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Дослгджено особливостi фазового складу та мгкроструктури шлакгв алюмотермiчного виробництва лггатур тугоплавких елементiв рiзних марок та окалини швидкорiжучоi сталi Р6М5 щодо природи присутностi легуючих еле-ментiв. Це необхгдно для забезпечен-ня зменшення втрат Мо, W та гнших легуючих елементiв сублiмацieю з пгдви-щенням температури при переробщ тех-ногенних вiдходiв. Фазовий склад визна-чали методом рентгенофазового аналiзу. Мгкроструктуру дослгджували на растровому електронному мгкроскопг в комплект з рентгенгвським мiкроаналiзом з використанням безеталоного методу роз-рахунку фундаментальних параметрiв. Визначено, що шлаки алюмотермiчного виробництва лггатур АХМ-50 та АМВТ складаютьсяз СаА1407та з'еднаньА^204 i Сг02. Це може обумовлювати певний рiвень легованостi шлаку тугоплавкими елементами. У шлаку вгд виплавки лгга-тури МФТА виявлено фази Al75Mo2oW5 та Мо^г, А1)з, що можуть бути представлен металевими вкрапленнями. Фази окалини сталi Р6М5 в основному представлен FeзO4, Fe2Oз та FeO. Також виявлено FeWO4, Мо02, WC, Мо2С, що обумовлюеться пгдвищеним ступенем легованостi W та Мо. Не виключено, що деяка частка атомiв легуючих елементiв, в тому числг Сг та V, може знаходити-ся в якостi атомiв замщення в оксидах Fe. Мгкроструктура дослгджених шлакгв та окалини характеризувалася розупо-рядковангстю часток рiзного розмiру та форми. Виявлено присутнгсть в окалин часток з вгдносно високим вмгстом легуючих елементiв. В дослгджених матерiалах вгдсутнг з'еднання з пгдвищеною схиль-нгстю до сублгмацп. Це зумовлюе вгдносно високий ступгнь використання легую-чих елементгв г зменшуе певнг обмеження додавання дослгджених шлакгв у шлакоу-творюючг сумгшг та температурнг обме-ження режимгв плавлення. Використання шлакгв алюмотермгчгого виробництва та окалини швидкоргжучих сталей в шихтг для виплавки легуючого сплаву забезпе-чило вилучення тугоплавких елементгв та додаткову леговангсть кгнцевого продукту
Ключовг слова: шлак алюмотермгч-ного виробництва, легованг техногеннг вгдходи, окалина сталг, рентгенофазовг
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UDC 669.15'28-198
|DOI: 10.15587/1729-4061.2018.140924|
STUDYING THE PHYSICAL-CHEMICAL PROPERTIES OF ALLOYED METALLURGICAL WASTE AS SECONDARY RESOURCE-SAVING RAW MATERIALS
S. Hryhoriev
Doctor of Technical Sciences, Professor* A. Petryshchev PhD, Associate Professor Department of Labour and Environment Protection Zaporizhzhia National Technical University Zhukovskoho str., 64, Zaporizhzhia, Ukraine, 69063
N. Sinyaeva PhD, Associate Professor Department of Chemistry** E-mail: sinyaeva_02@gmail.com A. Yurchenko* O. S klyar PhD, Professor, First Vice-Rector Department of technical systems of livestock technologies***
S. Kvitka PhD, Associate Professor Department of Electrical Engineering and Electromechanics***
V. Borysov Doctor of Pedagogical Sciences, Professor Department of Social Work Khortytsia National Academy Naukove Mistechko str., 59, Zaponzhzhia, Ukraine, 69017
V. Vlasiuk PhD, Teacher Department of Tactics National Academy of the National Guard of Ukraine Zakhysnykiv Ukrainy sq., 3, Kharkiv, Ukraine, 61001
B. T s y m b a l PhD
Department of occupational, technogenic and environmental safety National University of Civil Defence of Ukraine Chernyshevska str., 94, Kharkiv, Ukraine, 61023
S. Borysova PhD, Associate Professor Department of Pedagogy and Techniques of Technological and Professional Education Donbass State Pedagogical University G. Batiuka str., 19, Sloviansk, Ukraine, 84116 *Department of business administration and international management**
**Zaporizhzhia National University Zhukovskoho str., 66, Zaporizhzhia, Ukraine, 69600 ***Tavria State Agrotechnological University B. Khmelnytsky ave., 18, Melitopol, Ukraine, 72310
1. Introduction
One of the alternative sources for obtaining alloying materials containing W, Mo, Cr, V is the processing and return-
ing of the alloyed technogenic wastes to production. These include the slag from alumothermic production and the scale of rapid cutting steels. A specific feature of such waste is the presence of alloying elements in the form of oxide and com-
plex compounds. That necessitates taking into consideration the complex character of the physical-chemical interaction between elements when developing the technological conditions for processing.
