Thermochemical Treatment Process Research Articles

Abrasive Wear Resistance of Nodular Cast Iron After Selected Surface Heat and Thermochemical Treatment Processes

Abrasive Wear Resistance of Nodular Cast Iron After Selected Surface Heat and Thermochemical Treatment Processes

Micro- and Macroscopic Analysis of Fatigue Wear of Gear Wheel Top Layer-An Impact Analysis of Thermochemical Treatment.

Today, there are many diagnostic methods and advanced measurement techniques enabling the correct diagnosis and assessment of the type and degree of wear of cogwheels (gears, pumps, etc.). The present study presents an analysis of the surface defects of a cogwheel of an oil pump prototype (3PW-BPF-24). The test object operated for a certain number of hours under controlled operating and environmental parameters. The damage to the surface layer was caused by fatigue phenomena and previous thermo-chemical treatment. On the basis of the significant percentage share (~30%) of residual austenite in the volume of the diffusion layer, a hypothetical conclusion was drawn about the suboptimal parameters of the thermo-chemical treatment process (in relation to the chemical composition of the analyzed pinion). A large number of research studies indicate that the significant presence of residual austenite causes a decrease in tooth surface hardness, the initiation of brittle cracks, a sharp decrease in fatigue strength, an increase in brittleness and a tendency to develop surface layer cracks during operation. High-resolution 3D scans of randomly selected pitting defects were used in the detailed study of the present work. It was indicated that the analysis of the morphology of surface defects allowed some degree of verification of the quality of the heat/chemical treatment. The martensitic transformation of residual austenite under controlled (optimum) repeated heat treatment conditions could significantly improve the durability of the pinion (cogwheel). In the case analyzed, the preferred treatment was the low-temperature treatment. The paper concludes with detailed conclusions based on the microscopic and macroscopic investigations carried out.

An efficient approach to manufacturing carbon nanosheets from lignite and their impact on the mechanical performance of semi-crystalline thermoplastic composites with comprehensive benchmarking

Lignite-derived carbon nanosheets (CNS) offer a novel approach to producing carbon-based nanomaterials with unique advantages over other precursors. The primary mechanism successfully demonstrated the transformation of lignite into CNS by thermo-chemical treatment process through acid treatment (HNO3), catalyst impregnation (FeCl3), and carbonization (1000 °C, 5 min) steps resulting in the enrichment in the carbon content by maintaining the desired efficiency to be used as a filler in compounding process. Moreover, the produced CNS had superior characteristics in terms of carbon content reached 70 % and thermal stability even at 1000 °C compared to lignite. Subsequently, a comprehensive benchmarking study was conducted to achieve high compatibility and uniform dispersion between semi-crystalline thermoplastics such as HomoPP, CopoPP, PA6 and PA6,6 with CNS using a high-speed thermokinetic shear mixer. CNS exhibited enhanced compatibility with thermoplastics, leading to improved mechanical properties such as tensile and flexural modulus inpolymer composites. The benchmark studies revealed that a loading ratio of 0.5 wt% of CNS exhibited optimal reinforcement efficiency. Notably, PA6 matrix demonstrated the most significant improvement in yield strength, increasing by 12 %, while PA6,6 showed the highest increase in tensile modulus at 25 %. Similarly, PA6,6 exhibited the most notable improvement in flexural modulus with a substantial increase of 17 %. Conversely, HomoPP matrix displayed the highest improvement in flexural strength, increasing by 13 %. Furthermore, the incorporation of CNS into the polymer leads to an increase in the crystallization temperature from 182 °C to 194 °C for PA6-0.5 % CNS. These findings highlight the potential of CNS as versatile materials with promising polymer applications such as automotive and aviation.

