Effect Of Sintering Temperature On Advance Ceramics (Alumina)

ABSTRACT

The formulation of an advanced ceramics using alumina is for the purpose of light weight. Ceramics have been considered one of the most important materials for lightweight high impact applications due to their low density, high compressive strength, and high hardness. This work is on the effect of sintering temperature on the microstructure of an advanced alumina ceramics (Al₂O₃) which was studied and samples were prepared and evaluated with temperature 1300^oC – 1600^oC. The process to prepare this samples are mixing the alumina which is the main ceramic material (Al₂O₃) 96.2%, addictive (M_gO 0.5% and C_aO 2.3%) and the binder (Polyvinyl alcohol) 1% and then pressed into a mould using uniaxial pressing method and finally sintered at different temperatures to know the effect of temperature on the ceramics. The sintered samples where characterized using a scanning electron microscope test. From observation their results which were evaluated was discovered that the increase in temperature reduces the grain size of the alumina ceramic. Alumina having small grain size and high density yield good mechanical properties which are improved strength, hardness and wear resistance.

INTRODUCTION

For lightweight applications, low density and high hardness, Ceramics materials are considered as the most valuable materials due to their high compressive strength. _{(Silva, Al-Qureshi, Montedo, & Hotza, 2014)}

Various materials made of ceramics used from r high impact applications must be sufficiently rigid to fragment the bullet and reduce its speed, transforming it into small fragments that should be stopped by the layer of flexible material that supports the ceramic. Thus, it is necessary that the ceramic material presents high elastic modulus and high hardness _{(Silva, Al-Qureshi, Montedo, & Hotza, 2014)}

Fracture toughness is another mechanical property requirement for this application. Ceramic materials used commercially in the development of Ballistic (HIGH IMPACT) armours are (Al₂O₃), B4C, SiC, and ceramic matrix composites (CMCs) such as (Al₂O₃)/ZrO2. For a very reduced reduced cost ratio alumina is the best compared to other advance ceramics, it features high modulus of elasticity, high refractoriness, high hardness, and relatively lower cost. Because it has a ballistic performance, low fracture toughness and low flexural strength, alumina is lower when compared to S_iC and B₄C _{(Avila et al., 2011)}.

The property of aluminum oxide can be improved by adding zirconia, which increase fracture toughness and flexural strength by introducing tetragonal zirconia particles or ceramic fibers, respectively_{(Bhatnagar, 2006)}. Moreso, high impact vehicle protection system is done with ceramic materials. Cases like this has only rigorous control of the microstructure assured a reliable ballistic performance can be. The use of ceramics in armoured vehicles is more than the use of metallic materials because it leads to weight reduction, autonomy increase, and higher level of protection_{(Callister, 2003)}.

AIM AND OBJECTIVE OF THE PROJECT

AIM

Formulate and evaluate the effect of temperature on the microstructure characteristics of a sintered alumina ceramics for high impact application.

OBJECTIVES:

1. Formation and development of alumina ceramics
2. Microstructural characterizations of the sintered samples.
3. Analysis and comparing the result of the developed ceramics sample with
   the established/standard result.

REVIEW ON RELATED WORKS

(Dora, et al., 2015), Worked on the influence of sintering time on properties of alumina-based ceramic composite. The sintering time used was 1600^oC and was heated 100^oC per hour. The method adopted for the ceramics powder mixes, the specimens were compacted by uniaxial pressing. Also the research shows that the maximum values of hardness and mechanical bending strength were found at 5hours of sintering time.

(Silva, et al., 2014), Worked on mechanical characterization and ballistic test of alumina based armour plates. Different compositions (92, 96, and 99 wt% (Al₂O₃) were tested for 10 mm thick plates processed in an industrial plant. Samples were pressed at 110 MPa and sintered at 1600^oC for 6h and the samples where taking for test like Relative density, Vickers hardness, and four-point flexural strength measurements. Results showed that the strength values ranged from 210 to 300MPa which depends on the porosity, with lower standard deviation for the 92 wt% (Al₂O₃) sample. Using a metallic plate as backing and witness plates in the case of penetration or deformation. Standard NIJ-0108.01 was followed in regard to the type of projectile to be used (7.62 × 51 AP, Level IV, 4068 J). Five alumina plates were used in the ballistic tests and none penetrated or even deformed the metal sheet, showing that the composition containing 92 wt% (Al₂O₃) could be considered to be a potential ballistic ceramic, being able to withstand impacts with more than 4000J of kinetic energy.

