添加剂对锆质定径水口烧结性能和抗热震性的影响

采用粉末成型工艺,以粒度为0.045mm的斜锆石粉和粒度均为0.154mm和0.074mm的MgO部分稳定电熔氧化锆和CaO部分稳定电熔氧化锆为原料,分别加入不同添加剂Y2O3、CeO2和Y2O3 CeO2,在300MPa的压力下成型,并于1720℃烧后制成锆质定径水口试样。结果表明通过合理控制颗粒级配和优化工艺参数,当添加剂中Y2O3和CeO2的含量(w)分别为0.6%和0.4%时,氧化锆的稳定率约为70%,同时可得到显气孔率低,体积密度高,抗热震次数≥5次的锆质定径水口。     

Effect of flux-forming additives on the sintering temperature and the properties of a corundum-based ceramic

Conclusions The sintering behavior and the structure evolution of the corundum-based ceramics containing various flux-forming additives of eutectic compositions were studied.It was established that the addition of the flux-forming agent belonging to the CaO-B₂O₃-SiO₂-BaO system has the most favorable effect on the sintering process and the properties of the experimental corundum-based ceramic.We obtained a corundum material containing 97% Al₂O₃ and 3% flux-forming additive (consisting of 31.92% CaO, 26.25% SiO₂, 16.67% BaO, and 25.16% B₂O₃) and requiring a low temperature (up to 1500°C) for achieving complete sintering. The material possesses a fine-grained properties.Translated from Ogneupory, No. 8, pp. 31–33, August, 1986.     

添加剂对高纯氧化锆制品烧结性能的影响

以不同粒度的氧化锆砂颗粒和氧化锆细粉为主要原料,以单斜锆微粉、脱硅锆细粉、斜锆石微粉和Y2O3细粉为添加荆,分别于1 650、1 680、1 750和1 800℃下烧成后制备了高纯氧化锆制品,研究了添加剂种类对制品烧结性能的影响.结果显示:单斜锆微粉能很好地促进高纯氧化锆制品的烧结,当其占混合粉总质量的3%～8%时.高纯氧化锆制品的烧结性能达到最佳,且有些试样在低温下烧成的性能要优于未引入添加剂的试样在1 800 ℃时烧成的;脱硅锆细粉和斜锆石微粉对氧化锆制品烧结性能的影响不大;引入少量的Y2O3细粉也能显著促进高纯氧化锆制品的烧结.     

In situ synthesis of three-dimensional nanofiber-knitted ceramic foams via reactive sintering silicon foams

Three-dimensional ceramic nanofiber-assembled materials with large specific surface area and excellent thermal insulation properties are attracting increasing interests for their unique structure and promising applications. In this paper, we propose a facile methodology to fabricate three-dimensional silicon nitride nanofiber-knitted ceramic foams via in situ reactive synthesis from silicon foams. Silicon particle-stabilized foams are fabricated for the first time using long-chain surfactant cetyltrimethyl ammonium bromide as a hydrophobic modifier. First, the fabrication and stability of silicon foams are investigated. Based on the stable silicon foams, silicon nitride-based nanofiber-knitted ceramic foams are synthesized via in situ reactive sintering in nitrogen atmosphere. The novel ceramic foam materials consist of three-dimensional nanofiber-assembled strut wall and nanofiber-spheres in the pores. The diameter of obtained silicon nitride nanofibers ranges from 15 to 100 nm. The unique nanofiber-knitted foams may have potential applications in specific fields, including catalysis, adsorption, separation, and thermal insulation.     

Innovative milling of ceramic powders: influence on sintering zirconia alloys

The preparation of zirconia alloys precursors was carried out by several different methods to reduce firing times and sintering temperatures. Innovative milling processes such as mechanofusion (MF) and mechanical alloying (MA) were introduced on powders prepared from traditional oxides and from pyrolytic precursors. In order to evaluate the effect of innovative milling systems, the powders and related sintered bodies were characterized by XRD, SEM, EDAX and DSC techniques. ©     

Influence of pore distribution on the equivalent thermal conductivity of low porosity ceramic closed-cell foams

The microstructures of porous alumina materials with different porosities were established by introducing the departure factor of pore position and acentric factor of pore diameter to describe the distribution of pores in space and in size, respectively. The contribution of radiation and influence of pore distribution on the equivalent thermal conductivity were discussed based on numerical simulations by the finite volume method (FVM) considering both thermal conduction and radiation. When the pore diameter was less than 10?µm, the radiation component was less than 2%, and radiation could be neglected. Radiative heat transfer played a dominant role for materials with high porosity and large pore size at high temperatures. For micro pore materials (<?100?µm), broad pore size and non-uniform pore space distribution decreased the thermal conductivity across the entire temperature range. For materials with macro pores (>1?mm), broad pore distribution decreased the thermal conductivity at low temperatures and increased it at high temperatures. The basic prediction model of effective thermal conductivity for a two-component material, the Maxwell–Eucken model (ME1) and its modified model were corrected by introducing the pore structure factor. The results from experiments prove that the numerical values were satisfactory.     

