Enhancing microstructural properties of alumina ceramics via binary sintering aids

Alumina ceramics are widely used in many fields such as cutting tools,laser shock materials,roadbed board and refractory.Herein,Al_(2)O_(3)ceramics are prepared by a low-cost pressureless sintering technology,using the binary sintering aids of MgO and SiO_(2).The effects of sintering temperature and the ratio of binary sintering aids on the mechanical properties and microstructure of Al_(2)O_(3)ceramics are investigated.A spinel second phase(MgAl_(2)O_(4))is found out by the analysis of the results of XRD and EDS when MgO and SiO_(2)are introduced in the samples.The optimum properties are found when MgO content is 20 wt.%based on the total sintering aids and the sintering temperature is 1550℃.The bending strength and the bulk density reach a maximum value of 314 MPa and 3.73 g/cm^(3),respectively.The addition of appropriate amount of SiO_(2)makes the formation of liquid phase sintering and the removal of large pores.Meanwhile,a small amount of magnesium oxide doping has an effect on the grain refinement from the microstructure of the sample.Therefore,it is believed that MgO and SiO_(2)are the ideal sintering aids for promoting the densification and property of alumina ceramics.

LiCoO_(2) sintering aid towards cathode-interface-enhanced garnet electrolytes

Garnet-type Li_7La_(3)Zr_(2)O_(12)(LLZO) has high ionic conductivity and good compatibility with lithium metal.High-temperature processing has been proven an effective method to decrease the interface resistance of cathodeILLZO.However,its application is still hindered by the interlayer co-diffusion with the cathode and high sintering temperature(>1200℃).In this work,a new garnet-type composite solid-state electrolyte(SSE) Li_(6.54)La_(2.96)Ba_(0.04)Zr_(1.5)Nb_(0.5)O_(12)-LiCoO_(2)(LLBZNO-LCO) is firstly proposed to improve the chemical stability and electrochemical properties of garnet with high-temperature processing.Small doses of LCO(3%) can significantly decrease the LCOISSE interface resistance from 121.2 to 10.1 Ω cm~2,while the sintering temperature of garnet-type LLBZNO decreases from 1230 to 1000℃.The all-solid-state battery based on the sintered LLBZNO-LCO SSE exhibits excellent cycling stability.Our approach achieves an enhanced LCOISSE interface and an improved sintering activity of garnet SSE,which provides a new strategy for optimizing the comprehensive performance of garnet SSE.

Effect of CuO Addition on the Sintering Behavior and Electrical Conductivity of 3Y-TZP

Yttria stabilized tetragonal zirconia polycrystals （3Y-TZP） doped with CuO was prepared, to get two compositions, 0.3 and 1 mole fraction CuO, respectively. The dilatometric study of the samples showed sintering to be improved for the samples doped with 0.3 mole fraction CuO, and to be deteriorated for the samples doped with 1 mole fraction CuO. The 1 mole fraction CuO doped 3Y-TZP showed higher tetragonal/monoclinic phase transformation which was accompanied by grain growth. The electrical conductivity decreased with the addition of CuO.

Liquid Phase Sintering (LPS) and Dielectric Constant of α-Silicon Nitride Ceramic

The spark plasma sintering （SPS） was applied to prepare α-Si3 N4 ceramics of different densities with magnesia, silicon dioxide, alumina as the sintering aids. The mechanism of liquid phase sintering （LPS） wus discussed and the factors influencing the density of the prepared samples were analyzed. The dielectric constant of sintered samples was tested. The experimental results show that the density can be controlled from 2.48 g/ cm^3 to 3.09 g/ cm^3 while the content of the sintering aids and the sintering temperature alter and the dielectric constant is closely dependent on the density of obtained samples.

