Thermal Cycling Stability Research Articles

Three-Dimensional Macroporous rGO-Aerogel-Based Composite Phase-Change Materials with High Thermal Storage Capacity and Enhanced Thermal Conductivity.

Three-dimensional porous network encapsulation strategy is an effective means to obtain composite phase-change materials (PCMs) with high heat storage capacity and enhanced thermal conductivity. Herein, macroporous reduced graphene oxide (rGO) aerogels with adjustable pore size are prepared by the emulsion template method and hydrothermal reduction process. Further, the shape-stabilized rGO-aerogel-based composite PCMs are constructed after the combination of 3D porous rGO supports and paraffin wax (PW) through vacuum melting infiltration. By regulating the pore structure of the rGO aerogel network, the rGO-based composite PCMs achieve excellent energy storage properties with a phase-change enthalpy of 179.94 J/g for the loading amount of 95.61 wt% and an obvious enhancement in thermal conductivity of 0.412 W/m-1·K-1, which is 54.89% higher than pristine PW and enduring thermal cycling stability. The obtained macroporous rGO-aerogel-based composite PCMs with high thermal storage and heat transfer performance effectively broaden the application of PCMs in the field of thermal energy storage.

Flexible core–shell structured Al-Cu alloy phase change materials for heat management

The development of core–shell structured phase change materials (PCMs) with tunable melting points has been attracted much attention for thermal storage of solar energy, and a flexible shell is crucial for their practical applications. Herein, we prepared microencapsulated Al-Cu alloy PCMs (MEPCMs) with a flexible shell by a deposition-oxidizing calcination method. The Cu nanoparticles are chemically deposited on the surface of Al powders by a rapid replacement reaction, which further promotes the formation of Al-Cu alloy microspheres and the oxidation of Al to form Al2O3 shell during oxidation calcination. The prepared MEPCMs show excellent thermal cyclic performance and tunable melting point (549–592 °C). The presence of a thin film between the Al2O3 shell and Al-Cu alloy core may act as a buffer to accommodate volume change during melting-freezing process, obtaining a flexible core–shell structure. The heat storage density of Al-Cu alloy MEPCMs decreases by only 0.09% after 100 melting-freezing cycles, indicating high thermal cycling stability. In addition, the microencapsulated Al-Cu alloys present high latent heat (208.6–222.3 J·g−1) and relatively high thermal conductivity (∼1.8 W·(m·K)−1), which makes it attractive for application in high-temperature thermal storage systems.

Thermochemical heat storage utilization of MSWI fly ash after carbonation enhancement with ammonia water regulation: Carbon sequestration efficiency, heavy metal immobilization, and heat storage characteristics analysis

Accelerated carbonation is an effective method of treating municipal solid waste incineration fly ash (FA). However, the efficiency of CO2 sequestration is limited and the usage of products is uncertain. This study proposed a method for enhancing carbonation by ammonia water (NH4OH) regulation and thermochemical heat storage of its products. The influences of NH4OH on CO2 sequestration and heavy metals immobilization were investigated. The results demonstrated that the carbon sequestration efficiency improved from 65.2% to 98.3%, with the NH4OH addition increasing (0–20%). NH4OH promoted the conversion of calcium chloride (CaCl2) and calcium sulfate (CaSO4), which were not originally involved in the carbonation reaction, to calcium carbonate (CaCO3). Excess NH4OH increased the release of heavy metals into the liquid phase due to the chelation of heavy metals by ammonia ions (NH4+) and the effect of high pH. The appropriate amount of NH4OH (8%) offered a high-efficient immobilization of heavy metals. The energy density of FA samples increased from 226.6 kJ/kg to 1207.8 kJ/kg with the NH4OH addition increasing, positively correlating with the content of CaCO3. After the thermal cycle treatment, the non-ammonia carbonated FA had a serious sintering phenomenon with chlorellestadite (Ca5(P,Si,S)3O12(Cl,OH,F)), which was produced from the reaction between CaSO4 and other compounds; while the carbonated FA with NH4OH addition (8%) showed good thermal cycle stability with fine particles and single component (calcium oxide). Therefore, the carbonation treatment in this study is a novel and highly-efficient method, with the final products providing an alternative material for thermochemical heat storage.

