Homogenizing samples with heating and cooling options

The MM 500 control is a high-energy laboratory ball mill designed for dry, wet, and cryogenic grinding, operating at frequencies of up to 30 Hz. It is the first mixer mill available on the market that enables monitoring and control of the temperature during the grinding process.

The temperature range spans from -100 to 100 °C. To provide maximum versatility, the mill can be utilized with various thermal fluids, allowing for the integration of different tempering devices for either cooling or heating.

When using liquid nitrogen for cooling, the mill must be fitted with the optional cryoPad extension device. This innovative cryoPad technology facilitates the selection and regulation of a specific cooling temperature within the range of -100 to 0 °C during the grinding process.

MM 500 Control - Introduction. Video Credit: Retsch GmbH

The Only Mixer Mill with Temperature Control

Image Credit: Retsch GmbH

• Maximum speed of 30 Hz
• Horizontal oscillation generates significant impact effects for efficient sample processing.
• Accommodates feed sizes up to 10 mm and achieves a final fineness of 0.1 µm.
• Equipped with two grinding stations for jars ranging from 2 ml to 125 ml, including an adapter for 18 x 2 ml single-use vials.
• Offers various options for heating or cooling using thermal fluid or liquid nitrogen for cryogenic grinding, with temperature regulation capabilities between -100 °C and 100 °C, along with temperature monitoring.
• Features GrindControl for measuring temperature and pressure within the jar.
• Includes aeration lids to manage the atmosphere inside the jar.
• Designed as a bench-top model with a touch screen, facilitating easy jar clamping; jars can remain clamped for subsampling. It supports storable Standard Operating Procedures (SOPs) and cycle programs, and provides four different jar materials suitable for both dry and wet grinding.

Advantages Through Design

Mixer Mill MM 500 control. Image Credit: Retsch GmbH 

• Dry, wet, and cryogenic grinding can be performed at frequencies of up to 30 Hz for high-energy processing.
• Sample processing is both rapid and convenient, utilizing two screw-lock jars with a capacity of up to 125 ml each.
• The patented hermetically sealed fluid system guarantees the safe use of thermal fluids.
• A diverse selection of accessories is available, including ventilation lids and grinding jars that are free from heavy metals, suitable for cryogenic grinding as well.
• The ergonomic design of the jar clamping system, combined with a low noise level, enhances user experience, while parameter settings can be easily adjusted via a touch display.

Temperature Monitoring and Control

Temperature monitoring and control. Image Credit: Retsch GmbH

• Continuous temperature surveillance during the grinding procedure
• Temperature control is achievable within a spectrum of -100 to 100 °C
• The system can operate using liquid nitrogen or alternative thermal fluids
• There is significant adaptability in choosing a tempering apparatus for temperature management (such as LN₂ supply, cryostat, chiller, etc.)
• Grinding at low temperatures can be conducted without the use of LN₂

cryoPad

cryoPad. Image Credit: Retsch GmbH

• The cryoPad extension device is essential for functioning with LN₂
• This device controls the flow of LN₂ across the thermal plate
• The technology of the cryoPad enables the selection and maintenance of a precise cooling temperature within the range of -100 to 0 °C when utilizing LN₂.

Temperature Regulation Based on Thermal Plates

Patented concept of thermal plates. Image Credit: Retsch GmbH

The patented thermal plate concept facilitates the cooling and heating of the sample material, rendering the use of open liquid nitrogen baths or dry ice for sample cooling unnecessary. For tempering purposes, the grinding jars are simply positioned atop the thermal plates. Upon contact with the thermal plates, heat is efficiently transferred to or from the jars through the tempering device.

The innovative hermetically sealed fluid design enables the mill to operate with various thermal fluids, providing flexible and secure temperature regulation while requiring minimal user effort. Depending on the established operational setup, the temperature of the thermal plates can be adjusted within the range of -100 to 100 °C.

Control Configurations

It is essential to connect the mill to an external tempering device to regulate the temperature during the grinding process. Essentially, there are two alternatives:

1. Temperature Regulation with Liquid Nitrogen

Image Credit: Retsch GmbH

The mill operates using liquid nitrogen and is connected to a nitrogen tank. In this configuration, the mill must be enhanced with the optional extension device known as cryoPad.

The cryoPad features a patented PID (proportional–integral–derivative) system that regulates the flow of liquid nitrogen, thereby controlling the temperature of the thermal plates. This arrangement allows for the selection and maintenance of the thermal plates’ temperature at a predetermined value.

The desired temperature can be set through the touch display, with options ranging from -100 to 0 °C in increments of 10.

Setup 1: Extension device cryoPad and LN₂ tank for operation with liquid nitrogen.

2. Cooling or Heating with Liquid Thermal Fluid

Image Credit: Retsch GmbH

In this configuration, the mill can be connected to a cryostat, a chiller, or a water tap. The external tempering device controls the thermal fluid to maintain a specific temperature, which is then transferred to the thermal plates.

During the grinding process, a considerable amount of heat can also be generated within the jar, allowing for adjustments to the temperature of the thermal plates.

In summary, the actual temperature of the thermal plates is influenced by both the temperature of the thermal fluid and various grinding parameters, such as frequency, duration, jar volume, and the size of the grinding balls.

To ensure optimal control of the grinding process, the current temperature of the thermal plates is continuously monitored via the touch display.

Setup 2: Operation utilizing an external tempering device, such as a water tap, chiller, or thermostat.

Application Examples

The temperature control system of the MM 500 is specifically engineered for the handling of temperature-sensitive sample materials. The processes of cooling or heating can serve various purposes.

