Nanocrystalline Zirconia Research Articles

A Method for Quantitative Phase Analysis of Nanocrystalline Zirconium Dioxide Polymorphs.

A method based on X-ray diffractometry was developed for quantitative phase analysis of nanocrystalline zirconium dioxide polymorphs. Corresponding formulas were derived. The key factors therein were evaluated by rigorous theoretical calculation and fully verified by experimentation. A process of iteration was raised to make the experimental verification proceed in the case of lack of pure ZrO2 crystal polymorphs. By this method, the weight ratios of tetragonal ZrO2 (t-ZrO2) to monoclinic ZrO2 (m-ZrO2) in any a mixture that contains nanocrystalline t-ZrO2 and m-ZrO2 or their weight fractions in a mixture that is composed of nanocrystalline t-ZrO2 and m-ZrO2 can be determined only upon an XRD test. It is proved by both theoretical calculation and experimental test that mutual substitutions of t-ZrO2 and cubic ZrO2 (c-ZrO2) in a wide range show almost no impact on the XRD patterns of their mixtures. And plus the similarity in property of t-ZrO2 and c-ZrO2, they can be treated as one whole phase. The high agreement of the theoretical and experimental results in this work also proves the validity and reliability of the theoretical calculation based on X-ray diffractometry theory for such quantitative phase analysis. This method has the potential to be popularized to other materials.

Development of titanium oxide layer containing nanocrystalline zirconia particles with tetragonal structure: Structural and biological characteristics

This study investigated the microstructural, mechanical and biological properties of oxide layers containing tetragonal zirconia (t-ZrO2) particles on pure titanium produced by plasma electrolytic oxidation (PEO) process. For this purpose, PEO processes were carried out at an AC current density of 200mA/cm2 for 180s in potassium pyrophosphate (K4P2O7) electrolytes with and without t-ZrO2 powder. Structural investigations using transmission electron microscopy exhibited that the present nanocrystalline oxide layer evidenced the successful incorporation of a myriad of t-ZrO2 particles working as an intermediate medium to reinforce the adhesion strength between the substrate and oxide layer. Regarding biomimetic apatite formation, the t-ZrO2 particles uniformly spread were of considerable importance in triggering the nucleation and growth of biomimetic apatite on the surface of the oxide layer immersed in a simulated body fluid solution. The growth and proliferation rates of the osteoblasts (MC3T3-E1) cultured on the oxide layer with t-ZrO2 particles were higher than that without t-ZrO2 particles due to the higher roughness providing the better sites for the filopodia extension and interlocking.

In-situ TEM mechanical testing of nanocrystalline zirconium thin films

Mechanical behavior of nanocrystalline zirconium thin films was investigated in-situ inside a transmission electron microscope (TEM). The yield stress measured for specimens with <10nm grain size was around 450–500MPa compared to the bulk value of 250–300MPa. Similar grain size effects are seen on fracture stress and strain of about 0.9GPa and 1.5–2% respectively. Using in-situ TEM, we demonstrate control of grain size in the specimens using electro-migration stress and temperature. The experimental results suggest that the critical grain size for inverse Hall–Petch type relationship in nanocrystalline hexagonal close packed metals could be around 15nm.

Preparation of Nanocrystalline Calcia‐Stabilized Tetragonal Zirconia by High‐Energy Milling of Baddeleyite

For the first time, zirconia nanocrystalline powders were derived using baddeleyite as raw material by ultrafine milling. Powders containing 19 vol% of monoclinic phase were produced by milling of baddeleyite with addition of 11 mol% of CaO. Crystallite size of tetragonal and cubic phases in resulting powders is 3–5 nm and about 15 nm in the case of monoclinic phase. Typical agglomerate's size found by scanning electron microscopy ranges from ~0.1 to 10 µm. Sintered ceramics with tetragonal zirconia content of 95 vol% and crystallite size of ~50 nm are produced from the powders.

