MXPA00000641A - A composition comprising a metal salt and metal powder therefrom by the calcining thereof - Google Patents

Abstract

Disclosed is a composition of an essentially solid phase state having as components, a liquid hydrophilic organic polymer, an aqueous salt solution containing at least one metallic or metalloid element, and a coagulating agent. The composition on calcination provides a metal-containing powder having an average particle size of 1 micrometer or less. Such metal-containing powders are of value in the preparation of industrial catalysts, ceramics, electronic components, or as fillers in plastics, paints or cosmetics.

Description

A COMPOSITION THAT COMPRISES METAL POWDER METAL SALT OF THE SAME WHEN CALCINATING THE SAME This invention relates to a composition comprising a liquid hydrophilic polymer, an aqueous salt solution of a metal or metalloid element, and a coagulating agent; and a process for preparing a metal-based powder by calcining said composition. The submicron-size metal or metal oxide particles are a valuable industrial convenience which find use in many applications including, for example, in the manufacture of industrial catalyst as it may be employed in the chemical industry, in the manufacture of ceramics, of electronic components, and as fillers, for example, plastics, paints or cosmetics. A wide variety of techniques are available for the manufacture of metal or metal oxide powders that have a very fine particle size. Said techniques include gas phase and condensed phase solution and synthesis processes at high temperature. For a comparative review of the general techniques available, reference is made to the recent publication entitled "Chemical Engineering Aspects of Advanced Ceramic Materials" by V. Havacek and J.A. Puszynski, published in the Journal of Industrial Engineering and Chemical Research, pages 349-377, volume 35, Despite the numerous procedures available, a common problem to a lesser or greater extent with all methods is the difficulty of obtaining particles fine uniforms consistently of good purity. Procedures that can provide a greater consistency in this aspect invariably have high costs associated with its operation due to the complexity of the equipment required, the use of expensive and potentially dangerous raw material, or the high energy consumption. Recently, two closely related procedures were published that provide a means to manufacture submicron-sized metal powders without requiring complex and expensive equipment. EP-A-621,234 for making metal powders requires calcining a polyurethane polymer containing a metal salt; however, yields are relatively low. In another publication, WO 96/29280, this proposal for polyurethane has been modified by avoiding the use of polyisocyanate, a hazardous chemical, with the requirement to subject a gel or liquid to calcination. The gels are difficult to handle or manipulate in said calcination process; the handling of solids is highly preferred. Therefore, it would be desirable to develop an effective cost method leading to the production of metal or metal oxide powders having a fine particle size consistently. It would be particularly advantageous if said process could be operated by using raw material available soon and if it could be operated in the substantial absence of highly specialized equipment and costly solvents or chemical processing aids. Also an advantage would be if said process were able to provide the production of metal powders in a more attractive performance by calcination of solids in contrast to gels which are remarkably difficult to handle in industrial processes. In a first aspect, this invention relates to a composition with components such as: a) a liquid hydrophilic organic polymer; and b) an aqueous salt solution containing at least one metal or metalloid element; characterized in that the composition further comprises (c) a coagulating agent, and wherein the salt is present in an amount to provide the composition with metal or metalloid content of at least 1 weight percent based on the total weight of the composition. the composition. In a second aspect, this invention relates to a process for preparing a metal-based powder, having an average particle size of less than 1 micrometer, by calcining at a temperature of 300 ° C to 3000 ° C, a composition comprising: a) a liquid hydrophilic organic polymer; and b) an aqueous salt solution containing at least one metal or metalloid element; characterized in that the composition further comprises (c) a coagulating agent, and wherein the salt is present in an amount to provide the composition with metal or metalloid content of at least 1 weight percent based on the total weight of the composition. the composition. In a third aspect, this invention relates to a method for solidifying a mixture containing a liquid hydrophilic organic polymer with an aqueous salt solution of at least one metal or metalloid element which comprises adding to said mixture a coagulating agent or precursor to the same. During the present investigations, it has been found that when a coagulating agent is added to a mixture of a hydrophilic organic polymer, notably a polyether polyol, with an aqueous metal salt solution, the resulting composition assumes a substantially solid or semi-solid state. solid. Furthermore, it has been found that when said solid substance is calcined, a metal powder of submicron particle size is obtained wherein the BET surface area of the resulting powder can be improved through the use of a polyether polyol selected in consideration of which has a high oxyethylene content. The present invention provides a relatively simple and cost effective way to manufacture powders containing metal of submicron particle size. These particles find value in the manufacture of ceramic articles, electronics, industrial catalysts and as fillers in plastics, paints or cosmetics including creams and oils. When used as a filler, the smallest particle of the filler provides a minimum reflection of visible light that allows the exploitation of properties of the filler with minimal distortion to the transparency or properties of visible light transmission of the substance to be filled. The transmission or electromagnetic radiation of other wavelengths can be blocked by the presence of the filler. Herein, a composition is described which is a non-fluid substance of an essentially solid or semi-solid phase. The composition comprises as a first component, a hydrophilic polymer having a liquid phase before; as a second component, an aqueous salt solution of a metallic or metalloid substance and characterized in that it contains as a third component, a coagulating agent. The metal or metalloid element content of the composition, excluding the counterion and any water of crystallization, is at least 1 weight percent based on the total weight of the composition. Advantageously, the metal or metalloid element content is at least 3 weight percent, preferably at least 5 weight percent, and still more preferably at least 10 weight percent. Although in principle a smaller amount may be present, this goes against the interest of obtaining a high yield of metal powder in the subsequent calcination process. In practice, the higher amount of metal salt present will be limited by its water solubility limit and concomitantly the miscibility with the hydrophilic polymer.

