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Sintered MgO was prepared by using MgO powder with different particle sizes by calcination of by crystal magnesite as the raw material and CeO2 powder as an additive. In addition, the effect of the CeO2 addition on the performance of the sintered MgO was investigated. The results showed that (i) the densification of the sintered MgO with a small am...
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... ball was an agate ball in alcohol. The ball-topowder mass ratio was 5:1. After ball milling, the mixture of powder and medium was dried at 90 • C. Three types of MgO powders with different particle sizes 11.6, 6.18, and 3.90 m were obtained by ball milling at different times. The particle size characteristic of MgO and CeO 2 powders is shown in Fig. 1. 0-2 wt% of CeO 2 powder was mixed with the three MgO powders with different particle sizes. Compression was carried out using a uniaxial hydraulic press, and the mixture was loaded into the die with 20 mm diameter and compacted under 300 MPa. Then, the green bodies were sintered in air atmosphere at 1600 • C for 2 ...
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Citations
... [10][11][12] Magnesia-based aggregates are mainly prepared with magnesite by electrical fusion 13 or sintering methods. [14][15][16] These magnesia-based aggregates have dense structure, low porosity, and high thermal conductivity, which is not conducive to the insulation of furnace lining. Thus, Yan et al. put forward the lightweight design of using microporous aggregates to replace dense aggregates for fabricating working layer refractories, which can effectively reduce the thermal conductivity of refractories on the basis of ensuring high-temperature service performance. ...
Effects of sintering atmosphere on the microstructure and strength of magnesite were investigated using magnesite powder as raw material through X‐ray diffraction, scanning electron microscopy, mercury porosimetry measurement, and so on. The results showed that the sintering atmosphere strongly affected the sintering behavior of magnesite. The specimens sintered in the reducing atmosphere had more and finer micro‐sized pores inside the MgO particles compared with that in the oxidizing atmosphere at the same sintering temperature. Besides, MgO refractory raw material containing porous MgO microparticles with core–shell structure was obtained through the carbothermal reduction of MgO microparticles and subsequent oxidation of Mg vapor at the surface of MgO particles at 1500°C in the reducing atmosphere. At the reducing atmosphere and 1500°C, the microporous MgO refractory raw material with the core–shell structure of external dense and internal porous had an apparent porosity of 22.1% and a compressive strength of 51.6 MPa.
... Naturally, to obtain a high-quality sintered magnesia product, a thorough understanding of the difficulties in its preparation is required. Due to the unique decomposition characteristics of magnesite, it retains its original morphology after decomposition, forming so-called pseudomorphic aggregates, which seriously affects the subsequent densification process [13][14][15]. On an engineering level, engineers have minimized the adverse effects of aggregates by using two-(calcination → ball milling → sintering) and three-step (calcination → hydration → ball milling → re-calcination → re-ball milling → sintering) sintering methods [16]. ...
... On an engineering level, engineers have minimized the adverse effects of aggregates by using two-(calcination → ball milling → sintering) and three-step (calcination → hydration → ball milling → re-calcination → re-ball milling → sintering) sintering methods [16]. On a technical level, researchers have identified and reported many effective sintering aids, such as CeO 2 [13], La 2 O 3 [12], TiO 2 [17], Y 2 O 3 [18], and ZrO 2 [19]. However, most of the sintering aids become new impurities in the magnesia, as well as being potentially harmful to its high temperature properties. ...
Giving magnesia a denser microstructure is a goal relentlessly pursued by refractory scientists and related entrepreneurs. In this study, the effects of the key factors of ball milling, calcination temperature, and starting raw material (high-purity magnesite) size on the densification and grain growth behaviour of sintered magnesia were systematically investigated using a typical two-step sintering method. The results revealed that ball milling reduces the size of light-burned magnesia (pre-calcination product) to a certain extent, which is reflected in a higher tap density; moreover, both the density and grain size of the magnesia samples rise with increasing calcination temperature, implying that the activity of light-burned magnesia is not the only controlling factor for densification; in addition, the smaller magnesite particle size improves the density and grain size of the magnesia samples by weakening the negative effect of the pseudomorphic aggregates. More adequate ball milling, more moderate calcination temperature, and smaller size of magnesite (also for other magnesium salts), therefore, can be the preferred process for the two-step sintering preparation of sintered magnesia.
