Process for the preparation of osmium sponge

Abstract

A process for the preparation of osmium sponge comprising the steps of: (1) providing osmeth, an aqueous solution of ethanol and an aqueous solution of hydrazine- hydrate, (2) preparing a mixture of the osmeth and the aqueous solution of ethanol, both provided in step (1), (3) adding the aqueous solution of hydrazine-hydrate provided in step (1) to the mixture prepared in step (2), so forming an aqueous slurry of black-colored solid particles comprising osmium, (4) separating the black-colored solid particles comprising osmium from the aqueous phase of the aqueous slurry formed in step (3), (5) washing the black-colored solid particles comprising osmium separated in step (4) with water or preferably with an aqueous solution of ammonium chloride, (6) drying the washed black-colored solid particles comprising osmium obtained in step (5), and (7) heat treating the dry black-colored solid particles comprising osmium obtained in step (6) in a reducing and hydrogen containing atmosphere, so yielding osmium sponge.

Description

[0001] Process for the preparation of osmium sponge

[0002] The invention relates to a process for the preparation of osmium sponge.

[0003] The term “osmium sponge” used herein denotes a coarse-grained powder of elemental osmium, i.e. osmium metal, having an absolute particle size in the range of, for example, 0.075 to 0.5 mm.

[0004] The reduction of OsO4(osmium tetroxide) or alkali osmates like sodium osmate or potassium osmate is well-known in the art. It is challenging to reduce OsO4or osmates, especially with hydrazine. Osmium tetroxide reduction with hydrazine produces colloidal particles, which are problematic to filter. Osmate reduction with hydrazine is incomplete and colloidal. Osmate reduction with hydrogen gas produces impure osmium sponges containing high levels of included or entrained alkali metals, which require numerous washing and drying steps that do not guarantee sufficient removal. Reductions using sodium borohydride are avoided since they introduce additional alkali metals that need to be removed in addition to safety problems regarding hydrogen formation.

[0005] Object of the invention was to find a process for the preparation of osmium sponge preventing the difficulties and disadvantages mentioned in the preceding paragraph.

[0006] Unexpectedly, said object can be achieved by a process for the preparation of osmium sponge comprising the steps of:

[0007] (1) providing osmeth, an aqueous solution of ethanol and an aqueous solution of hydrazinehydrate,

[0008] (2) preparing a mixture of the osmeth and the aqueous solution of ethanol, both provided in step (1),

[0009] (3) adding the aqueous solution of hydrazine-hydrate provided in step (1 ) to the mixture prepared in step (2), so forming an aqueous slurry of black-colored solid particles comprising osmium,

[0010] (4) separating the black-colored solid particles comprising osmium from the aqueous phase of the aqueous slurry formed in step (3),

[0011] (5) washing the black-colored solid particles comprising osmium separated in step (4) with water or preferably with an aqueous solution of ammonium chloride,

[0012] (6) drying the washed black-colored solid particles comprising osmium obtained in step (5), and

[0013] (7) heat treating the dry black-colored solid particles comprising osmium obtained in step (6) in a reducing and hydrogen containing atmosphere, so yielding osmium sponge. The words "water" or "aqueous" used in various places in this disclosure are preferably to be understood as referring to deionized water. This is in particular true with regard to a special embodiment of the process of the invention disclosed below.

[0014] In step (1 ) of the process of the invention osmeth, an aqueous solution of ethanol and an aqueous solution of hydrazine-hydrate are provided.

[0015] Osmeth is known to the person skilled in the art; here, in particular a chemist familiar with platinum group chemistry. It is a complex formed of one molecule of HMTA (hexamethylenetetramine, 1 ,3,5,7-tetraaza-adamantane, methenamine, commonly also known as urotropine) and two molecules of OsO4 (C6H12N4 2OSO4), see “Tissue Fixation and Osmium Black Formation with Nonvolatile Octavalent Osmium Compounds”, Hanker et al. in Histochemistry 49, 263-291 (1976) or https: / / en.wikipedia.org / wiki / Osmium_compounds. Osmeth can be prepared by mixing an aqueous solution of OsO4with an aqueous solution of excess HMTA, and by separating the solid osmeth particles or crystals so formed from the aqueous phase. Examples of suitable solid-liquid separation methods include methods known to the skilled person such as decanting, squeezing, filtration, centrifugation or combinations thereof. Filtration may be supported by pressure or by suction. It is preferred to perform the separation in such a manner that free-flowing osmeth particles or osmeth powder is obtained.

