Production of Zirconium Oxide (ZrO 2 ) Micro and Nanoparticles by Pulsed Laser Ablation in Liquid

Pulsed laser ablation in liquid (PLAL) has become a technique of growing importance for the processing of micro and nano particles of metals and metal oxides. In comparison with different physical and chemical techniques, this approach has many advantages. This work was dedicated to the production of zirconium oxide (ZrO 2 ) micro and nano particles from a solid zirconium target submerged in distilled water using PLAL technique to study the effect of number of pulses on the structural and optical properties of the produced colloidal solution. Many kinds of tests such as Fourier transform infrared (FT-IR), UV-visible (UV-Vis.) and field emission scanning electron microscopy (FE-SEM) have been used to characterize the products. The (UV-Vis.) absorption spectra of all colloidal samples have shown broad peak at wavelength of 289 nm. The functional groups of (ZrO 2 ) in liquid media were also determined by Fourier transform infrared (FT-IR) analysis. Field emission scanning electron microscope (FE-SEM) images verified the micro and nanostructure of produced materials .


Introduction
ZrO2 is a white polymorphic powder whose crystal can be monoclinic, tetragonal or cubic. The monoclinic zirconia structure phase is stable at room temperature and it is formed at the temperature range of (400-1170 °C). It transforms above (1170 °C) into a tetragonal phase. The stability of tetragonal phase is up to (2370 °C), and the cubic phase of zirconia is formed at the temperature range between 2370 and 2600 °C [1]. This zirconia phase transformation affects its density as well as the physical characteristics; tetragonal and cubic structures of Zirconia, for example, have a higher densities and a higher crystallization temperatures compared to the monoclinic form [1,2]. ZrO2 has a broad band gap of approximately (5.0 -5.5 eV) depending on its phase (cubic, tetragonal, monoclinic or amorphous) and preparation process [3]. Micro and nano ZrO2 particles have drawn great interest of many scientists and researchers, due to their unique properties such as low thermal conductivity, efficient dielectric characteristics, strong thermal stability, chemical stability, high refractive index, high oxygen ion and conductivity, high fracture toughness, high thermal shock resistance, high hardness and mechanical strength [4][5][6][7][8], laser mirrors, broad band interference filters, ionic conductors, photo catalysis, sensors, coatings, waste water treatment, fuel cells and memory devices [9][10][11][12][13][14][15][16]. These fascinating properties of ZrO2 and its various applications in different areas led to develop a specific technique (PLAL) for synthesizing this oxide and investigating which aqueous medium is ideally suited for its synthesis.
PLAL technique is a simple and efficient process for the preparation of metal micro and nanoparticles, semiconductors and oxide isolators. Without the need for high vacuum chambers, high purity and stable particles can be created. In the PLAL process, by optimizing the laser parameters, material size can be controlled [17]. It is also possible to synthesize various types of particles free of surface-active substances and counter ions using this technique [18][19][20]. The plasma is created to produce particles through PLAL technique as a result of very high temperatures that occur when high power laser beam irradiates the target. The resulting plasma containing the target metal vapor expands adiabatically, resulting in rapid plasma plume cooling and thus forming particles [21,22].
The aim of this study is to prepare zirconium oxide solutions using the pulsed laser ablation technique in liquids and to study the optical and structural properties of the resulted nano/micro structured zirconium oxide solution and to investigate the surface nature of the prepared particles.

Results and Discussion
PLAL technique was applied to produce ultrafine particles of zirconium oxide in distilled water.
The structure and morphology of the particles obtained by pulsed laser ablation technique were studied using FE-SEM and FT-IR, and the optical properties were investigated by using UV-Vis. spectroscopy.

Results and Discussion
PLAL technique was applied to produce ultrafine particles of zirconium oxide in distilled water.
The structure and morphology of the particles obtained by pulsed laser ablation technique were studied using FE-SEM and FT-IR, and the optical properties were investigated by using UV-Vis. spectroscopy.

UV-Vis. Spectroscopic Analysis
The absorption spectra of ZrO2colloidal are shown in Figure (2). Clear peaks for all samples can be observed at wavelength of 289 nm which is due to the electronic transition from valance to conduction bands, which is recorded previously for metal oxide nanoparticles [23]. The produced colloidal solutions seem to be stable, and even after two weeks no precipitations were found at the bottom of the containers as recorded by other reports [24]. Several studies have shown that oxygen vacancies play a significant role in the stability of nano-crystalline cubic and tetragonal zirconium [25]. The spectra also show a broadband with a long tail towards higher wavelengths, suggesting that the produced particles are not homogeneous in size [25,26]. The results of the absorption spectra of zirconium oxide particles suspended in the liquid showed that with the increase in the number of laser pulses the absorbance increases where the lowest absorbance is obtained for the prepared sample with 250 pulses and the highest absorbance is obtained for the prepared sample with 2000 pulses. assuring the production of ZrO2 particles [27,28]. The broad absorption band observed in the (3000-3600 cm -1 ) region and some well-defined bands between (1300-1750 cm -1 ) correspond to the vibration of (O-H) bond mode as a result of that the synthesized (ZrO2) particles adsorbed water molecules or hydroxyl groups on the surface [29][30][31]. The hydroxylic group of moisture can also be assigned to these absorption peaks around (3000-3600 cm -1 ). The band appeared at (~1000 cm -1 ) is a characteristic of peroxide (O -O) groups [27,28].

Morphological studies
The morphological structure of the zirconium oxide solution was observed with field emission scanning electron microscope (FE-SEM). Figures (4) and (5) show the FE-SEM images of zirconium oxide ZrO2 which confirm that our produced material is in micro and nano-scale.
The FE-SEM image and size distribution of ZrO2 nanoparticles show a mixture of different

Conclusion
This research work has successfully produced pure zirconium oxide particles (ZrO2) by using a simple method of nanosecond PLAL technique.
The optical absorption of colloidal ZrO2 in D.W. solution reveals a broad band with a long tail toward the (271 nm) wavelength indicating the formation of inhomogeneous sizes and a particle coagulation shift in wavelength of maximum optical extinction. The FT-IR spectra confirm the