Mass spectrographic analysis of erbium, cerium and lutetium metal

420

JOURNAL OF THE LESS-COMMON METALS

MASS SPECTROGRAPHIC

ANALYSIS LUTETIUM

OF ERBIUM,

CERIUM

AND

METAL

J. W. GUTHRIE Sandia

Laboratory,

Albuquerque.

(Received

N. M. (U.S.A.)

July r7th, 1964)

SUMMARY A mass spectrograph equipped with an r.f. spark ion source and a photographic plate ion detection system is being used to obtain semiquantitative analyses of homogeneous bulk impurities in commercially available rareearth metals. Analyses of 50 elements in 6 different erbium samples, 41 elements in 2 different cerium samples, and 26 elements in 5 different lutetium samples have been made using a detection limit range of 0.1-20 p.p.m. atomic. Results for hydrogen, carbon, nitrogen, and oxygen by microcombustion and neutron activation techniques are in poor agreement with the mass spectrographic results. Nonhomogeneity can be a serious problem and an important factor when purity is stated for a given rare-earth metal.

INTRODUCTION

When research is being done with the rare-earth metals it is desirable to know as much as possible about the purity or relative purity of available samples so that a suitable choice of samples can be made. This choice is seldom possible with the limited information often furnished with a sample. The reason for sketchy information may be due to the limited analytical service available to a given supplier. Also, the meaning of the term “rare earth 99.9%” that may be furnished with a sample for example, is often misleading, for it is not always clear if the percentage quoted is with respect to other rare earths, total non-gaseous impurities, or a combination of various impurity types. Positive ions with ratios of mass to charge values covering a range of 36 to I were collected simultaneously on 2 x 15 in. Ilford Q2 photographic plates in a Consolidated Electrodynamics Corporation’s 21-110 modified Herzog-Mattauchr geometry mass spectrograph. No attempts were made to obtain extreme limits of detection (parts per billion atomic range) because the effects on experiments of interest for impurities even in the IO p.p.m. atomic range are largely unknown. Even though the absolute accuracy for the following analyses is unknown, the relative values between samples for a given element present as a homogeneous bulk impurity should be highly significant. J. Less-Common

Metals,

7 (1964) 420-426

MASS SPECTROGRAPHIC

ANALYSIS

RESULTS

AND

OF

Er, Ce

AND

Lu

421

DISCUSSION

Erbium and Cerium A ingot (I in. diam.) B wire (0.040 in. diam.) C ingot (I in. diam.) D wire (0.020 in. diam.) E wire (0.050 in. diam.) F sponge Cerium sample No. I ingot No. 2 ingot (No certificates of analyses were available from the suppliers since most samples were obtained from various laboratories which did not obtain analysis information from the supplier.) Sample size varied, but a typical ideal pair of electrodes would be 0.020 in. diam. wires, each one-half in. long. The samples were given no special cleaning before analysis other than an alcohol rinse. The sample electrodes were “pre-sparked” to remove surface contaminants before analytical exposures were made. An exposure range of 106 was covered in 13 separate exposures on each plate. The results were computed by an internal standard methodz, using visual and densitometer data, in which a comparison is made between the exposure required to produce two lines of equal opticaldensity-oneline from the impurity element and the other from the matrix element. Only singly charged ions were used, and allowances were made for plateresponse differences for ions of different mass and for variations in spectrum-line widths3. A minimum of two analyses was made for each sample, one analysis per plate. With the analytical method used, results could not be computed for elements present as nonhomogeneous bulk impurities. A nonhomogeneous impurity is detected by the erratic optical density of its spectrum as exposure increases. Results4 for the erbium and cerium samples are listed in Tables I and III. Additional information is given in the footnotes of the tables. Table II compares the mass spectrographic results for hydrogen, carbon, nitrogen, and oxygen in five erbium samples Erbium

sample

TABLE ERBIUM

Element

A

B

130

90

SAMPLES

C

I

(P.p.m.

atomic)

D

E

5

2

Detectimz

F

limit(a)

___ Th Au Pt w Ta Lu Yb Tm Ho DY Tb Gd

N;

