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On the formation and decomposition of zinc ferrite under sintering conditions 1956

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ON THE FORMATION AND DECOMPOSITION OF ZINC EERRITE UNDER SINTERING CONDITIONS by JOHN ROUGHLEY RAV/LING A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of Mining and Metallurgy We aocept this thesis as conforming to the standard required from candidates for the degree of MASTER OF APPLIED SCIENCE Members of the Department of Mining and Metallurgy THE UNIVERSITY OF BRITISH COLUMBIA August 1956 I Acknowledgements The author is indebted to the National Research Council of Canada for the financial assistance which was needed to complete this project. He is grateful to the members of the Department of Mining and Metallurgy at the University of B r i t i s h Golumbia for their advice and assistance, particularly to Professor P. A. Forward, Dr. E. Peters and Mr. J . P. Warner who co-directed the work. i i Abstract The formation of zinc ferrite from zinc and iron compounds, which reacted ander (sintering conditions, has been investigated. A mechanism of ferrite formation controlled by cation diffusion has been suggested and i t has been shown that the nature of the reagents affects the note of ferrite formation. The decomposition of zinc ferrite by alkaline earth compounds, which reacted under sintering conditions, has also been studied. Calcium ferrite was found to be more stable than zinc ferrite but, for kinetic reasons a metastable phase of zinc ferrite was formed more readily. i i i Table of Contents Introduction Page Nos. The constitution of zinc ferrite 1 Review of previous work 2 The crystal structure of spirals and ferrites k General properties of zinc ferrite 5 Scope and object of the present investigation 6 Experimental Procedure Materials used 7 Preparation of mixtures for sintering 7 Method of sintering samples 8 Methods of analysis 10 Recording of Results 11 Results and Discussion Physical Variables 11 The formation of zinc ferrite under sintering conditions lh The decomposition of zinc ferrite under sintering conditions 26 Summary, and Conclusions __ Suggestions for further Work ^3 Appendix A. Microphotographs of powdered reagent 39 mixtures prepared for sintering '"Appendix B. Analytical Methods kl Appendix Co Experimental Data 46 iv Appendix D» Debye=Scherrer diagrpms of reagents 65 used and sinter products obtained Bibliography 67 V L i s t of Figures Page HPS, Fig. 1 Sectional view of sintering furnace 9 Fig. 2 Effect of sintering mixture I at various temper* atures for periods ranging between 30 minutes and 2k hours. 1$ Fig. " 5 Effect of sintering mixture II at various temperatures for periods ranging between 30 minutes and 2k hours. 17 Fig. k Effect of sintering mixture III at various temperatures for periods ranging between 30 minutes and 2k hours. l 8 Fig. 5 ' Arrhenius-piots. 21 Fig. 6 Effect of temperature variations on the sintering of different starting mixtures of zinc and iron compounds. 2k Fig. . 7 Arrhenius plots. 25 Fig. 8 The effect of composition, sintering time and temperature upon the depomposition of zinc ferrite by calcium oxide. 29 Fig. 9 The effects of temperature and calcium oxide content upon sinter products. 32 Fig. 10 The effect of sintering time upon the composition of sinter products from a GaO-ZnO-FegOa ternary mixture. 3k 1 ON THE FORMATION AND DECOMPOSITION OF -ZINC FERRITE UNDER SINTERING .CONDITIONS INTRODUCTION) During the early development period of a hydrometallurgical process for the extraction of zinc, which took place towards the end of the nineteenth century, i t was noticed that, while most of the zinc present in the calcined ore could be leached using cold dilute sulphuric acid, there remained a residue which could only be extracted by prolonged boiling, It was recorded^) that the solution formed by leaching the Insoluble residue in boiling acid invariably contained zinc and iron i n the atomic ratio of one to two, with the conclusion that the iron present in the ore combined with the zinc to form a refractory compound. That this compound is the result of the combination of zinc and f e r r i c oxides during the dead roasting of sulphide ores and concentrates was suggested by Prost (j) and has been considered as probably by others ( l , hf 5). The Constitution of Zinc Ferrite The compound formed by the reaction of zinc and f e r r i c oxides has been placed In a general class of many such products Which are known as ferrites* In l&hj Ebelman (6) succeeded in syntheslsing a number Of spirtels by fusing the component oxides i n boric acldj among these7 was zinc ferrite which was obtained as small black octahedral crystals. Their general properties were as followss- Streaks dark brown Hardness? scratched felspar with d i f f i c u l t y Specific Gravity. 5»13. 2 Solubility, insoluble in dilute hydrochloric acid Slightly magnetic. Upon analysis, the compound was found to contain 66.5$ PegOa and 33".8j£ ZhO, corresponding to the formula ZnFeaO*. The synthetic compound was found to be similar In a l l respects to naturally occuring PrankllTirte. Subsequent investigations into the constitution of zinc ferrite made by other workers have contributed a variety of resultsj some have claimed that more basic compounds than Ebelman*s occur while others claim that this Is not possible. Similar disagreement i s found in the observation of magnetic properties. Recently Kushtoa and Amanuma (7) have concluded that zinc ferrite i s a stoichiometric compound having the formula ZnFe204 and i s normally nori magnetic. They found that, above 1025*C, solid solutions of both ferric and zinc oxides In zinc ferrite were formed and that, when heated to higher temperatures the dissolved f e r r i c oxide lost oxygen, forming magnetite, and the specimen became ferromagnetic. Review of Previous Work Most of the work done i n investigating the chemical properties of zinc ferrite (2, kt 8, 9, 10, 11, 12) has been directed towards the extraction of Its zinc content or the suppression of i t s formation during industrial roasting operations. Some work has been done in the investigation of the reactivities of reagents in solid state reactions^j) although the knowledge of reaction mechanisms i s limited. The physical condition of reagents In solid state reactions is' of major importance when the rate of reaction Is being considered. Clearly the surface area of components and the degree of mixing and 3 packing are important but the crystalline structure of reagents and products may also affect the rate of reaction profoundly. In the formation of ferrites i t has been shown (13) that the ferric oxide used has a widely varying reactivity depending on i t s physical form. ( l k s 15, 16) There are two principal forms of ferric oxide. The more stable form, o< PegOa, has a corundum structure and is formed by such processes as the oxidation of ferrous sulphate at high temper- atures (about 800*C). The other form. Feg03, has a spinel structure and x-ray analysis shows that i t s lattice spacing is almost Identical to that of magnetite. It is formed by carefully oxidizing magnetite at 200*C or by precipitating ferric hydroxide from aqueous solution and calcining the precipitate at about 200*C. At 550*C "ft FezO^ changes, non-reversibly, toe^FegOs. It has been shown (9S If) that the form of the fe r r i c oxide and the number of i t s lattice imperfections have a marked effect upon i t s reactivity during the formation of f e r r i t e s , the V ferric oxide being the most reactive. Methods of mixing reagents for the preparation of ferrites In the laboratory are of three main types. Ebelman (6) used a method in which the reagents were fused i n boraxj other workers have