放电等离子烧结和快速热压工艺制备具有低或负热 膨胀系数钨酸锆块体(英文)

采用快速热压工艺(放电等离子烧结和感应加热热压),利用ZrW2O5粉料制备了负热膨胀系数(coefficient of thermal expansion,CTE)钨酸锆 (ZrW2O8)陶瓷体材料.这两种工艺可在烧结过程中保留负CTE材料钨酸锆所需的结构和相组成.结果表明:改变工岂参数,如热压温度和保温时间, 可以调节ZrW2O8陶瓷的CTE从-9×10-6/K到+9×10-6/K变化.首次采用ZrW2O8作为填料与轻金属钛复合制备了零膨胀复合材料.     

锂辉石对红柱石基复相陶瓷烧结性能的影响

以红柱石、微米级PSZ(部分稳定氧化锆)、苏州土、滑石为主要原料,添加适量锂辉石,采用反应烧结法制备了红柱石基复相陶瓷。研究了锂辉石的添加量对红柱石基复相陶瓷烧结性能和力学性能的影响。利用X射线衍射仪、扫描电子显微镜以及万能试验机表征样品的物相组成、微观结构和力学性能。结果表明:在1400℃烧结温度下保温2 h获得了性能优良的红柱石基复相陶瓷,样品吸水率为0.28%,气孔率为0.74%,体积密度为2.61 g/cm~3,抗折强度达96.08 MPa;随着锂辉石添加量的增大,样品的体积密度增大。XRD、SEM分析结果表明,复相陶瓷的主晶相为莫来石和锆英石晶体,锆英石和α-方石英均布在莫来石的骨架中,提高了复相陶瓷的机械性能和断裂性能。红柱石复相陶瓷是一种有广阔应用前景的高温结构陶瓷材料。     

成型工艺对莫来石增强磷酸铬铝复相陶瓷的性能影响

以磷酸铬铝、氢氧化铝、熔融石英粉为原料,采用干压成型、注凝成型与等静压成型制备原位莫来石增强磷酸铬铝复相陶瓷,并进行对比研究。研究结果表明,等静压成型制备复相陶瓷的机械性能均优于干压成型和注凝成型制备的复相陶瓷,且复相陶瓷的介电常数比干压成型和注凝成型的复相陶瓷高。干压成型制备的复相陶瓷不够致密均匀,气孔较多;注凝成型和等静压成型制备的复相陶瓷结构均匀致密且气孔较少,复相陶瓷的晶粒发育较完善,短棒状莫来石晶粒和球状磷酸铬铝晶粒分布均匀且清晰可见。通过制品的性能参数和显微结构的比较,等静压成型制备的素坯结构均匀致密,强度高,收缩率小,等静压成型制备的莫来石增强磷酸铬铝复相陶瓷综合性能最优,复相陶瓷的密度、介电常数、维氏硬度及弯曲强度分别为2.85 g·cm~(-3)、4.76、6.2 Gpa、151 Mpa。     

锂辉石对碳化硅基复相陶瓷热膨胀及显微结构的影响

采用近零膨胀材料β-锂辉石作为高温结合剂，通过常压烧结制备碳化硅基复相陶瓷材料，研究β-锂辉石质量分数为25%～40%、烧结温度为1 500～1 600℃复相陶瓷的致密性、显微结构和热膨胀系数。结果表明：β-锂辉石高温熔融产生液相能包裹碳化硅颗粒，烧结过程中锂辉石的相变在一定程度提高了材料致密性。复相陶瓷中玻璃相含量是引起热膨胀系数升高的主要原因。当β-锂辉石添加比为35%时，在1 600℃烧结下的复相陶瓷的热膨胀系数低于1 550℃,且杨氏模量有小幅增加。     

注凝成型制备莫来石–钛酸铝复相陶瓷(英文)

引入10%(摩尔分数,相对于A12O3,下同)MgO和15%SiO2双组分添加剂合成了钛酸铝粉体.采用不同质量比的钛酸铝粉体和工业莫来石,用干压和注凝成型工艺制备了莫来石-钛酸铝(mullite-aluminium titanate,MAT)复相陶瓷.用X射线衍射分析了双组分添加剂对钛酸铝相组成和热稳定性的影响.通过扫描电镜表征了MAT复相陶瓷的微结构.研究了钛酸铝含量对采用于压、注凝2种成型工艺制备的MAT复相陶瓷的弯曲强度和平均热膨胀系数(室温～1 000℃)的影响.结果表明:MgO和SiO2双组分添加剂促进了钛酸铝的形成,增强了钛酸铝的热稳定性.通过注凝成型制备的MAT复相陶瓷比于压成型制备的MAT复相陶瓷具有史均匀的结构和更高的机械性能.当铸酸铝含量为lO%(质量分数,下同),运用注凝成型工艺 制备的MAT复相陶瓷的弯曲强度最大,达110.05 Mpa.     

