Nenad Tomašić

Study of thermal stability of (3-aminopropyl) trimethoxy silane-grafted titanate nanotubes for application as nanofillers in polymers

Protonated titanate nanotubes (TiNT-H) were surface-modified with (3-aminopropyl)trimethoxy silane (APTMS) by a novel method suitable for the syntheses of large amounts of materials at a low cost. The usage of prepared nanotubes for polymer reinforcement was studied. Since the thermal stability of the nanofiller was important to preserve its functional properties, its stability was studied by in situ high-temperature measurements. The most thermally stable nanotubes were silanized for 20 min and used for the preparation of epoxy-based nanocomposites. The nanofiller formed smaller (a few hundred nm) and larger (a few μm) aggregates in the polymer matrix, and the amount of aggregates increased as the nanofiller content increased. The APTMS-modified titanate nanotubes bonded well with the epoxy matrix since amine groups on the TiNTs surface can react with an epoxy group to form covalent bonds between the matrix and the nanofiller. A very small addition (0.19-1.52 wt%) of the nanotubes significantly increased the glass transition temperature and the modulus in the rubbery state of the epoxy-based polymer. Smaller nanofiller content leads to a larger increase in these parameters and therefore better dynamic mechanical properties due to the smaller amount of large aggregates. APTMS-modified titanate nanotubes have proven to be a promising nanofiller in epoxy-based nanocomposites.

Preservation of samarskite structure in a metamict ABO4 mineral: a key to crystal structure identification

Relics of the original samarskite structure were identified in a metamict ABO4 mineral from Beinmyr pegmatite, Norway, using selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The chemical composition of the sample confirmed the affiliation to the samarskite group giving general formula (REE0.322Ca0.269Fe0.231U0.142Mn0.031Pb0.011Th0.010Zr0.010Al0.00 4Sc0.002Na0.001K0.001)1.034(Nb0.707Ta0.267Ti0.069W0.017Sn0.007) 1.067O4 which corresponds well to the general ABO4 stoichiometry of the samarskite group. The structure identified by transmission electron microscopy (TEM) techniques is well related to the proposed low-temperature samarskite modification (Sugitani et al. 1985) crystallizing in Pbcn space group with the cell parameters a=5.69(2) A, b=4.91(2) A, c=5.21(2) A. The original mineral sample showed to be X-ray amorphous. Gradual recrystallisation in air in the temperature range between 400 and 1000oC yielded a pyrochlore phase being stable at all experimental temperatures. At 800oC a high-temperature samarskite phase (s.g. P2/c) co-crystallised with an increase in crystallinity at 1000oC. Recrystallisation in a reducing atmosphere (Ar/H2) did not yield the high-temperature samarskite phase solely. Unsuccessful recrystallisation of the high-temperature samarskite modification is mainly related to an alteration which shifted the composition of samarskite to pyrochlore as evidenced by occurrence of altered domains in the sample. Raman spectra of thermally untreated samarskite showed generally metamict nature of the mineral, although a few normal Nb-O vibration modes can be resolved indicating BO6 arrangement similar to the one of columbite.

Characterization and treatment of the phosphoric gypsum transport water

This paper presents a new treatment procedure applied on phosphogypsum transport water. Untreated transport water is highly acidic (pH 1.79), having fluoride content of 1540 mg/L and elevated values of phosphates (215 mg/L) and heavy metals (Fe = 25.8 mg/L; Zn = 5.7 mg/L; Mn = 2.7 mg/L, V = 1.7 mg/L). Neutralization/purification of the transport water was carried out with wood fly ash, otherwise a rich source of calcium, composed of calcite, dipotassium calcium carbonate and hydroxylapatite. Maximum removal efficiency of fluoride was observed at pH 7 (99.99%) and phosphate at pH 9 (96.29%). The removal of fluorides was a consequence of the formation of fluorite and fluorapatite mineral phases derived from the reaction of calcium (released from the fly ash minerals) and fluorides (from the transport water). The removal of phosphates resulted from the formation of fluorapathite and hydroxilapatite. At the optimum conditions removal efficiencies for the elements Pb, V, Cr(VI), Mn, Fe, Ni, Cu, and Zn were 95%, 98.14%, 91.11%, 100%, 99.71%, 96.33%, 97.24%, and 99.65%, respectively. Optimal heavy metal removal occurred in major cases at pH 7.

Dehydration processes in borate minerals: pentahydroborite and nifontovite from Fuka Mine, Okayama Prefecture, Japan

Abstract Data on the dehydration of pentahydroborite, CaB2O(OH)6・2H2O and nifontovite, Ca3B6O6(OH)12・2H2O from the Fuka mine, Japan are presented. Critical temperatures of the dehydration of the borates were determined by thermogravimetric analysis/differential thermal analysis measurements. The untreated mineral samples and their heating products were investigated by X-ray diffraction and Raman spectroscopy. Upon dehydration, both minerals decompose and undergo amorphization, and at greater temperatures crystallize as an orthorhombic calcium borate, CaB2O4 (Pnca). The dehydration paths of the two minerals are different, with nifontovite showing a greater resistance to decomposition and amorphization than pentahydroborite. Differences in the dehydration processes are related to the residuals of the water content and structural accommodation of the borate polyanion.

