Aunps and Agμps-functionalized zirconia surfaces by hybrid laser technology for dental implants

This work presents innovative zirconia surfaces functionalized with gold nanoparticles (Aunps) and silver microparticles (Agμps) through versatile laser technology where laser parameters and subtractive/additive strategies were combined to apply in dental implant surfaces regarding antibacterial potentialities. Au_nps-functionalized zirconia surfaces were produced by a hybrid process starting with nanoparticles production by Nd:YAG laser ablation, followed by its deposition through spray system and its adhesion to the zirconia surface by the laser CO₂ action, varying laser power and scan speed parameters. Ag_μps-functionalized zirconia surfaces were obtained through a hybrid laser process starting by laser texturing of the compacted zirconia surface, followed by allocation of Ag powder into the texture and its subsequent laser sintering, varying laser power. The functionalized zirconia surfaces were analyzed through SEM/EDS. In order to mimic the implant screwing effect, the samples were subjected to reciprocating friction tests against bone. It allows to evaluate the adhesion of the zirconia surface to the bone and the resistance to surface detachment. A purple colloidal solution of spherical gold nanoparticles with an average size of 5 ± 3 nm was successfully produced by laser. The friction tests revealed a good behavior of both functionalized zirconia surfaces indicating that their integrity is not affected during implant screwing insertion. A good dispersion of nanoparticles on the zirconia surface was observed indicating that the spray system is an effective way to deposit nanoparticles on the surface. A high amount of agglomerates was found for samples where low laser power (P = 11W) and scan speed (v = 1000 mm/s) were applied, probably due to the high density of energy (E). A decrease of defects on the sintered Ag layer with increasing laser power from 3 to 6 W was found, mainly related with the amount of laser energy density. The ion release showed to be strongly dependent on particle size.     

Effect of zirconia content on the mechanosynthesis and structural features of fluorapatite-based composite nanopowders

The influence of zirconia content on the mechanosynthesis of fluorapatite–zirconia composite nanopowders was investigated. The structural features of the specimens with different amounts of monoclinic zirconia (0–20 wt%) were examined after 5 h of mechanical activation. Results indicated that the formation of fluorapatite–zirconia composite was strongly influenced by the zirconia content. In the presence of 5–10 wt% monoclinic zirconia, fluorapatite–zirconia composite nanopowders were produced after 5 h of milling. With increasing zirconia content to 20 wt%, there was no trace of fluorapatite–zirconia composite. In the absence of zirconia, the average crystallite size, lattice strain and the volume fraction of grain boundary of fluorapatite were about 34 nm, 0.469% and 8.38%, respectively. These values reached 24 nm, 0.754% and 11.71% with the addition of 10 wt% monoclinic zirconia. In the presence of 10 wt% monoclinic zirconia, the fraction of crystalline phase considerably decreased after 5 h of milling. Results revealed that the lattice parameter deviations were affected by the zirconia content. Based on SEM observations, no significant differences in the size distribution and morphology of the agglomerates were observed.     

Structure of Zirconia Prepared by Homogeneous Precipitation

The structure of pure zirconia powders prepared by homogeneous precipitation was examined by electron microscopy. Some of these powders consisted of metastable tetragonal zirconia in the form of spherical aggregates up to 1 μm in diameter. The size of single crystals within these particles exceeded 100 nm, which is much larger than usually reported for metastable zirconia. We conclude that the existence of these large teragonal monocrystals is due principally to the very fine internal porosity within the domains, which gave rise to a surface area/volume ratio sufficient to stabilize tetragonal zirconia by the same mechanism as in nanocrystalline powders.     

Controllable synthesis of pure monodispersed zirconia nanopowders with tetragonal phase

Nanopowders of pure zirconia have been synthesized using citric acid (CA)-assisted lamellar liquid crystal template method. The microstructure of the zirconia powder prepared at the different mole ratios of CA to zirconium oxynitrate (ZN) was characterized by FT-IR, X-ray diffraction (XRD), laser particle size analyzer, Raman spectroscopy, and scanning electron microscope (SEM) methods. The phase structure of the sodium dodecyl sulfate (SDS)/C₁₀H₂₁OH/H₂O system before and after adding mixing solution CA and ZN was determined by POM (Polarizing Optical Microscope). The results show that lamellar structure of the SDS/C₁₀H₂₁OH/H₂O system after adding mixing solution CA and ZN is stable. The presence of CA inhibits agglomeration and growth of zirconia particle. The crystallite size of zirconia powders decreases and agglomerates lowly with addition of CA. Fourier transform infrared spectrometry (FI-IR) analyses reveal that the structure of chelating organic complex is maintained in zirconia structure at high-temperature calcination to cause oxygen vacancies which stabilizes the tetragonal phase of zirconia. The zirconia powders remained the single metastable tetragonal phase at the molar ratios of CA to ZN ranging from 1:3 to 5:1. The crystallite size of zirconia with spherical morphology varied from 32.2 to 20.1 nm with the increase of the molar ratio of CA to ZN in the range of 1:3 to 5:1.     