Giant room-temperature electrical switching effects in water-in-oil emulsions

Thermally-triggered electrical switching materials are of urgent demand for developing novel temperature sensors, overheat protection circuits, thermal controllers, battery management systems against overheating, etc. Here, we report a water-in-oil emulsion system with giant electrical switching ratios at room temperature prepared by a simple and efficient method. The temperature-sensitive phase transition process of alkanes as the oil phase causes the formation and collapse of conductive paths in the emulsion, resulting in electrical switching ratios of up to 6 orders of magnitude. The emulsions have good thermal cycle stability, and the switching ratio remains essentially unchanged after 100 cycles. The switching temperature can be easily adjusted by using alkanes of various chain lengths. In addition, the similar electrical switching effect is observed in four emulsions containing different neutral salts, ensuring the tunability and versatility of the system. The electrical switching emulsions offer a promising avenue to developing future high-performance, energy-saving, and low-cost electrical switching systems.

High Green Purity and Narrow Emission Ceramic‐Like Perovskite Nanocrystals Enabled by Solid‐Phase Reaction Process

AbstractHere, ceramic‐like CsPbBr3@SiO2 nanocrystals (NCs) with a high photoluminescence quantum yield of 98.7%, green purity of 90%, and narrow full width at half maximum of 22 nm are successfully achieved by a solid‐phase reaction process. The SiO2 shell covers the surface of the NCs, providing long‐term working and excellent thermal cycling stability. Ba2+ dopes the lattice of the perovskite structure under high‐temperature sintering at 700 °C, resulting in the red‐shift of the NCs emission due to the decrease of the bandgap caused by the lattice modulation with Ba2+. At the same time, the halogen vacancies are effectively passivated by a halogen‐rich environment of dopants (BaBr2). The Commission Internationale de l'Eclairage of the doped ceramic‐like NCs is (0.170, 0.760), which approaches the Rec.2020 standard. By means of this solid reaction process, red, green, and blue ceramic‐like perovskite NCs are prepared to achieve white light‐emitting diodes, covering 124% of the National Television Standards Committee.

Interfacial compatibility and thermal cycle stability for glass-sealed oxygen sensors

The oxygen sensors are extensively utilized in vehicles’ exhaust systems to monitor gases composition and control air-to-fuel ratio, thus reducing harmful emission and improving fuel economy. In equilibrium potentiometric sensors, the sealing performance is essential to ensure data accuracy. In this work, the 64SiO2–18TiO2–10Na2O–7K2O–1Al2O3 (wt%) glass was utilized as seals instead of traditional talcum in zirconium dioxide oxygen sensor. The interfacial compatibility with adjacent components (Fe–16Cr, Al2O3 and 8YSZ) and thermal cycle stability of seals were seriously evaluated in various ways. The equilibrium contact angles were lower 60° at high temperature, exhibiting better wettability and tight bonding at the interface. Besides, the leakage rates between glass and Fe–16Cr alloy were less than 0.01 sccm/cm at 650–800 °C and input gas pressures of 6.9–34.5 kPa. The oxygen sensor coupled with glass exhibited better thermal stability that leakage rate maintained around 0.004 sccm/cm under an input gas pressure of 200 kPa during 100 thermal cycles. Additionally, the oxygen sensor with sealed glass can generate continuous response and recovery, which is better than sealed talcum. Owing to these good performance, the glass is a suitable alternative for oxygen sensor sealing.

Modified sodium acetate trihydrate/expanded perlite composite phase change material encapsulated by epoxy resin for radiant floor heating

In this study, sodium acetate trihydrate was modified with urea, ethylene glycol, and disodium hydrogen phosphate dodecahydrate. The modified phase change material was impregnated into expanded perlite to obtain a composite phase change material, which was encapsulated with epoxy resin as the coating to obtain a coated composite phase change material with a phase change temperature of 46.4 °C, a latent heat of phase change of 132.7 J/g, and a low supercooling temperature of 0.6 °C. Leak tests and thermal cycle stability showed that the coating could effectively slow down the escape rate of the liquid phase and solve the macroscopic leakage problem. Moreover, the decrease in latent heat was only 1.8 % after 100 cycles, demonstrating excellent thermal cycle stability. The morphology and elemental distribution of the modified phase change materials and coatings were studied. In addition, laboratory insulation simulation tests were conducted, and the coated composite phase change material panels showed a significant delay in temperature reduction, while the insulation box showed longer lasting thermal performance. The excellent properties of the material find their application in radiant floor heating systems and play a key role in the expansion of coated phase change materials.

