Alumina-based Ceramics Research Articles

Effect of Al 2O 3 particle size on the mechanical properties of alumina-based ceramics

To study the effect of Al 2O 3 particle size on the mechanical properties of alumina-based ceramics, the monolithic nano-scale alumina ceramics and the Al 2O 3μ/Al 2O 3n/SiC n multi-scale nanocomposite materials were fabricated. The fabricating process, microstructure and the mechanical properties of the new materials were investigated in detail. The results showed that nano-scale Al 2O 3 ceramic material may be fabricated at a lower temperature with high density, and the flexural strength was improved compared with micro-scale monolithic alumina ceramics. With the optimal dispersing and fabricating technology, the intra/intergranular microstructure with well-dispersed nano-scale Al 2O 3 and nano-scale SiC was obtained in Al 2O 3μ/Al 2O 3n/SiC n composite. The improved mechanical properties may be mainly attributed to the grain fining, grain boundary reinforcement and transgranular fracture mode. The size matched effect and the different thermal expansion coefficient of the added nano-scale Al 2O 3 particles resulted in the higher mechanical properties compared with the Al 2O 3μ/SiC n composite.

Optimization of process parameters for ultrasonic drilling of advanced engineering ceramics using the Taguchi approach

The effect of process parameters on the cutting ratio (ratio of material removal rate to tool wear rate) for ultrasonic drilling of alumina-based ceramics using silicon carbide abrasive was studied. The parameters considered were workpiece material, tool material, grit size of the abrasive, power rating, and slurry concentration. Taguchi’s optimization approach was used to obtain the optimal parameters. The significant parameters were identified and their effects on cutting ratio were studied. The results obtained were validated by conducting confirmation experiments.

Bond strength of a resin cement to high-alumina and zirconia-reinforced ceramics: The effect of surface conditioning

The aim of this study was to evaluate the effect of two surface conditioning methods on the microtensile bond strength of a resin cement to three high-strength core ceramics: high alumina-based (In-Ceram Alumina, Procera AllCeram) and zirconia-reinforced alumina-based (In-Ceram Zirconia) ceramics. Ten blocks (5 x 6 x 8 mm) of In-Ceram Alumina (AL), In-Ceram Zirconia (ZR), and Procera (PR) ceramics were fabricated according to each manufacturer's instructions and duplicated in composite. The specimens were assigned to one of the two following treatment conditions: (1) airborne particle abrasion with 110-microm Al2O3 particles + silanization, (2) silica coating with 30 microm SiOx particles (CoJet, 3M ESPE) + silanization. Each ceramic block was duplicated in composite resin (W3D-Master, Wilcos, Petrópolis, RJ, Brazil) using a mold made out of silicon impression material. Composite resin layers were incrementally condensed into the mold to fill up the mold and each layer was light polymerized for 40 s. The composite blocks were bonded to the surface-conditioned ceramic blocks using a resin cement system (Panavia F, Kuraray, Okayama, Japan). One composite resin block was fabricated for each ceramic block. The ceramic-composite was stored at 37 degrees C in distilled water for 7 days prior to bond tests. The blocks were cut under water cooling to produce bar specimens (n = 30) with a bonding area of approximately 0.6 mm2. The bond strength tests were performed in a universal testing machine (crosshead speed: 1 mm/min). Bond strength values were statistically analyzed using two-way ANOVA and Tukey's test (< or = 0.05). Silica coating with silanization increased the bond strength significantly for all three high-strength ceramics (18.5 to 31.2 MPa) compared to that of airborne particle abrasion with 110-microm Al2O3 (12.7-17.3 MPa) (ANOVA, p < 0.05). PR exhibited the lowest bond strengths after both Al2O3 and silica coating (12.7 and 18.5 MPa, respectively). Conditioning the high-strength ceramic surfaces with silica coating and silanization provided higher bond strengths of the resin cement than with airborne particle abrasion with 110-microm Al2O3 and silanization.

Evaluation of support materials for the immobilization of sulfate-reducing bacteria and methanogenic archaea

This paper reports on the adhesion of sulfate-reducing bacteria (SRB) and methanogenic archaea on polyurethane foam (PU), vegetal carbon (VC), low-density polyethylene (PE) and alumina-based ceramics (CE). Anaerobic differential reactors fed with a sulfate-rich synthetic wastewater were used to evaluate the formation of a biofilm. The PU presented the highest specific biomass concentration throughout the experiment, achieving 872 mg TVS/g support, while 84 mg TVS/g support was the maximum value obtained for the other materials. FISH results showed that bacterial cells rather than archaeal cells were predominant on the biofilms. These cells, detected with EUB338 probe, accounted for 76.2% (±1.6%), 79.7% (±1.3%), 84.4% (±1.4%) and 60.2% (±1.0%) in PU, VC, PE and CE, respectively, of the 4′6-diamidino-2-phenylindole (DAPI)-stained cells. From these percentages, 44.8% (±2.1%), 55.4% (±1.2%), 32.7% (±1.4%) and 18.1% (±1.1%), respectively, represented the SRB group. Archaeal cells, detected with ARC915 probe, accounted for 33.1% (±1.6%), 25.4% (±1.3%), 22.6% (±1.1%) and 41.9% (±1.0%) in PU, VC, PE and CE, respectively, of the DAPI-stained cells. Sulfate reduction efficiencies of 39% and 45% and mean chemical oxygen demand (COD) removal efficiencies of 86% and 90% were achieved for PU and VC, respectively. The other two supports, PE and CE, provided mean COD removal efficiencies of 84% and 86%, respectively. However, no sulfate reduction was observed with these supports.