prepared mixtures of solid reagents by mechanical means (7, l8) or by precipi- tating them as carbonates or hydroxides from aqueous solution (7, l 8 ) . Again, some investigators have isolated ferrites from the leach r e s i - dues of industrial extraction processes (2, 10). The rate and mechanism of ferrite formation w i l l therefore be controlled by the method by which reagents are prepared. The preparation of ferrites from mixtures of solid reagents has generally been done by sintering i n furnaces whose temperatures were controlled within the limits of % 5®C or less. In most cases furnace atmosphere was not controlled except where ferrimagnetic ferrites were being formed for magnetic measurements(l8). The Crystal Structure of Spinels arid:Ferrites The spinel structure is one in which the oxygen ions are arranged in cubic close=packing and which contains two species of cations, A and B, having tetrahedral and octahedral coordination with the oxygens. The crystallographic unit c e l l contains thi r t y two oxygen atoms j there are equivalent positions for eight metal atoms, of species A, surrounded tetrahedrally by four oxygen atoms and for sixteen metal atoms, of species B, surrounded octahedrally by six oxygens. The unit c e l l may be consi- dered as containing eight AB2O4 units. Where A is a divalent cation and B is a trivalent cation i t has been calculated (19# 20) that the normal structure, as described above, is the stable one, = assuming that the crystals are completely Ionic. It i s concluded that M*** cations prefer octahedral sites with the exception of Fe***, In*** and Ga*** which prefer a coordination of four. Some divalent cations also show a strong preference for the tetrahedral sites and of these Zfi** i s one. Therefore while most ferrites are 'inverted' (i.e. some Fe*t* replaces M** in the tetrahedral sites e.g. Fe***(Mg** Fe***) O4,) zinc ferrite i s a normal spinel having the Znt* coordinated with four oxygens. 5 Bearing In mind the nature of the spinel structure and the energies of the tons associated with i t , i t is not d i f f i c u l t to believe that Fe3C\4, ( F e + + + (Fe 4 4 - F e + + + ) O4) can easily be converted to t FezOa which retains the cubic close packing of the spinel but which contains only 21 l / ? iron atoms per unit c e l l . In considering the ferrites of certain alkaline and alkaline earth elements i t i s found that, owing to the size of the cations, complex oxide structures prevail.(21) Thus calcium aluminate has the formula 3Ga0ol6Al2°3 and i t seems l i k e l y that calcium f e r r i t e w i l l also be of complex form.(10) It should be noted that In many of these complex oxides x-ray analysis shows that they are closely related to the spinel structure.(20) General,Properties of Zinc Ferrite The general chemical properties of zinc ferrite have been studied by a number of investigators in an attempt to find suitable methods by which this compound can be decomposed. I t has been found that, when the compound is heated above 560®C in a retort with carbon, i t dissociates giving zinc oxide and ferric oxide.(9, 12) In an atmoshpere containing 7.5$ sulphur dioxide i t was found that zinc: ferrite was decomposed at ^50*0 giving zino sulphate and ferric oxide (11, 12) The reaction was slow, however, and though i t has been tried on an industrial scale i n sulphating roasts i t was not successful. A more promising method of decomposition was indicated by Schwartz and K)rauskopt (10) who showed that zinc ferrite was decomposed by sintering with oxides of the alkaline earth elements. When magnesium oxide was used, no more than 37$ of the available zinc was rendered soluble n° matter how great an excess of 6 magnesium oxide was added. Using calcium oxide in the ratio of r 3Ga0iT ZnPeaO* as much as 8756 of the available zinc was rendered soluble. From x=ray diffraction studies i t appeared that magnesium oxide replaced the zinc oxide In the spinel lattice while in the case of the calcium oxide a new structure was developed. The properties of zinc ferrite have been summarised as follows?(8) Colours Deep orange brown Specific Gravityg 5»09 to 5.29 (57322 and '5'.'3^9 calculated from la t t i c e parameters) Hardness ? 5".5'- (mohr "s Scale) o Unit lattice? aQ=*8.k2i 0.01A (mean of 7 values) Melting Point? 1599C Crystal Form? Cubic •- octahedral Scope and Ob.leot of the Present Investigation The present Investigation has been made with the object of expanding the existing knowledge of the mechanisms by which zinc ferrite is formed and the conditions which favour i t s formation and decomposition during sintering. .At the outset, a study of physical variables affecting solid state reactions was made i n order to select an experimental procedure which yielded reproducible results. Following this preliminary investigation, the study was continued in three major sections, namelys- 1. Factors affecting the formation of zinc ferrite from various starting mixtures. 2. Factors affecting the decomposition of zinc ferrite by the addition of calcium and magnesium salts. 7 J. Factors affecting the formation and decomposition of zinc ferrite on sintering ternary mixtures of zino oxide, fe r r i c oxide and calcium oxideo EXPEKMEN'rfiL PROCEDURE" Materials Used A l l materials used i n this Investigation were of reagent grade with the exception of calcium and magnesium compounds which were a l l chemically pure. The fer r i c oxide used was prepared by the thermal decomposition of ferrous sulphate under controlled oxidising conditions at temperatures lying between 760®C and 950"Co Preparation of Mixtures for Sintering Three methods were used to prepare mixtures for sintering.- (a) Mechanical Mixing Mixtures of zinc and fer r i c oxides were prepared by weighing the required amounts of the constituents and rol l i n g them together in a bottle for twenty four hours. (b) Co-precipitation Zinc and ferric hydroxides and carbonates were co-preclpitated from an aqueous nitrate solution by the rapid addition of a strong solution of sodium carbonate. The precipitate was washed, f i l t e r e d and oalcined at 500 9G to decompose hydroxides and carbonates present. (c) B a l l Milling The desired components were mixed by grinding them in a quartz pebble mil l with a grinding f l u i d i n which they were insoluble. 8 Usually water satisfied this requirement but i n one ease, where zinc sulphate was being mixed, ethanol was used. The procedure f o r mixing was as followss- The charge, which varied from 120 to 350 grams of solids, was placed in the m i l l together w i t h 1000 to 1250 ml. of grinding f l u i d , the amount depending upon the size o f the charge. The mixture was then ground for two hours, washed f r o m t h e m i l l , f i l t e r e d and dried i n readiness for Sintering. Mixtures thus produced w e r e studied under the microscopej components appeared t o b e evenly distributed through the mixture and had an average particle diameter of about half a micron (see Appendix A). Method of Sintering Samples Two Identical furnaces were used for sintering (see f i g . 1). Each consisted of a fused s i l i c a tube 26 inches long and 1 inch l . d . surrounded by a 600 w a t t heating element i t s e l f contained In a f i r e - brick block 15 x 9 x 9 in overall dimensions. The element was connected i n series with t h e secondary of a variable transformer and, by suitably adjusting t h e l a t t e r , the power output could be adjusted u n t i l a minimum temperature fluctuation of the furnace was obtained. Temperature control w a s effected by a cbromel-alumel thermocouple which was placed i n the centre of the furnace tube and was protected by a fused s i l i c a well. The thermocouple was connected to a Wheelco pyro- meter which was capable of controlling the temperature to within t 5*C at 100*C| the pyrometer was calibrated by means of a potentiometer before each experiment. 