Application of principal component analysis (PCA) to the study of the influence of the thermochemical treatment process of tropical wood sawdust on the calorific, mechanical, physicochemical and combustion properties of the resulting fuel briquettes

Despite its potential for environmentally friendly energy production, lignocellulosic biomass has less advantageous physicochemical properties that limit its optimal industrial use. This study used principal component analysis (PCA) to evaluate the effects of two thermochemical processing methods (torrefaction and carbonization) on the calorific, physicochemical, mechanical and combustion properties of the resulting biofuels. Various types of tropical sawdust (Dabema, Dibetou, Fraké, Samba and Iroko) are subjected to these treatments, then densified and characterized for energy applications. Specific fuel consumption varies from Samba torrefied (Sam t: 0.69 kg/L) to Samba carbonized (Sam c: 1.48 kg/L). Higher heating values range from Samba torrefied (Sam t: 23983 kJ/kg) to Iroko torrefied (Iro t: 27,442 kJ/kg). Burning speed varies from Samba carbonized (Sam c: 3.07 g/min) to Iroko torrefied (Iro t: 4 g/min). The impact resistance index ranges from 187.5 to 500% for Dibetou torrefied (Dib t) and Samba carbonized (Sam c), respectively. Densities are between Samba carbonized (Sam c: 297.83 kg/m3) and Dibetou carbonized (Dib c: 393.69 kg/m3). The results indicate that these techniques are promising approaches for improving biomass properties. In sum, the PCA reveals that the effect of treatment type on fuel characteristics also depends on the properties of the initial biomass.

Investigation and characterization of changes in potato peels by thermochemical acidic pre-treatment for extraction of various compounds

Potato peel waste (PPW) is an underutilized substrate which is produced in huge amounts by food processing industries. Using PPW a feedstock for production of useful compounds can overcome the problem of waste management as well as cost-effective. In present study, potential of PPW was investigated using chemical and thermochemical treatment processes. Three independent variables i.e., PPW concentration, dilute sulphuric acid concentration and liberation time were selected to optimize the production of fermentable sugars (TS and RS) and phenolic compounds (TP). These three process variables were selected in the range of 5–15 g w/v substrate, 0.8–1.2 v/v acid conc. and 4–6 h. Whole treatment process was optimized by using box-behnken design (BBD) of response surface methodology (RSM). Highest yield of total and reducing sugars and total phenolic compounds obtained after chemical treatment was 188.00, 144.42 and 43.68 mg/gds, respectively. The maximum yield of fermentable sugars attained by acid plus steam treatment were 720.00 and 660.62 mg/gds of TS and RS, respectively w.r.t 5% substrate conc. in 0.8% acid with residence time of 6 h. Results recorded that acid assisted autoclaved treatment could be an effective process for PPW deconstruction. Characterization of substrate before and after treatment was checked by SEM and FTIR. Spectras and micrographs confirmed the topographical variations in treated substrate. The present study was aimed to utilize biowaste and to determine cost-effective conditions for degradation of PWW into value added compounds.

Energy Recovery from Residual Municipal Solid Waste: State of the Art and Perspectives within the Challenge to Climate Change

Among the technologies for the recovery of energy from waste, in particular residual municipal solid waste (rMSW), combustion is the most widely used thermo-chemical treatment process associated with thermal and electric power production by a steam cycle, named, shortly, Waste to Energy (WtE). Today, more than 500 WtE plants in the EU, about 400 in China and 76 in the USA are in operation, based on efficient technologies and advanced air pollution control systems. Energy recovery can be accomplished also by means of gasification; however, the presence of impurities together with the atmospheric pressure, at which syngas is normally produced, impose the feeding of syngas to a conventional steam cycle, leading to generally lower performances than WtE. The energy recovered by WtE offsets traditional energy sources such as fossil fuels and related emissions, providing savings in term of climate change. However, the savings obtainable by replacing electricity and/or heat will diminish as the energy systems will hopefully become increasingly renewable. Over this medium–long-term horizon, one possibility is to capture the CO2 from WtE flue gases and to store/use it. From the life cycle assessment perspective, it has been calculated that the introduction of CO2 capture and storage in WtE, despite energy penalties, is able to reduce the impact on climate change. The alternative approach, proposed to contain the emissions of greenhouse gases in the thermal treatment of waste, is using the carbon contained in it to produce commonly used chemical compounds (waste to chemicals). The benefits, in terms of reductions of greenhouse gases, are expected from the possibility of obtaining chemicals that can replace their analogue normally produced from fossil sources. To date, only one WtC demonstration plant is operating by being fed by rMSW-derived waste, and some similar initiatives are planned, but still adequate assurances in terms of robust knowledge of the involved complex processes, above all, if applied to highly inhomogeneous feed streams such as those obtained from rMSW, are not available. Once the several initiatives come to completion, it will enable waste management professionals to assess performance and to begin to consider such a facility in their planning.

