Thermoplastic mounting medium and a method of its manufacture

Abstract

A thermoplastic mounting medium (25) configured for embedding and subsequently fixating a sample material (10) in a moulding cavity (11) by means of sintering or melting the thermoplastic mounting medium (25) to become a monolithic bulk material at least partially accommodating said sample material (10) The thermoplastic mounting medium (25) includes a mixture of: polymer mixed with organic fibres, and thermally conductive filler having a thermal conductivity of minimum 5 W/(mK) wherein the thermally conductive filler is mixed homogeneously with the composite material and wherein that the thermally conductive filler represents at least 30% w. of the thermoplastic mounting medium.

Claims

1. A method of using a thermoplastic mounting medium for embedding and subsequently fixating a sample material in a moulding cavity, wherein said thermoplastic mounting medium includes: a composite material comprising a polymer mixed with organic fibres, and a thermally conductive filler having a thermal conductivity of a minimum 5 W/(mK) and wherein said thermally conductive filler represents at least 30% by weight of said thermoplastic mounting medium, wherein said polymer is mixed with said organic fibres in a % weight ratio of at least 20% polymer, 20-50% organic fibres and 30-50% thermally conductive filler, the method comprising: mixing the composite material and the thermally conductive filler; and sintering or melting the thermoplastic mounting medium to become a monolithic bulk material at least partially accommodating the sample material.

2. The method according to claim 1, wherein said thermally conductive filler has a thermal conductivity of at least two times the thermal conductivity of said polymer mixed with organic fibres.

3. The method according to claim 1, wherein said organic fibres constitute wood or plant fibres.

4. The method according to claim 1, wherein said polymer constitutes polypropylene or a polypropylene homopolymer.

5. The method according to claim 1, wherein said thermoplastic mounting medium is provided as pellets having a particle size of about 11 mm.

6. The method according to claim 1, wherein said thermally conductive filler is an inorganic filler.

7. The method according to claim 1, wherein said polymer mixed with organic fibres represent a maximum 70% by weight of said mounting medium.

8. The method according to claim 1, wherein the weight % ratio between said polymer mixed with organic fibres and said thermally conductive filler is 30-50% thermally conductive filler and 50-70% polymer mixed with organic fibres, 35-45% thermally conductive filler and 55-65% polymer mixed with organic fibres, or 40% thermally conductive filler and 60% polymer mixed with organic fibres.

9. The method according to claim 1, wherein the composition of the mounting medium is 24% +/5% by weight polymer, 40% +/5% by weight thermally conductive filler and 36% +/5% by weight organic fibres.

10. The method according to claim 1, wherein said thermally conductive filler is metal particles.

11. The method according to claim 1, wherein said thermally conductive filler is aluminum particles.

12. The method according to claim 1, further comprising: embedding and subsequently fixating materialographic or metallographic samples for preparation and subsequent analysis.

13. The method of claim 1, wherein the thermoplastic mounting medium further comprises a sample material embedded in the thermoplastic mounting medium according to claim 1.

14. The method of claim 1, wherein the thermoplastic mounting medium further comprises a sample material embedded in two or more layers of the thermoplastic mounting medium.

15. The method according to claim 1, wherein the mixing comprises: mixing said organic fibres and said thermally conductive filler during production in melted polymer.

16. The method according to claim 15, further comprising: pressing the mixture through a die with a cutting knife before the mixture sets to produce pellets having a particle size of about 11 mm.

17. A thermoplastic mounting medium for embedding and subsequently fixating a sample material in a moulding cavity, comprising: a composite material comprising a polymer mixed with organic fibres; and a thermally conductive filler having a thermal conductivity of a minimum of 5 W/(mK), wherein the thermally conductive filler is homogeneously mixed with the composite material, wherein the thermally conductive filler represents at least 30% by weight of the thermoplastic mounting medium, wherein the polymer is mixed with organic fibres in a percentage weight ratio of at least 20% polymer, 20-50% organic fibres and 30-50% thermally conductive filler, and wherein the thermoplastic mounting medium comprises a monolithic bulk material at least partially accommodating the sample material.

18. The thermoplastic mounting medium of claim 17, wherein the thermoplastic mounting medium is sintered or melted to form the monolithic bulk material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows, schematically, a sample material arranged in a compression mould.

(2) FIG. 2 shows, schematically, a sample material arranged in two different mounting media.

(3) FIG. 3 shows, schematically, a sample material arranged in two different mounting media and arranged in a compression mould.

(4) FIG. 4 shows values of thermal conductivity in the SI unit W/(mK) for various materials.

DETAILED DESCRIPTION

(5) The present invention will in the below be explained in more detail with reference to the figures.

(6) FIGS. 1 and 3 show a compression mould 1 including a lid or cover 5, walls 7 which may be embodied as a cylinder, and pressing means 9. The pressing means 9 may, as shown in FIGS. 1 and 3, be embodied as a ram. The pressing means are configured for applying pressure during the mounting process.