1. Fused s i l i c a thermocouple well. 2. Fused s i l i c a furnace tube. 3» Heating element. k ."The rmoc ouple. 5. Porcelain boat carrying charge. 6. Refractory Insulating material. To : Variable Transformer. Fig. 1 Sectional view of sintering furnace. 10 The furnace atmosphere, which was not controlled, consisted of a mixture of a i r and any gaseous products of calcination which were formed during sintering. Sintering operations were carried out as follows s The furnace was f i r s t run up to the required temperature and allowed to stand for about an hour u n t i l temperature fluctuations had decreased to less than t 5*C. The sample to be sintered (about 10 grams) was placed in a glazed porcelain boat (2 x 10 x 1.5" cm. in overall dimensions) which was then pushed into the centre of the furnace. After sintering, the boat was removed from the furnace and allowed to cool In a i r . In cases where the sintering period was only thir t y minutes in length, boats were preheated in the furnaces and small samples (3 or h grams) were added to reduce the time needed to bring them to temperature. Samples for analysis were prepared by grinding the sinters with pestle and mortar and then r o l l i n g them prior to weighing. They were then analysed by conventional chemical methods (see Appendix B.) In order to determine the t o t a l amounts of zinc and iron present and also the amounts of zinc which had not combined with ferric oxide to form zinc f e r r i t e . Since the zinc present as zinc ferrite Is relatively refractory, i t i s not d i f f i c u l t to separate i t from the zinc remaining as uncombined zinc oxide* carbonate or sulphate, hereafter referred to as soluble zinc. The solvent used was an ammonia-ammonium chloride solution as used by Methods of Analysis 11 Hopkins (8) and by many o f the o t h e r I n v e s t i g a t o r s I n t h i s f i e l d . B y t h i s means ' s o l u b l e 8 z i n c was d i s s o l v e d as an ammine l e a v i n g b e h i n d a r e s i d u e o f z i n c f e r r i t e and f e r r i c o x i d e . S o l u b l e f e r r o u s Ion was not d e t e c t e d . The r e s u l t s obta ined by c h e m i c a l a n a l y s i s were recorded and from them the amounts o f z i n c f e r r i t e i n s i n t e r e d samples were c a l - c u l a t e d . I n o r d e r t o compare the f e r r i t e y i e l d s o f m i x t u r e s c o n t a i n i n g d i f f e r e n t z i n c - i r o n r a t i o s the atomic r a t i o o f the z i n c present as f e r r i t e t o t o t a l i r o n was t a k e n as the a b s o l u t e y i e l d o f f e r r i t e . P h y s i c a l v a r i a b l e s such as p a r t i c l e s i z e , degree o f p a c k i n g and m i x i n g technique were i n v e s t i g a t e d i n o r d e r t o f i n d methods f o r t h e i r c o n t r o l I n subsequent e x p e r i m e n t s . T h e i r e f f e c t s upon f e r r i t e " f o r m a t i o n were not s t u d i e d f u r t h e r . ( a ) Methods... o f M i x i n g The v a r i o u s t e c h n i q u e s employed f o r m i x i n g reagents p r i o r t o s i n t e r i n g have been d e s c r i b e d above. M i x t u r e s o f z i n c and f e r r i c o x i d e s were prepared by each o f these methods and samples were t h e n s i n t e r e d over a range o f temperatures f o r f o u r hour p e r i o d s . S i n t e r p r o d u c t s were analysed and compared on the b a s i s o f t h e i r f e r r i t e y i e l d (Table I ) . R e c o r d i n g o f R e s u l t s RESULTS AND DISCUSSION 12 TABLE I Results of^ SInt erf R l fixtures of \Zl^irana^.FBrriq,403cldag. (approx molar ratio 1 sl) prepared by^^ry^Rbl^^^-Cc-rv.o precipitation .and Wet Grinding Methods. Prepared by Dry Rolling - mixtures A and B Prepared by Co-Precipitation - mixture G Prepared by Wet Grinding - mixtures D, Es F and G« Sintering Time - k hours F G Sintering Ratio =Zn combined as ferrite s Total Temp. *C. A B C D E 650 .050 - => 700 .050 .466 M9 A69 750 .161 - .458 A79 .48i 800 - .302 .446 .486 .487 850 .212 - .464 = - Calcine .372 .487 .488 A l l mixtures prepared contained 1 gram molecule of-zinc oxide and 1 gram molecule of ferric oxide except mixtures F and G which contained half a gram molecule each. 13 Results showed tbsSrt mixtures prepared by dry ro l l i n g (A arid B) did not sinter uniformly and gave a low yield of f e r r i t e . Sinters of the co-precipitated mixture were found to be uniform and a high yield of ferrite was obtained. However an anomalously large yield of fer r i t e was formed during the calcining process prior to sintering. I t was concludedo from comparing the results with those subsequently obtained by sintering a mechanical mixture of zinc carbonate and ferric oxide, that the ferric oxide produced by the copreclpitation method was highly reactive and did not resemble the form produced by roasting ferrous sulphate. Sinters produced from mixtures prepared by the wet grinding method yielded large amounts of fer r i t e and results were found to be reasonably reproducible even when the size of the b a l l m i l l charge was reduced by half. Contamination of the charge with s i l i c a from the m i l l was not great and averaged 0.5$ of the total charge, plus or minus 0.1$. Preparation of mixtures by dry rol l i n g was discarded in favour of one of the others since the results of sintering were not reproducible. Of the remaining two methods the wet grinding method had the advantages in that the components of the mixture could be chosen more freely, that mixtures were prepared more simply and the results of sintering them were reproducible. It was therefore used i n a l l subsequent experiments. (b) Effects -. df Packing Several tests were run in order to discover the effect of packing on sintering. Samples were prepared as loose powder and as bars com- pressed at "57000 p s i . "Results are tabulated i n Table 2 and show that the variation in sinter product was small. 1* TABLE' II Samples prepared by wet grinding Sintering throes- h- hours Types of Packings (l) Powder (2) Powder compressed into bars at 57000 psi. Sintering Temp. Atomic Ratio = Zn combined as ferrite? Total Fe. •C (i) ( i i ) 8oo 0.̂ 85 0.485 660 o A l O 0.4oi 6ko 0.270 0.261 620 0.110 0.102 THE FORMATION OF ZINC FERRITE UNDER SINTERING CONDITIONS (a) The Effects of Sintering Time on the Composition of Sinter Products obtained from mixtures of Zinc, and,Ferric Oxides. The rate of formation of zinc ferrite from sintered mixtures of zinc and fer r i c oxides was Investigated i n an attempt to establish the controlling mechanism of fer r i t e formation. Mixtures of varying prop- portions were used to observe their effect on the rate of formation of ferr i t e and to establish the solu b i l i t y limit of zinc oxide i n zinc fe r r i t e at the sintering temperatures selected. The following mixtures were prepared for sintering I. ZnO-Fe2C>3 (atomic ratio ZnsFe Ockjksi A ) ft Exact atomic ratios of ZnsFe were determined by analysis of the mixtures. 15 I I . ZnO-PegOs (atomic ratio ZnsFe 0.466.1) I I I . 2 ZnO-FegOa (atomic ratio ZnsFe 0.9^0si) Samples of these mixtures were sintered at selected temperatures between 60p*C and 10509C for periods ranging from 30 minutes to 2k hours In length. The results* of these experiments are summarised in f i g s . 