The Effect of Superplasticizers on Eco-friendly Low-Energy One-Part Alkali-Activated Slag

One-part alkali-activated materials (OP-AAM) have become a promising binder with low carbon and energy requirements associated with superior mechanical and durability characteristics. This study aims to employ commercial superplasticizers (naphthalene-based “Nb-SP” and polycarboxylate-based “PCb-SP”), as well as laboratory-prepared one (phenol–formaldehyde sulfanilate “PFS-SP”) in enhancing the properties of OP-AAM. The main problem of superplasticizers (SPs) in the AAM is their hydrolysis in the alkaline activator (NaOH) used in the activation reactions. Therefore, the thermo-chemical treatment process was utilized to mitigate the high activator alkalinity by impeding the NaOH in the aluminosilicate precursor matrix. The OP-AAM was fabricated from thermo-chemical treatment powder (TCT-P) resulting from sintering blast furnace slag (GGBFS) with 10 wt% NaOH at 300 and 500 °C. The XRD-pattern showed that NaOH was impeded in the GGBFS via sodium aluminum silicate phase formation after sintering at 500 °C. The results showed that the admixed OP-AAM prepared from TCT-P at 500 °C greatly enhanced the workability and mechanical properties. The PFS-SP proved its efficiency in improving the properties of OP-AAM prepared TCT-P at 300 and 500 °C, referring to its high stability in an alkaline medium. While PCb-SP reinforced the properties of OP-AAM prepared from TCT-P at 500 °C only, proving that PCb-SP promotes high capability in TCT-P-500 as well as in Portland cement.

Effects of thermo-chemical treatment and grinding process of external cylindrical surfaces on residual stresses in 13CrMo4-5 steel

This paper presents a study aimed at determining the effect of the carburizing treatment process and the subsequent grinding process on the residual stresses occurring in ring-shaped specimens made of 13CrMo4-5 steel.During the tests, vacuum carburizing was used, achieving an effective case depth ECD = 0.5 mm. Subsequently, the cylindrical outer surfaces of the samples were ground by conventional plunge grinding and with innovative kinematics using a test stand based on a conventional flat-surface grinding machine. As part of the study, microhardness and residual stresses were measured before and after grinding. Measurements were carried out to a depth of 1 mm. The main component of the stand is an original special device that allows the cylindrical specimen to be clamped. Then the angle between its axis of rotation and the axis of rotation of the grinding wheel is set with respect to the plane of the grinding machine’s magnetic table. In the described tests, the axis of rotation of the cylindrical specimen was deviated from its original position by 15 and set at an angle of 75 to the axis of rotation of the grinding wheel. The specimens were ground with a grinding wheel of noble electro-corundum marked 38A60K8V. In both kinematic cases of the grinding process, a machining allowance of 0.01 mm was removed.Grinding using innovative kinematics did not cause any significant changes in the microhardness distribution, either for vacuum or conventional carburizing. In addition, residual stress measurements using the Dawidenkov-Sachs method showed that innovative grinding enables a more favourable distribution than those obtained after conventional plunge grinding.Further research will focus on, among others, selecting the angular settings of the workpiece axes relative to the grinding wheel axes depending on their dimensions. Grinding guidelines should include coverage ratio, infeed value, grinding time, and peripheral speeds. In addition, the plan for future research includes measuring the components of the grinding force and the geometric structure of the surface.Grinding process is a crucial stage of steel treatment in almost every industrial branch. In sustainable manufacturing, it is extremely important to produce high-quality items while reducing the cost of manufacturing and taking care of the environment and workers’ health.The proposed test stand, together with the authors’ device, makes it possible to conduct machining of the external surfaces of cylindrical workpieces on a flat surface grinder. In this case, the innovation of the grinding process consists of the non-parallel alignment of the cylindrical rotational axis of the specimen and the rotational axis of the grinding wheel with respect to the plane of the magnetic grinding table.

