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Showing 12 results for Zirconia

Hadian A.m., Abu Fanas S.h.,
Volume 2, Issue 4 (12-2005)
Abstract

Enhancing the properties of dental resin composites is of interest to researchers. The objective of the present investigation was to improve the strength and fracture toughness of dental composites via addition of silicon carbide whiskers and substitution of commonly used filler materials with stabilized zirconia ceramic powder. It was also intended to study the effect of powder- to- whisker ratio on mechanical properties of the resultant composites. The flexural strength and fracture toughness of composite samples with different whiskers loadings were measured. It was found that addition of whiskers to the composites enhances the mechanical properties of the composites. The strength and fracture toughness increased by increasing the amount of whiskers. The flexural strength of a composite having 60wt% whisker and 10wt% zirconia powder was about 210 MPa while that of the composite having only 60wt% ceramic powder was about 110 MPa. The microstructural examinations revealed that reinforcing mechanism was whiskers pull-out as well as crack deflection.
Moore R.e., Karakus M.,
Volume 2, Issue 4 (12-2005)
Abstract

In situ refractories are defined as brick or unshaped products, which react internally or with furnace atmospheres and/or slag components so as to be enhanced in their performance. Examples of such products are discussed with emphasis on those that are currently employed and are being developed for the melting of iron and steel. Some strategies for the development of future in situ products are outlined.
Golazar M.a., Mostaghimi J., Coyle T.w.,
Volume 3, Issue 1 (6-2006)
Abstract

Partially stabilized zirconia (PSZ) has been proven to be an excellent candidate as a thermal barrier coating (TBe) for hot sections in, for instance, heat or internal combustion engines and gas turbine parts. The main functions of these coatings are reducing heat losses, reducing fuel consumption, increasing efficiency, and extending durability and life. One of the main problems involved is wear behavior in the development of such coatings for these applications. Using the air plasma spraying (APS) technique, conventional and nanostructured 8 wt % yttria partially stabilized zirconia (Y-PSZ) coatings were deposited on austenitic stainless steel (AISI304) disc-shaped substrates. The coated substrates were subjected to pin-on-disc wear tests, using 10 mm silicon nitride and zirconia balls as the pin. The coefficient of friction was recorded in real time. The weight loss of coated substrates was measured. Coatings were characterized before and after being subjected to wear testing by various techniques including optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and X-ray diffraction (XRD). Effects of various experimental parameters such as wear distance, test temperature, and counter face material were also investigated. Results obtained revealed that, regardless of experimental conditions applied, the nanostructured zirconia coating shows better wear and tribological properties than that of the conventional one.
M. Ghatee, M.h. Shariat,
Volume 8, Issue 1 (3-2011)
Abstract

Abstract: Zirconia solid electrolytes with nonequilibrium composite structure were prepared by impregnation of a porous 8YSZ matrix with a solution of Zirconia. Microstructures were characterized by XRD and SEM. The electrical properties were studied by impedance spectroscopy as a function of temperature. Biaxial flexural strength and fracture toughness of composite samples were measured by ring on ring and Vickers microhardness indentation methods respectively. The microstructures of the composite electrolytes were composed of cubic grains surrounded by tetragonal second phase grains. It was shown that the electrical and mechanical properties of the prepared electrolyte can be adjusted by controlling the amount of doped zirconia. Increasing the amount of doped zirconia increases the tetragonal phase content which improves fracture toughness and fracture strength. In addition, increasing tetragonal phase content of the composite electrolytes decreases the conductivity at high temperatures while the situation is reversed at low temperatures.
M. Bahamirian, Sh. Khameneh Asl,
Volume 10, Issue 3 (9-2013)
Abstract

