Microstructure and properties of Ag–Ti_3SiC_2 contact materials prepared by pressureless sintering

Ti3SiC2-reintbrced Ag-maJxix composites are expected to serve as eleclrical contacts. In this study, the wettability of Ag on a Ti3SiC2 subslxate was measured by the sessile drop melkod. The Ag-Ti3SiC2 composites were prepared from Ag mad Ti3SiC2 powder mix- tures by pressureless sintering. The effects of compacting pressure （100-800 MPa）, sintering temperature （850-950~C）, mad soaking time （0.5-2 h） on the microslxucture mad properties of the Ag-Ti3SiC2 composites were investigated. The experimental results indicated that Ti3SiC2 paxticulates were uniformly distxibuted in flae Ag matrix, wiflaout reactions at the interthces between flae two phases. The prepared Ag-10wt%Ti3SiC2 had a relative density of 95% mad an electrical resistivity of 2.76 x 10 3 m~）＇cm when compacted at 800 MPa mad sintered at 950~C for 1 h. The incorporation of Ti3SiC2 into Ag was found to improve its hardness without substantially compromising its electrical conductivity; INs behavior was attxibuted to the combination of ceramic and metallic properties of the Ti3SiC2 reinforcement, suggesting its potential application in electrical contacts.

Preparation of ZrN(ZrON)-SiAION Composite Ceramics via a Pressureless Sintering Process

ZrN-SiAlON composite materials were synthesized at 1 550 ℃ for 6 h via a carbothermal reduction nitridation route using fly ash （≤74 μm）,zircon （≤ 44 μm） and active carbon as starting materials.The processed ZrN-SiAlON composite micropowders were mixed with polyvinyl alcohol as binder to prepare ZrN （ZrON）-SiAlON composite ceramics by carbon-embedded pressureless firing at 1 450,1 500 and 1 550 ℃ for 1 h,respectively.Influences of firing temperature on the phase compositions,microstructure and sintering properties of the ceramics were investigated.The results show that：（1） β-SiAlON based composite ceramics with different compositions can be prepared by controlling firing temperature,and the main crystalline phases of the specimen fired at 1 550 ℃ for 1 h involve ZrN,ZrON and β-SiAlON （z =2,Si4Al2O2N6）; （2） ZrN （ZrON）,β-SiAlON and a Fe-Si based compound can be observed in the microstructures of the specimens fired at different temperatures.ZrN （ZrON） particles distribute homogeneously in the β-SiAlON matrix; （3） raising firing temperature can increase the shrinkage ratio of the ceramics,and the volume shrinkage ratio increases from 19.4％ to 40.3％ when the firing temperature rises from 1 450 to 1 550 ℃.

Pressureless sintering of La-Y-Sialon ceramics and grain growth in later period of sintering

The pressureless sintering process of Sialon ceramics added ( 1.5% La 2O 3+ 4.5% Y 2O 3) as sintering aids was studied. It is found that a β′ Sialon with relative density over 99% is obtained by sintering at 1?750?℃ for 1?h. Crystal grain growth was observed at room temperature by SEM for the samples sintered at 1?800?℃ holding for different time. It is proved that grain growth along c axis of β′ phase is a first priority, since (210) and (001) lattice plans have different activation energy. On the present conditions, logarithm of grain aspect ratio / of average grain length to average width is in proportion to sintering time because of proportion of lg to sintering time and proportion of to sintering time.

Fabrication and Pressureless Sintering of Silicon Carbide Refractories

This work studies the fabrication and pressureless sintering of silicon carbide(SiC)refractories.SiC particles were adopted as aggregates,introducing different amounts(20%,30%,40%,50%,and 60%,by mass)of submicron SiC powder,adding resin as the binder and the carbon source,and B4C as the sintering aid.It is found that when the mass ratio of B4C to the submicron SiC powder is 3%,the optimal sintering can be obtained.With the increase of the submicron powder addition,the sintering linear shrinkage increases and the mechanical properties enhance.The optimal sintering temperature is 2050-2100℃.

