Liquid Precursor Infiltration Research Articles

The rising crack resistance curve behavior and mechanism of La2O3 doped zirconia toughened alumina composites prepared via vat photopolymerization based 3D printing

In this study, we combined liquid precursor infiltration of high introduction amounts of bi-additives (20 wt%) and vat photopolymerization-based 3D printing to fabricate zirconia toughened alumina, and the infiltration systems consist of the four following systems Zr4+/La3+, Zr4+/Ce4+, Zr4+/Gd3+, and Zr4+/Er3+. The sample immersed with Zr4+/La3+ shows intense peaks of m-ZrO2 phase compared to the other samples while a new phase of rod-like LaAl11O18 grain occurs in the Zr4+/La3+ immersed sample, the existence of which could be confirmed by XRD and EDS. The fracture toughness of the Zr4+/Ce4+, Zr4+/Gd3+, and Zr4+/Er3+samples remained basically unchanged versus the crack size, with the fracture toughness between 4 MPa m1/2 and 5 MPa m1/2; while the measured fracture toughness values for the Zr4+/La3+ system show a rising crack resistance curve behavior, with the toughness enhanced from 6.37 MPa m1/2 to 8 MPa m1/2. The obvious enhancement of the toughness could be attributed to thermal expansion misfit and rod-like LaAl11O18 in the Zr4+/La3+ system. The toughening mechanism and the effect of residual stresses on the fracture mode are discussed on the basis of theoretical calculation and analysis. The rising crack resistance curve behavior could provide a new toughening strategy in ceramic 3D printing.

Comparative study of interphase evolution in polysiloxane resin-derived matrix containing carbon micro and nanofibers during thermal treatment

The work presents the results of research on composite materials made of silicon-containing polymer-derived ceramic matrix composites (PDC-Cs) and nanocomposites (PDC-NCs). Carbon micro and nanofibers (CFs and CNFs) were used as reinforcements. The interactions between carbon micro and nanofibers and polysiloxane matrix, as well as interphase evolution mechanism in composite samples during their heating to 1000 °C were studied. CF/resin and CNF/resin composites were prepared via liquid precursor infiltration process of unidirectionally aligned fibers. After heating to 700 °C–800 °C, decomposition of the resin in the presence of CNFs led to the formation of fiber/organic-inorganic composites with pseudo-plastic properties and improved oxidation resistance compared to as-prepared fiber/resin composites. The most favourable mechanical properties and oxidation resistance were obtained for composites and nanocomposites containing the maximum amount of carbon nanoparticles precipitated in the SiOC matrix during the heat treatment at 800 °C. The precipitated carbon phase improves fiber/matrix adhesion of composites.

Preparation of alumina-toughened zirconia via 3D printing and liquid precursor infiltration: manipulation of the microstructure, the mechanical properties and the low temperature aging behavior

In this study, we propose an integrated approach which combines 3D printing and liquid precursor infiltration together to prepare alumina-toughened zirconia (ATZ) composite. Controllable manipulation of the microstructure of the composite could be realized through different infiltration times and sintering temperature. The 3D-printed ATZ with infiltration and post-CIP sintered at 1550 °C possesses the highest relative density (98.11%), hardness (12.65 ± 0.24 GPa) and fracture toughness (6.42 ± 0.33 MPa m1/2). The rates of increase in the performance compared with the undoped zirconia sintered at 1550 °C are 1.8%, 8.4% and 34.6%, respectively. The dominated toughening mechanism of ATZ could be attributed to the effect of Al2O3 inclusion on crack deflection and energy absorption. The 3D-printed ATZ sample with infiltration followed by CIP sintered at 1550 °C shows the lowest aging rate and the lowest phase transformation depth compared with 3Y-TZP (Tetragonal Zirconia Polycrystal). Our integrated approach could not only realize the complex and ultrafine shape free of molds, but also suppress the low temperature aging behavior of dental implants, which has baffled dentists for a long time.

Ca-P spots modified zirconia by liquid precursor infiltration and the effect on osteoblast-like cell responses.

