钙铝硅涂层增强建筑陶瓷的制备及性能研究

以硅灰石、石英、Al₂O₃为原料制备具有较低膨胀系数的钙铝硅质涂层。通过调整涂层的组成来对基体产生适当的压应力,从而提高陶瓷的抗折强度。研究了涂层热膨胀系数、厚度及保温时间对抗折强度的影响,分析了涂层材料的物相组成。结果表明：当涂层中Al₂O₃含量为8.1 wt%、涂层厚度约为101μm,球磨时间3 h,烧成温度为1170℃,保温为30 min时,可获得抗折强度最优的钙铝硅质涂层复合陶瓷。此时基体和涂层的膨胀系数分别为8.73×10^-6℃^-1和6.06×10^-6℃^-1,制得的涂层复合陶瓷抗折强度(103±3 MPa)比无涂层样品(66±2 MPa)提高了56%。     

Ce-Y(Ca)-TZP陶瓷及Ce-TZP/Al2O3复相陶瓷的研究与应用进展

氧化铈稳定的四方氧化锆多晶陶瓷(Ce-TZP)具有良好的抗低温老化性和很高的断裂韧性(K_IC>20 MPa·m^1/2),但是弯曲强度较低(500 MPa左右)。如何在保留Ce-TZP陶瓷的抗低温老化性和高断裂韧性的同时,提高其强度,是本领域研究人员共同关心的问题。大量研究表明,通过添加其他固溶离子(如Y³⁺)达到共稳定效果和引入第二相(如Al₂O₃)获得细晶Ce-TZP基的复相陶瓷,可以显著提高材料的断裂强度,综合改善其力学性能。本文对CeO₂与其他氧化物共稳定的ZrO₂陶瓷及Ce-TZP/Al₂O₃复相陶瓷的研究进展进行了综述,并以义齿种植和增材制造为例介绍了其应用现状。     

钼纤维对氧化锆复相陶瓷性能影响研究

研究了钼纤维含量对钼纤维-氧化锆复相陶瓷性能的影响。以单斜相为主的氧化锆粉料和钼纤维为主要原料,配以氧化钇和氧化钙为辅料,改变钼纤维的含量,通过球磨、造粒等工艺制得复相陶瓷粉料,将造粒粉料干压制成试样,在1550℃温度下保温5 h烧成并测定其性能。结果表明:当钼纤维含量占复合陶瓷试样总质量的2%时,在适当的烧结温度下,复合陶瓷试样力学性能和抗热震性能达到最佳,试样的体积密度为5.49 g/cm~3,显气孔率为6.20%,抗弯强度为380 MPa,既可以保证足够的界面结合力,同时也能避免纤维结团现象。     

裂解碳包覆对SiC纳米纤维增强SiC陶瓷基复合材料性能的影响

以SiC纳米纤维(SiC_nf)为增强体,通过化学气相沉积在SiC纳米纤维表面沉积裂解碳(PyC)包覆层,并与SiC粉体、Al₂O₃-Y₂O₃烧结助剂共混制备陶瓷素坯,采用热压烧结工艺制备质量分数为10%的SiC纳米纤维增强SiC陶瓷基(SiC_nf/SiC)复合材料。研究了PyC包覆层沉积时间对SiC_nf/SiC陶瓷基复合材料的致密度、断裂面微观形貌和力学性能的影响。结果表明:在1 100 ℃下沉积60 min制备的PyC包覆层厚度为10 nm,且为结晶度较好的层状石墨结构;相比于纤维表面无包覆层的复合材料,复合材料的断裂韧性提高了35%,达到最大值(19.35±1.17) MPa·m^1/2,抗弯强度为(375.5±8.5) MPa,致密度为96.68%。复合材料的断裂截面可见部分纳米纤维拔出现象,但SiC_nf/SiC陶瓷基复合材料界面结合仍较强,纳米纤维拔出短,表现为脆性断裂。     

稀土离子掺杂0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3陶瓷的储能性能研究

弛豫铁电陶瓷由于优异的介电和储能性能，在陶瓷储能电容器中具有较大的应用潜力。本文采用固相烧结法制备了0.05 mol Nd³⁺、Sm³⁺和Gd³⁺稀土离子掺杂的0.6BaTiO₃-0.4Bi(Mg_1/2Ti_1/2)O₃陶瓷。结果表明，所有陶瓷均表现为典型的弛豫铁电体，其中Nd³⁺掺杂的陶瓷样品具有最小的介电损耗，获得了最大的击穿场强(350 kV/cm)和储能效率(94.38%);Gd³⁺掺杂的陶瓷样品具有最大的介电常数，获得了最高的可恢复储能密度(4.33 J/cm³)。     

