Willis Forsling

Surface complexation of calcium minerals in aqueous solution: 1. Surface protonation at fluorapatite—water interfaces

The amphoteric properties of hydrous fluorapatite surfaces have been investigated. The measurements were performed as potentiometric titrations in 0.1 M NaCl medium at 25°C using a glass electrode. The experimental data could be explained by a model that assumes the surface equilibria PO−+H+=POH logβs101(int.)=6.6±0.1(3σ) CAOH2+−H+=CAOH logβs-101(int.)=-9.7±0.1(3σ) The equilibrium constants were evaluated using the computer program FITEQL by Westall (Report 82-01, Department of Chemistry, Oregon State University, Corvallis, 1982), assuming a constant capacitance model for the electric double layer. The acidity constants result in a value of log[H+]pzc = −8.15, which shifts to log[H+]pzc = −7.13 upon exposure to atmospheric carbon dioxide.

On the transformation toughening of Y–ZrO2 ceramics with mixed Y–TZP/PSZ microstructures

Abstract Heat treatment of Y–TZP at high temperatures produces materials with a mixed Y–TZP/PSZ phase assemblage, which exhibit a unique combination of high mechanical strength and fracture toughness, uncommon in zirconia ceramics. The microstructure and crack growth resistance of the Y–TZP/PSZ materials developed by treating at 1650°C in air a fine-grained Y–TZP was studied. XRD as well as Raman spectroscopy results indicate that the obtained microstructure allow the retention of large tetragonal grains (up to ∼4 μm), resulting in both phase transformability enhancement and pronounced R-curve behavior. The large transformation zone, discerned from accurate measurements with Raman microprobe spectroscopy, sustains the above assessment and points out tetragonal to monoclinic phase transformation as the main toughening mechanism in the investigated Y–TZP/PSZ microstructures. This was confirmed by satisfactory agreement between the transformation toughening estimated from numerical analysis and the crack shielding experimentally determined from the R-curve measurements.

Sorption of atmospheric carbon dioxide and structural changes of Ca and Mg silicate minerals during grinding I. Diopside

Abstract Considerable sorption of atmospheric carbon dioxide by the ground mineral, alongside hydration due to atmospheric moisture, occurs in the course of prolonged dry grinding of natural and synthetic diopside in laboratory conditions. Grinding of natural diopside for 36 h results in about 10 wt.% of CaCO 3 in the ground sample. A unique double peak in the 1430–1515 cm −1 region in the FT-IR spectrum, attributable to the CO 3 2− group, shows that carbon dioxide is present in the ground diopside, in the same form as in synthetic and natural silicate glasses after dissolution of CO 2 at high temperatures and pressures relevant to the magma state. This conclusion is supported by the 13 C CP/ 1 H-decoupling MAS-NMR spectrum of ground diopside, which has a strong resonance signal at 167.4 ppm. Carbonate groups are present not only on the surface, but also in the bulk of mineral grains. The appearance of the new peak at approximately −108 ppm in 29 Si MAS-NMR spectrum of the ground diopside after 36 h of grinding shows that the Q 2 structure of crystalline diopside is partially transformed into the Q 4 structure. Together with XRD data, this result indicates the formation of quartz, which may occur through a re-polymerisation of an amorphous phase.

A new family of 3D 3d–4f heterometallic frameworks comprising 1D inorganic lanthanide ladders and organic CuI-bipyridine chains

A new family of the 3D heterometallic coordination polymers [{Ln2(SO4)2(H2O)2(pydc)2Cu2 (bpy)2·2(H2O)}]n (Ln = Sm (1), Eu (2), Gd (3), Tb (4) and Dy (5); pydc = 2,6-pyridine-dicarboxylate anion; bpy= 4,4′-bipyridine) have successfully been synthesized under solvothermal conditions (H2O/ethanol). All the coordination polymers obtained were characterized by elemental analysis, FT-IR analysis, differential thermal analysis/thermogravimetry (DTA/TG), fluorescent spectra and single crystal X-ray diffraction analysis. The most intriguing structural feature is that all the compounds exhibit 3D frameworks with 1D inorganic lanthanide ladders and organic CuI-bipyridine chains, which represent two types of 3d/4f coordination polymers (form I: Ln = Sm and Eu; form II: Ln = Gd, Tb and Dy) as the result of a so-called “gadolinium break effect”. Additionally, compounds 2 and 4 showed the characteristic emission spectra of the EuIII and TbIII ions, respectively, and appeared to have good fluorescence properties, while 1, 3 and 5 emitted fluorescence resembling CuI complexes. To our knowledge, the investigation of the effect of mixed ligands on the assembly of LnIII-CuI metal-based polymers has not been reported so far.

Surface hydration of aqueous γ-Al2O3 studied by Fourier transform Raman and infrared spectroscopy—I. Initial results

The hydration of γ-Al2O3 has been studied by Fourier transform (FT) Raman and infrared (IR) spectroscopy, and by X-ray diffraction (XRD). The initial findings are presented, along with a discussion of the possible causes for the major spectral changes that occur after hydration. The aims of the study and ongoing research are described.