Ca-P spots modified zirconia by liquid precursor infiltration and the cell responses were investigated. Pre-sintered zirconia specimens were immersed in Ca-P precursor solution. After dense sintering, scanning electron microscopy showed Ca-P spots were formed on the zirconia and anchored with zirconia substrates. The distribution density was increased with the extension of immersion time. Energy dispersive spectrometer confirmed the stoichiometric Ca/P ratio was about 1.67. After hydrothermal treatment, Ca-P spots turned into rod crystals where diffraction peaks of tricalcium phosphate and hydroxyapatite were detected by X-ray diffraction, and Ca2+ and PO43- release decreased slightly (p>0.05). There was no significant decrease on three-point bending strength (p>0.05). Osteoblast-like MC3T3-E1 cells attached and spread well and showed higher proliferation on Ca-P spots modified zirconia (p<0.05), though its initial alkaline phosphatase activity was not significant high (p>0.05). In conclusion, Ca-P liquid precursor infiltration is a potential method to modify the zirconia ceramics for improving bioactivity.

Fabrication of high-performance Al2O3-ZrO2 composite by a novel approach that integrates stereolithography-based 3D printing and liquid precursor infiltration

In this research, we creatively integrate the traditional methods of liquid precursor infiltration plus in-situ precipitation with stereolithography-based 3D printing for the fabrication of Al2O3-ZrO2 ceramics to ensure the homogeneous distribution of ZrO2 particle in the alumina matrix. Our characterization results shows that this combination leads to the materials with significantly better performance. The Al2O3 specimen is soaked in a Zr4+ ion solution to induce infiltration, in-situ precipitation and then sintered. X-ray diffraction analysis of the thus-treated sample indicated that Al2O3 was the primary phase and t-ZrO2 was the secondary phase. Microstructural and EDS analysis showed that the ZrO2 particles were homogeneously distributed in the Al2O3 matrix, leading to inhibited grain growth. The samples soaked in solutions for different Zr4+ concentrations and sintered both at 1450 °C and 1550 °C showed improved mechanical properties as compared to those of pure alumina. Futhermore, the sample infiltrated using the solution with a concentration of 1.5 mol/L and sintered at 1450 °C showed similar fracture toughness (4.97 MPa m1/2) with the sample sintered at 1550 °C (5.06 MPa m1/2) but much better hardness (20.95 Gpa) than the sample sintered at 1550 °C (19.71 GPa). Therefore, this method could not only enhance the mechanical properties via introducing the second phase, but also lowers the sintering temperature by at least 100 °C, which would be beneficial for energy conservation and leads to significant advances in the 3D printing of ceramic components.

Fabrication of fine-grained alumina ceramics by a novel process integrating stereolithography and liquid precursor infiltration processing

In this study, we report a novel approach, integrating stereolithography and liquid precursor infiltration techniques, to fabricate fine-grained alumina ceramics. The XRD patterns of the sample immersed with Zr4+ or Zr4+ (Y3+) show that the sintered body contains Al2O3 and t-ZrO2 as the major phase and minor phase, respectively. Moreover, the t-ZrO2 phase in the sample immersed with Zr4+ (Y3+) shows intense peaks compared to the composite immersed with Zr4+. On the other hand, the sample immersed with Mg2+ contained Al2O3 and MgAl2O4 as the major phase and minor phase, respectively. The microstructure of the sample immersed with Zr4+ shows that ZrO2 particles are homogeneously distributed in the Al2O3 matrix, thus inhibiting the grain growth of alumina particles. Moreover, the sample immersed with Mg2+ shows a more dense and fine-grained structure. Compared to the non-infiltrated sample, the average grain size of the alumina sample immersed with Zr4+ or Mg2+ decreased. The sample infiltrated with Zr4+ (Y3+) had the smallest alumina average grain size of 1.14µm. The ceramics prepared by infiltration showed a higher hardness (19.54GPa), but a slightly lower fracture toughness (4.02MPam1/2) compared to the samples (17.2GPa, 4.13MPam1/2) without infiltration.