TiB2对无压烧结B4C–TiB2复相陶瓷结构和性能的影响

以碳化硼(B₄C)、二硼化钛(TiB₂)、碳化钛(TiC)为原料,采用无压烧结法在2 130℃制备了含20%(质量分数)和30%TiB₂的B₄C基复相陶瓷,分析所制样品的密度、硬度、弯曲强度和断裂韧性。结果表明:在2 130℃,直接加入30%的TiB₂亚微米颗粒,复相陶瓷的抗弯强度和断裂韧性分别达到277.6 MPa和5.38 MPa·m^1/2。陶瓷中颗粒拔出和裂纹微桥接对复相陶瓷增韧作用显著。B₄C–TiB₂复相陶瓷的增韧机理主要是由于TiB₂与B₄C热膨胀系数不匹配产生的残余应力导致的微裂纹增韧和裂纹偏转增韧。     

YSZ短纤维增强日用陶瓷固废再烧结材料的研究全文替换

中国传统陶瓷固废排放量巨大，陶瓷固废的资源化利用不但可解决固废丢弃填埋引起的生态环境危害，而且可节约大量天然矿物原料，带来重要的社会经济效益。本文以烧结日用陶瓷固废为主要原料，并引入少量氧化钇稳定氧化锆(YSZ)短纤维作为增强相，制备了高固废掺比的再生陶瓷材料。研究了纤维含量和烧成温度对制备的固废再烧结陶瓷材料的晶相组成、微观结构和力学性能等的影响，结果表明：YSZ纤维的添加量对固废材料的烧结性能影响不大，引入少量YSZ可明显提高废瓷再烧结材料的力学性能，其中，YSZ纤维添加量为15%并在1 250℃烧成时，样品的抗弯强度为113 MPa,断裂韧性可达2.63 MP·m^1/2。     

基于亚硝酸根插层LDHs的高效水泥降铬剂研究

基于层状双氢氧化物(LDHs)结构可重建性，制备亚硝酸根插层的LDHs。将亚硝酸根插层的LDHs作为新型降铬外加剂掺入水泥，研究LDHs降铬效率、耐存储性和球磨温度处理条件下的稳定性，并揭示其还原和固化水泥中可溶性Cr⁶⁺的作用机理。结果表明，与水拌和后LDHs-NO₂层间释放的亚硝酸根离子能够快速还原水泥中的Cr⁶⁺,有效降低可溶性Cr⁶⁺含量。掺入0.2%(质量分数)LDHs-NO₂可使水泥中可溶性Cr⁶⁺含量从40.26 mg/kg降至9.36 mg/kg,同时水泥3 d抗压强度增加约2 MPa。还原后的Cr³⁺与层板中的Al³⁺进行离子交换进入LDHs层板，从而实现稳定的化学固化。亚硝酸根插层LDHs的还原效率优于FeSO₄·7H₂O,并且在长时间储存和球磨温度处理条件下仍能保持优异的还原能力。     

晶须/纤维增强3D打印氧化锆多孔陶瓷制备及性能研究

钇稳定氧化锆（YSZ）是一种抗氧化性和耐久性优异的陶瓷,够承受高温,非常适合作热防护材料。采用乳液/泡沫模板法将其制成具有微米级孔的多孔结构,再以氧化铝晶须或氧化锆纤维作为增强相,然后结合直写成型这种3D打印成型技术,又可在毫米级孔尺度上获得设计的自由。由此制备的梯度多孔结构,不仅可以增大材料的比表面积,减小体积密度,更能大大提高多孔YSZ的力学性能。研究增强体的类型、加入量及烧结温度对多孔氧化锆陶瓷微观形貌结构的影响,分析其与抗压强度的相互作用关系。结果表明,氧化铝晶须和氧化锆纤维的加入,均能有效提高多孔氧化锆陶瓷孔的抗压强度,晶须的增强效果更好。氧化锆纤维加入量为4wt%的多孔氧化锆陶瓷孔隙率最高,抗压强度提升最小,为166.6MPa。在1500℃烧结温度下,当氧化锆纤维加入量为8wt%时,抗压强度最大,达到269.36MPa。     