MM 500 control - Applications. Video Credit: Retsch GmbH

Cooling Can be Used for Example:

• Maintaining the integrity of temperature-sensitive analytes, such as volatile compounds or components in pharmaceuticals and food products
• Embrittlement
• Conducting wet grinding at temperatures lower than room temperature
• Mechanochemistry

Certain applications benefit from the heating of sample materials during the process. Examples of heating include:

• Paste making (in food industry)
• Intensifying mechanochemical reactions

Preserving Temperature-Sensitive Analytes

Certain analytes may be altered, destroyed, or vaporized when the sample material is subjected to excessive heat. If particular temperature thresholds are surpassed, the composition of substances such as proteins, pharmaceuticals, or food components can be significantly altered.

Maintaining a moderate temperature during the grinding process ensures that temperature-sensitive natural substances are physically retained in their original form for subsequent analysis.

Grinding of coffee beans at low temperatures for natural substance analysis. Image Credit: Retsch GmbH

Cryogenic Grinding

Temperatures that fall below 0 °C are conducive to the embrittlement and homogenization of materials such as ductile or sticky food. In cases where heavy-metal-free grinding is necessary, jars made of zirconium oxide or tungsten carbide may be utilized.

When cooled to -100 °C, it is also feasible to effectively embrittle certain polymers.

Fast milling of black Flurocarbon rubber (FKM) by embrittling the sample in two 125 ml jars at – 100 °C. Image Credit: Retsch GmbH

Wet Grinding < 30 °C

When utilizing a chiller, effective wet grinding can be conducted at 30 Hz and below room temperature without the need for any cooling intervals.

Particle size and temperature development for TiO₂ in a wet grinding process with 30 Hz and 2 × 125 ml jars. Image Credit: Retsch GmbH

Mechanochemistry

Maintaining a low temperature during the mechanochemical process helps to avoid the creation of unwanted derivatives. Controlled heating can be utilized to trigger chemical reactions and enhance product yields.

By keeping the temperature below 0 °C, the formation of non-porous zeolitic metal organic compound is inhibited. Image Credit: Retsch GmbH

Accessories for Maximum Flexibility

Grinding Jars in 3 Different Materials

The available sizes for grinding jars are 50 ml, 80 ml, and 125 ml. The materials used include stainless steel, tungsten carbide, and zirconium oxide, which guarantee contamination-free sample preparation. It is also possible to achieve heavy-metal-free grinding, even at temperatures as low as -100 °C.

Grinding jars in 3 different materials. Image Credit: Retsch GmbH

Aeration Lid (Video)

RETSCH provides a unique aeration lid for the grinding jars, specifically designed for applications that require the maintenance of a particular atmosphere within the ball mill jar.

Working with aeration lids. Video Credit: Retsch GmbH

GrindControl

The GrindControl system monitors both temperature and pressure within the jar. It comprises a sensor, a transmission unit, and analysis software.

Different grinding ball sizes and materials. Image Credit: Retsch GmbH

Multi-Cavity Jars and Adapter

The simultaneous processing of multiple small samples is achievable with the use of multi-cavity jars and an adapter designed for reaction vials. This capability is particularly essential in fields such as pharmaceuticals, chemicals, and biochemistry. The small cavity jars open up new avenues for mechanochemical research that involves limited quantities of chemicals.

The jars feature oval-shaped cavities that promote effective mixing. The pouring aids also facilitate safe sample handling. Constructed from stainless steel, the multi-cavity jars ensure efficient heat transfer to and from the samples.

The adapter can hold up to 18 disposable reaction vials of either 1.5 or 2.0 ml (for instance, Eppendorf vials) or nine 2.0 ml steel tubes. With its dual grinding stations, the MM 500 control mixer mill is capable of processing as many as 36 samples in a single operational run.

It is advisable to use 2.0 ml steel tubes when samples require freezing or heating, as polymeric reaction vessels are not designed to endure mechanical stress at extreme temperatures. The adapter is constructed from aluminum, allowing for effective heat transfer to and from the reaction tubes.

Multi-cavity jars of 4 x 10 ml and 2 x 25 ml, made of stainless steel, incl. PTFE pouring aids. Image Credit: Retsch GmbH

Adapter for 18 x 2 ml safe-lock reaction vials or 9 x 2 ml steel tubes, made of aluminum. Image Credit: Retsch GmbH

Typical Sample Materials

The MM 500 control can function with or without cooling, providing the mill with a broad range of applications. It is suitable for homogenizing various materials such as waste, soil, chemical products, coated tablets, pharmaceuticals, ores, grains, tissues, glass, hair, ceramics, bones, plastics, alloys, minerals, oil seeds, plants, sewage sludge, pills, textiles, wool, and more.

Raisins. Image Credit: Retsch GmbH

Coated tablets. Image Credit: Retsch GmbH

Polystyrene. Image Credit: Retsch GmbH

Soil. Image Credit: RETSCH GmbH

Cryogenic grinding of dried parsley in Mixer Mill MM 500 control with cryoPad. Video Credit: Retsch GmbH

Functional Principle

The grinding jars of the MM 500 control mixer mill execute radial oscillations while positioned horizontally. The inertia of the grinding balls leads to high-energy impacts on the sample material at the rounded ends of the jars, resulting in pulverization.

High-energy milling is achievable by operating at frequencies reaching up to 30 Hz. The combination of the grinding jars’ movement and the balls’ motion generates additional grinding effects through friction, which also enhances the effective mixing of the sample. Furthermore, the degree of mixing can be improved by incorporating multiple smaller balls.

Mixer Mill function principle. Video Credit: RETSCH GmbH

Technical Data

Mixer Mill MM 500 control. Source: RETSCH GmbH

*depending on feed material and instrument configuration/settings

Technical Data

cryoPad. Source: RETSCH GmbH