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Volumetric Determination of Boron in Boron Carbide V

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Volumetric Determination of Boron in Boron Carbide V B. A. R. C.-1017 ei GOVERNMENT OF INDIA ATOMIC ENERGY COMMISSION VOLUMETRIC DETERMINATION OF BORON IN BORON CARBIDE V. K. Manchanda and M. S. Subramanian Radiochemistry Division BHABHA ATOMIC RESEARCH CENTRE BOMBAY, INDIA 1979 B. A. R.C.-1017 GOVERNMENT OF INDIA ATOMIC ENERGY COMMISSION U erf < ffl VOLUMETRIC DETERMINATION OF BORON IN BORON CARBIDE by V.K. Manchanda and M. S. Subramantan Radlochernlstry Division BHABHA ATOMIC RESEARCH CENTRE BOMBAY, INDIA 1979 INIS Subject Category : Bll Descriptor a : BORON CARBIDES BORON QUANTITATIVE CHEMICAL ANALYSIS TITRATION ACCURACY ABSTRACT Boron carbide is used for oontrol rods and as a shielding material In nuclear reactors. As such, the boron carbide must conform to rigid chemical specifications. Impurities present have a significant effect on the life time of the control rods under conditions of high temperature and i neutron flux. Therefore, methods for the accurate determination of the various constituents in boron carbide is of utmost importance. This-report discusses p\volumetric procedure for i •_ . •' i : ((.•>;•" ••%. the, determination of boron content In boron carbide/ '•••>',••. A VOLtCIKTRIC DET3SIINATI0N 0? BCRON IN BORON CAR3IDE by V.K. Jfenchanda and M.S. Subramanian IU7R0DVCT10N Boron carbide is an important nuclear material a.3 it is used in nuclear reactors for control rods and as a shielding material « Preparation of boron carbide yields a product often contaminated with either unreacted carbon or boric acid. These impurities affect the physical, chemical and neutron absorption properties of the material, Particularly under conditions of high temperature and neutron flux in a reactor, tlie life time of the control rods depends on its composition. Thus it was of interest to develop analytical procedures for the precise quantitative determination of various constituents in boron carbide. Ya.P. Gokhstein et al' developed a method for the determination of free carbon in boron carbide, based on the difference in reactivities of free and combined carbon towards chromic acid-sulphuric acid mixture. Results of beveral experiments performed in our laboratory employing this method for Ihe estimation of free carbon suggested an interference due to combined carbon of the boron carbide sample. Similarly our attempts to develop a diffarenti al temperature technique to oxidize - 2 - freo car'aon preferentially ovor combined carbon in a stream of ojygin did not moat with success. In thi-s case too, combined e.irboti rras found to oxidise simultaneously with free carbon. Boron carbide being- covalent in Mature undergoes complete oxidation only at very high temperatures. 'Jha properties of the oxidation products are of prime consideration in predicting the oxidation boh-iviour of the material. The T,redorainant oxidation nrod'ict of boron carbide is a."norpho-.ia or vitreous boron oxidet P.1',. The melting point of this rrabrjtince is around yX)"C and below this tenpomture where B_0_ is too viscous to flow, a protective coitiwr of nmorphoun "O0 is observed en boron carbide. At hipfae.r twjB"r-itiirc3 vaporisation of B_0.,, and formation of miboxi.de B-0 ma.'?? tho oxidttion process conpiax in nature . It TT33 tho«,»ht desirable to explore th« poa'sibility of dsvclopin'.T a method for the estimation of baron content in the boron carbide simple. Boron carbide WM jTuoed Tith fusion mixture and subsequently treated with cone, hydrochloric acJrl. Wiis en rived the nuantifcitive conversion of boron prosent in the sample to boric ncid, ?i volunetric method OT.3 enployod for tfie estimation of'boric acid in a mixture of boric acid end hydrocliloric acid with a precision of + 1.2i. 