Patricio Rafael Ramirez Rivas

• National University of La Plata

By means of Perturbed Angular Correlation (PAC) analysis the resulting phases during mechano-chemical activation process on zircon (ZrSiO4) commercial fine powder (D50 ≅ 0.8μm) were accurately identified and characterized.A high energy planetary mill was employed with 850. rpm up to 120. min. The phenomenological macroscopic confirmation of the str...

Accepted June 18th 2017 - In ceramic industry, zircon sand is widely used in different applications because zirconia plays a role as common opacifying constituent. In particular, it is used as a basic component of glazes applied to ceramic tiles and sanitary ware as well as an opacifier in unglazed bulk porcelain stoneware. Natural zircon sands are...

Pearson correlation coefficients between 40K, 226Ra and 232Th activities and the total Fe phase fractions yielded by Mössbauer spectroscopy have been calculated for soils of the Province of Buenos Aires, Argentina. Total fractions of Fe phases have been obtained from the relative fractions reported in previous works weighted by the Fe soil content...

The mechanochemical activation process has proved to be an effective technique to enhance a solid-state reaction at relatively low temperatures. In such a process, the mechanical effects of milling, such as reduction of particle size and mixture homogenization, are accompanied by chemical effects. The actual chemical phases during the mechanical tr...

The activity concentrations of both natural (238U and 232Th chains and 40K) and anthropogenic (137Cs) radionuclides down along the soil profile have been determined in soil samples collected from inland and coastal areas of the La Plata River, located in the Northeastern region of the Province of Buenos Aires, Argentina. These studies were compleme...

The short range technique of the Perturbed Angular Correlation (PAC) and x-ray diffraction (Rietveld) methods have been employed to determine the phase content in commercial mullite–zirconia and zircon raw materials that are ordinarily used to produce ceramic materials. The PAC technique, which probes zirconium-containing compounds at nanoscopic le...

In the field of refractory materials, ceramics containing mullite–zirconia are the basis of those most used in the industry of glass and steel. It is known that the addition of zircon improves the behavior of the refractory used in service. Knowing that some mullite–zirconia composites properties as fracture strength and the elastic modulus E are a...

It has been already published that, at nanoscopic level, zircon exhibits wide regions of aperiodic material not detected by the ordinary techniques used to analyse the obtained product in the production of ceramic materials. In this paper it is reported how the Perturbed Angular Correlations (PAC) technique has assisted the interpretation of a mism...

The Perturbed Angular Correlations technique was used to determine the configurations around Zirconium ions and their thermal behavior in non-aggregated sub-micron zirconia spherical particles. Three residues containing- Zr surroundings were determined for the non-crystalline starting particles, which were identified under the assumption of a certa...

Solid solutions of ZrO2 and HfO2 are potential electrolyte materials for intermediate-temperature SOFC because both are oxygen-ion conductors. The main challenge for these compounds is to reduce the relatively high value of the activation energies vacancies diffusion, which is influenced by several factors. In this work the thermal evolution of CaO...

This paper deals with the phase stability of an aqueous suspension of tetragonal Zr(0.9)Pr(0.1)O(2) (20 wt%/vol%) at room temperature as a function of the aging time. The suspension is investigated in situ using the highly localized Perturbed Angular Correlations technique. The results indicate that an almost fully reversible degradation process to...

The hyperfine quadrupole interaction at Hf sites in films and powders of 14 mol% CaO–HfO2 and 20 mol% CaO–HfO2 has been determined as a function of temperature. Results indicate the formation of a cubic solid solution and other microstructures assigned to the ϕ1 (CaHf4O9) and ϕ2 (Ca6Hf19O44) phases. Dynamical effects on the electric field gradient...

A perturbed angular correlation (PAC) study as a function of temperature has been carried out on spray pyrolysis-derived powders and compacts of 2.5 mol% Y2O3–ZrO2 and 2 mol% Gd2O3–ZrO2 nanostructured tetragonal zirconias. The powders undergo the ordinary thermal transformation between the two known defective t′- and regular t-tetragonal forms and...

The Mössbauer effect and perturbed angular correlation techniques have been used to investigate the nature and thermal stability of Zr and Fe surroundings in a solid solution of zirconia and 15 mol% hematite obtained by mechanical mixing. Hematite incorporates completely into the zirconia lattice, resulting in a substitutional cubic structure that...

A Zr(10 mol % Pr)O2 powder obtained by high-energy ball milling has been investigated at nanoscopic scale using primarily the Perturbed Angular Correlations technique. The aim has been to determine the nanoconfigurations around Zr4+ cations present in the solid solution and their thermal evolution with the intention of providing knowledge on the st...