The individual components of the composition are described in detail below. The hydrophilic polymer component of the composition initially has a liquid phase and can be any inorganic or organic polymer exhibiting a hydrophilic trait including, as examples, polyethers, polyamides and polyesters. Organic polymers are preferred because of their ability to be calcined or pyrolyzed without any noticeable accumulation of a solid residue. Suitable hydrophilic organic polymers include polyether polyols, preferably poly (oxyalkylene-oxyethylene) polyols, and more preferably poly (oxyalkylene-oxyethylene) polyols wherein the oxyethylene content is randomly distributed in the molecule. The oxyalkylene portion of the polyol can be oxyethylene, however, oxypropylene or oxybutylene is preferred. When a poly (oxyalkylene oxyethylene) polyol is selected as the hydrophilic organic polymer component, advantageously the oxyethylene content of the polyol is at least 35, and preferably at least 50, weight percent by weight total molecular weight of the polyol. During the investigation, little or no influence of polyol molecular weight on the properties of the resulting metal-based powder was observed. However, for the convenience of preparing the composition, it is advantageous to select a polyether polyol having a molecular weight in the range of 500 to 10000, preferably 1000 to 6000. Examples of suitable polyether polyols include oxypropylene polyols initiated by glycerin such as VORANOL ™ 1055 (molecular weight 1000); and oxypropylene-oxyethylene polyols initiated by glycerin such as VORANOL 1421 (5,000 molecular weight, 75 weight percent randomly distributed ethylene oxide), both available from The Dow Chemical Company. The second component of the composition is an aqueous salt solution comprising one or more metal or metalloid elements. Advantageously, said metallic or metalloid elements are those as defined in the Periodic Table of Elements selected from groups 2a, 3a, 4a, Sa, 6a; 2b, 3b, 4b, 5b, 8b, 7b, 8, Ib and 2b; the elements of lanthanide; and the actinide elements. The metallic or metalloid element can in principle be any element from which it is desired to obtain a powder. However, those which at present have known industrial value and which are suitable for use in the present invention include lanthanum, barium, strontium, chromium, zirconium, yttrium, aluminum, lithium, iron, antimony, bismuth, lead calcium, magnesium, copper, boron, cadmium, cesium, cerium dysprosium, erbium, europium, gold, hafnium, holmium, lutetium, mercury, molybdenum, niobium, osmium, palladium, platinum, praseodymium, rhenium, rhodium, rubidium, ruthenium, samarium, scandium, sodium , tantalum, tone, thulium, tin, zinc, nickel, titanium, tungsten, uranium, vanadium or ytterbium, or a mixture of two or more thereof. The concentration of salt present in the water is as high as practically possible in consideration of its solubility limit. Wherever possible, it is preferred to use aqueous compositions which are essentially saturated solutions at room temperature. In this invention, by the term "coagulating agent" is meant generally any substance that is capable of inducing coagulation, i.e., inducing a change from a fluid state to a solid or semi-solid state. The coagulating agent can be an organic or inorganic substance with an aqueous pH value of less than 7 (acid), or more than 7 (basic). Advantageously, the substance should not leave any residue after pyrolysis / calcination. When the coagulating agent is an organic substance, primary or secondary amines, amides or alkanolamides are suitable. In particular, for example, monoethanolamine and diethanolamine are suitable. When the coagulating agent is an inorganic substance, suitable basic substances include, for example, ammonium hydroxide, ammonium hydrogen carbonate, ammonium carbonate. Examples of inorganic acid coagulating agents include hydrogen sulfide. In this invention, ammonium hydroxide is especially preferred as a coagulating agent due to its high basicity and attractive water solubility leading to a rapid coagulation result. Ammonium hydroxide can be introduced as an aqueous solution or alternatively generated in situ by the use of a precursor. Examples of precursors include gas and ammonia urea. Urea in thermal energy exposure passes through decomposition leading to the generation of nascent ammonia that in the aqueous environment provides immediate formation of ammonium hydroxide. The formation of ammonium hydroxide by means of urea provides a very effective distribution of the coagulating agent throughout the composition, which in many cases is superior to that which can be achieved by direct introduction and mechanical mixing. In the present it is believed that a high coagulation rate is required so that a fine dispersion of the salt in the polymer is obtained. In contrast, it is believed that a slower coagulation rate provides an undesirable opportunity for the growth of metal salt crystals during the case