How to cold mount

Some prerequisites have to be taken into account before mounting takes place. These are essential to obtain a good mounting:

Clean the specimen. The specimen must be cleaned prior to mounting in order to improve adhesion of the mounting medium to the specimen. Use acetone or at least alcohol. Cleaning in an ultrasonic bath may be necessary. Remember to dry the specimen well. Clean specimens should be handled with either gloves or tweezers.
Adjust the specimen size to the mounting cup size.

Types of cold mounting

Two Types of Cold-Mounting Resins Are Available. Epoxy resins and acrylic resins

Epoxy Resins

Epoxy resins are suitable for mounting of all types of materials and are especially recommended for vacuum impregnation. Epoxies have the lowest shrinkage of all cold-mounting resins. The curing time is relatively long, but adhesion to most materials is excellent. They polymerize through a chemical reaction after being mixed in the correct proportions. The hardened epoxy is duroplastic, and not affected by moderate heat or chemicals. Struers' epoxy systems consist of two components: a resin and a curing agent/hardener. Properties such as low vapor pressure, transparency, good adhesion, low viscosity, and no shrinkage are all specific to epoxies. As the stoichiometric resin:hardener ratio is critical; both parts should be weighed to obtain the best mounting result. If it is only possible to measure the amount by volume, use syringes to measure the quantities of resin and curing agent/hardener.

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Curing

The curing of epoxy systems depends on the amount of resin. With small amounts, the process may take longer because favorable conditions exist for removing excessive heat generated by the chemical reaction. Larger amounts of epoxy will, however, accelerate the curing process by storing heat due to the poor conductive properties of the system. Under certain conditions it is possible to experience peak temperatures of around 150-200° C/302-392° F. To avoid this and achieve more uniform mounting results, a dryer unit can be used to control the temperature during the curing process. The resin hardens by polymerization. Polymerization is a chemical reaction that generates heat. The heat will vary, depending on the type and quantity of the mounting medium. Some mounting media will develop temperatures significantly higher than 100° C.

Vacuum Impregnation

Porous materials, such as ceramics or sprayed coatings, require vacuum impregnation. Vacuum impregnation is carried out in a vacuum chamber at approx. 0.1-0.15 bar. All pores connected to the surface fill with resin. Consequently, the resin reinforces these fragile materials. Preparation artifacts such as pull-outs, cracks, or unopened porosity can be minimized. Only epoxy resins can be used for vacuum impregnation due to their low viscosity and low vapor pressure. A fluorescent dye can be mixed with epoxy to allow easy identification of all filled pores in fluorescent light. Position the specimen in the middle of the mounting cup and place it in the vacuum chamber. Close the lid and evacuate the chamber. Evacuation lasts a few minutes to make sure that no air is left in small pores and cracks. Open the valve to allow the epoxy to be sucked into the chamber. When the specimen is completely covered by the mounting media, close the valve and turn off the vacuum pump. Atmospheric pressure will press the epoxy inside the pores and cracks.

Acrylic Resins

Acrylics are easy-to-use resins with short curing times, very limited shrinkage, and excellent mounting properties. They are well-suited for both serial mounting of irregularly shaped specimens and for routine work or single specimens. Acrylics are available with and without a mineral filler. Dye can be used if color coding is needed. When mixing acrylic resins, it is recommended to add powder to the liquid (hardener) – this will result in the most uniform resin mixture.

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Selection of Mounting Cup

Cup material and size have to be taken into consideration.

Size
A cup large enough to allow 5.0 mm distance from the specimen to the edge of the final mount is needed to minimize the risk of radial cracks. A large cup, relative to the specimen size, will cause the generation of excessive amounts of heat which can damage the specimen. Shrinkage will also increase with a larger resin to specimen ratio.

Material
Epoxy hardener will affect silicone cups and reduce the lifetime and transparency of the mount. Selection of cup material for acrylic resins does not have the same restriction.

