EXTRACTION OF ZIRCONIA BY OGDEN LIVERMORE THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN CHEMICAL ENGINEERING COLLEGE OF LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS 1922 1922 L 75 UNIVERSITY OF ILLINOIS THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY .QGJ3EH_JLI_VEmOEE. ENTITLED EXTRACT I Cj_i_ _0F_ JJJR£ONIA IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE degree OF Instructor in Charge Approved HEAD OF DEPARTMENT OF Ch.e_i.St rjT 500206 Digitized by the Internet Archive in 2015 https://archive.org/details/extractionofzircOOIive TABLE OP CONTENTS History 1. Discovery 2. Experiment in Uses Commercial Uses 1. Refractory 2. Enamel and Glass 3. Miscellaneous Occurrence 1. Relative quantity 2. Forms and Regions Purification methods from the Literature 1. Attempted methods and points of failure 2, Patented method Method Developed and Used 1. Basic principle 2. Procedure 3. The product Summary 1 EXTRACTION OP ZIRCONIA I HISTORY Zirconia was not discovered very early in history on account of its similarity in reaction to alumina and other earths. In 1789 Klaproth determined its existence with cer- tainty. He reported that in the Jargon of Ceylon he had found 31.5 per cent of silica, 0.5 per cent of iron and nickel ox- ides, and 68.0 per cent of some new earth. A few years later ♦ he identified the same material in the Hyacinth of Prance. In 1797 GO^ton de Morveau confirmed the work of Klaproth. At about the same time Vauquelin gave this new earth the name Zirconia and described some of its compounds. In 1798 Iromms- dorff tried to reduce Zirconia to Zirconium and failed, but in 1824 Berzelius perpared the impure metal and two years lat- er had a sample of sufficient purity to determine the atomic weight. After this many mistakes were made by chemiftts who thought that they had found a new oxide when in reallity they had only a mixture of Zirconia and some of the rare earths that occur in the same minerals. These mistakes were due to the difficulty and length of the processes for the isolation of Zirconia and its great similarity to the rare earths in action and appearance. Baddeleyite, the impure native Zirconia, was dis- covered in 1892 by two different men working independently in two different regions. Hussak found it in Brazil aid call- ■ . « ■ . . * . < . . . . t t . 2 ed it brazilite and at about the same time Fletcher found it in Ceylon and called it baddeleyite. Hussak retracted in fa- vor of Fletcher. It was not until about 1913 or 1914 that any exten- sive work was done on Zirconia in regard to its practical value. It was used to some extent before this in Drumond lights to replace the calcuim oxide. The more recent inves- tigations bring out its value as a refractory in many ap- plications. A Siemeus-Martin furnace in a steel works at Remscheider, Germany was actually operated with a Zirconia lining. The lining was in good condition after four months of use and statistics from the test showed a saving of fifty per cent in maintenance cost. It has also been found that the use of Zirconia is advantageous? in the metallurgy of cop- per, steel, bronze, and red brass for it does not absorb them or become weakened by the action of the molten metals or their oxides. In these various uses it has been found necessary to use some binding material with the Zirconia for it cannot be fused together at temperatures available at present; no doubt furnaces to fire it could be developed if it were more plenti- ful. Sodium silicate, starch, phosphonic acid, glycerine, tar, and borates have been used. Articles made with these binders have a specific gravity of about five. This weight is objectionable in some cases and it has been found that some material such as sawdust or ammonium salts added before fir- ing will cause porosity and consequent lightening of the ob- ject, This porosity would be detrimental for uses where 3 liquids or gasses were concerned "but does not lower the re- fractory power of the Zirconia. 4 II COMMERCIAL USES Thus, Zirconia, the oxide of zirconium, has been found valuable and wellsuited for a number of purposes. The great drawback to its extensive use is the fact that a small parr cent of impurity, especially of iron, greatly reduces, if not complete- 1 ly destroys, its value. It has been produced in the pure condi- tion by many methods but these methods have always been slow, too expensive for commercial use, and not easily adaptable to large scale commercial productions. The problem is to find some method that can handle sufficient quantities at a cost low enough so that the Zirconia can be produced in large amounts profitably. There is an extensive market for a low priced pur Zirconia in the field of refractory materials. It makes good quality furnace linings, combustion tubes and boats, crucibles, casting molds, pyrometer tubes. The pure Zirconia fuses at approximately 3000° C. , and does not volatilize below this tem- perature. The most nearly pure native material can endure only 1300°. 