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Second step: Mounting - hot or cold
- Mounting resins
Hot Mounting:
During hot (compression) mounting the sample is embedded under temperature and pressure. One advantage of compression mounting is in the very high hardness of our thermosetting polymers, which is not achievable with cold mounting materials. A further advantage is the ease of handling. With all hot compression mounts, cooling the sample under pressure is recommended, and is essential with thermoplastics in order to prevent the "cotton ball" effect. Buehler mounting presses are designed with an efficient linear cooling cycle. With the hot compression mounts, we differentiate between thermosetting polymers and thermoplastics: Thermosetting polymers are powders, and fuse under simultaneous pressure and heating. Fillers can improve hardness and shrinkage. Different powder sizes affect the flow characteristics. For ease of use and rapid handling, the Phenocure phenolic compound is available in a tablet form called Premoulds. They are available in different diameters and suitable to mount samples not sensitive to pressure. Premoulds are handy and shorten the embedding cycle. Thermoplastics are acrylic mounting materials that melt when heated, then polymerise when cooled under pressure, therefore requiring longer cooling times. Thermoplastics, unlike thermosetting polymers, can be melted after hardening. Thermoplastic curing is reversible and the mount can be melted again at any time. They are very suitable as embedding compounds for pressure-sensitive samples. Here the acrylic powder is melted without pressure and then subjected to pressure when the final temperature is reached and during cooling.
Cold Mounting:
The main advantage of cold mounting is the ability to mount specimens of irregular shape and size. It is often favoured for embedding individual samples, when the acquisition of a mounting press is not economically justifiable. Conversely, it is helpful for mounting large numbers of samples as quickly as possible. Cold mounting products fall into one of three categories: acrylics, polyesters and epoxies. They may consist of two or more components that need to be mixed together to make a solid cured specimen. Epoxide compounds exhibit the lowest contraction. The long curing time gives outstanding edge retention and very low shrinkage, and is chemically resistant. Acrylics have a short curing time and have a small amount of contraction that can be improved with fillers and curing under pressure e.g. Technomat. With polyester resins the curing times are relatively short, but often produce a poor quality mount and are only used due to low cost. After mixing the components, the hardening process takes place via an exothermic reaction. During curing, particularly with acrylics, this hardening process can generate over 80ºC, and one must be careful when working with temperature-sensitive materials, e.g. plastics, where the structure of the sample can be affected.
Vacuum Impregnation:
Porous materials, e.g. ceramic(s) or sprayed coatings should be vacuum impregnated with epoxy resin prior to sectioning. The porous or friable ceramic is strengthened and protected by the epoxy resin. Cavities, pores and cracks that are open to the surface are filled with the embedding material. For high contrast definition of pores and cracks, we offer Epo-Color resin which, under dark field lighting, appears a vivid red colour and thus makes the interpretation of the structure easier.
During hot (compression) mounting the sample is embedded under temperature and pressure. One advantage of compression mounting is in the very high hardness of our thermosetting polymers, which is not achievable with cold mounting materials. A further advantage is the ease of handling. With all hot compression mounts, cooling the sample under pressure is recommended, and is essential with thermoplastics in order to prevent the "cotton ball" effect. Buehler mounting presses are designed with an efficient linear cooling cycle. With the hot compression mounts, we differentiate between thermosetting polymers and thermoplastics: Thermosetting polymers are powders, and fuse under simultaneous pressure and heating. Fillers can improve hardness and shrinkage. Different powder sizes affect the flow characteristics. For ease of use and rapid handling, the Phenocure phenolic compound is available in a tablet form called Premoulds. They are available in different diameters and suitable to mount samples not sensitive to pressure. Premoulds are handy and shorten the embedding cycle. Thermoplastics are acrylic mounting materials that melt when heated, then polymerise when cooled under pressure, therefore requiring longer cooling times. Thermoplastics, unlike thermosetting polymers, can be melted after hardening. Thermoplastic curing is reversible and the mount can be melted again at any time. They are very suitable as embedding compounds for pressure-sensitive samples. Here the acrylic powder is melted without pressure and then subjected to pressure when the final temperature is reached and during cooling.
Cold Mounting:
The main advantage of cold mounting is the ability to mount specimens of irregular shape and size. It is often favoured for embedding individual samples, when the acquisition of a mounting press is not economically justifiable. Conversely, it is helpful for mounting large numbers of samples as quickly as possible. Cold mounting products fall into one of three categories: acrylics, polyesters and epoxies. They may consist of two or more components that need to be mixed together to make a solid cured specimen. Epoxide compounds exhibit the lowest contraction. The long curing time gives outstanding edge retention and very low shrinkage, and is chemically resistant. Acrylics have a short curing time and have a small amount of contraction that can be improved with fillers and curing under pressure e.g. Technomat. With polyester resins the curing times are relatively short, but often produce a poor quality mount and are only used due to low cost. After mixing the components, the hardening process takes place via an exothermic reaction. During curing, particularly with acrylics, this hardening process can generate over 80ºC, and one must be careful when working with temperature-sensitive materials, e.g. plastics, where the structure of the sample can be affected.
Vacuum Impregnation:
Porous materials, e.g. ceramic(s) or sprayed coatings should be vacuum impregnated with epoxy resin prior to sectioning. The porous or friable ceramic is strengthened and protected by the epoxy resin. Cavities, pores and cracks that are open to the surface are filled with the embedding material. For high contrast definition of pores and cracks, we offer Epo-Color resin which, under dark field lighting, appears a vivid red colour and thus makes the interpretation of the structure easier.
