-OH hydrotalcite sites, which were dehydroxylated at 420 • C and 322 • C, respectively. This reorganization was connected with the incorporation of anions and water molecules in the interlayer spacing of hydrotalcite, which was dehydrated at 234 • C. Hence, the thermal decomposition of a nano-structured matrix system containing mainly Mg 6 Al 2 CO 3 (OH) 16 ·4H 2 O consists of a complex sequence of dehydration, dehydroxylation and decarbonization, and this finally leads to the formation of inverse spinel MgAl 2 O 4 and periclase MgO through many intermediate stages containing the mixed tetrahedral-octahedral Al phase and MgO-like structure. Hence, the hydraulic bond that primarily existed was replaced by a ceramic bond at a relatively low temperature, i.e., 700 • C, where a spinel was formed. Important changes in oxygen coordination polyhedra around Al 3+ in the dehydrated-dehydroxylated hydrotalcite occurred between 600 and 1100 • C. instead of micro-scaled particles as magnesia and alumina sources results in an increase in the reactivity of nano-powders [13,14] and their ability to form Mg-Al-CO 3 hydrotalcite-like compounds [8].Due to the special lamellar structure, a new application has been found for hydrotalcite that enables refractory castable manufactures to use reactive nano-and micropowders of alumina (Al 2 O 3 ) and magnesia (MgO) as alternative cementitious materials. Various authors highlighted that materials with "in situ" formed Mg-Al hydrotalcite-like phases exhibit higher mechanical strength of the green body than hydratable alumina-free refractory systems. This advantage is related to the fact that the spinel-like phase can be formed at lower temperatures [15][16][17]. There are many publications about the methods of obtaining hydrotalcite-like phases; it can be obtained through mechanochemical synthesis, sol-gel syntheses or hydrothermal precipitation [8,[18][19][20]. Nevertheless, there are no published data concerning obtaining the hydrotalcite from a mixture of nanometric MgO and Al 2 O 3 oxides. According to the MgO-Al 2 O 3 -H 2 O system at low temperatures, the products of the reaction of magnesium and alumina oxides with water are single or/and double hydroxides. Layered double hydroxides (LDHs) are represented by the general formula [Mg 1−x Al x (OH) 2 ] x+ [(A n− ) x n ·yH 2 O] x− (where A n− is the exchangeable interlayer anion located between two LDH sheets and n-is a charge) [21,22]. The hydrotalcite structure is derived from the structure of brucite and the range of x can be varied, depending on literature sources, between 0.17 and 0.33...

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Solid state 27Al NMR and X-ray diffraction study of alumina–carbon composites

Cited by 16 publications

References 36 publications

Absorption of calcium ions on oxidized graphene sheets and study its dynamic behavior by kinetic and isothermal models

Absorption of calcium ions on oxidized graphene sheets and study its dynamic behavior by kinetic and isothermal models

High Fraction of Penta‐Coordinated Aluminum and Gallium in Lanthanum–Aluminum–Gallium Borates

In Situ Spinel Formation in a Smart Nano-Structured Matrix for No-Cement Refractory Castables

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