1.0 per cent of iron will reduce the melting point of the pure oxide from 3000° c., to 2500° C. The articles of Zirconia have a very low coefficient of expansion, 8.4 x 10“^, so that they can be quenched suddenly from high temperatures and will withstand wide variations in temperature. It has been discovered that where as quartz ware does not remain constant in structure but has transition points and gradually becomes crystalline, the Zirconia ware has no transition points • < 0 . • . . . . . . * . iC'Ol- i *t- n l lb ■ 7 5 and is more durable. Its property of low heat conductivity goes well with its high melting point in furnace linings or wherever a retention of heat is desired. As furnace lining it lasts several times as long as ordinary lining material for its reaction with strongly acid or basic slags is very slow. Fluorides and bisulphaties , and carbon in the electric furnace, are the only materials which tend to destroy it rapidly. It is practically impervious to liquids, and combustion tubes are gas tight up to 1000° C. In addition to the foregoing uses pure Zirconia is valuable as a constituent in glass and enamels as an opaci- fier. Many other salts of zirconium that are used in medi- cine, in sizing silks, in dyeing, in fire proofing cloth, and others are made by starting with the pure oxide. The im- pure oxide is used relatively extensively at present but it must not be confused in value with the purematerial, for the latter would be much better in nearly every case. Many of these uses are minor and the impure oxide is used because of its low price. The uses briefly enumerated merely outlines the beginning of the commercial possibilities for Zirconia. . . . .. , . . , , . 1 , • • . . . . 6 . Ill OCCURRENCE The element, zirconium, occurs in the earth* s crust in many forms and although it is only fairly abundant it is quite widely distributed. An estimation of the amounts of the more abundant oxides shows Zirconia to exist to the extent of 0.03 per cent in the crust. Its relative quantity can be judged from comparison with the quantities of other better known oxides and elements: C0 2 - -------- 0.49# CL 2 0.06# S .... 0.11# FeQ 2,63# MgO -------- 3.92# Ha 2 0 3.46" ZrO 2 ———————— 0.03# It is found most commonly combined in the minerals; zircon, a zirconium silicate; baddeleyite, sometimes known as brazilite, the impure native oxide; zirkite, a mixture of forms of zircon and baddeleyite; and zirkelite, a mixture con- sisting of baddeleyite, zircon, and a silicate differing from zircon in composition and structure. Of these four the badde- leyite is the most important from the stand point of commer- cial use. The silicate ores are more difficult to break down and do not contain as high a percent of Zirconia. Baddeleyite is found in Brazil, the United States, v - * . ■ . . . - ; « ; « . . « , 7 Ceylon, Sweden, and Italy. The most pure ore comes from Cey- lon but the deposits in Brazil are more extensive and workable. The other deposits are not used to any appreciable degree. The deposits in North Carolina reached a maximum yearly pro- duction of four tons in 1905. In Brazil the deposits are of two types, the alluvial pebbles containing 90.0 to 93.0 per cent Zirconia and the ore proper, zirkite, containing some zirconium silicate and the equivalent of 80.0 to 85.0 per cent Zirconia. Due to its content of more easily decompos- ible silicate, and of native Zirconia, and its occurrence in the same region zirkelite is mined with the zirkite. The boulders and large masses are too hard to drill for explosives and must be broken by the primitive method of heating the rock and then shattering it by sudden cooling. The silicate, zircon, is also used but to less extent and more often for gems and certain cutting tools than for re- fractory material. It is found in the United States, the Ural Mountains, Greenland, Norway, Transylvania, Bohemia, the Tyrol, France, Italy, Australia, New Zealand, and in rather small amounts ih many places. There are many other minerals, some of high Zirconia content, which are of little value either because of their occurrence in non-workable quantities or because of the diffi- culty of their decomposition and purification. The follow- ing list gives only those numerals which contain at least 20 per cent Zirconia: 1 V . . 