Effects of Al/Na and heat treatment on the structure and properties of glass ceramics from molten blast furnace slag

Glass ceramics with different Al/Na molar ratio from blast furnace slag were prepared using conventional melting-casting method. The structure and properties of glasses or glass ceramics were investigated by DSC, Raman, MAS NMR, XRD, and SEM. The DSC results indicated that the thermal stability (ΔT = T_c-T_g) and crystallization temperature (T_c) of the parent glass firstly increased and then decreased when Al/Na exceeded 1.21. The Raman and ²⁷Al MAS NMR spectra analysis revealed that [AlO₆] increased positively with Al₂O₃/Na₂O. The calculation of Qⁿ ([SiO₄] units with bridging oxygen atoms number of n) suggested an obvious decline of (Q⁰+Q²)/(Q¹+Q³) and that [SiO₄] mainly existed in the form of Q¹ when Al/Na exceeded 1.21, which accorded closely with T_c variation. The crystallization results determined by XRD showed that as Al/Na increased, the main crystal phase was transformed from akermanite to gehlenite and nepheline disappeared. Glass ceramics with Al/Na of 1.48 nucleated at 780 °C for 2 h and crystallized at 880 °C for 3 h exhibited the maximum value of flexural strength. Orthogonal experiment (L9(3⁴)) were carried out to investigated the optimum heat treatment of glass ceramics with a Al/Na of 1.48. The analyses indicated that nucleation time variation has little influence on the flexural strength, and the optimum heat treatment was determined as 760 °C – 1 h–900 °C – 1 h and the flexural strength was characterized as 81.310 MPa.     

Investigation of viscosity and structure of CaO-SiO2-MgO-Al2O3-BaO-B2O3 slag melt

The role of B₂O₃ in the viscosity and structural variations of CaO-SiO₂-MgO-Al₂O₃-BaO-B₂O₃ slag melt was examined using the rotating cylinder method, Raman spectroscopy, and ²⁷Al and ¹¹B magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra. The results showed that the viscosity of the slag decreased constantly with an increment in the B₂O₃ content although the polymerisation degree of slag enhanced. The addition of B₂O₃ induced the transformation from Q⁰ and Q¹ units to Q² and Q³ units in the Si-related structure. The concentration of [AlO₄] structural units increased while that of [AlO₅] and [AlO₆] units decreased. ¹¹B MAS-NMR spectra revealed that [BO₃]-trihedral units with a two-dimensional (2D) structure dominated the B-related structural units. The structural analysis confirmed the decrease in strength and stability of the entire network structure had a more significant effect on the viscosity of the slag due to the addition of B₂O₃.     

Ion Exchange in Molten Salts. II: The Occlusion of Lithium,Sodium, Potassium and Silver Nitrates in the Respective Forms of Zeolite A.

The occlusion of lithium, sodium, potassium and silver nitrates from the anhydrous melts in the respective zeolites has been studied by measuring the gain in weight and by direct analysis. The results in moles of occluded nitrate per formula weight of zeolite M₁₂^I[(AlO₂)₁₂(SiO₂)₁₂] are 11.7 for LiNO₃, 10 for NaNO₃ and 10 for AgNO₃ and essentially zero for KNO₃. A model is proposed for the structure of the occlusion compound Na₂₂[(AlO₂)₁₂(SiO₂)₁₂(NO₃)₁₀], in terms of four Na_I⁺ ions and four [Na_I - NO₃ - Na]⁺ groups at the apexes of the cubic unit cell and four [Na_II - NO₃ - Na]^+1/3 groups coordinated with two [NaNO₃]^?2/3 groups at the faces, to explain the properties of the occluded zeolites.     

Anionic polymerization of ethylene oxide with cryptates as counterions: 2

A kinetic study of the anionic polymerization of ethylene oxide has been made in tetrahydrofuran at 20°C, with the cryptate Cs⁺ + [TC] as counterion, [TC] being a spheroidal macrotricyclic ligand. Conductance measurements have been made on THF solutions of ?₄BCs + [TC]. Ionic associations higher than cryptated ion pairs are negligible for living end concentrations lower than 3 × 10^?4 moll^?1. k_± and the alkoxide ion pair dissociation constant K_D were determined from both sets of kinetic data obtained with and without added salt knowing the value of k_? from kinetic data performed with K⁺ + [222] as counterion. Free alkoxide ions are about twenty times more reactive than cryptated caesium ion pairs.     

