Elsevier

Materials Characterization

Volume 62, Issue 9, September 2011, Pages 912-916
Materials Characterization

Effect of binders on microstructural and mechanical properties of sintered alumina

https://doi.org/10.1016/j.matchar.2011.06.011Get rights and content

Abstract

This study examines the effects of organic binder content, plasticity and sintering temperature on the microstructural and mechanical properties of sintered samples prepared from alumina spray-dried powders.

Measurements of mechanical strength of sintered samples prepared from spray-dried alumina powders containing the two binders polyvinyl alcohol (PVA) or polyethylene glycol (PEG) are reported. This analysis revealed that the introduction of an optimal amount of binder in the composition of spray dried powders enhances the relative density and the mechanical strength of sintered samples prepared from these powders. The variation of mechanical strength of these samples with sintering temperature is compared to those prepared from alumina with no additive and discussed. For powders containing PVA as a binder, the samples' properties are better when the amount of PVA is lower. It was also observed a good deformability of alumina granules spray dried with the PEG binder which leads to get more homogeneous microstructure and therefore a good sintering and densification of samples.

Highlights

► Binder and sintering temperature affect the microstructural and mechanical properties of alumina. ► Binder enhances the relative density and the mechanical strength of sintered samples. ► The properties of samples containing PVA are better when the amount of PVA is lower. ► We note a good sintering and densification of samples prepared with PEG binder.

Introduction

Binders are typically long chain polymers that serve the primary function of providing strength to the green ceramic body forming bridges between the particles. In some forming methods, they also provide plasticity to the feed material and aid the forming process. A large number of organic substances can be used as binders, some of which are soluble in water, while others are soluble in organic liquids. They include the vinyls, acrylics, and the ethylene oxides (glycols) [1].

Dry pressing involves the uniaxial compaction of spray dried granules consisting of ceramic particles bound by an organic binder [2]. The spherical granules with a typical diameter of 100–200 μm, obtained by spray-drying, confer a good flowability necessary to achieve reproducible (i) filling of the mold, (ii) compaction behavior during pressing, and (iii) microstructure of the pressed green body. A hydrosoluble organic polymeric binder is generally added to ceramic suspension before spray drying in order to improve the strength of the granules and the green products during (ejection from die) and after (handling and machining) the forming step [3], [4], [5].

It was concluded that the addition of organic binder in spray-dried ceramic powder increases the mechanical strength of spray dried powder and pressed body [6].

The effects of binder content and binder plasticity on the compaction of PVA/PEG containing spray dried ceramic powder have been established. Although a lot of work has been published in literature concerning the influence of binders on the densification behavior of powder during compaction [7], [8], [9], [10], [11], very limited knowledge is available on the effect of binders on microstructural and mechanical properties of sintered bodies.

The aim of the present work was to investigate the effects of binders PVA/PEG on microstructural and mechanical properties of sintered alumina using the combination of “Brazilian test” and scanning electron microscopy (SEM).

In this research, we report also how the amount of binder and sintering temperature affect fracture behavior and physical properties.

Section snippets

Starting Materials and Preparation of Samples

The ceramic powder used in this study is an α-alumina (P152SB, Péchiney, France). The surface area and the mean particle size were respectively 3 m2 g−1 and 1.25 μm. The amounts of binder added are 3 wt% for PEG and 1 or 3 wt% for PVA (dry weight basis of alumina). Three batch compositions (Table 1) were tested using binder 1 wt % PVA, 3 wt% PVA, and 3 wt% PEG. De-ionized water was used as the solvent and ammonium polymethacrylate (Darvan C) was added as dispersant [6].

According to literature data,

Effect of Binder on Alumina Sintering

The effect of sintering temperatures on alumina pellet strength was investigated by discussing three factors: tensile strength, shrinkage and porosity, which changed with sintering temperatures.

The strength of compacts prepared from PEG 3 and PVA 3 powders is plotted versus sintering temperature and nature of binder in Fig. 1, where the data are also compared to the strength of compacts prepared from the original alumina powder, without organic additive.

According to these results, the

Conclusions

While the effect of organic binders on the compaction behavior of spray-dried powders and mechanical properties of pressed specimens has been well documented in literature, the present work indicates that the polymers also exert a deep influence on the physical and mechanical properties of sintered specimens.

Our work consists mainly in studying the influence of an organic additive (binder) on the ceramic product. The mechanical strength and microstructure of sintered products from alumina

References (14)

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