A protometric study on the speciation of zirconium(IV) was performed in an aqueous solution at 25 °C in KNO3 and four ionic strengths (0.2, 0.5, 1, and 2 mol·dm−3). This study indicates the formation of the soluble species Zr(OH)3+, Zr2(OH)7+, and Zr(OH)4 in the pH range 1.5–3.5. The use of an appropriate titration technique allows the precipitation of the zirconium hydroxide to be limited. The overall stability constants βmlh of these three hydroxo complexes were computed and refined, by the program PROTAF, for each ionic strength. The solubility product Ks of Zr(OH)4 was calculated by taking these βmlh constants into account. The thermodynamic values were determined by extrapolation at zero ionic strength (Specific ion Interaction Theory method): log β°10–3 = –0.52 (0.01); logβ°20–7 = –2.22(0.07); logβ°10–4 = –4.52 (0.07); logKs° = –55.26(0.08).

A protometric study on the speciation of zirconium(IV) was computed and refined, by the program PROTAF, for each ionic strength. The solubility product Ks of Zr(OH) 4 was performed in an aqueous solution at 25°C in KNO 3 and four ionic strengths (0.2, 0.5, 1, and 2 mol·dm -3 ). This study calculated by taking these β mlh constants into account. . Increasing zirconium concentration induces the formation of polynuclear species outstanding resistance to corrosion, as well as to a low neutron capture cross-section. It is an essential constituent of Zr m (OH) h (4mϪh)ϩ . In accordance with studies from Zielen and Connick [2] , Johnson and Kraus [11] , and Angstadt and the core of the nuclear power station and for confining fissile materials.Tyree [12] , Baes and Mesmer conclude that the existence of a trimer, Zr 3 (OH) 4 8ϩ or Zr 3 (OH) 5 7ϩ , and of the tetramer The running of nuclear installations relies on the proZr 4 (OH) 8 8ϩ is probable. cessing of nuclear fuels and fission by-products, but also on the long-term storage, in protected sites, of confined materiAja et al. [13] also published a review concerning the aqueals which have acquired an appreciable radioactivity.ous chemistry of zirconium(IV). They principally take into In the long-term one may expect the possibility of cor-account the results obtained by Russian scientists [5] [6] [8] [14] . rosion and fissuring of the confining containers leading to They consider that the values of the formation constants of a contamination of soils and waters.the mononuclear hydroxide complexes depend little on the ionic strength and the nature of the supporting electrolyte. Modelling programs which take into account the whole For these constants, they have retained average values which local physical parameters as well as the physicochemical are very different from those given by Baes and Mesmer. data allow the quantification of these contamination risks. The values used for these simulations, especially those relatMore recently, Adair et al. [15] published an article entitled ing to zirconium, have to be as reliable as possible in order "A review of the aqueous chemistry of the zirconium-water to yield realistic estimations.system" in which they simply give the same values of conThe chemistry of zirconium(IV) in aqueous media is stants that Baes and Mesmer indicated for the mono-and dominated by the complexation of Zr 4ϩ with OH Ϫ . The polynuclear zirconium hydroxide complexes at 25°C. data currently available on zirconium hydroxide complexes In short, numerous studies deal with the formation of comes from studies carried out (essentially) before zirconium-hydrolysed complexes in aqueous solution but. The advanced species formulae many discrepancies exist from one author to another conand, above all, the values of the corresponding comcerning the major species formed and the values of the corplexation constants, seem questionable.responding constants of formation. It must be pointed that Baes and Mesmer [10] have reviewed bibliographical re-in these studies the stoi...

Rubber materials with well-dispersed fillers and large mechanical reinforcement have been obtained by melt-processing a diene elastomer matrix and tailored nanocellulose powders having both a high specific surface area and a modified interface. Such filler powders with a specific surface area of 180 m2 g-1 and 100 m2 g-1 have been obtained by freeze-drying suspensions of short needle-like cellulose nanocrystals (CNCs) and entangled networks of microfibrillated cellulose (MFC) in tert-butanol/water, respectively. A quantitative and toposelective filler surface esterification was performed using a gas-phase protocol either with palmitoyl chloride (PCl) to obtain a hydrophobic but non-reactive nanocellulose interface, or with 3,3'-dithiopropionic acid chloride (DTACl) to introduce reactive groups that can covalently bind the nanocellulose interface to the dienic matrix in a subsequent vulcanization process. A set of filled materials was prepared varying the filler morphology, interface and volume fraction. Transmission electron microscopy images of ultrathin cryo-sections showed that modified nanocellulose fillers presented a relatively homogeneous distribution up to a volume fraction of 20%. The materials also exhibited a significant modulus increase, while keeping an extensibility in the same range as that of the neat matrix. Strikingly, in the case of the reactive interface, a strong stress-stiffening behavior was evidenced from the upward curvature of the tensile curve, leading to a large increase of the ultimate stress (up to 7 times that of the neat matrix). Taken together, these properties, which have never been previously reported for nanocellulose-filled elastomers, match well the mechanical characteristics of industrial carbon black or silica-loaded elastomers.

No abstract

No abstract