METALLIC FLUXES – SCULL MELTING – ENCAPSULATION TECHNIQUES

http://www.phys.umontreal.ca/~andrea_bianchi/index.php?n=Site.Teaching

ANDREA BIANCHI

“Growth of Single Crystals from Molten Metal Fluxes” by Z. Fisk and J. P. Remeika in the Handbook of the Physics and Chemistry of Rare Earths, Vol. 12, Chapter 81, K. A. Gschneider and L. Eyring, North Holland.

PeriodGroup**

1IA1A

18VIIIA

8A

11

H1.008

2IIA2A

13IIIA3A

14IVA4A

15VA5A

16VIA6A

17VIIA7A

2

He4.003

23

Li6.941

4

Be9.012

5

B10.81

6

C12.01

7

N14.01

8

O16.00

9

F19.00

10

Ne20.18

311

Na22.99

12

Mg24.31

3IIIB3B

4IVB4B

5VB5B

6VIB6B

7VIIB7B

8 9 10 11IB1B

12IIB2B

13

Al26.98

14

Si28.09

15

P30.97

16

S32.07

17

Cl35.45

18

Ar39.95

------- VIII-------

------- 8 -------

419

K39.10

20

Ca40.08

21

Sc44.96

22

Ti47.88

23

V50.94

24

Cr52.00

25

Mn54.94

26

Fe55.85

27

Co58.47

28

Ni58.69

29

Cu63.55

30

Zn65.39

31

Ga69.72

32

Ge72.59

33

As74.92

34

Se78.96

35

Br79.90

36

Kr83.80

537

Rb85.47

38

Sr87.62

39

Y88.91

40

Zr91.22

41

Nb92.91

42

Mo95.94

43

Tc(98)

44

Ru101.1

45

Rh102.9

46

Pd106.4

47

Ag107.9

48

Cd112.4

49

In114.8

50

Sn118.7

51

Sb121.8

52

Te127.6

53

I126.9

54

Xe131.3

655

Cs132.9

56

Ba137.3

57

La*138.9

72

Hf178.5

73

Ta180.9

74

W183.9

75

Re186.2

76

Os190.2

77

Ir190.2

78

Pt195.1

79

Au197.0

80

Hg200.5

81

Tl204.4

82

Pb207.2

83

Bi209.0

84

Po(210)

85

At(210)

86

Rn(222)

787

Fr(223)

88

Ra(226)

89

Ac~(227)

104

Rf(257)

105

Db(260)

106

Sg(263)

107

Bh(262)

108

Hs(265)

109

Mt(266)

110

---()

111

---()

112

---()

114

---()

116

---()

118

---()

Lanthanide Series*

58

Ce

140.1

59

Pr

140.9

60

Nd

144.2

61

Pm

(147)

62

Sm

150.4

63

Eu

152.0

64

Gd

157.3

65

Tb

158.9

66

Dy

162.5

67

Ho

164.9

68

Er

167.3

69

Tm

168.9

70

Yb

173.0

71

Lu

175.0

Actinide Series~

90

Th

232.0

91

Pa

(231)

92

U

(238)

93

Np

(237)

94

Pu

(242)

95

Am

(243)

96

Cm

(247)

97

Bk

(247)

98

Cf

(249)

99

Es

(254)

100

Fm

(253)

101

Md

(256)

102

No

(254)

103

Lr

(257)

La Jolla Housewife wins Nobel!

HEATING ELEMENTS

http://www.nabertherm.com/produkte/labor/labor_englisch.pdf  http://www.kanthal.com  

Kanthal Super MoSi2

Kanthal Globar SiC

Metallic heating elements

1425 C

1525 C

1850 C

Box furnace

+ Insulation: Refractories

HOW HOT IS THE FURNACE?

check the type and learn how to weld them!

PYROMETERS

SPECTROMETER

http://www.oceanoptics.com/products/usb2000+.asp

Spectrometer

optical fibre

“telecscope”

INDUCTION HEATING

.. and levitation

http://spaceflight.esa.int/impress/text/education/Glossary/

SKULL MELTING

CZOCHRALSKI PULLING – OXIDES AND GLASSES

W. Assmus and N. Whippey, Chem.-Ing.-Tech. 55, 716 (1983).

V. V. Osiko, et al., Ann. Rev. Mater. Sci. 17, 101 (1987).

ZrO3/Y2O3

BOROTHERMAL REDUCTION

A. V. Kovalev et al., Soviet Powder Metallurgy and Metal Ceramics 27, 717-720 (1988).

LaB6

THE POSSIBILITY OF OBTAINING PURE BORIDES OF RARE-EARTH METALS

A. V. Kovalev, V. N. Minakov, E. M. Dudnik, and Z. A. Zaitseva

UDC 621.762:661.65:661.865

Borides of rare-earth metals long ago attracted attention by their unique combination of physicochemical properties. Lanthanum hexaboride has found the greatest use as a cathode material in various electronic devices. Reproducibility of the parameters and service re- liability of thermal emitters is provided only by increased purity materials.