8. MINERAL COMPOSITION PER CENT ZR0 2 Adelfolith Weathered Zircon 47.42 Anderbergite (Si0 2 )i2*^ 3H 20 41.20 Anerbachite Weathered Zircon 55.18 Baddeleyite Native Zirconia up to 99.0 Beccarite Zircon with Ca & Fe 62.15 Brazilite sec baddeleyite 80.0 Cataplerite H 2 (Na 2 Ca)Zr Si 3 0 X1 30.-40.0 Cyrtolite Weathered Zircon 36.-61.0 Elpidite Na 2 Si 2 0 5 *Zr (Si 2 0 5 ) 2 20.50 Eudialyte Na 13 (Ca Fe)g (Si Zr) 2(j ° §| 10.-20.0 Hiortdahlite Zircon Pyroxene 21.5 Lovenite (Si°0 3 )2Mn Ca Fe*(ZrOF)Na 30.0 Oliveiraite 3Z r 0 2 * 2 Ti 0 2 *2 Hg 0 63.36 Orvillite 8 Z r 0 2 *6 Si 0 2 5 H 2 0 71.83 Polymignite Metazirconotitanate 14.-30.0 Pyrchlor Niobate - titanate 20.0 Tachyaphaltite Weathered Zircon 39.0 Uhligite (ZrTi) 0 5 *Ca ♦ ( Ti A1)0 & A1 22.0 Wohlerite Si Zr Na 0 F • Ca Na 10 3 2 42 3 10 5 15.-23.0 Zirlcelite Zirconium silicate 50.0 These names given to the various minerals of zirconium are often confusing for different men have used them at differ- ent times to mean different materials. This confusion in the names must be remembered when statements in the literature seem to be contradictory or ambiguous. 9 IV PURIiFI CATION - METHODS FROM THE LITERATURE Now with these main facts of Zirconia in mind the next step is its extraction and purification. There are numbers of methods given in the literature but only those which treera to be distinctive and to give promise of practability will be consi- dered here. There are two main ways to extract the Zirconia from the ore, upon which all methods for the production of the pure material depend. In the case of an ore such as baddeleyite con- taining a high per cent of the oxide the leaching method is us- ed. The ground ore is leached with acid, usually hydrochloric, which dissolves the Zirconia and also metallic impurities, notably iron, and leaves the silica and gangue behind. This gives an impure solution of Zirconium chloride. The second class of methods is more difficult to carry out. It consists of fus- ing the ore with some fluxing material to get a soluble compound of zirconium. This method is used where the ore contains sili- cates and other insoluble zirconium salts. Some of the fluxes used in the various procedures are sodium carbonate, sodium car- bonate and silica, or niter cake. Where sodium carbonate or sodium carbonate and silica is used a mixture of sodium silicate and sodium zirconate is produced. Upon leaching with water the silicate dissolves and the zirconate is hydrolyzed to give a precipitate of zirconium hydroxide, and as before, mixed with metallic impurities, the most objectionable of which is iron. . ■ - ■ * , . . . . , . , . ■ , . , • - - • •’ • >: . 10 This hydroxide is then filtered off and dissolved in acid giv- ing an impure zirconium salt solution. The material from the niter cake fusion i8 leached and the silica filtered out. This solution is nearly neutralized with sodium carbonate and zir- conium hydroxide precipitated by the addition of sodium thiosul- phate at boiling temperature. The precipitate is filtered and washed; the washing removes much of the iron. Then the dried cakes can be ignited for an impure Zirconia or redissolved in . - 2 acid. There is another type of acid solution method where hydrofluoric acid or fluorides are used to effect the solution of the zirconium compounds. Some of these methods accomplish their purpose very well but are not practical for large pro- duction of Zirconia on account of the cost of and difficulty in the handling of the hydrofluoric acid used or generated during the process. Some work has been done recently in the electric furnace in the line of breaking down zirconium ores and obtain- ing a pure compound but the results are rather uncertain and the process is expensive. Now having obtained a crude zirconium salt solution, it is necessary to remove the impurities. According to methods given in the literature this can be accomplished satisfactorily in many ways. No attempt will be made to describe all of the methods that are recommended. A number which seemed to be the more practical were tried and found to fail at some point or to be unsatisfactory in some other respect. . . ■ . ■ . • ■ . , ■ . , . F - \ . ' V it 11 First, there is the method of precipitating zirconium hydroxide from an almost neutral solution of the chloride by the introduction of sodium thiosulphate at boiling temperature. Here the iron and similar impurities are supposed to stay in so- lution while the hydroxide of zirconium is filtered off. 2Na 2 S 2 0 3 + 4 H 2 0 + Zr Cl 4 — 2S + Zr (OH) 4 + 2H 2 0 + 2 S0 2 +4 Na Cl In attempting to run this method it was found impossi- ble to neutralize the acid solution sufficiently for the thiosu- lphate to work without causing the zirconium, iron and others to precipitate before any thiosulphate was added. If the solution is made faintly alkaline after the iron is all reduced to the ferrous state and three times the weight of the oxides present is added in tartaric acid, the zirconium should not come down, and by passing hydrogen sulphide into the solution at 60°C., the iron, nickel, cobalt, manganese, zinc, and uranium that maybe present are precipitated. The precipitate is allow- ed to settle and filtered off. The hydrogen sulphide and tar- taric acid can be removed by boiling to dryness with sulphuric acid and nitric acid, adding the nitric near the end. The ma- terial obtained is zirconium sulphate. In trying to run this method it was found that the tartanic acid would not keep the zirconium in solution when the solution was made alkaline. Another one of the methods given uses sulphur dioxide or fresh sulphurous acid. The hydrochloric acid solution is neutralized with ammonia until the precipitate no longer goes 12 into solution with boiling; then hydrochloric acid is added drop by drop until the precipitate just goes. Then the solution is boiled with excess fresh sulphurous acid or sulphur droxide gas direct. The zirconium should come down leaving the iron and impurities in solution. Since appreciable amounts of am- monium chloride prevent the operation of this method it does not work well. In trying this method it was found that the sulphur dioxide caused no precipitation. It is claimed that a mixed solution of zirconium chlo- ride and ferric chloride in strong hydrochloric acid can be separated by the use of ether. But experiment showed that the ether takes the iron and some zirconium leaving the zirconium and some iron. It might be possible to get an almost complete separation of the two chlorides by sufficient repetition of the process but judging from trials the method is not at all satisfactory. Another method given is based on the fact that the dry chlorides of iron and zirconium are volatile at different tem- peratures 30 that theoretically a- :: separation can be made on this | basis. Hydrochloric acid gas and chlorine are passed over the oxides of the two metals at 200° C. The iron is volatilized and carried away while the zirconium is left behind. From trial it was found that this method would work quite well if certain mechanical difficulties could be overcome. It was not possible to bring the gas into contact with all particles of the mater- ial and the ferric chloride condensed in the cooler regions of the combustion tube. The method could not be made to work . . . . , . . . V • . . 13 . successfully with the equipment at hand. However, the ferric chloride was partially removed to the back of the tube. The original sources of these methods seem to be unknown or at least uncertain in all cases. There is a patented method for producing pure zirconia that was not given a trial. The solution of zirconium and im- purities as chlorides is adjusted to a certain acidity and 3 heated under pressure Zirconium Hydroxide comes down. < . . ■ . . . t ' 14 . METHOD DEVELOPED AND USED The method finally used to produce Zirconia has not been found to appear in the literature but there is no certain- ty that it has not been used before. It depends on compara- tively simple and well known primciples. The basis of the meth- od depends on the fact that zirconium hydroxide can be preci- pitated from an acid solution of ferrous and zirconium chlor4 ides without the precipitation of the iron. The solution must be kept in the reduced condition for as soon as oxidation occurs the iron will come down; ferrous hydroxide is soluble while ferric hydroxide is insoluble. The ore treated was a mixture of baddeleyite and some zirkite from Brazil. Its exact composition was not known but can be judged approximately from the composition of the two main mineral constituents.^ CONSTITUENT BADDELEYITE ZIRKITE Zr 0 2 96.52-97 .19 93.18-68.93 Si o 2 .19- .70 1.94-26.30 Ti 0 2 0- .48 .36- 3.12 EegOj • 41 — .92 .43-10.26 ai 2 ° 3 . 