ISSN 00360236, Russian Journal of Inorganic Chemistry, 2015, Vol. 60, No. 11, pp. 1333–1336. © Pleiades Publishing, Ltd., 2015. Original Russian Text © A.A. Gasanov, E.A. Lobachev, S.V. Kuznetsov, P.P. Fedorov, 2015, published in Zhurnal Neorganicheskoi Khimii, 2015, Vol. 60, No. 11, pp. 1457–1460.
SYNTHESIS AND PROPERTIES OF INORGANIC COMPOUNDS
Indium Monoiodide: Preparation and Deep Purification A. A. Gasanova, E. A. Lobachevb, S. V. Kuznetsovb, and P. P. Fedorovb a
LANKhIT, Moscow, Russia A.M.Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilova str., 38, Moscow, 119991 Russia email:
[email protected]
b
Received April 15, 2015
Abstract—We describe the method and hardware we used to prepare indium monoiodide InI from constitu ent elements and its refining by fractional distillation. We also have determined partition coefficients in liq uid–vapor systems for difficulttoseparate impurities, namely, antimony (0.9), lead (1.8), gallium (0.4), and iron (0.6). DOI: 10.1134/S0036023615110066
The indium iodide system forms indium mono, di, and triiodides [1]. Indium monoiodide InI is iso structural to the lowtemperature thallium iodide phase (orthorhombic space group Cmcm). It melts congruently at 365°C. Unlike most iodides, InI is not moisture sensitive; it slowly converts to indium hydroxide only upon logterm storage under air. Indium monoiodide is used in “metal” fluorescent lamps along with sodium, scandium, tin, and other metal halides [2]. Indium monoiodide is also used in lowtemperature syntheses of semiconductors, for example, InN [3]. The extensive application of InI as a catalyst in organic synthesis [4] is due to the ability of indium to form subhalide clusters [5]. The potential of indium monoiodide for use as detector materials has extensively being studied in recent years [6–10]. Those studies required the devel opment of vertical directional crystallization technol ogies of singlecrystal growth. For grown InI single crystals to have optical quality, the initial chemical should have high purity. There are three major strategies to prepare indium monoiodide in the literature [1, 11, 12]: 1) 2In + HgI2 = 2InI + Hg, 2) InI3 + 2In = 3InI, 3) 2In + I2 = 2InI. The first method is difficult to implement for some precautions are required in handling mercury and due to the involvement of synthesis of mercury iodide itself. The difficulty one faces in implementing the second method is the involvement of indium triiodide, which is highly moisture sensitive. The third method is optimal. Brauer [11] describes the preparation of InI in an ampoule 10 mm in diameter under argon, fol lowed by longterm purification to free the product from excessive iodine and other impurities.
The main method for deep purification of indium monoiodide is crystallophysical refining through directional crystallization or zone melting [7–10]. These methods are laborious. Toshiyuki Onodera et al. [8], for example, used 80 zone passes at 5 mm/h along an ampoule 400 mm long. Denisov et al. [13] deter mined effective distribution coefficients for copper, tin, nickel, and silver upon directional crystallization of InI. Meanwhile, InI has very favorable physicochemi cal parameters for fractional distillation: Tm = 365°C, and Tb = 715°C. Vacuum sublimation was employed to prepare InI in singlecrystalline platelets [14, 15]. Here, we describe our method, which does not require highpurity chemicals, and special hardware for preparing indium monoiodide from the constituent ele ments and for refining it by fractional distillation. EXPERIMENTAL Synthesis from the constituent elements and refin ing of indium monoiodide were performed at the atmospheric pressure using a setup made of silica glass (Fig. 1). The precursors were metallic indium (In0 grade) and iodine (pure grade). Xray powder diffraction patterns were recorded on a Bruker Advance D8 diffractometer (CuKα). TOPAS software was used for data processing. Impurities were determined by spark source mass spectrometry on a JMS01BM2 doublefocusing mass spectrometer. Liquid–vapor partition coefficients were deter mined by equilibrium distillation in an ampoule [16]. RESULTS AND DISCUSSION Until recently, hightemperature fractional distilla tion has not gone beyond the laboratory scale because of
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Inert gas
10 9
6 5 8
7
4 3
Inert gas
2 1
Fig. 1. Schematics of the setup we used for the fraction dis tillation of InI: (1) furnace, (2) reboiler, (3) column heater, (4) fractional distillation column, (5) thermocouple pocket, (6) pipe, (7) receiver heaters, (8) receiver, (9) con denser, and (10) needleshaped collector.
