Effect of Rare Earths on Alumina Ceramics
Russian crude oil shipments to Italian and Turkish ports rose to multi-week highs, suggesting that some southern European countries are quietly returning to the Russian oil market.
Specific figures show that Russian crude oil deliveries to Italian refineries rose to their highest level in seven weeks in the week to August 5, while shipments to Turkey reached the highest level in six weeks.
Separately, Spain received its first Urals this week since April, and Greece last week received its first shipments of crude from the Baltic Sea since February.
There are still four months to go before the EU sanctions on Rosneft come into effect. The recent increase in the flow of goods to several European countries has raised doubts about the implementation of the ban.
In addition to some southern European countries began to import Russian oil, Japan also reiterated that it will retain its stake in Russia's "Sakhalin 1" oil and gas project.
Last week, Russian President Putin signed an order banning personnel from "unfriendly" countries and regions, including Japan, from trading shares in Russian strategic projects, energy mining companies and some banks before the end of this year. It also mentioned the oil and gas project including "Sakhalin 1".
Because of the turbulent international situation, the supply and prices of many international bulk aluminum oxide are still very uncertain.
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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Europe's immediate goal of reducing its dependence on Russian gas in response to the conflict with Ukraine presents a rare opportunity for the United States, the world's largest gas producer. America's LNG exporters have made a fortune this time. Investors are bullish on the future of natural gas, as evidenced by the recent record high share price of Energy company Chenier.
But the outlook for more than a dozen new LNG projects is highly uncertain as construction costs rise, US gas prices soar and climate policymakers seek to move away from a long-term reliance on fossil fuels. Even the most advanced projects can take years to become operational.
Currently, the total U.S. LNG aluminum oxide are expected to continue to rise in the future.