Thus, it is a relevant task in metallurgy to save resources and energy with reducing the losses of alloying elements when processing and using the slag from alumothermic production and the scale from rapid cutting steels. For this purpose, it is necessary to study the phase composition and microstructure of technogenic raw materials that contain, along with the slag-forming components and iron, expensive refractory alloying elements.
2. Literature review and problem statement
Reduction with carbon [1], as well as with a complex of C and Si [2] during the reducing smelting, has positive practical results as a technique for processing oxide technogenic raw materials. This is especially true for scale and other fine-disperse technogenic waste contaminated with mineral oils and emulsions that require refining from harmful impurities.
Based on the research results by authors of work [3], the iron scale consists of Fe3O4, Fe2O3, FeO. Similar results were obtained by authors of paper [4] in the study of the rolling iron scale. The possibility of the presence of a Fe phase, along with the oxide phases, in the scale is indicated by authors of work [5]. When investigating scale of steel P18 in paper [6], in contrast to the non-alloyed raw materials, the authors did not rule out the possibility of the presence of oxide compounds with the content of refractory alloying elements. This is important, since the higher Mo and W oxides have, at a temperature increase, a relatively high susceptibility to sublimation. Such a feature might cause significant losses of refractory elements when processing technogenic raw materials.
Based on research results in [7], slag from the ferro-chrome production has 3.5 % Cr2O3 in its composition and can additionally contain about 9 % by weight of metallic Cr. Other components are represented by Al2O3, MgO, SiO2, CaO, FeO and SiC. In paper [8], authors determined using an X-ray phase diffraction analysis that the slag from alu-mothermic ferrochromium production consists mostly of the phases of Al2O3 and metallic Cr. Moreover, the diffraction peak of Cr had a relatively high intensity. This indicates the possibility of the presence of a significant residual content of Cr in the slag; hence the expediency for the further extraction of the refractory element.
The authors of work [9] studied the removal of V from the vanadium converter slag using the reducers C and Si. It was stated in work [9] that slag could consist of V oxides along with SiO2, FeO, MnO, and TiO. During reduction, the formation of carbide and silicide phases is not excluded. The reduction of vanadium slag using C and Si for the purpose of extracting V was investigated in practice by authors of work [10]. The amount of oxide V2Os in the slag was 4.35 % by weight. The oxides of FeO, CaO, Al2O3, MgO, SiO2, MnO, TiO, Cr2O3 and P2Os were also present. The achieved degree of removal of V was larger than 95 %. It should be noted that the higher oxide compounds of V in the slag have a relatively high susceptibility to evaporation. This is confirmed by studying the losses of V in the evaporation of oxides from the samples of vanadium-containing slag in the
system CaO-MgO-Al2O3-SiO2 by authors of work [11]. That indicates the expediency of reduction with the transfer of oxide compounds of V to carbides and silicide that are not susceptible to evaporation.
The authors of work [12] analyzed the slag formed in the alumothermic smelting of ligatures of grade AVTU (Al-V-Ti-C), AHMK (Al-Cr-Mo-Si) and ACMO (Al-Zr-Mo-Sn) by using an X-ray phase analysis. The main phases of slags AVTU and AHMK are Al2O3, CaAl12O19, CaOAl4O6. In all samples of the slag, CaF2 was identified, and a relatively small amount of KCl was present in the slag from the smelting of AVTU. CaAl2O4, CaZrO3, CaZr4O9 and Al2O3 were found in the slag from smelting the ligature ACMO. Based on the results from paper [13], the slag from AVTU smelting could contain elemental carbon, metallic and carbide phases. That is, the presence of compounds and metallic impurities of refractory and expensive elements is possible in the slag from the alumothermic production of ligatures, with the prospect for their further extraction and return to production.