Ce0.95SnxPr0.05-xO2系红色颜料及黄色氧化锆陶瓷的制备及性能探究

现如今大多数无机颜料含有Cd、Co、Cr、Hg等有毒元素，它们在使用过程中的析出会对环境和人体健康造成危害，所以需要研发环境友好型颜料来替代含有有毒元素的无机红色料。通过一定的工艺流程制备出一系列化学式为Ce_0.95Sn_xPr_0.05-xO₂(x范围为0～0.05)的颜料，得到的颜料颜色从深红色到砖红色再到浅白黄色，合成的颜料应用于彩色氧化锆陶瓷中，得到橙黄色至淡黄色到浅白黄色的陶瓷片样品。陶瓷样品的维氏硬度在11.33～12.97 GPa之间，断裂韧性在5.8～6.5 MPa?m^1/2之间；L*均在80以上，b*在19.5以上。结果表明：合成的红色颜料颜色饱满可调，可以成为传统有毒颜料的替代品；得到的氧化锆陶瓷样品均为纯四方相氧化锆，以化学式Ce_0.95Sn_0.01Pr_0.04O₂为颜料合成的陶瓷样品颜色显示效果最好(L*=83.81、a*=6.47、b*=31.77)。     

Method of Fabricating Ceria-Stabilized Tetragonal Zirconia Polycrystals

Most zirconia-based toughened ceramics need specialized processes to achieve their desired properties. In this paper, we report the fabrication of toughened ceria-stabilized tetragonal zirconia polycrystal by conventional processing, i.e., ball milling and cold-pressing followed by sintering. We believe that ball milling works here because a somewhat coarser particle size is actually beneficial in this case. Although the samples were not fully dense (they need not be), a composition of ZrO₂-12 mol% CeO₂ yielded a fracture toughness value of 14.1 MPa·m^1/2. This is comparable to values reported for materials processed by specialized techniques and can be rationalized in terms of R-curve behavior.     

A Novel Processing Route to Develop a Dense Nanocrystalline Alumina Matrix (<100 nm) Nanocomposite Material

A dense 3-mol%-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) toughening alumina matrix nanocomposite with a nanocrystalline (<100 nm) matrix grain size has been successfully developed by a novel processing method. A combination of very rapid sintering at a heating rate of 500°C/min and at a sintering temperature as low as 1100°C for 3 min by the spark-plasma-sintering technique and mechanical milling of the starting γ-Al₂O₃ nanopowder via a high-energy ball-milling process can result in a fully dense nanocrystalline alumina matrix ceramic nanocomposite. The grain sizes for the matrix and the toughening phase were 96 and 265 nm, respectively. A great increase in toughness almost 3 times that for pure nanocrystalline alumina has been achieved in the dense nanocomposite. Ferroelastic domain switching without undergoing phase transformation in nanocrystalline t -ZrO₂ is likely as a mechanism for enhanced toughness.     

Low-Temperature Processing and Mechanical Properties of Zirconia and Zirconia–Alumina Nanoceramics

The 1.5- to 3-mol%-Y₂O₃-stabilized tetragonal ZrO₂ (Y-TZP) and Al₂O₃/Y-TZP nanocomposite ceramics with 1 to 5 wt% of alumina were produced by a colloidal technique and low-temperature sintering. The influence of the ceramic processing conditions, resulting density, microstructure, and the alumina content on the hardness and toughness were determined. The densification of the zirconia (Y-TZP) ceramic at low temperatures was possible only when a highly uniform packing of the nanoaggregates was achieved in the green compacts. The bulk nanostructured 3-mol%-yttria-stabilized zirconia ceramic with an average grain size of 112 nm was shown to reach a hardness of 12.2 GPa and a fracture toughness of 9.3 MPa·m^1/2. The addition of alumina allowed the sintering process to be intensified. A nanograined bulk alumina/zirconia composite ceramic with an average grain size of 94 nm was obtained, and the hardness increased to 16.2 GPa. Nanograined tetragonal zirconia ceramics with a reduced yttria-stabilizer content were shown to reach fracture toughnesses between 12.6–14.8 MPa·m^1/2 (2Y-TZP) and 11.9–13.9 MPa·m^1/2 (1.5Y-TZP).     