Модифицирование поверхности быстрорежущего инструмента совместным насыщением вольфрамом и азотом

Research significance is contingent on the requirement strengthening for high-speed cutting tools performance and wide-spread introduction of automatic lines and NC-machines. An increase of the tool service life is also necessary for the reduc-tion of putting expensive alloying elements to use, primarily, tungsten. The solution of these problems requires the use of technologies for hardening cutting surfaces. Combined processes of thermochemical treatment processes, uniting diffusive surface alloying with nitrogen saturation have shown their effectiveness in the surface hardening of various steels. Now the aim is to study the process of combined surface tungsten and nitrogen saturation of high-speed steel for increasing small-sized tool durability. Experimental studies were carried out on samples and small-diameter drills made of P6M5 steel. For laboratory experiments connected with combined process of thermochemical treatment an installation for nitriding in multi-component media was used. Metallization with tungsten was carried out by the slip method with parallel nitriding of the tool in a glow discharge. To determine the regime that provides the necessary temperatures for oxygen and nitrogen saturation, the temperatures of the control steel samples were measured on the surface and in the core at different durations of the cur-rent pulse in the heating phase. Metallographic analysis proved that thermochemical treatment resulted in a modified sur-face layer with a thickness of 10…15 microns, formed in P6M5 steel. The structure of the layer is an internal nitriding zone, which consists of a solid tungsten and nitrogen solution in iron and dispersed inclusions of tungsten nitrides. Dispersion and solid solution hardening provide a two-fold increase in the microhardness of the modified W-N layer compared to the alloy base. A transitional diffusion zone of nitrogenous martensite has been revealed under the hardened layer, creating a smooth microhardness gradient from the layer to the core, protecting it from embrittlement, peeling and staining. Using a metallophysical simulated test in predeveloped methodology, the calculation of the hardening index of the modified layer (yield point increase) was made. It showed that with increase in the concentration of tungsten in the layer, the proportion of the component of the dispersion hardening by W2N particles also increases. Full-scale tests in production conditions showed that the tool with a hardened layer had increased resistance. The durability of drills, determined by the number of drilled holes made before its dropping-out, increases by 2,2 times when drilling on 30XGSA steel and by more than 7,0 times when drilling a titanium alloy VT-23.

Impact of single-piece flow thermo-chemical treatment process conditions on hole quenching deformation

Pulsed low-pressure carburizing (LPC) and omnidirectional high-pressure gas quenching (HPGQ) are innovative methods for quenching the surface layer. The thermo-chemical treatment carried out by this method reduces quenching geometric deformations, with detailed numerical values not available in the literature due to the short existence of this method.Sixteen toothed elements of EN 20MnCr5 steel were subjected to pulsed low-pressure carburising with omnidirectional jet quenching in 4 groups, varying the process temperature (920C, 960C) and in two groups performing a tempering treatment. The elements were tested before machining by measuring their internal hole diameters, radial runout, roundness and cylindricity. These values were tested again after treatment. The direction of change and the statistical significance of the effect of treatment and its parameters, temperature and tempering were analysed.Thermo-chemical treatment significantly affects geometric changes in diameters, roundness, cylindricity and radial runout compared to elements without heat treatment due to physical transformations occurring during this treatment (p<0.05). Changing the process temperature in the value range of 920C-960C affects the hole diameter (makes it smaller) (p<0.05), but does not affect radial runout, cylindricity and roundness. The observed dimensional changes in diameters have numerically small values (<0.005 mm). The tempering treatment can affect the values of average diameters. Its effect on roundness, cylindricity and radial runout was not observed.In the temperature range studied, the method of pulsed low-pressure carburising + omnidirectional high-pressure gas quenching makes it possible to raise the temperature of the process and shorten its duration without significant geometric changes in the treated elements.The method of pulsed low-pressure carburising and omnidirectional high-pressure gas quenching (HPGQ) ensures the maintenance of reproducible quenching deformations at a level significantly lower than conventional processing methods.The method of pulsed low-pressure carburising together with omnidirectional high-pressure gas quenching (HPGQ) is a method that has been used briefly in the industry, and there are few reports on it to date.

