Materials Science Forum Vol. 848

Abstract: B₂O₃- or P₂O₅-doped Li₂O-MgO-Al₂O₃-SiO₂ (LMAS) glass-ceramics were prepared by solid state method using Li₂CO₃, MgO, Al₂O₃ and SiO₂ as the raw materials, B₂O₃ or P₂O₅ as the additives. The effects of adding B₂O₃ and P₂O₅ on the phase separation, crystallization and thermal expansion coefficient were investigated by means of X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and thermal dilatometer, respectively. The results showed that B₂O₃ or P₂O₅ addition could promoted phase separation of glass and increased the size of spherical phase separation droplet. With the addition of B₂O₃ or P₂O₅, the crystallization temperatures (Tc) of LMAS system decreased from 764 ^oC to 726 ^oC and 764 ^oC to 750 ^oC, respectively. However, the crystalline phase compositions did not changed, and β-quartz solid solution (s.s) (Li₂Al₂Si₃O₁₀) was still the main crystalline phase, and lithium silicate (Li₂SiO₃) and forsterite (Mg₂SiO₄) were the minor phases. The thermal expansion coefficient (α) of B₂O₃-doped and P₂O₅-doped LMAS glass-ceramics in the temperature range 20-600 ^oC were 5.215×10^-6/ ^oC and 5.008×10^-6/ ^oC, respectively, which were higher than that of LMAS glass-ceramics (α=3.790×10^-6/ ^oC).

Abstract: The wide use of ceramic material in engineering is restricted by its brittleness, so the strengthening and toughening of ceramics is always a hot spot of research in material area. And in general, the modification of ceramics is achieved by changing its internal microstructure. In this paper the influence of confinement on the mechanical properties of ceramics and the specific use of this method were investigated. Firstly, the influence of confinement on ceramic’s fracture process was analyzed in theory. Then the three-point bending test was conducted using two types of ceramics, viz. Zirconia and Alumina. The experimental results showed that the fracturing load of zirconia increased from 4.3298 to 5.4639KN as the confinement was increased from 0 to 150MPa, 26.19% increase was found in the confined specimen. The same trend was observed in alumina, whose fracturing load increased from 3.0446 to 5.0259KN as the confinement was increased from 0 to 150MPa, 65.07% increase was found. After that, a series of ballistic experiments were performed. The target in this experiment was boron carbide ceramic, and it was confined by 45 steel. The results showed that with the constraint force was bigger, the ballistic efficiency factor was better and the depth of penetration was smaller. In other words, the confinement can increase the defensible performance of the target. In summary, the ceramic’s fracture toughness, defensible performance and ballistic efficiency factor can be increased by adding confinement to it.

Abstract: An innovative two-step route was successfully applied to the ionic liquid-assisted synthesis of C@ZrSiO₄ ceramic pigments, which is able to reduce the reflux time from many hours to a few minutes. The structure and morphology of the inclusion pigments were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). And the chromatic value of the pigments was measured by the CIE color system. The results show that the pigment in the absence of ionic liquid (IL) exhibited homogeneous single t-ZrO₂ phase, while the samples in the presence of IL showed coexistence of two crystal phases (m-ZrO₂ and ZrSiO₄). The CIE coordination L* value decreased with the increase of TEOS amounts due to the pure zircon formation. The as-prepared pigment showed high tinting ability, as L*=37.16, a*=0.71, b*=0.3, making it promising candidate for ceramic decoration.

Abstract: A series of ytterbium and erbium co-doped sodium yttrium fluoride (NaYF₄:Yb³⁺, Er³⁺) ceramics have been successfully prepared by pressureless sintering. The ceramic samples were characterized by X-ray diffraction (XRD), photoluminescence (PL), density and field emission scanning electron microscope (FESEM). The results showed that the phases of the NaYF₄:Yb³⁺, Er³⁺ ceramic samples transformed when the sintering temperature was changed. The ceramic samples sintered below 600 ^oC contained both cubic α-NaYF₄:Yb³⁺, Er³⁺ and hexagonal β-NaYF₄:Yb³⁺, Er³⁺. The sample sintered at 600^oC is the pure hexagonal β-NaYF₄:Yb³⁺, Er³⁺. When the sintering temperature is above 600 ^oC, the ceramic samples present the α-NaYF₄:Yb³⁺, Er³⁺ again. The fluorescence intensity increased firstly and then decreased with the sintering temperature increasing. The luminous intensity of the sample sintered at 600 ^oC was the highest. The densities of as-prepared ceramic sample increased with the sintering temperature rising. The samples sintered at 600 ^oC with different holding time possessed the similar crystal phases (β-NaYF₄:Yb³⁺, Er³⁺) and fluorescence intensity. As the holding time increased, the densities of the samples increased. To obtain more dense ceramics, the ceramics using β-NaYF₄:Yb³⁺, Er³⁺ powders were prepared by spark plasma sintering (SPS). The maximum relative density reached 97%.