Microencapsulated phase change material with chitin nanocrystals stabilized Pickering emulsion for thermal energy storage

The leakage during the phase change process and low thermal conductivity of PCMs limit their application area. In this study, Pickering emulsion stabilized with chitin nanocrystals (ChNCs) was used to prepare paraffin wax (PW) microcapsules by forming a dense melamine-formaldehyde resin shell on the surface of droplets. The PW microcapsules were then loaded into the metal foam to endow high thermal conductivity to the composite. The PW emulsions could be formed at low concentrations of ChNCs (0.3 wt%), and the PW microcapsules exhibits a favorable thermal cycling stability and a satisfactory latent heat-storage capacity over 170 J/g. Most importantly, the encapsulation of the polymer shell not only endows the microcapsules with high encapsulation efficiency of 98.8 %, non-leakage properties under prolonged high temperature conditions, but also with high flame retardancy. In addition, the composite of PW microcapsules/copper foam shows satisfactory performance in terms of thermal conductivity, thermal storage capacity and thermal reliability, which can be used for effective temperature regulation of heat generating materials. This study provides new design strategy of natural and sustainable nanomaterials stabilized PCMs, which shows promising application in the field of energy management and thermal equipment temperature regulation.

Hierarchical lath colonies induced by dislocation rearrangement improve thermal cyclic stability of NiTi shape memory alloy

High thermal cyclic stability is achieved in Ti-50.8at.%Ni alloy by fabricating hierarchical lath colonies along {112}B2 planes using isothermal compression and aging. Transformation temperature shift between the 1st and 20th thermal cycle is 0.03∼0.27°C, which results from boundary strengthening of hierarchical lath colonies. Hierarchical lath colonies are controlled by dislocations. Compression induces b=12[1¯11] screw dislocations on [1¯11](121¯) slip system with anti-phase boundaries (APBs) located on (121¯)B2 plane, while aging promotes dislocation motion and rearrangement, and adjustment of atomic site occupation in local structure near APBs. When distance of APBs is large, one-direction lath-colony boundaries and one-direction lath colony form. When distance of APBs reduces, clover-shaped lath-colony boundaries form, and hierarchical lath colonies are recognized. If area of APB reduces, lath-colony boundaries and lath colony vanish. These findings show the potential for improving properties of NiTi alloy by dislocation engineering.

Enhanced solar/electric-to-thermal energy conversion capability of double skeleton based shape-stabilized phase change materials

In this work, we developed a type of shape-stabilized phase change materials (SSPCMs) based on carbonized melamine foam/graphene aerogel (CMGA) as a supporting material and polyethylene glycol (PEG) as a phase change material. [email protected] SSPCMs were prepared by fabricating a series of CMGA double skeleton with different carbonization temperatures using freeze-drying and high-temperature carbonization, followed by vacuum impregnation of PEG into the CMGA double skeleton. The morphological structure, thermal storage property, shape stability, thermal conductivity, and solar/electric conversion behavior of the fabricated SSPCMs are investigated. The results showed that [email protected] SSPCMs exhibited excellent shape stability, high latent thermal storage capacity of 181.2 J/g, thermal cycling stability, enhanced thermal conductivity with 387% higher than that of pure PEG, solar-to-thermal energy conversion capability with high efficiency of 91.7% and electric-to-thermal energy conversion capability with high efficiency of 87.3%. The results of this work provide a strategy for the design and development of high performance, multiple energy conversion forms of SSPCMs for promising applications in solar energy utilization, energy-efficient buildings, and heat preservation.

