Research into Theory

 

Recently, the University of Maryland and Princeton University in the United States have jointly developed a new plasma technology that can easily reach 8000 degrees Celsius under normal pressure conditions. This new uniform, ultra-high temperature, stable plasma (USP) can be easily obtained with very low voltage and current (50V and 50A).

 

At 0:00 on November 30, 2023, Beijing time, this latest research result was published in the journal Nature under the title “A stable atmospheric-pressure plasma for extreme-temperature synthesis”. The research team was led by Professor Liangbing Hu of the Department of Materials Science and Engineering at the University of Maryland, and Professor Yiguang Ju of Princeton and Professor Ji-Cheng Zhao of the University of Maryland were co-corresponding authors. The first authors of the article are Dr. Xie Hua, Dr. Liu Ning and Dr. Zhang Qian.

 

It is worth noting that on April 19, 2023, Beijing time, the research team of Professor Hu Liangbing from the University of Maryland and the research team of Professor Ju Yiguang from Princeton University published a new study entitled “Depolymerization of plastics by means of electrified spatiotemporal heating” in the journal Nature. The study reported a reaction strategy based on electrojoule heating, which can selectively pyrolyze various types of plastic materials to obtain high-value-added monomer raw materials, providing a new idea for the chemical recycling of waste plastics. This study aims to solve the problems of poor selectivity of plastic pyrolysis reactions and low yield of high-value-added products when using traditional reaction modes. By combining the compilable electrojoule pulse heating technology and the multi-layer, porous reactor design, the reaction temperature can be precisely controlled in time and space, thereby effectively controlling the reaction path and product selectivity, and efficiently and continuously realizing the conversion of plastics to monomers.

 

 

Figure 1: Professor Hu Liangbing and Professor Zhao Jicheng of the University of Maryland in front of a new plasma device that can reach 8000 degrees Celsius

 

Plasma is the fourth state of matter besides solid, liquid and gas. It is mainly composed of positively charged ions and negatively charged electrons, both of which have roughly equal charges. Plasma can generally be produced by ionizing gases through strong discharges (such as lightning) or strong electromagnetic fields.

 

Professor Hu Liangbing pointed out, “The key to this invention is that we have made a new type of fuzzy electrode (Figure 2). Through a carbon felt electrode composed of an array of many fuzzy fiber tips, we created a stable and adjustable plasma with a temperature comparable to that of the surface of the sun. This plasma can be started and maintained with lower voltage and current.”

 

 

Figure 2: Ultra-high temperature and stable plasma is achieved using a tip array carbon felt electrode.

This unique tip array electrode consists of long and short carbon fibers on the surface of carbon felt (Figure 3). When voltage is applied, the Joule heat generated at the contact points or defect areas of the long fibers forms a small gap, significantly reducing the plasma breakdown voltage to below 50V, which is 30 times lower than the 1500V without fiber tips. At the same time, the vertically arranged array of short fiber bundles generates a concentrated electric field, which smoothly expands and increases the volume of the plasma.

 

Figure 3: Effect of carbon felt electrode surface fibers on USP formation.

 

Professor Ju Yiguang (Robert Porter Patterson Professor and Director of the Department of Energy’s Hydrogen Energy Research Center (EERC)) and his team at Princeton University’s Plasma Physics Laboratory (PPPL) have characterized this unique plasma formation process in detail (Figure 4). He pointed out: “The micro-discharges and enhanced secondary electron emission promoted by the carbon fiber tip on a scale close to the Debye length are key factors in reducing the breakdown voltage and increasing the uniformity and stability of the plasma.”

 

 

Figure 4: Left: Characterization and rapid response of USP plasma formation process; Right: Professor Ju Yiguang of Princeton University.

 

“Our USP device is the easiest way to create ultra-high temperature, stable plasma, and it can be conveniently operated at atmospheric pressure,” said Professor Jicheng Zhao, a member of the National Academy of Engineering and director of the Department of Materials Science and Engineering at the University of Maryland. “The temperature of 8000 degrees Celsius can melt or even evaporate almost all solids on the earth. We can use this to synthesize new materials by breaking and forming new chemical bonds; therefore, USP will become a new and transformative technology platform.” (Figure 5)

 

The team has used USP to synthesize a variety of extreme materials, including various refractory metal alloys and ultra-high temperature ceramics, such as hafnium carbonitride, which is predicted by first-principles calculations to have the highest melting point of all solids.

 

The highly flexible carbon felt electrode can be shaped into a variety of geometric shapes to meet different manufacturing needs. For example, a cylindrical design of a coaxial electrode can confine the plasma in the channel and serve as a prototype for gas-phase reactions, refractory metal alloying, and various atomization processes. The team also demonstrated that the focused USP beam can be used as a potential 3D printing method for ultra-high temperature materials (Figure 5).

 

Figure 5: USP applied to materials synthesis and device design flexibility.

 

Another important feature of USP is its ability to heat and cool quickly to enable synthesis at conditions far from thermodynamic equilibrium. In addition to material and chemical synthesis, USP can also be used to decompose unwanted and undesirable substances.

 

“Our USP technology will undoubtedly accelerate the discovery and development of new materials,” added Professor Liangbing Hu. “The versatile USP device provides a new paradigm for material synthesis and manufacturing with a wide range of application potential.”

 

The joint research team also includes researchers from the University of Houston, the University of Pittsburgh, the University of California, San Diego, and Oak Ridge National Laboratory.

 

In addition to ultra-high temperatures, USP also produces extremely bright light, with an intensity comparable to that of the sun. Just like avoiding looking directly at the sun with the naked eye, watching the USP process requires wearing appropriate sunglasses or filters to avoid eye damage.

 

Professors Liangbing Hu, Yiguang Ju, and Jicheng Zhao have co-founded a startup company, USPlasma, Inc. (www.usplasma.com), to scale up and commercialize this new thermal plasma technology.