无机复合涂层对多孔氮化硅性能影响的研究

利用溶胶-凝胶法制备在多孔氮化硅的表面制备了无机复相陶瓷涂层,利用扫描电镜、红外光谱等手段研究了涂层的形貌和结构,并采用三点弯曲法研究了材料的力学性能,讨论了涂层前后基体的性能变化,结果表明:涂层对基体的抗弯有明显的提高,最大提高20%;用涂层封孔后后,材料的气孔率和吸水率明显下降,对多孔氮化硅介电性能影响很小。     

低介电高强度多孔氮化硅陶瓷的研制

以氮化硅为基体,通过加入一定量的特殊无机添加剂,控制好相关工艺参数成功地制备出低密高强低介电的多孔氮化硅材料。采用有机涂层对多孔氮化硅材料表面进行封孔处理,通过对封孔前后材料电性能的对比分析得出:涂层对封孔后表面致密的整体材料电性能影响微小。     

制备工艺对多孔Si_3N_4陶瓷介电性能的影响(英文)

采用添加成孔剂和冰冻-干燥法制备具有不同气孔率(30%～60%)的多孔Si3N4陶瓷,研究了不同制备工艺对多孔Si3N4陶瓷介电性能的影响.结果表明:不同的成型工艺制备出具有不同孔分布的氮化硅多孔陶瓷,添加成孔剂制备的多孔陶瓷具有较大的孔,洞分布在致密的基体上:冰冻-干燥法制备的多孔陶瓷具有复合孔分布.对样品的介电特性的研究表明,随着样品的气孔率增加,其介电常数和介电损耗减小;添加成孔剂制各样品的介电常数小于冰冻-干燥法制备样品,而其介电损耗较大,多孔Si3N4陶瓷的介电常数和介电损耗分别在5.21～2.91和9.6×10-3～2.92×10-3范围内变化.     

α/β相变对多孔氮化硅陶瓷介电性能的影响

采用反应烧结工艺,通过添加硬脂酸,制备孔径为0.8mm,孔隙率在55%左右的具有宏观球形孔的低密度多孔氯化硅陶瓷,研究了α/β相变对多孔氮化硅陶瓷介电性能的影响.通过调节氮化温度和时间,可得到具有不同β相相对含量(质量分数,下同)的多晶氮化硅陶瓷.结果表明:氮化温度高于1 400℃时发生α/β相变,随着氮化温度的提高和...     

氮化硅基多孔陶瓷的制备技术、孔隙结构及其相关性能

氮化硅多孔陶瓷是近年来得到广泛关注的一类新型的结构?功能一体化陶瓷材料,在航空航天、机械、化工、海洋工程等重要领域有着广阔的应用前景。本文介绍了氮化硅基多孔陶瓷的主要制备技术,回顾了氮化硅基多孔陶瓷力学性能和介电性能的研究进展。考虑到高孔隙率氮化硅基多孔陶瓷力学性能难以提高,磷酸盐结合氮化硅基多孔陶瓷已经逐渐成为新的研究热点,因此,本文进一步对磷酸盐结合氮化硅基多孔陶瓷的制备技术、力学性能、介电性能、热学性能进行了综合评述,并对氮化硅基多孔陶瓷的应用前景进行了展望。     

烧结助剂对多孔氮化硅陶瓷的力学性能及介电性能的影响

通过添加烧结助剂,采用常压烧结工艺制备出不同气孔率(19%～54%)的氮化硅陶瓷.采用Archimedes法、三点弯曲法和Vickers硬度测试法测量了材料的密度、气孔率、抗弯强度及硬度.用X射线衍射及扫描电镜检测了相组成和显微结构.用谐振腔法测试了氮化硅陶瓷在10.2 GHz的介电特性.结果表明:材料具有优良的介电性能.随着烧结助剂的减少,样品中气孔率增加,力学性能有所下降,介电常数和介电损耗降低.添加Lu2O3所制备的氮化硅陶瓷的力学性能和介电性能优于添加Eu2O3或Y2O3制备的氮化硅陶瓷.当气孔率高于50%时,多孔氮化硅陶瓷(添加入5%的Y2O3或Lu2O3,或Eu2O3,质量分数)的抗弯强度可达170 MPa,介电常数为3.0～3.2,介电损耗为0.000 6～0.002.     

