GB1560251A

GB1560251A - Method for producing sigle crystals of alpha mercuric iodide

Info

Publication number: GB1560251A
Application number: GB214877A
Authority: GB
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1976-01-26
Filing date: 1977-01-19
Publication date: 1980-01-30
Also published as: JPS5291800A; BE850444A; NL7700358A; FR2338742B1; FR2338742A1; DE2702568A1

Description

(54) METHOD FOR PRODUCING SINGLE CRYSTALS OF ALPHA MERCURIC IODIDE (71) We, COMMISSARIAT A L'ENERGIE ATOMIQUE, an organisation created in France by Ordinance No.

45-2563 of 18th October 1945, of 29 Rue de la Federation, Paris 75015, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : - This invention relates to a method of production of single crystals of alpha mercuric iodide.

A number of different methods have been tried up to the present time in an attempt to obtain single crystals of alpha mercuric iodide of satisfactory crystal quality either by growth in solution or by growth in vapor phase. Of all these methods, there is only one known method which produces satisfactory results in regard to the quality of the crystals obtained.

This method forms the subject of patent pub lication No. 2,313,977 filed on June tilth, 1975 in the name of Commissariat à PEnergie Atomique. In accordance with this method, alpha mercuric iodide crystals are grown from a solution in an organic solvent of alpha mercuric iodide and of at least one ionic iodide such as ammonium iodide, hydroxylamine hydriodide or a hydriodide of an organic monoamine.

By virtue of the presence of said ionic iodide in the mercuric iodide solution, there are formed complex compounds of iodomercurate of the R+HgI3- type or of the R2+(HgI*)2- type in which R1 represents the organic cation, the ammonium cation or the hydroxylammonium cation.

The formation of these complex compounds which are soluble in the organic solvents employed increases the solubility of alpha mercuric iodide in the solution to an appreciable extent and considerably broadens the zone of metastability of saturated solutions of alpha mercuric iodide. Starinb from these solutions, it is possible to obtain single crystals of alpha mercuric iodide by employing conventional crystal growth techniques such as a decrease in temperature of the solution, evaporation of the solvent or recirculation of the solution between zones at different temperatures while preventing uncontrolled nucleation.

Although this method is wholly satisfactory, a disadvantage nevertheless arises from the need to carry out extreme purification of the ionic iodide employed in order to prevent this latter from containing impurities in the form of cations which would be liable to become subsequently adsorbed on the growing single crystals, thus forming traps which would be detrimental to the mobility and lifetime of the charge carriers within the mercuric iodide.

Moreover, in order to facilitate desorption of the organic cations or of the ammonium cations which are weakly adsorbed on the surfaces of the growing single crystals of alpha mercuric iodide, solutions containing low concentrations of ionic iodide are employed and a low growth rate is maintained.

The method in accordance with the invention overcomes the disadvantages recalled in the foregoing, especially insofar as single crystals of alpha mercuric iodide of very good quality can be obtained more rapidly from an alpha mercuric iodide solution having a higher concentration and containing an agent for increasing the solubility of the alpha mercuric iodide in the solution and consisting of a di alIlylsuiphoxide which combines with the mercuric iodide in order to form complex molecular compounds which are soluble in the organic solvents employed. The non-ionic character of these complexes serves to forestall any potential danger of adsorption of impurity cations, the solutions can be given a higher concentration and the rate of crystal growth can be increased without causing any damage to the single crystals.Furthermore, the dialkylsulphoxides are stable organic liquids which can readily be purified by distillation.

To this end, the method of production of single crystals of alpha mercuric iodide in accordance with the invention essentially consists in dissolving in an organic solvent alpha mercuric iodide and at least one dialkyisuiph- oxide, the molar ratio of the dialkylsuiphoxide with respect to the solvent being within the range of 0.01 to 0.1 mole of dialkylsuiph- oxide per mole of solvent and the molar ratio of the alpha mercuric iodide with respect to the dialkylsuiphoxide being within the range of 0.5 to 0.6 mole of alpha mercuric iodide per mole of dialkylsuiphoxide, and in growing single crystals of alpha mercuric iodide from said solution at a temperature above 400 C.

The diaalylsulphoxides employed in the method according to the invention are preferably selected from dimethylsulphoxide, methylethylsulphoxide and diethylsulphoxide.