Abstract: Porous Al₂O₃ ceramics were fabricated by directional freezing and low pressure drying with sucrose solution as the cryogenic medium. The pore structure of the porous ceramics was changed by annealing in the environment of higher than the glass transition temperature of sucrose solution after directional freezing because of changing the size and distribution of crystalline solid. The effects of the annealing time on the pore structure, open porosity and mechanical property of porous ceramics were investigated. The results showed that the pore size of porous ceramics increased substantially with the increase of annealing time. The open porosity of porous ceramics changed slightly with the increase of annealing time, while the compressive strength of porous ceramics showed a trend of decrease. The pore size range of porous Al₂O₃ ceramics fabricated is from 6.0μm to 110.2μm, the range of porosity was 40.35%-64.58%, the compressive strength range of porous Al₂O₃ ceramics was from 25.9MPa-126.6MPa. The porous Al₂O₃ ceramics with different pore structure can be obtained by changing the annealing time.

Abstract: B₄C ceramic tapes were prepared by aqueous tape-casting with boron carbide powders as starting material, deionized water as solvent, polymine (PEI) as dispersant, polyethylene glycol (PEG) as plasticizer, poval (PVA) or gelatin as binders. The influences of pH, dispersant content, kind and content of binder on the stability and rheological property of tape slurries were studied. The experimental results indicated that, when the pH was ranged in 3-4, the slurries with good stability and good rheology could be obtained with 0.8 wt% PEI, 4.0 wt% PVA or 6.5 wt% gelatin. PVA as binder made cast tape with certain strength, and gelatin as binder made cast tape with poor strength.

Abstract: For the urgent requirements of high performance castables in iron and steel making industry, effects of rare earth chlorides on properties of Al₂O₃-MgO castables were addressed. The prepared castables were compared in terms of phase compositions, apparent porosity, bulk density, permanent linear change and strength. It was demonstrated that cerium chloride and yttrium chloride exhibited a positive influence on in-situ reactions and volumetric stability of castables. The cation inversion degree of spinel and solid-soluted content of spinel and CaAl₁₂O₁₉ (CA₆) were both dependent on the temperature and addition. Cold modulus of rupture for castbles with rare earth chlorides additions calcined at 1450°C was similar to that for referenced castables though the former ones were relatively less at 1250 and 1350°C.

Abstract: Zircon whiskers were synthesized via non-hydrolytic sol-gel process combined with molten salt method by using anhydrous zirconium tetrachloride as zirconium source, TEOS as silicon source, anhydrous ethanol as solvent, and sodium molybdate as molten salt. The effects of heat treatment mode and cooling rate on the synthesis of zircon whiskers have been studied by means of XRD, FE-SEM, TG and TEM. The results indicate that well-developed whiskers can be prepared through heat treating the sample at 850°C for 3 h followed by a furnace cooling process. The zircon whiskers which were fabricated by this heat treatment mode grew along the [001] direction and showed diameter of 50~100 nm and aspect ratio of 20~30.

Abstract: Mullite whiskers were prepared via non-hydrolytic sol-gel process combined with molybdate molten salt using tetraethoxysilane and anhydrous aluminum chloride as precussor, anhydrous ether as oxygen donor, molybdate as molten salt. The effects of heat treatment temperature, molten salt amount, holding time on synthesis and morphology of mullite whiskers were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The results show that the mullite whiskers appeared at the lowest temperature of 800°C, and optimized mullite whiskers could be prepared at 900°C for 8 h with the mass ratio of xerogel and molybdate as 1:2, the diameter of the whiskers was in the range of 0.15-0.22 μm with the aspect ratio of more than 40.

Abstract: The ZnO:Al (AZO) films were deposited on glass substrates with Al₂O₃ buffer layers by RF magnetron sputtering. The obtained films had the hexagonal structure and preferred orientation of (002). Compared with AZO film without buffer layer, the grain size of the film with buffer layer was increased and the conductive property was increased greatly. the grain size of AZO films reached 27.9nm for those with buffer layers. The optical property of AZO films was decreased by the buffer layers. The resistivity of AZO films with Al₂O₃ buffer layer was about 6.6×10^-3 Ω·cm and the average transmittance was over 80% in the range of 450~900nm.