Preparation guide for geology and mineralogy Cutting | Mounting | Grinding & Polishing | Thin Sections

Optimize your mining processes with QATM’s advanced solutions

Materialographic sample preparation is an essential step in the qualitative and quantitative analysis of geological and mineralogical samples. Whether you want to analyze rocks, ores, minerals or fossils, you need a reliable and precise method to cut, mount, grind and polish your samples. With QATM equipment and consumables, you can optimize this process and achieve high-quality results.

In this guide, we present some of our most important products and applications for materialographic sample preparation for geology and mineralogy. You will find a brief description of the features and benefits of our cutting machines, mounting systems and grinding and polishing machines, as well as some examples of typical samples that you can prepare with our equipment and consumables.

The preparation process begins with cutting of a representative sample from starting material. The correct selection of the cutting process ensures the production of a sample without damage and with a flat surface that facilitates the subsequent process steps. An incorrectly selected or performed cutting process can lead to irrevocable damage to the sample. Brittle, porous or broken samples should be impregnated with suitable mounting materials before sectioning to prevent damage during cutting.

For powders or so-called 'soft rocks', it must be ensured that the samples are sufficiently deagglomerated and that the powder particles are securely enclosed by the mounting material to prevent them from breaking out later.

Mounting for geology and mineralogy

QATM offers various solutions for mounting and impregnating your rock samples, depending on your preferences and requirements. You can choose between hot and cold embedding, as well as between different mounting materials, such as epoxy resins or acrylates. With the mounting systems from QATM, you can stabilize, protect and prepare your samples for the subsequent preparation process.

Our mounting systems are ideal for mounting geological and mineralogical samples, e.g

• Rock samples that exhibit high hardness, porosity or fissuring, and that require uniform support and a good edge connection.
  
  
• Ore samples that have a high density, heterogeneity or sensitivity, and which require good filling and low shrinkage.
  
  
• Mineral samples that have a high transparency, color or structure and that require a clear view and low discoloration.

The most common method for mineralogical samples is cold mounting with epoxy resins. For thin sections, but also for thin sections of powdered samples, low-viscosity epoxy resins are used to fill pores and cracks well and, in the case of powders, to enclose them well with mounting material. The refractive index of these mounting materials should be similar to that of glass in order to avoid distorting the results later during light microscopic analysis.

The curing time of these epoxy resins is between three and 24 hours.

Warm inbedden

• Hot mounting is carried out in hot mounting presses at high pressures and temperatures.
• For hot mounting, both thermosetting thermosetting mounting agents for maximum hardness and thermoplastic embedding agents for transparent mounting are available.
• Hot mounting provides the best edge retention and planarity and is ideal for wet chemical etching.

Koud inbedden

• QPREP cold mounting materials are suitable for heat- or pressure- sensitive samples.
• Cold mounting uses chemical reactions to cure the mounting material, with acrylic resins, epoxy resins, and polyester resins available.
• The selection is based on properties such as reaction time, removal rate, and hardness.
• Cold mounting can be used for a variety of sample materials and shapes in various sizes.

UV inbedden

• UV mounting materials consist of filler-free modified acrylic resins.
•  They are cured under UV irradiation within a narrow wavelength range and require specially designed equipment.
• The UV initiators present in the resin absorb UV radiation for the initiation of the reaction.
• UV mounting is the fastest method without the need for high pressures or external heat.
• The 1-component systems used do not require mixing, result in transparent mountings, and enable safe work in the laboratory.

Pores and cracks must be filled with the mounting material under vacuum with the aid of the QATM vacuum impregnation device. The samples to be mounted are placed in the vacuum container, which is then evacuated with the help of the connected vacuum pump. The pores and cracks are emptied of air and the low-viscosity mounting material can then penetrate the cavities under vacuum. After filling the moulds with mounting material, the vacuum container can be vented and the samples can be removed for curing.

For polished specimens, it has proven useful to initially mount only a layer approx. 5 mm thick and then fill the specimen to a workable height in a second step after any specimen labeling.

To avoid bubble formation, the samples can be stored for two hours under 2 bar overpressure after filling the mounting mould with the mounting material.

Alternatively, a light-curing mounting material (Qprep UV50 & UV55) can also be used for mounting. Due to the higher viscosity of these mounting materials, complete impregnation of cracks and pores cannot usually be achieved.

Powdered samples can also be mounted in a hot mounting press under pressure and temperature. Common sample diameters are Ø 25 to 30 mm, and larger sizes are possible.

Specimens intended for grinding & polishing can be prepared directly after mounting, and specimens intended for thin sections must be processed further.

