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Production of M-type strontium hexaferrite magnetic powder with the high-pure magnetite concentrate via the ceramic process Production of M-type strontium hexaferrite magnetic powder with the high-pure magnetite...
Zhou, Yujuan; Jiang, Tao; Xu, Bin; Lin, Yuming; Zhang, Min; Liu, Lanming; Zhong, Shouguo; Wei, Chengzhi; Chen, Yufeng; Yang, Yongbin; Li, Qian
2022-04-03 00:00:00
JOURNAL OF ASIAN CERAMIC SOCIETIES 2022, VOL. 10, NO. 2, 292–305 https://doi.org/10.1080/21870764.2022.2077280 LETTER Production of M-type strontium hexaferrite magnetic powder with the high-pure magnetite concentrate via the ceramic process a a a b b b a a Yujuan Zhou , Tao Jiang , Bin Xu , Yuming Lin , Min Zhang , Lanming Liu , Shouguo Zhong , Chengzhi Wei , a a a Yufeng Chen , Yongbin Yang and Qian Li a b School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan, China; Chuanwei Group Mining Corporation, Chengdu, Sichuan, China ABSTRACT ARTICLE HISTORY Received 11 April 2022 The high-pure magnetite concentrate (HPMC) was studied for a substitution of iron scale to Accepted 10 May 2022 produce the magnetic powder of strontium hexaferrite via the conventional ceramic process in this work. The magnetic powder obtained under the optimum conditions had a magneto KEYWORDS plumbite structure, which was confirmed by X-ray diffraction (XRD). Scanning electron micro- Permanent ferrite; magnetic scope (SEM) depicted that ferrite grains were hexagon shaped and evenly distributed with an powder; the high-pure average particle size of about 1 μm. Furthermore, a comparison of magnetic powders sepa- magnetite concentrate; rately produced with HPMC and iron scale was made by detecting the magnetic properties of conventional ceramic method; M-type strontium their sintered magnets using a permanent magnetic measuring system. The results demon- hexaferrite strated that the HPMC magnetic powder had a superiority over iron scale magnetic powder, and it had fully achieved the level of Y30-1 product in China. In the final part, the economic feasibility of using HPMC for magnetic powder production was verified by the cost–benefit analysis. 1. Introduction most permanent ferrites are produced by the conven- tional ceramic process in industry due to its easy The strontium permanent ferrite SrFe O (SFO) as 12 9 operation, low cost, and large production capacity. a kind of fundamental material is widely applied in The raw iron oxide materials of permanent ferrites automobile and household appliances due to its high mainly include iron oxide red and iron scale. The for- curie temperature, large magnetocrystalline aniso- mer is generally applied to mid-grade and high-grade tropy, cost-effectiveness, and chemical stability [1–3]. ferrite products, while the latter is used for the low- The high-performance permanent magnet is made grade ferrite production due to its detrimental alloying from alloys of rare earth metals, especially neodymium elements such as manganese. The production of iron [4,5]. However, due to the increasing scarcity of rare oxide red is limited now due to the stricter environ- earth metals, their prices have been rising exponen- mental laws, and hence the price of iron oxide red is tially. The ferrite magnet took the lead over alloy mag- pretty high due to the short supply [18,19]. Iron scale, nets since the 1970s because the former was much a kind of byproduct from steel rolling, could be used as cheaper and easier to produce than the latter in a cooling agent for converter steelmaking or the oxi- industry. dizing agent for electric furnace steelmaking, and The permanent ferrite or, namely, hard ferrite is meanwhile the iron element of iron scale is recovered generally classified into the bonded magnet and the by entering into molten steel. As a result, the supply of sintered magnet. The sintered magnet with a high iron scale from iron and steel plants has been reducing coercivity (Hc) is suitable for certain special applica- in recent years because of the internal consumption, tions such as permanent magnet synchronous motor, especially the high-quality iron scale (TFe >73%) for which requires a good ability to resist demagnetiza- producing permanent ferrite. tion. In view of the increasing demands globally for The high-pure magnetite concentrate (HPMC) can motors in electric-powered cars and generators in be obtained from the magnetite concentrate, a kind of wind turbines, permanent ferrite will become more bulk commodity as raw material for ironmaking, by attractive. There are various kinds of methods for pre- simple magnetic separation having the advantages of paring permanent ferrites: sol-gel [6–10], hydrothermal no pollution and less energy consumption [20]. Thus, synthesis [11,12], co-precipitation [13], molten salt [14] the production of HPMC is cheap and environmentally and conventional ceramic method [15–17]. Generally, friendly. Besides, China is rich in high-class magnetite CONTACT Bin Xu xubincsu@csu.edu.cn School of Minerals Processing and Bioengineering, Central South University, Changsha, Hunan, 410083, China © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of The Korean Ceramic Society and The Ceramic Society of Japan. