Heating Regime Research Articles

An experimental evaluation of thermoelectric generator performance under cyclic heating regimes

AbstractThermal cycling is known to adversely affect the performance and lifespan of thermoelectric generators (TEGs) yet has received limited attention to date. The current study experimentally investigates the effect of thermal cycling on the performance of twelve nominally identical TEG modules. Six samples were subjected to the same thermal cycle profile with an average heating time of 154 s to examine the variation in their outputs. The maximum cycling temperature was varied between 170 °C and 190 °C for a further six samples to investigate the effect of maximum set-point temperature on performance. Degradation in performance was exhibited by all modules, with maximum power outputs between 28% and 57% of pre-cycling values and a decrease in the dimensionless figure of merit $$ZT$$ ZT of 21% to 56% upon cessation of cycling. Sudden ‘breakdowns’ or significant reductions in output power were observed for all TEGs, accompanied by increased electrical resistance, which is indicative of internal damage to the modules arising from the formation of micro-cracks at the interface between the semiconductor thermocouples and electrically conductive material. The rate of degradation post-‘breakdown’ appeared to be influenced by the maximum set-point temperature, with more rapid decreases observed for increasing temperatures.

Experimental Thermal Response Study of Multilayered, Encapsulated, PCM-Integrated Building Construction Materials

Thermal energy storage integration using phase change materials (PCMs) in buildings has great potential for energy conservation and greenhouse gas (GHG) emission reduction. Cutting-edge research and innovative ideas are required when using multilayered PCMs within typical construction materials to take advantage of their heat storage capability over a wide temperature range within buildings. This current study was carried out to experimentally test the efficacy of using dual PCMs RT28HC and RT21HC with different melting temperature ranges (28 °C and 21 °C) under variable thermal loading. The transient thermal response of various PCM-based configurations of concrete and cement blocks at different temperature inputs was obtained to determine the effectiveness of dual PCMs and their optimized configuration under experimental laboratory conditions. The range of the temperature input was varied from 22 °C to 50 °C, suitable for hot climatic conditions such as those in Pakistan. Laboratory ambient temperatures remained at ~17 °C for all experimental tests. Moreover, the results were compared using two parameters, i.e., decrement factor (DF) and time lag (TL). With DF and TL values of 0.10 and 5.72, respectively, in the high-temperature heating (HTH) regime and a low DF value of 0.08 and high TL of 5.17 in the moderate-temperature heating (MTH) regime, the RT28HC–RT21HC combination proved to be the most effective. The application of the RT28HC–RT21HC combination provided up to a 54.3% reduction in indoor temperatures in the HTH regime. This research contributes through experimental validation that these novel configurations are capable of providing substantial improvement in indoor thermal comfort.

Winter warming effects on soil nitrate leaching under cover crops: A field study using high-frequency weighing lysimeters

Leaching of nitrate (NO3−)—a reactive nitrogen form with impacts on ecosystem health—increases during the non-growing season (NGS) of agricultural soils under cold climates. Cover crops are effective at reducing NGS NO3− leaching, but this benefit may be altered with less snow cover inducing more soil freezing under warmer winters. Our objective was to quantify the effect of winter warming on NO3− leaching from cover crops for a loamy sand (LS) and a silt loam (SIL) soil. This research was conducted over 2 years in Ontario, Canada, using 18 high-precision weighing lysimeters designed to study ecosystem services from agricultural soils. Infra-red heaters were used to simulate warming in lysimeters under a wheat-corn-soybean rotation planted with a cover crop mixture with (+H) and without heating (-H). Nitrate leaching determination used NO3− concentration at 90 cm (discrete sampling) and high temporal resolution drainage volume measurements. Data were analyzed for fall, overwinter, spring-thaw, post-planting, and total period (i.e., November 1 to June 30 of 2017/2018 and 2018/2019). Warming significantly affected soil temperature and soil water content—an effect that was similar for both years. As expected, experimental units under + H presented warmer soils at 5 and 10 cm, along with higher soil water content in liquid form than –H lysimeters, which translated into higher drainage values for + H than –H, especially during the overwinter period. NO3− concentrations at 90 cm were only affected by winter heating for the LS soil. The drainage and NO3− concentrations exhibited high spatial variation, which likely reduced the sensitivity to detect significant differences. Thus, although absolute differences in NO3− leaching between LS vs. SIL and +H (LS) vs. –H (LS) were large, only a trend occurred for higher leaching in LS in 2018/2019. Our research demonstrated that soil heating can influence overwinter drainage (for LS and SIL soils) and NO3− concentration at 90 cm in the LS soil—important NO3− leaching controlling factors. However, contrary to our initial hypothesis, the heating regime adopted in our study did not promote colder soils during the winter. We suggest different heating regimes such as intermittent heating to simulate extreme weather freeze/thaw events as a future research topic.

