Graphite Heater Research Articles

Numerical model of aluminothermic reduction vessel preheating and charge heating with graphite heating rods

Numerical model of aluminothermic reduction vessel preheating and charge heating with graphite heating rods

Solar-Thermal Synthesized Graphitic Heat Spreader for Thermally Enhanced Organic Substrates

Solar-Thermal Synthesized Graphitic Heat Spreader for Thermally Enhanced Organic Substrates

CHAMBER FURNACE FOR SIMULATION OF CARBON MATERIALS HEAT TREATMENT IN ELECTROTHERMAL FLUIDIZED BED

Existing laboratory furnaces for high-temperature heat treatment of materials at around 3000°C, which have graphite heaters, allow samples to be heated at a rate two orders of magnitude lower than in electrothermal fluidized bed furnaces. This makes it impossible to use them in the research into the heat treatment of carbon materials because they do not meet the conditions of shock heating and do not allow to keep accurate residence time. The paper presents the research into the use of low-density composite carbon materials as heaters. Based on the results obtained, a high-temperature chamber furnace was designed, studied, and the temperature field in the heater was simulated. As a result, a high-temperature laboratory furnace was created with a sample heating rate of 20 °C/s - 100 °C/s, which made it possible to use it to simulate the heating process in the electrothermal fluidized bed furnace. Comparison of energy consumption in the furnace with a traditional graphite heater and a low-density carbon composite heater showed that heat loss in the furnace is reduced by 1.7 to 1.8 times.

A virtual thermometer for ultrahigh-temperature–pressure experiments in a large-volume press

Ultrahigh-temperature–pressure experiments are crucial for understanding the physical and chemical properties of matter. The recent development of boron-doped diamond (BDD) heaters has made such melting experiments possible in large-volume presses. However, estimates of temperatures above 2600 K and of the temperature distributions inside BDD heaters are not well constrained, owing to the lack of a suitable thermometer. Here, we establish a three-dimensional finite element model as a virtual thermometer to estimate the temperature and temperature field above 2600 K. The advantage of this virtual thermometer over those proposed in previous studies is that it considers both alternating and direct current heating modes, the actual sizes of cell assemblies after compression, the effects of the electrode, thermocouple and anvil, and the heat dissipation by the pressure-transmitting medium. The virtual thermometer reproduces the power–temperature relationships of ultrahigh-temperature–pressure experiments below 2600 K at press loads of 2.8–7.9 MN (∼19 to 28 GPa) within experimental uncertainties. The temperatures above 2600 K predicted by our virtual thermometer are within the uncertainty of those extrapolated from power–temperature relationships below 2600 K. Furthermore, our model shows that the temperature distribution inside a BDD heater (19–26 K/mm along the radial direction and <83 K/mm along the longitudinal direction) is more homogeneous than those inside conventional heaters such as graphite or LaCrO3 heaters (100–200 K/mm). Our study thus provides a reliable virtual thermometer for ultrahigh-temperature experiments using BDD heaters in Earth and material sciences.

Optimizing the performance of a graphite anode for innovative metal-ion batteries and hybrid capacitors

Herein, we present an optimum method for maximizing the electrochemical performance of graphite anodes using two heat treatment methods involving graphite intercalated compound (GIC) group within graphite, namely, thermal shock (TS; directly input target temperature) and gradual heating (GH; including ramping time). Different heating methods for preparing expanded graphite (EG) involve different reactions, relaxation times, and diffusion pathways for the diffusion of metal ions into EG. We find that rapidly shocking the layered structure can facilitate faster lithium and potassium ion diffusion from EG (TS) (heated for 30 min) via different intercalation/deintercalation processes compared to that from EG (GH). Consequently, EG (TS) exhibits the most significantly improved electrochemical performance among the lithium and potassium ion half-cells. For full lithium-ion hybrid capacitors (LIHCs), EG (TS)||activated carbon (AC) shows reasonable values of maximum power density (2.8 kW kg−1 with 59.12 Wh kg−1) and energy density (196.41 Wh kg−1), demonstrating its ultrahigh durability (capacity retention: 70.01%) over 12000 cycles at 2.0 A g−1. In addition, for potassium-ion hybrid capacitors (PIHCs), reasonable performance is achieved (average capacity of 82.02 mAh g−1 at 1.0 A g−1 over 2000 cycles with 94.35% capacity retention), demonstrating the high efficiency of PIHCs for substituting LIHCs without any systematic alterations.