0- .43 0- 1.0 Mn 0 Trace 0-Trace H 2° i 00 CM . .39 0- 1.56 Ca 0 0 - .55 Mg 0 0 - .1 Alkalies 0 - « to ----- 15 In the purification the main effort was directed to- ward the elimintation of the iron for the other impurities ex- ist in small quantities, some are eliminated at various points in the process, and none "but the iron have been found to he particularly objectionable in the Zirconia. Since the zirconium was present in silicate as well as in the oxide it was decided to use the fusion method of extraction. The fluxed used were sodium carbonate and silica. These were tried mixed in different proportions. It was found that a charge consisting of 30 g., of finely ground ore, 20 g. of silica, and 250 g of sodium carbonate in two of the ordinary fire-clay crucibles available for assaying gave the most satisfactory fusion from the stand point of complete fusi- bility, quiet fusion, and not excessive corrosion of the crucible. Other charges of 30 g. of ore, 10 g. of silica, and 250 g. of sodium carbonate; of 30 g. of ore, or 5 g. of silica, and of 250 g. of carbonate; and also one higher in silica consisting of 30 g. of ore, 25 g. of silica, and 250 g. carbonate were tried Those charges low in silica were fiund to remain unfused up to temperatures nearly as high as those in the assay muffles about 900° to 1000^ C, when suddenly they would melt and unless cooled considerably without delay would bubble up violently causing the material to be lost. Hence they required more attention than the charge containing twenty grams of silica and gave a no less viscous fusion. The charge higher in silica did not fuse well. Five of the charges containing thirty grams of ore were prepared so that one hundred and fifty grams of the ore was started. ' * * • . . ■ . • ' . ■ . . ■ 16 After pouring and cooling the fusion was crushed to about one hundred and fifty mesh and put to leach with water for several days, the liquior being poured off from time to time and the residue stirred up with new water* A total of about ten liters of water was used for three successive leach- ings. This leaching must be thorough for any sodium silicate left in the material will cause trouble when acid is added later; it foims the gelatinous silicic acid and clogs the filter The residue now is chiefly zirconium hydroxide and its impuri- ties, and a small amount of some rock gangue which did not decompose in the fusion. All possible leach liquor is drained off and hydrochloric acid is added to dissolve the zirconium hydroxide. This solution should be well diluted to facilitate filtering. The small amount of gangue mentioned above is fil- tered off. It was found that eight or ten layers of cheese cloth in the Buchner funnel made the best filtering mednim. Now the solution of chlorides must be reduced to al- low the precipitation of the zirconium without the iron. This is accomplished by means of a simplified Jones reducing column. A glass tube of about two inches diameter and three feet in length is filled with granulated zinc. A tube leads out of the stopper at the bottom; no nitrogen filled container is used. Above the stopper is first a Iyer of broken glass tubing, and then a layer of glass wool; these materials keep the five par- ticles of zinc from entering the tube or gathering at its mouth and stopping the flow of liquid. Before using the column to reduce the solution it is well to run some acid through to . : , • . . ' , . ■ * ■ . ■ . , ' . ' 17 carry off or dissolve the very small particles of zinc that would otherwise be carried into the solution and raise its zinc content unnecessarily. This is especially true when the column is not freshly filled and has been standing for some days. The impure solution of zirconium chloride is quite strongly acid and must be adjusted to proper strength to go through the re- ducer. The acidity must be sufficient to cause complet reduc- tion during two or three passages through the tube and yet not so strong as to cause violent evolution of hydrogen. When the acid is too strong it not only dissolves unnecessarily large a- mounts of the zinc but the excessive hydrogen formed rises in the column and prevents the rapid flow of the solution down- ward; the process is slowed up. As the solution comes from the reducing column it is run into a glass cylinder about six inches in diameter and twenty-four inches in height. The dimen- sions are not essential but the precipitate will settle better for washing, as will appear later, if the vessel used is tall and relatively narrow, ^hen reduction is complete the solution will be clear and colorless. It is necessary to keep air away from the solution as much as possible to avoid reoxidation. Therefore, the cylinder should have some form of air tight cover. The zorconium is pre- cipitated in this cylinder with ammonium hydroxide; it was found to be best to have the ammonia solution in the cylinder first and run the zirconium into it. There seemd to be less tei d- ency toward reoxidation and precipitation of the iron, probably due to the fact that the ammonia fumes would displace much of the air from the cylinder when given an opportunity. The am- . ' ■ ' . . 