[0016] The aqueous HMTA solution can be made by dissolving HMTA in water, such aqueous HMTA solution may have an HMTA concentration in the range of, for example, 7 to 14 wt.% (percent by weight). It is expedient to work with HMTA of purity grade >99 wt.%.

[0017] The aqueous OsO4solution can be made by dissolving OsO4in water; such aqueous OsO4solution may have an OsO4concentration in the range of, for example, 1 to 5 wt.%. Crude OsO4can be used for making the aqueous OsO4solution.

[0018] However, the special embodiment of the process of the invention aims at the preparation of osmium sponge of exceptionally high purity of >99.95 wt.% or having a total content of ruthenium plus sodium plus potassium of <500 wt.ppm (ppm by weight) or even at the preparation of osmium sponge of exceptionally high purity of >99.95 wt.% and having a total content of ruthenium plus sodium plus potassium of <500 wt.ppm. Here, it is not expedient to work with crude OsC ; rather, the OsC>4 itself is expediently made by oxidizing “impure” osmium sponge (i.e. osmium sponge having a purity in the range of, for example, 99.8 to <99.95 wt.%) under a stream of pure oxygen at a temperature in the range of, for example 550 to 800 °C and condensing the OsC>4 vapors in cold traps. The cold traps may be chilled with, for example, solid carbon dioxide pellets or liquid nitrogen. The so obtained OsC>4 can then be used for making an aqueous OsO4solution by dissolving it in water.

[0019] The aqueous solution of ethanol can be made by dissolving ethanol in water, such aqueous solution of ethanol may have an ethanol concentration in the range of, for example, 20 to 40 wt.%.

[0020] The aqueous solution of hydrazine-hydrate can be made by dissolving hydrazine-hydrate in water, such aqueous solution of hydrazine-hydrate may have a hydrazine-hydrate concentration in the range of, for example, 8 to 12 wt.%.

[0021] In step (2) of the process of the invention a mixture of the osmeth and the aqueous solution of ethanol, both provided in step (1 ), is prepared. Here, the weight ratio of osmeth : ethanol may be in the range of, for example, 2.66 to 5.33 : 1 . The free-flowing osmeth particles are added to the aqueous solution of ethanol and stirred until completely dispersed; in other words, said mixture is a suspension or slurry of osmeth particles in the aqueous solution of ethanol.

[0022] In step (3) of the process of the invention the aqueous solution of hydrazine-hydrate provided in step (1 ) is added to the mixture prepared in step (2) so as to form an aqueous slurry of blackcolored solid particles comprising osmium. Here, the weight ratio of osmeth : hydrazine-hydrate may be in the range of, for example, 13.32 to 19.98 : 1. It is expedient to control the addition rate of the aqueous hydrazine-hydrate solution, as the reaction in the course of which the blackcolored solid particles comprising osmium are formed is exothermic and it is expedient the temperature not to exceed 78 °C.

[0023] The term “black-colored solid particles comprising osmium” is used herein. Although the chemical nature of the black-colored solid particles comprising osmium has not been determined, it is assumed that these particles mainly comprise or even consist of hydrated OsO2.

[0024] In step (4) of the process of the invention the black-colored solid particles comprising osmium are separated from the aqueous phase of the aqueous slurry formed in step (3) once cooled. Examples of suitable solid-liquid separation methods include methods known to the skilled person such as decanting, squeezing, filtration, centrifugation or combinations thereof. Filtration may be supported by pressure or by suction. After conclusion of step (4) it may be expedient to crush or comminute the black-colored solid particles comprising osmium before performing step (5).

[0025] In step (5) of the process of the invention the black-colored solid particles comprising osmium separated in step (4) are washed with water or preferably with an aqueous solution of ammonium chloride. Such aqueous solution of ammonium chloride can be made by dissolving ammonium chloride in water, such aqueous solution of ammonium chloride may have an ammonium chloride concentration in the range of, for example, 25 to 45 wt.%. It is expedient to work with ammonium chloride of purity grade >99.5 wt.% and preferably with a total content of sodium plus potassium of <100 wt.ppm. The ammonium chloride kind of impregnates the blackcolored solid particles comprising osmium and suppresses or even prevents the risk of deflagration of those particles during process step (7).