It should be noted that there are significant results in studying the composition of scale from the non-alloyed grades of steels, reported in papers [3-5]. In addition, there are certain results in studying the scale of a tungsten rapid cutting steel, which are reported by authors of work [6]. However, the demonstration of the refractory elements of W and Mo in the composition of phases and compounds in the scale of tungsten-molybdenum grades of rapid cutting steels is studied insufficiently. One of the most common of them is the grade R6M5. There are also significant achievements in the research into the composition of slag from metallurgical production for the purpose of further processing, reported by authors of studies [7-11]. The slags of alumothermic production of ligatures of refractory elements are one of the most promising for processing and extraction of high-cost components; results of studying them are given in papers [12, 13]. However, at the same time, the nature of the phases and compounds in which there are refractory elements, is studied insufficiently. Research in this field can help reduce the losses of Mo, W and other alloying elements through sublimation with an elevated temperature when processing technogenic waste. In other words, it is expedient to conduct a comprehensive study into the phase composition and microstructure of slag from the alumothermic production of the ligatures of refractory elements of various grades and the tungsten-molybdenum scale from a rapid cutting steel of grade R6M5. Using a raster electron microscopy with an X-ray microanalysis will make it possible to significantly expand our understanding of the structure and composition of separate sections of the microstructure in the examined materials.
3. The aim and objectives of the study
The aim of this work was to study the features of the physical-chemical properties of slags from the alumother-mic production of ligatures, as well as scale from the tungsten-molybdenum rapid cutting steel R6M5, as the alloyed technogenic secondary raw materials. This is necessary to determine the parameters that reduce the losses of Mo, W and other elements through the sublimation of oxides in the processing of alloyed technogenic waste.
To achieve this goal, the following tasks were set:
- to determine the phase composition and microstructure of slags from the alumothermic production of ligatures of various grades regarding the nature of presence of the alloyed elements;
- to investigate peculiar properties of the phase composition and microstructure of scale from the tungsten-molybdenum rapid cutting steel R6M5 as the alloyed technogenic secondary raw materials.
4. Materials and methods to study the alloyed technogenic secondary materials
4. 1. Examined materials and equipment used in the experiment
The slags from the alumothermic production (TU 480514-34-87), obtained after smelting of ligatures of the refractory elements AMVT (TU 48-4-308-88), MFTA (TCU48-4-365-88) and AHM-50 (TU 48-4-365-88).
Requirements in the technical specifications TU 48-051434-87 to the content of components in slag, % by weight: aluminum oxide - not less than 68.0; silicon oxide - not larger than 2.0; iron oxide - not larger than 2.0; the sum of oxides of refractory elements (Mo, W, Cr, V, and others) - not larger than 8.0; calcium oxide - the rest. Grain size, mm - not larger than 80.0.
The scale from the rapid cutting steel grade R6M5 of the following composition, % by weight: С - 0.75; Si - 0.15; Mn - 0.21; Cr - 3.85; Mo - 4.81; V - 1.65; W - 5.75; Co -0.07; Ni - 0.24; Cu - 0.12; S - 0.009; Р - 0.027; О - 27.0; Fe - the rest.
An X-ray phase analysis of the samples was performed at the diffractometer "DRON-6" (Russia).
Photographs of the microstructure of samples were acquired at raster electron microscopes "REM-106I" (Ukraine) and "JSM 6360LA" (Japan). The microscopes are equipped with the system of an X-ray microanalysis to determine the chemical composition of separate plots of the samples' surface.
4. 2. Procedure for conducting the experiments and determining the indicators of samples' properties
Phase composition was determined using the method of an X-ray phase analysis, employing the monochromatic radiation of Co Ka (^=0.178897 A). Measurements were made at a voltage at the tube of U=30 kW and at an anode current of /=10 mA. The composition of phases was examined using the software package PDWin 2.0 (Russia).
We examined the microstructure of samples at the accelerating voltage of 20 -25 kW and a current of the electronic probe of 52-96 ^mA. Working distance to the examined surface was 10.8-12.3 mm. Phase composition was determined by the non-reference method for calculating fundamental parameters.