The breakdown of the Weibull behavior in dental zirconias

Here we attend to the controversy of the use of Weibull statistics for describing the strength distribution of dental brittle materials. Our approach is purely experimental by means of testing for the strength size effect, a requirement for Weibull materials. Zirconia materials of five important dental manufacturers were selected, each represented by two compositions, being one a 3 mol% Y₂O₃-stabilized zirconia, and the other being a “translucent” zirconia with 4 or 5 mol% stabilizer content. Specimens of increasing sizes were fractured, whether by using a biaxial flexure test in plates or a uniaxial bending test in beams, thereby sampling different ranges of effective surfaces and volumes. A systematic deviation from the Weibull behavior over the range of 1–40 mm² effective surface was demonstrated, regardless of manufacturer and Y₂O₃ content in the powder. Extensive testing using a wider range of specimen sizes narrowed down the threshold for the breakdown of the defect size distribution from the parent population to be located between 10 and 20 mm² effective surface. A comparable behavior was confirmed for the partly sintered white-bodies, with similar defect morphology to the fully sintered analogs, indicating a defect size distribution stemming from the pressing steps of manufacture. The defect shape related to open particle aggregate junctions, pointing to an association of their size distribution to that of the distribution of aggregate sizes in the source powders.     

Electrospinning Zirconia Fiber From a Suspension

A zirconia suspension containing 5–10 nm size zirconia particles was modified by adding different amounts of polymer solution to enable electrospinning of zirconia fibers from a range of compositions. The electrospun fibers were heat treated at 600° and 1200°C, and analysis of size distribution reveals that zirconia fibers down to about 200 nm in diameter can be prepared in this way, in contrast to other spinning processes, which are able to produce zirconia fibers having diameters ≥3000 nm.     

Nanosecond laser induced microstructure features and effects thereof on the wettability in zirconia

Zirconia are widely employed as a bone-substitute material for surgical implants due to its biocompatible and mechanical properties. However, implants introduced into the human undergo detachment from the host tissue due to poor biological performance. The laser-texturing can enhance the biological performance of the surface by altering surface properties and maintaining the bulk properties of the zirconia. In this work, laser-texturing microstructure features on zirconia are carried out to modify surface characteristics. Wettability are evaluated through water contact angles (WCAs) measurements. To characterize the influence of laser-texturing on pattern morphology, the produced surfaces are measured by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Micro cracks with melted material flowing along the scanning tracks in the untreated areas were observed from SEM. XRD results, in turn, show that the tetragonal → monoclinic phase transformation leads to many tiny cracks around the transformed particles. Wettability can be attributed to the modifications of the surface's microstructure depending on laser parameters and chemical composition. The stability tests prove that the super-hydrophobic surfaces produced by laser-texturing possess good abrasion resistance. This work may provide a simple method for producing zirconia surfaces with controlled wettability with the proper choice of laser parameter for extremely extensive industrial applications.     

Nonisothermal Synthesis of Yttria-Stabilized Zirconia Nanopowder through Oxalate Processing: I, Characteristics of Y-Zr Oxalate Synthesis and Its Decomposition

To obtain powder with a composition of 3 mol% Y₂O₃–97 mol% ZrO₂, a process of Y-Zr oxalate powder production has been optimized, to produce an oxalate with minimal particle size. The methodology of the nonisothermal decomposition of Y-Zr oxalate has been explained. Characteristics of the nonisothermal decomposition of different oxalates have been studied. Nanocrystalline Y₂O₃-stabilized ZrO₂ (YSZ) powder with a narrow size distribution of primary particles and aggregates was produced. The zirconia powder that was obtained from the smallest oxalate powder via nonisothermal decomposition had a particle size of 8–10 nm. The YSZ powder was weakly aggregated, with a narrow aggregate-size distribution of 70–90 nm.     