[0026] After conclusion of step (5) it may be expedient to crush or comminute the washed blackcolored solid particles comprising osmium before performing step (6).

[0027] In step (6) of the process of the invention the washed black-colored solid particles comprising osmium obtained in step (5) are dried. Drying may be performed, for example, by suction drying or by pressurized inert gas in a pressure filter.

[0028] After conclusion of step (6) it may be expedient to crush or comminute the dry black-colored solid particles comprising osmium before performing step (7).

[0029] The dry black-colored solid particles comprising osmium may contain some residual moisture; here, it may be expedient to further dry the particles; i.e. here, for example, it may be expedient that step (6) comprises a further sub-step in the course of which such residual moisture is removed by heat treating the particles in an inert gas atmosphere before performing step (7). Here, heat treating means that the particles experience a peak temperature (maximum object temperature) in the range of, for example, 60 to 95 °C, for a time period of, for example, 6 to 10 hours. “Inert gas atmosphere” means an atmosphere consisting of carbon dioxide, nitrogen and / or noble gas like in particular argon.

[0030] In step (7) of the process of the invention the dry black-colored solid particles comprising osmium obtained in step (6) are heat treated in a reducing and hydrogen-containing atmosphere so as to yield osmium sponge. To this end, the particles may be put into heat- resistant trays made of a material which does not interact with the particles. Examples include trays of silicon carbide, of fused silica and of quartz. Heat treating means that the particles experience a peak temperature in the range of, for example, 350 to 900 °C, preferably 500 to 650 °C for a time period of, for example, 4 to 12 hours. Said peak temperature may be reached in the course of a heating-up process which may be characterized by a continuously rising temperature curve or preferably by one which rises discontinuously, i.e. step-wise. The heat treatment may be performed in a static oven or in a conveyor oven. The reducing and hydrogencontaining atmosphere may consist of hydrogen or it may be comprised of >0 to 95 vol.% (percent by volume) of at least one inert gas and of 5 to <100 vol.% of hydrogen, wherein the vol.% total 100 vol.%. Examples of inert gases include carbon dioxide, nitrogen and noble gases like in particular argon. It is preferred that the reducing and hydrogen-containing atmosphere is provided in the form of a respective gas flow which purges the inner of the oven. It is expedient to first purge the inside of the oven with an inert gas or an inert gas mixture before starting to purge with the reducing and hydrogen-containing gas.

[0031] After cooling down, the osmium sponge may be comminuted.

[0032] It is expedient to package and store the osmium sponge in tight containers, e.g. in sealed ampules.

[0033] The process of the invention is a process for the preparation of osmium sponge; it yields osmium sponge. In its special embodiment, the process of the invention yields osmium sponge of exceptionally high purity of >99.95 wt.% and / or having a total content of ruthenium plus sodium plus potassium of <500 wt.ppm. Hence the invention relates also to osmium sponge of exceptionally high purity of >99.95 wt.% and / or having a total content of ruthenium plus sodium plus potassium of <500 wt.ppm, wherein the osmium sponge is obtainable by the process of the invention in its special embodiment.

[0034] Said exceptionally highly pure osmium sponge can be used in CVD (chemical vapor deposition) applications for the production of large single crystals of osmium.

[0035] Working example:

[0036] First of all, four aqueous solutions (i) - (iv) were prepared.

[0037] (i) An aqueous solution of HMTA was prepared by dissolving 1.4 kg of HMTA in 10 liters of water.

[0038] (ii) A 33 wt.% aqueous solution of ethanol was prepared by mixing ethanol and deionized water. (iii) A 10 wt.% aqueous solution of hydrazine-hydrate was prepared by mixing hydrazine-hydrate and deionized water.

[0039] (iv) A 27.7 wt.% aqueous solution of ammonium chloride was prepared by dissolving ammonium chloride in deionized water.