Generally accepted is the point of view [i] that the purest powders of rare-earth metal borides are synthesized in borothermal reduction of the oxides of the corresponding metals in vacuum and these materials may be obtained in the fused, zone-refined, and single-crystalline form by methods of crucible-free melting [2].

In developing a method of growing single crystals of lanthanum hexaboride the authors of this article encountered the instability of the zone melting process, which is revealed in a change in the coefficient of surface tension of the molten material in relation to the form of original raw material, which led to the formation of bulges and flowing out of the molten zone. It is natural to assume that impurities present in the material are responsible for these instabilities.

Powders of lanthanum hexaboride produced at Donetsk Chemical Reagent Plant by borocarbo- thermal reduction of lanthanum oxide using the following original materials were used for crucible-free zone melting: type LAOK-I lanthanum oxide (96.84% Lan03); amorphous boron (~93% base substance); PM-50 carbon black. The powders (Table i) meet Technical Specification 6-09- 03-8-75 (La ~67.9%, B ~31, Fe <~.0.5, C ~0. i) and the quantity of oxygen in them does not exceed 1.2%. In addition, spectral analysis detected insignificant quantities of the impur- ities AI, Cr, Ni, Mg, Mn, Mo, Si, Zr, Ti, and Ca in them. The lanthanum hexaboride powders were obtained under laboratory conditions by reduction of type LaO-i lanthanum oxide (99.9% La203) with black amorphous boron (~99.3% base substance) in vacuum. However, with the use of powders obtained from pure original components it was not possible to significantly stabil- ize the zone melting process. ~his apparently is related to the presenc&in them of oxides of lanthanum and boron and also of lanthanum borates (nLa203.mB203, n:m = 3:1, i:I, 1:3). Let us dwell in detail on the possible reason for the appearance of these impurities in the final product.

As is known, the reactions in the solid phase differ significantly from the processes occurring in the classical chemistry of solutions [3, pp. 116-121] in view of the fact that even with careful uniform mixing it is practically impossible to bring into contact that quantity of particles which corresponds to the equation of the reaction. Consequently even if diffusion processes are taken into consideration, full occurrence of synthesis is impos- sible. Therefore the appearance of unreacted original components and also of intermediate products may be expected in the final products.

The synthesis of lanthanum hexaboride occurs in two stages [4]:

2La203+I4B--~2LaBOs--}-2LaBo, 2LaBOs+16B--, ,-2LaB~+3B20~, (1) 2La203 + 30B = 4LaB e + 3B~O~ ~ .

Judging from the phase diagram of the LaaO3--BaOa system (Fig , 1) [5] in a d d i t i o n to LAB03 La3BO~, LaB306, and two eutectics exist in it. Compositions from almost pure B203 to 21.5% Lae03 above 1136 • 5~ have a broad area of immiscible liquids. The randomness of mixing of the original components, features of the kinetics of reactions in the solid phase, and the possibility of oxides of lanthanum and boron contained in the charge are all factors

Institute of Problems of Material Science, Academy of Sciences of the Ukrainian SSR. Translated from Poroshkovaya Metallurgiya, No. 9(309), pp. 46-50, September, 1988. Original article submitted December 3, 1987.

0038-5735/88/2709-0717512.50 9 1989 Plenum Publishing Corporation 717

ARC FURNACE

CZOCHRALSKI PULLING – ARC FURNACE

http://mbmlab.ucsd.edu/people/maple.html

CURRENT ANNEALINGR. G. JORDAN. D. W. JONES

Fig, 1. Photograph of the electrode assembly. A is the anode end, the position of which is adjustable. B is the cathode. A typical sample rod is shown on the right.

within the chamber. The chucks are machined from tantalum and are cut to ac- commodate samples between N 5-7 mm diam. Although the clamping nuts and bolts were originally of tantalum, their life time was so short that stainless steel nuts and bolts were later substituted. The chucks are connected to the current carrying arms with flexible tantalum strips (0.003 in. thick). Although designed to accommodate the thermal expansion of the sample during processing they also permit the sample to be loaded under slight tension thus reducing the tendency of the sample rod to bend. Samples between 60 and 160 mm in total length may be accommodated.

The direct current was supplied by a welding generator. The chamber was isolated electrically from both the high and low potential leads for safety.