The effect of Fe2O3 sintering aid on Gd0.1Ce0.9O1.95 diffusion barrier layer and solid oxide fuel cell performance

Solid oxide fuel cells (SOFCs) with the Gd0.1Ce0.9O1.95 (GDC) diffusion barrier layer require the densification of GDC to improve the performance of the cells. In this work, the addition of 0.5 mol% Fe2O3 in GDC diffusion barrier layer as sintering aid is studied. The symmetrical cell and the fuel cell are fabricated by hot-pressing, co-sintering and screen-printing technologies. It is found that the addition of Fe2O3 can make GDC barrier layer denser at a reduced sintering temperature of 1250 °C and prevent diffusion of Sr to form ionic insulating interface between YSZ (Y2O3 stabilized ZrO2) and La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF). The fuel cell based on the GDC-Fe2O3 barrier layer achieves better maximum power density of 0.89 W cm−2 at 800 °C than that of 0.68 W cm−2 without Fe2O3 addition. No obvious degradation was observed on fuel cell based on the GDC-Fe2O3 diffusion barrier layer after a stability test at 750 °C for 100 h under 0.75 V and the thermal cycling between 750 and 400 °C. The results indicate that the addition of Fe2O3 sintering aid in GDC diffusion barrier layer can promote the densification of GDC and exhibit good long-term stability and thermal cycle stability.

High internal phase-phase change composites for customized thermal management and anti-counterfeiting

Organic phase change composites (PCCs) research focuses on the trade-off between loading capacity and leakage-proof ability/flexibility. However, practical applications require high energy storage density, thermal cycling stability, and mechanical durability at the same time. Herein, we report the development of an innovative high internal phase PCCs (HIP-PCCs), which is based on the integration of deformable and polydisperse phase change materials (PCMs) capsules densely embedded within a chitin nanofibril matrix that is healable and reconfigurable. The form-stable HIP-PCCs not only possess unexpectedly high PCMs loading capacity of over 95 vol% and phase change enthalpy up to 209 J/g, but also show satisfied thermal cycling stability with negligible leakage (<5%) after 200 phase change cycles. Moreover, HIP-PCCs possess exceptional mechanical robustness (tensile strength of 9.3 MPa), flexibility, and self-adhesive properties. These attributes allow HIP-PCCs to be processed into customized shapes, so they can be tightly integrated with targets to achieve their full potential. Combining the above advantages and newly-acquired switchable optical properties, HIP-PCCs start a new scenario of exploiting PCMs for versatile smart devices with flexibility, sustainability and recyclability, and thereby extent their applications in more broad fields, such as cold-chain transportation, data security protection and temporary information recording.

Preparation of phase change microcapsules with high thermal storage and temperature sensitive for thermal management

Preparing microcapsules with core-shell structure by encapsulating phase change materials (PCM) in the shell is considered as an effective method to solve the leakage problem of PCM during use. Herein, a phase change microcapsule (MPCM) based on n-eicosane core and polyurea shell was prepared. This MPCM was prepared by interfacial polymerization of isophorone diisocyanate (IPDI) and ethylenediamine (EDA) using Pickering emulsion as a template and sulfonated lignin (SL) derived from industrial by-products as an emulsifier. The morphology, chemical structure and optimal preparation conditions of the MPCM were investigated by polarized light microscopy, fourier infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results showed that the SL emulsified n-eicosane oil-in-water emulsion particles had good dispersion and homogeneous particle size. MPCM-2 with combined optimal conditions in MPCM exhibited regular spherical shape, high enthalpy of phase change (209.8 J/g), high encapsulation ratio (82.9 %), good thermal cycling stability, and negligible leakage rate. When PDMS and MPCM-2 were compounded and applied to thermal management, the MPCM-2/PDMS composite exhibited a much slower temperature rise and fall. Moreover, a plateau period appears at the crystallization and melting temperatures. Moreover, the phase change energy storage of MPCM/PDMS could be easily observed by the change of color after the introduction of temperature-sensitive particles. In summary, the present MPCM has good thermal storage and thermal management capabilities and provides a good application prospect for thermal energy storage systems.

The influence of Ce doping on catalytic oxidation of toluene over Co3O4/iron mesh monolithic catalyst

In this paper, CeCoOx/iron mesh monolithic catalyst (CeCoOx/IM) was successfully prepared by hydrothermal method. The preparation conditions such as Ce/Co ratio, hydrothermal temperature as well as nitrate/urea ratio of the catalysts were optimized systematically. The catalytic performance results showed that when the Ce/Co ratio was 0.4, hydrothermal temperature was 160 °C and nitrate/urea ration was 1:8, the obtained catalyst possessed the best toluene oxidation activity, and the temperature at 50% and 90% toluene conversion (T50% and T90%) was 248 °C and 256 °C, respectively, which was lower than that of Co3O4/IM (260 °C and 267 °C, respectively). In addition, the active component is closely combined with the iron substrate with an exfoliation rate of 0.07%. H2-TPR results showed that the existence of rich Co3+ species and the strong interaction between Co and Ce was one of the reasons for this improvement performance. The introduction of Ce can also improve the thermal stability, water resistance and cycling stability of the catalyst. The reaction kinetics analysis showed that the Ea value was significantly reduced by Ce doping, which reached to 71.3 kJ·mol−1 for the best performance catalyst. We hope this study can provide a theoretical support for the practical application of catalyst.