The organic solvents which can be employed in accordance with the method contemplated by the invention include saturated aliphatic solvents which are moderately polar and stable in the presence of mercuric iodide. It is possible in particular to employ the esters derived from the esterification of acetic acid by saturated aliphatic alcohols, such as, for example, methyl acetate, ethyl acetate, propyl acetate and butyl acetate, the saturated al; phatic monoketones such as, for example, acetone, ethyimethylketone, diethyiketone and dipropylketone, and the saturated nitroalkanes, such as, for example, nitroethane and nitropropane.

When a dialkylsulphoxide having the general formula

in which R1 and R2 are either identical or dit- ferent alkyl radicals is dissolved with alpha mercuric iodide in accordance with the invention, a complex molecular compound is formed in accordance with the reversible reaction:

and this complex is soluble in the organic soN vents employed.

The formation of this molecular complex of mercury increases the solubility of the alpha mercuric iodide to an appreciable extent and considerably broadens the zone of metastability of the saturated solution of alpha mercuric iodide.

The interaction of dialkylsulphoxide with alpha mercuric iodide corresponds to a bond of the electron donor-acceptor type and is suf ficiently strong to dissolve the mercuric iodide in the dialkylsulphoxide solution and to form the molecule complex but is nevertheless sufficiently weak to ensure that said complex does not crystallize above 400C at the same time or instead of the alpha mercuric iodide from the saturated solution'of alpha mercuric iodide.

Thus in the method according to the invention, there may first be prepared a saturated solution of alpha mercuric iodide and of dialkylsulphoxide, the molar ratios of the dialkylsulphoxide with respect to the solvent and with respect to the mercuric iodide being within the ranges defined earlier and single crystals of alpha mercuric iodide may be grown from this solution by employing conventional techniques of crystal growth in solution, for example by reducing the temperature of the solution or by evaporating the solvent, or by recirculating the solution between zones at different temperatures.

At the time of growth of the single crystals of alpha mercuric iodide, the molecular com- plex is weakly adsorbed on the surfaces of the single crystals. However, by reason of the fact that the bond of the electron donoracceptor type between the dialkylsulphoxide and the mercuric iodide is labile, the adsorbed complex decomposes into a mercuric iodide molecule which crystallizes and into two di alkylsulphoxide molecules which are readily desorbed since they have no electric charge.

In consequence, within the range of the molar ratios mentioned in the foregoing and above 400C, the presence of this molecular complex does not prevent uniform growth of type-F faces layer by layer and the single crystals of alpha mercuric iodide thus obtained have a prismatic appearance, namely an appearance which essentially develops the stable type-F faces: {ill0}, {owl}, (101) and (oll), the faces (101) and (011) being of lesser importance.

One example of execution of the method in accordance with the invention is given hereunder without any limitation being implied, reference being made to the single accompanying figure.

In this example, in order to grow single crystals of alpha mercuric iodide from the starting solution, the technique of recirculation of the solution is employed. It is recalled that the technique of recirculation of the solution consists in making use of two tanks which communicate with each other; one tank contains polycrystals to be dissolved and the other tank contains seeds to be grown. The technique consists in maintaining the dissolution tank at a higher temperature than that of the growth tank and in continuously circulating the solution from one tank to the other.A stationary mass transfer is thus established as a function of the temperature difference between the tanks and of the rate of flow of the solution, thus producing a predetermined rate of growth of the single crystals, The method in accordance with the invention is carried out in the device which is shown diagrammatically in the accompanying figure.

This device comprises two tanks 1 and 2 which communicate with each other. The dissolving tank 1 contains polycrystals of alpha mercuric iodide in a Teflon (Registered Trade Mark) beaker 4 pierced with holes; the growth tank 2 contains four prismatic seeds of alpha mercuric iodide having a volume of a few mm3 and suspended beneath the impeller shaft 3.

These seeds of alpha mercuric iodide have previously been obtained in a special vessel by spontaneous seeding on Teflon threads by reduction of the temperature of a saturated solution of alpha mercuric iodide having the same composition as the solution which is subse- quently used for growing the crystals in accordance with the invention.

There is prepared at the same time the solution of alpha mercuric iodide and of dimethylsulphoxide which is intended to circulate between the tanks 1 and 2. This solution is prepared from highly purified alpha mercuric iodide and from "very pure" dimethylsulphoxide of the type which is employed in ultraviolet spectroscopy.