In the present study NiCrAlY bond coating layer was produced by electroplating against common atmospheric plasma spraying (APS). Both types of the bond coats were applied on IN738LC base metal then, the YSZ (ZrO2-8% Y2O3) thermal barrier top layer was coated by atmospheric plasma spray technique. Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBCs) which come as a result of molten salt effect on the coating–gas interface. In this investigation the hot corrosion behavior of coatings was tested in the furnace which was contain Na2SO4-55% V2O5 and mixed salts environment at 900°C up to 15 hr. dwell time. Optical microscopy, scanning electron microscopy (SEM / EDS) and X-ray diffraction analysis (XRD) was used to determine the crystallographic structure and phase transformation of the coatings before and after the hot corrosion tests. The transformation of tetragonal Zirconia to monoclinic ZrO2 and formation of YVO4 crystals as hot corrosion products caused the degradation of mentioned TBCs. The results showed NiCrAlY coated by economical electroplating method a viable alternative for common thermals sprayed bond coats in hot corrosive environments with same corrosion behavior
A. Ahmadi, A. A. Youzbashi, A. Nozad, A. Maghsoudipour, T Ebadzadeh,
Volume 11, Issue 4 (12-2014)
Abstract

Synthesis of YSZ nanopowder by alkoxide sol-gel method, through two different hydrolysis routes, one under careful control by using acetyacetone as ligand, and the other through basic hydrolysis, was investigated. The synthesized powders were characterized by various analytical techniques such as, XRD, STA, PSA, BET, SEM, and TEM. The results showed that, the YSZ powders prepared through the basic hydrolysis route consist of weakly agglomerated nanosized spherical particles whereas the products obtained through the controlled hydrolysis route, consist of hard irregular shaped agglomerates. Sinterability of these powders was examined at 1480 °C, which showed that the powder synthesized through the basic hydrolysis route attains a density of 94%, against 60% for the other case. It was therefore concluded that, alkoxide sol-gel method through basic hydrolysis route, can be more suitable for the synthesis of YSZ nanopowder and its subsequent sintering.
M. Khaleghian, M. Kalantar, S. S. Ghasemi,
Volume 12, Issue 2 (6-2015)
Abstract

Lead zirconate titanate (PZT) as a piezoelectric ceramic has been used widely in the fields of electronics, biomedical engineering, mechatronics and thermoelectric. Although, the electrical properties of PZT ceramics is a major considerable, but the mechanical properties such as fracture strength and toughness should be improved for many applications. In this study, lead monoxide, zirconium dioxide and titanium dioxide were used to synthesize PZT compound with chemical formula Pb(Zr 0.52 ,Ti 0.48 )O 3 by calcination heat treatment. Planetary mill with zirconia balls were used for homogenization of materials. Two-stage calcination was performed at temperatures of 600˚C and 850˚C for holding time of 2h. In order to improve the mechanical properties of PZT, various amount of ZnO and/or Al 2 O 3 particles were added to calcined materials and so PZT/ZnO, PZT/Al 2 O 3 and PZT/ZnO+Al 2 O 3 composites were fabricated. Composites samples were sintered at 1100˚C for 2 h in the normal atmosphere. Microstructural component and phase composition were analyzed by XRD and SEM. The density, fracture strength, toughness and hardness were measured by Archimedes method, three-point bending, direct measurement length crack and Vickers method, respectively. Dielectric and piezoelectric properties of the samples were also measured by LCR meter and d33metet tester, respectively. The results showed that by addition of ZnO and Al 2 O 3 to composite materials, the relative density of PZT based composites was increased in conjunction with a signification improvement of mechanical properties such as flexural strength, toughness and hardness. Moreover, the dielectric and piezoelectric properties of PZT such as dielectric constant, piezoelectric coefficient and coupling factor were decreased while the loss tangent was also increased.
A. M. Zahedi, H. R. Rezaie, J. Javadpour,
Volume 12, Issue 4 (12-2015)
Abstract

Different volume fractions (1.3, 2.6, and 7.6 Vol.%) of carbon nanotubes (CNTs) were dispersed within 8Y-TZP nanopowders. Mixed powder specimens were subsequently processed by spark plasma sintering (SPS) and effects of CNTs on the sintering process of 8Y-TZP/CNT composites was studied. Maintenance of CNTs through the SPS process was confirmed using TEM and Raman Spectroscopy. Studies on the sintering profile of zirconia-CNT composites (Z-xC composites) could, to some extent, clarify the effect of CNTs’ volume fraction on the densification rates of Z-xC composites. The specimen with the highest content of CNT (Z-7.6C) showed the lowest sintering rate while it was unable to reach full density.