2, 3 y and ko They show that the relationship between the yield of fe r r i t e and the square root of the sintering time is approximately linear u n t i l the reaction approaches completion, when the rate gradually decreases. The plots f a i l to Intersect the time axis at the origin, the length of the intercept being some inverse function of temperature. This i s suggestive of an Induction period In which nucleation takes place. In the f i r s t two series i t was noted that at the conclusion of the reaction a l l the available zinc was converted into f e r r i t e . In the third series, where excess zinc oxide was added, the atomic ratio of insoluble zinc to total iron, in the equilibrium condition, was rather greater than 0.5 and appeared to increase sl i g h t l y with temperature. This indicated that there i s limited solid s o l u b i l i t y of zinc oxide in zinc f e r r i t e . An explanation of the linear portion of the graphs obtained may be made by considering a diffusion controlled mechanism of ferrite formation which is analogous to that developed by Mott (23) to explain the formation of thin oxide films on certain metal surfaces. In the present case, where zinc and ferric oxides are i n contact, i t is suggested that zinc ferrite i s fqrmed at the interface and the rate of growth of the ferrite film ft see Appendix C for experimental data. Pig. 2 - Effect of sintering mixture I at various temperatures for periods ranging between 30 minutes and 2k hours. 17 0.5 "V Time - hours. Pig. 3 ^ Effect of sintering mixture U at various temperatures for periods ranging between 30 minutes and 2k hours. 18 Pig. k - Effect of sintering mixture H I at various temperatures for periods ranging between 30 minutes and 2k hours. 19 is determined by the rate of diffusion of the cations* through the film. The diffusion of one species of cation, say Z h + + , in zinc ferrite i s now considered.If n(x) is the number of zinc ions per unit volume at a distance x from the zinc oxide-ferrite Interface, the flow of ions i s given by J = ̂ n Di ... (1) 3 x where J is the number of ions diffused per unit area per unit time and Di is the d i f f u s i v i t y . It i s assumed that h=o at the f e r r i t e - f e r r i c oxide interface. I f no is the concentration of zinc ions In the ferrite i n equilibrium with zinc oxide then x The rate of growth of the fer r i t e film i s given by the expression dx = J a (3) dt where Si i s the volume of ferrite per metal ion. Substituting in equation (2) we have dx - no-ft Di (k) dt x and by rearranging and Integrating x 2 = ZnoQ. Di t - A (5) or x = V At . .. (6) where x, being a measure of the thickness of the fer r i t e film Is also proportional to the ferrite y i e l d . ft Mott assumes that oxygen ions cannot diffuse i n t e r s t i t i a l l y in such films owing to their relatively large size. 20 Arrhenius plots (see f i g . 5)were constructed from! the series of experimental data obtained from sintering mixtures I, "II"and III as described above. The plots were rather indefinite since the amount of data available was small. However, a linear plot was obtained from the results of series IX (mixture XT) and the points obtained from the other series appeared to belong to parallel but not coincident plots. The fact that the plots do not coincide indicates that different frequency factors were obtained for different mixes owing to variables which were beyond the experimental control adopted. The activation energies obtained from the Arrhenius plots are given in Table III below§ TABLE III \ Experimental Series Activation Energy Series I J6 K Gal. Series II 25 K Cal. Series III 26 K Cal. These values are of the order which might be expected for a diffusion mechanism. Lindner (2k) has measured the d i f f u s l v i t i e s of both zinc and iron i n zinc ferrite and found them to have approximately equal values, The activation energies of both processes, measured by him, are given below. Diffusion of Zinc In Zino f e r r i t e j Activation Energy 86 K Cal. Diffusion of Iron i n Zinc f e r r i t e | Activation Energy 82 K Cal. 21 0.0 • : Data obtained from series I. O i Data obtained from 'Uterlik I I . O i Data obtained from series I I I . 0.00108 0.00110 0.00112 1 T° abs. 0.00114 0.00116 Pig. 5 - Arrhenius plots. 22 These values are high in comparison with the ones obtained i n the present work. However results obtained by the radio tracer technique as used by Lindner, were subsequently shown to give erroneously high values in similar systems (25). There Is, therefore, the possibility that Lindner's work i s in error. The object of the following series of experiments was to discover the effect of reacting mixtures of different reagents, containing zinc and iron^ upon temperature of formation of zinc f e r r i t e , and i f possible, to determine the mechanisms of ferrite formation. The following mixtures were prepared for sinterings= Zn(GH)2 - Fe203 (atomic ratio ZnsFe O.530sl) Zn GO3 - Fe203 (atomic ratio ZnsFe 0.530si) ZnO - Fe203 (atomic ratio ZnsFe 0.482sl) ZnS04 - Fe 20 3 (atomic ratio ZnsFe 0.510jl) Samples of these mixtures were sintered for four hours at constant temperatures which ranged from 300*C to 1000®C. The results, summarised in Fig. (6), were similar for each series excepting that the temperatures of ferrite formation were different in each case. In the case of the zinc oxide-ferric oxide series, ferrite was formed i n the temperature range 575*0 -~ 675*0, whilst for the zinc carbonate-ferric oxide series this temperature range was lowered by some 30°C and for the zinchydroxide-ferric oxide series by about 75*C. 23 The results do not afford a satisfactory explanation of these phenomena^ In both the latter cases the zinc compounds could have been decomposed, forming a gaseous product and zinc oxide, below the temperatures at whioh ferrite formation occurred and i t i s considered that the lowering of the temperature of ferrite formation could be due to the presence of a more highly disordered and, con- sequently, more active form of zinc oxide than was present In the zinc oxide-ferric oxide mixture. In the case of the zinc sulphate-ferric oxide series i t was noticed that l i t t l e f e rrite was formed u n t i l the temperature of decomposition of zinc sulphate was reached, with the inference that, when zinc ferrite i s formed from zinc sulphate and fe r r i c oxide, the reaction goes in two stepss 1. Z n S 0 4 - » 2 n 0 •+ SO3 2. ZnQ + P e 2 0 3 -»Zn PegO^ Therefore It appears that the temperature of ferrite formation depends upon the thermodynamic properties of zinc sulphate. The reverse reaction, namely the formation of zinc sulphate from zinc ferrite by the action of an oxidising atmosphere containing sulphur dioxide has been observed at 450*C.(25) Arrhenius plots, constructed for each series of experimental data, are shown in f i g . 7 . They were found to be approximately linear except at low temperatures when their gradients were found to increase. This suggests that the activation energy for the formation of zinc f e r r i t e decreases with an increase i n temperature. Activation: energies 2k F i g . 6 - Effect of temperature variations on the sintering of different starting mixtures of zinc and:iron compounds. ZnSO* - Pe20 3 O . O O O 9 4 0.00096 O.OOO98 -AiV- 1 T°abs 0.00106 ZnO - Pe203 0.00108 0.00110 0.00112 O 0.00114 O -ZnCOa - FeaOs 1_ : 0.00110 0.00112 0.00114 P i g . 7 " Arrhenius plots 0.00116 O Zn(QH)2 - FeaOs _l I 0.00120 0,00122 0,00124 0.00126 T°abs 26 Were calculated from the stralghtest portion of the Arrhenius plots and are tabulated in Table -IV belows TABLE IV Activation Energies fojt?. the Ffraaatlon >of Zinc Ferrite from various starting mixtures. Starting Mixture Activation Energy Zn(OH)a - Fe s03 49 K Cal. Zn CO3 - FegOs 54 K Cal. ZnO - FegOs ?2 K Cal. ZnSC* - FegOs 54 K Cal. THE DECOMPOSITION OF ZINC FERRITE UNDER SINTERING CONDITIONS (a) The Effect. of Temperature on the j peoompos It iton of Zino Ferrite by In considering the decomposition of Zinc ferrite, i t was thought that zino might be replaced in the spinel structure by more basic elements such as the alkaline earths. Swartz arid Krauskopf (9) have already indioated that this is possible, at least to some extent, and i t was decided to extend their study by discovering the effect of sintering different oalcium and magnesium salts with samples of zinc ferrite. Zinc ferrite was prepared by sintering an equimolecular mixture of zinc and ferrio oxides at 850°C for six hours. Samples of ferrite were then mixed with one of the following compounds In approximately one to one5 molar ratio s- Calclum oxide; Calcium Carbonate; Calcium Sulphate; Magnesium oxide; Magnesium Sulphate. several Calcium and Magnesium Salts. 