Energy Crossovers in Nanocrystalline Zirconia

The synthesis of nanocrystalline powders of zirconia often produces the tetragonal phase, which for coarse-grained powders is stable only at high temperatures and transforms into the monoclinic form on cooling. This stability reversal has been suggested to be due to differences in the surface energies of the monoclinic and tetragonal polymorphs. In the present study, we have used high-temperature oxide melt solution calorimetry to test this hypothesis directly. We measured the excess enthalpies of nanocrystalline tetragonal, monoclinic, and amorphous zirconia. Monoclinic ZrO₂ was found to have the largest surface enthalpy and amorphous zirconia the smallest. Stability crossovers with increasing surface area between monoclinic, tetragonal, and amorphous zirconia were confirmed. The surface enthalpy of amorphous zirconia was estimated to be 0.5 J/m². The linear fit of excess enthalpies for nanocrystalline zirconia, as a function of area from nitrogen adsorption (BET) gave apparent surface enthalpies of 6.4 and 2.1 J/m², for the monoclinic and tetragonal polymorphs, respectively. Due to aggregation, the surface areas calculated from crystallite size are larger than those measured by BET. The fit of enthalpy versus calculated total interface/surface area gave surface enthalpies of 4.2 J/m² for the monoclinic form and 0.9 J/m² for the tetragonal polymorph. From solution calorimetry, the enthalpy of the monoclinic to tetragonal phase transition for ZrO₂ was estimated to be 10±1 kJ/mol and amorphization enthalpy to be 34±2 kJ/mol.     

Toughening of Layered Ceramic Composites with Residual Surface Compression

Effects of macroscopic residual stresses on fracture toughness of multilayered ceramic laminates were studied analytically and experimentally. Stress intensities for edge cracks in three-layer, single-edge-notch-bend (SENB) specimens with stepwise varying residual stresses in the absence of the crack and superimposed bending were calculated as a function of the crack length by the method of weight function. The selected weight function and the method of calculation were validated by calculating stress intensities for edge cracks in SENB specimens without the residual stresses and obtaining agreement with the stress-intensity equation recommended in ASTM Standard E-399. The stress-intensity calculations for the three-layer laminates with the macroscopic residual stresses were used to define an apparent fracture toughness. The theoretical predictions of the apparent fracture toughness were verified by experiments on three-layer SENB specimens of polycrystalline alumina with 15 vol% of unstabilized zirconia dispersed in the outer layers and 15 vol% of fully stabilized zirconia dispersed in the inner layer. A residual compression of ∼400 MPa developed in the outer layers by the constrained transformation of the unstabilized zirconia from the tetragonal to the monoclinic phase enhanced the apparent fracture toughness to values of 30 MPa^.m^1/2 in a system where the intrinsic fracture toughness was only 5 to 7 MPa^.m^1/2.     

Morphology and Phase Stability of Nitrogen–Partially Stabilized Zirconia (N-PSZ)

The surface layer of yttria-doped tetragonal zirconia materials that have been heat-treated with zirconium nitride was observed to consist of a nitrogen-rich cubic matrix with nitrogen-poor tetragonal precipitates. The precipitates had a thin, oblate-lens shape, similar to those observed in magnesia–partially stabilized zirconia. Because of the fast diffusion of N⁴⁻ ions, the precipitates grew rather large, up to ∼5 μm in length, and remained stabilized in the tetragonal form at room temperature. Because the nitrided layer grew in the two-phase field, the size and distribution of the precipitates each was very irregular. The nitrogen content was observed to determine the proportion of cubic and tetragonal phases in the same way as in conventional cation-stabilized partially stabilized zirconia. A ternary phase diagram for the zirconium(yttrium)–nitrogen–oxygen system was suggested to explain the concentration gradient in the cubic matrix and the phase distribution of the nitrided layer.     

