Production of nanoparticular compressed tablets / pellets, compressed tablets / pellets produced by the process and use thereof

Description

[0001] The invention relates to a process for producing nanoparticulate pressed tablets / pellets from synthetic and / or natural materials, comprising the steps: Producing an analytically finely ground powder with a grain size of < 75 µm and pressing at least one aliquot thereof in a high-pressure press to form a tablet / pellet.

[0002] Furthermore, the invention relates to a pressed tablet or a pellet and uses thereof.

[0003] In addition to mobile X-ray scanners, microanalysis methods for determining element concentrations directly on solids are becoming increasingly universally applicable and are widely used, for example, in research, for the quality assurance of materials or for exploration in mining.

[0004] However, there is hardly any material suitable as standards with sufficient homogeneity to calibrate the corresponding analytical methods and to secure measurement results.

[0005] Natural materials homogeneous on the micrometer scale, such as crystals, are extremely rare or very difficult to produce. Homogeneous synthetic glasses are difficult to produce, and not all materials can be used. Pressed tablets made from powders, also referred to as pellets, have so far been too coarse for microanalysis and usually contained a binder.

[0006] A manufacturing process for corresponding pellets is known from the prior art, which is the publication "Nano-particulate pressed powder tablets for LA-ICP-MS" by D. Garbe-Schönberg and S. Müller published on April 16, 2014, in The Royal Society of Chemistry, J. Anal. At. Spectrom., 2014, 29, 990. The prior art from this publication is explicitly incorporated into this publication.

[0007] Aurélie Cardin's dissertation, "High Throughput Method for the Development of Bulk Lead-Free Piezoelectric Ceramics," published in Saarbrücken in 2009, describes a process for the production and testing of piezoelectric ceramics in the form of sintered pellets, with the focus on optimizing the time required to produce the test pellets. The pellets are sintered, and the particle size in the pellets is 5 µm after sintering.

[0008] The following briefly lists the problems of the prior art which are addressed here and which are solved by the disclosure here, namely: Problem of analytical chemistry: For the calibration and validation of microanalyses directly on solids, standard reference materials (SRMs) are required, the properties of which should be as similar as possible to those of the unknown samples (matrix matching).

[0009] These SRMs must be so homogeneous at every point that microanalyses with, for example, 1µm to 100µm spatial resolution always produce the same result within a given confidence interval, and this also applies to trace and ultratrace elements, although it is extremely difficult, expensive and time-consuming to find such homogeneous materials in nature or to produce them technically.

[0010] Natural or synthetic glasses, natural or synthetic minerals, metals or metal alloys, powder-pressed tablets made of natural or synthetic substances or mixtures of substances have so far been used as SRMs. Glass: Many materials cannot be melted and processed into a homogeneous glass. During melting, volatile compounds from the original material are lost. Glasses have different properties than, for example, crystalline materials. There are very few naturally homogeneous glasses. Metals: Diffusion within the metal creates heterogeneity during production. Minerals: Natural minerals that are sufficiently homogeneous over larger areas (mm-cm scale) and occur in the required quantities (>300-500g) are very rare.

[0011] During the production / growth of synthetic minerals, heterogeneity arises and it is very difficult to produce crystals that exhibit the necessary homogeneity over larger areas. Powder-pressed tablets: Until now, durable powder-pressed tablets could often only be produced with the addition of binders.

[0012] The particle sizes of "normal" finely ground powder, ranging from 10 to 100 µm, are far too coarse and therefore unsuitable for microanalysis with a spatial resolution of 1 to 100 µm. Nanoparticle pellets produced using the bottom-up (SdT) method are extremely expensive, and their material adaptation to natural materials with complex compositions (50+ elements) is virtually impossible.

[0013] The object of the invention is to demonstrate new possibilities for producing homogeneous standards for a variety of materials.

[0014] Pressed tablets / pellets from synthetic or natural materials are to be produced using a newly developed grinding and pressing process.

[0015] These problems are solved with the corresponding combinations of features according to the main claim and the subordinate claims.

[0016] The process for producing nanoparticulate pressed tablets / pellets from synthetic and / or natural materials comprises the following steps: Producing a powder with a particle size of <75 µm that has been ground to analytical fineness and compressing at least one aliquot thereof in a high-pressure press to form a tablet / pellet, wherein between the aforementioned steps, the powder with a particle size of <75 µm that has been ground to analytical fineness is first wet-ground in a grinding arrangement, jet mill grinding arrangement and / or high-energy ball mill grinding arrangement to form a ground material; subsequently, the ground material is transferred and dried, thermally dried or freeze-dried to form a nanopowder, and the dried nanopowder is subsequently rehomogenized, wherein the at least one aliquot for pressing is selected from the dried and rehomogenized nanopowder, the pressing is carried out without the addition of a binder, and a nanopowder with particle sizes in the range of 30-150 nm is formed.

[0017] Using this "top-down" principle, nanoparticles are produced that can be pressed into stable tablets without the need for additional binding agents.

[0018] The very small particle sizes ensure excellent homogeneity down to the micrometer range.

[0019] The low porosity and excellent surface quality of the tablets also allow them to be measured using electron or ion beam measuring methods in high vacuum.

