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Microwave digestion is a commonly used device in chemical analysis. It uses the penetration and activation reaction ability of microwaves to heat reagents and samples in a closed container. Although microwave digestion technology is very mature, some users are still worried about operational safety. In fact, as long as you choose equipment from regular manufacturers and operate it strictly in accordance with the instructions, the safety risk is extremely low and there is no need to worry too much. So, what is the main reason for the pressure relief phenomenon during microwave digestion? Today, we will focus on this issue.

The key factors of microwave digestion of samples include:

Digestion temperature and digestion time: The appropriate digestion temperature can accelerate the chemical reaction and improve the digestion efficiency, while the reasonable digestion time ensures that the sample is fully digested to avoid incomplete reaction or excessive decomposition.

Choice of digestion solution: Different sample components need to be matched with suitable digestion solutions to ensure that the sample can be efficiently dissolved. For example, the optimized combination of acid mixtures (such as HNO₃, HCl, HF, etc.) can enhance the digestion ability and improve the element recovery rate while reducing side reactions and matrix interference.

By optimizing the digestion temperature, time and digestion solution type, the efficiency and reliability of microwave digestion can be improved, providing high-quality sample solutions for subsequent analysis.

What is the pressure relief phenomenon?

When the pressure in the digestion tank approaches its design upper limit, the microwave digester will automatically start the pressure relief system to prevent the tank from bursting. During the digestion process, the temperature can reach up to 180-240℃, the pressure can reach up to 100-150 bar, and it is accompanied by strong acid vapor, forming a triple effect of "high temperature, high pressure, and strong acid", which puts strict requirements on experimental safety.

In order to reduce the risk of pressure relief, we recommend the use of a low-power, staged temperature and pressure increase program for digestion. The ideal microwave digestion program should achieve rapid and thorough sample decomposition at the lowest possible temperature to ensure efficient and safe experimental results.

In actual operation, the microwave digestion program can be optimized according to the characteristics of the sample matrix, and the heating rate and reagent ratio can be reasonably adjusted to reduce the safety hazards caused by high temperature and high pressure, while improving the digestion efficiency.

The main causes of pressure relief

The inner tank mouth or lid is contaminated and absorbs microwaves

During microwave digestion, the sensor only monitors the solution temperature and cannot directly measure the tank mouth temperature. If the tank mouth or lid is contaminated and absorbs microwaves, its temperature may exceed the set value by a large margin, even exceeding 260°C, causing the material to soften, the pressure resistance to decrease, and eventually causing pressure release. Regular inspection and cleaning of the inner tank and lid to ensure that they do not absorb microwaves is the key to preventing such problems.

Ceramic tube breakage

If the experiment is continued with a damaged ceramic tube, the main control tank will not be able to maintain normal pressure, resulting in unstable temperature. The instrument may misjudge the power shortage and automatically increase the microwave power, causing the temperature of other digestion tanks to go out of control, eventually causing pressure relief. The integrity of the ceramic tube should be checked before the experiment to ensure the normal operation of the system.

Uneven placement of digestion tanks

Although microwaves are evenly distributed in the cavity, they still have a penetration depth. If the main control tank is surrounded by two digestion tanks, the microwave power it absorbs will be reduced by about 1/3. For example, when digesting 5 samples at the same time, if the main control tank is surrounded by two digestion tanks in close proximity, and two samples are spread on the opposite side, the efficiency of the main control tank in absorbing microwaves will decrease, which may cause its temperature to be lower than that of other tanks, thereby causing local overheating and pressure relief after exceeding the pressure limit. Reasonable placement of digestion tanks to avoid excessive shielding of the main control tank can effectively reduce risks.

Pressure relief is usually caused by overheating, excessive pressure or sealing problems. Optimizing the digestion procedure, properly placing the digestion tanks, and regularly checking the equipment status are the key to preventing pressure relief. Welso strives for excellence in safety design and adopts advanced safety control technology to ensure the stability and reliability of the digestion process.

Microwave stability and uniform heating

The 360° continuous rotation technology is used to ensure the uniformity of microwave heating, which is particularly suitable for high-throughput sample digestion, where precise control of uniform heating is required.

Equipped with non-pulse continuous microwave intelligent adjustment mode, the microwave output is stable and efficient, ensuring that each sample is fully and evenly heated.

Temperature and pressure control technology

Combining non-contact mid-infrared temperature measurement technology with high-precision multi-fiber pressure measurement technology, as well as scanning integration and separation technology, independent temperature and pressure measurement of each digestion tank is achieved, ensuring precise control of temperature and pressure, and further improving the safety and reliability of the digestion process.

Self-recovering double pressure relief structure

The digestion tank is equipped with a self-recovering double pressure relief structure. When encountering overpressure during the digestion process, it can automatically release pressure and quickly restore the sealing state to avoid scrapping of batch samples. At the same time, it effectively prevents damage to the digestion tank and ensures long-term stable operation.

Finally, I would like to remind you again that before using the microwave digestion instrument, you must strictly read the manual and understand the operating procedures, precautions and safety guidelines of the equipment in detail. Make sure to master the correct operating methods, set parameters reasonably, and check the equipment status regularly to ensure the efficiency and safety of the experiment and avoid operating errors and equipment damage.