立方氮化硅粉体的超高压烧结特性

以冲击波合成的立方氮化硅(γ-Si3N4)粉体为原料,添加Y2O3-Al2O3-La2O3系烧结助剂,进行了超高压烧结,研究了在不同烧结温度与压力下,烧结样品的相对密度、力学性能、物相变化及显微结构.经5.4～5.7 GPa和1670～1770 K,保温保压15 min超高压烧结后,烧结制备的氮化硅陶瓷主要由长柱状晶粒组成,显微结构均匀,y-Si3N4已完全转化为β-si3N4.烧结样品的最高相对密度与Vickers硬度分别为99.16%,23.42GPa.     

微波烧结制备陶瓷材料的研究进展

微波烧结是一种新型的利用微波加热来对材料进行烧结的方法,它是一种快速制备高质量新型材料和使传统材料具有新的性能的技术手段。简要介绍了微波烧结的发展史、基本原理、制备陶瓷材料的研究进展、微波烧结技术存在的一些问题,并对微波烧结技术的前景进行了展望。     

陶瓷材料微波烧结工艺与机理研究现状

微波烧结作为一种新型材料烧结技术,在陶瓷材料制备领域受到越来越多的关注.与传统烧结技术相比,微波烧结具有快速高效、节能环保以及改善材料微观结构,提高材料性能的优点.本文介绍了传统烧结和微波烧结的特点,对比了传统烧结和微波烧结陶瓷材料的烧结工艺和力学性能;列举了运用微波烧结法制备的典型结构陶瓷的烧结工艺及其力学性能;全面综述了陶瓷材料微波烧结机理;最后提出了微波烧结在未来发展中亟待解决的问题.     

微波烧结陶瓷结合剂金刚石砂轮研究

为了提高陶瓷结合剂金刚石砂轮的性能,采用微波烧结技术,通过一系列试验,分析了陶瓷结合剂金刚石砂轮的微波烧结温度、陶瓷结合剂含量和金刚石磨料粒度对其性能的影响。结果表明:微波烧结温度是影响陶瓷结合剂金刚石砂轮性能的最主要因素,远超其余二者;陶瓷结合剂金刚石砂轮试样的洛氏硬度和抗弯强度在740 ℃时达到极大值且气孔率较小,此时洛氏硬度为66 HRB,抗弯强度为76.5 MPa,气孔率为17.8%;由微观组织观察可知陶瓷结合剂金刚石砂轮在740 ℃时可以实现陶瓷结合剂对金刚石磨料的均匀包裹,并且气孔较少。     

烧结助剂对低温制备碳化硅多孔陶瓷性能的影响

分别采用十二烷基苯磺酸钠、氢氧化钠以及NaA分子筛残渣为烧结助剂,碳粉为造孔剂,干压法成型,在1150℃空气气氛下烧结制备碳化硅多孔陶瓷支撑体。考察了助剂添加量对微结构、平均孔径、孔隙率以及抗热震性等方面的影响;分析了添加助剂的低温烧成机理。研究结果表明：三种添加剂均有助于提高支撑体的气体渗透性、抗弯强度和耐热震性;添加NaA分子筛残渣助烧结剂获得的碳化硅多孔陶瓷各项性能最佳,气体渗透率为1300 m³/(m²·h·kPa),强度可达27 MPa,且抗热震性能良好。     

ZrO2陶瓷的微波烧结制备及其性能

以微波热解制备的氧化锆粉体为原料、氧化钇为烧结助剂,采用微波烧结方式制备氧化锆陶瓷,研究了不同氧化钇含量对氧化锆陶瓷的微波烧结行为、物相组成、显微结构及致密化的影响。结果表明:在微波烧结过程中,随着Y_2O_3含量的增加,ZrO_2陶瓷的物相从m-ZrO_2逐渐转变为m-ZrO_2与t-ZrO_2(c-ZrO_2)并存,且ZrO_2陶瓷的晶粒随着烧结助剂含量的增加而逐渐变小,样品致密度下降。当烧结温度为1 450℃时,微波烧结获得的未添加烧结助剂的样品致密度达到99%,远远高于传统电阻烧结所获得样品的致密度。     

多晶YAG陶瓷的制备及力学性能

本实验采用共沉淀方法制备YAG微粉 ,Al和Y元素分布均匀 ,在 90 0℃煅烧 2h即可全部转变为YAG粉体 ,无过渡相 .15 0 0℃热压 1h可获得致密烧结体 ,其抗弯强度为 2 45MPa ,断裂韧性为 2 .0MPa·m1 /2 ,晶粒大小为 3～ 6μm ;14 0 0℃放电等离子烧结 5min可获得相对密度为 93 %的烧结体 ,其抗弯强度为 3 4 8MPa,断裂韧性为 2 .1MPa·m1 /2 ,晶粒大小为 1～ 2 μm .     

