Investigation of electrical, corporeal, ocular, and aquaphobic properties of zirconia thin-films by varying substrate temperature for high voltage insulators

ABSTRACT

The addition of ZrO₂ nanoparticles to porcelain insulators and its influence on their electrical and corporeal characteristics are studied throughout a wide range of sintering temperatures. The DC magnetron sputtering with a 99.99% pure zirconium target is utilized to create zirconium oxide thin films on glass and silicon substrates in a 12-inch-diameter chamber. Different temperatures were used to sinter the produced samples (room temperature (RT) − 400°C) for 1 h with gas pressure of 15 mTorr for all depositions. Scanning electron microscopy (SEM) was used to characterize the microstructures of a subset of the samples. In order to assess the physical and microphysical changes brought on by an increase in substrate temperature, the phase composition of various nanocomposites samples was determined using X-ray diffraction (XRD). The breakdown strength, electrical resistivity, and dielectric constant were measured to assess the electrical attributes of the various samples. The obtained findings showed that the electrical and corporeal characteristics of samples sintered at RT were the best. In addition, the sample of nanocomposite porcelain sintered at room temperature has excellent insulating qualities, confirming the possibility of electro-technical porcelain manufacture (water contact angle = 103.5º), dielectric constant = 24.4, refractive index = 2.15, and bandgap = 5.33.

KEYWORDS:

• Corporeal
• bandgap
• aquaphobic
• coarseness
• thin film

1. Introduction

Because of its superior electrical, mechanical, and thermal qualities, insulators are frequently employed in supplying power to utility systems. As a result of the severe environments in which these systems operate, they get affected from environmental factors like dust, mild rain, etc. [1–3]. Despite the development of more modern materials like plastics and compounds [2,4–7], porcelain insulators (PI) have been utilized in electrical applications for centuries. One of the most difficult ceramic materials and the subject of much research due to their potential use in cutting-edge engineering [7–9] are PI. When it came to low and high voltage tension insulation, porcelain insulators were among the most often utilized ceramics. Researchers have made significant progress in the last 20 years in enhancing the insulating qualities of porcelain materials [10–14]. Many studies have been conducted to boost the efficiency of conventional electrical porcelains [15–17] in order to meet these requirements and keep up with technical advancements in the porcelain insulator industry. Instead of just being thrown away, scrap porcelain may be put to good use in several different fields. The feasibility of using porcelain shards in cement, concrete, and permeable pavement aggregate has been the subject of several investigations [18,19]. Plastic shaping for insulators can be used to overcome mechanical resistance requirements and textures defect by incorporating minced scuffle of scorched insulators onto “alumina PI” as a relatively rough rare material [20]. The use of porcelain scraps in the creation of insulators has been proven to increase the strength of the insulators by a factor of 10, according to a study published in the [21].

One cutting-edge option for improving insulators’ ultimate qualities is nanotechnology. While research into the use of nanomaterials in porcelain insulators is limited in contrast to that of other ceramics, the results that have been published so far are highly encouraging and intriguing [22–26]. Properties of samples sintered at 1250 degree Celsius after being subjected to uniaxial pressing were analyzed to determine the impact of nano-sized titanium dioxide (TiO₂). The microhardness, compressive strength, bulk density, and porosity were used to characterize the material’s physical and mechanical characteristics. Nanostructured porcelain compositions outperformed conventional siliceous porcelain by a factor of 65 in terms of mechanical strength. Incorporating nano-TiO₂ into traditional silicious porcelain had a beneficial influence on the microhardness of the material, as the nanostructured variant demonstrated a 15% improvement over plain porcelain [27].

The loss of dielectric strength in a porcelain insulator is utmost probable attributable to the occurrence of apertures. It needs to be pure to maintain the insulating characteristics of porcelain [28]. The features and relative amounts of distinct phases in porcelain determine its dielectric properties [29–31]. Zirconia (ZrO2) nanoparticles offer excellent corrosion resistance, a high melting point, a low specific gravity, a lovely expected color, high forte, a high conversion durability, a high natural constancy, and a high resilience to chemicals and microbes [32,33].

Owing to its high dielectric constant and supplementary desirable properties, zirconia is also a promising candidate for use as an insulator [34,35]. The zirconia crystals used to create nano-sized ZrO2 (zirconia) particles have excellent mechanical qualities, including high strength and flexibility, and a low thermal conductivity [36]. Zirconia’s high oxygen ion conductivity and heat-insulating properties open a wide range of possible applications [37,38].