常压烧结制备多孔氮化硅陶瓷研究

选用Al2O3、Y2O3、Lu2O3三种氧化物作为烧结助剂,采用凝胶注模成型和气氛保护常压烧结工艺,成功制备了具有高强度和高气孔率的多孔氮化硅陶瓷材料.本文研究了三种烧结助剂对多孔氮化硅的力学性能、介电性能和微观结构的影响,以及对氮化硅陶瓷的烧结促进作用,结果表明Y2O3具有最佳的烧结活性促进作用,其微观结构表明β-Si3N4棒状晶粒搭接结构是使多孔氮化硅陶瓷材料具有较好力学性能的重要原因.     

多孔氮化硅陶瓷制备及其性能研究进展

多孔氮化硅(Si_3N_4)陶瓷由于具有优异的力学性能、良好的抗热震和低介电常数等特点,在极端力/热环境下具有很大的应用潜力。研究表明:不同的制备工艺对多孔氮化硅陶瓷晶粒尺寸、微结构有很大影响,从而影响材料的力学性能;介电性能受气孔率、相组成影响;渗透率受气孔率、气孔尺寸、弯曲度的影响。综述了多孔Si_3N_4陶瓷的烧结工艺、成型工艺及其相关性能研究,并结合目前的研究热点,指出了未来多孔氮化硅陶瓷研究的发展方向。     

多孔氮化硅陶瓷透波材料研究进展

多孔氮化硅陶瓷透波材料具有优异的机械性能、耐热性能及介电性能,成为透波材料科学研究领域中的热点之一。本文介绍了多孔氮化硅陶瓷的主要制备技术,并对国内外多孔氮化硅陶瓷透波材料的应用研究进展进行了综述。     

固相含量对多孔Si3N4显微结构及性能的影响

以氮化硅为原料,以叔丁醇为溶剂,采用凝胶注模成型工艺,在无压烧结温度1780℃、保温时间1.5h、流动氮气气氛下,成功制备出具有高强度和高气孔率的多孔氮化硅陶瓷透波材料.通过对材料的密度、孔隙率、压缩强度和介电性能测试及显微组织观察,系统分析了固相含量对透波多孔陶瓷性能的影响.研究结果表明:随着固相含量的提高,孔隙率与...     

多孔氮化硅陶瓷的研究进展

综述了多孔氮化硅陶瓷材料的国内外研究现状和进展,介绍了多孔氮化硅陶瓷的主要制备方法,分析了微观组织对多孔氮化硅陶瓷力学性能的影响,并与其他多孔陶瓷进行了性能比较,最后展望了多孔氮化硅陶瓷的发展前景.     

碳化硅基材料抗氧化涂层的研究进展

碳化硅基材料具有优良的高温性能,但作为非氧化物陶瓷,碳化硅材料的高温氧化造成的性能衰减限制了其进一步的广泛应用.本文通过分析碳化硅的氧化机理,对比和总结了碳化硅抗氧化涂层的制备方法和涂层体系,并结合实际工作对碳化硅抗氧化涂层的研究提出了具体的见解.     

氮化硅陶瓷在四大领域的研究及应用进展

氮化硅陶瓷不仅具有较高的力学性能还具有良好的透波性能、导热性能以及生物相容性能,是公认的综合性能最优的陶瓷材料。作为轴承球的致密氮化硅陶瓷广泛应用在机械领域;作为透波材料的多孔氮化硅陶瓷广泛应用在航空航天领域;随着对氮化硅陶瓷材料的深入研究,其在导热性和生物相容性方面的优异特性逐渐被科研工作者认识并得到开发和应用。本文详细阐述了氮化硅粉体的制备方法,并综述了氮化硅陶瓷作为结构陶瓷在机械领域和航空航天领域的研究进展,此外还介绍了其作为功能陶瓷在半导体领域、生物制药领域的研究和应用现状,最后对其未来发展进行了展望。     

Conduction and Luminescent Properties of Wet Porous Silicon

Carrier transport and photoluminescence-quenching mechanisms in reverse-biased p-type porous silicon in contact with an aqueous electrolyte are investigated. Concerning transport mechanisms investigation, experiments are based on the study of the photo-induced current as a function of the porous layer thickness. The liquid-impregnated porous silicon skeleton is found under equipotential conditions. Transport of electrons (supplied by the substrate) in porous silicon is shown to be dominated by a diffusion process. Photoluminescence-quenching is investigated by using a reverse-biased p-type porous silicon illuminated at 365 and 809 nm simultaneoulsy. The first illumination generate photoluminescence and the second supplies carriers in the substrate. A progressive photoluminescence-quenching has been observed, under a constant applied voltage, by increasing progressively the electron concentration in the porous layer. This original experiment allows to reject the hypothesis of an electric-field-induced separation of carriers as the photoluminescence-quenching mechanism in wet porous silicon, while it strongly supports the mechanism based on Auger recombination.     

