PREPARATION of 2-5 µm MAGNETITE POWDER from HIGH CARBON FERROCHROME (Fe-Cr) ALLOY

Transcription

1 PREPARATION of 2-5 µm MAGNETITE POWDER from HIGH CARBON FERROCHROME (Fe-Cr) ALLOY Hossam Halfa 1, Walid M. Daoush 2 1. Steel Technology Department, Central Metallurgical R&D Institute (CMRDI), Helwan, Egypt hossamhalfa@cmrdi.sci.eg; 2. Faculty of Industrial Education, Helwan university, Cairo, Egypt Abstract In the present work, a ferrochrome powder scrap was used for preparing fine chromium powder by leaching process in hydrochloric acid. On the other hand, the remaining iron chloride was used for produce magnetite powder by thermal decomposition of organo-metallic compound of iron chloride with EDTA. Particle size and magnetic properties of prepared chromium and magnetite powders as well as the starting ferrochrome were studied. Chemical composition and structure of prepared chromium and magnetite powders as well as the starting ferrochrome were determined and evaluated. The experimental results show that, the prepared chromium powder has acicular particle shape with around 20 µm particle size. On the other hand prepared magnetite powder has spherical like particle shape with around 2-5 um particle size. The results of the magnetic measurements show that, the starting ferrochrome scrap powder has a ferromagnetic property with a saturation induction 6.5 emu/g but the produced chromium powder has a non-magnetic property with a magnetic permeability 1.1. On the other-hand the prepared magnetite has a ferromagnetic property with a saturation induction value of 86 emu/g. Keywords: Ferrochrome Powder leaching EDTA - Magnetite 1. INTRODUCTION Many of the iron, cobalt and nickel alloys contain high levels of chromium metal. ferrochrome, an alloy of iron and chromium, is used as an additive in steel making. Chromium metal can be made either pyrometallurgically or electrolytically. In the pyrometallurgical [1] method, chromium oxide (Cr2O3) reacts with aluminum powder in a refractory lined or by reduction with silicon in an electric arc furnace [2]. On the other hand, in the electrolytic method a chromium salt solution undergoes electrolysis process which the chromium was deposited on the cathode [3-5]. Magnetite (Fe3O4) nano-particles have attracted an increasing interest in the fields of nanoscience and nanotechnology because of the unique and novel physiochemical properties [6]. Various methods of preparing Fe3O4 nano-particles have been carried out by several techniques [6-9], including co-precipitation, spray pyrolysis, microwave irradiation of ferrous hydroxide, micro-emulsion technique, hydrothermal preparation technique, etc. Recently, mechanochemical processing, a process that makes use of chemical reactions activated by high-energy ball milling, has been successfully used for preparing high quality ferrite nano-particles. In the presence work a ferrochrome powder scrap was used for preparing fine chromium powder by leaching process in hydrochloric acid. The remained iron chloride was used for produce magnetite powder by thermal decomposition of organometallic compound of iron chloride with EDTA.

2 2. EXPERIMENTAL WORK 2.1 Leaching process In the present work, high carbon ferrochrome is ground and leached with a hot solution of 30% hydrochloric acid for 5hr with continues stirring. Hot solution of 30% hydrochloric acid is added, and the remaining is filtered to remove the undissolved solids, which are mostly chromium metal. The filtrate (The remained iron chloride) was used for produce magnetite powder by thermal decomposition of organometallic compound of iron chloride with EDTA. The prepared magnetite and undissolved solids (chromium powder) and are collected, washing and packaging for further investigation. Fig. 1 represents the flow chart of experimental work during the course of this work. Ferrochrome Powder Leaching in 30% HCl for 5hr. Chromium Powder Iron Chloride Fe EDTA Complex formation Particle Size Fig. (3-3) laser particle sizer Analyestte 22 Magnetic Properties Thermal Decomposition CHARACTERIZATIONS Magnetite Fig.1: Flow chart of experimental work. 2.2 Chemical composition and Phase identification of raw and produced powders The chemical compositions of the ferrochrome (raw material), produced powders from leaching process and thermal decomposition process were determined by XRF spectrometer. The ferrochrome sample was prepared for the analyses by crushing and grinding to (20-mesh) size. Identification of various phases presented in the ferrochrome(fine powders), as well as produced powder from leaching process has been carried out by X-Ray diffraction (XRD) technique using Cu kα ( λ = nm) with a nickel filter and a secondary beam monochromatic. Samples are scanned from 10 o to 80 o with scanning rate 2 o /min. The measured (d) values with their corresponding intensities have been compared with the data reported in standard ASTM card index for the identification of the desired phases.