[0020] The nano-tablets also offer better properties for X-ray fluorescence (X-ray scanner) measurements than previously used powder compacts. This makes the tablets a new, universal material that can be analyzed using many different microanalytical methods and therefore has great potential for suitability as a certifiable standard reference material, both for elemental and isotopic composition.

[0021] The manufacturing process involves ultra-fine grinding, also referred to as the "top-down" principle, to nanoparticles, followed by freeze-drying, and the pressing of the nanopowder, particularly with sapphire discs, in a preferably programmable high-pressure press.

[0022] An optional and preferred reinforcement of the tablets externally (edge, back) with pressing aids such as cellulose, boric acid (sandwich) is possible and useful.

[0023] This process enables the production of stable pressed tablets (compressed pellets) from synthetic and / or natural materials, which are converted into nanoparticles according to the top-down principle, thus making it possible to convert even very complex materials.

[0024] The extremely small particle size enables very good homogenization of substances / mixtures of substances (10-100 µm scale).

[0025] Compared to the state of the art, for example as described in Garbe-Schönberg and Müller, 2014 (see introduction to the SdT), the process used here is now two orders of magnitude better in terms of particle size and surface quality of the tablets due to continuous improvement of the state of the art.

[0026] Significant changes to the state of the art include the type of mill used, the milling protocol, and a fundamental change in the pressing process during tablet production.

[0027] The pressing of the aliquot is preferably carried out in a high-pressure press in the working range of 2 to 80t, 3 to 40t, or 5 - 20t.

[0028] Furthermore, pressing can preferably be carried out in the high-pressure press with polished sapphire, glass and / or diamond discs and form factors adapted to the area of ​​application using pressing tools.

[0029] To avoid contamination of the tablet surface by the metallic press punch and to achieve a very smooth and even surface, a sapphire disc can be placed between the powder and the press punch.

[0030] In particular, wet grinding can be carried out with a liquid, which liquid can be water, de-ionized water and / or an organic solvent.

[0031] Regarding the grinding protocols, the key parameters that vary depending on the material are the amount of water and the grinding time, although other parameters such as rotation speed (acceleration), etc., can also be varied. The following grinding protocols for geological / environmental materials are listed as examples: - Ores, fly ash: 30 min, 10 ml DI water - Basalt (mafic rocks): 45 min, 5 ml DI water - Carbonate / Phosphate: 15 min, 10 ml DI water - Granite etc.: 60 min, 5 ml DI water - Ultramafic rocks: 45 min, 5ml DI water

[0032] The pressed tablets / pellets produced using one of the previously described pressed tablet / pellet production processes for nanoparticulate pressed tablets / pellets made of synthetic and / or natural materials are also worthy of protection.

[0033] Furthermore, the use of the preceding pressed tablets / pellets, produced using one of the preceding pressed tablet / pellet production processes of nanoparticulate pressed tablets / pellets made of synthetic and / or natural materials, as reference material for solid analysis methods, in particular certified according to ISO guidelines, is particularly advantageous.

[0034] Furthermore, the above pressed tablets / pellets produced using one of the above pressed tablet / pellet production processes of nanoparticulate pressed tablets / pellets made of synthetic and / or natural materials can be used as a medium for direct solid analysis.

[0035] The perspective of this development is that in the future, wet laboratories for the digestion of solids will no longer be required, as these types of wet laboratories involve considerable effort for purity and great risks from hazardous substances.

[0036] Overall, the following advantages arise: In order to produce mechanically stable tablets from undiluted original powder, the very high cohesion of the nanoparticles eliminates the need for the addition of a binder, which means that there is no dilution or material change to the original material; the extremely small grain size of the nanoparticles < 100 nm results in very low heterogeneity in analyses with spatial resolution in the range of 1-100 µm; it is the ideal option for homogenising natural or synthetic materials; the mixing and homogenisation of different solids is possible; stability in high vacuum and under high-energy rays (electron beam, ion beam) is guaranteed; the surface is extremely even and smooth (roughness < 30-150 nm); pellets are ultra-homogeneous, stable and have an extremely smooth and even surface.Extremely homogeneous solids, also manufactured according to ISO and REMCO guidelines, suitable as certified standard reference materials (SRMs) for a wide variety of materials for elemental and isotopic composition; addresses the worldwide extreme shortage of homogeneous solids that can be used as micro-SRMs; is suitable for many micro-analytical methods using X-rays, lasers, electron beams and ion beams, thereby solving the very major problem of the worldwide lack of homogeneous SRMs; Self-contained analytical methods for the elemental analysis of solids for major to ultra-trace element composition are possible, whereby wet laboratories with hazardous substances can be eliminated; No need for the addition of grinding or pressing aids; Homogeneous mixture of different materials as nanopowder without phase separation.

[0037] An exemplary embodiment of the invention is described in detail below with reference to the accompanying drawings. These are intended to illustrate the invention and are not to be considered limiting. Furthermore, the prior art is discussed.

[0038] They show: Fig. 1 is a schematic representation of an embodiment of the manufacturing method known in the prior art and Fig. 2 is a schematic representation of an embodiment of the manufacturing method disclosed here.