红柱石基刚玉-莫来石复相陶瓷的显微结构及性能

以红柱石颗粒为主要骨料,辅以莫来石颗粒和刚玉颗粒,硅微粉、铝微粉为基质料,经混合、困料及成型后,经不同温度下烧成4h,制得莫来石基刚玉-莫来石复相陶瓷,分析了烧成温度对复相陶瓷的物相组成、显微结构、烧成性能、力学性能及热学性能。结果表明:红柱石在高温下转化成针状和柱状莫来石改善复相陶瓷的烧成性能和抗热震性能;在1480℃烧成时,红柱石刚玉-莫来石复相陶瓷具有优越性能,其抗折强度为15.4MPa,耐压强度为91.6MPa,热膨胀系数为5.5×10-6/K,1100℃下水冷的抗热震次数达到99次。     

透锂长石-磷酸盐质复合低膨胀陶瓷的研究

以透锂长石、华林高岭、贵州高岭、广西滑石和山西紫木节为主要原料,添加适量的人工合成低膨胀磷酸锆钠(NaZr2(PO4)3),采用普通陶瓷工艺,制备了透锂长石-磷酸盐质复相低膨胀陶瓷材料.研究了合成温度对磷酸锆钠合成的影响,结果表明1450℃保温1 h时合成的NaZr2(PO4)3的含量最多,其热膨胀系数最低.当添加5wt%的合成磷酸盐后,在1250℃下保温30min,可以制成热膨胀系数为1.38×10-6/℃的透锂长石-磷酸盐质复相低膨胀陶瓷.     

莫来石含量对堇青石-莫来石复相陶瓷性能的影响

以合成堇青石(≤0.074 mm)和合成莫来石(0.45～0.9 mm)为主要原料,a-Al2O3微粉(≤0.044 mm)、镁砂(≤0.054 mm)和熔融石英(≤0.054 mm)为添加剂,经细磨、造粒、成型后,于1 370℃4 h烧成后制备了莫来石质量分数分别为15%、20%、25%、30%、35%和40%的堇青石-莫来石复相陶瓷材料,研究了莫来石含量对复相陶瓷材料烧结性能、抗折强度、热膨胀性及抗热震性的影响.结果表明:随着莫来石含量的增加,堇青石一莫来石复相陶瓷材料的体积密度、显气孔率和热膨胀系数都呈上升趋势,而抗折强度呈降低趋势;适当提高莫来石含量有利于复相陶瓷材料的抗热震性,当莫来石含量达到30%时,材料的抗热震性最好.     

磷酸锆材料及其应用

本文综述了磷酸锆合成方法以及磷酸锆在高温区的显微结构对热膨胀系数、强度的影响状况。并介绍了磷酸锆陶瓷、磷酸锆——锆英石复合陶瓷、磷酸锆——氧化铝复合陶瓷的研制与应用。     

氧化锆-莫来石复合材料的机械性能和热性能

以ZrO2和电熔莫来石为主要原料,制备出了氧化锆-莫来石复合材料.研究了不同温度下ZrO2添加量对莫来石陶瓷的抗弯强度(σ)、断裂韧性(KIC)和热膨胀系数(CTE)的影响.结果发现,ZrO2的加入促进了莫来石陶瓷的烧结.1550℃下添加20wt%ZrO2的试样的σ和KIC最高分别达到268.23MPa和4.05MPa·m1/2,针状莫来石晶体交错排布以及亚微米级ZrO2颗粒的钉扎作用是材料强度和韧性提高的主要原因.材料的线性热膨胀系数随着ZrO2添加量的增加而增大.     