ND3

100

300 830

650 ND ND 500 I

NS IO

300

‘5 I

180

50

20

IO

ND(b) ND ND II0

440 ND ND IO0 3 530 ND 7

N; 130 I000 3 3 170 100 IO IO

7

4 150 130 IO

35 ND IO

330 170 10

20

ND ND ND

I I 3 3 I I

ND ND ND ND

3 I

‘5 4500

I

40 *5 75

4 1 7 Continued

J, Less-Common

Metals,

7 (1964)

overleaf

420-426

J. W. GUTHRIE

422

I (continued) __

TABLE

F Sm Nd Pr Ce La

5 7oo

Ag Pd Rh RU MO Nb Y As Ga Zn cu Ni Fe Mn V Cr Ti SC Ca K Cl P Si Al Mg Na

NG ND ND ND ND

: 6

2 2

47 5

ND

ND

12

20

0.6

6

2

2

0.3 N: ND 14 0.6 0.5 20

64 Nr; ND ND ND 240 I 0.6

ND 16 370 600

60 2 20

20

NIG ND ND ND 275 0.4 SO

ND ND ND 3 5 20

N;5 ND ND ND ND 0.8

80 ND ND ND 50 (c) 100

230 ND : ND ND 120

ND ND ND 50 9 100 0.2

NIZ

NIS

2

40 td7

NG 1000

I

ND

I

IO

(6) 90 I

IO

I

90

30 0.5

IO IO

r7o (c) 830(e) 3500 3oo 5000 0.5 ND

8:: 90 3 32 8 3500 30 9oo N;

1300

(i)

NI?

;I?

4

0.7

&n N c B Li H (g) Purity (% atomic)

ND

98.5

(6) 0.3 IO00 IO0 3oo 0.4 ND 2600

98.9

2

ND2

0.4

340 4 15 0.5

2

110

30 0.8

99.4

ND 7

I; 75 (c) 1300(e)

(4

0.4 40 50 (c) (6) ‘5

1200

1200

200

1000

1800

800

5000 98.8

Nr7 5

NII 5000 99.0

5 2 0.6

0.7 0.6 0.6 I

0.3 I I

0.3 0.2 0.1 0.2

0.4 0.2

0.4 0.1 0.1 0.1

Nl?

0.1

7oo ND

0.2 0.1 0.1

I”; G)

0.1 0.1 0.1

NG 1400

0.1

2

0.1

5

0.1

0.2

0.1

3500 ‘75 7000 0.8

$2

ND 190 ND ND ND ND ND ND ND ND ND 1300 ND ND ND 30

0.2 (4 !h)

2

0.1 0.1 0.1 0.1 0.1

0.03

c&I(j)

(a) Limit of detection was computed from the longest exposure made, using the most abundant isotope of a given element free of interference from any isotope of any other element listed in Table I. The values listed can be decreased by increasing the exposure range. Because of slight differences in realized plate response between samples, the values listed may vary slightly from plate to plate and therefore the values are average. (b) ND: none detected. (c) In the spectrum, but erratic in density with increasing exposure; therefore, it is considered nonhomogeneous. (d) 4*Ti+ and QeMo++ with M/&A4 = 10561 were not resolved and lines for other titanium isotopes were not visible. (e) ErF+ was observed in the spectra in addition to F+. (f) It is assumed that all sources of Cl, F, 0, N, C and H in the material are sampled in the spark process. (g) Separate exposures at a reduced magnetic field were used to record the H+ spectra. (h) No analysis was made. ii) Based on analyzed elements. (j) Does not include a result for hydrogen. J. Less-Common

hfctals, 7 (x964) 420-426

MASS SPECTROGRAPHIC

TABLE COMPARISON

Sample

Hydrogen (p.p.m. atomic)

Carbon (p.p.m. atomic)

Mass spec.

Mass spec.

.\

1300

B C D E

26”” 26”” j"""

JO””

Microcomb.

5""" 9”” 3””

3324"" 66,800 3314”” 1"","""

18""

8””

33,400

5600 ,400 7”“” 2800

AND

Lu

423

II RESULTS

Nitrogen (p.p.m. atornic) -Mass spec.

Microcomb. 28””

OF Er,Ce

ANALYSIS

3”” 3” I”” 2”” I”“”

Neutron act.