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. JOURNAL OF ASIAN CERAMIC SOCIETIES 293 resources in Anhui, Sichuan province, etc., and HPMC chemical compositions of HPMC and its contents of can be steadily produced in quantity, which is bene- total iron, silicon dioxide, and aluminum sesquioxide ficial for its use in permanent ferrite industry. are 71.46%, 0.35%, and 0.23%, respectively. The iron Conventional raw materials of red iron oxide and content of ideal magnetite is 72.36% according to the iron scale are faced with problems like short supply chemical formula of Fe O , and the purity of HPMC in 3 4 and high cost, and hence the replacement of these raw this study is calculated to be 98.8% based on the iron materials with HPMC may be a good choice for perma- content. The XRD characterizes that the primary nent ferrite production. A minority of researchers have mineral in HPMC is magnetite as shown in Figure 1 reported that HPMC could be used for low grade per- (b). Reagents like SrCO , SiO , H BO , CaCO and Al O 3 2 3 3 3 2 3 manent ferrite production [21]. However, those works used here are all analytical grade. have not been systematically and deeply implemen- ted. In this paper, a systematic work for preparing 2.2. Experimental setup and procedure magnetic powder with HPMC was carried out. The effects of the average particle size of the ground The permanent ferrite in this study was obtained via HPMC, the molar ratio of Fe O /SrO on the composi- 2 3 a conventional ceramic process as shown in Figure 2. In tion and the pre-oxidation process on the performance the first stage, HPMC was wet-ground and thoroughly of magnetic powders were studied. The influences of dried at the beginning. The HPMC and strontium car- calcination temperature and dwell time on micromor- bonate were weighed according to the stoichiometric phology and grain size of the magnetic powder were formula SrO·nFe O , where n was the molar ratio of Fe 2 3 2 investigated. In addition, the ferrite magnets sepa- O to SrO and approximately equal to 6.0. The mixture rately prepared by HPMC and iron scrap were com- of starting powder was charged into the planetary pared in terms of comprehensive magnetic grinding mill with an angular velocity of 100 rpm, performances. In the final part, a preliminary analysis and the mass ratio of ball to powder to water was of the cost and benefit of this preparation process was 14:1:1.5. The ground mixture was dried in the oven at made. The results of this study are valuable for the 110°C for 24 h, and then was shaped into cylindrical substitution of iron scale with HPMC to produce low- briquettes (diameter 8 mm and height 10 mm) under grade ferrite magnetic powder, which is widely used a pressure of 2000 N. The compacted briquettes were among small household applications. The replacement pre-oxidated and calcinated in the muffle furnace for of red iron oxide by HPMC to produce mid-grade or a certain time, which was equipped with an air pump even high-grade ferrite magnetic powders will be to increase oxygen supply, and then were cooled in the introduced in our following study. furnace under air atmosphere. After crushing, the mag- netic powder of strontium hexaferrite was obtained. In the second stage, the magnetic powder was sifted 2. Experimental through a 120-mesh screen, and then was wet-milled together with sintering aids, such as CaCO , SiO , Al 3 2 2 2.1. Materials and reagents O , H BO , and so on in the planetary grinding mill 3 3 3 The ash black HPMC powder (Figure 1(a)) used in the with an angular velocity of 300 rpm for 110 min. The study is from Chuanwei Group Mining Co., Ltd in mass ratio of ball to powder to water was 14:1:2. The Sichuan province, China. Table 1 illustrates the main fine-ground slurry with an average particle size of (a) (b) Figure 1. The appearance and XRD pattern of HPMC. 294 Y. ZHOU ET AL. Table 1. Quantitative chemical compositions of HPMC. Quebec, Canada). The magnetic properties of the mag- composition TFe SiO Al O CaO MgO S P netic powder were measured at room temperature 2 2 3 content/ (wt. %) 71.46 0.35 0.23 0.07 0.03 0.03 0.02 using a vibrating sample magnetometer (MPMS XL-7, USA) with a maximum field of 20 kOe. The permanent magnetic measuring system (NIM-2000HF, China) was about 0.8 μm was drained and then pressed into disk- used to test the magnetic properties of sintered ferrite shaped compacts (diameter 30 mm and thickness magnet. 15 mm). The compacting was under 100 MPa pressure and 8000Gs induced magnetic field, and the magnetic field direction was parallel to the pressure direction. 3. Results and discussion The green compact was sintered in the muffle furnace 3.1. Effect of average particle size of HPMC and then cooled in furnace under air atmosphere. After polishing and testing, the ferrite magnet was even- The average particle size of HPMC has a vital effect tually obtained. both on the mixing effect and thermal reaction rate of solid-state powders [22]. In general, the fine particle size of HPMC is beneficial for solid-state reactions. 2.3. Analysis and characterization Therefore, HPMC needs to be finely ground first, The particle size of the sample was detected by Fisher whose original average particle size is as coarse as sub-sieve sizer (WLP-216, China). The density of ferrite 9.2 μm. HPMC was charged into a planet grinding magnet was tested by an electronic densimeter (DPO- mill with a ball-material-water mass ratio of 14:1:1.5 6000, USA). Quantitative chemical assay of the main and an angular velocity of 150 rpm. The average par- elements in HPMC was performed by acid digestion ticle size of HPMC as a function of grinding time is followed by an inductively coupled plasma-optical shown in Figure 3. emission spectrometer (ICP-OES, PS-6, Baird). The average particle size of the ground HPMC Mineralogical composition of the sample was identi- sharply decreased as time prolongs within 1 h. fied by an X-ray diffractometer (XRD, D/Max 2500, After that, the decrease in average particle size Rigaku) with a scanning angle from 5° to 80°. The became