27 Samples of the mixtures obtained were sintered for two hours at 750*C, 850°C, 950'C and 1050*C and then were analysed. The results, given In Table"V, show that zinc ferrite was decomposed by a l l the compounds added with the exception of calcium sulphate. TABLE V Effect of Temperature, on the Decomposition of Zinc Ferrite by several Calcium and Magnesium salts. Added Compound Ratios- Insoluble Zinc/Total hon. 750*C 850°C 950®c 10509C CaO 0.462 0.451 0.4io 0.524 CaCt>3 0.457 0.451 0.578 0.289 CaS04 0.454 0.453 0.448 0.444 MgO 0.448 0.598 O.554 O.561 MgS04 0.442 0.419 0.259 0.299 Atomic Ratio Total Zn/Total Fe - 0.466sl (b) The Effects of Composition. Sintering Time and Temperature upon the Decomposition of ZInc Ferrite by Calcium Oxide. An attempt was now made to explain the mechanism by which zinc i s replaced In zinc ferrite by calcium and magnesium when mixtures of zinc fe r r i t e and a compound of calcium or magnesium are sintered together. Calcium oxide was chosen as the added compound since the reaction between oxides in ferrite formation is probably simpler than those which occur between other salts and since calcium was found to react more favourably than magnesium by previous investigators (10). 28 Zino ferrite was prepared by sintering an equimolecular mixture of zinc and iron oxides for eight hours at 850'"C. Three samples of zinc ferrite were then mixed with calcium oxide In the approximate molar ratios'(ZnFeaO^sCaO) I s l , Is2, and 1?4 respectively. Samples of each of these mixtures were then sintered at 850*C, 950°C and 1050*C for periods varying from one to eight hours. The results show that zinc previously combined as ferrite is rendered soluble In varying amounts. Zinc oxide was identified in the sinter productrby the comparison of x-ray diffraction patterns* of pure zinc oxide and of the sinter product. Rate curves were plotted (see f i g . 8) for the decomposition of zinc ferrite by calcium oxide. The amount of zinc rendered soluble, being proportional to the amount of calcium reacted, was plotted against a time base. It was noted that the reaction went very quickly at the start but approached equilibrium very slowly. The amount of zinc rendered soluble increased with the lime content u n t i l 90$ of the zfLnc could be rendered soluble i n a mixture of kCaOslZnFeaO*. No explanation for the mechanism of the reaction was apparent. Soluble zinc present In sinters formed at l O ^ C was found d i f f i c u l t to extract. Resampling and redetermining,soluble zinc in these sinters after further grinding showed an increase In the yield obtained. This indicates that soluble zinc determinations made on sinters produced at 1050°C are unreliable and results have therefore & See Appendix D. 29 80 h 60 h 4 0 20 4Ca0 - ZnFejjO^ V - 950°C 0 - 850°C 2Ca0 - ZnFeoO. A - 950°G • - 850°C CaO - ZnFe20A O «= 950°C O - 850«!C 4 6 Time -.hours. Pig.8 - The effect of composition, sintering time and temperature upon the decomposition of zinc f e r r i t e by calcium oxide. 3 0 been discarded. Similar treatment of lower temperature sinters produced no variation in soluble zinc content. ! The sinter products obtained at 1050®C ; were found to be much more strongly cemented than those produced at lower temperatures. This Observation together with those of the previous paragraph suggests that incipient fusion took place at about 1050°C.. THE FORMATION AND DECOMPOSITION OF ZINC FERRITE ON SINTERING TERNARY MIXTURES OF ZINC OXIDE, FERRIC OXIDE AND CALCIUM OXIDE. Having shown that zinc ferrite i s decomposed by sintering with calcium oxide, It was decided to investigate the possibility of using calcium oxide to inhibit the formation of zinc ferrite during the sintering of mixtures containing zinc and ferric oxidesg- (a) The Effects of Temperature and Calcium Oxide content upon Sinter Products Mixtures of the three component oxides were prepared using the molar proportions CaOsZnOsFeaOs of l s l s l and 3 ? l i l respectively. Samples were sintered for four hour periods at constant temperatures which ranged from 600*C to 3 . 0 5 0 9C. The results of these experiments are shown in f i g . 9« They show that, i n the sintering period chosen, l i t t l e zinc was rendered insoluble u n t i l a sintering temperature of 6 5 0 9 C was reached and that a maximum yield of insoluble zinc was obtained at 7 5 0®C. In comparing the results obtained from the Zinc oxide-ferric oxide binary system, (see f i g . 6 ) i t can be seen that the temperature at which an appreciable 31 amount of zinc ferrite was formed under the selected sintering conditions was Increased by some sixty degrees. It seems probable that this Is due to the calcium oxide acting as a comparatively;inert diluent in the lower range of sintering temperatures. About 7 5 0 * 0 the amount of insoluble zinc was found to decrease slowly in the case of the lean calcium oxide ternary and more rapidly In the case of the richer mix with the inference that, between 750°C and 1050*C, calcium ferrite is more stable than zinc ferrite. The experiments show that calcium oxide may Inhibit the formation of zinc ferrite during the sintering of CaO-ZnQ-FesOa systems by one or i ' : more of three mechanismss- 1 . By acting as a'diluent which makes zinc ferrite formation less rapid. 2. By combining with ferric oxide to form calcium ferrite. 3 . By displacing zinc oxide in zinc ferrite to form calcium ferrite. (b) The-Effect of.Sintering Time, on the composition of Sinter Products The maxima shown in f ig . 9 have not been explained. They may be caused by one of two conditionsg 1 . Zinc ferrite may be thermodynamically more stable than calcium ferrite below 750*C whilst the reverse may be the case above that temperature. 2. Calcium ferrite may be thermodynamically more stdble than zinc ferrite over the whole temperature range considered, but, owing to the large kinetic barrier involved in the formation of calcium 0 . 4 0 . 3 " O.i - 0 . 1 - _o O = CaO - ZnO - O = 3CaO - ZnO - Fe203 Sintering time - 4 hours. O O o o o _L_ X ; 1000 1100 800 900 Temperature - °C Fig.9 - The effects of temperature and calcium oxide content upon sinter products. 33 f e r r i t e , zinc ferrite i s formed as a metastable phase before equilibrium Is reached. A rate study of the sintering process of the 3Ca0-Fe2O3~ZnO system was therefore made In order to explain the phenomenon. Samples of the mixture 3Ca0-FeaO3-Zn0 as used i n part (a) of this section were sintered for periods varying from 30 minutes to l 6 hours at TOO'C, 750 PC and 800°C. The results of the study are given i n f i g . 10. They show that, when ternary mixtures, CaO-FegOs-ZnO, were sintered at temperatures varying 700°C to 800'C, zinc ferrite tended to form at f i r s t . This was later decomposed by the action of calcium oxide which combined with ferric, oxide to form calcium f e r r i t e . As the sintering temperature was increased the maximum zinc ferrite yield appeared after progressively shorter sintering periods indicating that the rate of both reactions was increased and, since the maximum yield of zinc ferrite did not vary greatly with temperature, the corresponding increases in the reaction rates were estimated to be approximately equal to each other. It i s concluded that, whilst calcium ferrite i s thermodynamically more stable than zino f e r r i t e , the rate at Ithich zince ferrite i s formed Is greater than that at which calcium f e r r i t e forms and, as a result, a metastable zinc ferrite phase is produced before the equilibrium condition i s approached. The composition of the sinter product Is, therefore kinetically controlled. F i g . 