Thermal conductivity of highly porous zirconia

Highly porous zirconia ceramic with nanometric sized grains was prepared from an 8 mol% yttria stabilised zirconia suspension mixed with a commercial latex. The pore volume fraction was varied from 45 to 75% by adjusting the thermal treatment between 750 and 1100 °C. Observations of the microstructure reveal variation in pore shape and size. Mean grain sizes are less than 70 nm. Mercury porosimetry measurements reveal a bimodal pore size distribution. Thermal diffusivity measurements were made with the laser flash technique in order to determine the thermal conductivity at room temperature. The thermal conductivity approaches a lower limit of 0.1 W m⁻¹ K⁻¹. Experimental results were shown to agree closely with predictions made with Landauer's effective medium expression for a two-phase system. The agreement was improved even further by taking into account the interfacial thermal resistance of the grain boundaries and the pore size distribution.     

Monoclinic Zirconia Microfiltration Membranes: Preparation and Characterization

Microfiltration zirconia membranes were prepared by slip casting from two pure zirconia powders derived from different processing techniques. Powders had almost the same mean particle size but were different in surface area, particle size distribution and morphology. Rheology of zirconia slips was studied in order to prepare a well-dispersed slip suitable for slip casting. The powders showed different dispersibility in the preparation of slips by colloidal processing. The effect of sintering temperature and holding time on porosity, pore size distribution, phase composition, microhardness and microstructure of unsupported membranes are studied and discussed in relation to the membrane processing and properties of powders resulting from different processing routes. Pore size distribution of membranes reflected the differences in morphology of particles and the state of agglomeration in the green samples.Isothermal sintering at 1100°C resulted in some tetragonal phase retained at room temperature in the monoclinic structure. Cracking occurred in membranes sintered above 1150°C due to the volume change in phase transformation. Densification behavior, removal of porosity and the hardness property showed differences that are attributed to the differences in powder processing and characteristics of powders. Crackfree membranes can be prepared by sintering at 1100°C from both powders.     

In-situ sol–gel synthesis of zirconia networks in flexible and conductive composite films

The conductive and stretchable films with improved hardness are suitable for the fabrication of flexible electronic devices. This study describes the sol–gel technique to prepare a novel conductive and flexible film consisting of epoxidized natural rubber (ENR), doped polyaniline (PD) and zirconia. The zirconia networks were directly synthesized in-situ in ENR/PD solution and flexible conductive composite film with improved hardness was obtained. The morphology study revealed the size of PD decreased significantly from 77.89 ± 43.95 nm to 4.32 ± 1.13 nm and highest electrical conductivity of 1.9 × 10⁻³ S/cm was achieved with 10 wt.% percolation threshold of zirconia precursor. The binding energy of Zr3d_5/2 and Zr3d_3/2 decreased, suggesting that zirconia was converted to the lower oxidation state. Furthermore, the shape of PD changed from spherical to rod-like structure with root mean square value of 2 nm, while the hardness and reduced modulus improved to 1.72 MPa and 36.7 MPa, respectively.     

Fabrication of functional zirconia surfaces using a two-beam interference setup employing a picosecond laser system with 532-nm wavelength: Morphology,microstructure, and wettability

The aim of this work was to evaluate the feasibility of the fabrication of microtextures in zirconia using the direct laser interference patterning (DLIP) technique. A green ultra-short pulsed laser (532 nm, 10 ps) with a two-beam interference setup was used to produce line-like structures with a spatial period of 3 µm. For a fixed set of fluence and pulse-to-pulse overlap values (6.2 J/cm², 81%), periodic structures were successfully created for different hatch distances. The average depth of the features ranged from 0.37 µm for a hatch distance of 14.4 µm up to 0.84 µm for a hatch distance of 12.4 µm. However, a further decrease in hatch distance did not result in an increase in depth since the region of the ridges is also ablated. Scanning electron microscopy analysis showed pores formation on the laser grooves, but no sign of micro-cracking could be observed. Wettability tests showed an increase in hydrophobicity after DLIP. These results bring exciting perspectives on the fabrication of micro-textures with DLIP on zirconia surface.     