Mounting Process

Choose a mounting cup and place the clean and dry specimen in it. Measure the correct amounts of resin components carefully by either volume or weight. Mix the components thoroughly, pour the resin-mixture over the specimen, and leave the filled mounting cups to cure. Mixing and curing times are important parameters in a high quality mount, and recommendations from the instruction manual should be followed.

Resistance to Common Chemicals

All cold-mounting medias are resistant to common etchants. Some cold-mounting medias react with organic solvents like acetone, alcohol, etc.

Fixation of Specimen

Fixation clips (metal or plastic) ensure that thin plates, foils, and wires remain upright. Double adhesive foil can be used to keep irregularly shaped specimens upright. Liquid adhesives may react with some types of cold mounting media. Specimens too small to be fixed by a clip (e.g. some electronic components) can be held in a vertical position during embedding by cementing them to the bottom of the mold with a trace of fast-drying glue.

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Selection of Resin / Selection Guide

The choice of resin/mounting media is important in order to obtain the required result and fulfill the mounting requirements.

The purpose of this guide is to give detailed information, hints, and tricks about the various cold mounting materials. Go to Cold Mounting Selection Guide

Acrylic resin

Special applications	Edge retention / general usage
Resin name	ViaFix*	ClaroCit	LevoCit	VersoCit-2	DuroCit-3
Application	Vias & Microvias Excellent characteristics for filling Vias & Microvias, due to its low viscosity.	Extraordinarily clear Crystal clear mounts for universal use. Usable for target preparation, and curing under pressure will improve transparency.	Edge retention & low temperature Excellent for non-ferrous metals and soft ferrous metals as well as heat sensitive specimens.	Fast - Routine Routine examination of soft to medium hard materials. Mounts completed in only 10 minutes.	Edge retention Minimum shrinkage and very good edge retention on medium hard and hard ferrous metals as well as ceramics, carbides etc. Also applicable for protecting layers of coated materials and for filling voids and cracks.
Shrinkage level	Medium	Medium	Low	High	Very low
Edge retention	Fair	Fair	Good	Fair	Good
Removal rate	High	High	Medium	High	Low
Mount hardness	83 Shore D	85 Shore D	84 Shore D	82 Shore D	85 Shore D
Curing time**	20 min	20 min	20 min	10 min	30 min
Peak temperature	115 °C / 239 °F	90 °C / 194 °F	75 °C / 167 °F	100 °C / 212 °F	138°C / 280 °F
Viscosity	Low	Medium	Medium	Medium	Medium

Epoxy resin

Edge retention / general usage	Speed optimized
Resin name	EpoFix	SpeciFix-40	CaldoFix-2	ProntoFix standard	ProntoFix accelerated
Application	Vacuum & low temperature Very low shrinkage and ideal for vacuum impregnation of pores and cracks. Ideal for heat sensitive specimens & cover all materials.	Extreme adhesion Very clear mounts that cures relatively fast. Cures in oven or Drybox, while maintaining low shrinkage.	All-round vacuum Short curing time and low viscosity for optimal impregnation. Hardest Struers epoxy mount available.	Fast without oven Speed optimized epoxy resin. Excellent adhesion and superior penetration of cracks & pores when using vacuum impregnation. Use of standard vs. accelerated version depends on mounting cup diameter and lab temperature - see table:
Shrinkage level	Very low	Very low	Very low	Very low
Edge retention	Good	Good	Good	Good
Removal rate	High	High	High	High
Mount hardness	78 Shore D	82 Shore D	85 Shore D	83 Shore D
Curing time	12 hours*	3½ hours* (oven at 50 °C / 122 °F)	90 min* (oven at 75 °C / 167 °F)	90 min**	90 min***
Peak temperature	40 °C / 104 °F	100 °C / 212 °F	170 °C / 338 °F	140 °C / 284 °F	140°C / 284 °F
Viscosity	Low	Low	Low	Very low