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When the calcination temperature is low, the intermediate might not be decomposed completely. Different size crystals have different surface energies. Crystal size is proportional to its surface energy, so the process of small crystals turning into large crystals happens automatically. The process proceeds very quickly, especially at high temperature.

With prolonged calcination time, the process will be achieved completely. The crystal size grows for long times at high calcination temperatures Shi et al. Thus, large size nanoparticles can be obtained. For the same reason, although the intermediate can be decomposed completely very quickly at high calcination temperature, large size nanoparticles readily form in order to decrease their surface energy.

For nanoparticles obtained by the sonication method, the smallest size was around 6 nm. With the increase of calcination time more than 1. When the calcination time reached 3. Thus, through controlling calcination temperature and calcination time, nano-MgO with different sizes could be obtained. Shi et al. The heating rate of calcination can affect the size of nanoparticles.

When the heating rate of calcination is very fast, aggregation of nano ZnO happens more easily, due to urgent collapse of the intermediate. When the heating rate of calcination is low, nano MgO exists for a long time at high calcination temperatures, which will decrease production efficiency Shi et al. So, an optimized heating rate of calcination must exist.

Accordingly, nanoparticles with different sizes could be obtained by controlling the calcination conditions. The size distribution of nano MgO is presented in Figure 4.

The size of the nanoparticles was around 15 nm. The distribution was narrow. From Fig. MgO nanoparticles could be dispersed well. Very little aggregation could be found. All peaks were consistent with the peaks of standard MgO with high crystallinity.

XRD patterns showed broadening of the peaks, indicative of the ultra fine nature of the crystallite material. The crystal sizes calculated using Scherrer's formula were about 14 nm. No peaks from any other phases of MgO were observed.

The results of liquid N 2 adsorption measurements aid in understanding the formation of nanoparticles. This low surface area is due to the long calcination time. Ultrasound irradiation has been routinely used in the field of materials science. The chemical effect of ultrasound irradiation arises from acoustic cavitation formation, growth and collapse of microbubbles in liquid.

The extremely high temperatures, pressures and cooling rate attained during cavitation lead to unique properties in the irradiated solution Shi et al. These extreme conditions have been exploited to prepare nanoscale metal oxides Huang et al. We also tried in our lab results not shown the thermal decomposition method, but small nanocrystal could only be obtained under a very high stirring rate since mechanical power is used to prepare nanoparticles. For these two methods, the mechanism of preparing the nanoparticles is different and the characteristics of the nanoparticles are also different.

Acoording to this work, the sonication method for the preparation of nanoparticles is more powerful than the thermal decomposition method. The lethal effect of nano-crystalline MgO was evaluated on L.

The results are shown in Table 1. From Table 1 , with the increase of calcination time, the lethal effect of MgO nanoparticles increased after 6 h or 24 h exposure at ppm or ppm. When the sample MgO, sonication, C, was used, the lethal effect on L. Yamamoto et al. Impurities can conceal active sites of nanoparticles.

With increasing calcination time, the antibacterial activity of MgO nanoparticles increased. But, when the calcination time was increased to 10 h, the MgO nanoparticle weight loss from TGA results not shown is similar.

The addition of MgO into the coal of 5 contributed to the pyrolysis of the pulverized coal, therefore, the peak intensity increased. In addition, the peak intensity, which reflected the degree of condensation of the aromatic rings in the coal, also revealed an obvious change. The higher the condensation degree, the stronger is the diffraction intensity. As we know, MgO is basic [ 23 , 24 , 25 ].

Under certain conditions, chemical adsorption between MgO and the acidic carboxyl groups in the coal occurred, which contributed to dehydrogenation and the removal of the carboxyl groups of the coal.

Therefore, the peak intensity of 5 coal was higher than that of the raw coal. Based on the above analysis, it can be concluded that an additive containing MgO in the pulverized coal could increase the combustion of the coal in the tuyeres to near completion.

A mixture of slag and MgO was injected in the tuyeres for testing in the lab. First, two types of slags with different MgO contents were compounded using chemical reagents. During the melting process, they were stirred with a molybdenum rod to form standard slag samples. The MgO contents in different standard slag samples are listed in Table 4. The sampling points are shown in Figure 9. The test results are presented in Table 5. The MgO content and its difference as a function of time are obtained, as shown in Figure It can be clearly seen from Table 5 and Figure 10 that after melting for 10 min, the distribution of MgO in 8 sample, with 2.

In fact, owing to the constantly strong stirring of the air and high temperature in the tuyeres, the mixing speed and uniformity of the MgO injected and the slag are better than those obtained from the test. Therefore, the MgO injected into the furnace is beneficial for the formation of slag in the hearth. The main chemical components of the slags are listed in Table 6. In particular, the viscosity was minimum 0. In addition, as shown in Figure 11 c , with an increase in the content of MgO, the melting temperature rose linearly.

Therefore, MgO injection into the tuyeres could improve the properties of the primary slag. The softening-melting properties are the most important for the burden.

It is noteworthy that the MgO content that the BF needs has been confirmed. If MgO is injected into the furnace with pulverized coal, the MgO content of the burden will decrease. Therefore, testing for different MgO contents of the burden in a high-temperature furnace will reveal the effect of MgO on the softening-melting properties of the burden.

The main components of the burden and coke are listed in Tables 7 and 8 , respectively. The softening-melting properties are presented in Table 9. The relationship between MgO content and S is shown in Figure The change in akermanite content is the biggest distinction in the burden with different MgO contents.

With an increase in the content of MgO, the akermanite content increases, and the temperature range over which akermanite exists is also widened; as a result, the properties of the slag deteriorate, which leads to an increase in the resistance loss [ 27 ]. From Table 9 , it is easy to observe that when the MgO content is 0. However, when the MgO content is 2. The reason for this phenomenon is that the flowability of the slag showed an obvious deterioration with the addition of MgO, as a result, the permeability of the softening-melting zone in the BF became worse, which affected BF operation.

The addition of MgO to pulverized coal was favorable for increasing the R of the coal. MgO showed catalytic activity for dehydrogenation and carboxyl group removal from the coal; as a result, with increasing MgO content, the combustion and pyrolysis ratios of the coal improved, which had a significant effect on increasing the utilization rate of the pulverized coal, decreasing the amount of coke, and improving BF operation.

Consequently, MgO injection into the tuyeres could improve the properties of the primary slag. With increasing amount of MgO added to the burden, the softening-melting properties of the burden worsened. Therefore, the technology of injecting MgO into the tuyeres with pulverized coal was beneficial for BF operation. Matsumura, M.

Hoshi and T. ISIJ Int. Eiki, S. Yorito, K. Takazo, et al. Fan, W. Li, M. Gan, et al. South Univ. Search in Google Scholar. Fan, M. Gan, X. Chen, et al. Iron Steel, 44 6— Wu, H. Han, W. Jiang, et al. Beijing, 31 — Yao, J. Yang, D. Han, et al. Iron Steel, 50 12— Lv, F. Wang and H. Iron Steel, 51 19— Wang and S. Iron Steel Res. Fu, X. Bi, G. Zhou, et al. Iron Steel, 44 24— Okvist and J. Adrian Yes, but Ping is to check connectivity, and asker wants to detect if Session.

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