Design and Numerical Study of Induction-Heating Graphitization Furnace Based on Graphene Coils

Induction-heating graphitization furnaces are widely used to produce high-purity graphite products due to their high heating rate, high-limit temperatures, safety, cleanliness, and precise control. However, the existing induction-heating systems based on copper coils have limited energy efficiency. This paper proposes a new induction-heating graphitization furnace based on graphene coils. Due to the excellent high-temperature resistance of the macroscopic graphene material, the coil can be placed closer to the graphite heater, which improves the electromagnetic efficiency; the coil itself does not need to pass cooling water, which reduces the heat loss of the furnace and ultimately results in a higher energy efficiency of the induction furnace. In this paper, a numerical model of the induction-heating process is established and verified, the temperature-field and electromagnetic-field distributions of the heating process are analyzed by using the model, and the energy balance calculations are performed for the original furnace and the new furnace. Through a comparison, it was found that the new furnace possesses an electromagnetic efficiency of 84.87% and a thermal efficiency of 20.82%, and it can reduce the energy consumption by 33.34%, compared with the original furnace. In addition, the influence of the coil parameters on the performance of the induction furnace is discussed. By changing the coil conductivity, the induction furnace can achieve an energy efficiency of 17.76%–18.11%. This study provides new ideas for the application of macroscopic graphene materials in high-temperature induction heating.

Developing Preventative Strategies to Mitigate Thermal Runaway in NMC532-Graphite Cylindrical Cells Using Forensic Simulations

The ubiquitous deployment of Li-ion batteries (LIBs) in more demanding applications has reinforced the need to understand the root causes of thermal runaway. Herein, we perform a forensic simulation of a real-case failure scenario, using localised heating of Li(Ni0.5Mn0.3Co0.2)O2 versus graphite 18650 cylindrical cells. This study determined the localised temperatures that would lead to venting and thermal runaway of these cells, as well as correlating the gases produced as a function of the degradation pathway. Catastrophic failure, involving melting (with internal cell temperatures exceeding 1085 °C), deformation and ejection of the cell componentry, was induced by locally applying 200 °C and 250 °C to a fully charged cell. Conversely, catastrophic failure was not observed when the same temperatures were applied to the cells at a lower state of charge (SOC). This work highlights the importance of SOC, chemistry and heat in driving the thermal failure mode of Ni-rich LIB cells, allowing for a better understanding of battery safety and the associated design improvements.

Graphitizable Pitch from Microwave Plasma Pyrolysis of Natural Gas.

An innovative approach of microwave plasma was utilized to convert natural gas into tar, from which a highly graphitizable pitch was derived using fractional distillation. The natural gas-derived pitch (NGDP) was thoroughly characterized, and the graphitizability of the carbonized NGDP was assessed using polarized light microscopy. The NGDP and, for comparison, needle coke, petroleum coke, and shot coke were subjected to graphitization heat treatment (GR) at 2500 °C. Results indicate that the graphitizability of the NGDP exceeds those of all industrial standard cokes. The GR-NGDP showed the highest degree of graphitization and crystallite size among all samples.

Thermodynamic Modeling of Radioactive Graphite Heating in Nitrogen and Oxygenized Air

Thermodynamic Modeling of Radioactive Graphite Heating in Nitrogen and Oxygenized Air

Rigorous Reliability Testing of an Encapsulated Thermal Pyrolytic Graphite (TPG) Heat Spreader for Passive Thermal Management Applications

Continued microelectronic miniaturization has resulted in higher power density, increasing the need for high performance thermal management. One possible solution for board-level thermal management is to fully encapsulate a high thermal conductivity material, such as Thermal Pyrolytic Graphite (TPG; ~1700 W/mK) in a metal (such as 6061 aluminum), producing an efficient passive heat spreader for thermal dissipation. The metal shell provides sufficient mechanical strength at a small detriment to the overall thermal conductivity. Reliability and consistent performance over time are critical for thermal management systems, especially in Defense and Aerospace applications. MIL-STD-883H provides test parameters for reliability involving exposure to mechanical shock (Method 2002.5), mechanical vibration (Method 2005.2), and thermal shock (Method 1011.9), with traditional evaluation criteria involving microelectronic device performance and/or a visual examination. For this work, the reliability of aluminum encapsulated TPG test coupons was evaluated with more demanding criteria: a visual examination, X-ray inspection, acoustic microscopy, and thermal conductivity performance testing, both before and after the previously discussed MIL-STD-883H exposures. The encapsulated coupons showed excellent robustness; the thermal conductivity properties remained constant with an average value around 965 W/mK, and the non-destructive imaging revealed excellent bond quality for the metal encapsulation, with no evidence of delamination. This more stringent evaluation criteria after MIL-STD-883H testing provides a better way to evaluate the reliability of passive thermal management systems. The study results also demonstrate the metal encapsulated TPG heat spreader as a superior thermal management solution with high performance and high reliability for demanding applications.