Preparation of Nanocrystalline Powders of ZrO2, Stabilized by Y2O3 Dobs for Ceramics

The purpose of this study was to develop a synthesis conditions and produce samples of nanocrystalline zirconia powder in a high-temperature phase state. To increase the stability of this state at room temperature, Y2O3 was used as a dop in the two-stages chemical method including coprecipitation mixture of the corresponding hydroxides and air drying. To reduce agglomeration of nanoparticles during heat treatment of precursors the microwave oven instead of a muffle was used. Different characterisation methods have been used to determine that the obtained powders are nano-scale corresponds to a high-temperature tetragonal phase of ZrO2. It is shown that such nanocrystalline powders may be used to produce highly-dense nanoceramics.

Structural, Morphological and Optical Properties of Nanoproducts of Zirconium Under Laser Ablation in Water and in Aqueous SDS Solutions

Abstract. The paper deals with structural, morphological and optical properties ofnanoproducts which undergone zirconium laser ablation in water and in aqueous SDS solutions.Depending on experiment conditions the indicated products can appear as different crystallinephases of zirconia and organic-inorganic composites, which include SDS alkyl chains intercalatedbetween layers of zirconium oxides or hydroxides. The formation of zirconium dioxide-basedhollow nano- and microstructures is demonstrated. It is suggested that ablation-formed gas-vapor bubbles can serve as templets for generation of hollow structures.Key words: laser ablation, metal nanocompositions, zirconium dioxide, RAMAN spectra,gas-vapor bubbles.Numerous publications devoted to bothsynthesis and investigation of properties of nanodispersed zirconia have appeared by now [12, 17,34, 46, 49, 52, 54, 63]. The interest is determinedby unique mechanical, chemical, optical and otherproperties that open way to a broad practicalapplication of the material in science andtechnology [7, 26, 10, 60, 64]. Synthesis of oxidesand other metal nanocompositions by laser ablationin a liquid environment is one of perspectivemethods [25, 30, 58]. However, the data onzirconia generation by the mentioned way is farnot sufficient [11, 14, 15, 19, 33]. The experimentswere carried out mainly at low laser pulsesrepetition rate (~ 10 Hz), that limits the perspectiveof establishing productive technologies, potentialinvestigations of a number of physical andchemical processes accompanying the synthesisand affecting properties of the final product.Thus, the given work is devoted to theattempt of generating nanocrystalline zirconia bylaser ablation of zirconium target in aqueoussolutions of a surfactant. A copper vapor laser(CVL) with the power output 10–15 W, radiationpulse duration 20 ns, and pulse repetition rate10kHz was used as radiation source.Experimental sectionPhysical and technical descriptions oflaser ablation in liquid are given in detail innumerous original articles and reviews [8, 53,70]. CVL generation was performed at twowave lengths: 510.6 and 578.2 nm, line powerratio was correspondingly 2:1. UV light (255,271 and 289 nm) was obtained by nonlinearconversion of the Cu laser radiation (510.6 and578.2 nm) in a BBO crystal [3]. The laser beamwas focused on the target surface by anachromatic lens with focal distance of f = 280mm, that provided the spot diameter of less than100 µm. The target was placed into a glass cellwith deionized water or aqueous solutions of asurfactant. The volume of the liquid in the cellwas ~ 10 cm

Nano-crystalline zirconia: a viable adsorbent for the column chromatographic separation of 58Co from neutron irradiated nickel targets

This paper described the utility of tetragonal nano-zirconia (t-ZrO2) for the column chromatographic separation of 58Co from 58Ni(n, p) reaction in neutron irradiation of natural Ni target. A careful scrutiny of the adsorption parameters of t-ZrO2 was systematically carried out to arrive at the optimum separation conditions. The radiochemical procedure developed herein consisted of selective retention of 58Co from an acidic solution of neutron irradiated Ni target on a chromatography column containing t-ZrO2 followed by elution of 58Co in 0.1 M HCl, which was validated using real samples. The overall recovery of 58Co was >90 % with appropriate radiochemical and radionuclide purity.

