Dongnan Zhao

In this paper, steel slag powder was used to replace part of the cement in road concrete, and group tests were carried out on coarse aggregates with different water–cement (W/C) ratios, different steel slag parameters, and different particle sizes. A sample of 100 mm × 100 mm × 100 mm was prepared and cured for 3 days, 7 days, and 28 days. In addition, the fluidity and compressive properties of the samples were also tested. The outcomes of this study revealed that, at a constant W/C ratio, increasing the proportion of steel slag improved the concrete’s fluidity but reduced its compressive strength; the 3-day (3 d) compressive strength of 40% steel slag was lower because the early activity of steel slag was lower than that of cement; steel slag also decreased the early-hydration rate of concrete. Comparisons across different W/C ratios demonstrated that steel slag made a more significant contribution to lower W/C ratios than higher ones. The water requirement for steel slag was relatively moderate, and the compressive strength of steel slag concrete with a high W/C ratio notably improved in the later stages. Based on the experimental conditions, the optimal content of steel slag was found to be 35%. Reusing steel slag as a replacement for sand in coarse aggregate can effectively lower costs and offer an innovative approach to steel slag treatment.

To realize the energy recovery of wheat straw, the pyrolysis behavior of wheat straw was studied at three heating rates (10, 20, and 30 K/min) based on thermogravimetric analysis (TG–DTG). Kinetics and thermodynamics were analyzed using Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) model-free methods, and the reaction mechanism was determined using the Coats–Redfern (CR) model-fitting method. The results show that there are three weightlessness stages in the pyrolysis process, of which the second stage was the main weightlessness stage and two distinct peaks of weightlessness were observed in this stage. With increasing heating rate, the main pyrolytic weightlessness peaks of the DTG curve shift to the high-temperature side. The pyrolysis activation energies calculated by the FWO and KAS methods are 165.17–440.02 kJ/mol and 163.72–452.07 kJ/mol, and the pre-exponential factors vary in the range of 2.58 × 10¹²–7.45 × 10³⁶ s⁻¹ and 1.91 × 10¹²–8.66 × 10³⁷ s⁻¹, respectively. The thermodynamic parameters indicate that wheat straw has favorable conditions for product formation and it is a promising feedstock. Its pyrolysis reaction was nonspontaneous and the energy output is stable. CR method analysis shows that the A_1/3 random nucleation model is the most suitable mechanism to characterize the pyrolysis process and random nucleation may be in charge of the main pyrolysis stage. This study can provide a theoretical basis for the thermochemical conversion and utilization of wheat straw.

To realize the energy recovery of wheat straw, the pyrolysis behavior of wheat straw was studied at three heating rates (10, 20, and 30 K/min) based on thermogravimetric analysis (TG–DTG). Kinetics and thermodynamics were analyzed using Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) model-free methods, and reaction mechanism was determined using Coats–Redfern (CR) model-fitting method. The results show that there are three weightlessness stages in the pyrolysis process, of which the second stage was the main weightlessness stage and two distinct peaks of weightlessness were observed in this stage. With increasing heating rate, the main pyrolytic weightlessness peaks of DTG curve shifts to higher temperature. The pyrolysis activation energy calculated by FWO and KAS methods are 165.17–440.02 kJ/mol and 163.72–452.07 kJ/mol, and the pre-exponential factor vary in the range of 2.58×1012–7.45×1036 s-1 and 1.91×1012–8.66×1037 s-1, respectively. The thermodynamic parameters indicates that wheat straw has the favorable conditions for product formation and containes potential energy to be utilized for bioenergy production, its pyrolysis reaction was non-spontaneous and the energy output is stable. CR method analysis shows that the A1/3 random nucleation model is the most suitable mechanism to characterize the pyrolysis process, and random nucleation may be in charge of the main pyrolysis stage. This study can provide a theoretical basis for the thermochemical conversion and utilization of wheat straw.

High-strength tire cord steel is mainly used in radial ply tires, but the presence of brittle Ti inclusions can cause failure of the wires and jeopardize their performance in production. In order to control the titanium content during steel production, a thermodynamic model for predicting the titanium distribution ratio between CaO–SiO₂–Al₂O₃–MgO–FeO–MnO–TiO₂ slags during the ladle furnace (LF) refining process at 1853 K has been established based on the ion–molecule coexistence theory (IMCT), combined with industrial measurements, and the effect of basicity on the titanium distribution ratio was discussed. The results showed that the titanium distribution ratio predicted by the developed IMCT exhibited a dependable agreement with the measurements, and the optical basicity is suggested to reflect the correlation between basicity and the titanium distribution ratio. Furthermore, quantitative titanium distribution ratios of TiO₂, CaO·TiO₂, MgO·TiO₂, FeO·TiO₂, and MnO·TiO₂ were acquired by the IMCT model, respectively. Calculation results revealed that the structural unit CaO plays a pivotal role in the slags in the de-titanium process.

The presence of MgO·Al₂O₃ inclusions in 51CrV4 spring steel is detrimental to the alloy’s castability and fatigue properties. To effectively suppress these inclusions during production, accretions were collected from the immersion nozzle, and the MgO·Al₂O₃ inclusions in the steel billet were investigated. The generation mechanism of the inclusions was evaluated based on the ion–molecule coexistence theory, and the mass action–concentration model of CaO–SiO₂–Al₂O₃–MgO–FeO–MnO slag was developed. Industrial experiments showed that nozzle clogging was primarily caused by MgAl₂O₄ spinel inclusions, and the MgO·Al₂O₃ spinel inclusions in the steel billet were investigated by non-aqueous electrolysis. The model calculation results indicate that the Mg content increased with an increasing basicity, CaO/Al₂O₃ ratio, and Al content during the ladle furnace (LF) process. In contrast, the Mg content decreased with increasing CO pressure under Ruhstahl-Hausen vacuum degassing process (RH) conditions.