Small impact cratering processes produce distinctive charcoal assemblages

Abstract The frequency of crater-producing asteroid impacts on Earth is not known. Of the predicted Holocene asteroid impact craters of <200 m diameter, only ~30% have been located. Until now there has been no way to distinguish them from “normal” terrestrial structures unless pieces of iron meteorites were found nearby. We show that the reflective properties of charcoal found in the proximal ejecta of small impact craters are distinct from those produced by wildfires. Impact-produced charcoals and wildfire charcoals must derive from different heating regimes. We suggest that charcoal with specific reflective properties may help to recognize the meteoritic origin of small craters.

Many-body parametric resonances in the driven sine-Gordon model

We study a quantum many-body variant of the parametric oscillator, by investigating the driven sine-Gordon model with a modulated tunnel coupling via a semi-classical Truncated Wigner Approximation (TWA). We first analyze the parametric resonant regime for driving protocols that retain our model gapped, and compare the TWA to a Time-Dependent Variational Principle (TDVP). We then turn to a drive which closes the gap, resulting in an enhanced energy absorption. While the TDVP approach breaks down in this regime, we can apply TWA to explore the dynamics of the mode-resolved energy density, and the higher-order correlations between modes in the prethermal heating regime. For weak driving amplitude, we find an exponentially fast energy absorption in the main resonant mode, while the heating of all remaining modes is almost perfectly suppressed on short time scales. At later times, the highly excited main resonance provides effective resonant driving terms for its higher harmonics through the non-linearities in the Hamiltonian, and gives rise to an exponentially fast heating in these particular modes. We capture the strong correlations induced by these resonant processes by evaluating higher order connected correlation functions. Our results can be experimentally probed in ultracold atomic settings, with parallel one-dimensional quasi-condensates in the presence of a modulated tunnel coupling.

Environmentally Safe Microwave Heating of Non-Polar Materials

The current research presents results for the theoretical basis of heat transfer and experimental studies of a microwave method of heating uranium hexafluoride for safe evaporation from containers, including defective, and low- and medium-temperature heating of oil fractions. The process is environmentally safe because heat generation occurs in the bulk of the heated medium and is easily controlled. The proposed method is based on uranium hexafluoride evaporation at the expense of heat energy transferred from substances absorbing microwave energy. The conducted investigation on a laboratory bench with a direct heating regime of samples by microwave field of a travelling wave of lowest mode H10 and in the process studied, samples were heated both individually and in combination with UF6. The results show that it was determined that uranium oxides are the most preferable for use as heat absorbing agents for the microwave heating process. A demonstration on a pilot scale was designed for testing the feasibility of this process. The dielectric characteristics of two components mixing were studied. The penetration depth of microwave into the mixture and heat-absorbing agent amount for process implementation has been determined. Several experimental tests on the environmentally safe technology at pilot scale installation were conducted at various continuous modes. The results revealed from the pilot unit showed that the microwave method of evacuation of DUF6 from steel containers allows them to be emptied safely with practically cold (T<1000C) walls, with high efficiency of using microwave energy (η≈97%) while maintaining the level of pressure in the containers.

Ab initio calculations for the transport properties of metals within Boltzmann transport theory: From equilibrium to nonequilibrium heating regime

The paper offers an approach to ab initio calculations for predicting the electron transport properties of solid-state metals in a case of nonequilibrium heating. Formulas for the electrical resistivity (also static conductivity) and thermal conductivity of metals at different electron and lattice temperatures were derived within a method proposed by Allen [Phys. Rev. B 17, 3725 (1978)] for the solution of the Boltzmann transport equation. The approach works well under equilibrium heating too when electron and lattice temperatures are equal. It performs most effectively if it is necessary to allow for the Fermi smearing of the electron distribution function over quantum states and the energy dependence of the electron-phonon spectral function. Four metals---Cu, Ag, Au and Pd---are considered as examples. We succeeded to reproduce well the temperature dependencies of electrical resistivity and thermal conductivity of studied metals in a wide range of temperatures under equilibrium heating. For the nonequilibrium regime of heating, calculations reproduce quite well the temporal evolution of the static electrical conductivity of gold, observed in recent experiments for the interaction of thin gold foils with ultrashort laser pulses.

