Strontium Production from Strontium Oxide Using Vacuum

UCTEA Chamber of Metallurgical & Materials Engineers Proceedings Book

Strontium Production from Strontium Oxide Using Mehmet Buğdaycı¹,², Ahmet Turan², Y. Cucurachi¹, Vacuum Aluminothermic Process Onuralp Yücel¹ ¹İstanbul Technical University, ²Yalova University - Türkiye

Abstract Strontium is produced only by the thermal method for industrial use. Timminco Metals, Ontario, Canada used a In this present study production of strontium metal from its method similar to the Pidgeon Process in the production of oxide was studied under the pressure of 1-5 mbar by strontium. However complete details on the actual strontium metallothermic process. In the experiments SrO which has production route is not determined clearly [8]. In this study, 99 % purity was used. Effects of Al powder addition (100, production of strontium metal from its oxide was studied. 200, 300 % of stoichiometric ratio) and time were The present work aims to investigate the parameters investigated on recovering of metallic strontium. Effects of effecting the aluminothermic reduction of SrO using BaO addition (100 %, 200 %, 300 %) was also investigated. aluminum metal. In the experiments, charge composition, The final residues were examined for their chemical amount of reducing metal and time were taken as variables composition. XRD, AAS and Flame Photometer devices in order to obtain high recovery efficiencies. were used for chemical analysis. More than 90 % of strontium metal recovery was observed. Theoretical investigations

¨G0-T diagram for oxide formation indicates that SrO 1. Introduction reduction with aluminum is only possible beyond 2000 0C.

In order to obtain strontium metal at lower temperatures for Strontium is an element which is used in many advanced Eq. 1, partial pressure of the strontium vapour and/or activity technology applications. Barium strontium titanat, strontium of Al should be lowered. For this aim, vacuum technique and bismuth titanat, and strontium bismuth tantalat thin films are additions of BaO for formation of a basic slag (BaO.Al O ) promising materials in ferroelectric and Schottky-based 2 3 are needed. microelectronics technologies, especially for memory

applications. Physical vapor deposition (PVD) techniques as 3 SrO + 2Al + BaO = 3Sr + BaO.Al O (Eq. 1) magnetron sputtering, thermal evaporation and molecular 2 3

beam epitaxy (MBE) are the most widely used methods for By using the FactSage 5.2 thermodynamic program the growth of these thin films [1-3]. In these techniques high- Figure 1 was simulated for aluminothermic reduction of SrO purity of Sr metal is used as evaporation sources and by Al powder at different temperatures under 1 bar and 1 sputtering targets. Furthermore, metallic strontium is used as mbar of vacuum atmosphere [9]. As can be seen in the figure a "getter" in electron tubes, and as an alloying elements in reduction of strontium oxide starts at around 1050 0C and it aluminum alloys [4]. totally reduced to metallic Sr under pressure of 1 mbar.

The most used Sr compound is SrCO3 and widespread process used in production of SrCO3 is the hydrometallurgical carbonation of celestite. Although there are considerable amount of Selestite reserves, SrCO3 and strontinum metal are not being produced in Turkey, yet [5].

Concentrated celestite (SrSO4) is conversed to SrCO3 in carbonate media. Black ash and direct conversion processes are currently used methods. There are many satisfactory studies about hydrometallurgical carbonation of celestite and decomposition of SrCO3 [6, 7]. Since strontium metal is SURGXFHG IURP LW¶V R[LGH 6U2 6U&23 is need to be decomposed to SrO.

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chemically. The degree of Sr metal recovery was calculated as

Sr Recovery, % = 100 ± [(Wt x % Srt)/(W0 x % Sr0)] x 100

where Wt the weight of the residue at time t, % Srt the weight percent of the strontium in the residue at time t, W0 is the weight of the briquette, and % Sr0 the weight percentage of the strontium of the briquette.

)LJ¨*± T diagram of Al2O3 and SrO under pressure

of 1 bar and 1 mbar.

Fig. 3. Schematic diagram of experimental setup. 1- 2. Experimental Procedure Furnace, 2- retort made from Incoloy 800H/HT alloy, 3- Briquetted charge, 4 Sr condensation section, 5-Cooling Raw materials: In the experiments, synthetic SrO is used as water in and out, 6-Vacuum connection, 7-Vacuum pump, strontium source. Al powder was used as reducing agent and 8-Digital pressure gauge, 9- EL 18 thermocouple, 10-Ice BaO was used for slag formation. water box, 11-Temperature measuring unit.

