Al2O3 Ceramic Materials Research Articles

Gradient Structure Formation in the Subsurface Layers of a ZrO2(Y)–Al2O3 Ceramic Material Under Low-Energy, High-Current Electron Beams

The role of a low-energy, high-current electron beam on the microstructural state of subsurface layers of a composite ZrO2(Y)–Al2O3 ceramic material is investigated. It is found out that irrespective of the initial porosity of the ceramic material an electron beam treatment gives rise to formation of a characteristic microstructure in the subsurface layers of the specimens. Grains are observed to orient towards the specimen surface. The layers immediately below the surface are characterized by finer grains than those in the bulk.

A Dilatometric Study of Sintering of Composite Ceramics Manufactured from Ultrafine Zro2(Y)–Al2O3 Powders Under Different Thermal-Temporal Firing Conditions

UDC 666.3 Using dilatometry, kinetic principles of sintering of composite ZrO2(Y)–Al2O3 ceramic material made from ultrafine powders synthesized at the Siberian Chemical Integrated Works are investigated. It is shown that under heating conditions, sintering of the composite ceramics under study occurs within a few stages that are closely related to the structural-phase transformations taking place in the composite powder mixture. At the firing temperatures Т  1500С and during long isothermal times, negative phenomena develop in the ceramic material, which give rise to its undesired dilatation and cracking in the course of cooling.

Fabrication of biomorphic Al2O3 ceramics with hierarchical architectures by templating of cotton fibers

This work presents an effective method for fabricating hierarchical Al2O3 ceramic fibers with high surface-to-volume ratios. To do this, the microscaled Al2O3 fibers are fabricated via a simple biotemplate method employing cotton fibers as bio-templates. The hierarchical architectures are designed by in situ growth of AlOOH nanocrystal on surface of Al2O3 microtube walls in a closed hydrothermal system. The developed facile route is highly valuable and feasible for hierarchical porous Al2O3 ceramic materials for applications in research and industrial fields.

Shear Strength of Joints Fabricated by Solders with High Indium Content

Feasibility of pure indium and solders containing high amount of indium as 70In30Sn to wet the different types of metallic and ceramic materials at application of power ultrasound was studied. The shear strength of soldered joints fabricated on metallic (Cu, Ni, Al, Ti, AISI 316 steel) and ceramic substrates was assessed. The shear strength of In solders on Al2O3 and SiC ceramic materials varied from 3.5 to 7 MPa. The shear strength on metallic materials attained from 12.5 to 71 MPa. Joint fracture in most cases occurred in the solder and was of ductile character. Failure took place by shear mechanism.

Single Discharge Machining Insulating Al2O3 Ceramic with High Instantaneous Pulse Energy in Kerosene

A technique of machining insulating Al2O3 ceramic with a thin copper sheet assisting electrode and high instantaneous pulse energy is developed. The process uses the high peak voltage and large capacitor with high instantaneous pulse energy, and there is no current-limiting resistor in the discharge circuit, so the discharge energy and discharge explosive force are high, and the process is able to effectively machine insulating ceramics. To further explore the process characteristics, the single pulse discharge experiments have been carried out in kerosene. The effects of polarity, capacitance, peak voltage, and current-limiting resistance on the process performance such as the crater volume, crater depth, tool wear ratio (TWR), and assisting electrode wear ratio (AEWR) have been investigated. The microstructure of the discharge crater has been examined with a scanning electron microscope (SEM). The results show that the insulating Al2O3 ceramic materials are mostly removed by spalling, at the center region of the discharge some materials are removed by melting and evaporation.

Physical and technological factors determining Y–ZrO2–Al2O3 composite nanostructured ceramic density

The particulars of the sintering process for Y–ZrO2–Al2O3 ceramic materials with different initial structural modifications (tetragonal or cubic) are studied. The effect of cold isostatic compaction on the volume density of such materials sintered at high-temperature is determined.