Pyrolysis in the Chemical Industry and Its Major Industrial Applications

Pyrolysis is an irreversible thermochemical treatment process of materials at elevated temperatures in an inert atmosphere. Pyrolysis is used heavily in the chemical industry to produce many forms of carbon and other chemicals from petroleum, coal, wood, oil shale, biomass or organic waste materials, and it is the basis of several methods for producing fuel from biomass. The end products of pyrolysis include solid residual coproducts and ash, noncondensable gases and condensable liquids. These products can be controlled by optimizing pyrolysis parameters such as temperature and residence time.

Machine-learning-aided thermochemical treatment of biomass: a review

Thermochemical treatment is a promising technique for biomass disposal and valorization. Recently, machine learning (ML) has been extensively used to predict yields, compositions, and properties of biochar, bio-oil, syngas, and aqueous phases produced by the thermochemical treatment of biomass. ML demonstrates great potential to aid the development of thermochemical processes. The present review aims to 1) introduce the ML schemes and strategies as well as descriptors of the input and output features in thermochemical processes; 2) summarize and compare the up-to-date research in both ML-aided wet (hydrothermal carbonization/liquefaction/gasification) and dry (torrefaction/pyrolysis/gasification) thermochemical treatment of biomass (i.e., predicting the yields, compositions, and properties of oil/char/gas/aqueous phases as well as thermal conversion behavior or kinetics); and 3) identify the gaps and provide guidance for future studies concerning how to improve predictive performance, increase generalizability, aid mechanistic and application studies, and effectively share data and models in the community. The development of biomass thermochemical treatment processes is envisaged to be greatly accelerated by ML in the near future.

Study of the Influence of V, Mo and Co Additives on the Carbide Formation and Microhardness during Thermal Diffusion Chrome Planting of X35CrNi2-3 Steel

Saturation diffusion with chromium has not been adequately studied among all the surface thermochemical treatment (STCT) processes of steels. Especially, the complex saturation behavior when several elements are added directly for chemical treatment needs to be systematically studied. This work aims at determining the effect of V, Mo, and Co on the parameters of chromium thermal saturation diffusion (thickness, phase composition, microstructure, and microhardness) of the surface layer in X35CrNi2-3 steel. The process was carried out at a temperature of 1000 °C for 24 h. The results showed that complex structural chromium plating together with the addition of strong carbide-forming elements (V and Mo) has a significant effect on the phase composition of the fabricated layer, where the formation of VC and Mo2C carbides significantly increases the microhardness of the samples to 2000 HV and 2500 HV, respectively. On the other hand, the addition of Co with a less carbide-forming affinity has little effect on the phase composition of the coating, and nitride compounds predominated in the microstructure similar to the single-element chromium plating. The results indicate the possibility of improving and accelerating the traditional thermal chromium plating processes and opening up new horizons for obtaining gradient coatings with superior tribological properties.

Compressive strength and deformation behavior of the hybrid S phase layer under micro-pillar compression

Austenitic stainless steel of medical grade was subjected to low-temperature thermochemical heat treatment process which forms a distinctive layer on the surface of the material. The distinctive layer is commonly known as ‘S phase’, and resulted due to diffusion of elemental species present in the heat treatment atmosphere. A cross-sectional microstructural investigation confirms that the layer thickness increases with the increase of methane (CH4) contents in the carrier gas and the microstructure contain abundance of structural defects like slip bands, stacking faults, twins, and dislocations. Subjected to micro-pillar compression, the ultimate compressive strength of this layer was up to 190% more than that of bulk material which comes in expense of limited strain accommodation of such layer. Consequently, the critically resolved shear stress of the S phase layers were higher than that of the bulk material and microstructural defects contribute up to 83.17 MPa on that. On course of the micro-pillar compression, the S phase layers show catastrophic cleavage type brittle fracture in contract of progressive ductile fracture of the bulk material.