Development of low thermal expansion mono crystalline Sr-feldspar phase via Sr-cordierite ceramic/borosilicate glass composite

The present work focuses on fabrication of low thermal expansion monoclinic Sr-feldspar through sintering of Sr-cordierite ceramic/borosilicate glass composite. The prepared composites were sintered between 1200 and 1350?°C. Bulk density and apparent porosity of sintered composites were measured according to Archimedes technique. Phase composition and microstructure of sintered composites were tested by X-ray diffraction and scanning electron microscope attached with EDAX unit. Thermal expansion coefficient and dielectric constant of sintered composites were also determined. The results revealed that mono crystalline Sr-feldspar was formed after sintering up to 1350?°C especially in the composites that contain higher ceramic content. As indicated from the result of microanalysis conducted by EDAX, the obtained Sr-feldspar was deficient in SiO₂ and SrO. In the composites with higher glass content, little amounts of quartz or cristobalite were also formed, depending on the cooling conditions. The sinterability was increased with increasing sintering temperature and decreased with increasing ceramic content. The obtained sintered composites exhibited low thermal expansion coefficient and dielectric constant. The composite that contains 90% ceramic exhibited thermal expansion coefficient 2.533?×?10^?6 °C^?1 and dielectric constant value 8.42.     

Thermal expansion of β-eucryptite in oxide-based ceramic composites

This paper presents an experimental investigation on the thermal expansion behaviour of β-eucryptite (E) when it is used for processing alumina/β-eucryptite (AE) or zirconia/β-eucryptite (ZE) composites. Composite materials were prepared from a β-eucryptite powder synthetised in our laboratory and commercially available alumina or zirconia nanopowders. In order to preserve the β-eucryptite crystalline phase in sintered materials, the pressureless sintered step was performed at relatively low temperatures (<1300 °C). It is experimentally shown that in well-densified oxide-based composites, the β-eucryptite lost its slightly negative thermal expansion coefficient. This behaviour could be related to compressive residual stresses applied on β-eucryptite grains due to the thermal expansion mismatch between alumina or zirconia and the β-eucryptite.     

堇青石基低膨胀陶瓷材料研究

堇青石是一种优异的抗热震性原料,天然矿物原料很少,一般采用人工合成方法制取。纯堇青石烧成范围非常窄,难以获得致密烧结体。将堇青石原料与磷酸盐,锂铝酸盐复合烧结。可以降低材料的烧结温度,提高其密度,同时仍具有低的膨胀系数。     

Sintering and properties of borosilicate glass/Li-Na-K-feldspar composites for electronic applications

Glass/ceramic composites are considered as one of the most important materials for electronic applications. In the present work, an attempt for using Li-Na-K containing feldspar in addition to borosilicate glass to fabricate glass/ceramic composites having good properties was conducted. Firstly, the glass frit was prepared and grinded by high energy ball mill to get nano powder. Then, five designed batches of glass/feldspar composites containing 10, 20, 30, 40 and 50 wt% feldspar were mixed, pressed and sintered at 850 °C. Bulk density and apparent porosity of sintered specimens were determined by Archimedes method. Identification of the formed phases was examined by X-ray diffraction (XRD) analysis. Microstructure of sintered bodies was examined by scanning electron microscope. Microhardness of sintered samples was determined using Vickers indentation technique whereas the fracture toughness was determined by Indentation Fracture (IF) method. The dielectric constant of sintered composites was measured at 1 MHz. The thermal expansion coefficient (TEC) was also measured in the temperature range from room temperature to 1000 °C. The results revealed that Li-Na-K feldspar and borosilicate glass were successfully used to fabricate composites with good electrical properties and thermal expansion suitable for electronic applications. The inhibition of cristobalite amount and the formation of beta spodumene in addition to the quartz were responsible for the improvement of the electrical and thermal properties. The formed amount of beta spodumene was the ideal amount after which the higher amount can cause crack in the body due to the volume change occurred by the differences in thermal expansion of alpha and beta spodumene.     

Mullite/ β-spodumene composites: Preparation and characterization

Mullite/ β-spodumene composites were fabricated by the addition of 5 up to 20 mass% β -spodumene powder to mullite matrix. Both mullite and β-spodumene were prepared by sol-gel technique. The batches were uniaxially pressed into discs and rectangular bars, then pressureless sintered at 1400 °C up to 1700 °C for 1 h. Mechanical and thermal properties, as well as microstructure and phase composition were carried out on the sintered composites. The results show that although the increase in the soft β-spodumene reduces the hardness and the thermal expansion of the composites, they lower the firing temperature and enhance the flexural strength. The study indicates that β-spodumene content has a noticeable effect on the composites thermal expansion coefficient. It also shows that it is possible to tailor mullite/ β-spodumene composite with adjusted thermal expansion coefficient by changing the mullite to β-spodumene ratio.     