slow. The average particle sizes of HPMC thermal characteristics of HPMC were obtained from were 1.9 μm and 1.0 μm after milling for 1 h and the TG curve using a thermogravimetric analyzer (TGA- 4 h, respectively. The fitting curve was nearly hor- 5500, British) at a heating increment of 10 K/min in air. izontal after 4 h, which denoted that HPMC was Microcosmic morphology of the magnetic powder was hard to be levigated when its average particle size observed by scanning electron microscope (SEM, approached 1 μm. This was likely because the MIA3, TESCAN), following an ImageJ application to magnetic agglomeration among particles was analyze and collect grain size of digital photographs. intensified when the particle size of HPMC turned The phase diagram calculations were performed using too small, causing the decrease in grinding the software FactSage 7.3 (Thermfact/CRCT, Montreal, efficiency. Figure 2. The flowchart of preparing ferrite magnet with HPMC by conventional ceramic process. JOURNAL OF ASIAN CERAMIC SOCIETIES 295 powders. In addition, the positions and intensities of the main peaks of (107) and (114) for these samples were nearly identical, which revealed that the average particle size of HPMC had no evident influence on the crystallinity of SFO in the study range [1]. 3.1.2. Magnetic properties The saturation magnetization (Ms), remanent magne- tization (Mr) and intrinsic coercivity (Hcj) of magnetic powder were determined from the obtained hysteresis loops Figure 5(a), and their values are shown in Figure 5(b). The values of Hcj were rapidly increased with the decrease of HPMC particle size before 1.9 μm, while they decreased when the particle size was below 1.9 μm. The values of Ms and Mr slightly increased as the decrease in the average particle size before 1.9 μm, Figure 3. The average particle sizes of HPMC with respect to and after that their values fluctuated. The Mr, Hcj and grinding time. Ms reached their maximum values of 28.38 emu/g, 1162.22 Oe, and 51.78 emu/g at an average particle 3.1.1. Phase identification analysis size of 1.9 μm. The ground HPMC powder inevitably The magnetic powders were prepared by HPMC with included a part of microparticles (<1 μm), and those different average particle sizes of 9.2, 1.9, 1.2, and microparticles reacted fast during the solid-state reac- 1.0 μm. The molar ratio n of Fe O to SrO for starting tions causing overgrowth of SFO grains in magnetic 2 3 materials was 5.9, and slightly excessive strontium car- powder. The value of Hcj was mainly dependent on the bonate was added to compensate for the burning loss grain size and grain size distribution of magnetic pow- of strontium. Starting powder above was roasted at der [23], and as a result, those coarse grains could be 800°C for 1 h to eliminate ferrous iron in HPMC, and responsible for the decrease of Hcj. While Mr and Ms then calcined at 1300°C for 2 h with a heating rate of mainly depended on the intrinsic composition and 7°C/min in an oxidizing atmosphere. homogeneousness of materials, and thus the average The XRD patterns of magnetic powders with differ - particle size of HPMC had no evident influence on ent average particle sizes of HPMC are presented in them. It can be concluded that the optimum average Figure 4. The patterns of those magnetic powders were particle size of HPMC for preparing magnetic powder compared with those of standard SrFe O which was 1.9 μm. 12 19 exhibited hexagonal magneto plumbite crystal struc- ture with space group P63/mmc (JCPDS card, NO. 33– 3.2. Effect of pre-oxidation process 1340). All samples in Figure 4 shows a pure SFO phase and no impurity phase occurred in the magnetic The overall reaction equation for strontium hexaferrite generation is summarized as Eq. (1) [24], and it can be divided into four steps as Eqs. (2–5). The oxidation of Fe O starts at around 200°C as shown in Figure 6. The 3 4 decomposition of SrCO begins at around 840°C. The initial generation of SrFeO is generally over 1000°C, 3-x and the rapid generation of SrFe O happens over 12 19 1200°C [25–28]. Overall reaction: 4Fe O + O + SrCO = SrFe O + CO ↑ (1) 3 4 2 3 12 19 2 Step reactions: 2Fe O + 1/2O = 3Fe O (2) 3 4 2 2 3 SrCO = SrO + CO ↑ (3) 3 2 1/2Fe O + SrO + 1/2(0.5-x) O = SrFeO (4) 2 3 2 3-x Figure 4. The XRD patterns of magnetic powders with various average particle sizes of HPMC. SrFeO + 5.5 Fe O = SrFe O + 1/2(0.5-x) O ↑ (5) 3-x 2 3 12 19 2 296 Y. ZHOU ET AL. (a) (b) Figure 5. Magnetic properties of magnetic powders with different average particle sizes of HPMC. Figure 6. The TG and DTG curves of HPMC ranging from 25 to 1000°C in air atmosphere. As for the oxidation of HPMC, the thermogravimetry HPMC contains around 30 wt.% ferrous oxides, and curve (TG) and the derivation curve (DTG) of HPMC ferrous oxide easily reacts with silicon dioxide and ranging from 25°C to 1000°C in air are given in produces ferrous silicate, which is a kind of nonmag- Figure 6. The mass of HPMC increased with increasing netic substance with a relatively low melting point of temperature in the study range. The first peak of the 1050°C [29]. The binary alloy phase of a FeO-SiO sys- DTG curve occurred at point I (325°C), which indicated tem used to observe the formation of ferrous silicon that the surface of the sample was quickly oxidated (Fe SiO ) is given in Figure 7(a). The red curve indi- 2 4 into ferric oxide. The mass increasing rate decreased cated that the formation temperature of ferrous silicon after point I probably because the thickened ferric was above 800°C according to the Y-coordinate inter- oxide layer impeded oxygen from entering into the section. The blue curve implied that the metal iron inner part of mineral particles causing the decrease in could be formed if the content of silicon dioxide was oxidation reaction rate. When the temperature over 29 wt.