Surface reactions in aqueous metal sulfide systems: 2. Ion exchange and acid/base reactions at the ZnSH2O interface

Abstract The amphoteric properties of hydrous ZnS surfaces as well as an ion exchange reaction between surface coordinated Zn 2+ ions and H + ions of the aqueous phase have been established. The measurements were performed as potentiometric titrations in 0.1 M NaClO 4 medium at 25°C. Besides measuring −log[H + ] by using a glass electrode, −log[S 2− ] was recorded (Ag/Ag 2 S selective electrode). In addition, the total concentrations of H + , Zn 2+ , and S were analyzed as a function of −log[H + ] of the bulk solution. Synthetically prepared ZnS and the mineral sphalerite were studied. Bro¨nsted acidity constants pK 1 s = 6.91 and pK 2 s = 10.28 for synthetic ZnS, and pK 1 s = 7.14 and pK 2 s = 10.29 for sphalerite, were established, which implies −log[H + ] of zero proton condition equal to 8.60 and 8.72, respectively. Furthermore, the ion exchange reaction SZn + 2H + ⇆ SH 2 + Zn 2+ was characterized within the range 4 ⩽ −log[H + ] ⩽ 7, with log K = 9.59 and 9.65. Experimental data were evaluated on the basis of the constant capacitance model by using the computer program FITEQL. The “best” fit to experimental data was obtained by assuming no charge dependence of K 1 s and K 2 s .

The structural reorganisation of bis(diethyldithiocarbamato)morpholine–zinc(II) and –copper(II) in the course of solid-state solvation with morpholine and benzene molecules studied by ESR, solid-state 13C and 15N CP/MAS NMR spectroscopy and single-crystal X-ray diffraction

Abstract Six forms of both non-solvated and solvated adducts of bis(diethyldithiocarbamato)–zinc(II) and –copper(II) with morpholine, of general formulas [M{O(CH2)4NH}{S2CN(C2H5)2}2] and [M{O(CH2)4NH}{S2CN(C2H5)2}2]·L (M=Zn(II) (1): L=O(CH2)4NH (2), C6H6 (3); M=Cu(II) (4): L=O(CH2)4NH (5), C6H6 (6)), have been prepared and studied by means of ESR, solid-state natural abundance 13C and 15N CP/MAS NMR spectroscopy and single crystal X-ray diffraction data. The existence of two conformers, which are correlated as rotation isomers, was unambiguously established for both zinc(II) and copper(II) non-solvated adducts 1 and 4. These two isomeric forms are characterised by different modes of spatial orientation of the non-planar morpholine ring relative to the two four-membered metallochelate rings. The geometry of the adduct molecules is close to square pyramidal, C4v, and therefore the ground state of the unpaired copper(II) electron corresponds to the 3dx2−y2 atomic orbital (AO). Solvation of the studied adducts in the solid state leads to their significant structural reorganisation at the molecular level, i.e. their structural unification yielding qualitatively new structural states with: (i) different lengths of the ZnN bond; (ii) reoriented heterocyclic ring of the coordinated morpholine molecule; and (iii) an enhanced contribution of trigonal-bipyramidal character to the geometry of the coordination polyhedra of the central atom (from 7.5 and 22.7% in original adducts to ∼75% in solvated forms). The type of geometry of the coordination polyhedrons in the solvated forms of the adducts (intermediate between trigonal bipyramid D3h and square pyramid C4v) correlates with the fact that the ground state of the unpaired copper(II) electron is a mixture of 3dz2 and 3dx2−y2 AOs. All observed ESR and NMR resonances have been assigned and are in agreement with the structures obtained from X-ray diffraction data.

A spectroscopic study of the solvation of 1-vinyl-2-pyrrolidone and poly(1-vinyl-2-pyrrolidone) in different solvents

The solvation of 1-vinyl-2-pyrrolidone and poly(1-vinyl-2-pyrrolidone) in solvents of varying polarity, specifically water, ethylene glycol, chloroform and carbon tetrachloride, was investigated by ...

Interfacial interactions and mechanical properties of mineral filled polymer composites: wollastonite in PMMA polymer matrix

Abstract The nature of stearic acid and polymethylmethacrylate (PMMA) adsorption onto wollastonite has been studied from basic, neutral and acidic organic solvents by infrared (IR) spectroscopy. The roles of acid-base interactions on adsorption and wollastonite dispersion in polymer matrix have been discussed with the determined mechanical properties of surface-treated (stearic acid) and untreated wollastonite-filled PMMA polymer composites. Maximum adsorption of either stearic acid or PMMA occurs from a nonpolar solvent, and the adsorption is found to decrease with increasing acidity or basicity of the solvents. The adsorption corresponds to two geometrical layers either from nonpolar (carbon tetrachloride) or from slightly basic (benzene) and acidic (methylene dichloride) solvents. Increased acidity (chloroform) or basicity (tetrahydrofuran) of solvents led to a monolayer or a fraction of the monolayer coverage. The primary adsorption of stearic acid is thought to be the formation of hydrogen bonds between surface hydroxyl groups and carboxylic acid groups. The tensile and impact strength properties of the composites that are filled with stearic acid-treated wollastonite are improved when compared to the untreated filled composite. The results suggest a stronger interfacial bonding between stearic acid and filler than that of polymer to the filler. Thus, the application of stearic acid for surface modification of acidic fillers such as wollastonite is emphasized.

The degradation kinetics of ethyl-xanthate as a function of pH in aqueous solution

Xanthate degradation kinetics plays an important role in sulfide mineral flotation and in the treatment of flotation tailings. Increasing environmental concern about consequences of flotation taili ...