Effect of TiO_(2)Addition on Properties of Al_(2)O_(3)Ceramics Prepared by Digital Light Printing(DL.P)

Ceramic slurry of 78 mass%solid loading was prepared using photosensitive acrylic resin and dispersant SP-710 as the liquid phase,Al_(2)O_(3) powder(d50=2.38μm)and TiO_(2) powder additive as the solid phase.Alumina ceramics were prepared by DLP,sintering for 4 h at 1450,1500,1550 or 1600℃,respectively.The effects of the TiO_(2) addition(0,1%,2%,3%and 5%,by mass)on the properties of the ceramics were studied.The results show that the addition of TiO_(2) can improve the sintering of Al_(2)O_(3) ceramics,significantly improve the densification,and reduce the sintering temperature.With the optimum TiO_(2) addition of 3%and the optimum sintering temperature of 1600℃,the obtained Al_(2)O_(3) ceramics have shrinkage of 15.7%,15.8%and 23.8%at the x axis,the y axis,and the z axis,respectively,the porosity of 2.4%,the bulk density of 3.74 g·cm-3 and the three-point bending strength of 251.1 MPa.Compared with the undoped alumina ceramics,the doped alumina ceramic has increased bulk density by 0.56 g·cm-3,decreased apparent porosity from 20.2%to 2.4%,and the three-point bending strength increases by 2.5 times.Therefore,the density and the strength of DLP prepared ceramics can be improved effectively by adding an appropriate amount of TiO_(2),and the performance of the DLP prepared ceramics is close to that of the pressed samples.Thus,it is hopeful to apply DLP in refractories field.

The Effect of Fabrication Conditions for GDC Buffer Layer on Electrochemical Performance of Solid Oxide Fuel Cells

A Gd-doped ceria（GDC） buffer layer is required between a conventional yttria-stabilized zirconia（YSZ） electrolyte and a La-Sr-Co-Fe-O3（LSCF） cathode to prevent their chemical reaction. In this study,the effect of varying the conditions for fabricating the GDC buffer layer, such as sintering temperature and amount of sintering aid, on the solid oxide fuel cell（SOFC） performance was investigated. A finer GDC powder（i.e., ultra-high surface area）, a higher sintering temperature（1290℃）, and a larger amount of sintering aid（12%） resulted in improved densification of the buffer layer; however, the electrochemical performance of an anode-supported cell containing this GDC buffer layer was poor. These conflicting results are attributed to the formation of（Zr, Ce）O2 and/or excess cobalt grain boundaries（GBs） at higher sintering temperatures with a large amount of sintering aid（i.e., cobalt oxide）. A cell comprising of a cobalt-free GDC buffer layer, which was fabricated using a low-temperature process, had lower cell resistance and higher stability. The results indicate that electrochemical performance and stability of SOFCs strongly depend on fabrication conditions for the GDC buffer layer.

Mechanical Properties and Friction/Wear Behavior of Copper Alloyed Powder Composites

Copper alloyed powder composites containing nanoparticles were developed by hot pressing. Effects of nanoscale activated sintering aid and fine ceramic particles Al_2O_3 on hardness, working quality, and behaviors of friction and wear of the composites have been studied, compared with the composites including microscale activated sintering aid and microscale ceramic particles. The microstructures of the samples were analyzed by SEM. The results show that the materials with nanoscale sintering aid and fine ceramic particles have betuer mechanical properties and abrasive resistance than the materials with microscale activated sintering aid and microceramic particles. Moreover, element mutual transfer occurs between samples (strip) and abrasive wheel (ring).

Effect of LiF on the Optical Transmittance of Magnesium Aluminate Spinel

The effect of LiF as a sintering aid to the optical transparency of magnesium aluminate （MgAl2O4） spinel ceramics is studied. The spinel ceramics is prepared in a process proved to be suitable for commercial production. LiF, in different concentrations ranging from 0-2.5 wt%, is doped into MgAl2O4 powders prepared by sol-gel method. Sample MgAl2O4 ceramic discs are fabricated by ball milling, cold pressing, and hot-pressing, or hot-isostatic-pressing of the powder mixtures. Optical transparency measurements show that, hot-pressed samples exhibit higher transparency when more LiF is added. While for hot-isostatic pressed samples, excessive LiF content leads to a decrease in optical transparency. The optimal LiF doping quantity is suggested for the present technique.