%. The ternary phase diagram of the FeO- increased to point II (550°C), the mass of the sample SiO -SrO system at 1000°C is drawn in Figure 7(b) for increased fast again. High temperature speeded up the the simulation of ferrous silicon occurrence during the heat motion of gas molecules and thus helped oxygen early stage of the calcination procedure. It was clear overcome the hindrance of the ferric oxide layer. The that the ferrous silicate could be generated and stably DTG curve began to decline after point III (760°C), existed in a wide area when the ferrous iron occurred. which implied that the oxidation reaction of the sam- The proper amount of ferrous silicate could form ple was close to the endpoint. a glassy phase between grain boundaries, and thus JOURNAL OF ASIAN CERAMIC SOCIETIES 297 Figure 7. The binary alloy phase diagram of FeO-SiO from 25°C to 1800°C and (b) the ternary phase diagram of FeO-SiO -SrO at 2 2 1000°C. the magnetic performance of magnetic powder was unchanged with pre-oxidation time. The content of improved by impeding the excessive growth of grains. ferrous oxide in magnetic powder was reduced rapidly Meanwhile, an overdose of ferrous silicate would at the early stage, from 0.52% at the pre-oxidation time decrease magnetic performance as it was a kind of of 15 min to 0.30% at 30 min in Figure 8(b). The nonmagnetic substance. reduction in ferrous oxide improved Ms and Hcj, The pre-oxidation temperature was set to be 800°C, which contributed to the enhancement of SFO purity which was below the temperature of ferrous silicon and normal grain growth by reducing the production occurrence. The pre-oxidation time of HPMC here was of nonmagnetic substances like Fe SiO , The results 2 4 set from 15 min to 60 min with an increment of 15 min. above indicated that the optimum pre-oxidation time Hysteresis loops of the magnetic powders with differ - was 30 min, at which the content of ferrous oxide left ent pre-oxidation time and their magnetic property in magnetic powder was only 0.3%. results are displayed in Figure 8(a). With the increase in pre-oxidation time, the values of Ms and Hcj both 3.3. Effect of Fe O /SrO molar ratio increased till 30 min and reached their maximum 2 3 values of 55.71 emu/g and 1018.39 Oe, respectively, Strontium hexaferrite with the stoichiometric formula and then their values slightly decreased with time of SrFe O or SrO·6Fe O denotes that the theoretical 12 19 2 3 prolonging. The values of Mr basically remained molar ratio of Fe O to SrO is six. Since both partial 2 3 Figure 8. (a) Magnetic properties of the magnetic powders with different pre-oxidation times and (b) the changes of ferrous iron content. 298 Y. ZHOU ET AL. burn loss of SrO and inevitable introduction of worn card NO. 33–1340), which demonstrated that no iron during the grinding process increase the molar impurity occurred in all samples. All values of c/a in ratio, a properly excessive amount of SrCO should be Table 2 were in the range of 3.91 ~ 3.93. The magneto added at the beginning. Besides, the deficiency of iron, plumbite structure of the magnetic powder could be caused by slightly excessive addition of SrCO , pro- verified if the value of c/a < 3.98 [31], and hence the duces lattice vacancies, which are favorable for ions M-type structure of the samples was determined. immigration [30–33]. As a result, the solid reaction rate is improved. However, overlying addition of SrCO may 3.3.2. Magnetic properties decrease the magnetic properties of the sample The hysteresis loops of magnetic powders with various because extra nonmagnetic substances such as stron- molar ratios are given in Figure 10(a) and the results of tium silicate (Sr SiO ) are produced, as shown in magnetic properties are summarized in Figure 10(b). The 2 4 Figure 7. Therefore, it is of great importance to deter- values of Mr and Ms increased with the increase in molar mine the optimal molar ratio of Fe O to SrO, which is ratio from 5.7 to 6.0, and reached their maximum values 2 3 implemented under the conditions given as follows: of 29.24 emu/g and 54.07 emu/g at the molar ratio of the average particle size of HPMC 1.9 μm, the pre- 6.0. While the values of Hcj kept increasing before the oxidation temperature 800°C and time 0.5 h, and the molar ratio of 5.9, and then decreased after that. The calcination temperature 1300°C and time 2 h. maximum value of 1138.6 Oe for Hcj was obtained at a molar ratio of 5.9. The values of Mr, Ms, and Hcj increased significantly from the molar ratio of 5.7 to 5.9 3.3.1. Phase identification analysis because the practical molar ratio of Fe O /SrO gradually 2 3 The lattice constants “a” and “c” of magnetic powders approached the theoretical value of 6.0, which meant are listed in Table 2. Here, “a” and “c” were calculated that the proportion of magnetic phase SFO rose in the out from interplanar spacing values d for the main hkl magnetic powders. When the molar ratio was over 5.9, peaks of (107) and (114) based on equation (6), where the values of Mr and Ms increased slowly, while the h, k and l were the Miller indices [34,35]. value of Hcj decreased likely because the generation of � � 1=2 2 2 2 α-Fe O impurity decreased the material homogeneity, 2 3 4 h þ hkþ k l d ¼ � þ (6) hkl 2 2 which was not detected by XRD due to its low content 3 a c [36–39]. The above analyses indicated that the optimum The X-ray diffraction patterns of magnetic powders molar ratio of Fe O /SrO was 5.9 and also confirmed