微波烧结制备碳化硅粉体的研究

以乙炔炭黑和硅粉为原料,采用微波烧结技术合成制备了粒度不同的碳化硅粉体.研究了反应温度和保温时间对碳化硅粉体产率和粒度的影响.结果表明:在900℃反应30 min,所得产物的主要物相为β-SiC和仍残余少量金属Si.随着反应温度的升高,产物中SiC的含量不断增加,残余金属Si的含量则明显下降.当反应温度升高至1100℃以上时,则得到单相的β-SiC.在1200℃下反应5min,产物中主要物相为SiC,存在着少量未反应的金属Si,当反应时间延长到15 min时,即得到单相的β-SiC.     

一种高烧结活性氧化铝粉体的制备方法

本发明提供了一种制备高烧结活性氧化铝粉体的方法。其特征在于以含铝无机盐为主要原料，碳酸氢铵为沉淀剂，生成NH4Al(OH)2CO3，更确切地说，铝无机盐为硝酸铝，氯化铝和硫酸铝铵中一种，含铝的无机盐浓度为0．1－1mol/L，碳酸氢铵浓度为1-4mol/L，反应温度为5－50℃，沉淀陈化时间2－24h，沉淀物经去离子水洗涤至无在1100－1200摄氏度煅烧，使之转变为α－Al2O3，晶粒尺寸小于400nm的亚微米及纳米级氧化铝粉体，该方法制取的氧化铝粉体具有硬团聚少和烧结活性高的特点，非常适合于高档氧化铝陶瓷材料的制备。     

热压烧结制备纳米Y-TZP材料形貌及结构的分析

研究分析了热压烧结纳米ZrO2(3Y)粉体制备的Y－TZP材料的形貌和结构。结果发现：热压烧结制备纳米Y－TZP材料有很多新的特点,最明显的包括所得样品侧面内凹、断口轴向大气孔呈梯度分布。研究结果还表明：侧面内凹的现象主要是由于纳米粉体颗粒小、比表面能大而烧结所引起的。样品断口大气孔从外向内呈梯度分布的现象不是由样品内外压差或温差造成的,而是由于样品各部分塑性滑移不均匀的结果。     

原料预合金化对微波无压烧结金刚石工具性能的影响

以Fe₆₀Cu₄₀预合金粉和单质粉为基础原料,利用微波无压烧结在850 ℃制备了FeCu/WC基金刚石复合材料刀头。通过探讨物料在微波场中的升温特性设计了微波无压烧结制度。采用扫描电子显微镜（SEM）、万能试验机、激光拉曼光谱等表征手段,对比研究了预合金粉和单质粉微波烧结样品的组织形貌等微结构信息,并获得了样品的硬度、致密度、横向断裂强度等力学性能。结果表明,与常规烧结方法相比,微波强化烧结可将温度降低至900 ℃以下,金刚石颗粒没有出现石墨化转变;FeCu/WC基配方在850 ℃微波烧结样品的洛氏硬度、相对致密度、横向断裂强度分别达到102.7 HRB、98.5%、1 035 MPa。并对微波烧结的强化机制和原料预合金化对于基体的增强机理进行了初步探讨,微波无压烧结对于预合金粉体金刚石刀头的制备表现出良好的应用前景。     

The toughening mechanism and mechanical properties of graphene-reinforced zirconia ceramics by microwave sintering

ABSTRACT

The graphene/ZrO₂ composites were fabricated by impregnating graphene dispersion into the ZrO₂ ceramic matrix and sintered by microwave, and the microstructure and mechanical properties were investigated. The results showed that the graphene was well dispersed in the ceramic matrix and refined the grain size. The fracture toughness reached 8.62?MPa?m^1/2, confirmed by single-edge notched beam, which was 42% higher than that of the pure ZrO₂. Also, the toughening mechanisms were investigated by micro-hardness testing and showed that a combination of crack deflection, micro-crack and crack bridging increased the fracture toughness.     

