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The vapor pressure of a meta-stable copper lattice Oswald, Drummond Wilson 1931

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> ,j<«*«-i * « * * 1-3 ^  I CAT HO. I~E?.I$7. MH Hh- , Q g | ACC. NO. -^L££jL£~ THE VAPOR PRESSURE OF A META-STABLE COPPER LATTICE BY DRUMMOND WILSON OSWALD A THESIS submitted as part f u l f i l l m e n t of the requirements for the degree of MASTER OF ARTS IN THE DEPARTMENT OF CHEMISTRY THE UNIVERSITY OF BRITISH COLUMBIA MAY 1 9 3 1 TABLE OF CONTENTS Introduction The Copper Atmosphere Production, Duration and Nature of Atmosphere Determination of the Apparent Vapor Pressure Method of obtaining Deposition Discussion of Results I. Effect of Local Heating I I . A Lleta-Stable Copper Lattice Conclusion Appendix I Appendix II Table I Table I I Figure I Bibliography THE VAPOR PRESSURE OF A META-STABLE COPPER LATTICE Introduction -In the common demonstration experiment - the reduction of Cupric Oxide with Hydrogen - the tubes used to contain the Oxide were often found to he heavily plated with Copper, a f t e r the reaction. Preliminary work showed not only that a s i m i l a r effect could he produced using Carbon Monoxide as the reducing agent, but also that t h i s deposit of Copper was not due to the formation and consequent decomposition of Copper Carbonyl. Also, the ;:ydrogen p l a t i n g was not due to an Hydride of Copper, since no Copper Hydride forms under the conditions of temperature employed. The reactions Cu 0 4- H 2 » Cu 4- H20 and Cu 0 f CO = Cu f C0 2 have been investigated "by Pease and Taylor, and Jones and Taylor respectively, and i n each case were found to be autocatalytic; the reduction taking place at the Oxide - Metal interface. The Copper Atmosphere. Since the transfer of Copper was not accomplished "by the decomposition of an unstable compound on the walls, i t must be due to the condensing of Copper vapor on the - 2 -w a l l s . The atmosphere of Copper vapor must-he set up by the v o l a t i l i z a t i o n of Copper during the reduction of the Oxide. Production, Duration, and Mature of the Atmosphere. The Copper Oxide was reduced by Hydrogen i n a boat, above which was an iron tube with a c i r c u l a r aperture in the side. Inside, a close f i t t i n g glass tube received any of the Copper vapor which passed through the aperture. V i s i b l e patches of Copper, representing deposition for ten seconds, could be seen as many as eight times. Since the reaction i s auto-c a t a l y t i c , the reduction usually proceeded along the mass of Oxide~in the boat, in the direction of the gas flow. Hence the vapor-producing area w i l l move along under the aperture. In each series, the visual i n t e n s i t y of the deposit increased to a maximum and then decreased rapidly, as would be expected. The time-extent of the series of depositions varied from eighty to one hundred seconds. When the receiving Screen was not very close to the aperture, the image of the edge of the aperture was not sharply defined, but was blurred, as would be expected from a body of vapor diffusing through an - 3 -aperture, with i t s greatest d i f f u s i o n gradient normal to the plane of the screen. Determination of the Apparent Vapor Pressure. Since the reduction of Copper Oxide under these conditions produces an atmosphere of Copper vapor, a measure of the concentration of the Copper atoms in the vapor would give an apparent vapor pressure. I f t h i s measurement were obtained in the centre of the mass of Oxide, there would "be no effects due to d i f f u s i o n , such as would preva i l at the surface of the mass. From the amount of Copper deposited on unit area i n a given time, the pressure of Copper vapor may he calculated from 4 Langmuir's equation fc I M where p = vapor pressure m - weight of material deposited t - time of deposition S - molecular gas constant M = molecular weight