On-chip beam rotators, adiabatic mode converters, and waveplates through low-loss waveguides with variable cross-sections

Photonics integrated circuitry would benefit considerably from the ability to arbitrarily control waveguide cross-sections with high precision and low loss, in order to provide more degrees of freedom in manipulating propagating light. Here, we report a new method for femtosecond laser writing of optical-fiber-compatible glass waveguides, namely spherical phase-induced multicore waveguide (SPIM-WG), which addresses this challenging task with three-dimensional on-chip light control. Fabricating in the heating regime with high scanning speed, precise deformation of cross-sections is still achievable along the waveguide, with shapes and sizes finely controllable of high resolution in both horizontal and vertical transversal directions. We observed that these waveguides have high refractive index contrast of 0.017, low propagation loss of 0.14 dB/cm, and very low coupling loss of 0.19 dB coupled from a single-mode fiber. SPIM-WG devices were easily fabricated that were able to perform on-chip beam rotation through varying angles, or manipulate the polarization state of propagating light for target wavelengths. We also demonstrated SPIM-WG mode converters that provide arbitrary adiabatic mode conversion with high efficiency between symmetric and asymmetric nonuniform modes; examples include circular, elliptical modes, and asymmetric modes from ppKTP (periodically poled potassium titanyl phosphate) waveguides which are generally applied in frequency conversion and quantum light sources. Created inside optical glass, these waveguides and devices have the capability to operate across ultra-broad bands from visible to infrared wavelengths. The compatibility with optical fiber also paves the way toward packaged photonic integrated circuitry, which usually needs input and output fiber connections.

A dehydration kinetic model of calcium silicate hydrates at high temperature

AbstractDehydration of calcium silicate hydrates, the primary binding phase of cement paste, contributes significantly to the degradation of cementitious materials at high temperatures. Kinetics of the dehydration process is usually parameterized as the product of the classic Arrhenius equation and a kinetic expression, calibrating the influence of the temperature and the reaction degree, respectively. By means of the Exp‐function approximation, an improved kinetic expression is proposed and the differential equation is solved by utilizing the Mean‐value Theorem for integrals. The established dehydration model is validated by comparing with independent experimental measurements, concerning different heating regime and molar ratios of calcium‐to‐silicon. Both the temperature history and the calcium‐to‐silicon molar ratios influence the kinetics and the final status of the dehydration process. The established model provides access to further investigation of the microstructural evolution of heated concrete, containing supplementary cementitious materials.

Really Trapped in the Heat?

This paper aims to account for the role of occupants' efforts in reducing the space-heating costs of panel apartments linked to district heating systems. We present the findings of a questionnaire survey among residents of North-West Budapest (Hungary). Our results show that the roles of efforts are limited in the panel housing context, but wider access to appropriate information on those (limited) opportunities could significantly alleviate the burden on households trapped in an inadequate space heating regime.

Soil Heating in Fire (SheFire): A model and measurement method for estimating soil heating and effects during wildland fires.