Influence of milling time on the synthesis,microstructure and mechanical properties of ZrB2SiCZrO2f ceramic composites

Zirconium diboride toughened by silicon carbide and zirconia fiber (ZrB₂SiCZrO_2f) was prepared by using planetary ball mill and the effect of milling time was investigated. The results showed that both the length of fiber and particle size of ZrB₂SiC-matrix were reduced as the ball milling time increased. When milling time varied from 8 h to 12 h, the accumulated fibers and agglomerated particles were observed. The production of a homogeneous ceramic could be successfully achieved by using a combination of 20 h milling time and hot-pressing at 1850 °C for 60 min under a uniaxial load of 30 MPa. The optimal flexural strength and fracture toughness of the hot-pressed ZrB₂SiCZrO_2f ceramics reached 1084 MPa and 6.8 MPa m^1/2, respectively. The main toughening mechanisms were fiber debonding, fiber pull-out and transformation toughening. The results indicated that the ball milling technique was proposed as a potential and simple method to obtain usable quantities of ZrB₂SiCZrO_2f ceramic.     

Deformation Bands in Ceria-Stabilized Tetragonal Zirconia/Alumina: I, Measurement of Internal Stresses

The residual stresses within a deformation band in a ceriastabilized tetragonal zirconia/alumina (Ce-TZP/Al₂O₃) ceramic composite are measured by piezo-spectroscopy, in the zirconia phases from their Raman spectra and in the alumina phase from its Cr³⁺ fluorescence. The concentrations of monoclinic zirconia across the deformation band are obtained from Raman spectra recorded from locations across the band. These measurements show that the deformation bands are associated with a localization of the tetragonal-to-monoclinic transformation and that although the overall residual stress in the bands is compressive, the tensile stress in the tetragonal zirconia phase is enhanced. The experimental data are compared with the predictions of a stochastic theory for three-phase materials and with models for the stress distribution within a deformation band. The region ahead of the deformation band is subject to an additional, superimposed tensile stress whose magnitude compares favorably with the predictions of a superdislocation model presented.     

Strengthening of Porous Mullite and Zirconia CMC Matrices by Evaporation/Condensation

A processing method using evaporation/condensation sintering in an HCl atmosphere was developed for strengthening porous materials without shrinkage. Strengthening without shrinkage is useful in preventing voids and cracks that might be formed during constrained densification, e.g., a porous matrix in a continuous fiber reinforced ceramic composite. Mixtures of mullite and zirconia (monoclinic, tetragonal (3 mol% Y₂O₃), and cubic (8 mol% Y₂O₃)) were studied and exposed to HCl vapor at temperatures up to 1300°C. It was observed that the evaporation–condensation mass transport process produced a porous material with minimal shrinkage. As the crystal structure of the starting tetragonal and cubic zirconia powders did not change after extensive coarsening, it appeared that zirconium and yttrium were transported in the same proportion via evaporation/condensation. The process produced significant coarsening of the zirconia grains, which made the material resistant to densification when heated to 1200°C in air. Because the sintering produced coarsening without shrinkage, the pores also coarsened and a porous microstructure was retained. Mixtures of mullite and zirconia were used because mullite does not densify under the processing conditions used here, namely, heat treatments up to 1300°C. The mullite particles acted as a non-densifying second phase to further inhibit shrinkage when the mullite/zirconia composite was heated up to 1200°C in air. The coarsened cubic zirconia plus mullite mixture had the least densification after heat treatments in air of 100 h at 1200°C.     

Chemical Interactions Promoting the ZrO2 Tetragonal Stabilization in ZrO2–SiO2 Binary Oxides

Metastable tetragonal ZrO₂ phase has been observed in ZrO₂–SiO₂ binary oxides prepared by the sol–gel method. There are many studies concerning the causes of ZrO₂ tetragonal stabilization in binary oxides such as Y₃O₂–ZrO₂, MgO–ZrO₂, or CaO–ZrO₂. In these binary oxides, oxygen vacancies cause changes or defects in the ZrO₂ lattice parameters, which are responsible for tetragonal stabilization. Since oxygen vacancies are not expected in ZrO₂–SiO₂ binary oxides, tetragonal stabilization should just be due to the difficulty of zirconia particles growing in the silica matrix. Furthermore, changes in the tetragonal ZrO₂ crystalline lattice parameters of these binary oxides have recently been reported in a previous paper. The changes of the zirconia crystalline lattice parameters must result from the chemical interactions at the silica–zirconia interface (e.g., formation of Si–O–Zr bonds or Si–O⁻ groups). In this paper, FT-IR and ²⁹Si NMR spectroscopy have been used to elucidate whether the presence of Si–O–Zr or Si–O⁻ is responsible for tetragonal phase stabilization. Moreover, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy have also been used to study the crystalline characteristics of the samples.