烧结法制微晶玻璃的机理研究

微晶玻璃是近些年来在材料科学上的一项重大发现,在国防尖端技术和建筑业等多种领域起到了举足轻重的作用。微晶玻璃更具有高机械强度、绝缘性和良好的耐酸耐碱性等优点,本文通过烧结法就微晶玻璃的材料特征、微观结构和性能、降低烧结温度的方法等做了详细的介绍。     

Comparison of a laboratorial scale synthesized and a commercial yttria-tetragonal zirconia polycrystals ceramics submitted to microwave sintering

Conventional sintering techniques of yttria-tetragonal zirconia polycrystals (Y-TZP) ceramics have presented limitations regarding the sintering time and temperature, increasing the cost of the final dental and biomedical products. Herein, microwave sintering comes to be an interesting alternative by providing fast heating, high densification, and grain-size control. The aim of this study was to compare the effect of microwave sintering of Y-TZP dental ceramics prepared from a pre-sintered commercial block and produced from powders synthesized in a laboratorial scale by the precipitation route. The synthetized and commercial discs were submitted to microwave sintering at 1450°C and 1350°C for 15, 30, and 60 minutes. Densification, fracture toughness, grain size, and crystalline phase quantification of the sintered groups were evaluated. Both synthetized and commercial groups sintered at 1450°C for 15 and 30 minutes showed the higher densification results (98% TD). XRD quantitative phase analysis indicates that samples present 89% tetragonal and 11% cubic phases, except for the group prepared from coprecipitated powders sintered at 1450°C for 30 minutes, that presented 79% and 21% of tetragonal and cubic phases. The microwave sintering at 1450°C allows hardness and fracture toughness values comparable to conventional sintering.     

Fabrication and mechanical properties of large-scale SiC impeller via vacuum gelcasting and pressureless sintering

Impeller is the key part of centrifugal pump to convey liquid. And combined with the engineering practice, we fabricated two types of open and semi-open SiC ceramic impellers with diameter of 100 mm and 160 mm via gelcasting and pressureless sintering. B4C and C were used as the sintering additives and sprayed drying granulation method was adopted for the starting SiC powder processing. Given the size and shape complexity of impeller, the optimized pH value, dispersant content, and solid-loading content for the fabrication of the SiC impellers were determined to be 10-11, 0.8 wt%, and 40 vol%, respectively. For the open impeller, blade height, cover board thickness, drying shrinkage, and sintering shrinkage are 10.5 mm, 4 mm, 10.3%, and 21.3%, respectively. For the semi-open ones, the corresponding parameters are 41 mm, 10 mm, 10.3%, and 21.3%, respectively. The average density of the two types of impellers is 3.15 g/cm3, and the mechanical properties of both impellers, including average hardness, flexural strength, compressive strength, and fracture toughness are 2478 HV, 436 MPa, 2093 MPa, and 3.17 MPa·m1/2, respectively. All variation coefficient values are smaller than 5%, which indicates a good uniformity in densities and mechanical properties of both the impellers.     

Fabrication of ceramic bioscaffolds from fly ash cenosphere by susceptor-assisted microwave sintering

Cenospheres (CS) are ceramic hollow microspheres and have been used to prepare composite foams for applications such as medical implants. However, its potential standalone application in the biomedical field is not fully explored. Herein, a susceptor-assisted microwave (SMW) sintering approach was used for producing CS foam scaffolds. Owing to the hybrid heating mechanism offered by the SMW process, sintering of the low-dielectric cenospheres was realized. We found that sintering was initiated at a lower temperature (1100 °C) compared to conventional heating (1250 °C) as reported in the literature, probably due to the lower activation energy required by SMW sintering. The physical and compositional properties of the sintered CS specimens were examined, and in vitro studies were performed. The as-fabricated CS foam possessed minimal effect on cell viability. Cells migrated and adhered well within the pores of the specimens, which indicates the potential of the CS as scaffold materials for cell engineering applications.     