Fire has transformative effects on soil biological, chemical, and physical properties in terrestrial ecosystems around the world. While methods for estimating fire characteristics and associated effects aboveground have progressed in recent decades, there remain major challenges in characterizing soil heating and associated effects belowground. Overcoming these challenges is crucial for understanding how fire influences soil carbon storage, biogeochemical cycling, and ecosystem recovery. In this paper, we present a novel framework for characterizing belowground heating and effects. The framework includes (1) an open-source model to estimate fire-driven soil heating, cooling, and the biotic effects of heating across depths and over time (Soil Heating in Fire model; SheFire) and (2) a simple field method for recording soil temperatures at multiple depths using self-contained temperature sensor and data loggers (i.e., iButtons), installed along a wooden stake inserted into the soil (i.e., an iStake). The iStake overcomes many logistical challenges associated with obtaining temperature profiles using thermocouples. Heating measurements provide inputs to the SheFire model, and modeled soil heating can then be used to derive ecosystem response functions, such as heating effects on microorganisms and tissues. To validate SheFire estimates, we conducted a burn table experiment using iStakes to record temperatures that were in turn used to fit the SheFire model. We then compared SheFire predicted temperatures against measured temperatures at other soil depths. To benchmark iStake measurements against those recorded by thermocouples, we co-located both types of sensors in the burn table experiment. We found that SheFire demonstrated skill in interpolating and extrapolating soil temperatures, with the largest errors occurring at the shallowest depths. We also found that iButton sensors are comparable to thermocouples for recording soil temperatures during fires. Finally, we present a case study using iStakes and SheFire to estimate in situ soil heating during a prescribed fire and demonstrate how observed heating regimes would influence seed and tree root vascular cambium survival at different soil depths. This measurement-modeling framework provides a cutting-edge approach for describing soil temperature regimes (i.e., soil heating) through a soil profile and predicting biological responses.

Plasma electron acceleration in a non-resonant microwave heating scheme below the electron cyclotron frequency

Microwave heating of over-dense plasmas is routinely achieved in the stellarator TJ-K. In contrast to usually applied heating scenarios in tokamaks or stellarators, an operational regime is described where the heating occurs well below the electron cyclotron frequency but still well above the lower hybrid frequency. Microwave energy is deposited at the so-called O-resonance, accompanied by a small population of high-energy electrons with an energy up to 100 keV. These electrons are responsible for a significant toroidal net current and the occurrence of hard x-rays. Requirements for achieving this heating regime are described together with a novel scheme for plasma-electron acceleration.

High-Temperature Characterization of Melted Nuclear Core Materials: Investigating Corium Properties Through the Case Studies of In-Vessel and Ex-Vessel Retention

During a severe accident in a nuclear reactor, the molten core—or corium—may be relocated into the reactor vessel’s lower plenum in case of core support plate failure. The severe accident management strategy for In-Vessel Retention—or IVR—consists in stabilizing the corium within the reactor pressure vessel by external cooling of the vessel’s lower head. If now, the vessel fails due to excessive thermal loading on its walls, the Ex-Vessel Retention—or EVR—strategy is adopted. In this case, the core melt stabilization can be achieved by effective corium spreading, either in the reactor vessel cavity or in a dedicated “core-catcher”, and cooling by water. The success of both strategies highly depends on the corium behavior at high temperatures, conditioning vessel’s integrity for IVR, and promotion for the spreading of the EVR. This involves a variety of fundamental mechanisms closely related to heat and mass transfer regimes prevailing at the system scale, which requires further analytical and experimental insight to determine the primary mechanisms and feed the modeling tools, allowing the numerical simulations of severe accident scenarios.Within the framework of corium characterization at high temperatures, the present study aims at filling the lack of such fundamental data as density, surface tension, liquidus and solidus temperatures, and viscosity. In order to accurately measure these properties at high temperatures, the VITI facility is designed with various configurations. Concerning IVR, the influence of density and surface tension is particularly highlighted through VITI-SD and VITI-MBP configurations, and practical applications of experimental results are finally discussed, in link with the focusing effect issue at the thin upper metallic layer of the corium pool. Concerning EVR, the properties of interest are solidus/liquidus temperature and dynamic viscosity, and typical experimental results obtained through VITI-VPA and VITI-GFL configurations are discussed in view of characterizing corium spreading.

Remote Geotechnical Monitoring of a Buried Oil Pipeline

Extensive but remote oil and gas fields in Canada and Russia require extremely long pipelines. Global warming and local anthropogenic effects drive the deepening of seasonal thawing of cryolithozone soils and enhance pathological processes such as frost heave, thermokarst, and thermal erosion. These processes lead to a reduction in the subgrade capacity of the soils, causing changes in the spatial position of the pipelines, consequently increasing the number of accidents. Oil operators are compelled to monitor the daily temperatures of unevenly heated soils along pipeline routes. However, they are confronted with the problem of separating anthropogenic heat losses from seasonal temperature fluctuations. To highlight heat losses, we propose a short-term prediction approach to a transformed multidimensional dataset. First, we define the temperature intervals according to the classification of permafrost to generate additional features that sharpen seasonal and permafrost conditions, as well as the timing of temperature measurement. Furthermore, linear and nonlinear uncorrelated features are extracted and scaled. The second step consists of selecting a training sample, learning, and adjusting the additive regression model. Forecasts are then made from the test sample to assess the accuracy of the model. The forecasting procedure is provided by the three-component model named Prophet. Prophet fits linear and nonlinear functions to define the trend component and Fourier series to define the seasonal component; the third component, responsible for the abnormal days (when the heating regime is changed for some reason), could be defined by an analyst. Preliminary statistical analysis shows that the subsurface frozen soils containing the oil pipeline are mostly unstable, especially in the autumn season. Based upon the values of the error metrics, it is determined that the most accurate forecast is obtained on a three-month uniform time grid.

