Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 446 of 707

umetric flask 1liter and dilute with deionized water to mark. Solution 2: 0,5g of Mg – (4.181g MgCl2 x6H2O), 500 ml of solution 1 dilute to 1liter with deionized water. The solution 2: magnesium chloride was standard- ized against 0,02M EDTA solution, as follows: transfer 20ml of 0.02 M EDTA solu- tion into the beaker. Add 100 ml of distilled water and 5ml of solution NH4OH (1:1). Add indicator Eriochrom Black T to blue color. Titrate with St.solution mag- nesium chloride to change color from blue to reddish. The end point is reached when the solution turns reddish such that one additional drop of titrant produced no visible change in color. Hydrochloric acid (1:1). Mix 1volume of concentrated HCl (d- 1.19g/cm3 ) with 1volume of distilled water. Glycerin (chemical pure). Barium chloride 10%. Dilute 10g of BaCl2 into 100 ml of deionized water. Ammonium hydroxide (1:1). Mix 1 volume of concentrated NH4OH (25%, anal.) with 1volume distilled water. Safeguard Centrifuge (Clay-Adams Inc) was used for centrifuging of the solu- tions. Glass centrifuge tubes (h-135mm, d-25mm); Paster pipet (borosilicate glass l-140mm). Device for separating the solution in the centrifuge tube from the precipitate barium sulfate and aluminum alloys heating block [Al-200mm x 85mm x 125mm (h)] with openings for centrifuge tubes were used in this work. Procedure. Pipette 4.0ml of plating solution into 50 ml glass centrifuge tube. Place the centrifuge tube with solution into beaker with distilled water (water bath). Add 10ml HCl (1:1) and 10ml glycerin and mix the solution by stirrer – Cr (VI) reduced to Cr (III). Place water bath (with centrifuge tubes) on the hot plate and heat to about 75°C. Add 15ml of barium chloride, 10%. Maintain the tempera- ture of the suspension around 75°C for 2 hours, while stirring the suspension dur- ing the first hour. Cool the suspension to room temperature. Centrifuge the sus- pension for at least 10 min. Separate the solution from the precipitate, being careful not to lose any of pre- cipitate of BaSO4. Wash the precipitate with 40 ml of deionized water. Separate solution from the precipitate by the same way. Chromium (III), excess BaCI2, and other ions are separated efficiently from the barium sulfate precipitate after centrifuging and washing 5 times. Add 5 ml NH4OH (conc.) and 20ml of 0,02 M EDTA into centrifuge tube with precipitate. Place centrifuge tube into an alu- minum heating block with openings for centrifuge tubes. Heat the block with four centrifuge tubes on the hot plate and stir constantly with stirrer until all pre- cipitate has dissolved. Cool the solution to room temperature. Transfer the solution into the beaker and wash centrifuge tube with deionized water. Add 5ml of NH4OH (1:1) and indicator Eriochrom Black T, to make the solution light blue. Titrate the solution with standardized magnesium chloride solution. The end- point is reached when the solution turns reddish such that one additional drop of titrant produces no visible change in color. SO4 g/l = [A-KxB]x1.9212 C 445

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