Synthesis, structural and optical characterization of ZrO2 core–ZnO@SiO2 shell nanoparticles prepared using co-precipitation method for opto-electronic applications

Nanocrystalline Zirconia (ZrO2) and Zinc oxide (ZnO) as well as Silica (SiO2) coated ZrO2 core–shell structures were synthesized by both Co-precipitation and seeded polymerization technique. The phase analysis and the core–shell structure formation were confirmed by X-ray diffraction (XRD), FESEM and high resolution transmission electron microscopy (HRTEM) analysis. The existence of SiO2 on ZrO2@ZnO was characterized by FT-IR measurement. UV–Vis study reveals coating of ZnO over Zirconia shows red shift in the absorption spectra. Photoluminescence studies show the non-monotonous variation in luminescence behavior of these core–shell nanoparticles. This investigation explains that the interfacial effect between the core (ZrO2) and the shell materials (ZnO and SiO2) can be exploited to tune the optical properties of the material. This implies that we can envisage the core–shell materials as potential candidates for optical–electronic devices.

Calcia Stabilized Ceria Doped Zirconia Nanocrystalline Ceramic

Calcia-stabilized cerium doped cubic zirconia nanocrystalline ceramic was synthesized using poly (vinyl alcohol) as a polymeric precursor. Obtained ceramic was pressed into a cylindrical pellet and sintered at 850 °C. The calcined and sintered ceramics were characterized by XRF, XRD, BET and SEM. The XRD pattern of the calcined ceramic shows that the ceramic has a face centered cubic crystal structure. The SEM results show that the grain size of the ceramic was increased after sintering. The BET surface areas were determined as 13.236 and 4.397 m2 g−1 for the calcined and sintered ceramics, respectively.

Effect of Grain Size on Phase Transformation and Photoluminescence Property of the Nanocrystalline ZrO2 Powders Prepared by Sol–Gel Method

Nanocrystalline zirconia (ZrO2) powders were prepared by a sol–gel process followed by annealing treatments from 500 to 1200 °C. Phase transformation, microstructural features and photoluminescence properties were characterized by X-ray diffraction, transmission election microscopy and photoluminescence spectra, respectively. The results show that both monoclinic phase and tetragonal phase exist in the nanocrystalline ZrO2 powders at annealing temperature in the range of 500–900 °C, and the concentration of monoclinic phase increases with increasing the annealing temperature. Tetragonal phase is totally transformed to monoclinic phase when annealing temperature is up to 900 °C. The average grain size of the powders also increases when annealing temperature increases. Two emission peaks centered at 390 nm (named as I390) and 470 nm (named as I470) exist in the photoluminescence spectra, and the intensity ratio of I390 to I470 decreases with increasing annealing temperature. The grain size is proposed to be responsible for the phase transformation in the nanocrystalline ZrO2 powders.

The role of local structural distortions in the stabilisation of undoped nanocrystalline tetragonal zirconia

Nanopowders of pure or very lightly doped zirconia were studied by means of total scattering and pair distribution function analysis, with the aim of understanding how the size of the particles (if a size limit of about 20 nm is not exceeded) tends to stabilise the tetragonal polymorph at room temperature. Total scattering and PDF analyses, together with Rietveld refinements, showed that the tetragonal model is indeed applicable to the average structure of these nanocrystalline zirconia samples, and provided comparable results. However, all the samples, with no influence from the dopant content, showed a similar local distortion for r < 10 Å. In this region, the data were fitted with two slightly different tetragonal structures, with a tetragonal distortion that decreases with the Rmax used, giving rise to a structure closer to the average tetragonal one (given by Rietveld as well as by average PDF refinements). In the first coordination shell, however, an orthorhombic distortion fits very well both in intensity and in position. This distortion may be responsible of the increased RMS strain local level, and therefore of the stabilisation of the high temperature structure at room temperature.

