Ceramic Heat Research Articles

Low-temperature hot-press sintering of AlN ceramics with MgO–CaO–Al2O3–SiO2 glass additives for ceramic heater applications

Aluminum nitride (AlN) is used a ceramic heater material for the semiconductor industry. Because extremely high temperatures are required to achieve dense AlN components, sintering aids such as Y2O3 are typically added to reduce the sintering temperature and time. To further reduce the sintering temperature, in this study, a low-melting-temperature glass (MgO–CaO–Al2O3–SiO2; MCAS) was used as a sintering additive for AlN. With MCAS addition, fully dense AlN was obtained by hot-press sintering at 1500 °C for 3 h at 30 MPa. The mechanical properties, thermal conductivity, and volume resistance of the sintered AlN–MCAS sample were evaluated and compared with those of a reference sample (AlN prepared with 5 wt% Y2O3 sintering aid sintered at 1750 °C for 8 h at 10 MPa). The thermal conductivity of AlN prepared with 0.5 wt% MCAS was 91.2 W/m∙K, which was 84.8 W/m∙K lower than that of the reference sample at 25 °C; however, the difference in thermal conductivity between the samples was only 14.2 W/m∙K at the ceramic-heater operating temperature of 500 °C. The flexural strength of AlN–MCAS was 550 MPa, which was higher than that of the reference sample (425 MPa); this was attributed to the smaller grain size achieved by low-temperature sintering. The volume resistance of AlN–MCAS was lower than that of the reference sample in the range of 200–400 °C. However, the resistivity of the proposed AlN–MCAS sample was higher than that of the reference sample (500 °C) owing to grain-boundary scattering of phonons. In summary, the proposed sintering strategy produces AlN materials for heater applications with low production cost, while achieving the properties required by the semiconductor industry.

Design and modeling of a multiscale porous ceramic heat exchanger for high temperature applications with ultrahigh power density

The efficiency of a heat engine can be significantly improved by operating in a high-temperature and high-pressure environment, which is crucial for a wide range of applications such as hybrid and electric aviation as well as power generation. However, such extreme operating conditions pose severe challenges to the heat exchanger design. Although recently developed superalloys and ceramics can survive high-temperature and high-pressure loads, using these materials in a traditional heat exchanger design requires high cost and yields low power density. In this work, we propose an ultrahigh power density ceramic heat exchanger for high-temperature applications enabled by a multiscale porous design. By optimizing the design of centimeter-scale macrochannels and microchannels, significant improvement to both heat transfer and structural strength is predicted, with a negligible pressure drop penalty (< 1%). Based on finite element simulations, an optimized heat exchanger core design is expected to achieve power densities of 717 MW/m3 and 300 kW/kg, which indicates more than 2.5× enhancement in thermal performance compared to printed-circuit heat exchanger design. Furthermore, the heat exchanger design features low material costs and scalable fabrication, enabling highly customizable applications in aerospace and terrestrial power generation.

Experimental study on waste heat recovery characteristics of inorganic ceramic membrane flue gas

The wet saturated flue gas discharged by coal-fired utility boilers leads to a large amount of low-temperature wasteheat loss. Inorganic ceramic membrane is acid-base resistant and has strong chemical stability. It is an ideal material forrecovering low-temperature waste heat from flue gas. The experiment of waste heat recovery of flue gas was carried outwith inorganic ceramic membrane as the core, and the characteristic parameters of low-temperature flue gas at the tailof the boiler were analyzed; taking 316 L stainless steel as the comparative object, the strengthening effect of inorganicceramic film on improving heat recovery power and composite heat transfer coefficient was discussed. The results showthat the waste heat recovery of flue gas is mainly the evaporation latent heat recovery of water, accounting for about90%; circulating water is used as cooling medium, and the waste heat recovery capacity of flue gas is stronger;compared with circulating water, when air is used as the cooling medium, the effect of inorganic ceramic membraneflue gas waste heat recovery is more significant, and the enhancement coefficient is as high as 9; increasing the flue gasflow is helpful to improve the heat recovery power and composite heat transfer coefficient; at the same time, inorganicceramic membrane can also recover condensate with high water quality. The results of this paper can provide areference for the application of inorganic ceramic membrane in flue gas waste heat recovery.