1 0 - The effect of sintering time upon the composition of sinter products from a Cab ternary mixture. - ZnO - Fe 203 35 The formation and decomposition of zinc ferrite by sintering mixtures of powdered reagents has been studied. Mechanisms for the various reactions encountered were sought but the limitations of the experimental procedures adopted prevented these from being clearly shown; the effects of some form of nucleation process encountered and of the small particles used masked the true reaction mechanisms. Mecbaaical variables such as particle size and packing of particles were controlled to obtain reproducible mixtures, however other variables, such as crystalline perfection of reagents were not controlled but were thought to affect reaction rates. In the formation of zinc ferrite from zinc and ferric oxides, reaction took place following an induction period which varied as some inverse function of temperature. The amount of ferrite produced was found to be proportional to the square root of the sintering time. It is suggested that the reaction was diffusion controlled as the activation energy for the reaction Was found to be of the order expected for such a mechanism. It was found that the maximum amount of zinc oxide rendered insoluble during sintering increased slightly with temperature indicating that a limited range of solid solubility of zinc oxide in zinc ferrite exists. When different zinc compounds were sintered with ferric oxide, i t was found that the rates of ferrite formation were varied. Thus compounds which decompose below the temperature range of ferrite formation (e.g. zinc hydroxide and zinc carbonate) formed ferrite at 36 lower sintering temperatures than did zinc oxide-ferric oxide mixtures in equal sintering periods. On the other hand those compounds which decomposed above the normal temperature range of fe r r i t e formation (e.g. zinc sulphate) retarded the formation of zinc f e r r i t e . It Is concluded that as zinc f e r r i t e forms only from zinc oxide and ferrio oxide other compounds must be decomposed prior to ferrite formation. However, such decompositions may produce highly active forms of the oxides required and therefore the rate of ferrite formation may be increased i n the case of easily decomposed compounds but Is retarded when compounds are decomposed at high temperatures. Zinc ferrite was found to be decomposed by various calcium and magnesium compounds and zinc oxide was liberated. Of the com- pounds selected a l l except calcium sulphate appeared to have an effect upon zinc f e r r i t e . This may be due to the fact that calcium sulphate i s decomposed at a temperature far above the sintering temperatures selected and behaves In accordance with the theory developed i n the previous paragraph. Replacement of zinc oxide by calcium oxide i n zinc ferrite was found not to be a simple molecule for molecule substitution| about four molecules of calcium oxide were found to replace one of zinc oxide* In sintering ternary mixtures of zine oxide, calcium oxide and ferric oxide, It was found that , though calcium ferrite i s more stable than zinc f e r r i t e , the rate of formation of zinc ferrite i s more rapid and a metastable zinc ferrite phase tends to form before 57 an equilibrium condition Is reached. Therefore, the composition of the sinter product obtained is controlled kinetically rather than thermodynamically. It is thought that the use of oalcium oxide as a ferrite Inhibitor in zinc roasting operations would be of doubtful value for two main reasons s 1. The kinetics of the process favour the formation of zinc ferrite rather than calcium ferrites this wpuld be accentuated by the close association of Iron and zinc Id marmatlte ore,s. 2. In order to free the zinc combined as ferrite, calcium oxide would be consumed In quantities of the order of one ton per ton of ferrite treated. 3 8 Suggestions for Further Work While the results may suggest that a parabolic diffusion law controls the formation of zinc ferrite this hypothesis has not been conclusively proved. It could possibly be done by comparing the activation energies associated with diffusion of cations i n samples of ferrite and with the diffusion of cations during the formation of zinc f e r r i t e . I f the activation energies of the two processes were found to be of the same order then the parabolic diffusion law would be established as the controlling mechanism. The experimental method suggested is one using labelled isotopes to determine reaction rates by sectioning or possibly by the decrease in surface activity method.(25) 39 A P P E N D I X A Microphotograptas of powdered reagent mixtures prepared for s inter ing» Plate III Zn(OH)2 - Fe 2 0 3 hi APPENDIX B Analytical Methods K2 1. Volumetric Determination of Zinc (aV Solutions Potassium Perroojranlde 21.65 gm/lltre. Potassium Ferricyanide 10 gm/litre. (b) Standardisation 0.2 gm of granulated zinc were accurately weighed and dissolved in 5"ml of hydrochloric acid. The solution was diluted to about 100 ml w|.th d i s t i l l e d water and a few drops of potassium ferricyanide ̂ solution were added. It was then titrated against the potassium ferro- cyanide solution to a potenticiietricaily determined end point. A mean of three such standardisations was taken. (c) Determination of the Total Zinc Content of Sinter Products A 0.5 gm sample was weighed and dissolved in 5 ml. hydrochloric acid. 20 ml d i s t i l l e d water was added followed by excess ammonium hydroxide to precipitate the iron. The mixture was brought to the b o i l and the precipitate f i l t e r e d off and washed thoroughly* Both f i l t r a t e and washings were collected and evaporated to a convenient bulk. The residue was dissolved i n a l i t t l e hot concentrated hydrochloric acid and then reprecipitated with ammonium hydroxide. The mixture was treated as before, the f i l t r a t e s from each cycle being added together. The cycle was repeated a third time. The collected f i l t r a t e was neutralised with hydrochloric acid in slight excess and a few drops of potassium ferricyanide were added. The sample was f i l t r a t e d against standardised potassium ferrocyanide solution. 4 3 (d) Determination of the Soluble Zinc Content^of^ Sinteg;Products 1. Ammonia - Ammonium chloride leach solutiont- NH4CI l6d gnu aq. NH40H(SpGr. 0.88) 100 ml. D i s t i l l e d water 900 ml. 2. Determination. A sample of sinter product was, weighed and leached in 50 ml of ammonia-ammonium chloride leach solution for sixteen hours. The size of the sample used depended upon Its estimated soluble zinc content 2 for sinters containing less than 5# soluble zinc 2.5 gm samples were needed while for those containing greater amounts 0.5' go samples were suggiclent. Following leaching, the residue was fi l t e r e d off and the f i l t r a t e was neutralised with hydrochloric acid in excess. A few drops of potassium ferrlcyanide were added and the sample was titrated against standard potassium ferrocyanlde solution. 