Effect of Cu particles on the ablation properties of C/C composites

To improve the ablation property, Cu particles were introduced into carbon/carbon (C/C) composites through liquid precursor infiltration combined with in-situ reaction. Compared to pure C/C composites, the modified composites displayed better mechanical property and ablation resistance under oxyacetylene torch when the Cu content was below 8 wt. %. For C/C–Cu composites with 8 wt. % Cu, a 14% decline of linear ablation rate was obtained while defective fibers and laminar matrix survived after ablation. Analyses of ablation behavior depending on ablation time indicated that overflowing of Cu gas weakened the scouring of ablation gas and the Cu gas reduced the partial pressure of oxidizing species, which led to the improved ablation property.

Application of Doping Ceramics via Infiltration on Translucent Alumina Ceramics

The feasibility to homogeneously incorporate additives and fabricate translucent alumina ceramics via liquid precursor infiltration technique was substantiated.Pre-sintered alumina compacts with various thickness values were infiltrated with aqueous yttrium nitrate solutions of different concentrations under various conditions.Line-scanning result of yttrium along the sample depth direction was investigated to characterize the doping homogeneity.It is found that better distribution homogeneity and more stringent control of a desired amount of dopants can be realized as the sample thickness and the solution concentration are decreased.By assuming all pores are open and completely saturated,the theoretical model is proposed to predict the amount of incorporated species by infiltration.Finally,translucent alumina ceramics were fabricated.Compared with ball-milling prepared counterparts,samples with improved microstructure and enhanced optical properties are achieved by infiltration.

Synthesis of mullite bonded porous SiC ceramics by a liquid precursor infiltration method: Effect of sintering temperature on material and mechanical properties

Mullite bonded porous SiC ceramics were synthesized by infiltrating a SiC porous compact with a liquid precursor of mullite followed by sintering at 1300–1500°C in air. Different volume fractions (0–0.26%) of petroleum coke powder were used as pore former. SiC particles bonded by mullite and oxidation derived SiO2 formed an interconnected porous network. Porosity varied in a range of 31–48vol%. The flexural strength and the Young's modulus of the porous ceramics varied in the ranges of 19.3–43.8MPa and 16.6–42.9GPa respectively and the mechanical property–porosity relationship could be explained by the minimum solid area (MSA) model.

Fabrication of coloured zirconia ceramics by infiltrating water debound injection moulded green body

The authors developed a new technique combining ceramic injection moulding and liquid precursor infiltration, presenting a new strategy for fabrication of coloured zirconia ceramics. The authors’ strategy includes ceramic injection moulding 3Y‐TZP powder using a water debinding binder system, debinding moulded parts in water and drying, immersing debound parts in solutions containing different colouring ions and then sintering and creating coloured zirconia ceramics. The fabricated coloured ceramic bars exhibit a core shell structure, and the thickness of the coloured shell can be tailored by adjusting immersion time and temperature. Using solutions containing different colouring ions, ceramic bars with various colours can be prepared.

Methylene-bridged carbosilanes and polycarbosilanes as precursors to silicon carbide—from ceramic composites to SiC nanomaterials

Polymeric and oligomeric carbosilanes having Si atoms linked by methylene ( CH 2 ) groups were used to prepare nano-sized tubules and bamboo-like SiC structures by both CVD and liquid precursor infiltration and pyrolysis inside of nanoporous alumina filter disks, followed by dissolution of the alumina template in HF (aq). These initially amorphous SiC structures were characterized by SEM, EMPA, TEM, and XRD. Typical outer diameters of the SiC nanotubes (NTs) were 200–300 nm with 20–40 nm wall thicknesses and lengths up to the thickness of the original alumina templates, ca. 60 μm. In the case of the CVD-derived SiC NTs, annealing these structures up to 1600 °C in an Ar atmosphere yielded a nanocrystalline β-SiC or β-SiC/C composite in the shape of the original NTs, while in the case of the liquid precursor-derived nanostructures, conversion to a collection of single crystal SiC nanofibers and other small particles was observed.