OPTIMASI PARAMETER KARBURISASI TEMPERATUR RENDAH PADA BAJA TAHAN KARAT AUSTENITIK MENGGUNAKAN METODE TAGUCHI

Austenitic stainless steel is a popular material for its corrosion resistant properties, however it has low hardness which limits its application. Low-temperature carburizing can be used to improve the mechanical properties of the austenitic stainless steel by producing expanded austenite layer. In order to get a high-quality layer and an efficient processing operation, the carburizing process must be optimized. In this research, a Taguchi method was utilized to investigate the effect of processing parameters related to the formation of the expanded austenite layer depth in austenitic stainless steel. Four factors were selected to be optimized namely temperature, gas flow rate, time, and gas composition with three levels each. L9(34) orthogonal array was applied with nine experimental tests to get the diffusion depth value of carbon in the expanded austenite layer. S/N ratio was used to determine the optimum factor combination with nominal-the-better quality characteristic and the most significant factor was obtained by applying the Analysis of Variance. Temperature was found to be the most significant factor with 54.91% contribution. The optimum combination was also successfully defined with temperature at 450°C (level 2), gas flow rate at 15 liter per minute (level 2), time at 12 hours (level 3), and gas composition at 15% CH4 – 5% H2 – 80% N2 (level 3). Clearly, in this study the Taguchi method was proven to be appropriately used as one of robust tools in optimizing the thermochemical treatment process parameters.

Utilization of chemically modified coal fly ash as cost-effective adsorbent for removal of hazardous organic wastes

Disposal of dyes wastewater into aquatic streams is considered as a major challenge due to its effect on water ecosystem. Direct dyes have a complex aromatic structure. Therefore, it is difficult to separate them from industrial wastewater. Conversely, fly ash is a main by-product pollutant generated from coal burning to fulfill energy requirements. In this study, thermochemical treatment process was applied to coal fly ash (CFA) in order to increase its surface area, improve its pore’s structure and enhancing its adsorption capacity for direct blue 78 dye (DB78) removal. The treated coal fly ash (TCFA) was characterized by physicochemical analyses such as XRD, XRF, TGA, SEM, FTIR, surface area (SBET) and particles size analysis. Batch experiments were conducted to analyze the adsorption behavior for TCFA and to examine the DB78 dye removal efficiency. The physicochemical analysis results indicated that a higher increase in CFA surface area from 9.6 to 60.4 m2g−1 was obtained due to the modification process. The maximum removal efficiency using TCFA was 99.7% for initial dye concentration 10 mg/L and TCFA dose 2 g/L. The adsorption isotherm was studied by Langmuir and Freundlich model using different dye concentrations. The results showed that equilibrium data followed closely Langmuir isotherm model (R2 = 0.99) indicating monolayer and homogeneous adsorption process.

Responses of hybrid S phase layer to nanoscratching

A low-temperature hybrid gas diffusion of thermochemical heat treatment process at 475 °C for 12 h was employed to treat the surface of medical grade 316LVM austenitic stainless steel that formed S phase layer. In this study, cross-sectional nanoscratch tests were performed to evaluate the response and changes in tribological characteristics of such S phase layer for load ranges of 10–50 mN. The nanoscratch of the bulk as well as S phase layer was examined using scanning electron microscopy and surface profilometer after nanoscratch tests. The experimental results demonstrated that there was no delamination across the interface for all applied normal loads. Cracks propagation was observed at the top of a scratch groove near the top surface showing the brittle fracture of the S phase layer. Plastic flow from scratching significantly improved for the heat-treated layer compared to the bulk metal. The amount of CH4 content during surface treatment also influenced the wear resistance coefficient of the S phase layer.