Light from heat lamps affects sow behaviour and piglet salivary melatonin levels

The light environment regulates animal physiology and behaviour. As widely used supplementary heat sources in creep areas, the effect of visible light radiated by infrared heat lamps on pigs is worth investigating. To investigate the effects of light from heat lamps on the behaviour of sows and piglets and possible endocrine mechanisms, 24 primiparous sows were randomly assigned to three supplementary heat source treatments: (1) 250 W non-luminous ceramic heat lamps (CE, n = 8), (2) 175 W red heat lamps (RL, n = 8), and (3) 175 W transparent heat lamps (TL, n = 8). All heat lamps were turned off on Day 15 postpartum. Piglets were weighed on days 3 and 21 postpartum. The number and duration of suckling within 24 h were analysed via video recordings on days 4, 8, and 16 postpartum. Sow posture changes during the day and night were detected using the YOLOv4 target detection network model. One marked piglet from six litters randomly selected from each treatment was used for saliva collection. Saliva samples were collected at 0800, 1400, 2000, and 0200 (+1 d) on days 10 and 20 postpartum. The results showed that the mean postural change frequency of TL sows was higher than that of CE sows (P < 0.05), while that of RL sows was not different from that of CE and TL sows. However, the duration of the sows being in each posture was not affected by the treatment. The total suckling duration of TL piglets was significantly longer than that of CE piglets, but there was no significant difference in the performance of the piglets. The melatonin concentrations in the saliva of piglets at 10 and 20 days of age in the three treatments showed different diurnal rhythms, but there was no significant difference in the levels of melatonin in TL piglets between night and day. Differences in salivary cortisol levels only appeared between the CE and RL groups at 20 days of age. Based on the present results, the illuminance and spectrum of the transparent heat lamps were sufficient to stimulate sow activity and inhibit melatonin levels in piglets. However, the stimulating effect on suckling was not sufficient to significantly improve the performance of piglets. Exposure to red heat lamps, rather than ceramic lamps, resulted in the strongest circadian rhythm of salivary melatonin in piglets.

Development of a silicon carbide ceramic based counter-flow heat exchanger by binder jetting and liquid silicon infiltration for concentrating solar power

A silicon carbide ceramic counter-flow heat exchanger with integrated headers was printed by binder jetting additive manufacturing process. Multiple phenolic binder infiltration cycles (3 or 5) followed by pyrolysis were conducted to increase the net carbon content of the printed SiC specimens. Subsequently, to attain full densification, silicon melt infiltration was used. The microstructure and mechanical properties were comprehensively characterized on the densified material. The chemical compositions and visual distribution of the various regions in the specimens were determined via scanning electron microscopy, while X-ray diffraction and synchrotron μ-computed tomography were used to provide a quantitative assessment of the volume fractions of the identified phase regions. Microhardness measurements showed dependence on the local microstructure. The fracture strength of the material was correlated with the specimen density and agreed with the reported values in the literature. High-temperature exposure at 750 °C for up to 200 h did not degrade the strength for the specimens with three phenolic-binder infiltrations; however, the strengths degraded for ones with five phenolic-binder infiltrations. The associated fracture toughnesses of the specimens were ∼3.4 MPam1/2 at room temperature and 750 °C, and the thermal conductivities varied from >150 W/mK at room temperature to ∼45 W/mK at 750 °C. Hence, this study validated the use of the binder-jetting printed SiC ceramic materials for high-temperature heat exchanges. Finally, we also present in this work the first successful fabrication of a binder-jetting printed one-piece dense SiC ceramic heat exchanger body with unblocked channels that can be used for the flow of heat transfer fluids.