Homogeneity of Oxide Air-Sphere Crystals from Millimeter to 100-nm Length Scales: A Probe for Macroporous Photonic Crystal Formation

We study the homogeneity of photonic air-sphere crystals made of oxides. This important class of macroporous materials is prepared via liquid precursor infiltration of opal templates and subsequent removal of the template by calcination. We have synthesized highly ordered structures of macropores in a solid backbone consisting of two consecutively infiltrated materials: the oxide pairs zirconia/titania (ZrO2/TiO2) and alumina/titania (Al2O3/TiO2). The ordered arrangement of the air spheres was confirmed by scanning electron microscopy. To determine the spatial distribution of the materials, energy-dispersive spectroscopy was used. It was observed that there are variations in the distribution of oxide materials throughout the sample on length scales ranging from 1 mm to 100 nm. We propose that the spatial variations originate from the reaction process where the precursors hydrolyze and possibly also from the densification that occurs in the calcination step. Since many light emitters are quenched on semic...

Preparation of machinable Ce–TZP/CePO4 composite ceramics by liquid precursor infiltration

A novel process has been used to fabricate Ce–TZP/CePO 4 composite ceramics: namely infiltrating CePO 4 liquid precursor into Ce–TZP porous ceramic. Sintered Ce–TZP ceramic preform with 35 vol.% open pore volume was developed by adding graphite 30 vol.%. The Ce–TZP/CePO 4 composite ceramics containing different CePO 4 contents were obtained by infiltration and pyrolysis cycles. The machinability and mechanical properties of these materials were investigated. Results show that the Ce–TZP/CePO 4 composite ceramics can be cut and drilled using conventional tungsten carbide metal-working tools. Measurement of normal grinding force was used to compare the ease of machining in these materials. The machinable Ce–TZP/CePO 4 composites containing a range from 2.3 to 7.5 vol.% CePO 4 has good machinability as well as maintaining outstanding mechanical properties. The relation between microstructure and mechanical properties of the materials was discussed.

Liquid Precursor Infiltration Processing of Powder Compacts: II, Fracture Toughness and Strength

Si3N4 powder compacts were infiltrated with liquid precursors which produce either Zr(Y)O2 (3 mol% Y2O3) solid solution or amorphous Si3N4 after pyrolysis at relative low temperatures and without shrinkage. Results show that cracks which occur within a thin, surface layer of the precursor during pyrolysis can extend into the powder compact. As suggested by theory, this cracking phenomenon could be avoided either by making the powder compact stronger before infiltration or by removing the thin precursor layer before pyrolysis. The mechanical properties of these materials were studied as a function of residual porosity. It was observed that crack extension occurred within the second phase produced by infiltration and pyrolysis. The second phase appeared to govern the critical stress intensity factor (Kc) of the material. Kc was found to be a linear function of the change in residual, relative porosity divided by the initial, relative porosity in the powder compact. Reasonable flexural strengths (∼300 MPa) could be achieved despite considerable residual porosity.

Laser CVD vs. Hot Wall CVD : Coating of Fibres for Ceramic Composites

Based on a technological 5 kW cw-CO 2 laser, an atmospheric pressure laser assisted CVD process has been established which performs a continuous high rate coating of carbon fibre rovings. Layers of pyrolytic carbon have been deposited from CH4 with a rate of 0.6 μm/s which enhances the tensile strength and Weibull modulus of fibres. In another variant, pyro-C layers have been deposited in a technological thermal hot-wall CVD reactor on fabrics and on preforms. The layer thickness is uniform over the cross section of the fibre bundles, but variations in flow direction have been detected. Composite materials with SiC matrix have been processed by both liquid precursor infiltration using Si-polymers and by converting a carboneous matrix being infiltrated with liquid silicon. Preforms with uncoated and coated fibres have been infiltrated. The resulting composites are characterized by high tensile strength and crack resistance due to the favourable pull-out behaviour of coated fibres.