High temperature internal friction measurements of 3YTZP zirconia polycrystals. High temperature background and creep

Abstract This work focuses on the high-temperature mechanic properties of a 3 mol% yttria zirconia polycrystals (3YTZP), fabricated by hot-pressureless sintering. Systematic measurements of mechanical loss as a function of temperature and frequency were performed. An analytical method, based on the generalized Maxwell rheological model, has been used to analyze the high temperature internal friction background (HTB). This method has been previously applied to intermetallic compounds but never to ceramics, except in a preliminary study performed on fine grain and nano-crystalline zirconia. The HTB increases exponentially and its analysis provides an apparent activation enthalpy which correlates well with that obtained from creep experiments. This fact shows on the one hand the plausibility of applying the generalized Maxwell model to ceramics, and on the other hand indicates the possibility of using mechanical spectroscopy as a complementary helpful technique to investigate the high temperature deformation mechanism of materials.

A Sonochemical‐Assisted Synthesis of Pure Nanocrystalline Tetragonal Zirconium Dioxide Using Tetramethylethylenediamine

Pure nanocrystalline zirconia has been successfully synthesized by sonochemical‐assisted route from zirconyl nitrate and tetramethylethylenediamine (TMED) as starting materials. Here, TMED for the first time was used as precipitating agent to generate nanocrystalline tetragonal zirconia via a sonochemical‐assisted route. The effect of solvent and concentration of TMED on the morphology and crystallite size was studied. It was found that these parameters have significant influence on the morphology and crystallite size of the products. The products were characterized by SEM, UV–vis absorption and TEM images, XRD patterns, PL, FTIR, and EDS spectroscopy.

Abatement of chromium by adsorption on nanocrystalline zirconia using response surface methodology

Application of nanocrystalline zirconia was investigated for the removal of chromium from aqueous solutions. The nanozirconia was synthesized by ‘precipitation method’. The parameters namely initial concentration (5–65ppm), pH (0.5 to 10.5), adsorbent dose (2 to 10g/l) and temperature (298K to 318K) were optimized employing central composite design of response surface methodology. The removal of Cr was most affected by pH, followed by an initial concentration and adsorbent dose. Maximum removal (%) was achieved at an initial concentration of 20ppm, pH=3, adsorbent dose=4g/l and temperature 313K. The experimental data were best fitted in Langmuir's isotherm equation and the removal followed pseudo second order kinetics. The mechanism of removal was explained by boundary layer diffusion via intraparticle diffusion and was further confirmed by Boyd plot. Thermodynamic parameters revealed that the removal process was spontaneous, endothermic and physiosorptive in nature. Adsorbent was regenerated with hydroxides (0.1N NaOH, KOH and NH4OH) for further reuse.

Creep in nanocrystalline zirconia

Grain boundary sliding remains a dominant deformation process during creep in both nanocrystalline and submicron-grained zirconia. The level of segregation of Y to grain boundaries is reduced by a factor of similar to 2 in nanocrystals. However, a scaling relationship for compression creep was valid in a 3 mol.% yttria-stabilized tetragonal zirconia with grain sizes in the range of similar to 65-400 nm, indicating the same deformation mechanism over this range of grain sizes. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Low temperature synthesis and pressureless sintering of nanocrystalline zirconium diboride powders

In the present study, we report on the synthesis and pressureless sintering of nanocrystalline zirconium diboride (ZrB2) prepared by a solution based chemical method in which zirconium oxychloride, boric acid and citric acid (as both gelling agent and carbon source) were used. The zirconium diboride precursors gelled from solutions were prepared and calcined from 1100 to 1500°C under argon atmosphere. ZrB2 powder with mechanical activation as well as Fe and Ni addition was compacted and then sintered at 1750°C for 5h. The powders and sintered samples were characterized by XRD, TG–DTA, SEM and TEM. ZrB2 powders prepared at 1500°C had a surface area of 1.6m2/g and hexagonal rod-like morphology with 60nm of crystallite size. ZrB2 ceramics fabricated from activated powders in wet environment were sintered to a relative density of 86% and Vickers׳ hardness of 3.9GPa without sintering aid, while hardness and density values were found to be 15.8GPa and 94.8% for Ni addition and 14.9GPa and 99.9% for Fe addition.