5. Results of studying the properties of the alloyed technogenic secondary materials
Based on the results of the phase study, the slag samples from the alumothermic production of ligature AMVT mostly contained the oxide CaAl4O7 and the vanadium-contain-
ing compound AlV2O4 (Fig. 1). The compound CaAl4O7 was also identified in the slag samples from the production of ligature AHM-50. A chrome-containing component is represented by the oxide CrO2 (Fig. 2). Slag samples from the production of ligature MFTA mostly consisted of the complex compounds Al75Mo20W5 and Mo(Si, Al)3 (Fig. 3).
Fig. 1. Fragment of diffractogram of slag from the alumothermic production of ligature AMVT
Fig. 2. Fragment of diffractogram of slag from the alumothermic production of ligature AHM-50
Fig. 3. Fragment of diffractogram of slag from the alumothermic production of ligature MFTA
Fig. 4. Fragment of diffractogram of scale from steel R6M5
The scale of rapid cutting steel grade R6M5 is represented by the oxides of Fe3O4, Fe2O3 and FeO (Fig. 4). Along with this, we identified the demonstration of the complex oxide FeWO4. Molybdenum-containing compounds are represented by the oxide MoO2 and carbide Mo2C. Demonstration of the carbide WC was observed as well.
The microstructure of the examined technogenic materials is disordered, it consisted of the particles with different size and shape (Fig. 5). The content (% by weight) of W and Mo in the examined plots of scale from steel R6M5 was within 3.45-10.73 and 2.17 - 6.65, respectively (Fig. 6, Table 1). We also identified a plot with the content (% by weight) of Cr and V - 1.23 and 1.18, respectively.
The content of oxygen in the examined plots was within 8.52-23.16 % by weight. Fe formed the base.
Table 1
Results of the X-ray microanalysis of reduced products according to Fig. 5, d
Sample plot Content of elements, % by weight Total
O Al V Cr Fe Mo W
1 15.84 0.00 0.00 0.00 78.54 2.17 3.45 100.00
2 8.52 0.00 0.00 0.00 74.10 6.65 10.73 100.00
3 23.16 0.18 1.18 1.23 65.89 3.12 5.24 100.00
4 18.67 0.00 0.00 0.00 75.09 2.38 3.86 100.00
c d
Fig. 6. Spectrograms of the X-ray microanalysis of different plots of the scale microstructure, steel grade R6M5, corresponding to Fig. 5, d a - 1, b - 2, c - 3, d- 4
6. Discussion of results of studying the properties of the alloyed technogenic secondary materials
The study into slags from the aluminothermic production of smelting the ligatures AHM-50 and AMVT shows that the base consisted of CaAl4O7 (Fig. 1, 2). This agrees well with the results in study [12]. At the same time, the difference is in the detection of compounds with refractory elements: AlV2O4, CrO2 (Fig. 1, 2). According to a research reported in paper [14], CrO2 decays at a temperature of about 783 K, and it is stable at lower temperatures. That indicates the possibility of CrO2 formation when cooling the slag within temperatures below 783 K and the presence in the respective samples, which were examined using an X-ray phase analysis.
Jv ; fa ./^ti
2U.00kV x2.00k 20um
Fig. 5. Photographs of the microstructure of technogenic materials at magnification ><2000 based on the examined plots of diffractograms: a - Fig. 1, b - Fig. 2, c - Fig. 3, d- Fig. 4; 1- 4 - plots of an X-ray microanalysis of the sample of scale
b
a
c
The samples of slag from the production of ligature MFTA contained the phases of Al75Mo20W5, Mo (Si, Al)3, which could be present in the form of metallic inclusions (Fig. 3). The respective examined samples probably had the clusters of inclusions of these phases. This is consistent with the results of papers [7, 8, 13], which noted in the examined samples the presence of a metallic component. The microstructure of the examined slags is heterogeneous, consisting of disordered particles (Fig. 5).
The research we conducted indicates that the phase composition of scale from steel R6M5 is mostly represented by Fe3O4, Fe2O3, FeO (Fig. 4). This agrees well with the results in papers [3-6]. The difference is the detection in the composition of compounds with the participation of refractory elements: FeWO4, MoO2, WC, Mo2C, due to the increased degree of W and Mo doping. The presence of particles with a relatively high content of alloying elements in the scale is confirmed by the results of an X-ray microanalysis (Fig. 5, d, Table 1). At plot 2, the content of W and Mo reached 10.73 % by weight and 6.65 % by weight, respectively. At plot 3, the content of Cr and V content 1.23 % by weight and 1.18 % by weight, respectively. It is not excluded that a certain part of the atoms in the alloying elements, including Cr and V, could be included as the replacement atoms in Fe oxides. The microstructure of scale was characterized by the disordered particles of different size and shape (Fig. 5, d).