that 2 3 with various molar ratios of Fe O /SrO are depicted in 2 3 slightly excessive SrCO addition was necessary. Figure 9. The diffraction peaks of the samples were compared with that of standard SrFe O (JCPDS 12 19 3.4. Effect of calcination temperature 3.4.1. Phase identification analysis Table 2. Crystal parameters of the magnetic powders with various molar ratios. In this section, the magnetic powder was prepared using Molar ratios a c c/a HPMC with an average particle size of 1.9 μm under the 5.7 5.87921 23.04513 3.9198 conditions of molar ratio of Fe O /SrO 5.9, pre-oxidation 2 3 5.8 5.87873 23.04450 3.9203 temperature 800°C and time 30 min, and calcination 5.9 5.87953 23.03518 3.9179 6.0 5.87601 23.05124 3.9229 time 2 h. The diffraction patterns of samples with differ - ent calcination temperatures, as shown in Figure 11, were compared with that of standard SrFe O (JCPDS 12 19 card, NO. 33–1340). The XRD results of magnetic pow- ders all showed a pure SFO phase. With the increase in the calcination temperature, no impurity phase occurred. In addition, the values of c/a were all <3.98 as indicated in Table 3, and therefore the hexagonal M-type structure of the samples could be identified [31]. 3.4.2. Microcosmic morphology study As shown in Figure 12, the magnetic powder obtained under 1270°C contained a certain number of irregular ferrite grains. When the calcination temperature increased to 1280°C, those grains turned out to be more regular and hexagonal. The micrograph for 1290°C depicted that the hexagonal grains were more evenly aligned. Below the calcination temperature of Figure 9. The XRD patterns of magnetic powders with various 1300°C, the mean size of grains increased to be as coarse molar ratios. JOURNAL OF ASIAN CERAMIC SOCIETIES 299 Figure 10. (a)The hysteresis loops and (b)magnetic properties of the magnetic powders with various molar ratios. grew up (>4 μm), as presented in Figure 13, and thus Mr, Ms, and Hcj all decreased. As a result, the optimum calcination temperature was chosen to be 1290°C. 3.5. Effect of calcination time 3.5.1. Phase identification The magnetic powder samples in this section were prepared using HPMC with an average particle size of 1.9 μm under the conditions of molar ratio of Fe O 2 3 /SrO 5.9, pre-oxidation temperature 800°C and time 30 min, and calcination temperature 1290°C. It was clear that magnetic powder samples with various cal- cination durations presented a single magneto plum- Figure 11. The XRD patterns of magnetic powders with var- bite structure by comparing their XRD patterns with ious calcination temperatures. that of standard hexagonal ferrite (JCPDS card, NO. 33– 1340) in Figure 14. With the increase in calcination time, no impurity phase occurred in these samples. In Table 3. Crystal parameters of magnetic powders with various calcination temperatures. addition, the values of c/a were all <3.98 in Table 4, and Temperature/°C a c c/a hence the M-type structure of the samples could be 1270 5.87839 23.04899 3.92097 confirmed [31]. 1280 5.87680 23.04303 3.92102 1290 5.87819 23.03514 3.91875 1300 5.87738 23.04840 3.92154 3.5.2. Microcosmic morphology study As shown in Figure 15, the magnetic powder calci- nated for 1.5 h contained quite a few small and irre- as 1.27 μm due to the overgrowth of some grains, whose gular ferrite grains (<0.5 μm). The micrograph for 2 h grain size was over 4 μm as indicated in the statistical depicted that ferrite grains turned out to be more histogram. angular, and that grains were evenly distributed with a mean grain size of 1.03 μm. When the calcination 3.4.3. Magnetic properties time prolonged to 2.5 h and 3.0 h, grains grew further The hysteresis loops of samples with various calcination and some coarse grains (around 3 μm) appeared at temperatures are given in Figure 13(a), and the results 3.0 h due to their overgrowth. of magnetic properties are presented in Figure 13(b). The values of Mr, Ms and Hcj increased with the increase 3.5.3. Magnetic properties in calcination temperature from 1270°C to 1290°C, and The hysteresis loops of magnetic powders with differ - reached their maximum values of 45.07 emu/g, 73.19 ent calcination durations are given in Figure 16(a), and emu/g and 1331.56 Oe, respectively. When the tem- the results of magnetic properties are shown in perature exceeded 1290°C, partial grains excessively Figure 16(b). The values of Mr and Ms increased first 300 Y. ZHOU ET AL. Figure 12. SEM images of the magnetic powders with different calcination temperature. Figure 13. (a) The hysteresis loops and (b) magnetic properties of magnetic powders with various calcination temperatures. Table 4. Crystal parameters of magnetic powders with various calcination times. Time/h a c c/a 1.5 5.8782 23.0453 3.9205 2.0 5.8782 23.0351 3.9187 2.5 5.8785 23.0527 3.9216 3.0 5.8784 23.0427 3.9199 and then basically kept unchanged with the calcination time, and separately reached their maximum values of −1 45.07 emu/g and 73.19 emu·g at 2.0 h. The optimum value of 1331.56 Oe for Hcj was obtained at 2 h, and then it gradually decreased. The ferrite grains become more regular and even in size with the increase in calcination time before 2.0 h, as exhibited in Figure 14. The XRD patterns of magnetic powders with var- Figure 16, which could be responsible for the ious calcination times. JOURNAL OF ASIAN CERAMIC SOCIETIES 301 Figure 15. SEM images of magnetic powders with calcination durations of 1.5, 2.0, 2.5 and 3.0 h. Figure 16. (a) The hysteresis loops and (b) magnetic properties of magnetic powders with different calcination durations. Table 5. Chemical compositions and average particle sizes