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R. Sarjahani, M. Sheikhattar, S. Javadpour, B. Hashemi,
Volume 13, Issue 1 (3-2016)
Abstract

Surface smoothness of ceramic glazes is always an important characteristic of ceramic glazes as a point of surface engineering studies. Surface roughness affects chemical resistivity, glossiness and stainabiliy of glazes. In fact, less surface roughness improves cleanability of the surface by the least usage amount of detergents. In this investigation, surface topography of two common opaque glazes, zirconia and titania-based, has been investigated. Crystallinity of the surface has been studied from SEM images, and comparison of EDS elemental results with phase analysis results of XRD. Surface roughness profile measured by Marsurf M300, shows that titania-based glaze is almost 24% percentage more smooth than zirconia based glaze. Surface smoothness is in relation with crystallinity of glaze surface, crystal type and crystal distribution in amorphous matrix phase

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N. Radhika, R. Raghu,
Volume 13, Issue 4 (12-2016)
Abstract

Functionally graded aluminium/zirconia metal matrix composite was fabricated using stir casting technique followed by horizontal centrifugal casting process and a hollow cylindrical functionally graded composite (150 x 150 x 16 mm) was obtained with centrifuging speed of 1200 rpm. The microstructural evaluation and hardness test was carried out on the outer and inner surface of the functionally graded composite at a distance of 1 and 13 mm from the outer periphery. In Response Surface Methodology, Central Composite Design was applied for designing the experiments and sliding wear test was conducted as per the design using a pin-on-disc tribometer for varying ranges of load, velocity and sliding distance. The model was constructed and its adequacy was checked with confirmation experiments and Analysis of Variance. The microstructural examination and hardness test revealed that the outer surface of FGM had higher hardness due to the presence of  particle rich region and the inner surface had lesser hardness since it was a particle depleted region. The wear results showed that wear rate increased upon increase of load and decreased with increase in both velocity and sliding distance. Scanning Electron Microscopy analysis was done on the worn specimens to observe the wear mechanism. It was noted that wear transitioned from mild to severe on increase of load and the outer surface of FGM was found to have greater wear resistance at all conditions.


Z. Valefi, M. Saremi,
Volume 14, Issue 2 (6-2017)
Abstract

In this paper the effect of plasma spray parameters, atomizing gas and substrate preheat temperature on microstructure and phase composition of YSZ coatings produced by SPPS process have been investigated. The experimental results showed that increasing the power of plasma, using hydrogen as the precursor atomizing gas and increasing substrate preheat temperature decrease the amount of non-pyrolyzed precursor in the coatings. At low plasma power most of the deposited precursor is in non-pyrolyzed state, and consequently the applied coatings are defective. The increase in substrate temperature beyond 800oC either by preheating or heat transfer from plasma torch to the substrate, prevent the coating formation. In SPPS coating formation, up to a special spray distance the optical microscopy image of the coatings showed a snowy like appearance. XRD analysis showed that in this situation the amount of un-pyrolyzed precursor is low. Beyond this spray distance, spherical particles, are obtained and XRD analysis showed that most of the precursor is in un-pyrolyzed state.


H. Aydın,
Volume 16, Issue 4 (12-2019)
Abstract

Mullite–zirconia composites were prepared using lanthanum oxide (La2O3) additive which three different mole ratio by the reaction sintering (RS) route of alumina, kaolinite and zircon. Starting materials were planetary milled, shaped into pellets and bars and sintered in the temperature range of 1450–1550 0C with 5 h soaking at peak temperature. In this work, the mullite-zirconia composites were characterized by thermal expansion coefficient, physical, microstructures and mechanical properties. The XRD method were employed for determining the crystalline phase composition of these composites. Microstructure of the composites was examined by SEM. ZrO2 takes part in both the intergranular as well as intragranular positions. However, intragranular zirconias are much smaller compared to intergranular zirconias.


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