When comparing the results of research into the properties of slags from the alumothermic production and the scale of steel R6M5, it should be noted that they are similar in the presence of refractory elements in the composition of compounds. In this case, refractory elements were bound in oxide or complex compounds, which predetermines the application of additional reduction processes and the recycling for reuse. According to the research results, the examined materials contain no compounds with a relatively high susceptibility to sublimation In other words, there is no need to create special conditions that prevent the evaporation and loss of alloying elements with the gas phase. That also predetermines an increase in the degree of using alloying elements and reduces certain restrictions for the addition of the examined slags to slag-forming mixtures and temperature limitations for melting regimes.
As a shortcoming, we should note the absence of results from an X-ray microanalysis of plots in the microstructure of slags from alumothermic production.
This study might be developed in the direction of expanding the range of examined slags from the alumothermic smelting of ligatures for further processing, such as niobium or zirconium-containing.
The slag of alumothermic production and the scale of rapid cutting steel were used as components of the charge to smelt the alloying and deoxidizing alloy in accordance with TU 14-146-87-90. Introduction of scale to charge makes it possible to ensure the specified degree of alloy doping by refractory elements when disposing of fine-disperse oxide
waste. At the same time, shavings from the power grinding of the surfaces of commodity billets and metal-abrasive dust containing silicon carbide were introduced to the charge. The slag-forming mixture consisted of the flux AN-295, fluoric spar, and slag from the alumothermic production of ligatures. Testing the specified slag-forming mixture in the composition of charge during smelting of the alloying and deoxidizing alloy was conducted in the three-tones electric arc furnaces SKB-6069 with a coal lining. The ignition was conducted in a furnace bath with the loaded charge, followed by melting and finishing to a temperature of 1,813-1,833 K. Aging at a predefined temperature was conducted to average and stabilize the chemical composition throughout the entire volume of the furnace bath. The discharge was performed on a roller into metal pallets or on a booth with molds. The alloy was obtained in pieces with a weight not exceeding 180 kg (typically, 20-30 kg). The obtained alloy complied with TU 14-146-87-90 with a mass share of elements: C - 2.0-4.5; Si - 1.0-4.5; Cr - 1.0-6.0; Mo - 2.0-5.0; V - 1.0-2.0; W - 3.0-6.0; Mn - not larger than 0.6; Mn - not larger than 0.6; Co - not larger than 0.6; S - not larger than 0.03; P - not larger than 0.03; Fe -the rest. The practical significance of introducing slag from the alumothermic production is to ensure the refining capacity of the slag mixture, the possibility for additional extraction of refractory elements from slag and to lower the cost of the alloy. Introduction to the charge composition of slag from the alumothermic production according to TU 48-0514-34-87 in the range of 4.5-14.5 % by weight ensured the increased doping of the alloy. We have achieved an increase in the content of refractory elements through the reduction from oxides and the removal of metallic inclusions from slag within 1.89-6.09 kg/t. There was also a somewhat increase in the alloy desulphurization.
7. Conclusions
1. It was determined that the base of slags from the alu-mothermic production of ligatures AHM-50 and AMBT is CaAl4O7. At the same time, a compound was detected with the refractory elements AlV2O4 and CrO2. The phases of Al75Mo20W5 and Mo(Si, Al)3 were identified in the slag samples from smelting the MFTA ligature. The microstructure was heterogenous, and consisted of the disordered particles.
2. The phase composition of scale of steel R6M5 mostly consisted of Fe3O4, Fe2O3 and FeO. In addition, compounds with the refractory elements FeWO4, MoO2, WC, Mo2C were detected. The plots of microstructure with a relatively high content of W and Mo were found, as well as the plots with the presence of Cr and V. The replacement of part of Fe atoms with the atoms of the refractory alloying elements is possible in oxide compounds. The microstructure of scale was characterized by the disordered particles of various size and shape.