Investigation of a protective conducting silica film on n-silicon

This paper concerns an attempt to dope a protective SiO₂ layer on n-Si so that the latter could act as a stable photo-anode. A SiO₂ film was electrochemically grown over an n-Si surface on which a submonolayer amount of Pt had been deposited. Thereafter the electrode was subjected to a heat treatment. There resulted an electrode which was photoactive for more than 100 h.Pt is present in the film at 0.25 (at Si/SiO₂) to 0.03 (SiO₂/solution) atomic per cent. Its form is as Pt and PtO. The energy level of the Pt is close to the n-Si valence band edge.The photocurrent density passes through a maximum when the Pt present in the film corresponds formally to 0.25 monolayer. Higher activities probably cannot be obtained because Pt also diffuses into Si and causes recombination of hole-electron pairs. An indirect estimate of the film resistance shows a specific conductance of 10^?9 mho cm^?1. The corresponding mobility would be around 10^?7 cms^?1 (V cm^?1)^?1 and hence too small for a charge carrier in band conduction. It is suggested that electrons tunnel between Pt atoms. A 30% decrease of photocurrent in 100 h is probably due to residual film growth. The approach has advantages but requires the seeking of improved doping.     

The dependence of Co2+-exchange into zeolite FAU on its Si/Al ratio

Three single crystals of fully dehydrated, largely Co²⁺-exchanged zeolites X and Y were prepared by the exchange of Na₈₀-X (|Na₈₀|[Si₁₁₂Al₈₀O₃₈₄]-FAU, Si/Al = 1.40), Na₇₅-Y (|Na₇₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU, Si/Al = 1.56), and Na₇₁-Y (|Na₇₁|[Si₁₂₁Al₇₁O₃₈₄]-FAU, Si/Al = 1.70) with aqueous streams 0.05 M in Co(NO₃)₂, pH = 5.1, at 294 K for 3 days. This was followed by vacuum dehydration at 673 K. Their crystal structures were determined by synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{3}\) m at 100(1) K. In all three crystals Co²⁺ ions occupy the 6-ring sites I, I’, and II; Na⁺ ions occupy sites II’ and II. The number of Co²⁺ ions exchanging into the zeolite was about 30 per unit cell for all three crystals. The number of residual Na⁺ ions, however, decreased sharply as Si/Al ratio increased, and the number of H⁺ ions co-exchanging into the zeolite decreased nearly to zero. Some dealumination of the zeolite framework was seen in the first crystal (initial Si/Al = 1.40).     

Ionic liquid-based extraction and separation trends of bioactive compounds from plant biomass

Ionic liquids have been projected as the best solvent for extraction and separation of bioactive compounds from various origins. This review offers a collection of the published results, using ionic liquids for the extraction and purification of biomolecules. Ionic liquids have been studied as solvents, co-solvents and supported materials for separation of bioactive compounds. The ionic liquids-based extraction procedures were previously reported, such as ionic liquids-based solid-liquid extraction, liquid-liquid extraction and ionic liquids-modified materials are reviewed and compared to their performance. In this review, the main activities and future challenges are discussed, with major gaps identified using ionic liquids in extraction procedures and by advancing few steps to overcome these drawbacks.

