The characterization and identification of the rare-earth chloride hydrates by differential thermal analysis

VOL. 21 (1959)

POLAROGRAPHIE

DU &

439

Nous tenons Q remercier R-I.L. GIERST, chef de travaus H l’lfniversit6 de 13ru~efles ties suggestions qu’il nous a donnt5espour i’intcrpr~t~tion de nos rQultats. On observe, cn pr&scncc de zirconium, unc ontlc dc r&luction cntnlytique ilcs ions nitratc, S. I’ltilcctrodc tz gouttc de merctirc. Cettc on& peut servir au closngc qunntitatif,.sles. ions nitrate. On cionne, en qutrc, le mbxnisme du proccssus de rfduction. SUMXIARY In the prcsencc of zirconium, one observes a catalytic reduction wnvo of nitrate ions nt tlu.? mercury dropping electrode. This wave can bc used for tbc quantitntivc ~~~~~rn~is~ati~t~ of nitrate ions. The mechanism of the reduction is cxplsinccf. %UShXIRlENFMX5UNG In Cegcnwart van ~~rk~nium gebcn Nitrat-fonen an dcr Qt~ccksitbcrtro~~fciektrotle cinc Wck, die einc katalytiscirc Rctiuktion anzeigt. IXcsc Wcilc knnn zur quantitntivtcn ~3cstit~~~n~lngvon Nitrat-Xoncn vcrwcndct wcrdcn. Einc ErklSrung fiir den Mechanismus dcr Rctluktion ist gcgcbcn. , UfBI.fOGiZ1\PH

tE

AND IDENTIFICATION OF THE THE CHARACTERI%ATION HYDRATES BY DIFFERENTIAL RARE-EARTH CHLORIDE THERMAL ANALYSIS

Although there are a number of techniques that can bc used to identify the rarcearth elements, a simple and convenient method, differential thermal analysis (DTA), has long been neglected. By this method, the qualitative identification of a rare-earth compound is possible by determining the temperatures at which cxothermic (cxotherms) or endothermic (endothe~s~ reactions take place as the substance is hcatedi. Under similar conditions of sample size and packing, furnace heating rate, and type of recorder, these cxotherm and endotherm temperature maximas are reproducible enough so as to be useful for the identification of a series of rare-earth compounds. This method is valuable for the identification of the indivic+.l rare-earths or, in certain cases, for mixt&es of them. defeve*1ces p. 442,

440

W. W. WENDLANDT,

J. L. BEAR

VOL.

23

(T959)

For our first investigation, the thermal decomposition of all of the rarc-carth chloriclc hydrates (except Pm) wcrc stuclicd by lITA. ‘I’hc metal chloriclcs were in the form of the G- or 7-hydrates and were the same compounds that had previously been studicd on the tllCrmohnli~nCe’r~:l.

xc-c:lrtli COlli~lOllrl~~S wcrc obtnincrl Chemicals, Inc., Ilurlxmk. Calif., l’J~c purity was tltat listcri by tlsc supplier.

‘I’lic rare-c;rrth

cllloritlc

IlyclI%tcs

in tlic form of tlicir oxitlcs of W.c,‘;<, purity frcJm i.~ntl tlic Lintbay <3lcmical Co., \Vcst Chicago, 111.

wore I)rclmrc~l

as prcvitrusly

clcscribcrl I.

a motes-tlrivcn vari;rMe Tttc :~pp;rmttts C~JnsiWxl 0f il StilirllcSS steel s;rmplc hcrlclc:r :lnd fttrniLcc: tr:msfc,rmcr to control tlic filrnacc hating rxtc; nncl $1strip-chart microvolt recurtlcr~. ‘I’llc tliffcrmcasurctl wit11 28 ~;LII~C phtinrrm--c)o’%, platinum--ro’x, rhodium ctltiill tcmpcraturcs wcrc tlicrlnoct,ltplcs. Snmplc sixes r:rngctl in wciyht frcim 0.200 to 0.2 15 g axi were nlixctl with ignitcci was :IIHO twx1 in the rcfcrcncc cltamber. ‘I’hc frtrnncc irlttmina in a f : 1 mtict; ignited alnminn wcrc rccordctl on 5 in. wiclc chart pnpr using IlCi~tillji rate was alx~ut 1o.a50 par min. Tl~crmogriltns

a cliart

spcctl of G in. lxx II.

“The thermograms of the rare-earth chloride hyclrntes ;lr(: given in Figs. r-3. ‘I’he prominent endotherm maxima temperatures :Lrc given in Table I. On tlic basis of the tlicrmograms, it is convcnicnt, for purposes of discussion, to classify the thcrmd ~(~c~)rnl~osition patterns into 4 main groups : Group I-La, Ce, Pr, and Nd ; Group II- S-n, Eu, and Gel ; Group I I I- ‘I%, Dy, Y, Ho, I+, and ‘I’m ; Group IV-Yb and ILL ‘I’hesc groups arc just arbitrary but unpublishccl results on the tltcrmal clccomposition of the rarc-carth nitrate hyclrutcs rcvcal much the same clnssification. -------

t

100 2003CQ400Lx3o600700 TEMFERAllRK. C Fig. 1. Thermograms clllorich hydrates.

