Calcination shrinkage is an essential factor in the evaluation of a gypsum‐bonded mold. Typically, if traditional fillers are used in a gypsum‐bonded mold, it is difficult to maintain sufficient strength due to the high dosages of fillers. Herein, a new filler system of gypsum, boehmite, is proposed to more efficiently compensate for shrinkage, while minimizing the impact on the strength. The effects of the fillers on the calcination shrinkages and mechanical properties of the gypsum‐bonded molds are studied. The phase transition and thermal expansion behaviors of the gypsum‐bonded molds are tested by thermal gravimetric analysis/differential scanning calorimetry (TG/DSC) and a thermal dilatometer. The microstructures of the fillers and gypsum‐bonded molds are characterized by a scanning electron microscope (SEM). The results show that the dosage of boehmite for near‐zero shrinkage is reduced to about 35 wt%, with the bending strength of the gypsum‐bonded mold remaining above 2 MPa throughout the whole calcination process. The mechanism of calcination expansion is revealed and ultimately attributed to the splitting of boehmite particles. This research provides a novel gypsum‐bonded mold for required high dimensional and mechanical properties, elevating the ability to form complex structures.
Response surface method (RSM) was used to optimize hawthorn blanching process based on single-factor experiments. There were two numerical (time and temperature) and one categorical variable (POD enzyme activity) that was used for the evaluation of the hawthorn blanching quality. The changes in POD enzyme activity, procyanidin content, and total flavonoid content were also analyzed. The regression model (P< 0. 05) was obtained through Central-Composite experimental design, indicating that the model could evaluate the residual POD enzyme activity in the blanching process under different parameters. The results show that time 103s and temperature 92.5°C were the best blanching conditions. Under these optimized conditions, the residual POD enzyme activity of hawthorn was within a reasonable range, which was 0.7731 U⋅g-1⋅min-1. The calculated results were basically consistent with the model predicted values (0.7989 U⋅g-1⋅min-1).
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