Monoclinic ZrO2 has been milled for various times down to a crystallite size of 145 Å. Using the time-differential perturbed-angular-correlation technique, it was possible to associate the resulting growing amount of disordered material with two different, very distributed and milling-time-dependent hyperfine interactions: one (Y) of quadrupole fre...

This paper deals with a perturbed angular correlation investigation of the microstructure and subsequent thermal evolution of a commercial ZrO2-2. 8 mol% Y2O3 ceramic powder and of a pellet obtained upon sintering the powder at 1450°C. The perturbed angular correlation results, complemented by those of X-ray diffraction and Raman spectrometry, indi...

Zirconia powders, prepared by a sol-gel method using zirconium n-propoxide (ZNP) and different H2O/ZNP and alcohol/ZNP ratios, were investigated by the perturbed-angular-correlation method, along with X-ray diffraction (XRD), Raman spectroscopy, differential thermal analysis (DTA), and thermogravimetric analysis (TGA) techniques. The hyperfine inte...

By using Perturbed Angular Correlation Spectroscopy, a suitable technique to explore internal fields at nanoscopic scale, the electric field gradients at Zr4+ sites in the Pr2Zr2O7 compound have been determined as a function of temperature. Three nonequivalent nanoconfigurations are present, which have been interpreted with the aid of point charge...

The nature and thermal evolution of nanoconfigurations around cations in a sol-gel derived solid solution of a ZrO2 15 mol % Fe2O3 nominal concentration have been investigated by means of the hyperfine techniques of the Mössbauer effect at the Fe sites and perturbed angular correlation spectroscopy (PAC) at the Zr sites, assisted by X-ray diffracto...

A nanocrystalline ZrO2–10 mol% Y2O3 powder synthesized by a nitrate–citrate gel-combustion process and stabilized in the metastable t′′-form of the tetragonal phase has been characterized using mainly the Perturbed Angular Correlations technique. The determined hyperfine interaction allows a clear distinction between the zirconium surroundings in t...

This work focuses on the microwave-assisted hydrothermal synthesis of praseodymium-doped zirconia and on the subsequent evaluation of the effect of synthesis conditions on powder properties. Pure and 10 mol% Pr-doped zirconia samples have been analyzed by X-ray diffraction (XRD) and the perturbed angular correlations hyperfine technique, which prob...

The PrxZr1-xO2 ceramic system obtained by coprecipitation has been investigated at zirconium sites as a function of Pr content (1, 10, and 15 mol %) and of annealing temperature by means of the perturbed angular correlations (PAC) technique. Praseodimium enters zirconia forming a tetragonal solid solution whose extent increases with Pr content. In...

Sol-gel-derived powder samples of zirconia (ZrO2) prepared via the dissolution of zirconium n-propoxide in methanol, ethanol, and 2-propanol have been characterized mainly using perturbed angular correlations spectroscopy, as a function of temperature. Results indicate that the nanostructures and subsequent thermal evolution are alcohol dependent:...

The thermal behavior of the hyperfine interaction at Zr sites on two sol-gel derived 6 mole% CaO-ZrO2 powders, obtained from the particulate and non-particulate regimes, has been studied by Perturbed Angular Correlations and complementary techniques. The aim was to get experimental support on the thermal stability of the obtained material in order...

Two sol-gel derived zirconia powders were prepared at pH = 0.5 and pH = 5.5. They were investigated as a function of temperature using mainly perturbed angular correlation spectroscopy. The aim was to elucidate the relationship between the nanoscopic configurations around Zr4+ ions and the morphology and structure of the powders. The highly porous...

Tetragonal compact bodies obtained by quenching from the melt a ZrO2–2.8 mol% Y2O3 commercial powder have been investigated between room temperature and 1150°C, using mainly perturbed angular correlations spectroscopy. The resulting nontransformable t′ phase observed by optical micrography is characterized at nanoscopic level by a hyperfine interac...

The aim of this work has been to investigate the influence of two coloring dopant ions on the ZrSiO4 host lattice. Pure, vanadium-doped and praseodymium-doped zircon powders have been synthesized by the ceramic method and analyzed using X-ray diffraction and the perturbed angular correlations (PAC) hyperfine technique, which probes the nearest envi...

Two powder samples of ZrO2-5 wt.% Al2O3 derived from precursor solutions of different pH – 2 for sample (C) and 4 for sample (D) – were prepared by the precipitation method. They were studied using PAC between RT and 1150ºC and XRD after heating at increasing temperatures. According to XRD, the addition of Al2O3 causes the complete stabilization of...