4 . .. . . . raonia solution reoxidizes the iron to some extent anyway and this must be due to air carried in the ammonia solution. Bet- ter results might be obtained if liquid ammonia were used. Zinc hydroxide from the zinc of the reducer column comes down at the same time as the zirconium but redissolves in an excess of ammonia and is carried away in the washing. The precipi- tate is allowed to settle; then the liquid is siphoned off care fully so as not to lose any of the zirconium hydroxide. The hydroxide is washed a number of times with recently boiled dis- tilled water. The distilled water contains too much air as it comes from the tap. Each time the wash is siphoned off after the precipitate has settled. After three or four washings the wash is tested for iron. When there is little left the washing is discontinued and the hydroxide is redissolved and reduced as before, using care to have the acidity adjusted cor- rectly for the column. Precipitation and washing are repeat- ed. This cycle of operations must continue until no reaction for iron is obtained from a solution of a little of the zir- conium hydroxide taken from testing. An average of six repeti- tions was found necessary. The repeated solution, reduction, precipitation, end washing of the zirconium hydroxide is neces- sary on account of its light and bulky nature. It holds much solution in the particles of precipitate so that thorough wash- ing is impossible. Finally the zirconium hydroxide is filtered from the liquid, dried, and ignited to Zirconia. Time became short so that all the ore started was not run completely through but it is estimated that the yield, would be about fifty grams ■ . . < 19 of Zirconia. The largest loss during the process occurs in the amount of material that sticks to the crucibles after fusion. If the processes of reduction, precipitation and wash- ing were carried out in closed vessels and the liquid transfer- red from one place to another in tubing so that there would be no contact with air there would not be necessity for as many repetitions of this purifying process. In working with open ves- sels and pouring solutions through the air some reoxidation oc- curs and must be corrected the next time. Absolutely if on free Zirconia could not have been produced by this method for a geometrically decreasing fraction of the iTon always remains. However, the material is very nearly pure white and gives none of the common reactions for iron. ■ ' - ■ . VI £0 SUMMARY Zirconia was discovered in 1789 and from then until about 1912 or 1914 it was studied quite widely but was used commercially to a small extent. Beginning about 1912 or 1914 more extensive investigations of it properties were carried out and it was found to be valuable for a number of uses especially as a refractory. It is available in large quantities for 0.05 per cent of the earth* s crust is Zirconia. Deposits occur in nearly all parts of the world. These deposits are chiefly the native Zirconia or Zirconium silicates. In the attempts made to extract Zirconia it was found that a number of methods that are reputed to be satisfactory would not work, A method was developed in which the zirconium is precipitated as the hydroxide Y/ith ammonia from a reduced hydroehloric acid solution leaving the chief impurities in solution. The hydroxide is ignited to Zirconia. V ■ , V . , . 2 * 1. Zirconium and its Compounds ------ F. P. Venable 2. Mineral Foote-Notes - - July & August, 1918 - - - Bradford 3. C. A. 10 - 255 - - - U. S. Patent 1,158,769 Separation of Iron from Zirconia ------ Askenasy 4. Mineral Foote-Notes March 1918 .. - . . . - • 22 REFERENCES Arnold - - Zirconia J.Soc. Chem.Ind . 37 - 743A Rodd - - - Zirconia as a Refractory. J.S.C.I, 37 - 213, Wedekind and Lewis ------ Preparation and Properties of Impure Metallic Zirconium. C. A. 4 - 1434 Annalen 371 - 366 - 88 Bayer - - - Preparation of Vessels from Zirconia C.A. 4 - 1527 Z. angew. 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Soc. 16 9 121 (Anonymous) Zirconia Enamel C.A. 6 - 1665 Ceramique 14 - 204 Foote Mineral Company - - Mineral Foote-Notes for: March 1918 24 March & April - - Nov* & Dec. - - - May & June - - - July & August - - Browning - -Introduction to the Barer Elements Phillips - Minerology. S. I. Levy - Bare Earths. Martin - - Industrial Inorganic Chemistry. Schoeller and Powell - Analysis of Minerals and Ores Barer Elements. F. P. Venable - Zirconium and its Compounds. 1919 1919 1920 1918 of the