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Abstract The purpose of this work was to investigate the feasibility of using black tea powder produced through green technology (plant-source material and biotechnology) as multifunctional admixture for the hemihydrate gypsum. The hemihydrate gypsums were mixed with black tea, and the setting times, densities, hydration characteristics and strengths of different plasters were discussed, and the mechanisms responsible for their performance variations were explored by isothermal calorimeter, X-ray powder diffractometry and scanning electron microscopy. Besides, the economic and environmental compatibilities were also considered. The results indicate that black tea lowers the water requirement and improves the normal consistency, and then the high density is acquired. It prolongs the setting times. Moreover, this prolongation is more remarkable as more black tea is introduced. The gypsum strength is related to the content of black tea. Moderate black tea has the positive role in the improvement of strength, but the excessive black tea poses a negative effect. Furthermore, black tea alters the gypsum hydration process. It decreases the hydration rate and delays the hydration time of gypsum. Although more black tea seriously delays the gypsum hydration, all hemihydrate gypsum thoroughly converts into dihydrate gypsum after 28d. SEM results show that black tea changes the gypsum crystal morphology. All gypsum crystals are long and needlelike in the hardened pastes with less than 1% black tea. However, these crystals become shorter and larger as more black tea is mixed. Various crystal morphologies mainly contribute to the strength alteration of gypsum with black tea. These results show that black tea can serve as an alternative to the traditional functional admixture and then acquire a green and sustainable technology for the preparation of hemihydrate gypsum functional admixture, but also expand the commercial utilization of black tea in the building materials industries and foster the development of building industry towards green-oriented and sustainability. Highlights • Black tea lowers the water requirement. • Moderate black tea improves the paste strength. • Black tea alters the gypsum hydration process. • Black tea changes the gypsum crystal morphology. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the feasibility of using the plant-source polymer of the matcha powder as a composite admixture for hemihydrate gypsum. Hemihydrate gypsum was mixed with different contents of matcha powder, and then the water requirement for the normal consistency, setting times, density, strength, hydration and microstructure of the hardened mixture were evaluated. The experimental results showed that it increased the water requirement for the normal consistency, and it regulated the setting times and reduced the density. Hemihydrate gypsum with more matcha powder had the higher water requirement, longer setting times and lower density. Less than 1% matcha powder had slight impact on the strength of hardened paste, but more than 1% matcha powder had a remarkable one. Matcha powder changed the hydration process and prolonged the induction and acceleration period. Small needlelike crystals were transformed into longer, larger and thicker ones as more matcha powder was mixed. This case is closely related to the prolongation of the induction and acceleration period. Besides, more and larger pores were observed in the hardened paste with more matcha powder. It is attributed to the appearances of the tea polyphenol in matcha powder and the larger and longer crystal morphology in hardened paste as well as the high water requirement for the normal consistency. These results are important to the application of matcha powder as a composite admixture for the hemihydrate gypsum as well as the prosperity and development of the tea industry. [ABSTRACT FROM AUTHOR]

• Columnar surface strengthening by scanning electron beam technology. • The effect of curvature on the microstructure of the fusion zone is investigated. • The relationship between microhardness distribution and curvature is established. • The carbon content of the sub-surface is higher than that of the near surface. To conquer the shortcomings that the column-faced 45 steel is susceptible to wear and failure, scanning electron beam was conducted to strengthen it, the microstructure and microhardness of the modified layer under variable workpiece curvature were investigated. The results revealed that the modified layer was composed of fusion zone and heat-affected zone, the depth of the modified layer manifested an ascend tendency as the increment of curvature. Martensite dominates the modified layer, and the carbon content of martensite for the sub-surface is higher than that of the near surface, moreover, the grain size of martensite first reduced and then increased with increasing of curvature. The position of the maximum microhardness along the direction of depth as the curvature increases, and the maximum microhardness of 1/20 curvature is 688.26 HV, which is about 3.13 times that of the matrix. This study demonstrated the potential of using scanning electron beam to reinforce column-faced 45 steel. [ABSTRACT FROM AUTHOR]