of coagulation. Said crystal formation provides a locally high concentration of metal salt within the polymer which after calcining can lead to the formation of particles having a larger particle size. The composition of this invention can be prepared by a variety of addition sequences that include simultaneously mixing all the components, or alternatively mixing any two components and then introducing the final component. To facilitate the final formation of metal powders having a small average particle size / large surface area, it is advantageous to first mix the hydrophilic organic polymer with the aqueous metal solution and then introduce the coagulating agent. When using urea as a coagulating precursor, after the initial mixing it is necessary to induce decomposition of the urea by subsequent exposure to, for example, thermal energy. Alternative energy sources can also be used for the same purpose. Any equipment commonly used for mixing viscous liquids can be employed to produce the composition of this invention. Such equipment provides efficient mixing, under high shear conditions, of controlled amounts of aqueous base solution with the aqueous composition comprising both the metal salt as the polymer composition. The composition described when it is calcined under controlled conditions, by providing removal of all the organic substance, results in the formation of a metal-containing powder, free of agglomerate, formed substantially uniform in size. Typically, the calcination conditions require exposing the composition at a temperature of 300 ° C to 3000 ° C, and preferably 400 ° C to 1000 ° C for a period of a few minutes to many hours. To help remove the organic polymer, before calcining, a pyrolysis step can optionally be employed. The term "metal-containing" may mean that the powder contains metal as an element, or an oxide, or other adduct including, for example, a carbide or an alloy thereof, a sulfide or a nitride. If a powder that is obtained will be a metal, a metal alloy, an oxide or a carbide, it will depend on the metal salt (s) present in the composition and on the conditions of pyrolysis or calcination. It should also be appreciated that the same factors can influence the characteristics of the particles including their size and surface area. The metal-containing powder obtained in accordance with this invention is characterized in that it has an average particle size of less than 1 micrometer (1000 nanometers), preferably less than 0.1 micrometer (100 nanometers), and more preferable less than 0.02 micrometer (20 nanometers). With reference to the particle size, it should be appreciated that there will be a particle size distribution where less than 50, preferably less than 25, and more preferably less than 10 percent of the particles will have a particle size in excess of the size of the aforementioned average particle. By the term "particle size" is meant the size of the particle in its largest dimension. The powder is further characterized in that it has a BET surface area of at least 5, preferably at least 25, more preferably at least 50 m2 / gram. In a preferred embodiment, the metal-containing powder has an average particle size of less than 0.1 micrometer and a BET surface area of at least 25 m2 / gram. The powder obtainable in accordance with this invention can comprise any desired metal. Advantageously, the metal, in a zero or appropriate oxidation state, is one or more of the elements lanthanum, barium, strontium, chromium, zirconium, trio, aluminum, lithium, iron, antimony, bismuth, lead, calcium. , magnesium, copper, boron, cadmium, cesium, dysprosium, erbium, europium, gold, hafnium, holmium, lutetium, mercury, molybdenum, niobium, osmium, palladium, platinum, praseodymium, rhenium, rhodium, rubidium, ruthenium, samarium, scandium , sodium, tantalum, tone, thulium, tin, zinc, nickel, titanium, tungsten, uranium, vanadium or ytterbium. The metal-containing powders described having a submicron particle size are of value in the manufacture of ceramic articles, industrial catalysts, electronic components, and as fillers for plastics, paints or cosmetics. When used as a filler, the metal-containing powder will be present, based on the total weight of the volume matrix and powder, typically in an amount of 0.1 to 50 and more usually in an amount of 1 to 25 weight percent. The volume matrix may be, for example, a plastic including a thermoset or thermoplastic polymer, a paint, or a cream or oil of cosmetic composition. The invention is illustrated by means of the following examples. Unless otherwise indicated, all quantities are expressed as parts by weight (pbw). Example 1 A number of compositions were prepared by mixing the components in the sequence as shown in accompanying table 1. The sequence was indicated by. { number} where . { 1} It was first, { 2} It was second and so on. The salt solution was prepared by dissolving 50 g of ZrO (NO3) 2 »xH2O / Ce (NO3)» 6H2O in portions by 6.14: 1 ratio in 40 g of H2O.