Transparent high-performance piezoceramics through pressureless sintering

Piezoelectricity offers an electromechanical coupling that is widely utilized in transducer applications.There has been a consistent demand for transparent piezoelectric materials for optoelectrical applications.Therefore,despite the inherent tradeoff between the transparency and the piezoelectricity,numerous strategies have been explored to develop the transparent piezoelectric materials.Nonetheless,the most transparent piezoelectric materials developed to date is either a single crystal or materials that achieve transparency via hot-press sintering,limiting its industrial applicability.Therefore,we introduce a novel piezoelectric material that ensures transparency through co-doping and pressureless sintering of polycrystalline ceramics.In this study,we employed a compositional optimization approach to enhance the synergistic effect between the transparency and the piezoelectric properties of 0.71Pb(Mg_(1/3)Nb_(2/3))O_(3)–0.29PbTiO_(3)(PMN–0.29PT)ceramics.By utilizing the tape casting process for mass production and large-area manufacturing,our Pb_(0.913)La_(0.0145)Sm_(0.0145)(Mg_(1/3)Nb_(2/3))_(0.71)Ti_(0.29)O_(3)(TP2.9)ceramics exhibited over 60%transparency and large piezoelectric coefficient(d33)of 1104 pC/N.This material holds considerable promise for a wide range of industrial applications in both the optical and electronic domains.

Densification,microstructure and mechanical properties of multicomponent(TiZrHfNbTaMo)C ceramic prepared by pressureless sintering

A multicomponent(TiZrHfNbTaMo)C ceramic has been fabricated by pressureless sintering at temperatures from 2100℃to 2500℃,using an equimolar multicomponent carbide powder synthesized by carbothermal reduction as the starting material.Influence of sintering temperature on densification,microstructure and mechanical properties of the ceramics was investigated.The relative density increases with increasing sintering temperature,and a nearly fully dense sample is achieved by pressureless sintering at 2500℃.Average grain size increases from 3.7 to 15.2μm with increasing sintering temperature from 2300 to 2500℃.The(TiZrHfNbTaMo)C ceramic sintered at 2400℃exhibits a single phase fcc structure with homogeneous chemical composition,an average grain size of 7.0μm and a relative density of96.5%,while its measured hardness is 33.2 GPa at 100 mN and 23.2 GPa at 9.8 N.

Grain growth kinetics and densification mechanism of(TiZrHfVNbTa)C high-entropy ceramic under pressureless sintering

The grain growth kinetics and densification mechanism of(TiZrHfVNbTa)C high-entropy carbide ceramic are investigated in this work.A single phase carbide with a rock-salt structure is formed until 2300°C,below which an apparent aggregation of V,Zr and Hf exists.It is associated with the slow diffusion rate of V element as well as the relatively poor solubility of VC in HfC(as well as ZrC).The grain growth mechanism gradually changes from surface diffusion to volume diffusion and then grain boundary diffusion with increasing sintering temperature.This is attributed to the variation of activation energy of grain growth.The densification mechanism is principally dominated by the mass transport through lattice diffusion with the activation energy of 839±53 k J/mol.Through the design of two-step sintering,it is verified that the solid solution formation can effectively promote the densification process.

Effect of CeO_2 on low temperature pressureless sintering of porous Si_3N_4 ceramics

Porous silicon nitride（Si_3N_4） ceramics were fabricated by low temperature pressureless sintering, using carbonized rice husk and α-Si_3N_4 powders as raw materials, and MgO-CeO_2 as sintering additives. The effects of CeO_2 concentration and sintering temperature on phase composition, microstructure, porosity and flexural strength of the sintered products were investigated by X-ray diffraction（XRD）, scanning electronic microscopy（SEM）, Archimedes＇ displacement method and three-point bending strength, respectively. The results suggested that MgO-CeO_2 was a much more effective sintering additive for Si_3N_4 than MgO alone. When CeO_2 concentration was 4 wt.%–5 wt.% and sintering temperatures were in a range of 1500 to 1550 oC, the obtained porous silicon nitride ceramics had the porosity of 45.78%–42.81% and flexural strength of 49.44–84.09 MPa. Moreover, when sintering temperature was 1550 oC and CeO_2 concentration was 5%, large elongated β-Si_3N_4 grains were well developed.

Preparation of Gd_2O_2S:Pr Scintillation Ceramics by Pressureless Reaction Sintering Method

Fabrication of Gd2O2S：Pr scintillation ceramics by 2Gd2O3.（Gd,Pr）2（SO4）3.mH2O precursor was made Gd2O3, Pr6O11 and H2SO4 as the starting materials pressureless reaction sintering was investigated. The by hydrothermal reaction using commercially available Then single phase Gd2O2SO4：Pr powder was obtained by calcining the precursor at 750℃ for 2 h. The Gd2O2SO4：Pr powder compacts can be sintered to single phase Gd2O2S：Pr ceramics with a relative density of 99% and mean grain size of 30um at 1750℃ for 2 h in flowing hydrogen atmosphere. Densification and microstructural development of the Gd2O2S：Pr ceramics were examined. Luminescence spectra of the Gd2O2S：Pr ceramic under 309 nm UV excitation and X-ray excitation show a green emission at 511 nm as the most prominent peak, which corresponds to the ^3p0-3H4 transition of Pr^3＋ ions.