Investigating the Water Jet Erosion Performance of HVOF-Sprayed WC-10Co Coatings on 35CrMo Steel Utilizing Design of Experiments

To enhance the surface of a material with the desired qualities for diverse applications in service, a variety of thermal and thermo-chemical surface treatment processes are used. Due to the high-velocity impact inherent in the process, high-velocity oxy-fuel (HVOF) spray is now frequently employed in industrial applications for its ability to generate a high-quality coating with appropriate hardness and low oxide content. In this investigation, a high-velocity oxy-fuel (HVOF) thermal spraying process was utilized to coat WC-10Co powders on a 35CrMo steel substrate. A water jet erosion test was also used to examine the substrate and coated samples’ erosion behavior. The erosion rate was systematically investigated using water jet variables such as the angle of impingement, water jet velocity, standoff distance, and erodent discharge. For the development of multiple regression models, experiments were performed utilizing the central composite rotatable design and the response surface methodology. The angle of impingement had the most impact on the rate of coating erosion, leading to the water jet velocity, standoff distance, and erodent discharge.

Nanostructure and Morphology of the Surface as Well as Micromechanical and Sclerometric Properties of Al2O3 Layers Subjected to Thermo-Chemical Treatment

The article presents the effect of the thermo-chemical treatment of Al2O3 layers on their nanostructure, surface morphology, chemical composition as well as their micromechanical and sclerometric properties. Oxide layers were produced on EN AW-5251 aluminium alloy (AlMg2) by the method of direct current anodizing in a three-component electrolyte. The thermo-chemical treatment was carried out in distilled water and aqueous solutions of Na2SO4·10H2O and Na2Cr2O7·2H2O. It was shown that the thermo-chemical treatment process changes the morphology of the surface of the layers (the formation of a sub-layer from the Na2SO4·10H2O and Na2Cr2O7·2H2O solutions), which directly increases the thickness of the layers by 0.37 and 1.77 µm, respectively. The thermo-chemical treatment in water also resulted in the formation of a 0.63 µm thick sub-layer. The micromechanical tests indicated a rise in the surface microhardness of the layers in the case of their thermo-chemical treatment in water and the Na2SO4·10H2O solution and a decrease in the case of the layers modified in the Na2Cr2O7·2H2O solution. The highest microhardness (7.1 GPa) was exhibited by the layer modified in the Na2SO4·10H2O solution. Scratch tests demonstrated that the thermo-chemically treated layers had better adhesive properties than the reference layer. The best scratch resistance was exhibited by the layer after thermo-chemical treatment in the Na2SO4·10H2O solution (the highest values, practically for all the critical loads) which, together with its low roughness and high load capacity, predispose it to sliding contacts.

Minimizing energy consumption to produce safe one-part alkali-activated materials

Recently, alkali-activated binders have emerged as a promising sustainable solution in the construction industry. There is great demand to promote the development of one-part alkali-activated materials (OP-AAMs) to overcome the hazardous, irritating, and corrosive nature of alkaline activator solutions while sustaining their superior engineering properties. This study's main objective is to reduce the temperature of the thermochemical treatment process used to produce one-part alkali-activated slag (OP-AAS) by using an amorphous active aluminosilicate precursor. The effect of different treatment temperatures (1000 °C, 800 °C, 500 °C, 350 °C, and 300 °C) on the fresh and hardened properties of OP-AAS pastes was studied. The phase composition and microstructure were investigated using X-ray diffraction analysis and scanning electron microscopy equipped with energy-dispersive X-ray analysis. A viability/cytotoxicity test was performed on selected mixes to investigate the effect of the prepared OP-AAS on the human skin. It is concluded that the optimum treatment temperature to prepare OP-AAS is ranged between 300 °C and 500 °C. Therefore, with low-energy consumption, the production of OP-AAS is accessible, economical, and safe for the commercial application of alkali-activated materials in the construction industry.