Reaction sintered zirconium titanate-zirconia bulk materials from 3Y2O3-stabilized zirconia and TiO2. Phase composition and their potential for thermal shock applications

This work evaluates the potential of zirconium titanate-zirconia composites for thermal shock. Materials with Zr_0.97Y_0.03O_1.985:TiO₂ molar ratios 50:50 (Z(Y)T50) and 70:30 (Z(Y)T70) were obtained from Y₂O₃ (3 mol%)-stabilized ZrO₂ and TiO₂ mixtures colloidal processed and reaction sintered at 1773 K with low cooling rate (2-5 K/min). The crystalline phases and their unit cell parameters were determined by Rietveld analysis of high resolution X-ray diffraction patterns. The zirconium titanate phase in these materials is o-TiZrO₄, being the major phase in Z(Y)T50 in which c-ZrO₂ is secondary phase. Z(Y)T70 has t-ZrO₂ as main phase, o-TiZrO₄ as secondary phase and c-ZrO₂ and m-ZrO₂ as minor phases. The Hasselman thermal shock resistance factors, calculated using the experimental values of the involved properties, Young's modulus, thermal expansion coefficient, and fracture strength, have demonstrated the high potential of zirconia-zirconium titanate composites for thermal shock applications in oxidizing atmospheres.     

Effect of Ni additives on pressureless sintering of SHS ZrB2

Abstract

Pressureless sintering of ultrafine zirconium diboride ZrB₂ produced by self-propagating high temperature synthesis (SHS) was carried out over a temperature range of 1573 to 1873 K using a nickel additive. The additive improved densification behaviour and a maximum densification of 88% was achieved at 1873 K. The XRD pattern showed formation of Ni₃Zr phase during pressureless sintering. The microhardness of sintered ZrB₂ was found to increase with Ni content and a maximum hardness of 1150 kg mm^?2 was found at 40 wt-%Ni addition. The coefficient of thermal expansion of different sintered samples was also investigated.     

Effects of barium zirconium titanate on the properties of β-tricalcium phosphate bioceramics

In the present work, a new composite between β-tricalcium phosphate (a bioceramic material) and barium zirconium titanate (a ferroelectric material) were fabricated. Beta-tricalcium phosphate (β-TCP) powder was synthesized from egg shells while barium zirconium titanate powder was synthesized from metal oxide powders. The composites were fabricated by a solid-state reaction method. Effects of barium zirconium titanate on many properties of the composites were investigated. Barium zirconium titanate additive improves the electrical properties of the composites such as dielectric, ferroelectric and piezoelectric properties. Furthermore, the mechanical properties, such as hardness are improved by the additive. In-vitro bioactivity test suggests that β-tricalcium phosphate has a higher apatite forming ability as compared to the BZT. The obtained results indicate that the composites are a promising biomaterial candidate.     

Sintering and Mechanical Properties of Yttria-Doped Tetragonal ZrO2 Polycrystal/Mullite Composites

Yttria-doped tetragonal ZrO₂ polycrystal (Y-TZP)lmullite composites were sintered at 1450° to 1500°C in air to disperse rodlike mullite grains at the grain boundary of Y-TZP and the mechanical and thermal properties were investigated. The aspect ratios of mullite grain were >2. High fracture strength of 1000 MPa and fracture toughness of 12 MPa·m^1/2 were obtained by dispersing <20 vol% of mullite into Y-TZP. The thermal expansion coefficient of Y-TZP/mullite composites decreased with increasing mullite content. The thermal shock resistance of Y-TZP was greatly improved by dispersion of rodlike mullite grains.     

Development of cordierite/mullite composites using industrial wastes

Ceramics containing cordierite and mullite as their principal phases are promising for many applications, due to properties such as a low coefficient of thermal expansion, high durability, low dielectric constant, resistance to thermal shock, and refractoriness. The objective of this study was to produce ceramic composites suitable for use as refractory materials. The raw materials were subjected to chemical characterization and the formulations to physical, chemical, and mineralogical characterization. The specimens were formed by pressing, dried at 110°C, and sintered from 1150°C to 1300°C for 2 hours. The following properties were then determined: linear shrinkage, water absorption, apparent porosity, and flexural modulus of rupture. The phases formed, crystal morphology, and coefficient of thermal expansion were evaluated. The cordierite and mullite phases were observed in all formulations at 1250°C and 1300°C. The results obtained from the formulations with a higher content of fine kaolin residue suggest that these formulations have the potential to be used for the manufacture of refractory materials such as furnace rollers and supports.