Effect of Rare Earths on Alumina Ceramics

Russia's insistence on paying for Russian gas in rubles has rattled European countries: Greece held an emergency meeting of suppliers, the Dutch government would urge consumers to use less gas, and the French energy regulator told consumers not to panic. Russian gas meets one-third of Europe's annual energy needs.

Russia said they could expand their demand for ruble payments for other commodities, including oil, grain, fertilizer, coal, and metals, which raised the risk of recession in Europe and the US. 

Moscow is expected to unveil its ruble payment plan in early April, but it said it would not immediately ask buyers to pay for gas in rubles.  

Western countries have said paying in rubles would be a breach of contract, and renegotiation could take months or longer. This uncertainty has pushed commodity market prices higher.

The supply and prices of other commodities like the aluminum oxide could also be affected.

Aluminum oxide ceramic has the characteristics of high mechanical strength, high hardness, wear and corrosion resistance, high temperature resistance, light weight, and good insulation. Alumina is widely used in textile, coal, petroleum, chemical, electronics, construction and other industries. It is a low-cost and widely used ceramic material.
 
However, the toughness of pure alumina ceramic is poor, and its strength and wear resistance need to be improved, which limits its application field to be further broadened. The synergistic modification of multi-phase has become the research direction to improve the mechanical properties and wear resistance of alumina ceramics.
Rare earth elements have special electronic structure, and the modified alumina has important applications in catalytic materials, ceramic materials and other industries.
The radius of rare earth cations is much larger than that of aluminum ions, and the difference in ion radius makes them difficult to dissolve, so rare earth elements mainly exist on the grain boundary of alumina, and the rare earth oxides with glass network structure are large and difficult to move, which hinders the migration of other ions, reduces the migration rate of grain boundaries, restrains the abnormal growth of grains and makes the structure compact. Rare earth oxides doped with grain boundary glass phase can improve the strength of glass phase and enhance the mechanical properties of ceramics. The more rare earth oxides are added, the more obvious the effect of reducing the sintering temperature is, but the excessive addition will make the mechanical properties of ceramics worse.
 
Effect of rare Earth elements on Microstructure of Alumina Ceramics
After doping nanometer lanthanum oxide, nanometer yttrium oxide and nanometer cerium oxide, the grain size of ceramics will decrease, indicating that rare earth oxides can refine the grains. However, with the increase of rare earth oxide content, the ceramic grain size increases gradually, at the same time, the liquid phase content also increases gradually. This phenomenon may be explained as follows: because the ion radius of rare earth ions is much larger than that of aluminum ions, rare earth ions hardly dissolve in alumina and mainly exist in the glass phase of grain boundary. At the same time, rare earth oxides with glass network structure hinder the migration of ions, inhibit grain growth and refine grains, but excessive addition of rare earth oxides will increase liquid phase volume, reduce liquid phase viscosity, promote ion migration and make grains grow excessively. The grain size becomes larger.
 
Effect of rare Earth elements on hardness of Alumina Ceramics
The hardness of alumina ceramics doped with rare earth oxides such as nanometer lanthanum oxide and nanometer yttrium oxide increases at first and then decreases with the increase of content. The possible reason for this phenomenon is that the addition of appropriate amount of rare earth oxides can refine the grains, increase the amount of liquid phase, fill the grain gaps, increase the density and hardness, but with the excessive addition of rare earth oxides, the negative effects of grain size and interstitial increase on density and hardness can not be offset, showing that the hardness decreases gradually.
 
Effect of rare Earth elements on friction and Wear Properties of Alumina Ceramics
It is found that the worn surface of alumina ceramic goes through four processes: the fracture and pull-out of grains, the formation of friction layer, the increase of friction layer area and crack. The grains shedding off alumina ceramic during wear will remain on the friction interface. A smooth friction layer is formed under the action of surface stress. The friction layer is composed of two kinds of wear debris, which can reduce the wear rate of ceramics. The wear mechanism of alumina ceramics is mainly abrasive wear, and an appropriate amount of rare earth oxide doping can improve the wear resistance of alumina ceramics.
 
Effect on relative density of alumina ceramics
It is found that the relative density of alumina ceramics doped with Y2O3 and CeO2 increases at first and then decreases with the difference of doping amount. At the same time, it is found that the relative density of alumina ceramics with Y2O3 is lower than that of alumina doped with CeO2 and La2O3. It may be because:
The radius of rare earth ions is large, so it is difficult to form solid solution with alumina, which mainly exists in liquid phase, which reduces the viscosity of liquid phase. At the same time, rare earth oxides can promote the chemical reaction of alumina with other additive components and increase the amount of liquid phase. The addition of a small amount of rare earth oxides is beneficial to the formation of liquid phase, accelerate the elimination of pores and improve the density of ceramics.
In addition, the addition of rare earth oxides with high melting point increases the sintering temperature of ceramics, while rare earth ions have a larger ion radius, which hinders the migration of other ions. Excessive addition of rare earth oxides is not conducive to ceramic sintering and reduces the degree of densification.
 
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The Japanese minister of Economy, Trade, and Industry recently held talks with the U.S. Secretary of Commerce and industry in Washington, where he is visiting, and agreed to include basic principles on joint research and development of semiconductors and strengthening of supply chains.  Japan's economy, Trade and Industry Minister has asked the United States to increase the aluminum oxide will continue to increase in the future.

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