Simulation of Fabrication for Al<sub>2</sub>O<sub>3</sub> Ceramic Tool Materials

The new Monte Carlo Potts model that couples with fabrication parameters and considers pores and additives has been developed in order to simulate the fabrication of single-phase ceramics tool materials. The microstructure evolution for single-phase Al2O3 ceramic tool materials is simulated with the different technology parameters. At the same time, the single-phase Al2O3 ceramic tool materials are fabricated with the corresponding technology parameters. The errors of grain size between the simulated and the experimental is 12.1 and18.2%.

Wettability and shear strength of active Sn2Ti solder on Al2O3 ceramics

PurposeThe purpose of this paper is to investigate the wettability of an active Sn2Ti solder on an Al2O3 ceramic material at temperatures of 700°C and higher. Based on the results of the wettability study, soldered joints of Al2O3 ceramics/Sn2Ti solder/steel type AISI 321 were fabricated and the variation of shear strength with time was determined.Design/methodology/approachFor determining melting points, differential scanning calorimetry analysis was performed. The wetting angle of Sn2Ti solder on Al2O3 ceramics was measured using specially developed equipment with a 10‐3 Pa vacuum at temperatures of 700, 800, 850 and 900°C. The wetting angle on AISI 321 steel at a temperature of 850°C was also determined. The joints of Al2O3 ceramics/Sn2Ti solder/steel type AISI 321 were prepared at 900°C, in a vacuum for times 5, 10, 15 and 20 min.FindingsThe best wettability of Sn2Ti solder was achieved at a temperature of 900°C. The wetting angle at the parameter of 900°C/ for 15 min was 47.5°. The joints of Al2O3 ceramics/Sn2Ti solder/steel type AISI 321 attained a strength of 18.3 MPa. It was found that the microstructure of Sn2Ti solder consists of a tin matrix with the presence of a αTi6Sn5 phase.Originality/valueThe results of the work are of significance for the further development of soldering with active solders in a vacuum, as well as with the application of power ultrasound. The possibility of soldering Al2O3 ceramics with SnTi‐based solders was thus demonstrated.

Fabrication and Mechanical Properties of Nano-Al<sub>2</sub>O<sub>3</sub> Based Composite Ceramic Tool Material

The Al2O3(nm)/SiC（μm）/Al2O3（μm）ceramic tool materials were fabricated by the hot-pressing technique. Effect of the compositions on microstructure and mechanical properties is investigated. With nano-particles content decreasing, the flexural strength increased and fine grains can be obtained. When the nano-alumina content is 60wt%, the grain of this sample is fine, the Vickers hardness and flexural strength are 16.24 GPa and 678 MPa, respectively.

Micro Machining of Nonconductive Al2O3 Ceramic on Developed TW-ECSM Setup

Advanced ceramic materials are gradually becoming very important for their superior properties such as high hardness, wear resistance, chemical resistance, and high strength to weight ratio. But machining of advanced ceramic like Al2O3-ceramics is very difficult by any well known and common machining processes. Normally, cleavages and triangular fractures generate when machining of these materials is done by traditional machining methods. It is essential to develop an efficient and accurate machining method for processing advanced ceramic materials. For effective machining of Al2O3-ceramics, a traveling wire electrochemical spark machining (TW-ECSM) setup has been developed. The developed TW-ECSM setup has been utilized to machine Al2O3 ceramic materials and subsequently test results are utilized to analyze the machining performance characteristic. Different SEM photographs show the actual condition of the micro machined surfaces. The practical research analysis and test results on the machining of Al2O3 ceramics by developed TWECSM setup will provide a new guideline to the researchers and manufacturing engineers.

Initial stage of bi-modal microstructure in TiO2-doped α-Al2O3 ceramics induced by SiO2 impurity

Abstract Uni-modal and bi-modal microstructures were concurrently observed in a TiO2-doped -Al2O3 ceramic material with some SiO2 impurity. The segregation of Ti and Si to grain boundaries was systematically evaluated to reveal their role at the start of anisotropic grain growth. In general, in the bi-modal area grain boundaries exhibit higher Si excess than those in the uni-modal area. However, the basal plane of anisotropic grains was always found to contain more segregated Si while the non-basal planes were found to contain less Si. Such enrichment of SiO2 was also found at the basal planes of equiaxed grains in the uni-modal area, which occurred in the initial stage of anisotropic grain growth. Before and after this stage, the grain boundary composition was relatively uniform with the mole ratio of SiO2 to TiO2 as 2.3: 1 and 5.8: 1, respectively. The latter should be related to the composition of eutectic liquid formed during the sintering, which is responsible for the development of the bi-modal microstructure.