Electron-beam heating of ceramics to moderate temperature at fore-vacuum pressure

We have studied the electron-beam heating of ceramic targets (AlN, ZrO2, and Al2O3) in the fore-vacuum pressure range (2–5 Pa) to temperatures below their phase transformation temperatures (melting, evaporation; < 1700 0C). It is shown that in this temperature range, conductive heat transfer through the lower face plays a dominant role in the thermal balance of the ceramic target; heat transfer by thermal conduction through the gas, and by thermal radiation play no significant role in heat removal from the target. Mass-to-charge analysis of the ion composition of the beam plasma, generated by the electron beam itself, shows that even at these moderate temperatures, intense sublimation of low melting point volatile components of the ceramic target occurs. Depositing on the substrate surface, these components may negatively affect the coating parameters and properties. Our investigations indicate the necessity of taking special measures to minimize the effect of ceramic target volatile components prior to their intense evaporation during the deposition of protective and functional coatings.

Nd3+-doped glass-ceramic fiber fabricated by drawing precursor ceramic and successive heat treatment

Optical fibers have been formed by replacing precursor glass core with precursor ceramic core, in which drawing process, the precursor ceramic melted to fill the space of the core region while the clad glass was softened. Nd3+ doped LaNbO4 nanocrystals were precipitated in the core after heat treatment. X-ray diffraction, Raman spectra, high-resolution transmission electron microscopy, electron paramagnetic resonance, optical microscope, and photoluminescence were used to characterize the obtained fiber. No crystallization, cracking, bubble, or undissolved substance is observed in the core region of precursor fiber. Nd3+ doped LaNbO4 nanocrystals are precipitated in the core region after thermal treatment. Under the pumping source of 808 nm, three emission bands located at ∼887 nm, ∼1064 nm, and ∼1337 nm are observed, which makes this GC fiber a promising material for the NIR fiber amplifier.

Simulation the effectiveness of heat recovery of the regenerative ventilator using different approaches

Today buildings should be designed for energy efficiency class not less than C. This requires ventilation with heat recovery. On the market, there are different compact heat recovery ventilation units for decentralized ventilation. Regenerative ventilators represent a promising area of effective ventilation with exhaust air heat recovery. They operate cyclically for the inlet and outlet of air. These kinds of ventilators should work in a blocked pair(s) – one for input and one for output in each pair. If not, the effectiveness will decrease. A mathematical model of the ceramic heat regenerator in the regenerative ventilator “Twin Fresh” by Vents has been created to improve the efficiency of its operation. In previous works, on the basis of two different approaches, the operation of the heat regenerator was simulated. The first one uses M. Mikheev’s formula for the Nusselt number. The second one is computational fluid dynamic simulation by SolidWorks Flow Simulation. The efficiency coefficients obtained as a result of the simulation had a significant difference – up to 66.5 %. The aim of the work is to find alternative methods for adequately determining the efficiency of the ventilator. A mathematical simulation was performed using a different formula from “Novyi spravochnik khimika i tekhnologa. Protsessy i aparaty khimicheskikh tekhnologii”. This formula takes into account the Grashof number. Values obtained are significantly different from both previous ones – up to two times. There is no information in the literature about the experimental conditions for determining the Nusselt number, which was used in the simulation. Therefore, we can’t assume, what approach is closer to the conditions of the ceramic regenerator. There is a need to conduct experimental studies to determine the efficiency of the regenerative heat exchanger.

Enhancement of 3D Mass and Heat Transfer within a Porous Ceramic Exchanger by Flow-Induced Vibration.