The quantities in pbw of the various components mixed in the order and manner indicated were the following: POLYOL 30 pbw SAL 38.9 pbw SALT SOLUTION 70 pbw BASE 20 or 60 pbw Subsequent pyrolysis / calcination of the resulting compositions at 700 ° C resulted in metal powders with a BET surface area as described by 5. Brunauer, P.H. Emmett and E. Teller, J. Am. Chem. Soc. 60. (1938) 309. All BET measurements were carried out using a PULSE CHEMISORB 2700 from Micromeritics Instrument Corporation. Particle sizes were calculated from surface areas of BET in combination with CeO2 and ZrO2 densities as recorded in the Handbook of Chemistry and Physics, 76th edition, CRC Press, 1995. Metal salt: ZrO (NO3) 2 »XH2OICe (NO3)« 6H2O in parts by 6.14: 1 ratio CP1421 an oxypropylene-oxyethylene polio initiated by 5000 molecular weight glycerin having a randomly distributed oxyethylene content of 70 weight percent. CP1055 an oxypropylene polyol initiated by glycerin of molecular weight 1000. Base Ammonium hydroxide, 25 percent aqueous solution Salt solution of metal salt as above in water at maximum solubility. Examples 1 to 14 and 33 were comparative examples, 15 to 32 were supportive for the described invention. The data in Table 1 demonstrate the following: a) Use of an aqueous metal salt solution in preference to a dry salt provides a metal powder with a larger surface area; b) A three component system usually provides metal powder that has a larger surface area than a two component system; c) Use of a polyoxyalkylene-oxyethylene polyol was preferred over the use of a polyoxyalkylene polyol when it is desired to obtain metal powder with a larger surface area; d) Examples 21 to 26 suggested that the order of sequence addition does not significantly influence the surface area property of the resulting metal powder.