The preliminary manufacture of this highly purified alpha mercuric iodide is carried out by initially making use of "super-pure" iodine and of 7N mercury (that is, mercury having a purity of 9999999 /O)- This preliminary pre- paration of highly purified alpha mercuric iodide is carried out, for example by dissolving "super-pure" iodine in a solution of "very pure" dimethylsulphoxide in ethyl acetate for electronic uses by introducing 7N mercury in excess and by agitating at 700C until the reaction of the iodine proceeds to completion.

The iodine reacts slowly with the mercury which is present at the bottom of the flask and the mercuric iodide which is thus formed dissolves in the solution and crystallizes, thus forming a crust on the flask walls which are at a lower temperature at the upper end. The alpha mercuric iodide thus obtained can be purified to a greater extent by successive recrystallizations, this being achieved by making use of solutions having the same composition as those used in the preparation of the alpha mercuric iodide.

There is then prepared a saturated solution of alpha mercuric iodide which is intended to circulate between the tanks 1 and 2 by dissolving 380 grams of highly purified alpha mercuric iodide prepared in the manner described in the foregoing and 116 milliliters of "very pure" dimethylsulphoxide in four liters of ethyl acetate for electronic uses.

The above-mentioned solution is then circulated between the two tanks 1 and 2 while maintaining between these latter a temperature difference of the order of a few degrees centigrade: for example, the dissolution tank 1 is maintained at 520C and the crystalgrowth tank 2 is maintained at 500C.

Mass transfer of the alpha mercuric iodide takes place between the two tanks by convection currents. The impeller shaft 3 rotates at a speed of 30 revolutions per minute with a -change in direction of rotation at 30-second intervals. After a period of a few months, there are thus obtained four practically isometric single crystals of alpha mercuric iodide having a volume of a few cm3. On completion of the growth process, the solution is discharged and the single crystals of alpha mercuric iodide are allowed to cool slowly within the tank 2 to room temperature.

The single crystals of alpha mercuric iodide thus obtained have a prismatic appearance, are isometric, perfectly transparent and free from any inclusions of solution. Growth of the single crystals takes place freely in solution without either mechanical stress or thermal shock, thus making it possible to obtain single crystals of alpha mercuric iodide of high crystalline perfection (the proportion of dislocations is only of the order of about ten per cm2). Moreover, by virtue of the method according to the invention, the rate of growth of single crystals is higher than that which can be obtained from solutions of mercuric iodide and ionic iodide and this results in a saving of time of the order of 15% in the production of single crystals of alpha mercuric iodide.

The single crystals of alpha mercuric iodide obained by means of the method in accordance with the invention can be employed in particular in the manufacture of X- and gamma- radiation detectors and spectrometers.

WHAT WE CLAIM IS: 1. A method of production of single crystals of alpha mercuric iodide, wherein alpha mercuric iodide and at least one dialkylsulphoxide are dissolved in an organic solvent, the molar ratio of the dialkylsulphoxide with respect to the solvent being within the range of 0.01 to 0.1 mole of dialkylsulphoxide per mole of solvent and the molar ratio of the alpha mercuric iodide with respect to the dialkylsulphoxide being within the range of 0.5 to G.6 mole of alpha mercuric iodide per mole of dialkylsulphoxide and wherein single crystals of alpha mercuric iodine are grown from said solution at a temperature above 40or.

2. A method according to claim 1, wherein the dialkylsulphoxide is selected from dimethylsulphoxide, methylethylsuiphoxide and diethylsulphoxide.

3. A method according to claim 1 and claim 2, wherein the organic solvent is selected from the esters of acetic acid with the saturated ali- phatic alcohols, the saturated aliphatic monoketones and nitroalkanes.