Abbreviation: [(HSO₃)C₄MIM]⁺: 1-(4-sulfonylbutyl)-3-methylimidazolium; [(C₆H₃OCH₂)₂im]⁺: 1,3-dihexyloxymethylimidazolium; [C_nC₁MIM]⁺: 1-alkyl-2,3-dimethylimidazolium; [C_nMIM]^{+; [Cn, 2, 3, 4, 6, 8, 10, 12]}: 1-alkyl-3-methylimidazolium; [C_nC₁pyr]⁺: 1-alkyl-3-methylpyridinium; [C_nim]⁺: 1-alkylimidazolium; [C_npyr]⁺: 1-alkylpyridinium; [aC_nim]⁺: 1-allyl-3-alkylimidazolium; [C₇H₇MIM]⁺: 1-benzyl-3-methylimidazolium; [C₄(C₁C₁C₁Si)im]⁺: 1-butyl-3-trimethylsilylimidazolium; [(HOOC)C₂MIM]⁺: 1-carboxyethyl-3-methylimidazolium; [(OH)C_nMIM]⁺: 1-hydroxyalkyl-3-methylimidazolium; [(C₂H₅O)₃SiC₃MIM]⁺: 1-methyl-3-(triethoxy)silypropyl imidazolium; [(NH₂)C₃MIM]⁺: 1-propylamine-3-methylimidazolium; [C_wH_xN_yO_z]⁺: Chirally functionalized methylimidazolium; [P_{10(3OH)(3OH)(3OH)}]⁺: Decyltris(3-hydrox- ypropyl) phosphonium; [N_111(2OH)]⁺: N,N,N-trimethyl-N-(2-hydroxyethyl) ammonium (cholinium); [N_00nn]⁺: N,N-dialkylammonium; [N_0nn(2OH)]⁺: N,N-dialkyl-N-(2-hydroxyethyl) ammonium; [C₁₀C₁₀C₁gluc]⁺: N,N-didecyl-N-methyl-d-glucaminium; [N_11(2(O)1)0]⁺: N,N-dimethyl(2-methoxyethyl) ammonium; [N_{11(2OH)(C7H7)}]⁺: N-benzyl-N,N-dimethyl-N-(2-hydroxyethyl) ammonium; [P₆₆₆₁₄]⁺: Trihexyltetradecylph- osphonium; [P_i(444)1]⁺: Triisobutyl (methyl) phosphonium; P.minus: Polygonum minus; NPs: Nanoparticle; ZnO : Zinc oxide nanoparticles ; Ni NPs: Nickel nanoparticles; MO: Methyl orange; UAE: Ultrasonic-assisted extraction; LLE: Liquid-liquid extraction; ABS: Aqueous biphasic system ; [Ace]^?: Acesulfamate; [Ala]^?: alalinate; [TMPP]^?: bis(2,4,4-trimethylpentyl)phosphinate; : ; [NTf₂]^?: bis(trifluoromethylsulfonyl)imide; [[Br]^–]: [Br]omide; [Calc]: calkanoate; [Cl]^–: chloride; [Bz]^?: benzoate; [PF₆]^?: hexafluorophosphate; [HSO₄]^?: hydrogenosulfate; [OH]^?: hydroxide; I^–: iodide; [Lac]^?: lactate; [NO₃]^?: nitrate; [[Cl]O₄]^?: perchlorate; [Phe]^?: phenilalaninate; [BF₄]^?: tetrafluoroborate; [SCN]^?: thiocyanate; [C(CN)₃]^?: tricyanomethanide; [CF₃CO₂]^?: trifluoroacetate; [CF₃SO₃]^?: trifluoromethanesulfonate; [FAP]^?: tris(pentafluoroethyl)trifluorophosphate; ILs: Ionic liquids; Ag NPs: Silver nanoparticle; Cu NPs: Copper nanoparticle; MB: Methylene blue; MR: Methyl red ; MAE: Microwave-assisted extraction; SLE: solid-liquid extraction.     

Pure-silica MFI zeolite membrane by cooperative templating approach for ethanol-water separation

Pure-silica MFI zeolite membrane composed of intergrown four prism crystals was fabricated by using tetrabutylammonium (TBA⁺) and tetraethylammonium (TEA⁺) as cooperating templates and the induced function of MFI seeds under synthesis solution with molar composition of 1TEOS:0.2TBAOH:0.2TEABr:180H₂O. The ethanol/water separation factor was 64 with a flux of 1.40 kg m⁻² hr⁻¹ for 5 wt% ethanol/water mixture at 60°C. In contrast, single TBAOH and TEAOH template led to formation of uncontinuous MEL and MFI membrane respectively, without ethanol-selectivity. The behavior of quaternary ammonium (TBA⁺ and TEA⁺) varied in different system: (a) In “TBA⁺+ TEA⁺” system, TBA⁺ and TEA⁺ were incorporated into MFI zeolite channel simultaneously; (b) In “TPA⁺+ M⁺” system (M = TEA or TBA), either TEA⁺ or TBA⁺ could not be occluded into channel, however, appropriate amount of TBA⁺ could accelerate membrane crystallization, meanwhile increase in TEA⁺ slowed down crystallization rate of MFI membrane. This work extends the alternative preparation approaches of ethanol perm-selective MFI membrane.     