Pressureless reactive sintering mechanism of nanocrystalline Bi_2O_3-Y_2O_3 solid electrolyte

The nanocrystalline Bi2O3-Y2O3 solid electrolyte material was synthesized by pressureless reactive sintering process with Bi2O3 and Y2O3 nano mixed powder as raw materials, which was prepared by a chemical coprecipitation process. The study on the behavior of nano δ-Bi2O3 formation and its grain growth showed that the solid solution reaction of Y2O3 and δ-Bi2O3 to form δ-Bi2O3 occurs mainly in the initial stage of sintering process, and nano δ-Bi2O3 crystal grains grow approximately following the rule of paracurve （（D-D0）^2=K.t） during sintering process. After sintered at 600℃ for 2 h, the samples could reach above 96% in relative density and have dense microstructure with few remaining pores, the δ-Bi2O3 grains are less than 100 nm in size.

Preparation and thermoelectric properties of ternary rare earth sulfide γ-Ce_(3–x)Eu_xS_4

The effect of Eu-substitution on the density and thermoelectric properties of ternary sulfide Ce3-xEuxS4 （0≤x≤0.8） compacts was investigated. Ce3-xEuxS4 powders were prepared via the sulfurization of the oxide using CS2 gas at 1473 K. The pressureless sintered Ce3-xEuxS4 compacts in the atmosphere were crystallized in the T-phase. The density of the Ce3-xEuxS4 compacts increased with the increasing of Eu-substitution. Eu-substitution yielded a higher Seebeck coefficient and lower electrical resistivity. The highest value of the thermoelectric power factor of 1.41×10^-4 W/K^2m was obtained for the Ce2.2Eu0.8S4 compact at 673 K. It indicated that Eu-substitution was effective for improving thermoelectric properties of Ce3-xEuxS4.

Microstructure and Mechanical Properties of TiB_2-Al_2O_3 Composites

Effects of Al2O3 and Ni as the additives on the sinterability, microstructure and mechanical properties were systematic studied. The experimental results show that only a relative density about 96.2% of hot-pressing TiB2-30%Al2O3 can be attained due to the plate-like TiB2 particle and its random orientation and excessive Al2O3 grain growth. When sintering temperature is higher than 1 700 ℃, TiB2 grain growth can be found, which obvious improves flexural strength of TiB2 matrix but decreases toughness. It seems that mechanical properties of TiB2-Al2O3 composites are mainly depended on relative density besides grain growth. otherwise, they will be determined by relative density and TiB2 matrix strength together. Anyway, Al2O3 addition can weaken the grain boundary and thus improve the toughness of the materials. A flexural strength of 529 MPa, Vickers hardness of 24.8 GPa and indentation toughness of 4.56 MPa·m1/2 can be achieved inTiB2-30vol% Al2O3.

Microstructure and properties of Si_3N_4 ceramics obtained from addition of β-phase seeds and celsian

The silicon nitride based ceramics obtained by the addition of β-Si3N4 seeds was fabricated using celsian as the additive and by pressureless sintering. The microstructure of the material was observed and analyzed using XRD, SEM, and TEM and the mechanical response of this array microstructure was characterized for flexural strength and fracture behavior. The result shows that the growth of the larger aspect ratio grains initiate mainly from the seeds through the heterogeneous nucleation mechanism during the process of phase transformation, and the intergranular phase BaAl2Si20s services as good refractory materials. In contrast to conventional processing, a stable bimodal microstructure and complicated component with a lower cost can be achieved using the abovementioned process theoretically and practically.

Thermal shock and fatigue behavior of pressureless sintered Al_(2)O_(3)-SiO_(2)-ZrO_(2) composites

The thermal shock and fatigue behavior of pressureless sintered Al_(2)O_(3)-SiO_(2)-ZrO_(2)(ASZ)composites was studied.The influence of the thermal shock and fatigue on the strengthening response of ASZ has been investigated by measuring the strength retention and microstructural changes.The magnitude of the flexural strength and fracture of the ASZ has been compared with that of the monolithic Al_(2)O_(3)(A)and Al_(2)O_(3)-SiO_(2)-ZrO_(2)(AZ)composites under the same experimental conditions.Results indicated that the ASZ composites possess the highest resistance against thermal shock and fatigue,in comparison with A and AZ.The improvements were attributed to the enhancement in the fracture toughness of ASZ and the presence of multi-phase reinforcement.