The role of uranium(V) ion in the chemical composition of meta-autunite from pegmatites of Quintos de Baixo, Brazil

Meta-autunite from the pegmatite mineralization of Quintos de Baixo, Brazil was investigated. The total uranium content and elemental analysis yield the formula Ca(UVIO2)2-x(UVO2)x(H3O+)x(PO4)2.(6-x)H2O for the meta-autunite. The natural sample crystallizes tetragonally in the space group P4/nmm having unit cell parameters a=6.990(1) A ; ; ; , c=8.445 (1) A ; ; ; and V=412.6(1) A ; ; ; 3 calculated from X-ray diffraction data. Thermal analysis showed a weight loss of 16.03 wt% in four distinct processes up to 1500o ; ; ; C. Electron paramagnetic resonance (EPR) spectroscopy provides evidence that part of the uranium present in meta-autunite is in the pentavalent state. High temperature diffraction data show lowering of the symmetry, decreasing the unit cell parameters and finally, the breaking of the structure of the phosphate phase and formation of monoclinic uranium oxide and an amorphous phase. At 80°C meta-autunite I transforms into the meta-autunite II with orthorhombic symmetry, while further heating produces changes in the diffraction pattern due to dehydration, although all the heating products could be by analogy identified as meta-autunite II. The calculated unit cell parameters for this phase decrease from a=7.253(4) A ; ; ; , b=6.537(3) A ; ; ; , c=7.008(4) A ; ; ; at 82°C to a=6.38(2) A ; ; ; , b=5.82(1) A ; ; ; , c=6.68(1) A ; ; ; at 204°C. Uranium oxide phases originating from the breakdown of the phosphate structure show temperature dependant stability. At 1050°C hexagonal U2O3 analogous with  -Al2O3 is present with symmetry (R c) and unit cell parameters (a=4.806(1) A ; ; ; , c=13.138(4) A ; ; ; , V=262.9(1) A ; ; ; 3).

Copper and Zinc Fractionation in Apple Orchard Soil in the Village of Bukevje (Croatia) Using the Revised Four-Step BCR Extraction Procedure

Abstract The aim of this study was to establish the fractionation of copper and zinc in a small apple orchard using the revised (four-step) Bureau Communautaire de Reference (BCR) sequential extraction procedure and assess their potential mobility in soil. Soil samples were collected at the depth of 10 cm to 25 cm, sixteen from the orchard and five control samples from a meadow located some 200 m away from the orchard. As the distribution of trace-element concentrations in the control samples was normal, they were used for comparison as background levels. We also determined soil mineralogical composition, carbonate content, soil pH, cation exchange capacity, and soil organic matter. The extraction yields of Cu and Zn from the control soil were lower than from the orchard soil (25 % vs. 34 % and 47 % vs. 52 %, respectively), which pointed to natural processes behind metal bonding in the control soil and greater influence of man-made activities in the orchard soil. Compared to control, the orchard soil had significantly higher concentrations of total Cu (P=0.0009), possibly due to the application of Cu-based fungicides. This assumption was further supported by greater speciation variability of Cu than of zinc, which points to different origins of the two, Cu from pesticides and Zn from the parent bedrock. Copper levels significantly better (P=0.01) correlated with the oxidisable fraction of the orchard soil than of control soil. Residual and organically bound copper and zinc constituted the most important fractions in the studied soils. However, the use of Cu-based fungicides in the apple orchard did not impose environmental and health risk from Cu exposure. Sažetak Analizirani su uzorci tla iz obiteljskog voćnjaka u selu Bukevju kako bi se utvrdilo ponašanje metala u tragovima u okolišu u kontekstu poljoprivrednih postupaka proteklih nekoliko desetljeća. Unos kemijskih sredstava za zaštitu bilja navodno je nizak. Nakon provedene tzv. BCR sekvencijske ekstrakcijske analize, kemijski oblici bakra i cinka razmotreni su iz geokemijskoga/geološkoga gledišta. Uzeto je šesnaest uzoraka tla iz voćnjaka te pet uzoraka kontrolnog tla s obližnje livade. Analize su obuhvaćale određivanje mineralnog sastava tla, kationsko izmjenjivačkog kompleksa (KIK), pH tla i gubitka žarenjem. Koncentracije mjerenih varijabli u kontrolnim uzorcima, određene XRF metodom, upućuju na njihove prirodne razine na temelju normalnosti raspodjela. Tlo iz voćnjaka neznatno je onečišćeno bakrom, moguće od primjene fungicida na bazi bakra, što je utvrđeno Mann-Whitneyevim U testom, koji je pokazao statistički značajno više koncentracije ukupnog Cu (P = 0.0009) u tlu voćnjaka u usporedbi s uzorcima kontrolnog tla. Učinkovitost BCR ekstrakcije bakra i cinka izračunata za kontrolno tlo (25 % odnosno 47 %) bila je niža nego ona izračunata za tlo iz voćnjaka (34 % odnosno 52 %). Bakar, potječući djelomice od fungicida, pokazao je veću specijacijsku varijabilnost u istraživanim tlima u usporedbi s cinkom, za koji se pretpostavlja da potječe uglavnom od trošenja stijenske podloge. Mann-Whitneyev U test pokazao je statistički značajno (P = 0,01) više vrijednosti Cu povezane s frakcijom tla iz voćnjaka podložnoj oksidaciji u odnosu na istu frakciju kontrolnih uzoraka. Bakar i cink u istraživanim tlima čvrsto su vezani za rezidualnu i organsku frakciju, a ukupne im vrijednosti ne premašuju maksimalno dopuštenu količinu onečišćujućih tvari u poljoprivrednom zemljištu, pa ne bi trebali predstavljati toksikološku opasnost za ljudsko zdravlje.

57Fe Mössbauer study of iron distribution in zeolite A during zeolite crystallization process

Abstract Fe-exchanged samples of zeolite A were prepared and their time-dependent properties during hydrothermal crystallization were studied by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Rutherford backscattering (RBS) and 57Fe Mossbauer spectroscopy. The relative amounts of various iron species deduced from 57Fe Mossbauer spectra of the Fe-exchanged samples are in a good correlation with the extent of ordering during the hydrothermal crystallization