Messi Biology said, in the preparation and production of advanced ceramics, magnesium oxide is a common additive, what is its role? In the sintering process, what changes it will bring to the ceramics? Here we understand through several cases.
The effect of magnesium oxide on alumina ceramics
1, magnesium oxide on alumina ceramic sintering temperature and densification of the impact
First of all, magnesium oxide as a common sintering aid, is able to effectively reduce the sintering temperature of alumina ceramics. With high-purity a-Al2O3 powder as raw material and magnesium oxide as sintering aid, alumina ceramics were prepared by discharge plasma sintering technology (SPS), and the effects of magnesium oxide addition and sintering temperature on the densification process and microstructure of alumina ceramics were studied, and the diffusion and evolution of pores during the sintering process were analyzed. The results showed that the addition of appropriate amount of MgO can reduce the sintering temperature, inhibit the grain growth and improve the densification of alumina ceramics, and 0.25% (mass fraction) is the best addition amount of MgO.
2, magnesium oxide on alumina ceramics mechanical properties and grain growth of the impact
Using alumina powder as raw material, magnesium oxide as additives, two-step sintering process to prepare alumina ceramics, and analyze the changes in additives on alumina ceramics density, mechanical properties and microstructure of the influence of the law.
It was found that the relative density, flexural strength and hardness of the sintered alumina ceramics showed a tendency to increase and then slightly decrease with the increase of magnesium oxide addition. When the content of magnesium oxide is lower than the solid solution limit, magnesium accelerates the diffusion of grain boundaries and has a certain refining effect on the grains, and the density and mechanical properties are better; when the content of magnesium oxide exceeds the solid solution limit, although the refining effect on the grains is enhanced, but the formation of magnesium-aluminum spinel at the grain boundaries will prevent the pore discharge.
In terms of grain growth, with the increase of MgO addition, the grain size and homogeneity of the samples showed a trend of rising first and then slightly decreasing. When the content of magnesium oxide is 0.25%, the average grain size is the smallest and the grain distribution is more concentrated, the best performance; when the content of magnesium oxide is 0.5%, the grain is finer and the grain distribution is more uniform, the largest grain size is only 2.2μm, but the denseness is the worst.
3, magnesium oxide on alumina transparent ceramic optical properties of the impact
Magnesium oxide on alumina transparent ceramic mechanical properties and densification of the influence of the law similar to ordinary alumina ceramics, the appropriate amount of magnesium oxide added to its mechanical properties, densification, inhibit grain growth has a positive effect.
As for the optical properties of transparent alumina ceramics, when the doping amount of magnesium oxide is low, the optical transmittance of transparent ceramics is higher, which is due to the appropriate amount of magnesium oxide can inhibit the rapid movement of grain boundaries, which makes the pore discharge more complete, the ceramics more dense, and the transmittance is higher.
But with the increase of doping amount, the magnesium oxide content exceeds the solid solution degree in Al2O3, the second phase will be formed locally, forming the light scattering center, resulting in the decrease of transparent ceramics transmittance.
Effect of MgO doping on ZnO linear ceramics
Zinc oxide linear ceramic resistors in industrial manufacturing have the advantages of large resistivity variation range, high flux density, low nonlinear coefficient, and small resistance temperature coefficient, and are widely used in power-electronics, transportation, communication, and household appliances. However, traditional ZnO composite ceramics still have many problems, such as poor structural uniformity, low industrial production repeatability, poor stability, and inadequate theoretical studies.
The effects of magnesium oxide doping on the nonlinear coefficient, resistivity and temperature resistance coefficient of ZnO linear ceramics were investigated. The results show that the addition of magnesium oxide can help improve the temperature resistance coefficient of ZnO ceramic resistance, and the right amount of magnesium oxide can promote the sintering and improve the densities of ceramics, but the excessive addition will make the densities of ceramics decrease.