Preparation of excessively Ni2+-exchanged zeolite Y (FAU,Si/Al = 1.70) and its single-crystal structure

A single crystal of excessively Ni²⁺-exchanged zeolite Y (FAU, Si/Al = 1.70) was prepared by exchange of |Na₇₁|[Si₁₂₁Al₇₁O₃₈₄]-FAU with an aqueous stream 0.05 M Ni(NO₃)₂ at 293 K and pH 4.9, followed by vacuum evacuation at room temperature and 1.3 × 10^?4 Pa. Its crystal structure was determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{ 3}\) m and was refined to the final error indices R ₁/wR ₂ = 0.0554/0.1557 for |Ni_24.7(NiOH)_12.1(Ni₂O(OH)₂)_4.8(Ni₄AlO₄)_1.7Na_17.0(H₃O)_6.9|[Si₁₁₇Al₇₅O₃₈₄]-FAU. Crystal has about 53 Ni²⁺ ions per unit cell, indicating the uptake of excess Ni(OH)₂, perhaps as NiOH⁺ ions. Some dealumination of the framework occurred during Ni²⁺ exchange. In this structure, Ni²⁺ ions occupy sites I, I′, II′, II, and III′. The residual Na⁺ ions are found at sites II′ and II. Due to the low pH of the Ni²⁺ exchange solution, some H₃O⁺ ions are observed. Nonframework oxygen atoms as oxide and hydroxide ions and orthoaluminate coordinate to some of Ni²⁺ ions to give NiOH⁺, Ni₂O(OH)₂, and Ni₄AlO₄ ³⁺ groups.     

Effect of Al Speciation on the Structure of High‐Al Steels Mold Fluxes Containing Fluoride

To design suitable mold fluxes for the casting of high‐Al steels, the structure of mold fluxes based on CaO–SiO₂, CaO–SiO₂–Al₂O₃, and CaO–Al₂O₃ was examined by Raman spectroscopy and magic‐angle spinning nuclear magnetic resonance. The results showed that Si atoms are replaced by Al atoms as the network formers with the increase in Al₂O₃ in the mold fluxes. This converts the silicate slags (CaO–SiO₂ mold fluxes) into aluminosilicates slags (CaO–SiO₂–Al₂O₃ or CaO–Al₂O₃ mold fluxes). The F^? ions in the mold flux containing Al₂O₃ are classified into three categories, according to function: Bridging F's, Nonbridging F's, and Free‐F's. The Al³⁺ ion holds three distinct coordination environments: ^IVAl, ^VAl, and ^VIAl. The addition of F affects the coordination environment of Al³⁺ to form AlO₃F and AlO₂F₂ that accommodate the network structure of slags. The network structure in the CaO–SiO₂ mold fluxes is mainly connected through Si–O–Si linkage. However, the network structure of the mold fluxes containing elevated content of Al₂O₃ is mainly connected through Si–O–Si, Al–O–Al, Al–O–Si, and Al–F–Al linkages. Hence, the structural characteristics of high‐Al steels mold fluxes must be considered during the designing step of the mold fluxes.     

The Effect of Alkali Ions on the Incorporation of Aluminum in the Calcium Silicate Hydrate (C–S–H) Phase Resulting from Portland Cement Hydration Studied by 29Si MAS NMR

The incorporation of aluminum in the calcium–silicate–hydrate (C–S–H) phases formed by hydration of three different white Portland cements has been investigated by ²⁹Si MAS NMR. The principal difference between the three cements is their bulk Al₂O₃ contents and quantities of alkali (Na⁺ and K⁺) ions. ²⁹Si MAS NMR allows indirect detection of tetrahedral Al incorporated in the silicate chains of the C–S–H structure by the resonance from Q²(1Al) sites. Analysis of the relative ²⁹Si NMR intensities for this site, following the hydration for the three cements from 0.5 d to 30 weeks, clearly reveals that the alkali ions promote the incorporation of Al in the bridging sites of the dreierketten structure of SiO₄ tetrahedra in the C–S–H phase. The increased incorporation of Al in the C–S–H phase with increasing alkali content in the anhydrous cement is in accord with a proposed substitution mechanism where the charge deficit, obtained by the replacement of Si⁴⁺ by Al³⁺ ions in the bridging sites, is balanced by adsorption/binding of alkali ions in the interlayer region most likely in the near vicinity of the AlO₄ tetrahedra. This result is further supported by similar ²⁹Si MAS NMR experiments performed for the white Portland cements hydrated in 0.30M NaOH and NaAlO₂ solutions.     