References
1. Utilization of nickel slag using selective reduction followed by magnetic separation / Pan J., Zheng G., Zhu D., Zhou X. // Transactions of Nonferrous Metals Society of China. 2013. Vol. 23, Issue 11. P. 3421-3427. doi: https://doi.org/10.1016/s1003-6326(13)62883-6
2. A study of environmentally friendly recycling of technogenic chromium and nickel containing waste by the method of solid phase extraction / Hryhoriev S., Petryshchev A., Shyshkanova G., Zaytseva T., Frydman O., Krupey K. et. al. // Eastern-European Journal of Enterprise Technologies. 2018. Vol. 1, Issue 10 (91). P. 44-49. doi: https://doi.org/10.15587/1729-4061.2018.121615
3. Preparation of iron Powders by Reduction of Rolling Mill Scale / Mechachti S., Benchiheub O., Serrai S., Shalabi M. // International Journal of Scientific & Engineering Research. 2013. Vol. 4, Issue 5. P. 1467-1472.
4. Shatokha V. I., Gogenko O. O., Kripak S. M. Utilising of the oiled rolling mills scale in iron ore sintering process // Resources, Conservation and Recycling. 2011. Vol. 55, Issue 4. P. 435-440. doi: https://doi.org/10.1016/j.resconrec.2010.11.006
5. Influence of hot-rolling parameters on the microstructure and corrosion-resistance of oxide scales / Liu S., Wu H.-B., Yu W., Wang L.-D., Cai Z.-X., Tang D. // Cailiao Kexue yu Gongyi/Material Science and Technology. 2013. Vol. 21, Issue 6. P. 84-90.
6. Determining the physical-chemical characteristics of the carbon-thermal reduction of scale of tungsten high-speed steels / Hry-horiev S., Petryshchev A., Belokon' K., Krupey K., Yamshinskij M., Fedorov G. // Eastern-European Journal of Enterprise Technologies. 2018. Vol. 2, Issue 6 (92). P. 10-15. doi: https://doi.org/10.15587/1729-4061.2018.125988
7. Wastes generation and use in ferroalloy production / Zhdanov A. V., Zhuchkov V. I., Dashevskiy V. Ya., Leontyev L. I. // Energy efficiency and environmental friendliness are the future of the global Ferroalloy industry: Proceedings of the Fourteenth International Ferroalloys Congress INFACON XIV. 2015. P. 754-758.
8. Extraction of Chromium from Carbon Ferrochromium Residual Wastes / Lazarevskiy P. P., Gizatulin R. A., Romanenko Y. E., Valuev D. V., Valueva A. V., Serikbol A. // IOP Conference Series: Materials Science and Engineering. 2015. Vol. 91. P. 012038. doi: https://doi.org/10.1088/1757-899x/91/1Z012038
9. Reduction of metals from vanadium converter slag by means of carbon and silicon / Nokhrina O. I., Rozhikhina I. D., Dmitrien-ko V. I., Golodova M. A., Efimenko Y. A. // Steel in Translation. 2014. Vol. 44, Issue 2. P. 99-102. doi: https://doi.org/10.3103/ s0967091214020156
10. Lindvall M., Rutqvist S., Ye G. Recovery of vanadium from V-bearing BOF-slag using an EAF // The Twelfth International Ferroalloys Congress. Sustainable Future. Helsinki, 2010. P. 189-196.
11. High-temperature mass spectrometric study of the vaporization processes of V2O3 and vanadium-containing slags / Wang H., Stolyarova V. L., Lopatin S. I., Kutuzova M. E., Seetharaman S. // Rapid Communications in Mass Spectrometry. 2010. Vol. 24, Issue 16. P. 2420-2430. doi: https://doi.org/10.1002/rcm.4657
12. Phase composition and thermal properties of ladle smelting slags of AVTU, AKhMK and ATsMO foundry alloys / Vokhmentsev S. A., Larionov A. V., Gulyaeva R. I., Chumarev V. M. // Tsvetnye Metally. 2017. Issue 11. P. 60-64. doi: https://doi.org/10.17580/ tsm.2017.11.11
13. Fazoviy sostav produktov alyuminotermicheskoy vyplavki ligatury Al-V-Ti-C / Vohmencev S. A., Chumarev V. M., Larionov A. V., Zhidovinova S. V., Taranov D. V. // Titan. 2017. Issue 3 (57). P. 20-23.
14. Ryabuhin A. G., Gruba O. N. Entropiya kristallicheskih oksidov hroma // Izvestiya Chelyabinskogo nauchnogo centra UrO RAN. 2005. Issue 4 (30). P. 36-40.