ND,<83oo* ND,<83,ooo ND,< 10,700 ND,<83,000 r55,000~60,000**

Oxygen (p.p.m. atomic) Mass spec.

35”” 35”” I”“” l2”” I200

Seutvo?z act.

50,000~6200 62,5”0+42,““0 1.5,7”“&42”” _j2,OOO,-t3I,OOO XD,< lo,400

* ND: none detected. Limit established from one standard deviation of the oxygen or nitrogen blank value. ** The plus and minus values are standard deviations estimated from counting statistics only. Sate : The same sample pieces used for the nitrogen and oxygen analyses were used for the hydrogen and carbon analyses. Sample weights were: A, 1.6386 g; B, 0.1615 g; C, 1.926j g; D, 0.2524 g; E, 0.3968 g. Different sample pieces were used for mass spectrographic analyses, where less than 5 mg of each sample was consumed for the complete analyses of all elements listed in Table I.

with results from other methods.

A microcombustion

technique

was used for analysis

of hydrogen and carbon, and a neutron activation technique Sandia) for the analysis of oxygen and nitrogen. An investigation attempt

to explain

(not performed by is being made in an

the large discrepancies.

Lutetium Sample

I II

scrap-like

pieces

scrap-like

pieces

III IV

scrap-like pieces ingot piece

V ingot piece. Three of the five samples (I, III, IV) all from different suppliers, were accompanied by certificates of analysis for Tm, Y, Si, Mg, and Ca. It was interesting to note that the results were identical. It was also very interesting that none listed Ta, which is the largest metal impurity. Three of the samples (II, III, IV) had identical lot numbers; and the evidence is that the three samples came from the same source even though they were received from different suppliers. Sample I had a different lot number assigned,

but the results in Table IV indicate

that it is very similar to samples III and

IV. Since better

photographic

plates5 were available

for the lutetium

analyses

than for

the erbium and cerium work, a densitometer method similar to one described by OWENS3 was used for computations. The mass spectrograph was also modified to allow 28 spectra to be placed on one plate instead of 15, thus enabling a duplicate analysis to be put on a single plate. The lutetium samples were also rinsed in alcohol before placement in the spark source chamber and were “pre-sparked” before the analytical exposures were made. Ion yields3 were normalized to the longest exposure by using the ratio of beam moni-

J. W. GUTHRIE

424

TABLE CERIUM

Element

III

SAMPLES

(P.p.Ill. atomic)

No.

No. z

Detection limit (a’)

350 80

3 3

I

-

Th Ta

325 ND@‘) 80

Hg Lu Yb

2 20

Tm Er Ho

2 20 6

DY Tb

2

6

ND 25 9

110

30

Gd Nd Pr La Ba

70 320 I75 I75 250

MO Y Zn cu Ni

230 30 75

co Fe Mn Cr V

6 630 30 30 3

100

70

:; 1000 100

30 570 ND

15 7 2 2 20

ND 20

5 ‘64 3 ND 50 6

(d; (d) 270 2.5

Si Al Mg Na F

(d) (d) (d) I

75

I I

I I

0.5 I I 0.4

560 (d) 50

$7

5 0.3 0.3 0.3

650

0.2

(e) 570 6000 3 I

(e) 65 4400 0.4 ND

200

4

I

I

(@? ND

SC Ca I< Cl P

0 N C B Be

IO

N3D” 25

Li H(f) Purity

30 -

(% atomic) k)

98.9

(67

ND -

0.2

0.3 0.2

0.3 0.3 0.3

99.2

See footnote (a) in Table I. ND: none detected Could not be determined because of interference from iasCeF+. Appears as “nonhomogeneous” in the spectrum. Value computed is probably meaningless since sample oxidation, CeO+, was observed. No analysis made. Based on analyzed elements.

evidenced by considerable

J. Less-Common Metals,

7 (1964) 420-426

MASS SPECTROGRAPHIC ANALYSIS OF

Er, Ce AND Lu

425

tor charges2 of the spectra from which ion yields were calculated and the longest exposure spectrum. The low-level impurities could usually be determined only once in each of the longest exposure spectrums of the duplicate run; however, for higherlevel impurities, ion-yields were calculated in several exposures, normalized, and then averaged. An attempt was made to use lines whose optical densities were on the linear portion of the plate calibration curve. A previously prepared plate calibration curve5 using ratios of erbium isotopes was used because the two lutetium isotopes (175Lu : 97.41%. 176LU : 2.59%) have an undesirable3 abundance ratio for use in plate calibrations. A change in instrument slit widths, after the erbium and cerium analyses were made, decreased the sensitivity at a given charge because of increases in line widths. Also, the exposure range used was less than that previously used. A 90% transmission was used as a basis for calculations of detection limit in the lutetium analyses. Results for the lutetium samples are listed in Table IV.