Effects of sintering temperature on structural and electromagnetic properties of MgCuZn ferrite prepared by microwave sintering

Nanocrystalline magnesium–copper–zinc (Mg_0.30Cu_0.20Zn_0.50Fe₂O₄) ferrites were prepared by microwave sintering technique. The effects of the sintering temperature on particle size and magnetic properties were investigated. In this article, optimum sintering temperature required for MgCuZn ferrite system for obtaining good electromagnetic properties, suitable for applications in low temperature co-fired ceramics (LTCC) chip components was studied. The grain size, initial permeability, dielectric constant and saturation magnetisations were found to increase, and dielectric loss was found to decrease with the increasing sintering temperature. Mg–Cu–Zn ferrites with a permeability of μ?=?1110 (at 1?MHz) were fully densified at the standard LTCC sintering temperature of 950°C.     

Fabrication of highly dense Si3N4 via record low-content additive system for low-temperature pressureless sintering

Dense Si₃N₄ ceramics were fabricated by pressureless sintering at a low temperature of 1650°C with a short holding period of 1 h under a nitrogen atmosphere. The role of ternary oxide additives (Y₂O₃–MgO–Al₂O₃, Y₂O₃–MgO–SiO₂, Y₂O₃–MgO–ZrO₂) on the phase, microstructure, and mechanical properties of Si₃N₄ was examined. Only 5 wt.% of Y₂O₃–MgO–Al₂O₃ additive was sufficient to achieve >98% of theoretical density with remarkably high biaxial strength (∼1200 MPa) and prominent hardness (∼15.5 GPa). Among the three additives used, Y₂O₃–MgO–Al₂O₃ displayed the finest grain diameter (0.54 μm), whereas Y₂O₃–MgO–ZrO₂ produced the largest average grain diameter (∼0.95 μm); the influence was seen on their mechanical properties. The low additive content Si₃N₄ system is expected to have superior high-temperature properties compared to the system with high additive content. This study shows a cost-effective fabrication of highly dense Si₃N₄ with excellent mechanical properties.     

Increasing the tensile strength of oxide ceramic matrix mini-composites by two-step sintering

Adapting conventional sintering (CS) techniques of monolithic ceramics for the production of oxide ceramic matrix composites (Ox-CMCs) comes along with a few drawbacks, such as fiber degradation. Thus, the applicability of two-step sintering (TSS) for the production of Ox-CMCs based on Nextel™ 610 fibers and porous alumina matrix is investigated in this study for the first time. Uniaxial tensile tests were performed to evaluate the performance of mini-composites produced by TSS and compared with those produced by CS. Parameters known for influencing the mechanical behavior of the mini-composites, such as grain size, porosity, shrinkage, as well as matrix properties, were analyzed. Both sintering techniques resulted in similar grain size distributions, whereas TSS showed higher total porosity and lower amount of sintering-induced cracks. As a result, TSS samples showed a higher tensile strength of 230±27 MPa when compared to 133±8 MPa for CS. In general, it was observed that most of the densification happens during the first phase of TSS, while the matrix is slowly strengthened during the second step. Therefore, the reported TSS process is a very promising and easy-to-apply heat treatment for producing Ox-CMCs with controlled microstructure.     

Improvement of the hydroxyapatite mechanical properties by direct microwave sintering in single mode cavity

The main purpose of this study consists in investigating the direct microwave sintering of hydroxyapatite (HA) in a single mode cavity. Firstly, stoichiometric HA powders were synthesized by a coprecipitation method from diammonium phosphate and calcium nitrate solutions and shaped by slip-casting. Then, using the one-step microwave process, dense pellets with fine microstructures were successfully obtained in short sintering timespan. A parametric study permitted to determine the influence of powder grain size, sintering temperature and dwell time on the sintered samples microstructures. The Young's modulus (E) and hardness (H) were measured by nanoindentation and the values discussed according to the microstructure. Finally, the resulting mechanical properties determined on the microwave sintered samples (E = 148.5 GPa, H = 9.6 GPa, σ_compression = 531.3 MPa and K_IC = 1.12 MPa m^1/2) are significantly higher than those usually reported in the literature, whatever the sintering process, and could allow the use of HA for structural applications.