This work investigates heat transfer enhancement for a porous ceramic heat exchanger. The effect of flow-induced vibration of exchanging air flow through porous tube banks has been tested. A numerical model able to assess the vibration effect on heat and mass transfer inside a porous ceramic exchanger has been carefully developed. A three-dimensional unstructured control volume finite element method (CVFEM) is developed to simulate the transport phenomena that arise during convective exchange. In this respect, several numerical tests have been conducted. The time evolution of temperature, liquid saturation, and pressure of the porous domain are analyzed and compared for two cases: with and without vibration. It is found that the vibration highly enhances the heat and mass transfer inside the ceramic exchanger. As a result, the gain of exchanging time to reach the thermal equilibrium between the hot air and the porous domain was 75% for the case of air vibration under sawtooth type at a frequency of fv = 5 Hz and Vmax = 10 m/s compared to nonvibrating exchange.

A Study on Ceramic Heater Devices Based on Si3N4 with a MoO3 Protective Layer

Currently, the need for high performance heaters for industrial application is increasing, and repeated wear, rapid temperature change, and uneven temperature can cause deteriorating quality and reduced productivity. The ceramic heater in this study consists of a substrate, an electrode layer, and a protective layer, and low-melting temperature glass frit was used for all layers to allow low-temperature processing. As a substrate for the ceramic heater, Si3N4, which is twice as strong as AlN and has excellent wear resistance, was used. As the electrode material, Ag-Pd, which provides good adhesion to the Si3N4 substrate and high electrical conductivity was used, and MoO3 powder was mixed 8 : 2 to make a paste. The MoO3 adjusts the resistance of the Ag-Pd electrode, thereby supplementing the heater performance. Si3N4 powder and glass frit were used for the protective film layer that protects the electrode, and MoO3 was added to unify the materials between the layers.

Additive manufacturing and testing of a ceramic heat exchanger for high-temperature and high-pressure applications for concentrating solar power

Heat exchangers with excellent corrosion and oxidation resistances are essential for the next-generation concentrating solar power (CSP) plants using a molten salt heat transfer fluid and a supercritical CO2 Brayton power cycle that can operate at temperatures >700 °C for higher efficiencies. Techniques were developed for additively manufacturing ceramic materials for applications involving high temperature, high pressure, and high corrosion resistance as needed for the CSP application. Based on a previous ceramic heat exchanger design with its cross-section geometry of the flow channels optimized for heat transfer and mechanical strength, lab-scale prototype heat exchangers, with integrated headers and incorporated flow channel dimensional compensations, were fabricated by using the binder jetting process. The printed prototype heat exchangers were successfully densified through the processes of liquid polymer infiltration and pyrolysis. In addition, thermophysical properties of the densified silicon carbide parts were measured to provide necessary design information. Experimental heat transfer testing of the lab-scale prototype heat exchanger was conducted, and the experimental data agreed reasonably well with the simulated results. This agreement provides validation of the simulation models for their applicability to the development of a full-scale ceramic heat exchanger.

A dual-functional micro-focus X-ray source based on carbon nanotube field emission

A micro-focus X-ray source with miniature pressure sensor was developed based on the multi-walled carbon nanotube (MWNT) field emission. The field emitters for both X-ray cathode and the pressure sensor were synthesized by direct chemical vapor deposition growth of MWNTs on catalytic substrates. MWNTs exhibited excellent field emission properties with the threshold field at 10 mA/cm2 of 2.30 V/μm, and the high current density of 10 A/cm2 could be reached at the field of 4.36 V/μm. The field emission electron gun was constructed with the aid of electrostatic simulations on the electron beam trajectories and the focal spot size (FSS) on the target with the demagnification factor of 5. The practical objects, including the semiconductor chip and the ceramic heating element, were tested by the X-ray source with the spatial resolution of less than 35 μm, and the fracture of the ceramic element inside metal case could be clearly detected. The pressure sensor monitored the in-situ pressures inside the source during the processing and after the sealing-off. The pressures in the sealed sources were generally in 10−4 Pa level and could rise to 10−2 Pa level during the operation.