Production of meso- and giga-porous zirconia particles — An improved multi-step particle aggregation process

Macro- and giga-porous zirconia supports were prepared from a 20% colloidal sol of zirconia (ZrO₂) by a combination of a polymer-induced colloid aggregation (PICA) process and the oil emulsion (OE) method. The effect of the pH of the initial sol on the size of the PICA particles, and subsequently on the final product, made by oil-emulsion assisted aggregation of the PICA particles was thoroughly investigated. Both the PICA and the OE methods were further optimized for performance. Particle morphology and porosity of the resultant particles were characterized by scanning electron microscopy, mercury intrusion-extrusion porosimetry, and nitrogen adsorption-desorption sorptometry. The supports were comprised of stable aggregates of 50-250 μm in size. The pore and throat size distributions showed narrow bi-modal distributions over two distinct size scales: 10-100 nm and 600-3000 nm. In addition, different combinations of aggregation techniques and porous supports prepared in previous steps for use in a subsequent aggregation were evaluated. Optimal amounts of zirconia sol and 10-100 micron porous spherical particles produced by the OE method in an earlier step were combined in an additional OE process to yield stable giga-porous supports. Porous zirconia particles obtained after calcination and sintering had particle sizes of 0.15-3.5 mm and multimodal pore and throat distributions over a range of 50 nm-8 μm.     

Surface Enthalpy, Enthalpy of Water Adsorption, and Phase Stability in Nanocrystalline Monoclinic Zirconia

A fundamental issue that remains to be solved when approaching the nanoscale is how the size induces transformation among different polymorphic structures. Understanding the size-induced transformation among the different polymorphic structures is essential for widespread use of nanostructured materials in technological applications. Herein, we report water adsorption and high-temperature solution calorimetry experiments on a set of samples of single-phase monoclinic zirconia with different surface areas. Essential to the success of the study has been the use of a new ternary water-in-oil/water liquid solvothermal method that allows the preparation of monoclinic zirconia nanoparticles with a broad range of (BET) Brunauer–Emmett–Teller surface area values. Thus, the surface enthalpy for anhydrous monoclinic zirconia is reported for the first time, while that for the hydrous surface is a significant improvement over the previously reported value. Combining these data with previously published surface enthalpy for nanocrystalline tetragonal zirconia, we have calculated the stability crossovers between monoclinic and tetragonal phases to take place at a particle size of 28 ± 6 nm for hydrous zirconia and 34 ± 5 nm for anhydrous zirconia. Below these particle sizes, tetragonal hydrous and anhydrous phases of zirconia become thermodynamically stable. These results are within the margin of the theoretical estimation and confirm the importance of the presence of water vapor on the transformation of nanostructured materials.     

Zirconia with Defined Particle Morphology and Hierarchically Structured Pore System Synthesized via Combined Exo‐ and Endotemplating

Highly porous zirconia with defined particle morphology can be prepared by impregnation of spherical activated carbon as an exotemplate with a zirconia nanoparticle sol. The resulting zirconia spheres show a particle size distribution between 0.2 and 0.4 mm and exhibit high specific surface areas and specific pore volumes up to 104 m²g^–1 and 0.56 cm³g^–1, respectively. Addition of a triblockcopolymer (TBC) as an endotemplate during the synthesis leads to the formation of an additional pore system. The corresponding spherical zirconia products possess a hierarchically structured pore system with a bimodal pore size distribution with maxima at ca. 3 and 20 nm. The relative fraction of pores originating from the endotemplate can be varied by changing the endotemplate content in the zirconia nanoparticle sol. The presence of the TBC also has an influence on the specific surface area and the specific pore volume. Using the ratio of TBC to zirconium of n_TBC/n_Zr = 0.027, a material can be prepared that exhibits a specific surface area and a specific pore volume of 161 m²g^–1 and 0.62 cm³g^–1, respectively. These values are more than twice as high as for zirconia prepared by a conventional precipitation method (68 m²g^–1 and 0.11 cm³g^–1, respectively).     

Preparation and characterization of monodisperse zirconia spherical nanometer powder via lamellar liquid crystal template method

Cubic phase spherical zirconia nano-powderwas prepared by a direct template route in the lamellar liquid crystal formed by polyoxyethylene tert-octylphenyl ether (Triton X-100)/sodium dodecyl sulfate (SDS)/H₂O. The precursor powder and zirconia powder were characterized by XRD, FT-IR, TG/DSC, TEM, and SEM methods. Results show that the stability of the lamellar liquid crystal is controlled by NH₃ · H₂O concentration. The size of nanoparticles is greatly affected by NH₃·H₂Oand ZrOCl₂ · 8H₂O concentrations. The zirconia nanoparticles shownarrow particle size distribution of 10-30 nm.     

