Overpressure Relief of Microwave Digestion System
Whether the pressure can be released safely in time is related to safety and is the most important.The control method of the general microwave digestion system is to stop the microwave heating when the detected temperature and pressure reach the target temperature and pressure, but the chemical reaction in the actual digestion tank does not necessarily stop immediately, so it may cause overpressure, and it must be timely and safe pressure relief. If there is no pressure relief method, the pressure resistance of the digestion tank must be much greater than the maximum working pressure to ensure a sufficient safety factor.
Microwave Digestion System Temperature Measurement and Pressure Measurement Method
According to whether it is in contact with the inside of the digester, it can be divided into: contact type and non-contact type. If only a temperature and pressure sensor is inserted in one of the digestion tanks, the temperature and pressure of other digestion tanks cannot be controlled, and there is an inevitable hidden danger of exceeding the target temperature and pressure.
The best way is to measure the temperature and pressure of all digestion tanks without contact, and once any digestion tank reaches the set temperature and pressure, stop heating.Because despite rotating heating, and even some manufacturers carry out "magnetic stirring", the inhomogeneity of microwave heating still exists to a certain extent. Therefore, even if the samples are the same, the amount of sample weighing and the amount of acid added are exactly the same. It cannot guarantee that the temperature and pressure in the digestion tank after microwave heating are exactly the same.
The Material of the Digestion Vessel of the Microwave Digestion System
Generally, there are fluoroplastics TFM, PTFE, PFA and quartz. The highest service temperature of TFM is not lower than that of PTFE, and its surface finish, impermeability under high temperature and high pressure, and deformation resistance under high temperature and high pressure are all better than PTFE. Although PFA is translucent, its maximum service temperature is not as good as PTFE. Therefore, TFM is the material of choice for digestion vessels.The manufacturer's digestion vessel is generally PTFE, which can only be used as a medium and low pressure digestion vessel.
Is the Microwave Digestion System an Integrated Tank?
The integrated tank does not need to be disassembled and is easy to use.It is best to use a pure TFM digester, but the working pressure is also limited.At present, the digester with a working pressure up to 100bar has a jacket or a reinforcement ring.
Sheath Material of Microwave Digestion System
Generally, there are PEEK and ceramics.Its strength is much greater than that of TFM, but no material can compare with TFM, PTFE, PFA and other fluoroplastics in terms of acid corrosion resistance.
The Maximum Working Temperature of the Digestion Tank of the Microwave Digestion System
The maximum operating temperature cannot exceed the maximum operating temperature of the digestion vessel material.Therefore, 260°C is generally the highest operating temperature for all fluoroplastic digestion tanks.Some manufacturers claim that it can reach 300°C, but cannot reach the highest pressure at the same time.The service life of the fluoroplastic digestion vessel will definitely be affected at 300°C.The maximum working temperature of the quartz digestion vessel can be very high, but it is limited by its sheath or bracket, so generally it can only reach 300°C.Usually, most microwave digestion can be completed at 170-220°C.
Maximum Working Pressure of Microwave Digestion System
The pressure in the digestion tank is mainly determined by the organic matter content of the sample, the vapor pressure of the acid, and the temperature.The higher the organic matter content of the sample, the higher the pressure in the digester.Usually nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid are used.Sulfuric acid has the least volatility, and the highest temperature is generally only possible when using sulfuric acid.
The Maximum Digestible Sample Volume of the Microwave Digestion System
Different types of digestion tanks have different maximum digestible sample volumes.The maximum amount of digestible sample depends on the organic matter content of the sample, the type of acid, the set temperature, the volume of the digestion tank, and the maximum working pressure of the digestion tank.