of improvement of magnetic properties. When the dura- HPMC and iron scrap. tion was over 2.0 h, the decreased Hcj was possibly due Composition (wt. %) TFe SiO Al O CaO MnO Particle size 2 2 3 to grain overgrowth. So, the optimal calcination time HPMC 71.46 0.35 0.23 0.07 <0.001 9.2 μm was 2 h. iron scrap 74.31 0.12 <0.01 0.03 0.50 2 ~ 5 mm 3.6. The comparison of HPMC with iron scrap for magnetic measuring system. To deeply understand preparing magnetic powders the difference between HPMC and iron scrap in produ- It is widely accepted that magnetic properties of mag- cing magnetic powder as iron-containing raw materi- netic powder are evaluated by testing its sintered als, comparative experiments were carried out. ferrite magnet in industry. As depicted in Figure 2, The main chemical compositions of HPMC and iron the production of ferrite magnet from magnetic pow- scale are given in Table 5. The contents of SiO and Al 2 2 der includes procedures of grinding, draining, wet- O impurities in HPMC were higher than that of iron compacting in a magnetic field, sintering, and polish- scrap, while iron scrap contained more manganese ing. The values of remanence (Br), magnetic coercive oxide, which was detrimental to the magnetic perfor- force (Hcb), Hcj, and the maximum energy product mance of magnetic powder/ferrite magnet [40]. The (BHmax) of ferrite magnet were calculated from the two kinds of magnetic powders from HPMC and iron demagnetization curves obtained by the permanent scrap were produced under the same experimental 302 Y. ZHOU ET AL. (a) (b) Figure 17. The demagnetization curves of sintered magnets prepared by HPMC(a) and iron scrap(b). conditions of average particle size of HPMC/iron scrap magnet produced by HPMC shrunk more because 1.9 μm, molar ratio of Fe O to SrO = 5.9, pre-oxidated there were more SiO and Al O in HPMC, which 2 3 2 2 3 temperature 800°C and time 0.5 h, calcination tem- could further transform into a liquid phase during the perature 1300°C and time 2 h. Calcium carbonate, sintering process. The sintered magnet from HPMC aluminum sesquioxide, silicon dioxide and boric acid was superior to that from iron scrap in terms of mag- were added into the obtained magnetic powders netic properties. In particular, the squareness (Hk/Hcj) before the second grinding, whose mass percentages of the former was as high as 0.98, which indicated that were 1.0%, 0.3%, 0.2%, and 0.5%, respectively. The the magnet from HPMC had a remarkable resistance to sintering was implemented at 1190°C for 2 h with demagnetization [1]. The data in Figure 18 illustrated a heating rate of 5°C/min, and the sintered ferrite that the magnetic properties of ferrite magnet from compacts were cooled in the furnace under an air HPMC had completely reached the level of Y30H-1 atmosphere. product in China (SJ/T 10410–2016). The demagnetization curves of sintered ferrite mag- nets produced by HPMC and iron scrap are shown in 3.7. Cost-benefit analysis Figure 17, and their magnetic properties are displayed in Figure 18. The diameters of these two green mag- A preliminary analysis of the cost and benefit of produ- nets were 30 cm, while the diameter of HPMC magnet cing per ton HPMC magnetic powder was conducted after sintering was 26.79 cm, which was slightly smaller to evaluate the economic feasibility of the production than that of iron scrap (27.27 cm). The shrinkage of process. The calculation was based on the experience magnet is mainly due to the volatilization of water. of related enterprises and the current market quota- Besides, the formation of silicate and aluminate liquid tions. For the total cost, the raw materials, fuel, phase densifies the ferrite causing shrinkage. The reagents, electric power, water, workers’ wage, equip- ment depreciation, etc., were taken into consideration. The expenditures of each project are listed in Table 6. The main costs were raw materials of HPMC and stron- tium carbonate, which reached 1376 CNY and 2100 CNY for per ton magnetic powder, respectively. The costs of fuel, workers’ wages and electric energy were all over 100 CNY. The investment in equipment was around 10 million CNY for a magnetic powder produc- tion line with a production capacity of 10,000 tons per year. Therefore, the equipment depreciation was 100 CNY per ton product assuming that the factory could continually run for 10 years. The total cost of magnetic powder was 4121.66 CNY per ton, and its sale price was 5200 CNY per ton, according to that of the Y30-1 product. Figure 18. The magnetic properties of sintered ferrite magnets produced by HPMC and iron scrap. JOURNAL OF ASIAN CERAMIC SOCIETIES 303 Table 6. Estimated cost and benefit for per ton HPMC magnetic powder. Project Price Calculation details Cost/benefit (CNY) The raw materials HPMC 1600 (CNY/ton) 1600 × 0.86 1376 SrCO 15,000 (CNY/ton) 15,000 × 0.14 2100 fuel mixed coal gas from iron and steel plant 270.6 −1 electric energy 1 (CNY/kw·h ) 102.2 water 2.88 (CNY/m ) 2.88 × 2 5.76 workers’ wage 200 (CNY/day) 140.4 equipment depreciation heavy machines like ball mill, rotary kiln, etc. 100.0 maintenance and others equipment maintenance 26.7 total expenditure summary of the cost involved 4121.66 revenue sale price 5200 profit sales revenue minus the cost 1078.34 return on investment the ratio of profit to investment 107.8% The consumption of HPMC was calculated according to the theoretical chemical formula SrO·5.9Fe O . The dosage of HPMC was 231.4 × 5.9 × 2/ 2 3 (3 × 98.8%) = 921.23 g for per molar ferrite, while SrCO dosage was 147.6/99% = 149.09 g. Here 231.4 and 149.6 were the relative molecular weight of magnetite and strontium carbonate, respectively. 