Porous alumina (Al₂O₃) beads were prepared via gel-dripping and pressureless sintering with α-Al₂O₃ as a raw material, nontoxic sodium alginate as a gelation reagent, and the calcium ions were introduced in the preparation using a calcium chloride solution. The effects of coagulation time and sintering temperature on the porosity, compressive strength and microstructure of porous Al₂O₃ beads were investigated. The results show that calcium ions can transfer and react readily with sodium alginate as the coagulation time increases. Alumina particles are solidified to form a bead green body by a three-dimensional network. The number of meso-pores decreases and the microstructure becomes well-distributed with increasing the sintering temperature. The porosity and compressive strength are 47.7%-78.1% and 1.2-36.0 MPa, respectively. The porosity, pore structure and compressive strength can be tailored by optimizing the coagulation time, sintering temperature and calcium ion concentration. The diameter, sphericity and property of porous alumina beads can be controlled through the simple gel-dripping method. The porous alumina beads can be used in many fields, such as catalyst support, adsorption, separation, purification, etc..

Tantalum (Ta) doped Li₇La₃Zr₂O₁₂ (Ta-LLZO) ceramics were prepared via conventional solid-state reaction. LiOH was used as a lithium source and a sintering additive for ceramics. The effect of LiOH on the microstructure and ionic conductivity of Ta-LLZO ceramics was investigated. The results show that LiOH as a lithium source can promote the formation of cubic Ta-LLZO, and LiOH as a sintering additive can effectively improve the densification of ceramics. The dense cubic garnet Ta-LLZO ceramics were obtained by sintering at 1 200 ℃ for 5 h. When the amount of the sintering additive is 6% (in mass fraction), the ionic conductivity of ceramics reaches 6.23×10^-4 S·cm^-1. It is indicated that Li₇La₃Zr₂O₁₂ prepared via solid-state reaction has a great potential in the application of all-solid-state lithium ion batteries.

Rapid preparation of dense BiFeO₃-BaTiO₃ lead-free piezoelectric ceramics at low temperatures is beneficial to preventing the Bi volatilization, reducing the energy consumption and developing novel materials with some unique properties. In this paper, dense BiFeO₃-BaTiO₃ ceramics with good ferroelectric and piezoelectric properties were prepared in an electric field of 200 V/cm with a current limit of 280 mA via reactive flash sintering of multiphase precursor powders (i.e., Bi₂O₃, Fe₂O₃, TiO₂ and BaCO₃) at 415 ℃ for 30 s. The solid-state reaction in sintering occurs during the flash event. The current limit has an effect on the phase transformation and densification. It is indicated that the reactive flash sintering technology could prepare the single-phase and dense ceramic material through flash sintering of starting precursors in one step, thus providing an effective approach for the rapid production of ceramic materials.

A holmium molybdate ceramic pigment with 'allochroic effect' was prepared via mechanical activation-assisted solid-state reaction. The effects of mechanical activation mode and time as well as sintering temperature on the properties of synthesized holmium molybdate pigment were investigated by laser particle size analysis, simultaneous thermal analysis, X-ray diffraction and scanning electron microscopy, respectively. The color properties and allochroic effect of the synthesized pigments were evaluated by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis) and colorimetry. In addition, the high-temperature stability and chemical stability of the pigments were also investigated. The results show that a sole phase of holmium molybdate can be obtained from mixed precursors ground at 1 h and sintered at 900 ℃ for 3 h, and the sintering temperature is reduced by 100 ℃, compared to that from each precursor ground separately for 2 h and then mixed or the mixed precursors unground. This is because mechanical activation pretreatment can effectively reduce the size and crystallinity of mixed precursor particles and enhance its solid-phase reaction activity, thus leading to the decrease of solid-phase reaction temperature. In addition, the pigment obtained from mixed precursors ground for 2 h has better color performance and allochroic effect under different illuminants. It is indicated that the allochroic effect of holmium molybdate pigment occurs due to the rich energy level structure of holmium ions in the visible range and the difference between relative spectral power distributions under different light sources. Meanwhile, holmium molybdate pigment can be used as a potential functional pigment in ceramic decoration and other related fields due to its high-temperature stability and chemical stability.

Single-phase anorthite porous ceramics were in-situ prepared by a foam gel-casting method with CaCO₃, α-Al₂O₃ and SiO₂ as raw materials and environmental-friendly gelatin as a gel. The influence of gelatin amount on the phase composition, microstructure and properties (i.e., porosity, density, compressive strength, and thermal conductivity) of the samples was investigated. The amount of gelatin has no effect on the phase composition of the prepared material, but it affects the properties. The total porosity decreases from 89.7% to 88.0%, the bulk density increases from 0.28 g/cm³ to 0.33 g/cm³, the compressive strength increases from 1.02 MPa to 2.54 MPa, and the thermal conductivity increases from 0.038 W/(m·K) to 0.059 W/(m·K) as the gelatin amount increases from 6% to 12%. It is indicated that porous anothite ceramics with a low density, a high strength and a low thermal conductivity could be prepared by this promising method.