The ZnO linear ceramic resistors with the base formulation of ZnO-Al2O3-MgO-Fe2O3-TiO2-SiO2 were prepared by the solid-phase sintering method. The effects of MgO doping on the microstructure, impedance, resistance-temperature characteristics and resistance-frequency characteristics of ZnO linear ceramic resistors were investigated. It was also concluded that the appropriate amount of MgO doping in ZnO linear ceramic resistors can effectively improve the resistivity and temperature resistance coefficient of the samples.
Effect of magnesium oxide on ferroelectric ceramics
1, the effect of magnesium oxide on the structure and properties of barium strontium titanate ceramics
Strontium barium titanate (BST) ferroelectric ceramic material with its high tunability and low dielectric loss in as phase shifter in phased arrays and microwave frequencies under the tunable devices have very good application prospects.
As the current variety of ferroelectric materials are deficient in certain aspects, improving their comprehensive performance by various means has become a key issue that must be solved for the large-scale application of barium strontium titanate materials.
In addition to A-site doping substitution with rare earth element ions, compounds such as Mgo, MgTiO3, and Mg2SiO4 can also be added to BST ceramics and films to reduce their dielectric constants and dielectric losses.
2, the effect of magnesium oxide on the performance of BaTiO3-based ceramics
Using uniform precipitation method to uniformly coat magnesium oxide on the surface of BaTiO3-based ceramic powder, the BaTiO3-based ceramic composite particles coated with magnesium oxide are prepared, and the effects of different coating amounts on the microstructure, microscopic morphology, dielectric properties, insulation properties and breakdown voltage of BaTiO3-based ceramics are studied.
The experiments show that the cladding agent MgO can effectively inhibit the grain growth to obtain a homogeneous ceramic, and this fine grain effect is due to the inhibiting effect of MgO in the grain boundary area; MgO can help to form a \”shell and core\” structure grain, reduce and broaden the ε-peak of BaTiO3-based ceramics, and increase the resistivity and breakdown voltage strength.
Effect of magnesium oxide on the sintering performance of YAG transparent ceramics
YAG transparent ceramics have high melting point (1950℃), high strength, high thermal conductivity, and stable physical and chemical properties, which show excellent application prospects as functional materials or structural materials.
YAG transparent ceramics were prepared by vacuum solid-phase reaction sintering technology, and the effect of the addition of magnesium oxide as a sintering aid on the microstructure and optical transmittance of YAG transparent ceramics was investigated in depth. It was found that the high quality YAG transparent ceramics could be prepared by using trace amount of magnesium oxide as a sintering additive and the vacuum solid-phase reaction sintering process.
Magnesium oxide as a sintering aid is beneficial to control the diffusion of grain boundaries, grain growth and the exclusion of pores. However, with the increase of magnesium oxide content, too much addition will form a second phase in the ceramic, or cause the ceramic sintering shrinkage too fast to form pores and can not exclude the grains, thus greatly reducing the transmission rate of YAG ceramics.
The effect of magnesium oxide on the mechanical properties of Sialon ceramics
Sialon is a Si3N4-based solid solution. In the synthesis of Sialon, due to the low diffusion coefficient of Si3N4, decomposition reactions generally occur when the sintering temperature of Sialon ceramics is reached (>1800°C), so low-temperature sintering is the development direction for the preparation of Sialon ceramics.
It is found that MgO increases the density of β-sialon ceramics and decreases the sintering temperature, and the flexural strength and fracture toughness of β-sialon ceramics increase and then decrease with the increase of sintering temperature, and when the sintering temperature is 1600°C, the prepared β-sialon ceramics are tightly bonded and the flexural strength and fracture toughness reach the maximum.
The above is a brief introduction of the influence of magnesium oxide in several ceramics\’ mechanical properties, microstructure and other aspects of Hebei Messi Biology Co., Ltd. It can be seen that magnesium oxide plays an important role as an additive in the production of advanced ceramics.