• TiN/Ni alloying of 38CrMoAl steel surface was carried out by continuous scanning electron beam. • The effect of process parameters on the surface microstructure of 38CrMoAl steel was studied. • The effect of process parameters on grain morphology and properties was studied. TiN/Ni alloying of 38CrMoAl steel surface was carried out by continuous scanning electron beam. The effect of electron beam process parameters on the surface microstructures and mechanical properties of 38CrMoAl steel was studied. The results shows that the sample surface was divided into three regions: alloying layer, heat affected zone and substrate. Alloying layer made up with equiaxed crystals and short columnar crystals, microstructure of the heat affected zone was acicular and lath martensite, microstructure of substrate was tempered sorbate. The microhardness of the sample section first increased and then decreased, at a depth of 400 μm, the microhardness reached a maximum of 817.9 HV. When the beam current reached 12 mA and the moving speed reached 5.5 mm/s, the surface microhardness of the sample reached the highest 1209HV and the abrasion loss reached the lowest 4.6 mg. [ABSTRACT FROM AUTHOR]

• Electron beam rotary polishing. • Surface roughness of column-faced Ti6Al4V is reduced by 16 times. • Sample cross-sectional microstructure shows gradient changes. • Columnar surface strengthening by electron beam. In order to reduce the surface roughness and improve the surface properties of column-faced Ti6Al4V, scanning electron beam was used for polishing and strengthening. The effects of electron beam rotary polishing on the surface morphology, microstructure and properties of column-faced Ti6Al4V were investigated. The results show that the surface roughness of column-faced Ti6Al4V after electron beam rotary polishing is 0.45 μm, which is 93.8 % lower than the initial surface roughness of 7.24 μm. The microstructure of the melted layer consists mainly of α' martensite, and the heat affected zone is composed of α' martensite, α phase and β phase. The circumferential microhardness of the column-faced Ti6Al4V after electron beam polishing is 454HV at the highest, which is 1.41 times higher than the matrix, and the radial hardness decreases non-linearly with increasing depth. [ABSTRACT FROM AUTHOR]

• A method of W alloying on 45 steel surfaces by scanning electron beam. • Influence of different power on the microstructure and hardness of the strengthened layer is investigated. • The cross-sectional structure of the sample shows a gradient change. • The maximum hardness of the sample surface is 1170HV, which is more than 5 times that of the matrix. Scanning electron beam surface alloying can effectively improve the surface properties of metal samples. After tungsten alloying treatment on the surface of 45 steel by scanning electron beam, a strengthened layer consisting of alloying zone and heat-affected zone was formed on the surface. The microstructure in alloying zone is acicular martensite and columnar crystal, the microstructure in heat affected zone is acicular martensite and ferrite, and the matrix microstructure is ferrite and pearlite. With the increase of electron beam power, the columnar crystal content in alloying zone increases, the acicular martensite content in heat affected zone increases and the ferrite content decreases. The thickness of alloy zone and heat affected zone increases nonlinearly, and the surface hardness increases gradually. The maximum hardness of the sample surface is 1170HV, which is more than 5 times that of the matrix. [ABSTRACT FROM AUTHOR]

• Better preparation of alloy coatings by scanning electron beam technology. • The coating prepared by scanning electron beam showed a composite gradient. • The elements in the melt pool are sufficiently stirred to create segregation. • Martensite structure in the superheated zone can also be delaminated. The surface WC/Ni-Co based alloying treatment of 30CrMnSi steel was carried out using scanning electron beam technology, and the tissue distribution after alloying were tested and investigated. The results show that the cross-section of the alloyed specimen consists of three parts: the alloy layer, the heat affected zone and the substrate. The thickness of the alloy layer was increased by 18.3 μm compared to the thickness of the pre-coated layer. The alloy layer is organised in a composite gradient, consisting of martensite and ledeburite with carbides. [ABSTRACT FROM AUTHOR]