Hydration Model and Evaluation of the Properties of Calcined Hwangtoh Binary Blends

Calcined hwangtoh is a pozzolanic material that is increasingly being used as a mineral admixture in the concrete industry. This study shows a hydration model for cement–hwangtoh blends and evaluates the various properties of hwangtoh-blended concrete using reaction degrees of binders. First, a kinetic reaction model is proposed for analyzing the pozzolanic reaction of hwangtoh. The reaction of hwangtoh includes three processes: the initial dormant period, boundary reaction process, and diffusion process. The mutual interactions between the binary reactions of cement and hwangtoh are thought to be in line with the items in capillary water and calcium hydroxide. Second, the reaction degrees of cement and hwangtoh are determined based on a blended hydration model. Furthermore, the chemical (chemically combined water and calcium hydroxide contents), mechanical (compressive strength), thermal (hydration heat), and durability aspects (carbonation depth) of hwangtoh-blended concrete are systematically predicted. The results show good agreement with experimental results.

Kinetic Study on Microwave Magnetizing Roast of Fe2O3 Powders

In this paper, the reaction kinetic mechanism of Fe2O3 powder containing carbon was studied by microwave magnetizing roast. Based on the temperature-rise curve and weight loss curve of Fe2O3 powder by microwave magnetizing roast, the kinetic parameters of Fe2O3 powder microwave magnetizing roast were calculated by non-isothermal methods. The controlling steps of different temperature-rising periods in microwave magnetizing roast process of Fe2O3 powder were calculated by the Achar-Brindley-Sharp-Wendworth method. The results indicated that the controlling step of microwave magnetizing roast was phase boundary reaction control of contracted cylinder in 250~450°C, and it was three-dimensional diffusion control of spherical symmetry in 450~650°C. The results showed that the starting temperature of reduction roasting of Fe2O3 powder was 250°C, which was lower than that under electrical heating, thereby, it proved in theory that microwave heating can enhance reaction rate.

Non-Isothermal Decomposition Kinetic of Polypropylene/Hydrotalcite Composite

P3O5-10 pillared Mg/Al hydrotalcite (HTs) as a functional fire-retarding filler was successfully prepared by impregnation-reconstruction, where the HTs was used to prepare polypropylene (PP) and HTs composite (PP/HTs). Thermal decomposition was crucial for correctly identifying the thermal behavior for the PP/HTs, and studied using thermogravimetry (TG) at different heating rates. Based on single TG curves and Málek method, as well as 41 mechanism functions, the thermal decompositions of the PP/HTs composite and PP in nitrogen atmosphere were studied under non-isothermal conditions. The mechanism functions of the thermal decomposition reactions for the PP/HTs composite and PP were separately “chemical reaction F3” and “phase boundary reaction R2,” which were also in good agreement with corresponding experimental data. It was found that the addition of the HTs increased the apparent activation energy Ea of the PP/HTs comparing to the PP, which improved the thermal stability of the polypropylene. A difference in the set of kinetic and thermodynamic parameters was also observed between the PP/HTs and PP, particularly with respect to lower ΔS≠ value assigned to higher thermal stability of the PP/HTs composite.

Hydration Kinetics of Composite Cementitious Materials Containing Copper Tailing Powder and Graphene Oxide

The hydration heat evolution curves of composite cementitious materials containing copper tailing powder (CT) and graphene oxide (GO) with different contents are measured and analyzed in this paper. The hydration rate and total hydration heat of the composite cementitious materials decrease with the increase of CT dosage, but improve with the increase of CT fineness and GO dosage. The hydration process of the cementitious systems undergoes three periods, namely nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D), which can be simulated well using the Krstulovic–Dabic model. The hydration rates of the three controlling processes of the composite cementitious system decrease with the increase of CT content, but improve slightly with the increase of CT fineness. GO enhances the controlling effect of the NG process of the cementitious systems with or without CT, thus promotes the early hydration as a whole.

Experimental carbothermal reduction of MgO at low pressure using concentrated solar energy

The improved solar reactor Sol@rmet allows to investigate the reduction of MgO in presence of carbon using concentrated solar energy in low vacuum conditions close to 900 Pa. The influence of the carbon type was studied and it was shown that a carbon issued from a biomass source was a great candidate. A gradual increase of the temperature during experiment allowed to obtain promising results. Powders with a high Mg content up to 97 m% and a high yield rate up to 50% were collected. Short time experiments at fixed locations under the focus of the solar concentrator were performed in order to obtain information on the kinetics of the carbothermal reduction of MgO. Notably, these experiments have underlined the temperature effect on the CO emission. 50 to 80% of the CO emission mainly occurred in 100 s after the beginning of the experiments. The phase boundary reaction between MgO and C appeared to be the dominant process at the initial stage of the carbothermal reduction. Calculated activation energy of this process is around 260 kJ mol-1.

Thermodynamic and kinetics analysis of the sulfur-fixed roasting of antimony sulfide using ZnO as sulfur-fixing agent

Currently, the commercial antimony metallurgy is mainly based on pyrometallurgical processes and oxidative volatilization of Sb2S3 is an essential step. This step includes the problems of high energy consumption and low concentration of SO2 pollution. Aiming at these problems, we present a new method of sulfur-fixing roasting of antimony sulfide. This method uses ZnO as a sulfur-fixing agent, and roasting with Sb2S3 was carried out at 673 K~1073 K to produce Sb2O3 and ZnS. By calculating the thermodynamics of the reactions, we can conclude that the Gibbs Free Energy Change (?G?) of roasting reaction is below -60 kJ/mol and the predominance areas of Sb2O3 and ZnS are wide and right shifting with the temperature increase, which all indicates that this method is theoretically feasible. The reacted products between Sb2S3 and ZnO indicated that the reaction began at 773 K and finished approximately at 973K. We used the Ozawa-Flynn-Wall, Kissinger and Coats-Redfern method to calculate the kinetics of the roasting reaction. The conclusion is as follows: The average values of apparent activation energy (E) and natural logarithmic frequency factor (lnA) calculated by Ozawa-Flynn-Wall, Kissinger and Coats-Redfern were 189.72 kJ?mol-1 and 35.29 s-1, respectively. The mechanism of this reaction was phase boundary reaction model. The kinetic equation is shown as follow, where ? represents reaction fraction: 1-(1-?)1/3 = 2.12 x1015 exp(-1.90x105/RT) t.