Effects of heterogeneous catalyst in hydrothermal liquefaction of dried distillers grains with solubles

Hydrothermal liquefaction of biomass is a promising technology for production of biofuels. In this work, the catalytic effect of a nanocrystalline zirconia catalyst on hydrothermal liquefaction of dried distiller’s grains with solubles (DDGS) was investigated using a stop-flow reactor system. Additionally, the catalytic effects originating from the reactor wall were also studied by means of an inert gold liner to isolate the reaction from the X22 reactor alloy. DDGS was converted into a crude bio-oil at a fixed reaction temperature (350°C), pressure (250bar) and reaction time (15min). The oil was characterized in terms of yield, char content, ash content, elemental composition, chemical composition and heating value. Neither the ZrO2 catalyst nor the reactor wall was found to have any significant effects on the yields and properties of the produced bio-oil. Consequently, ZrO2 appears to be a poor catalyst for hydrothermal liquefaction of biomass. The X22 alloy is found to be highly suitable for construction of hydrothermal liquefaction reactors.

The effect of He and swift heavy ions on nanocrystalline zirconium nitride

Recent studies have shown that swift heavy ion irradiation may significantly modulate hydrogen and helium behaviour in some materials. This phenomenon is of considerable practical interest for ceramics in general and also for candidate materials for use as inert matrix fuel hosts. These materials will accumulate helium via (n, α) reactions and will also be subjected to irradiation by fission fragments. Cross-sectional transmission electron microscopy and scanning electron microscopy was used to study nanocrystalline ZrN irradiated with 30keV He to fluences between 1016 and 5×1016cm−2, 167MeV Xe to fluences between 5×1013 and 1014cm−2 and also 695MeV Bi to a fluence of 1.5×1013cm−2. He/Bi and He/Xe irradiated samples were annealed at temperatures between 600 and 1000°C and were analysed using SEM, XTEM and selected area diffraction. The results indicated that post irradiation heat treatment induces exfoliation at a depth that corresponds to the end-of-range of 30keV He ions. SEM and XTEM analysis of He/Xe irradiated samples revealed that electronic excitation effects, due to Xe ions, suppress helium blister formation and consequently the exfoliation processes. He/Bi samples however do not show the same effects. This suggests that nanocrystalline ZrN is prone to the formation of He blisters which may ultimately lead material failure. These effects may however be mitigated by electronic excitation effects from certain SHIs.

Enhanced cell growth by nanoengineering zirconia to stimulate electrostatic fibronectin activation

We address the enhanced bone growth on designed nanocrystalline zirconia implants as reported by in vivo experiments. In vitro experiments demonstrate that the activation of adhesive proteins on nanoengineered zirconia stimulates cell adhesion and growth as shown by confocal microscopy. Fibrillar fibronectin (FN) forms a matrix assembly on the nanostructured surface in the cell adhesion process. We discuss the importance of FN dimer activation due to its immobilization on the designed nanocrystalline ZrO2 implant fabricated by ion beam assisted deposition. The Monte-Carlo analysis indicates that FN activation on the surface can be promoted by selective electrostatic interactions between negatively charged ZrO2 surface patches and oppositely charged FN domains.

Microwave Synthesis, Characterization, and Photoluminescence Properties of Nanocrystalline Zirconia

We report synthesis of ZrO2 nanoparticles (NPs) using microwave assisted chemical method at 80°C temperature. Synthesized ZrO2 NPs were calcinated at 400°C under air atmosphere and characterized using FTIR, XRD, SEM, TEM, BET, and EDS for their formation, structure, morphology, size, and elemental composition. XRD results revealed the formation of mixed phase monoclinic and tetragonal ZrO2 phases having crystallite size of the order 8.8 nm from most intense XRD peak as obtained using Scherrer formula. Electron microscope analysis shows that the NPs were less than 10 nm and highly uniform in size having spherical morphology. BET surface area of ZrO2 NPs was found to be 65.85 m2/g with corresponding particle size of 16 nm. The band gap of synthesized NPs was found to be 2.49 eV and PL spectra of ZrO2 synthesized NPs showed strong peak at 414 nm, which corresponds to near band edge emission (UV emission) and a relatively weak peak at 475 and 562 nm.