TABLE LUTETIUM

Element Th Ta Lu Tm DY Nd Pr Ce La Y CU Ni Fe Mn Cr Ti SC Ca P Si Al M8 F 0 N C B

I 40 9,600 (97.8%(s) atomic) 230 Nrl$6, 6 IO 6 20 45 30 170 6 15 8 I5 20 I5 160 100 ND (d) 7,800 (d) 3,200

I1

6-56%(c)

SAMPLES

IV (P.P.IIl.

atomic)

III

IV

v

40 8,700 (96.8% atomic) 240 ND ND 4

30 6,400 (96.4% atomic) 215 ND ND

40 9,500 (98.7% atomic)

4 4

N2; 100

IO

4

N2: ‘5 30 25 r4o 4 IO 7

NI;I IO

390 40 40 160

40 25 150 4 ‘5

Detection

limit

IO 2

5

15 3oo ; 20

IO

35 I5 14O 80 ND

NI;I

(d) 18,500 r3o 3.300 I

(d) 21,600

2

(4

ND

r7o 7,200 I

-

;; ND 920 50 750 (d) (d) 850 (d) G

0.5 0.5 I

(a) Based on impurities considered to be homogeneous and listed in Table IV. Values indicated by the supplier in wt%: I, 99.8; II, 99.9; III, 99.9; IV, 99.9; V, not given. (b) ND: None detected. (6) Because of the high level nonhomogeneityof Ta, results for other impuritieswere not computed. Vacuum evaporation techniques and density measurements were used to confirm this serious nonhomogeneity situation. (d) Nonhomogeneous. J. Less-Common

Metals.

7 (1964) 420-426

J.

426

W. GUTHRIE

CONCLUSIONS

Because of significant differences found for some impurites in the analyzed samples, each lot or batch of material from a given supplier, from different suppliers, and following local efforts at purification should be analyzed when basic studies are made using the rare earth metafs. (Based so far on the three rare earths analyzed.) The purity value listed by a given supplier for a rare-earth metal sample is often not reliable and at least needs clarification. Nonhomogeneities may go undetected because of the small amount of sample consumed in an analysis (few mg) and the small number of samplings usually made. One must, therefore, exercise care and use explanations when listing the purity of a rare-earth metal when the value listed is based on the type of mass spectrographic analysis described above even when nonhomogeneous impurities are known to be present, since a value for these impurities cannot be calculated by the analysis procedure used. The mass spectrograph is a valuable instrument for the analysis of homogeneous bulk impurities and the detection of nonhomogeneous impurities in rare-earth metals, and even though in its present state the results are only semiquantitative, it has the potential of yielding more accurate results. ACKNOWLEDGEMENT

The author work.

acknowledges

the assistance

of T. C.

BRYANT,

JR. in many phases of this

REFERENCES 1 J. MATTAUCH AND R. HERZOG, 2. Physik, 8g (1934) 447-786. 2 R. D. CRAIG, G. A. ERROCK AND 1. D. WALDRON,~~ 5. D. WALDRON (ed.),Advances in Mass Spectrometry, Pergamon Press, N&v York, 1959. 3 E. B. OWENS AND N. A. GIARDINO, Anal. Chem., 35 (9) (August, 1963). 4 J. W. GUTHRIE, &lass Spechgraphic Analysis of Erbism andCerium Metal, San&a Laboratory, SC-TM 343-63 (14). 5 J. W. GUTHRIE, Evalwztion of a Modified Ilford Q2 Photographic Emulsion for IMass Spectrographic Uses, Sandia Laboratory, SC-TM-64-534.

J. Less-Common

Metals. 7 (1964) 420-426