METHODOLOGY

MATERIALS

The major materials for the experiment are;

1. Alumina powder (Al₂O₃)
2. Additives (magnesium oxide M_gO and calcium oxide C_aO )
3. Binders (polyvinyl alcohol)

Equipment used are listed below

1. Mold
2. Pressing machine (110MPa)
3. Furnace
4. Mortar and pestle
5. Microstructural testing machine
6. Electronics balance
7. Power hack saw

EXPERIMENT PROCEDURE

MATERIAL SELECTION

This study required magnesium oxide (M_gO), calcium oxide (C_aO), high purity powdered alumina (Al₂O₃) and polyvinyl alcohol (PVA). Alumina powder was the major materials used for the research, produced by AdValue Technology, LLC, United States. Magnesium oxide (M_gO) and calcium oxide (C_aO), served as hardening additives and grain stabilizer to the powdered alumina
respectively. The polyvinyl alcohol (PVA) served as a binding agent. The
chemical analysis of 99.999% (Al₂O₃).

Formulation proportion

If you noticed temperature is the only parameter that is changing because I want to know the effect of sintering temperature on the ceramics I prepared

SINTERING

This is a process of heating at a very high temperature without liquefaction. This is the process whereby the ceramics material has gone through the process of mixing the powder with binder, deflocculant, water and the ceramics powder then sprayed because from the mixing a slurry is formed after which the dried powder is put into a mold and pressed it to form a green body. The green body is sintered to 1300^oC – 1600^oC at the heating rate of 25^oC per min in a furnace.

MICROSTRUCTURE TEST

Microstructure tests are done with Scanning electron microscope and energy dispersive X-ray analysis which are good tools in many field of science and it is found in many applications of problems of archaeological ceramics. S.E.M yield high resolution images of ceramics surfaces also the interior can be studied either as a polished section or as a fracture surface. SEM provides pictures which can easily be interpreted in terms of structural details_{(FROH, 2004)}.

Flow chat

RESULTS AND DISCUSSION

MICROSTRUCTURE CHARACTERISTICS

SEM (Scanning Electron Microscope) images of the dry pressed alumina samples at different sintering temperatures

fig 1 SEM Result of the sintered alumina at 1500^oC (X150)

fig 2 SEM Result of the sintered alumina at 1500^oC (X1000)

fig 3 SEM Result of the sintered alumina at 1500^oC (X500)

fig 4 SEM Result of the sintered alumina at 1400^oC (X150)

fig 5 SEM Result of the sintered alumina at 1400^oC (X500)

fig 6 SEM image of the sintered alumina at 1400^oC (X1000)

The difference in the microstructures of the two samples show the effect of the temperature on the result. From fig 1 the microstructure from the result of the test the temperature causes some deformation on the sample like the cracks shown and also from the fig 2 the temperature affected the grain size and also gave it a shiny surface.
Based on the observation the reactivity of the alumina of fig 4 sintering temperature 1400^oC, the alumina ceramics particles have an influence on the grain size of the microstructure and ensure homogeneous microstructure. With the increase of the sintering temperatures there were a small reduction of the values of hardness and fracture toughness of this material and there was consequent reduction of the average grain size. This reduction is in the toughness and it resulted of the lesser way to crack propagation as shown in Fig 1, therefore it has a great reduction of the amount of grain boundaries_{(Santos, et al., 2013)}. The microstructure result of the samples shows the effect of sintering temperature on the ceramics.

CONCLUSION
Conclusively, in this evaluation process the influence of the sintering temperature on the (Al₂O₃) ceramic lead to reduction in grain size as the temperature was increased, and it's influenced the properties of the ceramics under study. The results indicate that the temperature has influence in the densification of this material. Also, it has a soft reduction in the hardness and fracture toughness according to _{(Santos, et al., 2013)}, related with the grain growth. Alumina having small grain size and high density yield good mechanical properties which are improved strength, hardness and wear resistance _{(Khan, et al., 2016)}Fine grain size has high density of grain boundary that refines deformation of specimen in loading.

All tests where carried out in Convenant University Nigeria

All images are from pixabay, SEM images from the microstructure test in covenant university nigeria and screenshot from my laptop computer when putting the research together

References for More knowledge

Silva, D. S., Al-Qureshi, H. A., Montedo, O. R., & Hotza, a. D. (2014). Alumina-
Based Ceramics for Armor Application: Mechanical Characterization and
Ballistic Testing. Volume 2014,(Article ID 618154).
Dora, l., Akos, i., & Gomze, l. A. (2015). influence of sintering time on properties
of alumina-based ceramic composite . vol 812.
FROH, J. (2004). Archaeological Ceramics Studied by Scanning Electron
Microscopy. Netherlands : Kluwer Academic Publishers.
Santos, C., L.H.P.Teixeira, Daguano, J. K., Strecker, K., & C.N.Elias. (n.d.). Effect
of isothermal sintering time on the properties of the ceramic composite
ZrO₂-Al₂O₃.

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