Effect of Fabrication Parameters on Mechanical Properties of Al<sub>2</sub>O<sub>3</sub> Ceramic Tool Materials

In order to investigate the effect of hot-press fabrication parameters on mechanical properties of Al2O3 ceramic tool materials, the orthogonal experiment method was used. In the experiments, the three influence factors such as the fabrication temperature, pressure and duration time are considered. The experimental results are analyzed by a range analysis of orthogonal experiments. It is shown that the most important factor that affects the mechanical properties is the fabrication temperature and the followed factors are the fabrication pressure and the duration time of fabrication. Scanning electron microscope (SEM) reveals that the hot-press fabrication parameters will significantly affect the microstructure of ceramic tool materials, which can govern the mechanical properties. This has been validated by the orthogonal experiments in the present paper.

Thermal Shock Resistance of a New Ceramic Tool Material and Its Microstructural Characterization

Thermal shock resistance is one of the important properties for ceramic cutting tool materials in machining operation. Thermal shock resistance of a new SiC/Ti(C,N)/Al2O3 ceramic tool material is investigated in detail by means of the water quenching test. It indicates that the addition of Ti(C,N) and SiC is effective in the improvement of thermal shock resistance of the composite and the tested maximum temperature difference of thermal shock reaches about 330. Microstructures of the ceramic samples after thermal shock have been observed and analyzed by SEM focusing mainly on the morphologies of cracks and the peeling off of grains as well as the accompanied oxidation phenomenon at elevated temperatures.

Damage and loading rate effects on the microfailure behaviour of Al2O3-ceramics studied by SEM

A scanning electron microscopy (SEM)-X-ray combined experimental approach to qualitative and semi-quantitative characterization of microfailure behaviour of an Al2O3-ceramic material in terms of induced damage is presented. The qualitative approach was based on representative fractographical images and data obtained by SEM whereas the semi-quantitative approach was based on a new technique of the X-ray electron probe microanalysis (X-ray EPMA) capable to detect the localized subsurface damage. The damage was induced by a simple rotary notch-cutting procedure where the associated damage parameters can be controlled by the cutting rate. By correlating certain characteristic macro- and microfractographic features/patterns with well-known microfailure mechanisms it was possible to make qualitatively, in an indirect way, evident the existence of induced damage which was assumed to be ideal brittle having only microcracking component. In the same correlating way the stimulating effect of internal pores on the damage development was deduced. Observed loading rate effects on the fractographic behaviour expressed by changes in fracture roughness and micromorphology were attributed to pore-assisted microcracking linkage. Low porosity under high loading rates tends to lower the fractographic roughness, a fact which can be related with a reduction in the ability of energy dissipation. On the other hand, high porosity under increasing loading rates leads to non observable changes in the fractographic roughness, a fact which is indicative of corresponding no appreciable changes in the dissipative character of the material. The measured local damage distribution ahead of the notch-tip shows a monotonic increasing of damaging effects toward the tip. By means of this distribution the total or average damage degree and process zone length ahead of the notch-tip were evaluated. The increase of these two damage parameters is not proportional to the increase in the cutting speed i.e. the rate of damage development. Finally, by assuming brittle damage an experimental approaching procedure for the estimation of the induced energy required for the microcracking damage was proposed.

Ultrasonic grinding of fine ceramics for inductively coupled plasma atomic emission spectrometry using slurry nebulization technique

An ultrasonic internecine grinding technique was investigated for the direct slurry nebulization of sintered fine ceramics in inductively coupled plasma atomic emission spectrometry. A sample block was ground with the same sample pestle fixed on an ultrasonic horn along with the same sample coarsely crushed in water for 10 min. The finely ground sample of 10–20 mg (0.5–0.7 µm in mean particle size) was obtained with ultrasonic vibration. The pH of the resultant slurry was adjusted to 12 with tetramethylammonium hydroxide. This slurry was stable and easily nebulized through an ordinary sample introduction system with the similar sensitivity to aqueous standard solutions. The present method was successfully applied to analyses of sintered ZrO2–Al2O3 ceramic materials.