3» Limitations of the Method When free calcium oxide was present i n the samples i t was dissolved by the leach solution together with the zinc. During t i t r a t i o n i t was cpmplexed by the ferrocyanlde and enoncous zinc determinations resulted. Therefore a polarographic method was developed for soluble zinc i n samples which contained lime. 2* Pfilarographic ̂ t e r ^ i n a t i o h of Zinc (a) Standard Zinc Solution 0.5P0 gm of granulated zino were weighed out and dissolved In 5 ml. hydrochloric acid. The solution was made up to 1.0 l i t r e with- d i s t i l l e d water i n a volumetric flask. (b 1 Calibration ^ .. 5 0 ml. of the standard zinc solution was placed in a 5 0 0 ml volumetric flask together with 5 0 ml of ammonia-ammonium chloride leach soltuion * and 6 ml of hydrochlorio acid. The solution was diluted to volume with d i s t i l l e d water. A portion of the solution was now placed i n a 5 ml Heyrovsky electrolysis vessel and bubbled with nitrogen for five minutes to remove any dissolved oxygen. Mercury, for the electrode, was added to the c e l l and nitrogen was bubbled for a further fiye minutes* The sample was then electrolysed on the polarograph and the zinc wave height was measured. The procedure was then repeated using 1 0 0 ml and 1 5 0 ml abiquots of standard zinc solution. A calibration curve was drawn plotting zinc wave height wrtbe- ordinate and zinc concentration on the' abscissa'. Calibrations were made immediately before and after each series of determinations. (c) ^termination ;of .soluble zincvl^ A 0 . 5 gm sample of sinter product was leached In 50 ml of ammonia •Ammonium chloride solution for sixteen hours. The residue was then f i l t e r e d off and washed with d i s t i l l e d water, the f i l t r a t e and washings being caught In a 500 ml volumetric flask. The solution was neutralised by adding 6 . 0 ml hydrochloric acid and diluted to volume. The sample was then prepared for electrolysis on the polar-^ ograph in the manner described In section (b) above. The zinc waves obtained from the polarograph were measured and the zinc content v ft See Method 1(d). * 5 determinedby interpolation on the calibration curve. The limiting error of the method was estimated as t 2$. 3 . , YoluBfetr^ (a) Potassium Dichromate3 kak 9 / 1 indicators Vf> Solution pf diphenylamine in cone H2SO4. Buffer Solutions 3 0 # H2SO4130# H3FO4 kQ<f> HgO - by vol. (b) Standardisation 0 . 2 gm of iron wire was weighed out and dissolved i n 1 0 ml. HCI. The solution was diluted with d i s t i l l e d water and boiled with test lead u n t i l colourless. Boiling was continued for a further five minutes. The solution was then cooled and decanted off the test lead, the latter being washed free of a l l solution. 2 0 ml of Buffer solution were added together with six drops of indicator. The solution was titrated against potassium dichromate solution to the f i r s t permanent blue colour. 0 . 1 ml was subtracted as blank. A mean of three such standards Was taken. • (c) Dete'rmlination^Qf^^ • - 0 . 5 gm samples were weighed out and dissolved i n 1 0 ml. hydro- chloric acid. Procedure then followed that used i n the standardisation method above. 46 APPENDIX C Experimental Data 47 ,The.Effect of Sintering Time on the F o r m a t i o n • M ^ i ^ ^ r r i t ^ ' B r ^ Z i i n o • and Ferric Oxides.. S e r i e s ! Mixtures- ZnQ - Fes03 Atomic Ratio, ZnsFe 0.474sl. Table.1.1 Sintering Temperature 60Q*C Assays f> Sintering Total Total Soluble Insoluble Zn Time (hours) Iron Zinc Zinc Total Fe. 0.5 46.0 25*9 25.9 Tr. 1.0 46.0 25*9 25.8 0.002 2.0 46.2 26.1 25.6 0.006 8.0 47*1 26.6 24.3 0.034 16.0 47.1 25*9 23*3 0.048 Table ,1.2 Sintering Temperature 625 °C Assays # Sintering Total Total Soluble Insoluble Zn Time (hours) Iron Zinc Zinc Total Fe 0.5 46.2 25.6 26.1 Tr. 1.0 46.5 25*7 25.8 Tr. 1-5 46.2 25.7 24*6 0.022 2*0 46.5 25.7 24.5 0.026 2-9 46.5 25.7 23.5 0.047 3.0 46.2 25,6 23.4 0.048 4.0 46.4 25.6 21*9 0*08l 6.0 46.5 25.6 21.2 0.095 12.0 46.6 25.7 18.6 0.153 24.0 46.6 25.7 14.9 0.232 48 Table 1*5 Sintering Temperature. 650*C. Assays # Sintering Time (hours) Total Iron Total Zino Soluble Zinc Insoluble;,Zn "^Total Pe 0.5 46.7 26.0 25.1 0.015 1,0 46.5 25.9 22.9 0.055 1.5 46*4 25.9 20.9 0.091 2.0 46,6 26.0 21.1 0.090 2.5 46.5 25*9 18,7 0.132 3.0 46.6 26.0 18.1 0.145 k.o 46.6 26.0 15-3 0.194 6.0 46.5 25.9 12.8 0.240 16.0 47.2 26.2 2.6 0.426 24.0 46.5 26*0 5.4 0.420 Table 1.4 Sintering Temperature 750°C. Assays # Sintering Time (hours) Total Iron Total Zino Soluble Zinc Insoluble, Zn Total Fe 0.5 ^5.9 25-9 1.5 0*455 1.0 45.9 25.9 0.6 0.470 2*0 45.9 25.9 0.4 0.474 4.0 45.9 25.9 0.6 0.471 4 9 Series I I Mixtures ZnO - Pe203 Atomic Ratio, ZnsFe 0.466si Table 2.1 Sintering Temperature 6Q0*C Assays 56 Sintering Time (hours) Total Iron Total Zinc Soluble Zinc Insoluble Zn Total Pe 1.0 47.5 25.9 24.3 0.027 2.0 47.8 26.1 22.8 0.059 4.0 47^5 25.9 18.3 0.135 8.0 47.6 . 26.Q 12.0 0.250 16.O 47.8 26.1 6.9 0.342 24.0 47.5 25.9 4.2 O.389 Table 2.2 Sintering Temperature 625°C Assays 56 Sintering Time (hours) Total Iron Total Zinc Soluble Zinc Insoluble Zn Total Pe 1.0 47.4 25.9 22.7 0.056 2.0 47.5 25.9 19.1 0.122 4.0 47.2 25.8 12,6 0.238 8.0 47.9 26.2 6.7 O.347 16.0 47.8 26.1 3.6 0.401 24.0 47.4 25.9 1.9 O.432 50 Table 2.3 Sintering Temperatures 650°C Assays # Sintering Time (hours) Total Iron Total Zinc Soluble Zinc Insoluble Zn Total Pe 0.5 47.0 25.7 20.1 0.101 1.0 47.3 25.8 14.9 0.196 1.5" 47.3 25.8 12.3 0.233 2.0 47.1 25.8 9*6 0*276 3-0 47.3 25.8 6.6 0.328 4.0 47.5 26.0 4.3 0.369 8.0 47-3 25.8 2.0 0.430 16.0 47.5 25.9 0.6 0.454 Table 2.4 Sintering Temperature 660°C Assays $ Sintering Time (hours) Total Iron Total Zinc Soluble Zinc Insoluble Zn Total Pe 0.5 47.4 25*9 19.3 0*118 1.0 47.4 25.9 14.3 O.208 1-5 47.3 25.8 10.6 O.274 2.0 25.8 7.9 0.323 3.0 47.5 26.O 6.3 0.353 4.0 47*3 25.8 4.3 0*390 8.0 47.1 25.8 2.0 0.440 16.0 47.2 25.8 0.5 0.456 51 Series I I I Mixtures- ZnO-Feada Atomic; Ratio ZnsFe 0.94s! Table, 3.1 Sintering Temperature 625°C Assays Sintering Time (hours) Total Iron Total Zino Soluble Zinc Insoluble ! Total Fe 0.5 34.6 58.3 37-6 0.022 1.0 34.6 58.1 57.2 0.027 1.5 34.8 38.4 32.6 0.166 2*0 35.1 58.7 54.5 0.124 2.5 34.8 38.4 35.2 0.149 3.0 34.6 58.5 50.4 Q.250 4.0 55.1 38.7 28.0 0.504 6.0 55.1* 39.0 25.5 0.582 8.0 34.9 38.5 24.2 0.410 10.0 54.9 38.5 22.7 0.454 12.0 55.*. 39.0 22.8 0.459 24.0 55.4 38.6 19.7 0.552 52 • Table 3.2 Sintering Temperature - 650°c Assays * Sintering Time (hours) Total Iron Total Zinc Soluble Zinc Insoluble Zn Total Pe 0.5 35.7 39.2 30.2 0.252 1.0 '35.8 38.9 27.6 0.316 1.5 35.9 39.0 22.0 0.474 2.0 36.1 39.2 23.7 0.429 2.5 35.8 38.9 21.9 0.475 3.0 35.8 39.0 21.2 O.499 4.0 36.1 39.2 21.5 0.496 6.0 36.1 39.2 19'. 5" 0.545 8.0 36.0 39.1 19.3 0.550 10.0 36.2 39.2 19.1 0.558 12.0 35.8 38.9 19.1 0.548 24.0 36.2 38.5 18.6 0.552 Table 3.3 Sintering Temperature 1050°C Assays $ Sintering Total Total Spluble Insoluble Zn Time (hours) Iron Zinc Zinc Total Pe 0.5 36.1 39.0 18.4 0.572 1.0 35.6 38.5 18.5 O.560 1.5 35-9 38.8 18.4 O.566 2.0 35.6 38.5 18.3 O.565 2.5 36.1 39.0 18.9 0.559 3.5 35.6 38.5 18.2 0.570 6.0 35*6 38.5 18.2 0.570 8.0 35.9 39.0 17.9 O.588 53 The Effect of vSiwberlnR Temperature on the Formation of Zinc Ferrite From Mixtures Containing Various Compounds of Zinc and Ferric i$slde$ Series IV: • Mixtures Zn(OH)g - Fe 203 Atomix Ratio ZnsFe - 0.5381 Sintering Times- 4 hours • Tafele 4.1 • Assays $ Sintering Temp* Total Total Soluble Insoluble Zn *C Iron Zinc Zinc Total Fe 500 44.9 27.9 27.8 520 44.9 27.9 26.7 0.024 54© 44.9 27.9 19.4 0.162 563 44.9 27.9 7.0 0.396 580 44.9 27.9 4.4 0.446 600 44.9 27.9 3.5 0.464 668 44.9 27.9 3.2 0.470 5 4 Series V Mixture; ZnCQs - FegOs Atomic Ratio, Zn.Fe 0 . 5 3 M Sintering Timet - 4 hours Tenle 5.1 Assays % Sintering Temp •c Total Iron Total Zinc Soluble Zinc Insoluble Zn Total Pe 300 4 4 . 1 2 7 . 3 2 7 . 3 ca 5 0 0 4 4 . 8 2 7 . 7 2 7 . 3 0.009 5 5 0 4 4 . 6 27 .6 2 5 . 8 0 . 0 3 4 5 7 5 4 5 . 3 2 8 . 0 2 3 . 1 0 . 0 9 3 6 0 0 4 4 . 8 2 7 . 8 1 7 . 8 0 . 1 9 1 6 1 0 4 4 . 9 2 7 . 7 1 5 . 1 0 . 2 3 9 620 4 4 . 