(7) The walls 7, the lid 5 and the pressing means 9 together define a cavity 11 configured for receiving a sample material 10 and the mounting medium 25 in accordance with an aspect of the present invention.

(8) Temperature regulating means 30, i.e. heating and/or cooling means 30, is in the depicted embodiments according to FIGS. 1 and 3 shown as means encircling the walls 7 or the compression mould 1.

(9) In the embodiment according to FIG. 1, the sample material 10 initially is placed on the pressing means 9 inside the cavity 11 where after the cavity 11 is at least partially filled with pelletized mounting medium 25.

(10) In the embodiment according to FIG. 3, the sample material 10 initially is placed on the pressing means 9 inside the cavity 11. A second mounting medium 26, pelletized or not and in accordance with the present invention or not, is then filled in the cavity 11; possibly to cover the exposed faces of the sample material 10 resting on the pressing means 9. The second mounting medium 26 may be chosen in accordance with any desired properties or frames of costs etc. for the mounting medium 26. The first mounting medium 25 in accordance with the first aspect of the present invention may, as shown, be applied as a backing.

(11) In the embodiment according to FIG. 3, the mounting medium may, however, constitute the first mounting medium 25 only.

(12) The cover or lid 5 may be connected to the walls of the mould 1 by means of not shown threads or equivalent.

(13) The present invention is not in any way limited to a particular embodiment or type of mould; other types of mounting devices including alternative kinds of moulding cavities, or compression moulding cavities, may equally be applied without departing from the scope of the present invention.

(14) FIG. 1, shows the pelletized mounting medium 25 in a unsintered state prior to application of heat and pressure as described above.

(15) FIGS. 2 and 3 show the sintered mounting medium 25 in a settled state firmly embedding the sample material 10.

(16) The ideal thermally conductive filler, metallic or not, may be chosen to have the following properties: The thermal conductivity of the filler should in some embodiments be as high as possible in order to secure as high heat conductance during the mounting process as possible; thereby minimizing gradients throughout the mounting medium during heating and/or cooling, In case electrical conveyance of the embedding medium is desired, a filler having suitable electrical properties should be chosen, Galvanic decomposition of the mounted sample in some applications should be avoided. This requires the filler to be galvanic inert. Alternatively, the filler material should be the sacrificial anode when combined with the typical metallic samples such as different steel types, and low placed metals or alloys in the galvanic series. The filler should be acceptable with regards to safety and environmental impact,

(17) Aluminium filler, or aluminium alloy/aluminium based filler, fulfils the above criteria and is therefore in many embodiments preferable compared to other metals or inorganic compounds.

(18) The formation of oxide membrane on aluminium is, on the other hand, beneficial as the metal may be rendered passive as a result of the membrane.

(19) Furthermore, aluminium has the benefit of being compatible with scanning electron microscopy (SEM) and Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), which is frequently used with materialographic and/or metallographic samples.

(20) According to other embodiments, the thermally conductive filler may constitute calcium carbonate (CaCO3). Calcium carbonate may be beneficial as this mineral filler matches the workability of hard and medium hard samples better than soft filler materials such as aluminium.

(21) According to other embodiments, the thermally conductive filler may constitute titanium dioxide (TiO2). Titanium dioxide may be beneficial as this mineral filler allows

(22) matches the workability of hard and medium hard samples better than soft filler materials such as aluminium.

(23) FIG. 2 shows, schematically, an embodiment of the present invention wherein a sample material 10 is arranged in two different mounting media; a first backing mounting medium 25 according to the present invention and a second mounting medium 26. The second mounting medium 26 may be chosen in accordance with any desired properties or frames of costs for the mounting medium 26. The embodiment is particular beneficial in case the mounting medium 25 according to the present invention is undesirable as the sole mounting medium, e.g. in case the mounting medium 25 is too soft compared to the sample material 10 leading to rounding of the sample edges during the subsequent preparation steps. Moreover, in case the filer according to the present invention disturbs the process of preparing the sample 10 for examination, it may be desirable to apply the embodiment according to FIG. 2.

(24) When the sample is properly mounted in the mounting medium, the sample is ready for mechanical preparation and subsequent microscopic analysis or equivalent.

(25) FIG. 4 shows values of thermal conductivity in the SI unit W/(mK) for various materials. As can be seen, the thermal conductivity of aluminium, or aluminium alloys, is in the range of 1-300 W/(mK) whereas the thermal conductivity of polypropylene and wood is substantially less; i.e. in the region of 0.1 W/(mK).

(26) The present invention is not in any way limited to one or more of the illustrated embodiments. Features of one embodiment may be combined with, or replaced by, features of another, possibly not shown, embodiment without departing from the scope of the present invention.