'Ihe titration of hydrochloric acid aoninot stnncl«ird potassium hydroxide nolut'.on (carbonnt'e-froe) by the usual method imposes several limitations on the indicator to bo enployed. a) Qnl point colour of the indicator should be ouch as not to mask the pink colour of plienolphthloin end point uaed for borio acid titration. b) pK_ should bo as CI030 to 7.0 aa possible to avoid any excess of KOll which may react with borio acid. Oio conventional roethylorange indicator (pKjW - 3« lnvolvoo a substantial blank correction due to the fact that aosa hydrochiorio acid io alraaye loft uatifcrated at the ond point,, Colourloaa paranitropb.onol (pKy_ a 7^) which turns yellow at •fclB end point has been found to be the most suitable araonsat the various indicators « Borio acid acts as a weak monobasio aoid (Ka. - 6.4 X 10 ) and so it cannot bo titra'tod accurately wltii standard KOH. However by t!io addition of certain polyliydro^y corapound3 such as mnnitoX it aoto as & much strotgor acid (Ka ^ 7 x 10 ) and can be titrated to a phonolphthitoin end. point. The effect of polyiiydro:y cccipounda has been explained on the baaia of tl» fomation of 1f1 and 1,2 mole ratio complexes betwoon the borio acid and 1B2 diol aa follows i — C— OH / ^ B(OH) - o/t -f- - 4 - mannito boric acid complex acta as a monobasic acid. A known weight of the sample (<^ 10 mg) of particle size 0.074 mm aperture (tt- 200) was mixed with about 2 grams of fusion mixture and heated'in air in a platinum crucible inside a furnace at 75OPC for about one hour. EVision decompoai. tion of boron carbide is a critical step in the estimation of boron content and care must be taken to prevent Icos of boron by spattering: and assure complete decomposition. Spattering1 is minimised if the temperature increase is carefully controlled especially in the early stages of heating when the exothermic decomposition reaction occurs. In the present v/ork, ttie sample alonij with fusion mixture was heated in a muffle furnace (5.5 KV.') to 75O°C during 50 minutes and was kept at this temperature for 15 Minutes to ensure completion of decomposition. The fused mass was treated with concentrated hydrochloric acid to neueral-se the excess of fusion mixture thereby converting the boron present to boric acid. "One solution was made upto 50 ml and an aliquot of 10 ml was taken for further titration. A drop of paranitrophenol reagent was added to 10 ml of the above solution and titrated against standard potassium hydroxide solution. Ehd point was indicated by the appearance of light yellow colour. 2b this solution about one sram of raannitol was added and the -titration continued with standard potassium hydroxide solution to the appearance of pink colour with phenolphthlein - 5 indicator. Ihe end point was confirmed by further additiona of inannitol. Ttin- blank was determined by taking two gram3 of fusion mixture without tiie sample and following all the steps rigorously. CALCOIATI0H3 Yfeight of the boron carbide sample =• VI mg The fused, mass was treated with cone. Hd and the final volume was made upto 50 ml. 10 ml of this solution was titrated with standard carbonate free KOtt solution of normality » H. Titre value for phenolphthlein ,, , = v nu. and point iTcnnalitj- of boric acid solution «* •• y ••• Eq^ wt. of boric acid ' =61.34 (Basicity =1) '•'/t. of boric u.cid in 50 ral of n x V x 6i.e4 x 50 solution * 10x1000 *» .: of boron in the sample = ^ x V x 61.84 x 30 x 10.811 x 100 1000 x 10 x 61.84 x W Precision and Accuracy A well ground sample of boron carbide was repeatedly analysed to determine the precision of the method. Results of twelve determinations (Table 1) show a precision of 1.20;£ (vs-J). Due to the nonavailability of boron carbide standard, N33 Boric acid, 3RM 951 wa3 analysed to determine the accuracy of the volumetric titration procedure, which wa3 found to be + O.35,o. - 6 - ACKNOWLEDGEMENTS Authors are grateful to Extractive Metallurgy Section, Metallurgy Division, B.A.R.C. far the supply of boron carbide •ample3, Authors axe also grateful to Dr. M.V. Romanian, Director, Radiological Group for his keen interest in the work. REyGREMCES 1. Boron Carbide, Production, Properties, Applications by Dr, Alfred Lipp. Reprint from "Bechnische Rundechan" Nos. 14,28,33 (1965) and 7 0976). translated by Brulat G. Wolff. 2. Va.P. Gokhshtein aid S.V.Panrateva, ZavodsKaya laboratoriya, Vol. 36, 274 (1970). 3. Boron, Synthesis, Structure and Properties,, Proceedings of the Conf. on Boron, Edited by J.A. Xohn, ';!.?. Nye and O.K. Gaule, Plenum Press Inc., New York (i960), Page 175. 4. A text book of Quantitative Inorganic Analysis by A.I. Vogel, Longman (1961) Page 55. 5. A text book oi" Quantitative Inorganic Analysis by A.I. Vogel, Lf igman (1961) page 252 6. Analytical Chemistry of Boron Carbide by H.W. Stromatt, Jtep. HEDIr-SA-452, Conf. 721025-11. Analysis of a Boron Carbide Sample S.Ho. Weight of the sample (nig) i> of Boron 1 24.075 74.95 2 21.490 75.76 3 20.680 75.84 4 26.430 75.97 5 20.725 73.94 6 22.527 75.81 1 11.395 77.72 8 17.146 75.15 9 19.930 75.27 10 22.560 75.70 11 13.525 76.14 12 16.037 75.84 Average i> of Boron 75.67 Standard deviation (a— ) 0.9 # deviation 1.20.
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