Thermal Shock Behavior of Porous Silicon Carbide Ceramics

Using the water-quenching technique, the thermal shock behavior of porous silicon carbide (SiC) ceramics was evaluated as a function of quenching temperature, quenching cycles, and specimen thickness. It is shown that the residual strength of the quenched specimens decreases gradually with increases in the quenching temperature and specimen thickness. Moreover, it was found that the fracture strength of the quenched specimens was not affected by the increase of quenching cycles. This suggests a potential advantage of porous SiC ceramics for cyclic thermal-shock applications.     

不同铝源对SiC/堇青石复相多孔陶瓷的制备及性能影响

以碳化硅、氮化铝、层析氧化铝、氢氧化铝、氟化铝、滑石为主要原料,石墨为造孔剂通过原位反应烧结技术制备碳化硅/堇青石复相多孔陶瓷.研究了含铝化合物种类、烧结温度、石墨含量对SiC/堇青石复相多孔陶瓷相组成、微观结构、气孔率和抗折强度的影响,同时对S0组在1200℃烧结温度下制得的SiC/堇青石复合多孔陶瓷的孔径分布进行了测试分析.结果表明:以AlN为铝源在1200℃下烧结,石墨含量在15％时,堇青石结合SiC多孔陶瓷的抗弯强度和气孔率两项综合性能达到最优,气孔率为31.99％,相应的弯曲强度86.20 MPa.S0组的平均孔径大小在3.0191 μm.     

Diamond Coating of Porous Silicon

Diamond coatings on porous silicon (PS) samples have been obtained by the hot-filament chemical vapor deposition(CVD) technique. We focused our attention on the coating morphology, showing experimentally that high quality diamond coatings may be produced with the PS sample kept at 710°C. The deposited patterns consist of polycrystalline grains with a plane interface with the PS layer.At 790°C, the quality of the coating is improved but the PS layer becomes damaged, and at 650°C the coating consists of diamond-like carbon particles. Besides the temperature, other factors such as the porosity, roughness and chemical activity of the PS layer deserve attention. We observed that one of the limiting factors of the deposition process was the high nucleation time. Two nucleation mechanisms are involved in the growth process. The first nucleation mechanism occurs on the top of the sharp PS features, subsequently to the nucleation a superficial film, and then a second nucleation mechanism occurs over this surface, which allows the growth process to continue. We also observed the presence of ablue-shift in the luminescence spectra following the coating.     

Quantitative model for the viscous flow and composition of two-phase silicon nitride-based particles in plasma-spray deposition

Silicon nitride does not melt but decomposes at 1900 °C and so thermal spraying of pure silicon nitride powder is impracticable. However, the use of silicon nitride and other non-oxide ceramics as thick, thermally sprayed coatings has considerable engineering potential owing to their unique combination of properties. This research shows that embedding fine silicon nitride particles within an oxide matrix to form composite feedstock particles enables the formation of silicon nitride composite coatings with little decomposition of the silicon nitride. Successful deposition of the coatings depends critically on the flow of the feedstock particles on impact with the substrate. This paper concerns the design of oxide matrix systems for the deposition of silicon nitride composite coatings by thermal spraying. A quantitative model is developed for the viscous flow of two-phase feedstock particles at impact. A number of matrix systems are investigated, including a series of yttria–alumina and yttria–alumina–silica compositions. The research shows that certain oxide matrices can provide the required viscous flow and protect the silicon nitride from decomposition.     

Powder-Based Tin Oxide Microcomponents on Silicon Substrates Fabricated by Micromolding in Capillaries

With the introduction of soft lithography and micromolding in capillaries, low-cost microfabrication with liquid materials has become possible. In this article, we demonstrate how to fabricate porous ceramic lines of 10 μm width and several millimeter length on silicon wafer substrates by using colloidal suspensions of tin oxide. Microchannels of poly(dimethylsiloxane) (PDMS) served as molds that were spontaneously filled owing to capillary forces with suspensions of 0.1–40 vol% solid loading. The resulting ceramic lines have a height of about 7 μm and therefore differ from the usual ceramic thin film coatings. The capillary filling characteristics were observed under the microscope, and the implications of rheology and suspension chemistry are discussed and evaluated. Using the same capillaries, even smaller lines (2–3 μm width) of powder particles could easily be prepared by adjusting only the solid content of the suspensions.