of deposited molecule. T - Absolute temperature. "m" was determined by method outlined in Appendix I. - 4 -Method of obtaining Deposition. The glass reaction boat H c " (Figure I ) , open on the upper surface had glass tubes "B" sealed through i t s ends. The ends of the tubes were melted together u n t i l they would just allow the free passage of 20 gauge Mi chrome wire "D" and at the same time l i m i t the flow of gas through the tubes. The boat was secured in tube "A" by corks "F" to make a gas-tight reaction chamber. One cork also carried a tube "E" for the input of gas, and the other the Tron-Constantan thermocouple "G" . The boat was f i l l e d with Cupric Oxide and the whole was then placed in a small nichrome-wound furnace, which heated the central three-fourths of the tube. While the tube was being heated, i t was flushed with Carbon Dioxide, through S. When the desired temperature was reached the Carbon Dioxide stream was replaced by one of Hydrogen. Taking t h i s as zero time, the wire "D" was moved at d e f i n i t e i n t e r v a l s , usually ten seconds, a distance at least twice the opening "H", thus insuring no overlapping of deposits. The most dense deposits, occuring when the reduction surface was just passing the wire, were analysed "by the method given i n Appendix I. Since the three densest films gave very - 5 -s i m i l a r values for the amount deposited, i t was considered legitimate to take the central value as a measure of the vapor pressure at i t s maximum. Discussion of Results. The vapor pressure obtained (Table I) at 703 - 74-0°K gave 3*35 x 10~3crn. Mercury as the maximum value. At 893-903°K 1.56 x 10~3 wa8 the maximum although more data w i l l be obtained on the higher temperatures. Nevertheless the vapor pressure does not appear to increase with temperature. Theory I. The Effect of Local Heating. The experimental temperature r i s e of the Copper Oxide during reduction was obtained by burying the thermocouple i n the reaction mass. Various forms and p a r t i c l e sizes of the Oxide were used and gave a maximum temperature r i s e of l8o°. (Table I I ) . Prom calculations of the Heat of Reaction of Cu 0 +- H 2 • Cu f H 2 0 at this temperature (Appendix II) the result i n g temperature rise should be 1425° i f no heat were lo s t by radiation and conduction. The observed vapor pressure corresponded to a temperature of 1370°K or a r i s e of 6^0°. The low observed r i s e , and the fact that the surface of the reduced metal was not fused, would indicate that l o c a l heating cannot produce this abnormal vapor-pressure. Theory I I . A Meta - Stable Copper L a t t i c e . 2. The c r y s t a l of normal Copper i s face - centre-cubic inform, with a unit c e l l of side 3«60 Angstrom units. Cupric Oxide i s t r i c h n i c , with a - b * 3*74 A, c= 4.67 A, and i t s angles almost right angles. The removal of Oxygen from Cupric Oxide would produce a l a t t i c e similar to a Copper l a t t i c e (face - centre - cubic) which had been s l i g h t l y expanded i n the a and b directions and greatly expanded in the c d i r e c t i o n . Since interatomic forces are known to be very great, the energy released by the return to the normal c r y s t a l l a t t i c e could conceivably be absorbed by some of the atoms as k i n e t i c energy, thereby giving an appreciable vapor pressure. The apparent constancy of the vapor pressure from 720 to 9°00K could be explained by assuming that the rate of absorption of Hydrogen, at the Copper-Copper Oxide interface, decreases i n the same order as the rate of reaction increases, with temperature. ' This would give r i s e to a production of the Meta-etable Copper l a t t i c e at a comparatively constant rate over t h i s temperature range. The re-arrangement of the meta-stable to normal l a t t i c e would then follow the ordinary p r o b a b i l i t y equation. The similar effects with Carbon Monoxide