Samples from two completely different batches of Gd start material were investigated. Complete analyses of several samples from each of the two batches (termed Gd.B1/2 and Gd.01/2) are shown in Table II where all impurity levels in

!P. G. Mattocks et al., J. Less-Common Metals 53, 253 (1977).!

0 1 2 3 4 50

1

2

0 field50 kOe

CeCoIn5

[C-C

sch ]

/T (

J/m

ole

K2 )

temperature (K)

ρ(µΩ

cm)

χ(em

u/cm

3 )

T(K)

C. Petrovic et al., J. Phys.: Cond Mat. 13, L337 (2001).

CeCoIn5 – "clean limit"

R. Movshovich et al., PRL 86 5152 (2001)

d-wave superconductors:

"clean limit": k/T µ T2

"dirty limit": k/T µ const., independent of impurities

"universal limit" in CeCoIn5:

k/T = 0.1 W/K2 m

M. J. Graf et al., PRB 53, 15147 (1996).

0 . 1 1 10

0 . 01

0 . 1

1

10

k (W

/Km

)

T (K )

0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 00

1

2

k/T

(W

/K2 m

)

T 2 (10-2K 2)

Y. Kasahara et al., Phys. Rev. B 72, 214515 (2005).

Superclean regime: εF / Δ ≪ ℓ/ ξ

Bandstructure of CeCoIn5

T. Maehira, et al., J. Phys. Soc. Jpn. 72, 854 (2003).

DE HAAS -VAN ALPHEN – ORBITS

C. Capan et al., Phys. Rev. B 82, 035112 (2010).

Fields applied in the plane:

Magnetic moment formation in B20 phase silicides

M. G. Foeux, J.Phys. Radium 9, 37 (1938).

1. Introduction. – Les travaux relatifs aux alliages mettent souvent en évidence des combinaisons définies. On dit qu'il y a combinaison lorsque le diagramme figurant les variations d'une propriétés physique avec la composition, présente certaines particularités (maximum, changement brusque de direction...) pour un rapport simple entre les masses des constituants.!

L'étude de SiFe a été compliqué par une trace de ferromagnétisme; sa susceptibilité corrigée de celui-ci croit avec la température. Même interprétation que Pour SiMn. Résultats de même genre pour SiCo.!

http://crystdb.nims.go.jp/index_en.html

BINARY PHASE DIAGRAM

Kondo Insulators – FeSi

V. Jaccarino et al., Phys. Rev. 163, 476 (1967).! D. Mandrus et al., Phys. Rev. B 51, 4763 (1995).!

no inversion symm.

B20

0 200 400 6000

2

4

6

8

10

12

χ (

10

–4 e

mu/m

ol F

e)

Temperature (K)

Eg = 750 K, W = 750 K

Exp.

µ E

Eg

W

VAPOR TRANSPORTHarald Schäfer, Chemical transport reactions, Academic Press (1964).

( ) ( ) ( ) ( )2 2 21 / 2ZnO s Cl g ZnCl g O g⎯⎯→←⎯ +⎯+

the “problem”

“Chemical Vapor Transport Reactions–Methods, Materials, Modeling", by Peer Schmidt, Michael Binnewies, Robert Glaum and Marcus Schmidt, DOI: 10.5772/55547

FeSi Kondo Insulators – FeGe Ferromagnetic Metal

x

Tem

pera

ture

(K)

FeSi FeGe

FeSi1–xGex! : spin gap (Δs) ¿ : transport gap (Δt) £ : ρ minimum!" : Curie T (Tc)!Δs of x = 0.24 : 167 K

Tc of x = 0.27 : 150 K!xc ~ 0.25

S. Yeo et al., Phys. Rev. Lett. 91, 46401 (2002).!

1st first order phase transition!... and now Skyrmions in MnSi

T. B. Massalski in “Binary Alloy Phase Diagrams”, ASM International

BINARY PHASE DIAGRAMS

http://www.crystalimpact.com/pcd/Default.htm

PERITECTIC MELT

M. G. Kanatzidis, R. Pöttgen, and W. Jeitschko, Angewandte Chemie 44, 6996 (2005).

REMARKS

•Pre-melting in an arc-furnace brings down the temperature •Fibers from the quartz wool are not always innocent. Use tantalum foil strainer for example. •Getting rid of the oxides on the fluxes is often really helpful

CRUCIBLES

Simple is best: •none, eg. with a lot of flux SiO2 is fine. •carbon coating (add drops of acetone and heat it with the torch.) Standard: •Aluminium oxide: Coors are the best •Graphite: Can be “cheap” if you buy rod. Also, semiconductor-grade graphite is really clean. •Yttrium stabilized zirconia

•Magnesium oxide When in a bind: •Beryllium oxide: Deadly but good

SEALING STATION

FLAME SUPPRESSORS

CHEMICAL “RESISTANT” PUMP

THE TORCH

torches are cheap!

http://www.arnold-­‐gruppe.de

CENTRIFUGE

Flegel

•balance it •fibre frac for dampening

SEALED AMPULE AFTER SPINNING

EXCESS FLUX – NOW WHAT?