Anionic polymerization of ethylene oxide with cryptates as counterions: 1

A kinetic study of the anionic polymerization of ethylene oxide has been made in tetrahydrofuran at 20°C, with the cryptate K⁺ + [222] as counterion. The ion pair dissociation constant K_D has been deduced from conductivity measurements made on seeds solutions. Some ionic associations higher than cryptated ion pairs could be detected but they are negligible for living end concentrations lower than 6 × 10^?4 mol/l. k_± and k_? were determined from both sets of kinetic data obtained with and without added salt. Free alkoxide ions are one hundred times more reactive than cryptated ion pairs.     

Crystallization behavior and melt structure of typical CaO–SiO2 and CaO–Al2O3-Based mold fluxes

Crystallization behavior and melt structure of two typical mold fluxes A (CaO–SiO₂-based) and B (CaO–Al₂O₃-based) for casting high-aluminum steel were investigated using double hot thermocouple technology (DHTT), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results suggest that the crystallization temperature of Flux B is higher, and its crystallization incubation time is shorter compared with Flux A. The precipitated phase in Flux A is CaSiO₃, whereas BaAl₂O₄ and Ca₂Al₂SiO₇ form in Flux B. The structure analyses suggest that the degree of polymerization of Flux A is larger than that of Flux B. In addition, the major structural units of Flux A are Si–O–Si, Q₀^Si, Q₁^Si, Q₂^Si and Q₃^Si, but those of Flux B are mainly aluminate (Al–O–Al, Al–O^-), aluminosilicate (Al–O–Si) and silicate units (Q₀^Si, Q₁^Si, Q₂^Si and Q₃^Si). These different melt structures are the main reasons why the precipitated phases in these two mold fluxes are different, and the crystallization ability of Flux A is weaker than Flux B.     

Quantitative determinations in the molecular structures of polyaluminocarbosilane

The molecular structure of polyaluminocarbosilane (PACS) derived from polycarbosilane (PCS) was investigated by ¹H, ²⁹Si, ²⁷Al NMR and elemental analyses. Quantitative methods based on experimental data were established to determine the exact amounts of O-containing groups, namely Si−O−Al and Si−O−Si, and the relative numbers of linear and cyclic Si−C segments in PACS. The HSiC₂O groups and the SiH/SiH₂ in linear Si−C segments, single and condensed six-member Si−C rings were quantitatively distinguished. The results showed that PACS molecules consisted predominantly of single six-member Si−C rings. The introduction of Al into PCS led to H consumption through which Al was closely bonded to O by breaking Si−H or Si−CH₃ to form Si−O−Al cross-linking bonds and AlO_x (x = 4-6) groups in PACS. The AlO_x (x = 4-6) groups acted as linkage centers to bridge smaller PCS molecules through which the molecular weight and its distribution coefficient of PACS were both apparently increased.     

Hydrothermal conversion of FAU zeolite into aluminous MTN zeolite

The hydrothermal conversion of FAU zeolite into aluminous MTN zeolite is described here. In the presence of both benzyltrimethylammonium hydroxide (BTMAOH) and sodium chloride (NaCl) the highly crystalline and pure MTN zeolites with Si/Al ratios of 21-23 could be obtained from the hydrothermal conversion of FAU zeolite. Based on powder XRD refinement and ¹³C CP/MAS NMR spectra, BTMA⁺ ions were not present in cages of the obtained zeolites, but TMA⁺ ions existed instead. It means that BTMAOH underwent degradation during the conversion. Moreover, the effects of Si/Al ratio of starting FAU zeolite, synthesis parameters (BTMAOH/SiO₂ and H₂O/SiO₂ ratios) and the addition of alkali metal chlorides on the hydrothermal conversion of FAU zeolite into MTN zeolite are discussed. As compared to amorphous SiO₂/γ-Al₂O₃, which produced impurity, the hydrothermal conversion of FAU zeolite showed a fast crystallization rate and a high selectivity to MTN zeolite formation. These phenomena indicate that the assembly of locally ordered aluminosilicate species coming from the decomposition or dissolution of FAU zeolite should be taking part in the conversion process.     