at higher temperatures could be explained as above, the higher temperature being necessary because of a different adsorption and reaction rate with Carbon Monoxide. Conclusion -In the l i g h t of available data, the abnormal vapor pressure of Copper, 3«35 x 10""3ciri> as compared to the normal vapor pressure at 720°K, about 10'^cm. can only be accounted fo r by the production and disintegration of a meta-stable Copper l a t t i c e . The interest and suggestions of Dr. M.J.Marshall have contributed much to the success of this research and for these I express my sincere thanks. - 8 -APPENDIX I. Method of Determining Copper. A modified. G-ebhardt - Somrner Method ' The Copper deposits were dissolved in I c c . N i t r i c Acid by immersion of the portion of the wire carrying the deposit for 5 seconds. The acid was then neutralized with Sodium Hydroxide solution (litmus) After cooling I c.c. G l a c i a l Acetic Acid, I c.c. 10% Potassium Thiocyanate Solution and 10 drops of Pyridine were added and thoroughly s t i r r e d . The green Copper - Thiocyanate - Pyridine complex was then dissolved i n 5 c.c. Chloroform and the aqueous layer was pipetted o f f . The Chloroform layer was made up to 10 c.c. and compared i n a standard colorimeter with a s i m i l a r l y treated volume of known Copper content. Thus the amount of copper deposited on a known area was found. I f "H" - length of deposit on wire, r = radius of wire w - weight of Copper on length K then w =» wt. of Copper per unit area 2HTrH - 9 -APPENDIX I I . A l l data used was that of Randall-Neilson and West. Cu (s) Cp s 4 . 9 1 f . 0 0 3 , 2 2 T - . 0 0 0 , 0 0 0 , 5 4 T 2 . . • • (1) Cu 0 (s) CP s 8 . 3 2 + . 0 0 7 1 T • • (2) H 2 0 (g) °P * 8 . 8 l - . 0 0 1 9 T 4- . 0 0 0 , 0 0 2 , 2 2 T 2 . . • . (3) H 2 (9) °P • 6 . 5 1 4- . 0 0 0 9 1 . . . ( 4 ) Cu 0 (s) A H 2 9 8 . i =- - 3 7 , 1 5 0 • • • • (5) H 2O (9) A H 2 9 8 . i = - 5 7 , 8 2 0 • • . . (6) Reaction Cu 0 (8) f H 2(g) * Cu (s) f H 2 0 (g). AH - AH. -ACT ^wrr HAQT'+ From (1,23 & 4) BC p = - 1.10 - . 0 0 6 6 8 T + . 0 0 0 , 0 0 1 , 6 8 T 2 Whence JMQ - - 20,060 DH 7 2 0 - - 22175. (Cu (s) 4- H20 (g) ); Cp = 13.72 4- . 0 0 1 3 2 T +• . 0 0 0 , 0 0 1 , 68T2 c D = 15.54 p 7 2 0 .-. Temperature r i s e - 2217? - 1 4 2 5 ° 15-54 Hildebrand's Eguation of Vapor pressure of Copper l Q g P(atmos) ' i ^ 2 P . 5-64 for p =• 3-35 x 10*3 c m - 4 . 4 x io~5 atmos. T - i37e°K. - 10 -TABLE I. Vapor pressure of Copper. - time of deposition 10 seconds I n i t i a l temperature K. "m" grams. pressure - cm.Rg.xl0~3 703 .00241 I.43 733 .00231 1.29 733 .00276 1.56 740 .00330 1.95 703 .00402 2.28 703 .00430 2.24 728 .00531 3.30 730 .00204 (incomplete) 1.17 703 .00587 3-35 Average 2.l6 x 10~3 cm. maximum. 3*35 x 10~3cm. time of deposition 20 seconds. 893 .OOO89 .625 893 .00073 .515 903 .00313 1.01 903 .00487 1-56 Maximum I.56 cm. MO"3 - 11 -TABLE I I . Experimental Temperature r i s e . Form of Copper oxide. Temperature Temperature i n i t i a l f i n a l r i s e 0 CuO powder 530 705 175 Bakers lot.6l022 520 6^ 4 134 535 740 20 5 much s intering Cu 0 - dehydrate 530 640 110 Cu (OH)2 from Cu 0 above ( t i p of thermo couple exposed) Cu 0 wire - ground 530 600 70 520 610 90 Cu 0 wire ground - 530 710 l80 200 mesh. 535 655 120 530 685 155 530 67O 140 530 680 150 530 679 14-9 530 660 130 40 mesh 530 635 105 530 640 110 - 12 -A G ^ * =?=-}// 1 T . .. E 1 ^Cl/J_// f / f(/fj^ r " ~ \— ' JD BIBLIOGRAPHY. Gebhardt and Sommer. Ind. and Eng. Chem. A n a l y t i c a l . Vol. 3. 24 - 1931. International C r i t i c a l Tables. V ol. 1. p. 388 Jones and Taylor. Jour. Phys. Chem. 27,623,1923 E.Langmuir, Phys. Rev. 2, 329, 1913. D.W.Oswald. B.A. Thesis. Dept. of Chemistry U.B.C. 1929. Pease and Taylor. Jour. Am.Chem.Soc. 43,2179.1921. Randall Neils on and V/est. Ind. & Eng.Chem. 23,388, I93I Sievertz and Krumbhauer Zeit - Phys. Chem. 74.277• 


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