How to use portable Raman spectrometer to analyze and characterize carbon black materials?

Raman spectroscopy is a powerful analytical technique that can provide molecular fingerprint information. It is often used to study the molecular structure of substances, detect the concentration of chemical mixtures and identify specific molecules. Due to its non-destructiveness, no need for sample preparation, rapid and accurate detection and the appearance of portable Raman spectroscopy system in recent years, Raman spectroscopy analysis technology has really become a practical analysis technology widely accepted by the public.

Raman spectroscopy has become very popular in chemical, pharmaceutical and other enterprises. Its main applications include: rapid identification of unknown compounds; Quantitative analysis; Mixture analysis and raw material inspection in mixed system. The ratio of the peak intensity of the two Raman characteristic peaks usually provides some useful information about the phase transition, the crystallinity of the material, and the degree of structural order.

This paper mainly introduces a portable Raman spectrum which can analyze and characterize carbon black materials in real time. In SP2 hybridized carbon materials, some unique and beneficial data can be obtained according to the peak ratio of D peak and G peak, so Raman spectral analysis technique is extremely suitable for the analysis and characterization of carbon black materials. In this study, the versatility of Raman spectroscopic techniques is demonstrated by the portable Raman spectrometer, which also reveals the impact of the latest portable Raman spectrometers on different industries.

Carbon black material:

Carbon black material is an amorphous carbon. A light, loose, very fine powder may be considered as graphite with an amorphous structure, having a lower crystallinity than graphite. Carbon black is used mainly as a reinforcing filler in automobile tires and some rubber products. It is also commonly used in paints, pigments and carbon carbon paper. With the material structure is highly complex, and there is no clear standard test method, so the analysis of this kind of material characterization are generally confined to the traditional test methods, for example, using the iodine absorption quantity research level of carbon black, according to the area of value measuring particle size, use of toughening agent (phthalates potassium acid dibutyl) absorption quantity measuring the relative amount of oil can be absorbed by the carbon black, etc.

X-ray diffraction analysis or high-performance imaging analysis can show the structure of carbon black materials at the atomic level. However, none of these methods can analyze carbon black materials on the molecular level immediately. It is very helpful to evaluate, control and monitor the production process of carbon black material. Raman spectroscopy is extremely suitable for the analysis of carbon materials with different crystalline structures, because the microstructure of carbon materials is highly Raman active. The graphite crystal has a layered structure. The carbon atoms in each layer are arranged in a hexagonal shape, and the hexagons (six-membered rings) are arranged in a planar network structure. Each single crystal cell contains four carbon atoms.

The different faces are connected by the rotation and transformation of the axis of symmetry. For the symmetric group D4h of single crystal graphite, one of the vibration modes, E2g, has high Raman activity and is related to the Raman peak at 1582cm-1 (G peak). Therefore, graphite has a very high single crystallinity, which is famous for high sequence pyrolysis graphite (HOPG), showing a Raman peak at 1582cm-1. Carbon black material has amorphous microcrystalline structure, and there will be another Raman peak (D peak) near 1350cm-1.

The structural disorder similar to the microcrystalline structure will destroy the symmetric structure, as can be seen from the peak at 1350cm-1. The structural disorder of graphite materials can be characterized by Raman peak strength ratio ID/IG. According to the study, for the grain size larger than 2nm in carbon black materials, the value of ID/IG is inversely proportional to the grain size.

Experimental Procedure:

The portable Raman spectrometer ATR3110 was used to set the laser excitation wavelength at 532nm and the spectral resolution at 4.5cm-1 to analyze and characterize the commercially available carbon black materials. A portable video microscope sampling system is combined with a Raman spectrometer to ensure that the laser is accurately focused on the sample surface to be tested.

The laser power was set at about 40mW, the integration time was set at 120 seconds, and the Raman spectrogram was obtained at room temperature. In the Raman spectrometer, for the inductively coupled detector (CCD), the dark noise and output noise need to be as small as possible relative to the Raman signal due to the low efficiency of Raman. This experiment used in portable Raman spectrometer was used a thin back according to the type of CCD detector, and the traditional quantum efficiency is only about 50% of the former according to type of CCD detector in comparison, the thin back according to the type of CCD detector of quantum efficiency can reach 90%, because photons from the back into the CCD, and here is in order to improve the efficiency of light to the valid area CCD etching thin silicon substrate. In this way, quantum efficiency can be greatly improved by reducing photon loss. The cooling system of THE CCD device can greatly reduce the dark noise. When the temperature of the device is reduced by 7°C, the dark noise will be reduced by nearly 50%. The cooled detector allows longer integration times, such as the 120 seconds used in this experiment. This greatly increases the detection limit and also makes the application of weak light possible. In this experiment, Optosky software was used for data analysis, mainly including peak analysis and baseline correction. All fluorescence doping in Raman spectral signals can be removed by using the baseline correction function of the software. The feature is based on an innovative algorithm. By using this algorithm, the sum of error squares is iteratively varied between the fitting baseline and the original signal. After baseline correction, the peak intensity in the Raman spectrum can be obtained using the peak analysis function within the software. Then you can calculate the ratio of peak intensity between peak D and peak G.

The location of the D peak depends on the excitation wavelength of the excitation light. When the excitation wavelength of the excitation light changes from 488nm to 647nm, the position of the D peak also changes from 1360cm-1 to 1330cm-1. When the excitation wavelength of the excitation light was set at 532nm, the D peak appeared near 1337cm-1. For C1 and C2 samples, the ID/IG value is less than 1, which indicates that there is a certain degree of structural disorder in these two carbon black materials. For C3 samples, the ID/IG value is greater than 1, indicating that the sample material has a higher degree of disorder.

Conclution:

The high sensitivity of Raman spectrometer provides a quality guaranteed spectrogram for carbon black materials with characteristic D-peak, so it is possible to establish a relationship between Raman spectra and material structure. When the graphite material is in a single crystal form, the D peak represents the degree of structural disorder. The occurrence of D peak is closely related to the disorder degree of crystal structure with low symmetry. ID/IG ratio can be used to characterize carbon black materials in different aspects.Such as:

1. Structural disorder degree of carbon black material
2. Evaluation of grain size of carbon black material
3. Consistency study of the measurement of carbon black at different locations by multiple measurement method

Since the advent of portable Raman spectrometers and the ability to obtain good quality spectra, it has become possible to analyze carbon black materials in real time or in real time. This is very beneficial to the quality monitoring and quality control in the process of carbon black material manufacturing. Compared to the traditional desktop lab-level Raman spectrometer, the desktop lab-level Raman spectrometer can not treat test material samples for immediate analysis, but the portable Raman spectrometer can now do so. The latest generation of portable Raman spectroscopy has shown great potential in industrial applications, and it is believed that it will become more and more important in the near future with the continuous improvement and development of the technology.