1-D Modeling of Two Phase Flow Process in Concentric Annular Heat Pipe and Experimental Investigation

As the heat dissipation of smart devices increases, cutting-edge cooling solutions are becoming increasingly important. The heat pipe is an efficient device that boosts heat transfer and is recommended to reduce thermal management power. In this study, a concentric annular heat pipe (CAHP) with distilled water as a working fluid is proposed to enhance heat transfer, and experiments and one-dimensional analysis were carried out to predict thermal characteristics and evaluate performance. The CAHP was 90 mm in length, 62 mm in inner diameter, 70 mm in outer diameter, and 0.4 mm in thickness. At the outer surface of the internal CAHP, a two-layer screen mesh wick (500 mesh, Stainless Steel 304) that is 0.34 mm in layer thickness was installed. A ceramic heater (20 mm × 20 mm) was attached to the middle of the outer surface, and the hollow region with 48 fins was cooled by an electric fan. The experiment was carried out with variations in the heat load, the filling ratio of the working fluid, the pitch angle, the roll angle, and the airflow speed, and the one-dimensional analysis was modeled by AMESIM. The experimental results showed that the best thermal resistance of the CAHP was 3.74 °C/W with a supplied heat of 20 W, a pitch angle of −15°, and a Vair of 3 m/s. In addition, the CAHP’s 1-D simulation model using AMESIM was verified through the experimental results. However, although the modeling results according to the inclination angle could not be reflected due to the difficulty of implementing multiple orientation structures in the one-dimensional simulation model, the simulation results were found to be almost consistent with the experimental results. Case studies were conducted to understand the various characteristics of the CAHP using the model, and the optimal volume fraction, the porosity, and the number of layers of the wicks were determined to be 10, 0.345, and 2, respectively.

TWO BODY WEAR OF COMMONLY USED DENTAL CERAMICS AND ENAMEL”

Statement of Problem- Wear behaviour of a restorative materials is an important mechanical property to be considered during selection. Dental ceramics have been the mainstay of esthetic dentistry for more than 100 years. However, dentists remain suspicious about its potential abrasivity. Newer ceramics are being considered to be more wear friendly. Methodology- The present study evaluated and compared the wear resistance of one conventional dental ceramic, one low fusing ceramic and one heat pressed ceramic against human enamel. Human enamel specimens were taken as control. Wear simulation was performed in a pin on disc wear system with 18 N load, 120 rpm speed for 20000 cycles. Wear rate and loss of height was calculated for all specimens and subjected to one was ANOVA followed by post hoc Tukey b analysis. Results- Ceramics exhibited lower wear rate than human enamel specimens (p&lt;0.05). Among ceramics heat pressed ceramics showed least wear. For antagonist wear conventional ceramics and low fusing ceramics caused similar (p&gt;0.05) wear of enamel antagonists which was higher than heat pressed ceramics (p&lt;0.05). Conclusion- Newer ceramic formulations are more wear resistant than conventional ceramics and cause less wear of opposing teeth.

Evaluation of surface temperature uniformity of multi-zone ceramic heaters with embedded cooling channels for electrostatic chuck

Evaluation of surface temperature uniformity of multi-zone ceramic heaters with embedded cooling channels for electrostatic chuck

A High-Performance Lung-Inspired Ceramic 3d-Printed Heat Exchanger for High-Temperature Energy-Efficient Systems

A High-Performance Lung-Inspired Ceramic 3d-Printed Heat Exchanger for High-Temperature Energy-Efficient Systems

Electron-Beam Heating of Ceramics to Moderate Temperature at Fore-Vacuum Pressure

Electron-Beam Heating of Ceramics to Moderate Temperature at Fore-Vacuum Pressure

Influence of the method of out-of-furnace melt treatment on hydrogen content in 5083 aluminum alloy