800

of the rare-earth

LEtnthanttm

samarium.

to

Fig. 2. Thermograms chloritlc

hytlratcs.

of the x-arc-Garth Europium

holmium.

to

VOL.

21

(1959)

RARE-EARTH

CHLORIDE

HYDRATES

44*

In this group, the thcrmogratis are characterized by one or two small cndotherms which preceed the large dehydration endothtrms. These small endotherms are thought to arise from the heat absorbed by the partial fusion of the metal salts. -41~0observed in this group, with the exception of cerium, arc the endotherms in the 4oo”--650~

I:ig.

3. ‘I‘hcrrno~ratns

cl~IoritIc

hydrates.

of the

Erl~irmt

rare-earth to yttriut77.

temperature range. It is known from thermobalancc studies1 that the terminal thermal decomposition products are the metal oxychlorides and these cndothcrms are presumed to be due to their formation. As the atomic weight of the rare-car& metal ion increased, the metal osychlorides were obtained at progrcssivcly lower temperatures; this could explain the disappearance of these endotherms in the other groups studied.

ikurevxarth

'rempmfutc,

salt

.-

1 IO

lG3

190

CeCl~.Gl~l~O f’rCI3.7FfzO NtlCl3.6l-f2O SmCla.GI-120 E11Cls,6Ha0

100

7.5 ‘35 rGo tY0

‘70 120 ‘75 190 295

18s 180 IQ0 275 400

GtfCt3,6ti~0 TlKl3.6tIzO J>yCl3,6HzO iioC13,6J-JaO ErCf3*Gfi~O TmCl+GH# YbCl3,6W20 LuC~~~I-I~O YC13.6HaO

180 180 175 175 190 180 X80 280 185

300 220 205 210 240 255 227 235 220

390 380 355 350 400 320 310 325 380

I.LlC13.7HaO

References

p. 442

*c

--

.. 21s 250 190 27” 390

405 385 380 350

:

--

430

Iis0

2GO 400

4’0

525

W.

442

W. WENDLANDT,

J. L.

VOL..

BEAR

21 (1959)

In this group, the large dehydration ‘endotherms consisted entirely of just one maxima with several small endotherm ihoulders. There were sharp endotherms in range and broad endotherms in the 3go”-400” temperathe IGO -180~ tekperature ture range. ‘lk latter are presumed to be due to the formation of the metal oxychIoridcs; thcrmobafance studies appear to confirm this.

By far the largest poup, this group is characterized by the splitting of the dchyclration cndotherms into two maximas and also the splitting of the oxychloride formation cndothcrms. The splitting of the former rcsultcd in the formation of maximas in the 175”-190~ and the 205~--240~ temperature range. It is interesting to observe that the thermogram for yttrium appears to fit nicely between dysprosium and holmium, in agrccmcnt with results found from separation studies6.

In this group, the splitting of the dehydration endothcrms were again observed but new endothcrms appcarcd in the 3x0”-325” temperature range. These new cnclothcrms wcrc characterized by their rather sharp, narrow appearance ; in contrast to the broad ~xldotllersns found in this region in the Group I I I compounds. SUMMARY

The thcrmnl decomposition of all of tile ram-earth chloride 1Iytirnte.v way sturlicd by diffcrcntinl thermnl an&y&. By USC of the resulting tll~rIn~~r~~nl~, it is po?isiblc to apply tliiv method as iL means of idcntificstion of the indivitlunl rareearth clcmcnts. The cnclothcrm temperature mnxinl0.Y arc rccorclccl and cliucusuecl for all of the rsrc-carth compounds.

Unc &tuck2 stir In d&ompouition thcrmiqne Lcv par I’i~lldySC thcrmiquc cliffbxmticllc. l’itlcntific;~tiot~ clc ccs Glbmcnts.

dcs cltlorurcs thcrmogmmmcs

dc tcrrcs rams hydratds a &A cfff+dc ubtcnus pcuvcnt Otrc utilisbg pour

%USAMMBNL:ASSUNG Die thcrmisctic Zcnictzung clcr ~ii~uri~-~Iy~r~tc allcr dtancn Die crtdtcncn tinl-tllermoannIytiscIlcr Methodcn untcrsucht. Iclcntifizicrung dcr cinzelnc?n scltcncn 1Srdcn.

Erdan wurcicn Thurmogrammc

mit I-Iilfe diffcrencrmliglichcn tlic

REFERENCES

’ w.

J, ShlOTtI~RS

ANV

Y.

CIIIANG,

~iffcrclltiltt

I’hcYWld

.‘frM4~ySiS:

Theory

and

Pul~liuhing Co., Now York 1958. 2 \V.w. WI~NDLAND'r,~. IllOVg. CFtNZ
ClM??fl.,5 (1957) 118. WI~NDLANDT,~. Iaovg. ~9 N~~clectv. CJrem, 9 (I
3 W.

Prnctice,

Chemical

W.

John

Wiicy

ant1 Sons,

Inc.,

New York

1947,

p. ,lr.

reel Ttieiv Comfiouwds,

Reccivcd

April zgth,

rg59