Development of formulation and technology for the production of functional drinks using of cranberry fruits

Creation of new products with scientifically substantiated and proven properties that reduce the risk of developing diseases that are directly dependent on nutrition, and improve health due to the presence of various nutrients in their composition is one of the promising areas for improving the health of the population. The soft drinks market today is replete with both domestic and foreign manufacturers. In addition, public catering enterprises have the opportunity to sell their own products, which necessitates the improvement of the quality of drinks and their functional properties. A person consumes soft drinks throughout his life, while they represent the optimal basis for enrichment with biologically active food substances, since they most affect the endoecological rehabilitation of the human body. Natural non-alcoholic drinks based on healthy plant materials are becoming increasingly popular. We have developed soft drink compositions using cranberry, sea buckthorn, Japanese quince (chaenomeles), ginkgo biloba and basil leaves, containing vitamins A, C, E, known for their antioxidant properties. In order to preserve raw materials, shock freezing and dehydration by means of convective drying were used with a sparing temperature heating regime not exceeding 45 ℃, which made it possible to preserve the most vulnerable vitamin C to heat treatment. As a result of experimental studies, recipes and technologies for the production of drinks have been developed, as well as technical and technological maps indicating organoleptic indicators and energy value. Dry matter and acidity, which corresponds to the accepted allowable values have been determined. The values of the chemical composition of drinks have been obtained, allowing to state that, according to the content of the microelement potassium, drinks belong to general health-improving functional drinks, and, according to the content of vitamin C, to antioxidant and immune-supporting functional drinks.

EFFECT OF HEAT TREATMENT ON MYCELIA GROWTH AND SPORE GERMINATION OF Aspergillus niger OBTAINED FROM DECAYED CUCUMBER FRUITS (Cucumis sativus)

This work investigated effect of heat treatment on mycelia growth and spore germination of Aspergillus niger obtained from decayed cucumber fruits. Both mycelia disc and sample aliquots of the spore suspensions of Aspergillus niger were separately treated with hot air (HA) and hot water (HW) at the following heat regimes: 40°C and 50°C for 10, 20 and 30 minutes each while non-heated mycelia and spores served as control. Results showed that the mycelia growths of A. niger following each HA treatment increased in this order: 50°C – 10 minutes > 50°C – 20 minutes > 50°C – 30 minutes > 40°C – 10 minutes > 40°C – 20 minutes / 40°C – 30 minutes and 40°C – 20 minutes > 40°C -10 minutes > 50°C – 20 minutes > 50°C – 10 minutes > 50°C – 30 minutes > 40°C – 30 minutes following each HW treatment. Similarly, germinating spores of A. niger following each HA treatment increased in this order: 40°C - 10 minutes > 50°C for 20 minutes > 40°C – 30 minutes > 40°C - 20 minutes > 50°C - 30 minutes > 50°C - 10 minutes and 40°C - 30 minutes > 50°C - 20 minutes > 40°C – 10 minutes > 40°C - 20 minutes > 50°C - 30 minutes > 50°C - 10 minutes after each HW treatment. Thus, this probably implied that HA treatment at 40°C – 10 minutes, 50°C – 10 and 20 minutes and HW treatment at 40°C – 20 minutes, 40°C – 30 minutes could be effective in delaying the development of Aspergillus niger in cucumber fruits.