Reduction technique: The schematic diagram of the experimental set up was illustrated in Fig. 2. The temperature was measured by 6RhPt-30RhPt (EL-18) 3. Results and Discussion thermocouple. The reduction process was carried out in a retort made from Incoloy 800H/HT alloy [10]. In order to The effects of time and the stoichiometric ratio of reducing pump the retort for vacuum, a two stage compact rotary vane aJHQW RQ UHFRYHU\ ZHUH LQYHVWLJDWHG LQ WKLV ZRUN ,W¶V pump was used. observed that with increasing stoichiometric ratio of Al and BaO the recovery of strontium metal is increased. For The stoichiometric ratios of Al and BaO were together example 40,1% and 96,89 % of recovery of strontium is selected 100 %, 200 % and 300 %. The desired weight observed while the stoichiometric ratios of Al powder and ratios of SrO, BaO and Al metal powder were mixed BaO were 100 % and 300 % respectively. throughly. The mixture was weighted and briquetted. Briquettes were put in an alumina boat. The charged boat 7KHH[SHULPHQWVUHVXOWVZKLFKZHUHFDUULHGRXWDW& was inserted into the retort at room temperature. After for 60, 120, 180 and 240 minutes were shown in Fig. 4 and closing the retort cover, the inside pressure was decreased to Fig 5. It is observed that with increasing time the recovery 1-5 mbar. In order to condensate the strontium vapour of strontium metal also increased. For example, recoveries formed during the reduction reactions, a cooling copper tube of strontium were determined to be 40,1 % after 60 min. and was mounted at the retort cover. After the furnace attained 96,89 % after 240 minutes reduction time. Sr concentration to the required temperature, the retort was inserted into the in the residue decreased with increasing time. For example furnace. Since the furnace temperature decreases after strontium concentration in residue were determined to be 69 inserting the retort, initial time was started when the furnace % after 60 min. and 2,25 % after 240 minutes reduction time. reached the desired temperature.

At the end of the reduction experiments, the retort was left in the furnace at the same vacuum values and was cooled to room temperature. Then, the cover was opened and the condensed strontium metal on the cooling section and the residue left in the boat were weighted and analyzed

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References ϭϬϬ [1] J. Robertson, C. W. Chen, Schottky barrier heights of ϴϬ tantalum oxide barium strontium titanate lead titanate and ;йͿ strontium bismuth tantalite, Applied Physics Letters Vol. ϲϬ 74/8, 1168-1170, 1999 [2] R. Moazzami, Ferroelectric thin film technology for ƌĞĐŽǀĞƌǇ

semiconductor memory, Semiconductor Sci. Technology, 10, ϰϬ ^ƌ 39-85-390, 1995 ϭϬϬй [3] Matichny S., Fabrication and characterisation of ferroelectric ϮϬ ƐƚŽŝĐŚŝŽŵĞƚƌǇ lead zirconate titanate and strontium bismuth tantalate thin films, Otto-von-Guericke University Magdeburg, Doctrate Ϭ thesis, 2006 [4] Davis, J. R., 1996: ASM Speciality Handbook, Aluminum and Ϭ ϯϬ ϲϬ ϵϬ ϭϮϬ ϭϱϬ ϭϴϬ ϮϭϬ ϮϰϬ ϮϳϬ Aluminum Alloys, ASM International, Materials Park, Ohio, dŝŵĞ;ŵŝŶͿ USA [5] DPT (State Planning Organization), Eight Five±Year Fig. 4: Effect of time on strontium recovery Development Plan, 2001, Ankara. >@0(UGHPR÷OX6$\GR÷DQ0&DQED]R÷OXA kinetic study ϴϬ͕ϬϬ on the conversion of celestite (SrSO4) to SrCO3 by ϳϬ͕ϬϬ ϭϬϬй mechanochemical processing, Hydrometallurgy, 86 (2007), ϲϬ͕ϬϬ ƐƚŽŝĐŚŝŽ͙ 1-5.

;йͿ >@ 0 (UGHPR÷OX &DUERWKHUPLF UHGXFWLRQ RI mechanically ϱϬ͕ϬϬ activated celestite, Journal of Mineral Processing 92 (2009), ϰϬ͕ϬϬ 144-152 [8] J. Langlais, Strontium Reduction by Aluminothermic Reduction, ƌĞƐŝĚƵĞ ϯϬ͕ϬϬ McGill University, master thesis, 1991 ŝŶ [9] C.W. Bale, A.D. Pelton, and W.T. Thompson: FactSage 5.1: ^ƌ ϮϬ͕ϬϬ Thermochemical Software for Windows.TM Montereal, ϭϬ͕ϬϬ Quebec: Thermfact Ltd., (2002) Ϭ͕ϬϬ [10] ASTM B 409, B 408, B 407, B 564 Ϭ ϯϬ ϲϬ ϵϬ ϭϮϬ ϭϱϬ ϭϴϬ ϮϭϬ ϮϰϬ Ϯϳ dŝŵĞ;ŵŝŶͿ

Fig. 5: Effect of time on concentration of Sr in residue

4. Conclusion

On the basis of the results of the present study of aluminothermic reduction of SrO by Al powder under 1-5 mbar pressure for different stoichiometric amount of reducing agent and time, following conclusions can be drawn:

Highest Sr recoveries were determined as: 1) 96,89 % with addition of 300 % stoichiometric Al and BaO for 240 min., 2) 96,87 % with addition of 300 % stoichiometric Al and BaO for 180 min., 3) 86,45 % and 85,28 % with addition of 200 % stoichiometric Al and BaO for 240 min and 180 min respectively .

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