Effects of sintering on the mechanical and ionic properties of ceria-doped scandia stabilized zirconia ceramic

The effect of conventional sintering from 1300 to 1550 °C on the properties of 1 mol% ceria-doped scandia stabilized zirconia was investigated. In addition, the influence of rapid sintering via microwave technique at low temperature regimes of 1300 °C and 1350 °C for 15 min on the properties of this zirconia was evaluated. It was found that both sintering methods yielded highly dense samples with minimum relative density of 97.5%. Phase analysis by X-ray diffraction revealed the presences of only cubic phase in all sintered samples. All sintered pellets possessed high Vickers hardness (13–14.6 GPa) and fracture toughness (~3 MPam^1/2). Microstructural examination by using the scanning electron microscope revealed that the grain size varied from 2.9 to 9.8 µm for the conventional-sintered samples. In comparison, the grain size of the microwave-sintered zirconia was maintained below 2 µm. Electrochemical Impedance Spectroscopy study showed that both the bulk and grain boundary resistivity of the zirconia decreases with increasing test temperature regardless of sintering methods. However, the grain boundary resistivity of the microwave-sintered samples was higher than the conventional-sintered ceramic at 600 °C and reduced significantly at 800 °C thus resulting in the enhancement of electrical conduction.     

Novel glass ceramic foams materials based on red mud

Glass ceramic foams were prepared using red mud and fly ash with added CaCO₃ as foaming agents. The aim of the present work was to investigate the possibility of adding red mud, an alkaline leaching waste, in the raw material for the preparation of glass ceramic foams. The results of mineralogical analyses as well as the microscopic examination showed that the use of the red mud affect the mineralogical characteristics and structures of the as produced foams. The influence of amount of red mud on the bulk density and compressive strength of samples was further evaluated. The experimental results showed that relatively low bulk density foams (0.33–0.41 g/cm³) could be obtained by using low sintering temperature (760–840 °C) when the red mud/fly ash ratio does not exceed 40:60. The reduction of sintering temperature or, above all, the reduction of the holding time, was found to limit the coalescence and significantly improve the compressive strength of the foams (0.33–2.74 MPa).     

Field assisted sintering of ceramic constituted by alumina and yttria stabilized zirconia

We show that a two-phase 50 vol% 3YSZ-alumina ceramic flash-sinters at a furnace temperature of 1060 °C under an electrical field of 150 V cm⁻¹. In contrast undoped, single-phase alumina remains immune to field assisted sintering at fields up to 1000 V cm⁻¹, although single-phase 3YSZ flash sinters at 750 °C (furnace temperature). The mechanisms of field assisted sintering are divided into two regimes. At low fields the sintering rate increases gradually (FAST), while at high fields sintering occurs abruptly (FLASH). Interestingly, alumina/zirconia composites show a hybrid behavior such that early sintering occurs in FAST mode, which is then followed by flash-sintering. The specimens held in the flashed state, after they had sintered to near full density, show much higher rate of grain growth than in conventional experiments. These results are in contrast to earlier work where the rate of grain growth had been shown to be slower under weak electrical fields.     

Reticulated open-cellular aluminum nitride ceramic foams: Effect of sintering aids on microstructural,thermal, and mechanical properties

Open-celled aluminum nitride ceramic foams were prepared by the polymer sponge replication technique involving aqueous dispersions of passivated AlN. The amount of the Y₂O₃ and Dy₂O₃ as sintering aid was varied, and the effects on the densification, microstructure formation, phase composition, and finally, the thermal conductivity were investigated. A typical thermal conductivity of 1.1 W m⁻¹ K⁻¹ was determined for foams at a porosity level of 94.3 vol.%, on average. This measured foam thermal conductivity was subsequently modeled using different porosity ↔ thermal conductivity relations considering the different hierarchical levels of porosity in these foams. From these models, the thermal conductivity of the bulk AlN strut material was determined, correlated with the strut microstructure and the phase composition, and compared to literature data.     