Energy efficiency of operational regimes of combined heat and power plants of industrial enterprises

Enterprises with energy-intensive production have combined heat and power plants (CHP) in their structure. During the implementation of energy saving measures, it is possible to achieve different ratios between the indicators of the efficiency of consumption of thermal and electrical energy by enterprises for production. With certain ratios between specific heat and electricity consumption in production, the enterprise is forced to buy a certain part of the electricity in the district power system (DPS) to prevent the discharge of steam exhausted by the turbine into the atmosphere or to deliver excess electricity of its own generation to the DPS. The problem cited in the article indicates that the choice is determined by the prices for fuel for CHP and the ratio between the prices for electricity purchased in the DPS and delivered to the DPS. Although electricity consumption in the production of sugar does not exceed 11% of the energy of the fuel, it is profitable to generate it in excess (turbine generators operate at maximum, close to the nominal mode) and deliver it to the distribution zone at a price higher than the cost. The proposed method for selecting operating modes for CHP turbine plants using the example of a sugar plant, which can also be used for the construction industry, as well as a method for determining energy costs for all operating modes of a sugar plant turbine plant. The influence of the cost of electricity in the distribution zone on the choice of the mode of operation of turbine plants of the CHP, which provide the minimum financial costs for the energy supply of the enterprise, has been established. A method for determining the standard size of a CHP turbine plant that satisfies the specific indicators of heat and electricity consumption of an enterprise is presented.

Wheat variety carrying 2NvS chromosomal segment provides yield advantage through lowering terminal heat-induced oxidative stress.

A 2NvS chromosomal segment carrying bread wheat variety, BARI Gom 33 ('BG33'), showed tolerance to terminal heat stress andhigher yield over a heat-tolerant non-2NvS BARI Gom 26 ('BG26') and a heat-susceptible Pavon 76 ('Pavon'). This study aimed to ascertain the potential of the 2NvS 'BG33' in terminal heat-induced oxidative stress tolerance compared to non-2NvS 'BG26' and heat-susceptible 'Pavon' under two heat regimes at the reproductive stages viz. control (optimum sowing time) and heat stress (late sowing). We found that both 'BG26' and 'BG33' showed significantly higher tolerance to oxidative stress by limiting the generation of reactive oxygen species (ROS), methylglyoxal under heat stress. During terminal heat stress, both 'BG33' and 'BG26' exhibited greater cellular homeostasis than heat-susceptible 'Pavon', which was maintained by the increased accumulation of osmolytes, nonenzymatic antioxidants, and enzymes associated with ROS scavenging, ascorbate-glutathione cycle, and glyoxalase system. Lesser cellular damage in 'BG26' and 'BG33' was eventually imitated in a smaller reduction in grain yield (15 and 12%, respectively) than in 'Pavon', which had a 33% reduction owing to heat stress. Collectively, our findings revealed that the chromosomal segment 2NvS provides yield advantage to 'BG33' under terminal heat stress by lowering oxidative damage. As 2NvS translocation contains multiple nucleotide-binding domain leucine-rich repeat containing, cytochrome P450, and other gene families associated with plant stress tolerance, further studies are warranted to dissect the underlying molecular mechanisms associated with higher heat stress tolerance of 2NvS carrying 'BG33'.

Direct Thermal Charging Cell Using Nickel Hexacyanoferrate (ΙΙ) Anode for Green Recycling of Low-Grade Heat

Direct thermal charging cell (DTCC) converts heat to electricity by thermal charging and electrical discharging at high temperature and self-regeneration at low temperature. In this work, DTCC adopts recyclable NiHCFeII anode and environmentally friendly KCl electrolyte, realizing the green recycling via chemical treatment for electrodes after long-term operation. The newly designed DTCC achieves the heat-to-electricity conversion efficiency of 3.59% (26.2% of Carnot efficiency) at 70 °C, leaping to the forefront of existing thermoelectrochemical and thermoelectric systems in the low-grade heat regime. The developed system has the advantages of green technology, flexibility, cost-effectiveness, and scalability, making it promising in practical applications for direct energy conversion from low-grade heat sources.

Elevated Temperature Deformation of P/M Dispersion - Strengthened Copper and Aluminium

Abstract Paper deals with the low cost route of the preparation of SiC/Si3N4 nanocomposite. It is shown that SiC nanoinclusions distributed within the Si3N4 matrix can be produced by carbothermal reduction of fine SiO2 particles added into a starting mixture. The amount of SiC nanoinclusions can be adjusted by the appropriate amount of SiO2 + C additives. Almost full density of the final composite was achieved by hot-pressing at 1750 °C using a “special” heating regime allowing the outgasing of CO as a product of carbothermal reduction.