98.8% and 99% were the purity of HPMC and SrCO . So, per ton magnetic powder consumed 921.23/ (921.23 + 149.09) = 0.86 ton HPMC and 1–0.86 = 0.14 ton SrCO . The price of magnetic powder was determined according to that of the Y30-1 product. The return on investment was 1078.34 × 10,000/10,000,000 = 107.8%. Here 1078.34 CNY was the profit for per ton product, and 10,000 ton and 10 million CNY were the yield and investment of a factory. Thus, the profit for producing a ton HPMC magnetic The two kinds of magnetic powders, respectively, powder was 1078.34 CNY. An impressive rate of return produced with HPMC and iron scrap were compared on investment 107.8% was obtained without consid- by detecting their sintered ferrite magnets. The values eration of land cost. The results of cost–benefit analysis of Br, Hcb, Hcj, and BH of magnet produced by HPMC max indicate that there is a considerable economic benefit were superior to that of iron scrap, and furthermore the for this production process. More importantly, the former had a better resistance to demagnetization. The majority of Y30-1 products are produced with iron HPMC magnetic powder in this study completely scale in China. The price of high-quality iron scale achieved the level of Y30-1 product in China. The cost– (TFe >73%) for magnetic powder production, around benefit analysis indicated that there was a promising 1800 CNY per ton, is higher than that of HPMC (1600 industrial application prospect for the substitution of CNY per ton). Besides, the limited supply of iron scale is HPMC for iron scrap in magnetic powder production. hard to satisfy the need for magnetic powder produc- tion these days. The magnetic properties of HPMC magnetic powder in this study have fully achieved Acknowledgments the level of Y30-1 product, which indicates that the This work was supported by the innovative project for grad- conventional raw material of iron scale can be replaced uate students of Central South University by HPMC. The cost–benefit analysis illustrates that (No. 1053320190706) and National key research and devel- there is a promising industrial application prospect opment program of China (2020YFC1909800). The authors would like to acknowledge Chuanwei Company for the sup- for this replacement. ply of the experimental materials, and Hunan Aerospace Magnet & Magneto Co., LTD, for offering the help of tests. 4. Conclusion In this work, HPMC was studied to produce magnetic Disclosure statement powder as iron oxide raw material via the conventional No potential conflict of interest was reported by the ceramic process. The average particle size of HPMC had author(s). a vital influence on the magnetic properties of magnetic powder. The pre-oxidation procedure could effectively reduce ferrous oxide content in HPMC, and thus avoided Funding the mass generation of non-magnetic substances like This work was supported by the Fundamental Research ferrous silicate. The optimum technological conditions Funds for Central Universities of the Central South of the ceramic process established in this study were as University [1053320190706]; National Key Research and follows: the average particle size of HPMC 1.9 μm, the Development Program of China [2020YFC1909800]. molar ratio of Fe O /SrO 5.9, the pre-oxidation tempera- 2 3 ture 800°C and time 30 min, and the calcination tempera- ture 1290°C and time 2 h. Under the optimum conditions, References the magnetic powder with the single magneto plumbite [1] Pullar RC. Hexagonal ferrites: a review of the synthesis, structure was obtained, where ferrite grains were hexa- properties and applications of hexaferrite ceramics. gonal shaped and evenly distributed with a mean size of Prog Mater Sci. 2012;57(7):1191–1334. about 1 μm. 304 Y. ZHOU ET AL. [2] Luk PCK, Abdulrahem HA, Xia B. Low-cost [19] Gao Y, Yue T, Sun W, et al. Acid recovering and iron high-performance ferrite permanent magnet recycling from pickling waste acid by extraction and machines in EV applications: a comprehensive spray pyrolysis techniques. J Clean Prod. 2021;312 review. Etransportation. 2020;6(8):1–13. (24):346–358. [3] Granados-Miralles C, Jenus P. On the potential of hard [20] Arvidson BR. Processing high-grade concentrates from ferrite ceramics for permanent magnet challenging low-grade iron ore deposits. T Indian technology-a review on sintering strategies. J Phys I Metals. 2013;66(5–6):467–474. D Appl Phys. 2021;54(30):1–10. [21] Li JLJW, Zhang WH. M-type strontium ferrite prepared [4] Mounkachi O, Lamouri R, Abraime B, et al. Exploring from boyan obo super iron concentrate by solid state the magnetic and structural properties of Nd-doped sintering. Nonferrous metals engineering in China. cobalt nano-ferrite for permanent magnet 2020;10(12):29–37. applications. Ceram Int. 2017;43(16):14401–14404. [22] Shao LH, Shen SY, Zheng H, et al. Effect of powder [5] Munir S, Ahmad I, Laref A, et al. Synthesis, structural, grain size on microstructure and magnetic properties dielectric and magnetic properties of hexagonal of hexagonal barium ferrite ceramic. J Electron Mater. ferrites. Appl Phys a-Mater. 2020;126(9):1–7. 2018;47(7):4085–4089. [6] Liu XS, Zhong W, Gu BX, et al. Exchange-coupling inter- [23] Moon K-S, Kang Y-M. Structural and magnetic proper- action in nanocomposite SrFe12O19/gamma-Fe2O3 per- ties of Ca-Mn-Zn-substituted M-type Sr-hexaferrites. manent ferrites. J Appl Phys. 2002;92(2):1028–1032. J Eur Ceram Soc. 2016;36(14):3383–3389. [7] Al-Hwaitat ES, Dmour MK, Bsoul I, et al. A comparative [24] Li JW. Reaction mechanism of M-type strontium ferrite study of BaxSr1-xFe12O19 ferrite permanent magnets prepared from bayan obo super iron concentrate by prepared by ball milling and sol-gel routes. J Phys microwave sintering. Baotou: Inner Mongolia D Appl Phys. 2020;53(36):1–15. University of Science and Technology; 2020.master’s [8] Manglam MK, Kumari S, Mallick J, et al. Crystal struc- degree ture and magnetic properties study on barium hexa- [25] Yang YJ, Liu XS, Jin DL. Influence of heat treatment ferrite of different average crystallite size. Appl Phys temperatures on structural and magnetic proper- a-Mater. 