hardware embodiment problems. The main problem consists in the selection of hardware materials, which should meet the following main requirements: (1) thermal stability, (2) high purity, 3) chemical inertness at high temperatures, and Table 1. Liquid–vapor partition coefficients Impurity
Sb
Pb
Ga
Fe
A
0.9
1.8
0.4
0.6
4) mechanical strength. Iodine is a very reactive element at high tempera tures, so metals and alloys are unsuitable for use as hardware materials. Silica is the most widely used hardware material for deep purification technologies; its merits are purity, heat resistance and corrosion inertness at temperatures of up to 1100–1200°С. Figure 1 shows the scheme of the laboratory setup we used for hightemperature fractional distillation under atmospheric pressure. This setup comprises a plate column 40mm in diameter comprising 15 slot ted plates and downcomers. The column is equipped with a head for condensing the distilled iodide with a needle sampler collector. The fractional distillation is performed under an inert gas (argon). After the 1.5h period when the column was oper ated without fraction collection, heads containing vol atile impurities were collected. The amount of heads was 3–5% of the initial charge. The collection of the main fraction took 5–6 h. The bottoms amounted to 8–9% with account to the dynamic entrainment of the material into the column. Therefore, the direct prod uct yield was 85–88%. We studied separation coefficients in the liquid– vapor InI system for difficulttoseparate impurities, namely antimony, lead, gallium, and iron, using equi librium distillation in an ampoule. The results are compiled in Table 1. Massspectrometric data, which characterize InI purity after fractional distillation, are given in Table 2. Table 2 lists the contents of the main impurities; the other elements are below their detection thresholds. Thus, we may conclude that the thusprepared InI is a 99.998%+ pure material with respect to metallic impurities. The Xray powder diffraction pattern for the pre pared material corresponds to the InI pattern. The calculated orthorhombic unit cell parameters are a = 4.7630(5) Å, b = 12.792(1) Å, c = 4.9124(4) Å (Fig. 2). These values correspond to those reported in [17]. In discussing the above results, we will keep in mind that indium monoiodide is a strong reducing agent. Fedorov et al. [18] in attempting to alloy indium monoiodide with copper, mercury, bismuth, anti mony, arsenic, iron, cobalt, and tellurium iodides, found that these metal iodides were reduced with metal evolution. As a rule, the reduction process starts in a solid at temperatures of at most 220°С. Upon sublimation (where most impurities, except for those having high vapor pressures in the elemen tary state, should remain in the unsublimed residue), some metallic impurities can also occur in the form of halide complexes [19–24]. The crystallophysical refining is enough efficient to free InI from tin, lead, cadmium, nickel, silver, and copper and slightly less efficient in refining InI from
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 60
No. 11
2015
INDIUM MONOIODIDE: PREPARATION AND DEEP PURIFICATION
1335
100
I/I0, %
80
60
40
20
0
30
40
50
60
70
80
2θ, deg
Fig. 2. Indium monoiodide Xray powder diffraction pattern.
zinc and manganese. Thus, those two indium monoio dide refining methods are complementary. Fractional distillation can be used alone for preparing highpurity InI, but can also be beneficially combined with crys tallophysical refining. In summary, we have shown the potential of high temperature fractional distillation for producing high purity indium monoiodide. The hardware has been selected, and fractional distillation parameters deter mined. Partition coefficients have been determined for Table 2. Massspectrometry of prepared InI samples Element
Weight ppm
Element
Weight ppm
Al
0.1
Ni
0.4
Si
0.2
Cu
0.3
S
0.1
Ga
0.3
Cl
0.5
Zn
