JOURNAL O F RESEARCH of the National Bureau of Standards-A. Physics and Chemistry Vol. 68A, No. 3, May- Ju ne 1964 Crystallization of Anhydrous Copper Sulfate From Sulfuric Acid-Ammonium Sulfate Mixtures Faul M. Gruzensky * (November 26, 1962) The of CuSO, from a sol vent, co mp osed of (N ll ,hSO, an d H2SO, desenb ed . of CuSO, ]n solve nt s of va r. ving (N H ,),SO, to 1-l 2 SO, :'atlo, at 200 C, has been dete rmmed, as well as the te mperat ure dependen ce of th e solubili ty III 0. 35 (N H ')2S0,- 0.6 5H 2SO,. S in gle crystal specimens, \\'e ighi ng up to 150 rna h ave been obta in ed . b 1. Introduction Anhydrous e US0 4, isostru ctur al with orthorhom- bic ZnS0 4, is o( particuhr interest because of it antiferromagnet ic properties at low temperat ur es . Fundamental irwest igations on this co mp ound would be gr eatly enban ce d i( single cr ystal specimens were readil yayailabl e. Kokkoros and R entzeperis [1 ]1 ob tain ed CUS0 4 sin gle cr ystals up to 1 mm. in leno·t h by evaporation of an aqu eo us solu tion ob tained " by CuSO,·5H2 .O in water and adding H2S0 4, C on ditlOl1 S und er wluch tbe anhy dr o us salt m ay be o bt ained from an aq ueo us solution have been d e- scribed in the early li terat ure [2]. Kr eines [3], in ,w effor t to pr epare cr ystal spec imens o( this salt for magnetic susceptibil ity and aniso tropy st udi es CUS0 4 in molten (NH 4)2S0 4; then, by co ntrollmg the r ate of decomposition of the solve nt , he was able to obtain single crystaJs of CuSO,j we ighing up to 2 mg. Like many ot her sulfates, ('US0 4 und ergoes decompositi on before the melting point is reached so that gro wth from the melt und er Il ormall abor atory conditions is precluded. Th e use of a non a qu eo us sol vent appears to be the mo st pr omis in g approach, and experiments in our labora- tory indicate that a sulfuric acid-ammonium sulf ate mi xt ur e offers so me definite ad va ntages over the single components as a s olvent for CUS0 4 single cr ystal growth . 2. Experimental Results and Discussion Starting l' eagents used throughout this work were Baker "Analyzed Reage nt " grad e. Th e e uS0 4 '5H20 was further purified by r ecr ystalliz at ion from di stilled demineralized water , then dehy dra ted by h eating a muffle furnace at 35 0 °C for 24 hI' und er a dry mtro gen atmos ph ere. The anhy dr ous powd ered salt was sto red in a dessicator over phosphorous pentoxid e. 'Nat ional B ureau of Standards, Bo ulder, Colo. 1 Figures in brackets indicate the liter at ure references at tbe end of this paper. Th e sulfuric acid was adju sted to 100 percent comp osl tlOn by a ddin g fuming sulfmic acid to the commercial 96 per cent reage nt , the freezing point method [4] being used to d etermin e wh en the 100 per cent co mp os ition point was reached. Sol vents of . various eo mp os i Lions were then pre- pared by h eaLlt1 g a measur ed quantity of H2S0 4 to 150 DC H , nd ad ding a weighed amo un t of (NH 4)2S 04 to give the desired composition. :1'he solubili ty of CUS0 4 in sol vent s of varying (N H ')2 0 4-H 2S O. r at ios, at 200 "e , is indicated in fi gure 1: The exper imental points were determined by a ddll1 g powdered Cu 0 4 to the sol vent, main- ta ining the temperature at 200 °0 ± 2 °C for 24 lu' to ass ur e equiJibrimn , sampling the so lu tion, and the co pper content and ulf ate content an. d gravimetri cally, r es pectively. fhe s ulf ate anal YSIS was conecteci for tbe amo un t of sulfate present as CUS04 so tbat the ordin ates of fi gur es 1 and 2 show the ratio of co pper to sol vent s ulf ate in the soluti on . As fi gure 1 indicates, th e solubili ty of e US04 in pur e H 2S0 4 is relatively low, bu t increases rapidly as the (N H4)2S 04 content o( the solvenL increases. However, increasing the (NH 4)2S0 4 raLio also in- creases the viscosity of the solv ent at any given te mper at ur e, so th at hi gber Lemperatures arc neces- sary to m ain tain the so lven t in a fluid sta te. Prac- tical workin§o. temperature s are limi ted by the that (NH4 )2 0 4 und er goes consici erable decomposI- tion above 300 DC. Since cr ystal growth is dependent on diffusion through t he solu tion and since bigher visc os ities affect diffusion adv ersely, solven ts of hi gher mole ratio than 0.35 (N H 4)2S0 4 were not co nsidered. The temperatm e depend ence of CuSO. solubili ty in 0. 35(NH 4)2S0C O.6 5H 2S 0 4 is shown in fi gure 2. In determining the ex perimen tal poinLs, the temp er- at ure of the solu tion was co n trolled at the given valu e ± 2 °C and maintained for 24 hI' with occasional stirrings before sampling. A st ud y of the copper content of the solution as a function of time, at the lowest temperature shown in fig ure 2, indicated that 24 hI' was an adequate period to achieve equilibrium . Analyses for co pp er a nd sulfat e were made as indi- cate d abov e. 313 ----- ----