Electrical conductivity of sol–gel derived yttria-stabilized zirconia

A 3 mol% Y₂O₃ zirconia stabilized powder has been synthesized by destabilization of an aqueous zirconia sol prepared by the alkoxide hydrolysis method. The powder calcined at 500°C is ultrafine with tetragonal crystallites of about 8 nm, slightly agglomerated and with a narrow pore size distribution having an average pore size of 5.2 nm. Zirconia ceramics with density higher than 92%TD and grain size on the order of 100 nm have been obtained by uniaxial pressing at 500 MPa and vacuum sintering at 1000°C. Electrical conductivity of sintered samples, evaluated by complex impedance spectroscopy measurements, indicated that the zirconia stabilized with 3 mol% Y₂O₃ can potentially be used as an oxygen semipermeable dense membrane, but only at a relatively high temperature.     

Centimeter-scale low-damage micromachining on single-crystal 4H–SiC substrates using a femtosecond laser with square-shaped Flat-Top focus spots

Femtosecond (fs) lasers have been proved to be reliable tools for high-precision and high-quality micromachining of ceramic materials. Nevertheless, fs laser processing using a single-mode beam with a Gaussian intensity distribution is difficult to obtain large-area flat and uniform processed surfaces. In this study, we utilize a customized diffractive optical element (DOE) to redistribute the laser pulse energy from Gaussian to square-shaped Flat-Top profile to realize centimeter-scale low-damage micromachining on single-crystal 4H–SiC substrates. We systematically investigated the effects of processing parameters on the changes in surface morphology and composition, and an optimal processing strategy was provided. Mechanisms of the formation of surface nanoparticles and the removal of surface micro-burrs were discussed. We also examined the distribution of subsurface defects caused by fs laser processing by removing a thin surface layer with a certain depth through chemical mechanical polishing (CMP). Our results show that laser-induced periodic surface structures (LIPSSs) covered by fine SiO₂ nanoparticles form on the fs laser-processed areas. Under optimal parameters, the redeposition of SiO₂ nanoparticles can be minimized, and the surface roughness Sa of processed areas reaches 120 ± 8 nm after the removal of a 10 μm thick surface layer. After the laser processing, micro-burrs on original surfaces are effectively removed, and thus the average profile roughness Rz of 2 mm long surface profiles decreases from 920 ± 120 nm to 286 ± 90 nm. No visible micro-pits can be found after removing ~1 μm thick surface layer from the laser-processed substrates.     

Ultra-low density carbon foams produced by pulsed laser deposition

We report on the manufacturing of ultra-low density carbon foam produced by pulsed laser deposition. Mean mass density, morphology and structure were investigated within a broad range of process parameters. We have been able to obtain carbon foam layers having tunable mean density and thickness in the range 1–1000 mg/cm³ and 5–80 μm, respectively. Surface uniformity has been achieved over ∼1 μm² areas with mean pore size around 10 nm. The morphological/structural properties have been investigated by means of quartz crystal microbalance, scanning electron microscopy and Raman spectroscopy. Based on these results, this work shows how pulsed laser deposition can be exploited as a versatile tool for the deposition of carbon foams with tunable and tailored density, thickness and uniformity.     

Study of the effect of the concentration,size and surface chemistry of zirconia and silica nanoparticle fillers within an epoxy resin on the bulk properties of the resulting nanocomposites

Epoxy resin nanocomposites were prepared by curing bisphenol‐F with an aliphatic amine in the presence of SiO₂ and ZrO₂ nanoparticles as inorganic fillers. Both types of particles were prepared with diameters of around 10 nm and 70 nm to study size effects in the nanocomposites. The nanoparticles showed a different constitution: while silica was amorphous and spherical in nature, zirconia was crystalline and non‐spherical. Both nanoparticles were surface‐functionalized with novel diethylene‐glycol‐based capping agents to increase the compatibility with the epoxy matrix. The organic functionalities were attached to the nanoparticle surface via phosphonic acid (zirconia) and trialkoxysilane (silica) anchor groups. The homogeneity of the distribution of surface‐modified inorganic nano‐sized fillers in the matrix up to 5.8 vol% in case of silica and 2.34 vol% in case of zirconia was determined by small‐angle X‐ray scattering and transmission electron microscopy. Mechanical properties such as hardness and storage modulus were increased with increasing filler content while thermal stability of the obtained materials was nearly unaffected after incorporation of nanoparticles. Copyright © 2011 Society of Chemical Industry