[0039] In Fig. 1 is a schematic representation of an embodiment of the manufacturing method known in the prior art.

[0040] Here, the starting material p is first ground to analytical fineness (<75 µm) and then mixed with a binder b, e.g. cellulose, wax, boric acid, organic compounds, etc. A(b) and homogenized H. Subsequently, an aliquot of this (p+b) H is pressed in a hydraulic high-pressure press with 5 to 20 t to form a tablet / pellet t(p+b) H P.

[0041] Fig. 2 shows a schematic representation of an embodiment of the manufacturing method disclosed here.

[0042] In a first step, 3-4 g of analytically finely ground powder p of the original material are weighed into a grinding jar, for example made of agate, under a so-called clean bench in a particle-free atmosphere.

[0043] The grinding bowl already contains a certain amount of agate grinding balls, whereby the diameter and total mass of the grinding balls depend on the material (grinding protocol).

[0044] The grinding balls and bowls were previously cleaned by grinding high-purity (optical quality) quartz powder. Deionized water (DIW, > 18.2 MOhm) is then added, the amount depending on the material to be ground (grinding protocol), and is added in such a way that a suspension with an oil-like viscosity is formed during grinding. The grinding bowl is then sealed and placed in a ball mill.

[0045] This is followed by wet grinding M in a high-energy ball mill in interval operation.

[0046] The milling time is material-specific and has been optimized for a range of materials (milling protocol). This produces particles with grain sizes in the nanometer range (30-150 nm).

[0047] The finished ground nanopowder p M is rinsed from the beads and grinding jar as a suspension with DIW and transferred into a pre-cleaned plastic beaker using a pipette. The plastic beaker containing the suspension (approx. 50-100 ml) is shock-frozen at -80°C and then dried in a freeze-dryer G for 72-96 hours.

[0048] The dried nanopowder p MG is transferred into a hand mortar made of agate and rehomogenized H.

[0049] The rehomogenized nanopowder p MGH is weighed into the compression tool (approximately 600 mg for a tablet with a diameter of 13 mm), which is then inserted into a programmable hydraulic tablet press and the powder is then compressed at 10 t / cm2 (for a diameter of 13 mm; compression protocol) for 1 minute P.

[0050] To prevent contamination of the tablet surface by the metallic press die and to achieve a very smooth and even surface, a sapphire disc is placed between the powder p MG and the press die. Depending on the analytical application, tablets t(p MGH ) are produced with various diameters (e.g., 5, 10, 13, 32 mm). List of reference symbols

[0051] A Addition of a binder b b Binder GG Freeze-drying HRehomogenization M Grinding process / wet grinding P Pressing p Powder, analytically finely ground p M Powder, ground p MG Nanopowder / powder, ground and freeze-dried p MGH Homogenized nanopowder / powder, ground, freeze-dried and rehomogenized p+b Powder with binder (p+b) H Powder with binder, homogenized t Pellet, tablet

Claims

1. Compressed tablet / pellet producing method for nanoparticulate compressed tablets / pellets from synthetic and / or natural materials comprising the steps of: - producing a fine-ground powder (p) with grain size <75 µm and - pressing (P) at least an aliquot thereof into a tablet / pellet (t) in a high pressure press, wherein between the above-mentioned steps: - first a wet grinding (M) of fine-ground powder (p) is carried out in a grinding arrangement, jetmill grinding arrangement and / or high-energy ball mill grinding arrangement to produce a ground material (pM); - subsequently, a transferring and drying, thermal drying or freeze-drying (G) of the ground material (pM) to a nanopowder (pMG) occurs and - then a re-homogenizing (R) of the dried nanopowder (PMGR) takes place, wherein - the at least one aliquot for pressing of the dried and re-homogenized nanopowder (pMG) is selected, - pressing takes place without addition of binder, and - a nanopowder (pMG) with grain size in the range of 30-150 nm is formed.

2. Compressed tablet / pellet producing method for nanoparticulate compressed tablets / pellets according to claim 1, characterised in that the pressing (P) of the aliquots (pMGR) takes place in a high pressure press in the working range of 2 bis 80 t, 3 bis 40 t or 5 - 20 t.

3. Compressed tablet / pellet producing method for nanoparticulate compressed tablets / pellets according to claim 2, characterised in that the pressing (P) in the high pressure press occurs with polished sapphire, glass and / or diamond disks and by a pressing tool with form factors adapted to the area of application.

4. Compressed tablet / pellet producing method for nanoparticulate compressed tablets / pellets according to one of the preceding claims, characterised in that the wet grinding (M) is carried out with a liquid, wherein the liquid is water and / or an organic solvent.

5. Compressed tablets / pellets made with any of the foregoing pressed tablet / pellet manufacturing processes for nanoparticulate pressed tablets / pellets of synthetic and / or natural materials.

6. Use of the preceding compressed tablets / pellets produced with one of the preceding compressed tablet / pellet producing methods for nanoparticulate compressed tablets / pellets of synthetic and / or natural materials as a reference material for solid-state analysis or as a medium for direct solid-state analysis.