2021;127(2):1–8. ties of Sr0.50Ca0.20La0.30Fe11.15Co0.25O19 hexa- [9] Trukhanov AV, Darwish KA, Salem MM, et al. Impact of the gonal ferrites. J Magn Magn Mater. heat treatment conditions on crystal structure, morphol- 2014;364:11–17. ogy and magnetic properties evolution in BaM [26] Niu XF, Liu XS, Feng SJ, et al. Effects of presintering nanohexaferrites. J Alloy Compd. temperature on structural and magnetic properties of 2021;866:158961–158968. BaMg1.8Cu0.2Fe16O27 hexagonal ferrites. Optik. [10] Chawla S, Kaur P, Mudsainiyan RK, et al. Effect of fuel 2015;126(24):5513–5516. on the synthesis, structural, and magnetic properties [27] Chanda S, Bharadwaj S, Srinivas A, et al. Estimation of of M-type hexagonal SrFe12O19 nanoparticles. iron ion distribution at various sites contributing to J Supercond Nov Magn. 2015;28(5):1589–1599. saturation magnetization in barium hexaferrite at dif- [11] Liu CC, Liu XS, Feng SJ, et al. Effect of the Fe/Ba ratio ferent sintering temperatures. J Phys Chem Solids. and sintering temperature on microstructure and 2021;155(34):1–10. magnetic properties of barium ferrites prepared by [28] Zhang HB, Fan LN, Cao HC, et al. Microstructure, mag- hydrothermal method. J Supercond Nov Magn. netic, and dielectric properties of Co-Zr co-doped hex- 2018;31(3):933–937. agonal barium ferrites based on the sintering [12] Zhang M, Dai JM, Liu QC, et al. Fabrication and mag- temperature and doping concentration. J Mater Sci- netic properties of hexagonal BaFe12O19 ferrite Mater El. 2021;32(3):2685–2695. obtained by magnetic-field-assisted hydrothermal [29] Haberey RLF, Rosenberg M, Sahl K. Preparation and process. Curr Appl Phys. 2018;18(11):1426–1430. magnetic properties of LPE-grown hexagonal stron- [13] Wu Z, Zhang RN, Yu ZW, et al. The magnetic properties tium aluminoferrite films. Mater Res Bull. 1980;15 of permanent strontium ferrite doped with rare-earth (4):8. by chemical co-precipitation method. Ferroelectrics. [30] Yang YJ, Liu XS, Jin DL. The impact of the iron content 2018;529(1):120–127. on the microstructure and magnetic properties of [14] Kim M, Lee K, Bae C, et al. Magnetic and morphological M-type ferrites Sr0.45Ca0.25La0.30FexCO0.25O19. properties of Ca substituted M-type hexaferrite pow- Mater Sci Eng B-Adv. 2014;186:106–111. ders synthesized by the molten salt method. Aip Adv. [31] Yang YJ, Liu XS, Jin DL, et al. The effects of the iron 2021;11(5):1–7. content on structural and magnetic properties of [15] Sun R, Li X, Xia AL, et al. Hexagonal SrFe12O19 ferrite Sr0.80La0.20FexZn0.15O19 hexagonal ferrites. J Magn with high saturation magnetization. Ceram Int. Magn Mater. 2014;355:254–258. 2018;44(12):13551–13555. [32] Huang CC, Lin SH, Mo CC, et al. Development of opti- [16] Zhou EM, Zheng H, Zheng L, et al. Synthesis of dense, mum preparation conditions of Fe-Deficient M-type fine-grained hexagonal barium ferrite ceramics by Ca Sr La system hexagonal ferrite magnet. IEEE Trans two-step sintering process. Int J Appl Ceram Tech. Magn. 2021;57(2):1–8. 2018;15(4):1023–1029. [33] Trukhanov AV, Vinnik DA, Trofimov EA, et al. Correlation [17] Guzmán-Mínguez JC, Fuertes V, Granados-Miralles C, of the Fe content and entropy state in multiple substi- et al. Greener processing of SrFe12O19 ceramic per- tuted hexagonal ferrites with magnetoplumbite manent magnets by two-step sintering. Ceram Int. structure. Ceram Int. 2021;47(12):17684–17692. 2021;47(22):31765–31771. [34] Liu XS, Zhong W, Yang S, et al. Influences of La3+ [18] Amiri MC. Characterization of iron oxide generated in substitution on the structure and magnetic properties ruthner plant of pickling unit in mobarakeh steel of M-type strontium ferrites. J Magn Magn Mater. complex. J Mater Sci Technol. 2003;19(6):596–598. 2002;238(2–3):207–214. JOURNAL OF ASIAN CERAMIC SOCIETIES 305 [35] Rehman KMU, Liu XS, Feng SJ, et al. Influence of tem- [38] Chauhan CC, Kagdi AR, Jotania RB, et al. Structural, perature on Sr0.35La0.40Ca.25Fe11.6Co0.4O19 hexa- magnetic and dielectric properties of Co-Zr substi- gonal ferrites against structural, morphological and tuted M-type calcium hexagonal ferrite nanoparticles magnetic properties prepared by conventional cera- in the presence of alpha-Fe2O3 phase. Ceram Int. mic reaction methodology. J Supercond Nov Magn. 2018;44(15):17812–17823. 2018;31(3):925–932. [39] Chen W, Wu WW, Li MY, et al. Al3+ doped M-type [36] Huang TX, Peng L, Li LZ, et al. Low temperature sinter- hexagonal Ba-Co ferrites synthesized via ball-milling ing behavior of La-Co substituted M-type strontium assisted ceramic process: magnetism and its correla- hexaferrites for use in microwave LTCC technology. tion with structural properties. J Mater Sci-Mater El. J Rare Earth. 2016;34(2):148–151. 2018;29(10):8020–8030. [37] Liu CC, Liu XS, Feng SJ, et al. Microstructure and mag- [40] Ni JL, Feng SJ, Liu XS. Influence of manganese dioxide netic properties of M-type strontium hexagonal fer- and Ba2Co2Fe12O22-additives on the magnetic rites with Y-Co substitution. J Magn Magn Mater. power loss of Ni0.8Zn0.2Fe2O4 ferrites. Materialwiss 2017;436:126–129. Werkst. 2018;49(8):986–990
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