Acids: •HCl is always a good starting point •do not forget to buffer Bases: •Aluminium dissolved in sodium hydroxide solutions Halides: •molar solutions of halides (I2 or Br2) in organic solvents Isopropanol + HgCL •

T. Wolf, Phil. Mag. 92, 2458 (2012).

Before use they have to be extracted either mechanically, e.g. with a dentist’s drill orchemically by using a suitable solvent. The easiest way to remove solidified flux is todissolve it with acids or bases. When salts are used as a flux, extraction often can beachieved by immersing the regulus in water. In many cases, however, the crystals areattacked by the solvent, too. Then it is necessary to optimize the dissolution rates ofthe crystals and flux by adjusting etching time, concentration and temperature of thesolvent to keep the losses of the crystals as low as possible.

A very gentle method to eliminate adhering flux is use evaporation. This workswith metal fluxes, like Mg, Yb, Hg, Zn, etc., which exhibit vapor pressures in therange 0.1–1 mbar at relatively low temperatures. Of course, the vapor pressure of thecrystal phase has to be much lower. Here the solidified regulus is put into a silica tubewhich has to be pumped continuously. After heating the tube to an appropriatetemperature the flux starts to evaporate and then condenses at a colder part of thetube leaving behind crystals with extremely clean surfaces. Figure 4 shows a MgB2

platelet crystal grown from a Mg flux in a closed Mo ampoule. In this separationprocess a temperature of 600!C was sufficient to completely evaporate the fluxwithin 3 h.

In the following, a little-known separation method for fluxes like Mg, Al, Y orlanthanides will be discussed which works without using acids or bases. It is based onthe reaction of the flux metals with isopropanol. The underlying reaction,

Mþ 3C3H7OH###!HgCl2

M OC3H7ð Þ þ 1:5H2 þHg

ðM ¼Mg, Al, Y, rare earth elementÞ,

proceeds at temperatures of 80–100!C within hours up to days [3]. HgCl2 facilitatesthe reaction like a catalyst, but most likely, the formed Hg acts as a surfactant byremoving oxide layers from the metal surface. To start the separation process theregulus is placed into a round bottom flask of an evaporator together withisopropanol and 10#4mol HgCl2 per g-atom of flux metal and then heated up. Aftera few hours the solution has to be decanted. One has to bear in mind that the formedisopropoxide in the solution freezes quickly and may block a filter paper.Furthermore, it hydrolyzes rapidly in humid air, precipitating a compound which

Figure 4. MgB2 single crystal platelet after evaporation of the Mg flux.

2462 T. Wolf

Dow

nloa

ded

by [B

iblio

thèq

ues d

e l'U

nive

rsité

de

Mon

tréal

] at 1

4:19

20

May

201

4

TANTALUM TUBING

•“soft” annealed tubing •seamless •thick walled •clean in boiling H2SO4

“good” luck with sourcing: Try to get the leftovers from somebody for a good price

flatten in vice

•use your arc-melter for welding •absolutely use clamps to screw the flattened end to the copper hearth.

OHFC clamps

E-BEAM WELDING

K. Mattenberger, et al., Journal of Crystal Growth 67, 467 (1984).

the Good: •Niobium rod •“clean” weld the Bad: •UHV the Ugly: •high voltage •water cooling

http://cmp.physics.iastate.edu/canfield/photos.html

ICOSAHEDRAL QUASICRYSTAL

HoMgZn

TOP SEEDED SOLUTION GROWTH

A. Langsdorf and W. Assmus, Cryst. Res. Technol. 34, 261 (1999).

Salt encapsulation: LiCl-KCl

DIFFERENTIAL THERMAL ANALYSIS

J. Janssen et al., Journal of Crystal Growth 285 , 670 (2005).

AQUATIC CHEMISTRY

M. Martos, et al., Eur. J. Inorg. Chem. 2008, 3163 (2008)

Ce(NO3)3·6H2O

Zercor™ …

CONCLUSION

•honor your elders! (Go to the library!)

•simple is better

•creativity helps

•sometimes though, a tour de force is needed. (Just try all the fluxes, who knows!)