The primary objective of this study was to devise a process for the synthesis of an affordable PI with improved physicochemical and electrical properties by employing DC sputtering at varying substrate temperatures. Section 2 presents the experimental setup. Section 3 demonstrates the feasibility analysis and results. Section 4 concludes the proposed approach with possible future scope.

2. Experimental setup

DC magnetron sputtering with a 2-inch in diameter, 5-millimeter-thick zirconium target was used to deposit thin coatings on glass and silicon substrates in a 12-inch in diameter chamber. At first, the substrates were engrossed in a supersonic soak for cleaning and then air-dried for 5 minutes. A turbo pump assisted by a rotary pump successfully emptied the chamber. Initial pressure of the chamber was sustained at 5 × 10⁶ Torr (Figure 1). After that, the chamber was filled with ultra-pure (99.9%) oxygen and inert (Ar) gas. Both the oxygen and argon flows were maintained at 10 standard cubic centimeters per minute.

Figure 1. Schematic diagram of sputtering chamber.

Mass flow controllers were used to regulate the gas mixture ratio, while capacitance manometers were used to monitor pressure. For all deposits, the pressure of the gas was held constant at 15 mTorr. Since sputtering current is highly subtle to sputtering gas pressure, it was maintained at a consistent level for each deposition. One and a half hours of sputtering was performed at varying substrate temperatures. Following samples were prepared on the substrate with temperatures of 100°C, 200°C, 300°C, and 400°C. The same 60W of electricity was used. There was a gap of 40 mm between the target and substrate. Each deposition procedure used the same conditions (base pressure, power, sputtering pressure, and gas ratio) apart from the deposition temperature.

3. Results and discussion

Nanocrystalline thin films of zirconia were formed at various temperatures, and their XRD patterns are displayed in Figure 2. In all deposited samples, the appearance of wide bump at 2θ = 31.48° indicates the existence of (111) plane of the monoclinic ZrO₂ structure which is the most common ZrO₂ phase “JCPDS (reference code: 00-037-1484)” [39,40]. Zirconia’s (111) monoclinic phase is responsible for the main peak at roughly 31.48º of 2θ. The main peak, however, grows stronger when the substrate temperature is raised from ambient temperature to 400°C. Therefore, elevating the deposition temperature results in a layer with greater crystallinity. The standard Scherrer formula [41] was used to determine the typical crystallite size, t, of the samples. Crystallite size varies when the temperature rises or falls, as seen in Figure 3. As the temperature of deposition rises, so does the size of the crystallites [42].

Figure 2. Zirconia X-ray diffraction patterns at various temperatures.

Figure 3. Temperature effects on the crystallite size and surface roughness of zirconia films.

AFM was used to explore the surface morphology and roughness of the films. Micrographs of zirconia film acquired using AFM with a scan area of 2 μm on a side are displayed in Figure 4. It shows that the structure of the zirconia films is consistent. Figure 4(a–e) displays three-dimensional AFM pictures of the deposited films.

Figure 4. AFM images of the prepared films: (a) as deposited RT (b) 100°C, (c) 200°C (d) 300°C and (e) 400°C.

The AFM pictures show that the surface of the growing grains is smoother at room temperature (as deposited) (Figure 4a). Figure 4b shows how the substrate’s shape changes from a pyramidal type to a cluster type when the temperature is raised from 100°C to 400°C, as the grains merge to form larger grains. As-deposited films have a root-mean-square roughness of 45.4523 nm. After heating the substrate to 100º C, the XRD evidence of grain coalescence and the creation of zirconium oxide phases causes this value to rise to 69.179 nm [42]. The AFM’s supplementary software was used to assess the surface roughness. The XRD findings were corroborated by the AFM analysis. Figure 6 shows a scanning electron microscopy picture of a thin coating of nanostructured zirconia at a substrate temperature of 300°C.

The spectrum changes of transmission for the zirconia films formed onto glass substrate at various deposition temperatures were scrutinized transversely in the wavelength range of 300–800 nm, and Figure 5 displays the results of those measurements. The films that were deposited at varying temperature, had an average transmittance value in the visible range that is up to 90%, 91%, 92%, 93%, and 94% accordingly.