Thin Sections for geology and mineralogy

Samples intended for thin sections are ground flat after cutting and mounting. Depending on the material, an abrasive grain size of 65-75 μm can be used. Grinding is carried out with low contact pressure, low speed and good cooling. The sample should be checked under a stereomicroscope after each preparation step. Coarse scratches should be avoided.

After the sample has dried, it is glued to a glass slide with the ground side. The adhesive used is either Qpox 90, 92 or 94 or Qprep 50UV or 55UV with light curing. To avoid detachment or bubble formation, the sample should be pressed on with the QATM thin section press.

The glass slide to which the sample is glued must have a defined or known thickness for subsequent analysis procedures; if necessary, it should be pre-ground to a defined thickness. One side of the slide should be roughened for better adhesion of the adhesive. The QATM glass slides fulfill both the requirement for a defined thickness and the requirement for a roughened surface.

Glass slides for thin sections

• Low-stress glass to prevent glass breakage
• Glass thickness >1.5 mm also to prevent glass breakage
• Uniform glass thickness with low tolerances (±0.05 mm)
• For low removal (time and costs) during surface grinding I
• Ground edges (90°) to prevent injuries and chipping
• Defined refractive index
• Matting through selected (grain size) sandblasting process (optional)

After the adhesive has hardened, the sample is now 'pre- thinned' by cutting. To do this, the glass slide is clamped in a vacuum clamping device, which is available for the QATM Qcut 150 A and Qcut 200 A. The sample is now pre-cut to a thickness of 300 to 1000 µm while maintaining plane parallelism. The thickness to be achieved depends on the material, the mounting and the cutting machine.

The sample is then ground to a final thickness. This grinding process can be carried out on the QATM Qcut 150 A or 200 A precision cutting machines. The vacuum clamping device described above is then also used for clamping. Qprep diamond cup wheels of various grit sizes are used for grinding.

Diamant doorslijpschijf

If a specimen with parallel faces is desired after precision cutting the use of a diamond cup wheel for further processing is recommended. Used in our precision cutting machines Qcut 150 M, Qcut 150 A and Qcut 200 A with vacuum specimen holder, the QPREP diamond cup grinder enable the user to achieve optimum planar parallelism with high surface quality and reproducibility.

Productvoordelen Planar parallel sample preparation Stock removal with high accuracy Very high repeat accuracy

Aanbevolen toepassingen Target voorbereiding Defect analysis Thin section technology Petrographic examinations

This grinding process can be carried out on the QATM Qcut 200 A with optimum reproducibility thanks to the high-precision automatic Z-axis. Polishing the resulting thin sections is usually not necessary.

The grinding process can also be carried out on the QATM Qpol 300 A1 grinding and polishing machine, for example. Specimen holders for preparation in single or central pressure mode are available for this purpose. Preparation in single contact pressure is particularly flexible here. The specimens are pressed down particularly evenly using two pressure stamps. Silicon carbide abrasive papers with different abrasive grain sizes are available for grinding and, if necessary, polishing. Abrasive papers can be used for all minerals and ores. They offer optimum grinding results for soft and sensitive samples.

Qprep diamond grinding wheels with different bond types offer higher stock removal, excellent flatness of the samples and low relief formation.
For mineralogical samples, diamond grinding wheels with a resin or metal bond are mainly used.

VEGA diamond grinding disc

QPREP Vega is a grinding disc on a zinc-plated metal carrier for planar and pre-grinding of hard materials. On the back side the product is coated with a high-quality non-slip print. The grinding disc is equipped with diamonds bonded in nickel. The functional back print provides secure adhesion to the magnetic foil.

Productvoordelen High stock removal Particularly high planarity Very long life time

Aanbevolen toepassingen Hard ferrous materials Composites Ceramics Rocks Possible to grind unmounted samples Especially recommended for manual preparations

With this grinding process, the sample, glued to the glass slide is carefully ground to a final thickness of 20 to 30 µm. Pores or cracks opened by 'pre-thinning' (cutting to 300 - 700 µm thickness) must be closed before grinding. A suitable medium such as Qpox 94 should be used for this purpose. The final thickness of the sample depends on the material and the task. One criterion for the correct thickness is the inherent color of the material. For example, quartz is always white. If there is a yellowish tinge, the sample is still too thick. For easier assessment, the QATM sample holders for individual prints have an opening in the middle to allow the colors to be assessed without removing the samples. The grinding process can be completed with a grit size of 22 to 18 µm.

For an examination in reflected light, polishing must then be carried out. The following polishing cloths can be used for this purpose.