... In order to further improve the performance of sintered magnesia, many strategies have been proposed and reported. ZrSiO 4 [8], SiO 2 [9], Cr 2 O 3 [10], ZrO 2 [11], TiO 2 [12], Al 2 O 3 [13], Fe 2 O 3 [13], and CeO 2 [14] were proved effective for the densification and sintering of magnesia. Generally, this beneficial result is attributed to three reasons: lattice distortion, Zener (pinning) effect, and liquid phase sintering [7,15,16]. ...
The development of advanced refractories with low thermal conductivity and long service life is of great significance for optimizing the energy consumption structure of high-temperature industries. For this purpose, a series of magnesia refractories with large grain size, low thermal conductivity, and high slag resistance had been successfully prepared at 1600 °C, in which Al2O3 and La2O3 were chosen as the additives. The results show that with the introduction of additives, MgAl2O4 and LaAlO3 as the second phase are formed inside and at the grain boundaries of the MgO matrix grains, and further promote the growth of grains and improved certain properties. Meanwhile, the grown grains (from 4.92 to 29.51 μm, increased ∼5 times), the increased density, and the enhanced strength can be attributed to the activated sintering triggered by Al2O3; the lower thermal conductivity (from 18.49 to 15.73 W·m⁻¹·K⁻¹ at 500 °C, decreased ∼15%) and the better slag resistance can be ascribed to the formation of LaAlO3 and MgAl2O4. However, due to the Nener effect, the maximum grain size is obtained at additives of 4 wt%, but the thermal conductivity is not limited by this.
... China has abundant magnesite resources with a proved reserve of approximately 3.1 billion tons, nearly 90 % of which is distributed in Liaoning province [20]. Nowadays, most of magnesite is used to preparing magnesia-based refractories for iron-and steel-making processes, such as MgO, MgO-C, and MgO-Al 2 O 3 -C bricks [21,22]. However, as a non-renewable resource, the quantity of magnesite is gradually reduced due to unreasonable development and utilization. ...
In this study, magnesite was activated through hydration and balling treatment, and the received MgO with high activity and H3BO3 were used as raw materials for synthesizing Mg2B2O5 whiskers with the aid of KCl salt. Attention was paid to the effects of B/Mg ratio and reaction temperature on the phase transformation and morphology evolution of the produced whiskers, and their growth mechanism was proposed as well. The Mg2B2O5 ceramics were prepared based on the whiskers with different diameters via traditional pressing-sintering. Their physical properties, such as bulk density, apparent porosity and Vickers hardness (Hv), were studied. Particular emphasis was placed on the relationship between microstructure and microwave dielectric properties (ε, Q × f, and τf) of the Mg2B2O5 ceramics. According to the results, the higher B/Mg ratio and the lower reaction temperature were more suitable for the growth of Mg2B2O5 whiskers with high aspect ratio conforming to the liquid-solid (LS) mechanism. In particular, the Mg2B2O5 ceramics based on the whiskers with average diameter (AD) = 198 nm and sintered at 1250 °C exhibited good microwave dielectric properties (ε = 6.18, Q × f = 18,597 GHz, and τf = −82 ppm/°C). This new design principle provides a guidance for fabricating high value-added magnesia-based ceramics from magnesite.
Refractories have an important effect on the cleanliness of molten steel. The interaction between CeAlO3 refractories and Ce treated steel was explored and compared with that between Al2O3 refractories and Ce treated steel. The results show that the Ce content in steel decreases sharply after contact with Al2O3 refractories and the pick-up of dissolved Al occurs. Compared with the test of Al2O3 refractories, the loss of Ce content is less in the test of CeAlO3 refractory, and the total oxygen content and dissolved Al content in steel increase less. The dense and continuous Ce2O2S interface layer is observed at the CeAlO3 refractories/steel interface, which can serve as the metallurgical isolation layer and hinder the further interaction between refractories and steel. Therefore, the higher steel cleanliness and less penetration of refractories by molten steel are obtained in the test of CeAlO3 refractories. The CeAlO3 refractories show a promising prospect in the production of clean Ce treated steel.