Synthesis,Thermal Properties and Electrical Conductivity of Na-Sialate Geopolymer

This work aims to study the thermal behavior of basic-geopolymers derived from metakaolin (clay). The geopolymers were characterized by different techniques: thermal analysis (DTA, TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and impedance spectroscopy. Some physicochemical properties of the products were also determined: the phases obtained after geopolymer heat treatment and their electrical properties. The results obtained after drying and heat treatment showed that the products kept their initial shapes, but revealed variable colors depending on the temperatures at which they were treated. The products obtained are amorphous between 300 up to 600 °C with peaks relating to the presence of nanocrystallites of muscovites and zeolite, thus at 900 °C it is quite amorphous but only contains nanocrystallites of muscovites. From the temperature of 950 °C, we notice that the geopolymer has been transformed into a crystalline compound predominated by the Nepheline (NaAlSiO₄) with the presence of a crystalline phase by minor peaks of Muscovite, this crystalline character has been increased at 1100 °C to obtain a whole phase crystalline of a Nepheline. The treatment of this geopolymer for one hour at 1200 °C shows an amorphous phase again corresponding to corundum (α-Al₂O₃). This indicates that the dissolution of the grains by the liquid phase induces the conversion of the material structure from sialate [–Si–O–Al–O] to sialate siloxo [–Si–O–Al–O–Si–O–] and the formation of a new crystalline phase (α-Al₂O₃). This development of sialate to sialate-siloxo was confirmed by IR spectroscopy. As mentioned above, from 300 to 900 °C, Na-sialate geopolymer exhibits the same disorder structure of nepheline. The crystal structure of nepheline is characterized by layers of six-membered tetrahedral rings of exclusively oval conformation. The rings are built by Regularly alternating tetrahedral AlO₄ and SiO₄. Stacking the layer’s parallel to the c axis gives a three-dimensional network containing channels occupied by Na cations. This topology favors easy movement of Na⁺ ions throughout the structure. For this reason, ionic migration in nepheline is widely reported. The refinement of Na-Sialate geopolymer at room temperature gives bulk high ionic conductivity of about 5 × 10^?5 S cm^?1 and this is due to the probable joint contribution of H⁺ and Na⁺ ions. Above 200 °C, Na⁺ seems to remain the only charge carrier with a low activation energy of about Ea?=?0.26 eV. At higher temperatures, the characteristic frequencies become so close that it is impossible to distinguish the contributions. A total resistance comprising both grain and grain boundaries contribution is then determined.

     

The role of Al in C-S-H: NMR, XRD, and compositional results for precipitated samples

X-ray diffraction, compositional analysis, and ²⁹Si and ²⁷Al MAS NMR spectroscopy of Al-substituted tobermorite-type C-S-H made by precipitation from solution provide significant new insight into the structural mechanisms of Al-substitution in this important and complicated phase. Al occurs in 4-, 5-, and 6-coordination (Al[4], Al[5], and Al[6]) and plays multiple structural roles. Al[4] occurs on the bridging tetrahedra of the drierkette Al-silicate chains, and Al[5] and Al[6] occur in the interlayer and perhaps on particle surfaces. Al does not enter either the central Ca-O sheet or the pairing tetrahedra of the tobermorite-type layers. Al[4] occurs on three types of bridging sites, Q³ sites that bridge across the interlayer; Q² sites that are charge balanced by interlayer Ca⁺², Na⁺, or H⁺; and Q² sites that are most likely charge balanced by interlayer or surface Al[5] and Al[6] through Al[4]-O-Al[5,6] linkages. Although the data presented here are for relatively well-crystallized tobermorite-type C-S-H with C/S ratios ≤ 1.2, comparable spectral features for hydrated white cement pastes in previously published papers[30], [31] and [32] [M.D. Andersen, H.J. Jakobsen, J. Skibsted, Incorporation of aluminum in the calcium silicate hydrate (C-S-H) of hydrated Portland cements: a high-field ²⁷Al and ²⁹Si MAS NMR investigation Inorg. Chem. 42 (2003) 2280-2287; M.D. Andersen, H.J. Jakobsen, J. Skibsted, Characterization of white Portland cement hydration and the C-S-H structure in the presence of sodium aliminate by ²⁷Al and ²⁹Si MAS NMR spectroscopy, Cem. Concr. Res. 43 (2004) 857-868; M.D. Andersen, H. J. Jakobsen, J. Skibsted, A new aluminum-hydrate phase in hydrated Portland cements characterized by ²⁷Al and ²⁹Si MAS NMR spectroscopy, Cem. Concr. Res., submitted for publication.] indicate the presence of similar structural environments in the C-S-H of such pastes, and by implication OPC pastes.     