Effects of ceramic types on evolution of micrometer-sized features during sintering

In this work, ZnO and ZrO₂ ridges with 2 μm size are created based on a centrifuge-aided micromolding approach and then sintered with different time. Characterization of feature morphology, fidelity, grain size, relative density, and linear shrinkage has been conducted. The densification mechanisms for both ZnO and ZrO₂ are controlled by grain-boundary diffusion, but their grain growth mechanisms are dominated by gas diffusion and surface diffusion respectively. The sintering behavior for the bulk can be described with a N_g/N_b factor at 36, while for the features, a smaller N_g/N_b factor (15 for ZnO and 8 for ZrO₂) is needed. Attributed to their sintering mechanism difference, the grains in the ZnO features have a faster growth rate than those in the bulk, while the grains in the ZrO₂ features have a similar growth rate to those in the bulk. ZnO has a much faster grain growth behavior, leading to ridge fidelity loss and severe ridge destruction, while ZrO₂ has a much slower grain growth rate, resulting in high ridge fidelity and strong resistance to ridge destruction.     

Effect of addition of talc on the sintering characteristics of fly ash based ceramic tiles

The sintering characteristics of fly ash–talc mixtures having 0–100% talc (w/w) in the presence of 10% (w/w) sodium hexa meta phosphate (SHMP) have been studied. In the fly ash rich mixtures, the presence of needle shaped mullite and rhombohedral aluminum phosphate phases is responsible for providing impact strength to sintered tile bodies. On gradual addition of talc, the decrease in the concentration of sillimanite and increase in the concentration of sodium magnesium phosphate crystals is responsible for the observed improvement in the impact strength of tiles. With increase in talc content, initially the % water absorption decreases to reach a minimum for a fly ash–talc mix containing 60% (w/w talc) where after it again starts increasing. The apparent density of the tile samples increases with increasing talc content in the raw mix due to densification as well as higher density of talc as compared to fly ash.     

Effect of zirconia addition on pressureless sintering of boron carbide

This paper presents the results of experiments on pressureless sintering of boron carbide with varying addition of zirconia (ZrO₂: 0–30 wt.%). Green pellets were densified by sintering at 2275 °C in vacuum for 60 min and characterized by measurement of density, hardness, thermal conductivity and microstructure. Samples prepared with the addition of ≥5 wt.% ZrO₂ showed higher densities in the range of 93–96% ρth, compared to 86.63% ρth for boron carbide only. Addition of ZrO₂ was found to increase the hardness of sintered samples and regardless of ZrO₂ content, the hardness values ranged between 30 and 31.5 GPa. XRD of the sintered pellets showed the presence of ZrB₂. Optical microscope as well as electron probe microanalysis (EPMA) showed the presence of two phases, grey matrix with white precipitates. EPMA analysis of second phase revealed the presence of Zirconium in this phase. Fractography of boron carbide with 25% ZrO₂ showed the failure to be by mixed fracture (transgranular and intergranular). Thermal conductivity values of the samples measured in the temperature range of 400–1000 °C were marginally higher with the addition of ZrO₂.     

Determination of the porosity and pore size distribution of SiC ceramic foams by nuclear methodologies

Abstract

Abstract

Two nuclear methodologies were used for porosity and pore size distribution determination of SiC ceramic foams. Thirty samples were analysed, six of each one of the following pore densities: 30, 45, 60, 80 and 100 pores per inch (ppi). The two nuclear techniques employed were X-ray microtomography and gamma ray transmission. For the microtomography technique, the spatial resolution of the images was 32?μm. For the gamma ray transmission methodology, a NaI (Tl) scintillation detector and Am-241 radioactive source were used. The gamma transmission technique was precise for porosity determination in relationship to the nominal values supplied for the sample manufacturer. The 30 and 45?ppi samples analysed by the microtomography technique present average porosities equivalent to the nominal porosity, and the other samples present an average of 4·6% smaller values. The 30 and 45 ppi sample two-dimensional images show voids inside the structural solid material of the ceramic.     

Vacuum sintering of a ceramic based on zirconium dioxide

The results of a study of the phase composition and mechanical properties of a ceramic based on ZrO₂-Y2O₃ after vacuum sintering of powders with complex morphology in a wide range of temperatures and sintering holding times are reported. Dense ceramic materials with high mechanical properties were obtained.Translated from Steklo i Keramika, Nos. 5–6, pp. 27–29, May–June, 1994.     

Effect of pyrophyllite additions on sintering characteristics of fly ash based ceramic wall tiles

Abstract

The sintering characteristics of fly ash-pyrophyllite mixes containing 0-100 wt-% sericitic pyrophyllite have been studied, using 10 wt-% sodium hexametaphosphate as a binding agent and a firing temperature of 950°C. Increasing pyrophyllite content has been observed to increase the impact strength and apparent density and decrease the water absorption of sintered tile samples. Moreover, the presence of pyrophyllite imparted improved thermal shock resistance to the wall tile samples.