7 2 7 . 7 1 2 . 9 0 . 2 8 4 6 3 0 4 4 . 8 2 7 . 8 9 . 2 0 . 3 3 3 64o 4 4 . 8 2 7 . 7 7 . 0 0 . 3 9 4 650 4 4 . 8 2 7 . 7 4 . 8 0 . 4 3 6 660 4 5 . 0 2 7 . 8 3 . 9 0 . 4 5 4 6 7 0 4 5 . 0 2 7 . 8 3 . 1 ,0.468 680 4 5 . 4 28 .0 2 . 9 0 . 4 7 1 6 9 0 4 5 . 6 2 8 . 2 2 . 8 0 . 4 7 0 7 0 0 4 5 . 7 2 8 . 2 2 . 7 0.464 7 5 0 46 .3 2 8 . 6 2 . 6 O . 4 7 8 8 0 0 4 5 . 3 2 8 . 1 2 . 5 0.484 55 Series VT Mixture ZnO - FegOs Atomic Ratio ZnsFe 0.48sl Sintering Timei* 4 hours Table 6.1 Assays <f, Sintering Temp. °C Total Iron. Total Zinc Soluble Zinc Insoluble ! Total Pe 500 46.0 25.9 25.5 0.007 550 46.0 25.9 25.5 0.007 575 46.0 25.9 25.5 0.007 600 46.0 25.9 21.7 0.079 640 46.0 25.9 12.6 0.247 655 46.0 25.9 5.7 0.375 664 46.0 25.9 3.7 0.412 679 46.0 25.9 2.2 0.440 690 45.0 25.8 1.3 0.454 700 45.0 25.8 Q.5 0.470 750 45.0 25.8 0.5 0.470 800 45.0 25.8 0.3 0.474 850 45.O 25.8 0.3 0*474 900 45.0 25.8 0.3 0.474 950 45.0 25.8 0.3 O.474 1000 45.6 25.8 0.2 0.475 56 Series VII Mixture ZnSC-4 - Fe2©3 Atonic Ratio ZhsPe 0*51x1 Sintering Time? 4 hours Table 7.1 Assays Sintering Temp. °C Total Pe Total Zn Soluble Zn Insoluble Zn Total Pe 600 32.4 18.7 I8.7 0.000 700 32.2 18.6 18.3 0.009 750 33.5 19 o7 l 6 . 8 0.075 760 34.5 19.5 14.3 0.129 770 34.5 19.8 13.2 0.164 78O 39.1 20.2 11.8 0.184 790 4 l . 7 2?.I 7.1 0,327 800 44.4 26.2 1.6 0.475 810 45.0 25.9 2.1 0.452 850 46.4 27.O 1.2 0 A 7 4 900 46.4 26.6 1.2 0.477 950 46*4 27.2 1.3 0*478 1000 46.4 27.I 1.2 O.478 57 The Effect of Composition. Sintering Time, and Temperature upon the Decomposition of. Zinc Ferrite by Calcium Oxide Series VIII Approximate Ratio CaOsZnFeaO* l s l Table 8.1 Sintering Temperature 850*C Assays Sintering Total Total Soluble ^ Total Zn Time -hrs Fe l Zn J& Zn 4 In soluble Form 2 38.6 21 .fe 5.2 14.8 4 38.1 20.9 5.9 18.8 6 38.1 20.9 4.0 19.1 Table 8.2 Sintering Temperature 950°C Assays Sintering Total Total Soluble # Total Zn Time -hrs Fe <f> Zn $ Zn # In soluble form 1 39.4 21.6 5.4 24.9 2 59.2 21.5 6.2 28.8 4 39.2 21.8 6.8 51.4 8 59.0 21,4 6.7 51.4 58 Approxii^te r f t i o CaOgZBFegO^ 2g l Sintering Temperftere 850 ®C Assays Sintering Time Hbrs Total Fe $ Total Zn $ Solssbie Zn $ $ Total Zn . I a Soluble f< 51.9 17.3 %h 30.1 2.5 51.9 17.4 6.5 35.3 >.75 52.1 17.3 6.9 38.8 8 .0 31*9 17*3 7.4 40.4 Sin te r ing Temperature 9509C Assays Sitrterlng Time «*hrs Total Fe # Total Zn $ Soluble Zn j> $ Total Zn I n soluble form 1.0 32*9 17*8 9 3 52.6 2*0 33*2 l8o0 10v8 59*6 4*0 33*3 18*0 .11*8 65*2 8.0 33*2 18*0 12*9 71*7 59 Series X Approximate ratio of CaQsZhFegO* 4 si Table 10.1 Sintering Temperature 850*C Assays Sintering Time "l\rs Total Pe $ Total Zn $ Sbluble Zp * $ Total Zn In soluble form 1.0 26.0 13.6 8.3 61.0 2.0 25.7 13.5 10.6 78.5 4.0 26*3 13.8 10.7 78.O 8.0 26.5 13.9 11.8 84.7 Table 10.2 Sintering Temperature 950°C Assays Sintering Time -hrs Total Pe $ Total Zn $ Soluble Zn $> # Total Zn In soluble form 1.0 26.3 13.8 12.1 88.0 2.0 26.3 13.8 12.4 90.2 4.0 25.8 13.5 12.5 92.6 8.0 26.3 13.8 12.6 91.6 60 gb^Effet3ts of ̂ Temperature and Calcium, Oxide Content upon Sinter Products -. of 2i^H^|Oa-K?a0 fixtures Series XI . Approximate Ratio ZnO-PegOa-CaO 1:1:1 Table 11,1 Sintering Time 4 hours Assays 1> Sintering Temp - °C Total Pe Total Zn Soluble Zn Insoluble ' Total Pe 500 36.7 19.6 18.3 0.035 650 37,4 20.2 19.5 0,019 660 56.7 19.9 19.1 0.022 680 37*6 19.5 18.3 0.034 690 37.9 20.0 14.8 0.137 700 37.8 20.6 12.5" 0.214 710 37.9 19.7 11.6 0.2II 720 37-9 19.8 10.5 0.246 730 37.4 20 .1 8.5 0.310 740 37.1 I 9 . 9 7.9 0.323 756 '37o6 20.5 7.5 0.346 760 37.4 20.2 7.4 0.342 770 - 37V9 20.4 7.8 0.352 780 37.9 20.5 7.8 0*335 790 . ;37.6 20.9 7.8 0.351 800 - 57.6 19.1 6.8 0.328 900 38.1 21.2 9.3"" 0.312 1000 37.9 21.0 9.1 0.314 6 l Series XII Approximate Ratio ZnQ-FeaOa-Cao I;Ls3 Table 12.1 Sintering Time 4 hours Assays i» Sintering Temp - *C Total Fe Total Zn Soluble Zn Insoluble Zn Total Fe 600 2 5 . 2 13*9 13 .8 0 . 0 0 9 650 2 6 . 2 l 4 . 5 1 4 . 2 0.011 660 2 6 . 3 14 .4 13.7 0.027 670 2 6 , 5 l 4 , 5 13 .1 0 . 0 5 3 700 26.5 14*5 11?8 0.102 710 27.0 14 .8 9 . 8 0.185 7*0 2 8 . 0 15.1 9 .3 0.210 75P 2 7 , 2 1 4 . 9 9 . 0 0 .218 780 2 8 . 7 15 .7 1 0 . 0 O.I98 790 28.4 15 .5 11.4 0.146 800 27 .5 15*1 10.4 O.I7O 830 2 8 . 5 15 .9 12 .6 0.116 840 2 8 . 5 15.6 13.7 O.O69 850 2 8 . 3 15 .5 14*1 0 . 0 4 9 900 28.4 15 .5 1 3 . 9 0 .058 910 2 8 . 8 15 .8 14 ,7 0 . 0 3 6 920 2 8 . 8 15-8 14 .5 0.044 930 2 8 . 5 15 .6 14.9 0.024 940 2 8 . 5 15 .7 14 .§ 0 . 0 2 8 950 2 8 . 8 15 .8 14 .9 0 .031 960 2 8 . 6 15.7 13.5 0 . 0 4 2 -,Table 12.1 oontlnued Sintering Temp - \ C Total Pe Total Zn 970 28.8 15.8 980 28.8 15.8 990 28*8 15.8 1000 28.8 15.6 1010 29*2 16.0 1020 29.2 16.0 1030 28.9 15.8 1040 29.1 15.9 1050 29.1 15.8 Soluble Insoluble,Zn. Zn Total Pe 14.9 0.031 15.6 0.027 13.4 0.083 15.6 0.021 15.0 0.034 14.9 0.038 15.6 0.029 15.0 0.033 15-2 0.024 63 The Effect of Sintering Time upon the Composition of Sinter Products • from CaO^FegQa"Zr^ Ternary Mixtures; Series XIII Approximate Ratio CaO-FeaO3-Zn0s3sIsl Table 15.1 Sintering Temperature 700°C Assays Sintering Time -hrs Total Iron i> Total Zinc in Soluble Zinc i» Insoluble Zn Total Fe 0.5 26.0 14.3 13,4 0.020 1.0 26,0 14.5 14.9 0.000 2.0 26*0 14*3 13.0 0.043 3.0 26.3 14.4 12.0 0.078 4.0 26.5 l4*5 11.6 0.093 8.0 27.2 14.9 10.0 0,154 16.0 26.5 14.4 9.0 0,175 Table,13.2 - Sintering Temperature 750°c Assays Sintering Time -hrs Total Iron ^ Total Zino $ Soluble Zinc $ Insoluble Zri Total Fe 0.5 26.5 14.4 12.0 O.078 1*0 26*5 14.5 9.0 0.178 2*p 28.0 15-5 9.8 O.165 4.0 28.3 15.5 9-6 0.178 8.0 28.3 15.5 10.1 0.163 16*0 28.8 15.8 10.8 0.148 64 Table 15.3 Sintering Temperature 8pG*C Assays Sintering Time -hrs Total Iron $ Total Zino i» Soluble Zinc # Insolublei2n Total Pe 0*5 28.3 15.6 9*0 0.196 1.0 27.8 15.3 9*5 0*178 2.0 28.5 15*6 10.6 0.150 3.0 29*0 15-9 11*4 0.132 4.0 28,5 15.5 12*4 0.094 8.0 28*3 15.5 13*9 0.048 16.0 31*0 17*0 15.3 0.047 65 APPENDIX D Debye Scherrer diagrams of the reagents used and sinter products obtained Plate IV o< Ferric Oxide Plate VII Sinter Product obtained from a mixture of zinc ferrite and calcium oxide *7 BIBLIOGRAPHY 1. Ingalls W. R. Metallurgy of Zino and Cadmium p. 6, 32. Eng. Mining J . Press. (1903) 2. Tainton and Leyson. Trans. Am* Inst. Mining* Met, Engrs. JO. P. 486 (1924) 3. Prost. B u l l . Assoc. Beige. Chim. 10 p. 246 - 263 4. Wells J . S. C. Eng. Mining J . 86 p. 420 - 422 5. Hofman. Trans. Am. Inst. Mining. Met. Engrs. 55 p. 8 l l (1905 6« Ebelman. Ann, Chim (Phys.) Ser 5. 22. P* 55 (1851) 7. Kushima, I and Amanuma I. Mem Pao. Kyoto Univ. 16 p. 191 (195*0 8. Hopkins D. W. B u l l Iftst. Mining Met. ̂  p. 219 (1949) 9. Hopkins D. W. and Adlington A. G. B u l l Inst. Mining Met.. 60 p.117 (1950) 10. Swartz and Krauskopf. Trans. Am. Inst. Mining* Met Engrs. T.P. 40 (1928) 11. Guillessen and Van Rysselberghe, P. Trans. Am. Eleotrochem. Sec. 52 P« 95- (1951) 12. Ralston O.C. U. S. Bur. Mines B u l l . 296 (1929) 13. Huokel W. Structural Chemistry of Inorganic Compounds* Elsevier (1951) 14. Sidgewick N.V. Chemical Elements and their compounds. Oxford* Univ. Press. 15. Welo and Baudisch, Phys Rev. 25. p. 587 (1925) 16. Welo and Baudisch. Phil Mag. 5£ (6) p. 399 (1925) 17. Huttig and K i t t e l Z* Anor*. Chem. J6 p. 210 (1955) 18. Gorter. E. W. Phi l l i p s Res. Rep. 2 PP 295-520 (195*) 19. Verwey E.J.W. J . Chem Phys. 15. p. 174 (1947) 20. Verwey E. J . W* Ibid* p. l 8 l 21. Forestier H. Comptes Rend. 192 p. 842 (1951) 22* Wells A. F. Structural Inorganic Chemistry Oxford Univ. Press. (1950) 68 23. Mott. N. F. Trans. Faraday Soc. ,36 p. hj2 (194©) 2k, Lindner R. Proc. Intern.Symposium on Reaotive Solids. Gothenburg 1952 P t l . p. 195 (pub 1954) 25. Carter R. E. and Richardson F. D. J . Metals. 6 p. 1244 (1954)


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