Improvement of the corrosion resistance of alumina–chromia ceramic materials in molten slag

Abstract In the previous study, we found out that the corrosion of ceramic materials in molten slag depended strongly on the viscosity of the slag and the basicity gap between the ceramics and the slag. In this study, we propose experimental equation to predict the corrosion rate of a ceramic material in a molten slag as functions of the viscosity and the basicity gap on the basis of the corrosion tests. Cr2O3–Al2O3 ceramic materials were used for the tests in the SiO2–CaO–B2O3 based model molten slag. The obtained experimental equation is as follows: logΔ D=0.18 ∗ log Δ B−0.55 ∗ log η+C where, ΔD is the depth of corrosion (μm), ΔB the basicity gap between the slag and specimen, η the viscosity of slag (Poise). C is the constant that depends on the conditions of the corrosion. The value is 2.7 for the testing temperature of 1573 K, holding time of 3600 s and rotating speed of specimen of 5.2 cm s−1 within this corrosion test.

Nanopartículas catalisadoras suportadas por materiais cerâmicos

Neste trabalho são apresentados os procedimentos de preparação de materiais cerâmicos de SiO2, SnO2 e Al2O3 e, também, suas propriedades catalíticas nas reações de reforma do metano e do metanol. As análises dos resíduos de carbono, após testes catalíticos, sugerem que a modificação estrutural dos catalisadores pode minimizar os efeitos de sua desativação.

The ceramic-cup microwave ion source for sealed-tube neutron generator

A microwave proton source for sealed-tube neutron generator has been built in the radiation Technology Institute of Northeast Normal University. The plasma resonance chamber is made of 95%Al2O3 ceramic material. The microwave absorption as a function of the magnetic field and the pressure is studied. The microwave absorption efficiencies, (Pi−Pr)/Pi are more than 90% when the magnetic field at the microwave windows is 0.095 T and incident microwave power is 300–500 W, at the same time, the impedance between the microwave circuit and the plasma source is well matched. Two-grid multi-hole extraction electrodes are employed to extract ion. The maximum proton current of 30 mA is obtained when the extraction voltage is 5.4 KV and the incident microwave power is 300 W.

Structural model of low-temperature phase transformation and fracture of zirconia-based ceramic material

The variation of the structural parameters, including the interplane distanced(III), the amount of tetragonal phaset, and the size of regions of coherent scattering, in the process of the tetragonal-monoclinic transformation in cooling of a ZrO2−Y2O3−Al2O3 ceramic material with a variable phase composition from the sintering temperature (1500–1700°C) is considered. It is established that the dependences of the interplane distancesd(III) on the temperature behave nonlinearly in the temperature range of the phase transformation. It is shown from the data of an x-ray analysis that the tetragonal-monoclinic phase transformation occurs in at least two stages, one of which consists in rhombic distortion of the lattice and the other of which results in formation of a monoclinic phase. The suggested model is used to construct an elementary cell of the monoclinic phase and interpret the fracture behavior of a transformation-toughened ceramic material.

Transient liquid-phase bonding of alumina and metal matrix composite base materials

Transient liquid-phase (TLP) bonding of aluminium-based metal matrix composite (MMC) and Al2O3 ceramic materials has been investigated, particularly the relationship between particle segregation, copper interlayer thickness, holding time and joint shear strength properties. The long completion time and the slow rate of movement of the solid–liquid interface during MMC/Al2O3 bonding markedly increased the likelihood of forming a particle-segregated layer at the dissimilar joint interface. Preferential failure occurred through the particle-segregated layer in dissimilar joints produced using 20 and 30 μm thick copper foils and long holding times (≥20 min). When the particle-segregated layer was very thin (<10 μm), joint failure was determined by the residual stress distribution in the Al2O3/MMC joints, not by preferential fracture through the particle-segregated layer located at the bondline. Satisfactory shear strength properties were obtained when a thin (5 μm thick) copper foil was used during TLP bonding at 853 K.