(Ca,Sr,Ba)ZrO_(3):A promising entropy-stabilized ceramic for titanium alloys smelting

A novel entropy-stabilized(ES)(Ca,Sr,Ba)ZrO_(3) ceramic has been designed and synthesized by pressureless sintering of CaZr03,SrZr03 and BaZr03 powders mixtures at 1450℃,1500℃and 1550℃for 3 h.X-ray diffraction,scanning electron microscopy and transmission electron microscopy analyses collectively indicate that a single solid solution is formed with a homogeneous distribution of metal elements after sintering at 1550℃.The relative density and hardness of the ES(Ca,Sr,Ba)ZrO_(3) ceramic sintered at 1550℃are 97.79%and 10.840.33 GPa,re s pectively.This ES(Ca,Sr,Ba)ZrO_(3) exhibits lower thermal conductivity from 373 K to 1073 K than their constituting zirconates,CaZrO_(3),SrZrO_(3) and BaZrO_(3).Most importantly,the ES(Ca,Sr,Ba)ZrO_(3) ceramic possesses good corrosion resistance to TiNi alloy melt and no distinct reaction layer exists between TiNi alloy and ES(Ca,Sr,Ba)ZrO_(3) ceramic in the contact region.The combination of these properties indicates that ES(Ca,Sr,Ba)ZrO_(3) ceramic is promising for use as a novel crucible material for the melting of titanium alloys.

Effect of seed particles content on texture formation of Si_3N_4 ceramics by gel-casting in a strong magnetic field

In this paper, the textured Si3N4 ceramics were prepared by adding seed particles during gel-casting in the magnetic field of 6 T, followed by pressureless sintering. The effect of pH on the stability and dispersibility of Si3N4 slurry and the effect of seed particles content on texture formation of SiaN4 ceramics were both studied. Those results showed that the slurry with good stability and dispersibility was obtained when pH was about 11.6. The a or b-axis of Si3N4 particles or crystals was aligned parallel to the direction of the magnetic field in the magnetic field of 6 T. The degree of texture of Si3N4 ceramics further increased during sintering. With the increasing of additional β-Si3N4 particles in the magnetic field of 6 T, the degree of texture increased from 0.19 without seed particles to 0.76 with 9% （mass fraction） seed particles. The increase of seed particles content promoted the texture formation of Si3N4 ceramics.

Fabrication of Porous Si_3N_4-Lu_2Si_2O_7 Composite Ceramics

To improve the corrosion resistance of porous Si3N4 used in the high temperature environments,which contain water vapor and volatile species,porous Si3N4-Lu2Si2O7 composite ceramics were fabricated by a process of oxidation bonding and pressureless sintering in flowing N 2 atmosphere at the temperatures lower than 1550 ° C.The pores in ceramics were formed by removing the pore-forming agent（phenolic resin）.SiO2 derived by the oxidation of Si3N4 at 1250 ° C in air reacted with Lu2O3 at various sintering temperatures,leading to the formation of Lu2Si2O7 with excellent oxidation and corrosion resistance.The phase composition,microstructure,and mechanical properties of the porous ceramics depended on the sintering temperatures.Si3N4-Lu2Si2O7 composite ceramics with the porosity of 52% and the pore size of 0.2 μm were obtained by oxidation bonding at 1250 ° C for 1 h and pressureless sintering at 1550 ° C for 2 h using 4 wt pct Lu2O3 additive.

Preparation of hydroxyapatite ceramic through centrifugal casting process using ultra-fine spherical particles as precursor and its decomposition at high temperatures

Ultra-fine hydroxyapatite(HAp)powder with a diameter of about 10 nm was used as precursor for preparation of HAp ceramic.The precursor hydroxyapatite was single phase and highly crystallized without any additional thermal treatment.Highly densified HAp ceramic was fabricated through centrifugal infiltration casting(CIC),followed by pressureless sintering.The relative densities of compacts prepared at 1100°C and 1200°C were 77.8%and 94.1%,respectively.SEM micrographs of HAp ceramic sintered at 1100°C showed a porous microstructure with a grain size of 1μm.HAp ceramic fabricated at 1200°C revealed a dense microstructure with nano-sized sphericalα-TCP distributed at grain boundaries and triple points.The mechanism of decomposition from HAp toα-TCP at 1200°C was discussed on the basis of SEM,XRD and FTIR results.