Aluminum oxycarbides were prepared via a carbothermal reduction of alumina in vacuum at 1 300 - 1 500 ℃. The results indicate that the temperature required for the formation of aluminum oxycarbides from the carbothermal reduction of alumina in vacuum is lower than that in argon, a large amount of Al₄O₄C can be formed at 1 300 ℃, and the main component of the condensation products is Al₄O₄C, which is independent of the reaction extent of the raw materials. The condensation products consisting mainly of Al₄O₄C with a small amount of Al₄C₃ can be obtained under optimum conditions (i.e., n(α-Al₂O₃)∶n(C) of 2∶3, reaction temperature of 1 400 ℃ and reaction time of 20 min). It is confirmed that Al₄O₄C can be formed in two stages, i.e., alumina reacts with carbon to generate the gases containing aluminum Al₂O, Al and CO at higher temperatures, and the condensates mainly consisting of Al₄O₄C form at lower temperatures.

Hierarchical ZSM-5 zeolite was synthesized by a seed-assisted dry-gel conversion method, and the effects of seed amount, deionized water amount and crystallizing time on the structure and morphology of hierarchical zeolite were investigated. The results show that the crystallization rate of zeolite is increased with seed addition. Amorphous silica-aluminium gel can directly dissolve in the water film condensing on the seed surface and rapidly grew into ZSM-5 nano-zeolite near the seed. Simultaneously, nano-zeolites aggregate and some mesoporous channels are formed between the nano-crystals. The size of nano-zeolite and the resulting mesoporous pores can be adjusted by seed amount, deionized water amount and crystallizing time. The catalytic stability of the resulting hierarchical ZSM-5 zeolite is improved by nearly 5 times, compared with the conventional zeolite in the isomerization of styrene oxide to phenylacetaldehyde.

A glaze with a good quality and a unique decorative pattern was prepared with purple clay as a source of iron, Ca₃(PO₄)₂ and SnO₂. The effect of addition agents on the glaze color, microstructure and artistic textures was investigated by ultraviolet-visible spectroscopy, X-ray diffraction and scanning electron microscopy, and the color mechanism was analyzed. The results illustrate that the introduction of addition agents changes the chemical state of iron, and contributes to the formation of blue fancy glaze. The introduction of Ca₃(PO₄)₂ can cause the partial reduction of iron ions, leading to the glaze appearing blue and yellow, and Ca²⁺ ions promoting the separation of liquid phase to produce blue patterns. Also, the introduction of Ca₃(PO₄)₂ and SnO₂ for the increased reducibility of iron ions can increase the ratio of Fe²⁺ and Fe³⁺ ions, resulting in the glaze being blue-green, and the greater pattern and lightness value L*. The presence of Fe³⁺—O—Fe²⁺ in the vitreous is one of the color factors. The liquid separation forming the structure of the color is the auxiliary color of glaze color. The combined chemical color with structural color on the glaze becomes more colorful.

3-1 type and 3-3 type porous PZT ceramics were fabricated by the alginate ionotropic gelation process and gelcasting technology respectively. The resultant samples were sintered at different temperatures and characterized in terms of both microstructure and piezoelectric properties. It was noted that the porosity and grain size of porous PZT ceramics increased with the sintering temperature increasing from 1 150 to 1 250 ℃, which resulted in the increase of relative permittivity, piezoelectric efficient, thickness coupling coefficient k_t and compressive strength, the corresponding decrease of hydrostatic voltage coefficient and hydrostatic figure of merit (HFOM). Under the joint effects of unidirectionally aligned channels and the incorporation of Ca²⁺ into PZT matrix, the 3-1 type PZT ceramics possessed higher ε_r and compressive strength, lower d₃₃ and HFOM than that of 3-3 type PZT ceramics. However, the maximum HFOM value of 3-1 type PZT ceramics achieved 4 755×10^-15 Pa^-1, which makes it suitable for the application of underwater sonar detectors.

ZTA composite ceramics were prepared via pressureless sintering, and the influence of Cr₂O₃ doping on the microstructure and mechanical properties of ZTA ceramics was investigated. The results show that Cr₂O₃ can promote the growth of Al₂O₃ grains and obtain elongated Al₂O₃ grains. The density, hardness and fracture toughness of ZTA ceramics firstly increase and then decrease with the increase of Cr₂O₃ addition. ZTA ceramics with 0.6% Cr₂O₃ addition exhibit the optimum properties. However, the properties of ZTA ceramics with the excessive addition of Cr₂O₃ can be impaired due to the increased internal porosities. The mechanical properties of ZTA composite ceramics with Cr₂O₃ nano-sized particles are superior to those with Cr₂O₃ micron-sized particles. The addition of Cr₂O₃ nano-sized particles results in greater density and hardness of ZTA ceramics due to the smaller average grain size of Al₂O₃. Besides, the fracture toughness of ZTA ceramics improves due to the formation of more elongated grains and the consumption of more energy for crack propagation.