The activation mechanism of oxalic acid on γ-alumina and the formation of α-alumina

Converting the γ phase into the α phase completely is necessary in the presintering stage of industrial alumina (Al₂O₃), which requires high temperature and energy consumption. To reduce the presintering temperature, γ-Al₂O₃ was activated by oxalic acid. XRD, ²⁷Al-MAS-NMR and TG-DSC were used to characterize the γ - alumina before and after activation, and the phase transformation was studied. The formation temperature of α-Al₂O₃ decreased to 1029 °C for oxalic acid activated γ-Al₂O₃, and the α-fraction was 100% for activated γ-Al₂O₃ at 1300 °C. After oxalic acid activation, the diffraction peak intensity of γ-Al₂O₃ decreased significantly; the results of ²⁷Al-MAS-NMR suggested that octahedral [AlO₆] in γ-Al₂O₃ was easier than tetrahedral [AlO₄] to be attacked by oxalic acid, and the formation of pentavalent [AlO₅] with higher reaction activity, which was in favour of the lowering formation temperature of α-Al₂O₃. The dissolution concentration of Al increased after oxalic acid activation, and the dissolution process was controlled by surface reactions. Oxalic acid mainly attacked the octahedral aluminium in γ-Al₂O₃ and extracted Al as three complexes of [Al(C₂O₄)]⁺, [Al(C₂O₄)₂]^- and [Al(C₂O₄)₃]^3-. Oxalic acid activated γ - Al₂O₃ with a lower phase transformation temperature has broad application prospects in the alumina industry.     

A density functional theory study of the effects of metal cations on the Brøsted acidity of H-ZSM-5

Density functional theory calculations have been carried out to establish the influence of mono- and polyvalent cations on the Brønsted acidity of H-ZSM-5. The zeolite was modeled as a cluster containing 41-45 atoms, in the center of which is an Al⁽¹⁾(OH)SiOAl⁽²⁾(OM)unit, where M⁺ = H⁺, Li⁺, Na⁺, K⁺, Ca(OH)⁺, AlO⁺, Al(OH)⁺ ₂. The local geometry of the Brønsted acid site is affected by the nature of M⁺ and this in turn causes a change in the value of the proton affinity (PA) for the site. The highest value of PA is 330 kcal/mol for M⁺ = H⁺ and the lowest value of PA is 305 kcal/mol for M⁺ = AlO⁺. No correlation was found between the value of PA and the Mulliken charge on Al⁽¹⁾. With the exception of the case where M⁺ = AlO⁺ the binding energy of CO with the Brøsted acid proton is approximately 8.8 kcal/mol, independent of the nature of M⁺. When M⁺ = AlO⁺, the binding energy for CO is 11.1 kcal/mol. The present calculations suggest that different factors affect proton affinity and the binding energy for CO adsorption.     

Extraction of iridium(III) by ion-pair formation with 2-octylaminopyridine in weak organic acid media

To extract iridium(III), various physicochemical parameters were studied. 2-Octylaminopyridine was used for the extraction of iridium(III) from acetate medium at 8.5 pH. Quantitative extraction of iridium(III) was achieved via ion-pair formation of cation [2-OAPH⁺] and anion [Ir(CH₃COO)₄]^?. The stripping of iridium(III)-laden organic phase was carried out 2 M HCl (3 × 10 mL) . The stoichiometry of the extracted ion–pair complex was found to be 1:4:1 (metal: acetate: extractant). The extracted species [2-OAPH⁺. Ir(CH₃COO)₄^?] is assumed to be an ion association product of [Ir(CH₃COO)₄] ^? and [2-OAPH]⁺. The proposed method was successfully used in the separation of iridium(III) from binary and ternary mixtures. Analysis of various alloy samples was also carried out.