Manufacturing process optimisation for tool wear rate in ultrasonic drilling of engineering ceramics using the Taguchi method

The objective of this paper is to study the effect of process parameters on Tool Wear Rate (TWR) of ultrasonic drilling on alumina-based ceramics using silicon carbide abrasive. The parameters considered are workpiece material, tool material, grit size of the abrasive, power rating and slurry concentration. The optimal settings of the parameters are determined through experiments planned, conducted and analysed using the Taguchi method. The significant parameters are also identified and their effect on TWR is studied. The percentage contributions of parameters affecting both mean and variation are determined. The results obtained are validated by conducting the confirmation experiments.

Determination of dose rates from natural radionuclides in dental materials

Different types of materials used for dental prosthetics restoration, including feldspathic ceramics, glass ceramics, zirconia-based ceramics, alumina-based ceramics, and resin-based materials, were investigated with regard to content of natural radionuclides by means of thermoluminescence beta dosimetry and gamma spectrometry. The gross beta dose rate from feldspathic and glass ceramics was about ten times higher than the background measurement, whereas resin-based materials generated negligible beta dose rate, similarly to natural tooth samples. The specific activity of uranium and thorium was significantly below the levels found in the period when addition of uranium to dental porcelain materials was still permitted. The high-beta dose levels observed in feldspathic porcelains and glass ceramics are thus mainly ascribable to 40K, naturally present in these specimens. Although the measured values are below the recommended limits, results indicate that patients with prostheses are subject to higher dose levels than other members of the population. Alumina- and zirconia-based ceramics might be a promising alternative, as they have generally lower beta dose rates than the conventional porcelain materials. However, the dosimetry results, which imply the presence of inhomogeneously distributed clusters of radionuclides in the sample matrix, and the still unsuitable structural properties call for further optimization of these materials.

Instrumented Vickers microindentation of alumina-based materials

The adequacy of instrumented Vickers depth-sensing microindentation to determine Young's modulus of alumina-based ceramics was analyzed. Monophase alumina materials and alumina + 10 vol% aluminium titanate composites, with different microstructures, were tested to determine the effect of microcracking. The load–depth penetration of the indenter curves together with the observation of the imprints by scanning electron microscopy were used to analyze the behavior of the materials. Maximum stiffness was determined from the derivatives of the load-depth curves during unloading. The areas of the imprints measured optically were more representative of the behavior of the materials than the areas calculated from depth-penetration measurements. The formation of microcracks affected the shape of the unloading portion of the curves. Significant differences between the values of Young's modulus determined for different materials and definite relationships between the microstructural parameters of the materials and the Young's modulus were found.

Enhancement of Hydrophilic Properties of Alumina-Based Ceramics

An effective additive for enhancing the hydrophilic properties of alumina was identified. The mechanical and frictional properties of the resultant material were characterized. The contact angle varied greatly depending on the kind of additive. ZnO was found to be the additive that most reduced the water contact angle of conventional alumina. ZnO-added alumina, with such enhanced hydrophilic properties, naturally exhibited excellent frictional properties in the boundary-lubrication region. Its strength (388 MPa) was equivalent to that of conventional alumina.

Computer Simulation Studies on Sintering and Grain Growth

We have successfully developed a computer simulation technique for microstructural development such as sintering and grain growth of nano/micro-size particles. The molecular dynamic (MD) method, the Monte Carlo (MC) method and the finite element method (FEM) have been used for the simulations. The MD simulation, which was applied to alumina base ceramics, demonstrated the atomic structures and excess energy at grain boundaries and interfaces. The MC simulations were performed for the array of two- or three-dimensional lattices. Plural mechanisms of mass transport were introduced in the MC simulations of sintering and grain growth in ceramic systems, which involve a liquid phase and second solid particles. The combination method between MC and FEM has been developed to simulate precise shrinkage behaviors during sintering process.