Effect of Bi_2O_3 Additives on Properties of La_(0.7)Ca_(0.3)CrO_3

Sintering characteristics of Ca-doped lanthanum chromite [La(Ca)CrO_3] powder, prepared by gel-casting process were studied by measuring density and the evaluation of micro structural information. Bi_2O_3 is found to be an effective sintering additive for this material. The amount of Bi_2O_3 is altered to investigate Bi_2O_3 effect on the properties of La_(0.7)Ca_(0.3)CrO_3. The amount of 10% (mass fraction) Bi_2O_3 is suitable to increase sinter-ability of La_(0.7)Ca_(0.3)CrO_3. Increased concentration of point defects arising form substitution of Bi in La site is the plausible cause of enhanced sintering. Measurement of electrical conductivity and thermal expansion coefficient indicate that the doping of Bi_2O_3 does not have any significant effect on these properties.

Impact of Functional Additives on Properties of Al_2O_3-C Slide Gate Plate Refractories

Al2O3-C refractories are widely used as functional elements like nozzles, well blocks, sliding gate plates and stoppers in the continuous casting process of steel production. Application of silicon as a metallic agent in Al2O3-C slide gate plate production is usual. In fact, a non-oxide bond can be generated due to the reaction between silicon and carbon under reducing atmosphere in the plate matrix. This non-oxide bond can enhance the mechanical strength and abrasion resistance. In order to improve the mechanical and thermo-mechanical properties, functional additives can be aimed to lower the sinte- ring temperature and tailor the microstructure. For this reason, the effect of a special solid state sintering aid addition on the microstructure and thermo-mechanical properties of Al2O3-C slide gate plates in the presence of Si as a metallic component has been investigated. Two types of specimens were pressed at 150 MPa, tempered at 200 ℃ and fired in coke bed at 1 400 ℃ , respectively. Physical （ BD and AP ） , mechanical （ CCS and MOR ） and thermo-mechanical （ HMOR ） properties were determined; in addition, phase composition was characterized by X-ray diffraction analysis （ XRD ） and microstructure of specimens was investigated by field emission scanning electron microscopy （FESEM）. Results have shown that the addition of sintering aid increased the generation of cation vacancy in Al2O3 structure which enhanced the cation diffusion and densification process ; consequently, CCS, MOR and HMOR of specimens increased drasticallywhile bulk density and apparent porosity remained un- changed.

Fe-Mo-B Enhanced Sintering of P/M 316L Stainless Steel

Liquid-phase enhanced sintering of powder metallurgy（P/M）316L stainless steel by addition of sintering aids was studied.2%-8% of pre-alloyed Fe-Mo-B powder with two different particle sizes was added as sintering aids,and the specimens were sintered in vacuum at 1 200-1 350 ℃.The results show that the fine Fe-Mo-B powder（5-10 μm）has stronger activated effect.The sintered density increases with the increase in sintering aid content or sintering temperature.Warm compaction has a better effect on the control of dimensional precision of compacts.The prealloyed Fe-Mo-B powder deviated from Mo2FeB2 component can also be sintering aid of P/M 316L stainless steel.

Microstructure and piezoelectric properties of K_(5.70)Li_(4.07)Nb_(10.23)O_(3)0-added K_(0.5)Na_(0.5)NbO_(3) ceramics

Lead-free piezoelectric ceramics K_(0.5)Na_(0.5)NbO_(3)-xmol%K_(5.70)Li_(4.07)Nb_(10.23)O_(3)0(x=0-2.5,KNN-xmol%KLN)were prepared by conventional sintering technique.The phase structure and electrical properties of KNN ceramics were investigated as a function of KLN concentration.The results showed that small amount of KLN introduced into the lattice formed a single phase perovskite structure.The KLN modification lowered the phase transition temperature of orthorhombic-tetragonal(T_(O-T))and increased the Curie temperature(T_(C)).Some abnormal coarse grains were formed in a matrix when the content of KLN was relatively low(1 mol%).However,normally grown grains were only observed when the sintering aid content was increased to 2 mol%.Proper content of KLN decreased the amount of defects,thus the remanent polarization increased and the coercive field decreased markedly,and the sinterability of the KNN ceramics was simultaneously improved with significant increase of piezoelectric properties.