Many industries increasingly require materials that possess high specific strength and low density. To this end, various advanced materials have been explored and developed by researchers in recent years, with magnesium/eggshell composites proving particularly attractive.
A study published in the journal Materials Chemistry and Physics has investigated the influence of eggshells on low-density composite Mg materials during production.
Study: The influence of low-cost eggshell on the wear and electrochemical corrosion behaviour of novel pure Mg matrix composites. Image Credit: Ausra Barysiene/Shutterstock.com
The Need for Low-Density Materials
Human activity is producing increasing levels of carbon emissions and environmental pollution. For this reason, the need for low-density materials in the industry has gained prominence in recent years for their energy and resource-saving advantages.
The automotive and aerospace industries make significant use of magnesium alloys due to the material’s high specific strength and superior damping capacity. Whilst these properties make magnesium alloys useful for a variety of industrial applications, they are limited by other factors such as low wear resistance and mechanical strength. To this end, magnesium alloys are reinforced with elements such as SiC, TiC, and Al2O3.
Reinforcement elements improve the composite Mg alloy’s wear and mechanical properties, but there is still a challenge with their use. Currently used reinforcement elements significantly increase the cost of products that use these composite alloys. For this reason, attention has shifted to low-cost, sustainable waste material alternatives.
Exploring Low-Cost, Sustainable Waste Materials for Mg Alloy Composite Reinforcement
Some waste-derived alternatives that have been investigated as composite components include fly ash, CRT glass, fly ash cenosphere, red mud, and eggshell. There have been numerous studies in recent years on waste-derived composite Mg alloys that show some interesting results.
A study authored by Nguyenm et al. presented the fabrication of magnesium/fly ash cenosphere composites of differing fly ash cenosphere content. The composite material demonstrated improved compressive yield strength and micro-hardness. The team used a disintegrated melt deposition technique to manufacture the composite. CRT glass composite Mg alloys manufactured by Gopal et al. via powder metallurgy methods improved the magnesium matrix’s wear resistance and hardness.
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In 2020, Anandajothi et al. fabricated composite materials reported an Az91 (the most popular commercial-grade magnesium alloy) hybrid material using hydroxyapatite obtained from eggshell waste and SiO3 obtained from rice husk ash. The hybrid composite Mg alloy was manufactured with powder metallurgy.
Eggshell Waste as a Composite Material
Amongst waste-derived composite materials, eggshell is one of the most attractive targets. This waste material has a low density, contains elevated levels of Ca2O3, is readily available, sustainable, and cheap. Currently, there is limited literature on its use as an Mg alloy composite material.
Amongst the literature, it has been reported that eggshell additives increase the mechanical properties, damping properties, thermal stability, and microhardness of Mg alloys. Studies have also demonstrated enhanced corrosion performance of eggshell composites over Mg/Zn composites.
However, there is a lack of information on how eggshell composites affect the pure magnesium corrosion and wear properties. For this reason, there needs to be increased focus on pure Mg/eggshell composites.
Investigating Pure Mg/Eggshell Composites
The aim of the research paper in Materials Chemistry and Physics is to investigate pure magnesium/eggshell composite materials and their enhanced properties. Powder metallurgy techniques were used to manufacture the materials. The composite material’s electrochemical corrosion behavior, density, microstructure, wear, and hardness were investigated thoroughly. The surfaces of the materials were examined using scanning electron microscopy.
Results of the study demonstrated that eggshell composites significantly improved the mechanical properties of pure magnesium alloys. Different samples were prepared, with the Mg/10ES composite’s resistance to wear being the best out of all samples.
The pure magnesium’s wear rate decreased from 0.034 mm3/m to 0.014 mm3/m. Additionally, at high loads, the wear mechanism was delamination, compared to low loads where abrasion was the wear mechanism.
However, due to micro-galvanic corrosion, the corrosion performance of the pure magnesium was negatively affected when eggshell particles were added to them. It was observed in the study that one reason corrosion performance was impaired was the presence of Cl- ions that infiltrated through cracks in the corrosive layer, accelerating the process.
The results of the research provide a deeper understanding of the manufacturability of low-cost Mg/eggshell composites. The eggshell component reinforces the pure magnesium in the material, and the enhanced wear resistance properties of the material facilitate its potential for use in applications where this is desirable.
Eggshell waste is a readily available, low-cost, and sustainable material that imbues magnesium alloys with superior properties such as enhanced wear resistance. By providing significant knowledge and understanding of pure magnesium/eggshell reinforced composites, the authors behind the study have paved the way for future research in this field.
Demirdal, S & Aydin, F (2021) The influence of low-cost eggshell on the wear and electrochemical corrosion behaviour of novel pure Mg matrix composites [online] Materials Chemistry and Physis 277 | sciencedirect.com. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0254058421013031