Figure 5. Transmission spectra of ZrO2 as a function of temperature.

The films had a high optical transmittance in the wavelengths that were more than 400 nanometers. It rose when the temperature of the substrate grew to 400°C. It is clear from the graph that as deposition temperature increases, transmission increases. As described above, the films become rougher as the deposition temperature increases. The density of defect centers dropped as the substrate temperature increased, increasing the amount of light that could pass through the substrate [43]. This results in an increase in kinetic energy of ad-atom at substrate with temperature increase. When the temperature of the substrate was raised from RT to 400°C, there was an increase in the straight band gap of the films from 5.33–5.52 eV. The enhancement in the packing compactness and crystallinity of the film was the cause of the rise in the optical band gap due to an increase in the temperature of the substrate [44].

Using Swanepoel’s envelope approach, it could calculate the films’ refractive index (ɳ) based on the optical transmittance interference data [43]. The calculated refractive index at different deposition temperatures at 500 nm wavelength is shown in Table 1. As deposition temperature increases, refractive index increases. The films generally exhibited a rise in their refractive indices in response to an upsurge in photon energy. According to the findings of studies [45,46], the upsurge in the refractive index of the films that occurred when the substrate temperature was increased from RT to 400°C was documented as a rise from 2.15 to 2.19. Because of the increasing temperature of the substrate, the capacity of remaining gas molecules to disperse has improved, making it more challenging for the substrate to absorb them [47].

Table 1. Calculated parameters for ZrO₂ films.

Sample No.	Temperature (^0C)	Refractive index	Thickness by %T data (nm)	Thickness by SEM data (nm)	Bandgap (eV)
ZrO1	Room Temperature (27°C)	2.15	735	738	5.33
ZrO2	100	2.152	732	735	5.35
ZrO3	200	2.156	728	731	5.39
ZrO4	300	2.183	720	722	5.45
ZrO5	400	2.195	712	715	5.52

However, due to the high temperature of the deposited zirconia particles, any change in the substrate’s temperature has only a minor impact on the particles. As a result, the film will get denser, leading to an increase in its refractive index [48].

The equation that is presented in [44,47,49] may be used to calculate the thickness of the film. The calculated thickness and the measured thickness (SEM shown in Figure 6) of the zirconia films are shown in Table 1. Both findings are consistent with one another to a high degree. Furthermore, in Table 1 it has been shown that the substrate’s temperature did not significantly impact the thickness. This indicates that the deposition amount depends on the number of sputtered atoms that eventually make it to the substrate. Negligible are the other impacts, which include a drop in the local pressure in the sputtering plasma, a change in the sticking coefficients of zirconium or oxygen, and re-sputtering from the substrate [50].

Figure 6. Image captured by a SEM of a nanostructured zirconia sheet at a substrate temperature of 400°C.

The relationship between water contact angle and deposition temperature is seen in Figure 7. The contact angle increases as the deposition temperature increases. As temperature increases, surface roughness increases and hence hydrophobicity increases.

Figure 7. Changes in surface roughness and contact angle as a function of temperature.

Figure 8 illustrates how the resistivity and dielectric constant of a substrate change as a function of the temperature of the substrate.

Figure 8. Temperature-dependent shifts in resistivity as well as the dielectric constant.

The resistivity was decreasing as the temperature was increased [49,50]. The decrement in the resistivity may be due to higher packing density with temperature, while decrement in dielectric constant was due to decrement in the thickness of the film.

4. Conclusions and scope

An aquaphobic zirconia coating of shallow thickness on a glass insulator (substrate) was successfully deposited. It has been discovered that the aquaphobicity of the substrate rises along with an increase in the temperature of the substrate. It was determined that an increase in surface roughness was responsible for the correlation between temperature and aquaphobicity. The highest water contact angle (107°) was found at 400°C. Also, there is increase in transmittance but resistivity and dielectric constant were decreased as deposition temperature was improved. Results of the XRD reveal that crystallinity increases with increase in temperature. Hence, higher temperature cannot be considered as an optimum temperature as it will lead to more leakage current which is undesirable for insulators. Hence, as-deposited films are considered as the optimum films from the temperature point of view. So, at room temperature water contact angle, dielectric constant, refractive index, and bandgap was 103.5°, 24.4, 2.15 and 5.33, respectively.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Qatar National Library. Open Access funding provided by the Qatar National Library.