Table 1

Claims (15)

1. CLAIMS 1. A composition with components such as: a) a liquid polyether polyol; and b) an aqueous salt solution containing at least one metal or metalloid element; characterized in that the composition further comprises (c) a coagulating agent, in an amount sufficient to cause the composition of the polyol, the salt solution and the coagulating agent to solidify and wherein the salt is present in an amount to provide the composition with content of metal or metalloid element of at least 1 weight percent based on the total weight of the composition.
2. 2. The composition of claim 1, wherein the polyether polyol is a poly (oxyalkylene-oxyethylene) polyol.
3. The composition of claim 2, wherein the poly (oxyalkylene-oxyethylene) polyol has an oxyethylene content of at least 35 percent by weight based on the total weight of the polyol and said oxyethylene of the polyol is randomly distributed to through the polyol.
4. The composition of claim 1, wherein the salt is present in an amount to provide a metal or metalloid element content of at least 5 percent by weight.
5. 5. The composition of claim 1, wherein the metal or metalloid element comprises lanthanum, barium, strontium, chromium, zirconium, yttrium, aluminum, lithium, iron, antimony, bismuth, lead, calcium, magnesium, copper, boron, cadmium, cesium , cerium, dysprosium, erbium, europium, gold, hafnium, holmium, lutetium, mercury, molybdenum, niobium, osmium, palladium, platinum, praseodymium, rhenium, rhodium, rubidium, ruthenium, samarium, scandium, sodium, tantalum, thorium, thulium , tin, zinc, nickel, titanium, tungsten, uranium, vanadium or ytterbium, or a mixture of two or more thereof.
6. The composition of claim 1, wherein the coagulating agent is an organic or inorganic substance having an aqueous pH value greater than 7.
7. The composition of claim 6, wherein the coagulating agent is an organic substance that it comprises a primary or secondary amine, amide or alkanolamine.
8. The composition of claim 1, wherein the inorganic base is ammonium hydroxide.
9. The composition of claim 1, wherein the coagulating agent is an organic or inorganic substance having an aqueous pH value less than 7.
10. The composition of claim 9, wherein the coagulating agent is hydrogen sulfide.
11. 11. A process for preparing a metal-based powder having an average particle size of less than 1 micrometer consisting essentially of: a. mixing, under conditions of high shear stress, (1) liquid hydrophilic organic polymer, (2) aqueous salt solution containing at least one metal or metalloid element in an amount constituting at least 5 weight percent of the total of the liquid hydrophilic organic polymer, the salt solution and the coagulating agent, and (3) an amount of an effective coagulating agent to cause the mixture so obtained to solidify; b. calcining the solid mixture obtained in step (a); and c. recover the metal that contains the powder formed by which, said powder having a smaller average particle size than 1 micrometer The process of claim 11, wherein the powder containing the metal is recovered with a yield of at least 10 percent by weight. The process of claim 11, wherein the powder containing the metal has an average particle size of less than 0.1 microns and a BET surface area of at least 25 m2 / grams. The process according to claim 11, wherein the polymer is poly (oxyalkylene-oxyethylene) polyol having a randomly distributed oxyethylene content of at least 35 weight percent based on the total weight of the polyol; and wherein the coagulating agent is an alkanolamine. The process of claim 11, wherein the hydrophilic organic polymer is a polyol (oxyalkylene-oxyethylene) having a randomly distributed oxyethylene content of at least 35 percent by weight based on the total weight of the polyol; and wherein the coagulating agent is ammonium hydroxide.