Sulfur Powder Oil Content Testing (Low-Field NMR Method)

In the production of chemical powders such as sulfur, a certain amount of oil is added based on product quality and performance requirements. This enhances product handling and performance. In addition to oil, these powders may also retain moisture. The content of these liquids—oil and water—is a critical parameter that directly impacts product quality. To ensure stability and consistency in industrial production, fast and accurate measurement is essential. Low-field NMR technology enables rapid oil and moisture content detection with a simple sample preparation process, making it ideal for quality inspection and process control in manufacturing environments.

The traditional method for determining oil content in sulfur powder is solvent extraction. However, this approach is complex, time-consuming, and requires skilled operators. It is prone to human error and involves toxic reagents that pose safety risks to personnel. Due to these drawbacks, this method is becoming increasingly unsuitable for modern industrial applications.

Low-field NMR uses a spin echo sequence for measurement. As shown in the figure, after a 90° RF pulse is applied, the Free Induction Decay (FID) signal is measured at time t1. The amplitude of this signal (A1) is proportional to the number of hydrogen protons in the two liquid phases of the sample—namely, water and oil.

After a 180° RF pulse, the spin echo signal amplitude (A2) is recorded. At this point, the water signal has completely decayed, and A2 reflects only the oil component. Therefore, the difference between A1 and A2 (A1–A2) is directly proportional to the water content in the sample.

After calibrating the system with standard samples of known oil and moisture content, unknown samples can be tested within 30 seconds to 3 minutes. The process is fast, non-destructive, and perfectly suited for real-time, inline industrial applications.

Compared with chemical methods, NMR offers superior reproducibility, requires no chemical solvents, and can be operated by non-specialists with minimal training.

Oil Content Testing in Sulfur Powder (Low-Field NMR Method)