3 2.3 Powders Size Distribution 1. The Particle size distribution of ferrochrome as starting material, produced chromium and magnetite powders were measured using a laser light-scattering particle size analyzer (Model LB500, Horiba, Tokyo). In this approach, the distribution width is define by cite two values on the x-axis, the D50, and D90. The D50, the median, has been defined as the diameter where half of the population lies below this value. Similarly, 90 percent of the distribution lies below the D A semi automatic Carl Zeiss particle size analyzer was used in conjunction with scanning micrographs taken on polished specimen for determination the size distribution of different powders. The size evaluation is based on the equivalent circle area diameter (ECAD). 2.4 Magnetic properties The intrinsic saturation magnetization per unit mass (Bs) were performed in vibrating samples magnetomer (VSM) in VSM LDJ magnetomer. An applied magnetic filed is used to induce a magnetization in different powder samples. The magnetic fields was applied to max value of 5 KOe and then decreased stepwise to zero fields, i.e. from 5 to 0.25 KOe in step of 0.25 KOe, from 0.25 to 0 KOe in step of 0.05 KOe. The measurements were performed in decreasing field in order to create well-defined field history for the magnetization. 3. RESULTS AND DISCUSSIONS 3.1 Chromium powder Chromium has a wide range of uses in metals, chemicals, and material refractories. Its use in iron, steel, and nonferrous alloys enhances hardenability and resistance to corrosion and oxidation; the production of stainless steel and nonferrous alloys are two of its more important applications. Other applications are in alloy steel, plating of metals, pigments, leather processing, catalysts, and surface treatments. Ferrochrome starting powder was prepared by crushing ferrochrome bulk material and sieving then each size were packaged. Tab. 1 shows the chemical composition of high carbon ferrochrome starting powder. Tab. 1 reveals that chemical composition of ferrochrome powder changes with particle size. tab. 1 shows that, increasing ferrochrome powder size accompanying with increase the chromium and decrease iron contents. This result was attributed to small grain size powder has a large quantity of iron carbide and complex iron- chromium carbides (Fe-Cr)23C6 [10] in which iron and chromium are highly corrosion resistace so its too hard to dissolve it in leaching solution. In this work, ferrochrome powder with size 83µm used as starting material for leaching process. During leaching process, the leaching container divided into three parts, first one the undissolved solid (mainly the chromium metal with chromium carbides especially Cr23C6), second the solution mainly consists of iron chloride and, third is black slurry floated above the solution mainly silicon and other contents. After separation each parts undissolved solids are collected, washing and packaging for further investigation. Most of iron was dissolved in hydrochloric acid during leaching process this result was confirmed by comparison between XRD pattern of ferrochrome starting powder and produced chromium powder as shown in Fig. 2. Tab. 1 shows that the chemical composition of produced chromium powder after leaching process using hot 30 % hydrochloric acid for 5 hr. The result of this table confirmed that during leaching process most of iron are dissolved in the hydrochloric acid. The produced chromium particle size depended on initial particle size of ferrochrome starting powder. The Particle size distribution of a investigated material was measured using a laser light-scattering particle size analyzer (Model LB500, Horiba, Tokyo). Chromium powders with a mean particle sizes (d50) of 20 µm and d90 of 50µm are found. The particle size of investigated material characterized by d50 and d90 are

4 given in Tab. 2. The previous results confirmed by image analysis of scanning electron microscopy, SEM photo as shown in Fig. 3 and Fig. 5. Tab. 1: Chemical composition and particle size distribution of investigated powder Tab. 2: Particle size distribution of investigated powder Fig. 2: XRD patterns for the investigated materials where; a) the started ferrochrome powder scrap, b) the prepared chromium by leaching. Fig. 3: SEM micrographs for the prepared chromium by leaching

5 3.2 Magnetite (Fe 3O 4) powder The remained solution (iron chloride) was used for produce magnetite powder by thermal decomposition of organometallic compound of iron chloride with EDTA. X- ray diffraction pattern of decomposition produced was studied, as shown in Fig. 4. This Fig. emphases the high purity of magnetite (Fe3O4) powder and no contamination with other species. This result can be attributed to high affinity of hot hydrochloric acid to dissolve iron from the matrix of ferrochrome starting powder. The mean particle size of produced magnetite was ranged from 2µm to 5µm as shown in Tab. 2. The obtained result was confirmed by using image analysis conjunction with scanning electron microscopy photo. Fig. 5 shows the SEM photo for produced magnetite powder. Fig. 4: XRD patterns for the prepared magnetite powder by thermal decomposition of iron EDTA metallorganic compound. Fig. 5: SEM micrographs for the prepared magnetite powder. 3.3 Magnetic proprties To study the magnetic properties of investigated powders, investigated powders were testing using vibrating samples magnetomer (VSM) in VSM LDJ magnetomer. The results of the magnetic measurements show that, the starting ferrochromescrap powder has a ferromagnetic property with a saturation induction 6.5 emu/g but the produced chromium powder has a non-magnetic property with a magnetic permeability 1.1. On the other-hand the prepared magnetite has a ferromagnetic property with a saturation induction value of 86 emu/g. 4. CONCLUSIONS From this work we can concluded that: 1- Leaching processing can be used for the recovery of chromium metal in the form of powder has acicular particle shape with around 20µm particle size. 2- Thermal decomposition of organo-metallic EDTA complexes is a good method to convert iron EDTA complex to ferrimagnetic microsize Fe3O4 has a spherical like particle shape with around 2-5µm particle size. REFERENCES [1] Mehmet, H. Soner, M. Deniz, Fikret, T. Hexavalent Chromium Removal by Ferrochrome Slag. J. of Hazardous Materials B126.page 176. [2] Kirk, R.E., Othmer, D.F. Encyclopedia of Chemical Technology, Fourth edition, vol. 6. Wiley, New York, pp

6 [3] Chegwidden, J. Chromium Metal An Overview Paper presented at Meta..l Bulletin's 9 th Minor Metals Seminar, Budapest, May 5-7. [4] FitzGibbon, A. Briefing to the Committee on High-Purity Electrolytic Chromium, Marietta, Ohio, March 27. [5] Grayson, M.. Kirk, O. Encyclopedia of Chemical Technology, Volume 6, Third Edition. New York: J. Wiley. [6] Pileni, M.P. J. Phy. Chem Vol page [7] Deng, Y. Wang. L. Yang, W. Fu, S, Eaïssari, A. J. Magn. Mater Vol.194. page 254 [8] Battle, X, Labarta, A, J. Phys., D, appl. Phys Vol. 35. R15 [9] O Handley, R.C. Modern Magnetic Materials: Principles and Applications, John Wiely & Sons, Inc., New Yourk, C.-R. Lin et al./ Materials letters Vol. 60. S [10]