The work was carried out in laboratory conditions at the semicontinuous ingot casting installation (SICI) in the casting laboratory of the Siberian Federal University. The article presents the results of comparative studies of the dynamics of aluminum saturation with hydrogen over the entire hardware and technological scheme. The article gives a schematic diagram of the semicontinuous ingot-casting unit. Studies were carried out using a single- and two-stage aluminum melt filtration system with the use of ceramic foam filters with an alumosilicate binder bonded with stabilized borosilicate glass. The results of investigations of the ceramic foam filter heating temperature influence (less than 500 oC and higher than 500 oC) on hydrogen concentration in an aluminum alloy are presented. The hydrogen content studies have been carried out during complex passing of aluminum melt through a single- or two-stage filtration by a ceramic foam filter. The paper presents the results obtained by applying a degassing unit that operates on the principle of the molten metal inert gas blowing (argon). During the study, it was found that the average hydrogen concentration in an aluminum alloy before passing through a ceramic foam filter was 0.19 cm3/100 g Al, and that after passing through the filtration system with ceramic foam filters was 0.185 cm3/100 g Al. The paper shows that the ceramic foam filter heating degree does not affect the aluminum alloy saturation with hydrogen. In the course of the work, it was found that the most significant effect of reducing hydrogen concentration could be achieved by blowing aluminum with inert gas (argon) along with filtration by a ceramic foam filter (CFF), which was confirmed by a series of experiments. The research was carried out in the context a regional competition for the best projects of interdisciplinary fundamental scientific research conducted by the RFBR, the Government of the Krasnoyarsk Territory, the Regional Foundation and enterprises operating in the Krasnoyarsk Territory, as well as organizations participating in the Yenisey Siberia complex investment project (No. 20-48-242916).

Water-soluble sacrificial 3D printed molds for fast prototyping in ceramic injection molding

Fabrication of steel molds is a major expense (time and cost) in ceramic injection molding research and development. 3D printed resin molds for fast prototyping are therefore highly attractive and have gained increasing attention. This paper reports strategies to use sacrificial molds 3D printed by fused deposition modeling (FDM) from PVA or digital light processing (DLP) from water soluble resin. Usage of sacrificial molds allows injection molding of complex geometries, which are not accessible for simple two-part molds. Ceramic heating elements in diverse geometries were injection molded using a composite feedstock containing MoSi2, Al2O3 and feldspar. More parts with various geometries were produced from Al2O3 feedstock. A comparison revealed that DLP printed molds are better suited for parts with very small structural features due to the higher resolution of the DLP process as compared to FDM. Finally, ceramic heaters were fabricated using two-component ceramic injection molding and successfully tested.

Bimodal particle distributions with increased thermal conductivity for solid particles as heat transfer media and storage materials

Solid particles are being considered in several high temperature thermal energy storage systems and as heat transfer media in a variety of advanced power generation systems, particularly in concentrated solar power plants. The downside of such an approach is the low overall heat transfer coefficients caused by the inherently low thermal conductivity values of the low-cost solid media when coupled to heat exchanger for the power cycle working fluid. Choosing the right particle size distribution, emittance, and material of the solid media can all make a substantial difference in packed bed thermal conductivity. Current research though exclusively focuses on continuous unimodal distributions of particles. Here, we propose the use of a binary particle system with a bimodal size distribution to significantly increase packed bed thermal conductivity by reducing packed bed porosity. This is the first study related to ceramic solid particle heat transfer that has considered the thermal conductivity of non-unimodal size distributions at room and elevated temperatures. The following study found that for the binary particle system using Carbo particles CP 16/30 – CP 70/140 where the large particle volume fraction was 50% there was an 17–47% increase in packed bed thermal conductivity when compared with a nearly unimodal particle size distribution of CP 16/30 between 50 and 300 °C. Two different porosity and effective thermal conductivity models were studied, with one providing better prediction of porosity but both effective thermal conductivity models providing less predictive capacity. Importantly this approach can have a substantial impact of thermal performance, with little to no impact on the particle cost.