[0040] 50 liters of deionized water were heated to 50°C and then 2.5 kg OsC>4 (made by oxidizing “impure” osmium sponge having a purity of 99.8 wt.% under a stream of pure oxygen at 800 °C and condensing the OsC vapors in a cold trap chilled with solid carbon dioxide pellets) were added and dissolved. After complete dissolution of the OsO4the heating was stopped. The HMTA solution (i) was carefully added and, after the addition was completed, stirring was stopped to allow the solid osmeth particles which had formed to settle. Then the osmeth particles were separated from the aqueous phase by suction filtration and sucked until dry to yield 3.195 kg.

[0041] The osmeth particles were added into 3 liters of the 33 wt.% aqueous solution of ethanol (ii); this mixture was stirred until the osmeth was completely dissolved. Then 2 liters of the 10 wt.% aqueous solution of hydrazine-hydrate (iii) were slowly and carefully added while stirring until a black and thick aqueous slurry of black-colored solid particles comprising osmium had formed with no visibility of orange-colored particles of osmeth. Then the black-colored solid particles comprising osmium were separated from the aqueous phase by suction filtration and washed with the 27.7 wt.% aqueous solution of ammonium chloride (iv) while continuing the sucking filtration until the solid material was dry. Then the solid material was put in trays made of silicon carbide and put into a stationary oven having an inner volume of 1 .13 m3and which was heated and purged with gas according to the following scheme: After cooling the trays containing the so formed osmium sponge were taken out of the oven and the osmium sponge material was comminuted using a pestle and mortar and analyzed via ICP- OES for its osmium, ruthenium, sodium and potassium content. The osmium sponge was packaged in sealed ampules. Yield: 1 .725 kg of osmium sponge

[0042] Result of ICP-OES analysis:

[0043] Os: 99.99 wt.%

[0044] Ru: 5 wt.ppm

[0045] Na: <1 wt.ppm K: <1 wt.ppm

Claims

Claims1 . A process for the preparation of osmium sponge comprising the steps of:(1) providing osmeth, an aqueous solution of ethanol and an aqueous solution of hydrazinehydrate,(2) preparing a mixture of the osmeth and the aqueous solution of ethanol, both provided in step (1),(3) adding the aqueous solution of hydrazine-hydrate provided in step (1 ) to the mixture prepared in step (2), so forming an aqueous slurry of black-colored solid particles comprising osmium,(4) separating the black-colored solid particles comprising osmium from the aqueous phase of the aqueous slurry formed in step (3),(5) washing the black-colored solid particles comprising osmium separated in step (4) with water or preferably with an aqueous solution of ammonium chloride,(6) drying the washed black-colored solid particles comprising osmium obtained in step (5), and(7) heat treating the dry black-colored solid particles comprising osmium obtained in step (6) in a reducing and hydrogen containing atmosphere, so yielding osmium sponge.

2. The process of claim 1 , wherein the weight ratio of osmeth : ethanol is in the range of 2.66 to 5.33 : 1.

3. The process of claim 1 or 2, wherein the weight ratio of osmeth : hydrazine-hydrate is in the range of 13.32 to 19.98 : 1 .

4. The process of any one of the preceding claims, wherein the heat treating of step (7) means that the dry black-colored solid particles comprising osmium obtained in step (6) experience a peak temperature in the range of 350 to 900 °C, for a time period of 4 to 12 hours.

5. The process of any one of the preceding claims, wherein the reducing and hydrogencontaining atmosphere of step (7) consists of hydrogen or is comprised of >0 to 95 vol.% of at least one inert gas and of 5 to <100 vol.% of hydrogen, wherein the vol.% total 100 vol.%.

6. The process of claim 5, wherein the at least one inert gas is carbon dioxide, nitrogen, one or more noble gases or any mixture thereof.

7. The process of any one of the preceding claims, wherein the osmeth is prepared by mixing an aqueous solution of OsC>4 with an aqueous solution of excess HMTA, and by separating the solid osmeth particles or crystals so formed from the aqueous phase, whereinthe OsC>4 itself is made by oxidizing osmium sponge having a purity in the range of 99.8 to <99.95 wt.% under a stream of pure oxygen at a temperature in the range of 550 to 800 °C and condensing the OsO4vapors in cold traps.

8. Osmium sponge having a purity of >99.95 wt.% and / or having a total content of ruthenium plus sodium plus potassium of <500 wt.ppm, wherein the osmium sponge is obtainable by the process of claim 7.

Images