Improvement of thermal cycle stability of paraffin/expanded graphite composite phase change materials and its application in thermal management

Paraffin/expanded graphite (PA/EG) composite phase change materials (PCMs) were prepared by melt blending. The effects of EG particle size and pressing direction on heat transfer performance and thermal cycle deformation were studied. The results show that by reducing the particle size of EG, the thermal conductivity is enhanced and the deformation degree of PA/EG during the thermal cycle is alleviated. When the non-pressurized surface is used as the heating surface, PA/EG thermal conductivity is enhanced and the effect of deformation is avoidable. After that, the thermal management performance of PA/EG before and after packaging was experimentally studied. The results show that the reduction of EG particle size is beneficial to thermal management, and the average temperature of the hot surface of PA/EG100(a) is 46.1 °C, which is 1.1 °C lower than that of PA/EG50(a). PA/EG100(b) with the non-pressurized surface as heating surface has better thermal cycle stability, and the change of ambient temperature and heat flux will not affect heat transfer performance. Even for the packaged PA/EG samples, PA/EG100(b) still exhibits better thermal management performance due to the little deformation on heating surface. The present work proves that the non-pressurized surface of PA/EG as heating surface is a better choice for practical applications.

The role of H-phase in thermal hysteresis and shape memory properties in Ni50Ti30Hf20alloy

Ni50Ti30Hf20 high temperature shape memory alloy was aged at 550 °C for 10 h and 450 °C for 50 h which corresponds to the peak hardening state with equal gain in strength caused by different size/volume fraction ratio of nano-precipitation of H-phase. In order to determine the effect of such structures on the martensitic transformation, thermal cycling and shape-memory properties were measured. It is shown that finer precipitates with higher volume fraction provide superior dimensional stability, good thermal cycling stability and small transformation hysteresis.

Macro-encapsulation of metal balls prepared by waste aluminum cans in ceramic capsules with reserved space

Phase change materials (PCMs) form the core of thermal energy storage (TES) for enhancing solar and industrial waste heat recovery. Metals have attracted growing attention due to their unique advantages, including high latent heat storage and high thermal conductivity. The application of metallic PCMs in TES is limited by the absence of appropriate packaging technology. Volume expansion during the solid-liquid phase can cause breakage of the protective coatings. This study proposes a “double-layer coating, recycling inner layer” method for the encapsulation of metallic PCMs. Waste aluminum cans (WACs) were selected as the PCM for cost reasons. The alloy balls prepared using the WACs were sequentially coated with an alkane mixture and ceramic slurry. The alkane mixture melts and discharges during the baking process, leaving a void for the phase-change volume expansion. The shell was gradually densified, and the metallic PCM was completely encapsulated after the heat treatment. The prepared MAEPCMs heat-treated at 1200 °C showed excellent mechanical properties, high heat storage capacity, and thermal cycle stability. The force required for compressive failure was approximately 2623 N. In addition, the total heat storage capacity reached approximately 198.6 kJ/kg at the temperature range of 600–700 °C, of which the latent heat accounted for more than 98.5%. There was no erosion between the alloy and the shell material, and the cumulative mass change was less than 8 wt. % after 600 thermal cycles. This study provides a structurally stable and low-cost technique for the preparation of durable macro-encapsulated PCMs with a high heat storage capacity and high thermal conductivity.