4. A method according to any one of claims 1 to 3, wherein the single crystals of alpha

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The method in accordance with the invention is carried out in the device which is shown diagrammatically in the accompanying figure. This device comprises two tanks 1 and 2 which communicate with each other. The dissolving tank 1 contains polycrystals of alpha mercuric iodide in a Teflon (Registered Trade Mark) beaker 4 pierced with holes; the growth tank 2 contains four prismatic seeds of alpha mercuric iodide having a volume of a few mm3 and suspended beneath the impeller shaft 3. These seeds of alpha mercuric iodide have previously been obtained in a special vessel by spontaneous seeding on Teflon threads by reduction of the temperature of a saturated solution of alpha mercuric iodide having the same composition as the solution which is subse- quently used for growing the crystals in accordance with the invention. There is prepared at the same time the solution of alpha mercuric iodide and of dimethylsulphoxide which is intended to circulate between the tanks 1 and 2. This solution is prepared from highly purified alpha mercuric iodide and from "very pure" dimethylsulphoxide of the type which is employed in ultraviolet spectroscopy. The preliminary manufacture of this highly purified alpha mercuric iodide is carried out by initially making use of "super-pure" iodine and of 7N mercury (that is, mercury having a purity of 9999999 /O)- This preliminary pre- paration of highly purified alpha mercuric iodide is carried out, for example by dissolving "super-pure" iodine in a solution of "very pure" dimethylsulphoxide in ethyl acetate for electronic uses by introducing 7N mercury in excess and by agitating at 700C until the reaction of the iodine proceeds to completion. The iodine reacts slowly with the mercury which is present at the bottom of the flask and the mercuric iodide which is thus formed dissolves in the solution and crystallizes, thus forming a crust on the flask walls which are at a lower temperature at the upper end. The alpha mercuric iodide thus obtained can be purified to a greater extent by successive recrystallizations, this being achieved by making use of solutions having the same composition as those used in the preparation of the alpha mercuric iodide. There is then prepared a saturated solution of alpha mercuric iodide which is intended to circulate between the tanks 1 and 2 by dissolving 380 grams of highly purified alpha mercuric iodide prepared in the manner described in the foregoing and 116 milliliters of "very pure" dimethylsulphoxide in four liters of ethyl acetate for electronic uses. The above-mentioned solution is then circulated between the two tanks 1 and 2 while maintaining between these latter a temperature difference of the order of a few degrees centigrade: for example, the dissolution tank 1 is maintained at 520C and the crystalgrowth tank 2 is maintained at 500C. Mass transfer of the alpha mercuric iodide takes place between the two tanks by convection currents. The impeller shaft 3 rotates at a speed of 30 revolutions per minute with a -change in direction of rotation at 30-second intervals. After a period of a few months, there are thus obtained four practically isometric single crystals of alpha mercuric iodide having a volume of a few cm3. On completion of the growth process, the solution is discharged and the single crystals of alpha mercuric iodide are allowed to cool slowly within the tank 2 to room temperature. The single crystals of alpha mercuric iodide thus obtained have a prismatic appearance, are isometric, perfectly transparent and free from any inclusions of solution. Growth of the single crystals takes place freely in solution without either mechanical stress or thermal shock, thus making it possible to obtain single crystals of alpha mercuric iodide of high crystalline perfection (the proportion of dislocations is only of the order of about ten per cm2). Moreover, by virtue of the method according to the invention, the rate of growth of single crystals is higher than that which can be obtained from solutions of mercuric iodide and ionic iodide and this results in a saving of time of the order of 15% in the production of single crystals of alpha mercuric iodide. The single crystals of alpha mercuric iodide obained by means of the method in accordance with the invention can be employed in particular in the manufacture of X- and gamma- radiation detectors and spectrometers. WHAT WE CLAIM IS:

1. A method of production of single crystals of alpha mercuric iodide, wherein alpha mercuric iodide and at least one dialkylsulphoxide are dissolved in an organic solvent, the molar ratio of the dialkylsulphoxide with respect to the solvent being within the range of 0.01 to 0.1 mole of dialkylsulphoxide per mole of solvent and the molar ratio of the alpha mercuric iodide with respect to the dialkylsulphoxide being within the range of 0.5 to G.6 mole of alpha mercuric iodide per mole of dialkylsulphoxide and wherein single crystals of alpha mercuric iodine are grown from said solution at a temperature above 40or.

mercuric iodide are grown by reducing the temperature of said solution.

5. A method according to any one of claims 1 to 3, wherein the single crystals of alpha mercuric iodide are grown by evaporation of the solvent.

6. A method according ta any one of claims 1 to 3, wherein the single crystals of alpha mercuric iodide are grown by circulating said solution between a tank containing polycrystals of alpha mercuric iodide and a tank containing single-crystat seeds of alpha mercuric iodide, the latter tank being maintained at a lower temperature than the former tank.

7. A method according to claim 1 for the production of single crystals of alpha mercuric iodide, substantially as hereinbefore described with reference to the drawing.