Water-atomized powder of SUS316L stainless steel was spheroidized by DC arc plasma to obtain a spherical powder with high fluidity and high packing density at low cost. This process successfully spheroidized the raw powder and improved the powder characteristics. In the spheroidized powder, fluidity was enhanced by up to 100% versus raw powder; tapped density was likewise increased by up to 50% versus raw powder. We also formed a nanoparticle-modified spherical powder. Spark plasma sintering using spheroidized powders yielded high densities, including a relative density of 99.6% for the compact produced from nanoparticle-modified powder.

Steelmaking slags have been widely used as aggregate for road and civil engineering. The slags sometimes expand as a result of hydration, which may cause evolution of cracks at surfaces of roads when used as aggregate. Free magnesium oxide (free-MgO) in the slags is a potential cause of the expansion as well as free calcium oxide is. Thus, analytical methods to determine the free-MgO in the slag have been required for the accurate evaluation of the expansion. We present an accurate method to determine the free-MgO in steelmaking slags based on the combination of chemical extraction and thermogravimetry (TG). Free-MgO and magnesium hydroxide (Mg(OH) 2) in steelmaking slags are dissolved into an ethyleneglycol solution containing iodine and ethanol when heated. The amount of the magnesium species dissolved in the solution is determined by inductively coupled plasma atomic emission spectrometry. The amount of Mg(OH) 2 in the slags determined by TG independently is subtracted from that of the dissolved in ethyleneglycol to yield the amount of free-MgO. The established method can quantify less than 0.1 wt% free-MgO in steelmaking slags.

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BackgroundToday, high-strength coke is actively pursued to operate blast furnace with low reducing agent. 1) Caking properties are the important parameters in coal blending techniques to produce high-strength coke. 2) In particular, Gieseler plastometer method standardized by JIS M8801 have long been used for measuring 'fluidity' as caking properties. On the other hand, recently, the amount of high-quality coal with high fluidity has been limited. The tight supply and rising price of high-quality coal with high fluidity is an inevitable problem in Japan, therefore development of technique to utilize slightly and non-caking coals is required. To cope with this problem, caking additive method which improves fluidity of coal has been developed and commercialized. 3-7) It is known that caking additives improve coal fluidity, promote liquid-phase carbonization, increase anisotropic texture in coke. However, mechanism of caking additives for improving coal fluidity is still unclear. It is important to search for more effective chemical substances to clarify the mechanism of caking additives to improve fluidity of coal.In order to clarify effective chemical substances to improve coal fluidity, there are a number of studies on Coal fluidity is an important parameter in coal blending techniques for coke making because it strongly influences coke qualities. On the other hand, recently, the amount of high fluidity coal has been limited. To cope with this problem, caking additive method which improves fluidity of coal has been developed and commercialized. However, since tight supply of high fluidity coal is anticipated in the future, it is of great importance to develop more effective caking additive. Therefore, in this study, we investigated effect of 11 kinds of polyaromatic hydrocarbons which include oxygen, sulfur and nitrogen containing compounds on coal fluidity in order to search for more effective chemical substances. The additives were added to low fluidity coal, and fluidity analyses were carried out according to the Gieseler plastometer method. Addition of sulfur and oxygen containing compounds lowered fluidity of coal, whereas addition of aromatic amines enhanced fluidity of coal. Coal fluidity ameliorated with increasing the molecular weight of aromatic amine, and N,N'-di-2-naphthyl-1,4-phenylenediamine (DNPD) was the most effective aromatic amine in this study. Carbonization tests in an electric furnace were conducted to investigate an effect of DNPD on coke strength. As a result of adding only 1 wt% DNPD, fluidity of blended coal and coke strength (Drum Index) were highly improved. KEY WORDS: cokemaking; coal thermoplasticity; caking additive; aromatic amine; slightly caking coal.the interactions between coal and chemical substances. 8-10) Koyano et al. 9) investigated influences of polycyclic aromatics on coal fluidity. They reported that polycyclic aromatics with higher molecular weight and higher boiling point had superior effect on coal fluidity and coke strength. Tsubouchi et al. 10) investigated the e...

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