Fabrication of Porous Alumina-based Ceramics with Hydraulic Inorganic Binder

Fabrication of Porous Alumina-based Ceramics with Hydraulic Inorganic Binder

Fabrication of Porous Alumina-based Ceramics with Hydraulic Inorganic Binder (3)

Fabrication of Porous Alumina-based Ceramics with Hydraulic Inorganic Binder (3)

Evaluation of the performance of different nano-ceramic tool grades when machining nickel-base, inconel 718, alloy

High-speed machining of aerospace alloys can be enhanced by the use of advanced cutting tool materials such as nano-grain size ceramics that exhibit improved physical and mechanical properties than their micron grain counterparts. The performance of recently developed nano-grain size ceramic tool materials were evaluated when machining nickel base, Inconel 718, in terms of tool life, tool failure modes and wear mechanisms as well as component forces generated under different roughing conditions. The tools were rejected mainly due to wear on the tool nose. It is also evident that chemical compositions of the tool materials played significant role in their failure. The alumina base ceramics performed better than the silicon nitride base ceramics. Severe abrasion wear was observed on both rake and flank faces of the cutting tools while cutting forces increased with increasing cutting speed when machining with the silicon nitride base nano-ceramic tools. This is probably due to the lower superplastic flow temperature of the nitride base nano-ceramics. The alumina base ceramics are more susceptible to chipping at the cutting edge than the silicon nitride base ceramics despite their higher edge toughness.

Forming and sintering of alumina-based ceramics with hydraulic alumina

Forming and sintering of alumina-based ceramics with hydraulic alumina

Fabrication of alumina-based ceramics with hydraulic alumina

Fabrication of alumina-based ceramics with hydraulic alumina

Alumina-Based Ceramics for Cutting Application

Alumina-Based Ceramics for Cutting Application

Fabrication of Tailored Alumina-Based Ceramics Through Colloidal Processing

Fabrication of Tailored Alumina-Based Ceramics Through Colloidal Processing

Evaluation of the Machinability of Nickel-Base, Inconel 718, Alloy with Nano-Ceramic Cutting Tools

The machinability of difficult-to-cut aerospace alloys can be enhanced by the rapid development of cutting tool materials that can withstand machining at high-speed conditions. The performance of nano-grain size ceramic tool materials were evaluated when machining nickel base, Inconel 718, in terms of tool life, tool failure modes and wear mechanisms as well as component forces generated under different roughing conditions. Comparison tests were carried out with commercially available ceramic tool materials of micron-grain composition. The test results show that the micron grain size commercially available tool materials generally gave the longest tool life. The dominant failure mode is nose wear, while some of the nano-ceramic tools were rejected mainly due to chipping at the cutting edge. This suggests that physical properties and mechanical stability of the cutting edge of the ceramic tools influence their overall performance. It is also evident that chemical compositions of the tool materials played a significant role in their failure. The alumina base ceramics are more susceptible to premature fracture than the silicon nitride base ceramics with higher fracture toughness. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

Microstructure and Superplasticity in Various Zirconia-Dispersed Aluminas.

High-temperature tensile ductility in alumina-based ceramics is usually limited due to dynamic grain growth. In this study, superplasticity in zirconia-dispersed alumina has been achieved by colloidal processing using monoclinic, tetragonal and cubic zirconia powders. The densities and microstructures depend on the zirconia particles used as a second phase. Differences in the static alumina grain growth in various zirconia-dispersed alumina composites were caused by differences in distribution of the zirconia particles. The tensile ductility of these materials was found to depend on the type of zirconia used. Limited superplasticity seems to be caused by the density and dynamic alumina grain growth during deformation.

Surface treatment of alumina-based ceramics using combined laser sources

Alumina-based refractory materials are extensively used as linings in incinerators and furnaces. These materials are subject to molten salt corrosion and chemical degradation because of the existence of porosity and material inhomogeneity. Efforts to improve the performance of these materials have so far concentrated mainly on the optimisation of the manufacturing processes (e.g. producing denser refractory bricks) and in-service monitoring. Laser surface treatment has also been used to improve performance. The main problem identified with laser surface treatment is solidification cracking due to the generation of very large temperature gradients. The aim of this paper is to investigate the surface modification of alumina-based ceramics by using two combined laser sources in order to control the thermal gradients and cooling rates during processing so that crack formation can be eliminated. The material under investigation is 85% alumina refractory ceramic, used as lining material in incineration plants. The surface morphology and cross-section of the treated samples are analysed using optical and scanning electron microscopy (SEM) and compared with single laser beam treated samples.

Sintering of α-Al2O3-seeded nanocrystalline γ-Al2O3 powders

Abstract This paper demonstrates that seeding nanocrystalline transition alumina powders is a viable option for producing high quality, alumina-based ceramics. By using α-Al 2 O 3 concentrations of ⩾1.25 wt.% α-Al 2 O 3 seed particles (equivalent to 5 ×10 14 seeds/cm 3 of γ-Al 2 O 3 ) the sintering temperature is reduced from 1600°C for unseeded γ-Al 2 O 3 to 1300–1400°C in dry pressed powders. The scale of the sintered microstructure is related to N v −1/3 and thus a 100-nm grain size is obtained. It is apparent that seeding is necessary for producing dense, alumina-based ceramics from nanocrystalline transition alumina powders.