The hyperfine quadrupole interaction of CoHfF6.6H2O and ZnHfF6.6H2O was determined at room temperature for the first time. The thermal behaviour of the electric field gradient at hafnium sites in the compounds AHfF6.6H2O (where A is Co, Ni or Zn) determined using the time differential perturbed angular correlations (TDPAC) technique, is presented i...

The evolution of the phase content in zirconia powders that have been prepared by sol-gel acid hydrolysis has been investigated using the perturbed-angular-correlation (PAC) technique and X-ray diffractometry. As a consequence of performing annealing treatments at increasing temperatures between room temperature and 1,000 C, the amorphous starting...

Powders and coatings of zirconia doped with 2.5 mole% yttria have been produced via the sol-gel route. The phase structure and subsequent thermal evolution in heating and cooling cycles have been investigated using mainly perturbed angular correlations spectroscopy. Thermal analyses and XRD as a function of temperature have also been performed to o...

The evolution of the hyperfine quadrupole interaction in \beta-ZrF4 at Zr sites, is measured between 273 and 740 K via the Perturbed Angular Correlations technique. Two different quadrupole interactions, in a ratio 1:2 of relative fractions, are determined. It is observed that the compound remains stable all over the thermal range. Moisture exposur...

Powders and thin films of zirconia doped with 2.5 and 11.3 mole% Y2O3 have been fabricated via the sol-gel route. The phase structure and its thermal evolution have been investigated using mainly the hyperfine nuclear technique of Perturbed Angular Correlations. Both resulting structures, tetragonal and cubic, exhibited at least two different confi...

Yttria-stabilized cubic zirconia powders and coatings produced by the sol-gel method have been investigated by Perturbed Angular Correlation Spectroscopy (PAC). Results indicate that the metastable cubic phase is retained during heating and cooling cycles. The hyperfine interaction that describes this cubic phase, once crystallized, exhibits two co...

This paper deals with a perturbed angular correlation investigation of the microstructure and subsequent thermal evolution of a commercial ZrO{sub 2}-2.8 mol% Y{sub 2}O{sub 3} ceramic powder and of a pellet obtained upon sintering the powder at 1,450 C. The perturbed angular correlation results, complemented by those of X-ray diffraction and Raman...

Zirconia and zirconia-yttria coating films and powders obtained by the sol-gel route using a zirconium alkoxide as starting material and acid and neutral catalytic were investigated by the Perturbed Angular Correlations method (PAC), XRD, DTA and TGA. The hyperfine interaction was measured either during heat treatements or after annealing the sampl...

Monoclinic ZrO[sub 2] has been milled for various times down to a crystallite size of 145 [angstrom]. Using the time-differential perturbed-angular-correlation technique, it was possible to associate the resulting growing amount of disordered material with two different, very distributed and milling-time-dependent hyperfine interactions: one (Y) of...

Zirconia coating film and powder obtained by the sol-gel route using zirconium n-propoxide as starting material and acid catalyst were investigated by the Perturbed Angular Correlations method, X-Ray Diffraction and Differential Scanning Calorimetry and Differential Thermal Analyses. The hyperfine interaction, measured after annealing the samples a...

The time-differential perturbed angular correlation technique has been used to investigate the thermal behavior of a ZrO2−13.6 mole % MgO ceramic between room temperature and 1423 K. Two different quadrupole hyperfine interactions corresponding to a tetragonal structure have been found to result on cooling the ceramic from the single-phase cubic fi...

Time-differential perturbed-angular-correlation measurements on NiHfF6· 6H2O were performed as a function of temperature in the 77–521 K range. This compound was observed to dehydrate to NiHfF6 · 4H2O and NiHfF6 at 421 and 476 K, respectively. At higher temperatures the last substance undergoes a phase transition from the hexagonal to the cubic str...

The hyperfine interaction in Ni2HfF812H2O has been determined between 77 K and 1100 K by means of the time-differential perturbed angular correlation technique. From 200 K on, the one-site phase existing at lower temperatures undergoes a gradual phase transition until, at room temperature, the populations of both phases attain a 2:1 ratio. While th...

Using time-differential perturbed-angular correlation, two thermal reversible phase transitions have been observed in both isostructural compounds K3HfF7 and K3ZrF7: the orthorhombic-to-tetragonal transition, occurring in K3HfF7 around 275 K, and the tetragonal-to-disordered cubic transition, which developed from room temperature (RT) over a wide t...

