Papers by Keyword: Sintering Additive

Abstract: The paper describes the process of obtaining a high-density ceramic material based on magnesium aluminate spinel - material, which feature-wise will be lighter by mass of the used bullet-proof glass, and less resource-proof compared to modern ceramic armored. The sintering was carried out in a vacuum using a modifying gallium oxide additive to intensify the process. The effect of the additive concentration on the phase formation in the magnesium aluminate spinel-oxide gallium system, as well as the density and ceramics light transmission, is considered.

Abstract: The production of a precursor of magnesium aluminate spinel (AMS) by thermic synthesis to obtain a material with high-performance properties is reviewed in the work. The temperature synthesis of AMS is determined, the introduction of the additive is described in the range of concentrations of 3, 5, and 7 mol.%. The current processes during the firing of products have been investigated with a view to the further selection of the firing mode of the ceramic samples, which can be obtained.

Abstract: In this study, the environment-friendly egg white protein was used as foaming agents and binders to fabricate Al2O3 ceramic foams, owing to its excellent foaming and binding properties. The CaO-SiO2-MgO-ZnO-TiO2-B2O3 composite sintering additive was added into Al2O3 ceramic foam to develop the mechanical performance of Al2O3 ceramic foam and facilitate sintering. The modified Al2O3 ceramic foam was investigated on porosity, density, compressive strength, pore morphology and grain size. The investigation revealed that: compared with ordinary Al2O3 ceramic foam, although the samples adding sintering additive had lower porosity, larger density and bigger grain, its compressive strength was significantly much stronger than samples without sintering additive. The XRD result indicated that samples adding sintering additive had spinel, anorthite and a small amount of mullite phase besides the main corundum phase. Adding sintering additive is a new way to develop the mechanical performance of Al2O3 ceramic foam and facilitate sintering which can help grain growth, thereby improving the mechanical properties of Al2O3 ceramic foam.

Abstract: Silicon nitride (Si₃N₄) ceramic foam was prepared from water-based Si₃N₄ slurries via protein coagulation casting method with egg white protein as the foam agent. The open porosity of the as-fabricated ceramic foams was close to 80%, and the compressive strength was about 20 MPa. Further, the content of sintering additive on the phase composition, pore structure and pore size distribution were investigated. Results indicate that with the increasing of sintering aids, more windows appear on the wall of pore and the average size increases. Moreover, Pore size distribution of as-fabricated ceramic not only changes with sintering additive addition but also varies with pore size.

Abstract: CaB2O4 was added into hexagonal boron nitride (hBN) to improve the sintering behaviors of hBN. CaB2O4 and hBN were mixed and then pressed into plates. The plates were sintered at 2000°C for 5h under a N2 ambience. The phase compositions with different CaB2O4 contents were examined with X-ray diffraction analysis. The fracture cross-sections of the hBN plates were investigated by SEM. The apparent density and Rockwell hardness were also measured. The results show that the hBN particles had a plate-like shape and the grain sizes of hBN increased with increasing CaB2O4 contents. The apparent density and Rockwell hardness decreased with increasing CaB2O4 contents. When the CaB2O4 content was 15(wt) %, the hBN has the average grain sizes of 3μm in diameter and 200nm in thickness, the apparent density of 1.06 g/cm3 and the Rockwell hardness of 3, respectively.

Abstract: Different grain size of starting powder was choosed and different sintering additives were used to fabricate Si3N4 ceramics by pressureless sintering. Samples’ relative density and mechanical properties including Vickers hardness, bending strength and fracture toughness were tested. Then XRD, SEM and EDS were carried out to identify phase and observe microstructure and fracture morphology. The result shows that high purity α phase Si3N4 powder of 5 μm is suitable for sintering and combination of 5 wt.% MgO +5 wt.% Y2O3 is most effective within six kinds of sintering aids.

Abstract: The effects of ZnO-Bi2O3-B2O3-SiO2(ZBBS) glass addition on the sintering behavior, crystalline phase, microstructure and dielectric properties of 16CaO-9Li2O-12Sm2O3-63TiO2(CLST) ceramics were investigated. The results show that ZBBS glass can effectively decrease the sintering temperature of CLST ceramics to 1 000 °C by liquid phase sintering. With the increase of ZBBS content, the second phase，Sm2Ti2O7 is found and increase, which causes the dielectric constant and dielectric loss of CLST decrease. The temperature coefficient of the resonance frequency shifts to positive. The optimum dielectric properties of r = 71, Tan = 0.006, TCF= 5×10-6/°C were obtained in 10wt% LBS glass-doped CLST ceramics sintered at 1 000 °C for 3 h.

Abstract: Microstructure and mechanical properties of Si3N4 and Si3N4 + SiC nanocomposites sintered with rare-earth oxide additives (La2O3, Y2O3, Yb2O3 and Lu2O3) have been investigated. The composites exhibited smaller grain diameter compared to that of monolithic materials. The aspect ratio of β-Si3N4 grains increased with a decreasing ionic radius of rare-earth elements in the Si3N4 monoliths as well as in the Si3N4-SiC nanocomposites. The hardness of both systems increased with a decreasing ionic radius of rare-earth element. The fracture toughness of the materials with coarser microstructure and higher aspect ratio was higher due to the more frequent toughening mechanisms. No significant difference between strength values of monoliths and composites was observed and the strength in the composites was determined mainly by the present processing flaws. Significantly improved creep resistance was observed in the case of composites and for materials with smaller ionic radius of RE3+.

Abstract: Sm2O3 and MgO as a sintering additives to fabricated porous silicon nitride by reaction-bonded. The phase of as-produced silicon nitride characterized by XRD-diffraction. The microstructure of product was investigated by SEM. The samples were machined into test bar for flexural strength testing. Using Archimedes theory testing the porosity of porous silicon nitride. MgO have restrain effect on the growth of rod-like silicon nitride, because of produce a restrain layer which is MgO reacted with SiO2 on the surface of silicon., the microstructure of crystal is particle like, the maximum flexural strength is 48MPa with porosity of 35%. Sm2O3 can assistant the growth of high aspect ratio Si3N4 crystal at beginning temperature of 1300°C for it’s low melt point and low viscidity in liquid state, the as-product’s morphology is rod-like and the flexural strength is as high as 300 MPa when the porosity is 30%, high than the sample that of low rod-like crystal content.

Abstract: Commercial α−Si3N4, Al2O3 and a mixed yttrium and rare earth oxides, RE2O3, were used as starting-powders. Powder batches were milled using different Al2O3/RE2O3 contents, as additive. Hot-pressing was done at 1750oC-30 min-20MPa in N2 atmosphere. Specimens neat to 6x3x3mm3 were polished and characterized by XRD and SEM. Specimens were submitted to creep tests, under compressive stresses between 100 and 350 MPa at temperatures ranging from 1250 to 1300oC in air. Higher additive amounts resulted in larger grains of higher aspect ratios and in a decreased anisotropy in the hot-pressed ceramics. The compressive creep behavior depends on the intergranular phase content. While higher amounts of additives resulted in higher creep rates, • ε , and higher stress exponents, n, the activation energy Qss, has been inferior for samples with lower additive contents. Grain sliding has been identified to be the predominant mechanism responsible for creep deformation of these ceramics.