Study Of High Temperature Behavior Research Articles

Study of high-temperature behavior of a heat-protective coating of zirconium dioxide by laser heating

When studying the high-temperature behavior of the heat-protective coating of zirconium dioxide, the method of laser heating has been tested. The coating was applied by the method of high-energy plasma spraying on the intermetallic sublayer of the Ni–Co–Cr–Al–Y system made of a powder material of the composition (ZrO2 + 7% Y2O3) of spherical morphology.The aim of this work was to study the processes of structural-phase transformations, melting and crystallization occurring in a ceramic coating material under the action of a single laser pulse with a duration of 14 ms with different energies (5, 10, 15, and 20 J). It was found that after spraying, the coating in the initial state has a two-phase composition (T-ZrO2 + K-ZrO2), and a layered microstructure with a columnar structure of zirconium dioxide grains. Laser heating with a pulse energy of 5 J stimulates the phase transformation T-ZrO2 → K-ZrO2, the appearance of porosity and microcracks. With an increase in the pulse energy to 10 and 15 J, the processes of melting and ultrafast crystallization, accompanied by grain refinement, intensively occur on the coating surface. According to the theoretical estimates, the reflow processes affect surface layers with a thickness of 2.2 to 6.6 μm, and phase transformations take place at a depth of ~11 μm. With an increase in the laser pulse energy to E = 20 J, the process of destruction of the coating was initiated by the mechanism of cracking with delamination of fragments of the surface layer 5–10 μm thick.The laser heating method is recommended as an express diagnostics for comparative tests of the heat resistance of ceramic coatings obtained by different methods and from different starting materials.

Synthesis, vaporization and thermodynamic properties of superfine yttrium aluminum garnet

The study of high temperature behavior of Y3Al5O12 is urgently required for development of high temperature materials of the new generation including ultra-high temperature ceramics. The superfine Y3Al5O12 powder was obtained by the glycol-citrate method; the aggregation process of the sample synthesized was investigated under calcination conditions at different temperatures. Using the Knudsen effusion mass spectrometric method vaporization processes and thermodynamic properties of Y3Al5O12 as well as of the melts in the Y2O3-Al2O3 system were studied at temperatures higher than 2270 K. The simultaneous transition to the gaseous phase of both Al2O3 and Y2O3 from the melt under study was observed during isothermal keeping of the Y3Al5O12 sample at the temperature 2675 K with the predominant alumina removal. Analysis of the values of the thermodynamic properties obtained in the Y2O3-Al2O3 system showed negative deviations from ideal behavior despite the possibility of existence of the miscibility gap at the temperature 2675 K.

Measurement of ZrC properties up to 5000 K by fast electrical pulse heating method

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Infrared Spectroscopic Study of High Temperature Behavior of the Brønsted Acidic Hydroxyl Groups on Zeolites

Abstract Quantitative analysis of the high-temperature behavior of the Brønsted acidic hydroxyl groups on H-ZSM-5 and H-mordenite zeolites was conducted by in situ IR spectroscopy. The integrated intensity of the Brønsted acidic hydroxyl band on H-ZSM-5 was decreased to 67% at 873 K compared with that at room temperature. This was considered to reflect the deprotonation of hydroxyls at high temperature. Attributing the decreased OH groups at high temperature region to the conversion to IR inactive dissociated species, we estimated the energy difference between the nondissociated and dissociated hydroxyls as 24 kJ mol−1 on H-ZSM-5.

A study of high temperature behavior and microstructures of Al 2O 3ZrO 2 composites with a 3MV high voltage electron microscope

Al2O3-ZrO2 composites have been extensively investigated with a 3MV electron microscope on the effect of oxide additives such as ZrO2, MgO and Y2O3 on microstructures and determination of the most suitable heat treatment conditions to increase the toughness. The results obtained are: (1) MgO and ZrO2 additive powders generally suppress the growth of Al2O3 grains, (2) voids are almost completely eliminated by ZrO2 addition due to not only enhancement of sintering around very fine ZrO2 powders but also good affinity between Al2O3 and ZrO2, (3) grain sizes of both Al2O3 and ZrO2 in Al2O3-ZrO2 composites are not affected with a small amount of MgO, (4) ZrO2 in Al2O3+ZrO2 composites is monoclinic at room temperature, but ZrO2 in Al2O3+YTZ (Yttria Toughened Zirconia) composites is tetragonal in general, (5) grain sizes of both Al2O3 and ZrO2 in Al2O3+YTZ composites are not sensitive to the addition of a small amount of MgO. Furthermore, in the present experiment, using a very-high temperature stage, annealing and mechanical phenomena of Al2O3-ZrO2 composites have been studied up to 2300K by in situ experiments with a 3MV electron microscope.

A Study of High Temperature Behavior and Microstructures of Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> Composites with a 3MV High Voltage Electron Microscope

A Study of High Temperature Behavior and Microstructures of Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> Composites with a 3MV High Voltage Electron Microscope