Analysis Principles and Techniques of Hydrogen and Oxygen in NdFeB Permanent Magnets
Principle and technology of oxygen analysis
Commonly used methods for determining oxygen in metals, alloys, rare earth metals and other materials are inert gas protection-pulse heating sample melting-infrared absorption method.
The entire analysis system uses inert gas as the carrier gas, generally high-purity helium or argon, with a purity greater than 99.999%. The sample diameter is limited to Φ8mm, and the sample carrier is a graphite crucible, generally spectral pure graphite. The shape of the graphite crucible varies according to the electrode design of each manufacturer.
First, the graphite crucible is placed between the upper and lower electrodes of the pulse heating furnace, the furnace is closed, and the entire analysis system is flushed with carrier gas (pressure 0.1MPa, flow rate 0.3~0.5L/min). After the prepared sample is weighed, it is added to the sample waiting area through the sample adding device of the instrument.
The analysis program first controls the heating of the heating furnace to heat the empty crucible and the system, that is, pretreatment, to remove the background (blank) of the system. This process is called a deoxidation process or a flushing process. The heating conditions are degassing power and degassing time, flushing power and flushing time respectively. The process is to flush the furnace with large air flow, and the general flushing flow rate is 1.8L/min. After degassing and flushing, the system enters a waiting state, and the airflow returns to the normal analysis flow rate. The waiting state stabilizes the state of the infrared detector of the detection unit, that is, eliminates baseline fluctuations caused by air flow switching.
After waiting, the sample is automatically injected from the waiting area into the heated graphite crucible, and the heating power of the graphite crucible at this time is the analysis power. The sample is heated and melted in the graphite crucible. The oxygen in the sample (usually in the form of oxide inclusions) reacts with the carbon in the graphite crucible at high temperature to form carbon monoxide, which is carried by the carrier gas out of the pulse heating furnace. This process is the sample The release process of oxygen. The release conditions of the sample (ie heating temperature and time) are determined by the characteristics of the sample, that is, the maximum temperature required for the reaction of oxide inclusions and carbon in the sample is met. The maximum heating temperature of the pulse heating furnace can reach 3000 ℃ (6000W power). Generally, the analysis power is set to about 4000~5000W, and the oxygen released is the total oxygen in the sample.
The released carbon monoxide is carried by the carrier gas into the catalytic converter (copper oxide furnace). Under the catalysis of copper oxide, carbon monoxide is converted into carbon dioxide, other impurities such as hydrogen are converted into water and absorbed by the reagent, and the carbon dioxide is carried by the carrier gas into the infrared detector for detection. Finally, the mass percentage of total oxygen is obtained.
Principles and technology of hydrogen analysis
The common method for determining oxygen in metals, alloys, rare earth metals and other materials is inert gas protection-pulse heating sample melting-thermal conductivity detection method.
The entire analysis system uses inert gas as the carrier gas, generally high-purity nitrogen or argon, with a purity greater than 99.999%. The sample diameter is limited to Φ8mm, and the sample carrier is a graphite crucible, generally spectral pure graphite. The shape of the graphite crucible varies according to the electrode design of each manufacturer.
First, the graphite crucible is placed between the upper and lower electrodes of the pulse heating furnace, the furnace is closed, and the entire analysis system is flushed with carrier gas (pressure 0.1MPa, flow rate 0.3~0.5L/min). After the prepared sample is weighed, it is added to the sample waiting area through the sample adding device of the instrument.
The analysis program first controls the heating of the heating furnace to heat the empty crucible and the system, that is, pretreatment, to remove the background (blank) of the system. This process is called a deoxidation process or a flushing process. The heating conditions are degassing power and degassing time, flushing power and flushing time respectively. The process is to flush the furnace with large air flow, and the general flushing flow rate is 1.8L/min. After degassing and flushing, the system enters a waiting state, and the airflow returns to the normal analysis flow rate. The waiting state stabilizes the state of the infrared detector of the detection unit, that is, eliminates baseline fluctuations caused by air flow switching.
After waiting, the sample is automatically injected from the waiting area into the heated graphite crucible, and the heating power of the graphite crucible at this time is the analysis power. The sample is heated and melted in a graphite crucible, and the hydrogen in the sample (usually in free form) is precipitated at high temperature to form hydrogen, which is carried by the carrier gas out of the pulse heating furnace. This process is the release of hydrogen in the sample. The conditions for hydrogen release (ie heating temperature and time) are determined by the characteristics of the sample, that is, the maximum temperature required for the reaction between oxide inclusions and carbon in the sample is met. The maximum heating temperature of the pulse heating furnace can reach 3000 ℃ (6000W power). Generally, the analysis power is set to about 2000W, and the hydrogen released is the total hydrogen in the sample.
The released hydrogen is carried by the carrier gas into the catalytic converter (Schutz reagent). Carbon monoxide is converted to carbon dioxide, which is absorbed by the reagent. The carrier gas carries hydrogen into the thermal conductivity detector for detection, and finally obtains the mass percentage of total hydrogen.
The content of this article comes from "Sintered NdFeB Rare Earth Permanent Magnet Materials and Technology" edited by Zhou Shouzeng, Dong Qingfei, Gao Xuexu