The quadrupole hyperfine interaction of the tetragonal phase of the zirconium oxide has been measured at 1523 K using the time-differential perturbed angular correlation technique. The electric field gradient at zirconium sites was determined to beV zz =(17.50.4)1017 Vcm−2 and axially symmetric.

The quadrupole hyperfine interaction of ZrF4.3H2O is reported. This compound is observed to dehydrate to ZrF4 at 325 K. Spectra taken on cooling were observed to be time dependent, and the rehydration process involved was investigated at 293, 298 and 302 K. Contrary to what had previously been determined in HfF4.3H2O, no intermediate compound was o...

The thermal behavior of the quadrupole hyperfine interaction in Rb2HfF6 and Rb2ZrF6 has been studied between 293 and 800 K with high-resolution time-differential perturbed-angular-correlation equipment. Both compounds exhibit a very similar temperature dependence, undergoing a phase transition near 740 K. An embryonic state of the high-temperature...

The thermal behavior of the hyperfine interaction in K2HfF6 was investigated by means of the time-differential perturbed-angular-correlation technique between 293 and 750 K. The quadrupole parameters associated with the monoclinic, orthorhombic, cubic, and trigonal phases have been determined. An activation energy Ea=86±16 kJ/mol could be calculate...

The quadrupole hyperfine interaction in Li2ZrF6 and Li2HfF6 has been studied as a function of temperature. Both lattices are characterized by very similar low and symmetric electric field gradients at probe sites and no phase transitions were observed up to 770 K. On heating, between 700 and 830 K, the Li2ZrF6 undergoes chemical reactions which giv...

A TDPAC investigation has been accomplished on (NH4)2 HfF6 between 14 and 620 K. A phase transition was observed below 390 K. The low temperature phase is characterized by two non-equivalent sites for hafnium atoms in a 1∶1 ratio. The high temperature phase, on the other hand, is depicted by a unique quadrupole interaction. Above 400 K, the compoun...

The thermal evolution of the hyperfine interaction in α-ZrF4 is investigated between 293 K and 788 K. The first change, observed ay 534 K, is attributed to the appearance of the non-stoichiometric compound ZrO1.3F1.4. During the transformation, the relative fraction of the latter shows an Arrhenius behaviour with an activation energyE a=(22.6±5.5)...

The hyperfine quadrupole interaction of HfF4.3H2O at Hf sites is investigated from 14 to 820 K. No transitions have been found. After the complete dehydration of this compound at 393 K, chemical reactions take place which give rise to hafnium oxifluorides and metastable forms of hafnium oxide. Heating treatments at increasing temperatures make HfO2...

Wie mit Hilfe der Titelmethode und komplementären RÖntgen-Beugungsanalysen gezeigt wird, läuft die thermische Zers. der Titelverbindung im Temp.-Bereich 400-800 Kgemäß Reaktionsfolge A ab.

Via the TDPAC technique and complementary x‐ray diffraction analysis, the thermal decomposition of (NH4)2ZrF6 has been observed to occur in the range 400–800 K according to the thermolysis scheme (NH4)2ZrF6→485 KNH4ZrF5→560 KNH4Zr2F9 →620 KZrF4→760 KZrO2. Assuming that the first transformation takes place through the simple chemical reaction (NH4)2...

Quadrupole hyperfine interactions in HfF4 and HfF4·3H2O determined by time differential-perturbed angular correlations technique are reported. Changes in the hyperfine interactions of HfF4·3H2O with temperature are interpreted in terms of a dehydration process. The reversal process is studied at room temperature as a function of time. Assuming that...

The thermal dependence of the hyperfine quadrupolar interaction of181Ta at Zr sites in K2ZrF6 has been studied by TDPAC between RT and 511 °C. Four phases of ever increasing symmetry have been found in the range RT-437 °C. The possible existence of a healing mechanism with an activation energy of 0.187±0.040 eV is discussed for the lattice recovery...

The thermal evolution of the hyperfine quadrupole interaction in (NH4)2ZrF6 has been investigated via TDPAC from 14 to 400 K. A phase transition is detected near 370 K. The low-temperature phase exhibits two sites equally populated for181Ta probes. The associated electric field gradients are described by both high asymmetry parameters and high inte...

Time-differential perturbed angular correlation (TDPAC) measurements in NH4Hf2F9 were performed between 15 and 580 K. The compound was found to be stable in the whole temperature range and no phase transitions were observed. Experimental results could be explained assuming two equally populated quadrupole interactions which suggest a neat inequival...