Multifunctional BiOI/SiO2/Fe3O4@n-Docosane Phase-Change Microcapsules for Waste Heat Recovery and Wastewater Treatment

Waste heat and organic contaminants are significant issues in water pollution, which has caused ecological problems and threatened human health. To provide an effective solution for wastewater recovery, we designed a novel type of multifunctional phase-change microcapsule. This type of microcapsule was synthesized using n-docosane as a core and a SiO2/Fe3O4 composite as a base shell through in situ interfacial polycondensation with the assistance of a Fe3O4 nanoparticle as a Pickering emulsion stabilizer, followed by the deposition of BiOI nanosheets on the surface of the SiO2/Fe3O4 composite shell. Benefiting from the n-docosane core, the resultant microcapsules obtained phase-change enthalpies of 46.8-115.7 J/g for absorbing waste heat from wastewater. The deposited BiOI nanosheets promoted photocatalysis for the microcapsules to degrade organic contaminants in wastewater. Owing to the magnetic response of the Fe3O4 nanoparticles, the separability and recyclability of the microcapsules were improved significantly by magnetic separation. Moreover, the microcapsules demonstrate outstanding phase-change reversibility, thermal cycling stability, and shape stability due to the tight SiO2/Fe3O4 composite shell. This study provides a promising approach for designing and developing multifunctional phase-change microcapsules for waste heat recovery and wastewater treatment.

Reversible Thermochromic Nanofiber Membrane for Energy Storage and Thermoregulation

In this research, a series of reversible thermochromic nanofibrous membrane-containing phase change materials (RT-NFMPCMs) are fabricated successfully. The microstructure of RT-NFMPCMs with outstanding latent heat storage–release properties is modified and characterized systematically. The cores of RT-NFMPCMs comprise green dye GN-2 as a thermal colorant, bisphenol AF as a color developer, and n-butyl stearate as a cosolvent. The factors influencing the encapsulation process, for instance, shell solution concentration, core solution flow rate, and thermal cyclic stability, are characterized to clarify the effects of various experimental conditions. The surface morphology, core thickness, and core–sheath structure of RT-NFMPCMs are characterized by transmission electron microscopy (TEM) and thermal field emission scanning electronic microscopy (TFE-SEM). The fusion crystallization temperatures and enthalpies of RT-NFMPCMs are determined by differential scanning calorimetry (DSC) under different conditions. The thermal stability of RT-NFMPCMs is well illustrated by the properties of thermogravimetric (TG) measurements. In addition, the absorbance obtained using a spectrophotometer certainly allows visualization of the color change characteristics of RT-NFMPCMs as well. The experimental results demonstrate that a nanofiber membrane with a smooth surface and apparent core–shell structure is prepared successfully. With the increase of the core rate of RT-NFMPCMs, the enthalpy also increases accordingly within a certain range. Moreover, the encapsulation effect of the nanofibrous membrane is obvious, and the energy storage efficiency is 73.8%. The color change phenomenon of the prepared RT-NFMPCMs could be observed when the encapsulated n-butyl stearate undergoes a melting or crystallizing process, indicating that the fabricated RT-NFMPCMs present perfect thermochromic performance. Furthermore, the RT-NFMPCMs exhibit excellent stability because the latent heat is almost unchanged even after 100 heating–cooling cycles. Therefore, the RT-NFMPCMs developed in this study have a certain guiding significance for intelligent thermoregulatory textiles and other thermal regulation fields.

Exploration of steel slag for thermal energy storage and enhancement by Na2CO3 modification

Development of thermal storage material from recycled solid waste resources can further enhance the economic and environmental benefits of thermal energy storage system. Thermal properties of steel slag as sensible heat storage material are examined and further enhanced by Na2CO3 activation. The steel slag remains stable until 1200 °C in TG-DSC test, and the morphology kept unchanged after 200 thermal cycles (400–900 °C), indicating good thermal cyclic stability. The thermal energy storage density of steel slag is 797.9 kJ·kg−1 (400–900 °C), the thermal conductivity was measured as 0.505, 0.532 and 0.670 W·(m·K)−1 at 25, 250 and 500 °C, respectively. When the steel slag is further modified by Na2CO3, the morphology and phase of the material remained stable, and the DSC curve trend unchanged after thermal cycle. The thermal energy storage density reaches 997.0 kJ·kg−1 (400–900 °C), which is 25.3% higher than original steel slag. Even more, the thermal conductivity is 1.331, 1.323, 0.889 W·(m·K)−1 at 25, 250, and 500 °C, respectively, which is 32.7% higher than that of steel slag. Hence, the thermal properties of steel slag have been significantly improved by the developed Na2CO3 activation process.