Customized measuring station for Peltier modules

Peltier modules control temperatures in niche products such as wine coolers and camping fridges or are used to precisely temper processes as for example the duplication of DNA sections. Accurate characterization and long term stability of the modules is crucial in order to meet the high reliability requirements especially in critical applications such as in space or medical technology markets. While most of the measurement stations are designed for thermoelectric generators, especially in regard to long term testing, the measurement of peltier modules is rarely described. In this contribution, we show a customized measuring station specifically for the combination of the characterization of peltier modules and their long term stability. With this measurement station, it is possible to determine temperature dependent properties such as the maximum current Imax, the maximum cooling power ▪, the maximum temperature difference ▪ and the coefficient of performance (COP) while performing cycling tests in between the characterization measurements. In this setup, both sides consist of water driven heat exchangers with a range of ▪ to ▪. The heat flow through the module is measured via two graphite heat flux meters.Thereby, it is possible to completely characterize a peltier module within this measuring system. An error analysis for the measured properties is given as well. In addition to the characterization of the modules, the long-term stability of the modules can be measured not only with static current and temperature but also at cyclical stimulation of temperature or current changes meaning that application-oriented long-term tests are possible.

Modified graphene film powder scraps for re-preparation of highly thermally conductive flexible graphite heat spreaders

Graphene film (GF) is widely used for heat dissipation in portable electronic devices by virtue of its lightweight and high thermal conductivity (K). However, in practical applications, mold-cutting GF inevitably generates plenty of scraps with high K, so it is worthwhile to investigate the secondary utilization of scraps. This contribution first used polydopamine (PDA) to surface-modify the crushed large-sized graphite nanosheets (GNs) powder scraps to obtain GNs@PDA. Then the GNs@PDA was mixed with graphene oxide (GO) sheets to prepare graphene/GNs@PDA (G/PG) composite films via self-assembly. After graphitization, the graphitized PDA “welded” the GNs to the derived graphene through covalent bonds. The resulting long-range ordered defect-free lamellar stacking structures effectively facilitated the transfer of phonons and electrons, thus significantly enhancing the K and electrical conductivity of the G/PG film. The in-plane K and electrical conductivity of the G/PG film are up to 1301.8 W/mK and 5939.0 S/cm, respectively. Furthermore, G/PG films also exhibit superior mechanical properties, foldability, and electromagnetic shielding performance. This work provides ideas for the preparation of flexible heat spreaders and realizes the reuse of GF scraps.

APPLICATION OF CARBON-CARBON COMPOSITE MATERIALS FOR THE MANUFACTURE OF HIGH-TEMPERATURE HEATERS OF HEAT EXCHANGERS WITH AUTOMATIC TEMPERATURE CONTROL


 The article justifies the use of high-temperature heaters made of carbon-carbon composite material (CCCM) for the thermal unit of a silicon single crystal growth chamber. The conducted analysis confirms that the electrical properties of composite materials, specifically their specific resistance, allow for the creation of heating elements for high-temperature vacuum furnaces or furnaces operating in inert atmospheres at temperatures up to 2200°C.
 The use of heaters made from carbon-carbon composite material eliminates the main drawback of graphite heaters - uncontrolled energy dissipation during resistive heating due to the presence of transient electrical resistance at the junctions of graphite plates, and ensures a more uniform temperature field throughout the chamber volume. The capabilities in terms of the maximum permissible temperature of such a CCCM heater exceed the working temperature by more than two times, which also positively affects the service life.
 The modes of thermal processes occurring during crystal growth are determined by the technological process depending on the composition of the raw material and require high uniformity of heating in the working zone, high precision, and stability of the heater's temperature control. For precise temperature regulation, it is proposed to additionally measure the integral temperature in the chamber indirectly, which is based on measuring the electrical current passing through the heater, which is in thermodynamic equilibrium with the object. Thus, the heater is considered as a system susceptible to various thermal influences that determine the heat transfer process and the temperature change within the chamber and in the zone of the thermal unit's bricks.
 An improved structural diagram of a step-type extremal control system is proposed for automatic temperature control of a high-temperature heater using modern power electronics, sensors, microprocessors. To ensure speed and accuracy in temperature control, the pulse-phase control method implemented with modern specialized thermoregulator with PID-regulation was applied.
 Experimental tests conducted on the «Redmet-30» installation under factory conditions confirm the energy efficiency of using high-temperature heaters made of CCCM.

Graphite Slurry Heat Treatment Temperature for Improving the Durability of CNWs Anode Materials of Lithium-Ion Batteries

Graphite Slurry Heat Treatment Temperature for Improving the Durability of CNWs Anode Materials of Lithium-Ion Batteries

LaB6 hollow cathode with a novel graphite heater

In this study, the design and experimental characterization of a LaB6 hollow cathode utilizing a novel heater made of graphite are presented. Hollow cathodes commonly use heaters where a refractory metal wire is wound around a high temperature ceramic insulator with grooves. These heaters have issues related to thermal fatigue and the recrystalization embrittleness of the heater wire at high temperatures causing the cathode to malfunction, leading to short lifetime. Rather than using refractory metals, a heater made of graphite is designed and integrated into an existing hollow cathode. The graphite can be manufactured easily and does not show any embrittlement at high temperatures, which increases its operational life time. Additionally, due to its lower sputtering yield, undesirable operational conditions are eliminated. A zig-zag shape is used to tailor the geometry to reach desired resistance value of the heater. The presented graphite-heater eliminates these problems as long as enough care is taken in its initial manufacturing and assembly stage. Additionally, the design of the graphite-heater can be modified in such a way to provide heating to a targeted area, which help decrease the required heater power as well as increase the heating speed of the cathode insert material. Successful tests of the hollow cathode with the novel graphite heater indicate long lifetime and steady operation performance, making it suitable for use in real space missions.

Thermodynamic Modeling of Thermal Processes Involving Radionuclides of Uranium, Plutonium, Europium on Heating of Nuclear Graphite in Air

Thermodynamic Modeling of Thermal Processes Involving Radionuclides of Uranium, Plutonium, Europium on Heating of Nuclear Graphite in Air

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Code Benchmark of the HTTF Pressurized Conduction Cooldown Test Using SAM

The High Temperature Test Facility (HTTF) at Oregon State University is an integral system test facility to simulate postulated reactor transients of prismatic high-temperature gas-cooled reactors(HTGRs). A series of test campaigns was launched, providing abundant test data that could be used to benchmark reactor system analysis codes like the System Analysis Module (SAM). In this study, a SAM model of the facility is developed based on the two-dimensional (2D) ring model approach. All components including the ceramic matrix, graphite heaters, helium coolant channels, core barrel, upcomer, pressure vessel, and reactor cavity cooling system are modeled as concentric cylindrical rings. The model is used to simulate one of the benchmark problems—Pressurized Conduction Cooldown (PCC)—within the scope of the Organisation for Economic Co-operation and Development Nuclear Energy Agency International HTTF Benchmark. The simulations consist of two parts. In the first part, operating and boundary conditions as well as thermophysical properties of materials are specified for the benchmark problem. Results from the first part will be used in code-to-code comparison. In the second part, the SAM model is used to simulate Test PG-27, which is the first PCC test carried out in the HTTF, with only two of the ten heater banks activated. The results in the second part are used for code-to-data comparison. Because the helium coolant flow rate is not measured in this facility, it is estimated using the input power and inlet/outlet coolant temperatures. Additionally, radial heat flow in the ceramic blocks is complicated by hundreds of cylindrical coolant channels and heater rods embedded in them. As such, it is necessary to deduce an effective thermal conductivity for the ceramic to analyze the core thermal behavior. SAM predictions of the helium coolant and ceramic temperatures are compared with test data measured in three equivalent sectors. Overall, the SAM results agree reasonably well with test data within the variation of data among the three sectors, which demonstrates SAM’s capability in capturing transient effects in HTGR using the simplified 2D ring model.

Spectroscopic Properties of Pb2+-Doped BaF2 Crystals

Various concentrations of PbF2-doped BaF2 crystals were grown by the Bridgman method using a shaped graphite heater. The room temperature optical absorption spectra showed two UV absorption bands (labeled A and D), characteristic of the Pb2+ ions. The structure of the bands was analyzed using the Gaussian multi-peak fitting. The distribution of the Pb2+ ions along the crystals and the effective segregation coefficient were studied using the optical absorption method. The obtained effective segregation coefficient was >1. The Pb2+ ions were not uniformly distributed along the samples. High intensity emission bands were observed in the near UV domain and the visible region.

Effect of heating rate, temperature, and residence time during graphitization on the mechanical and electrical properties of isotropic graphite blocks

The present study aimed to determine the correlation between graphitization parameters during the manufacturing of isotropic graphite blocks, including temperature, residence time, and heating rate, and the physical properties of the obtained graphite blocks. It was found that during graphitization, nitrogen- and sulfur-containing gases were generated, and the isotropic graphite blocks exhibited volume shrinkage, and their apparent density and bulk density increased, regardless of any changes in the process parameters, due to the intrinsic microstructure of the isotropic coke. Graphite blocks with varying graphitization temperatures and residence time exhibited increased bulk density and open porosity but decreased flexural strength and electrical resistivity compared to carbonized blocks. It was also confirmed that the heating rate process parameter was related to gas release rates and crystallization. In addition, it was observed that micron-sized pores were created around the developed graphite layered structure with increasing graphitization degree.