Up-scalable preparation of nano zirconium carbide powder in liquid polymeric precursor and its pyrolysis mechanism

Nano size ZrC powder was prepared by liquid polymeric precursor method. Zirconium n-butoxide (Zr(OⁿBu)₄) and benzoylacetone (BA) were mixed directly with different molar ratios to synthesize transparent liquid zirconium carbide single-source precursors. The carbon content in the precursor could be changed by adding different amount of BA. X-ray pure ZrC was obtained when the molar ratio of BA/Zr(OⁿBu)₄ was 4.6:1. The viscosity of the precursor was very low (<8 mPa s) without the addition of solvents. Zirconium carbide powders were fabricated by the pyrolysis at 800 °C in argon and subsequent heating at various temperatures in vacuum for carbothermal reduction reaction. The pyrolysis behavior, phase composition and transformation, and microstructure of the as-fabricated ZrC powders were analyzed. The gases of CH₄, CO and CO₂ released due to decomposition and evaporation of the organic component and transformation from ZrO₂ to ZrC during pyrolysis resulted in total 60–70% mass loss. The average grain size of the synthesized X-ray pure ZrC powders was less than 30 nm. Meanwhile, the pyrolysis mechanism of nano zirconium carbide powder was deduced.     

Synthesis and pyrolysis behavior of a soluble polymer precursor for ultra-fine zirconium carbide powders

A soluble polymer precursor for ultra-fine zirconium carbide (ZrC) was successfully synthesized using phenol and zirconium tetrachloride as carbon and zirconium sources, respectively. The pyrolysis behavior and structural evolution of the precursor were studied by Fourier transform infrared spectra (FTIR), differential scanning calorimetry, and thermal gravimetric analysis (DSC–TG). The microstructure and composition of the pyrolysis products were characterized by X-ray diffraction (XRD), laser Raman spectroscopy, scanning electron microscope (SEM) and element analysis. The results indicate that the obtained precursor for the ultra-fine ZrC could be a Zr–O–C chain polymer with phenol and acetylacetone as ligands. The pyrolysis products of the precursor mainly consist of intimately mixed amorphous carbon and tetragonal ZrO₂ (t-ZrO₂) in the temperature range of 300–1200 °C. When the pyrolysis temperature rises up to 1300 °C, the precursor starts to transform gradually into ZrC, accompanied by the formation of monoclinic ZrO₂ (m-ZrO₂). The carbothermal reduction reaction between ZrO₂ and carbon has been substantially completed at a relatively low temperature (1500 °C). The obtained ultra-fine ZrC powders exhibit as well-distributed near-spherical grains with sizes ranging from 50 to 100 nm. The amount of oxygen in the ZrC powders could be further reduced by increasing the pyrolysis temperature from 1500 to 1600 °C but unfortunately the obvious agglomeration of the ZrC grains will be induced.     

Synthesis of nanosized zirconium carbide by a sol–gel route

Nanosized zirconium carbide was synthesized by a new simple sol–gel method using zirconium n-propoxide, acetic acid as chemical modifier, and saccharose as carbon source. When heat-treated at 900 °C under flowing argon, gels transformed into intimately mixed amorphous carbon and nanosized tetragonal ZrO₂. Further heat treatments above 1200 °C led to the formation of zirconium carbide with some dissolved oxygen in the lattice. Oxygen content could be reduced by increasing the heat treatment temperature from 1400 to 1600 °C, which unfortunately also induced a mean crystallites size increase from 90 to 150 nm. Short heat treatments above 1600 °C were carried out to further purify the samples and to limit the particles growth. A compromise between purity and average crystallite's size could then be found. Powders were assessed using X-ray diffraction, thermal analysis and scanning electron microscopy.     

Synthesis of micro-and nanosized PbS with different morphologies by the hydrothermal process

PbS micro- and nanostructures with different morphologies and particle sizes were obtained via a simple hydrothermal reaction between lead oxalate, Pb(C₂O₄)₂, and thioglycolic acid (TGA) as Pb²⁺ and the sulfur source and the capping agent, respectively. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy and Fourier transform infrared (FT-IR) spectra. The effects of temperature, reaction time and the type of Pb²⁺ source on the morphology and particle sizes of products were investigated.     

Preparation and characterization of three-dimensional carbon fiber reinforced zirconium carbide composite by precursor infiltration and pyrolysis process

Three-dimensional carbon fiber reinforced zirconium carbide composite (3D C/ZrC) was fabricated for ultra high temperature applications by precursor infiltration and pyrolysis (PIP) process using the mixture of zirconium butoxide (Zr(OC₄H₉)₄) and divinylbenzene (DVB) as precursor of zirconium carbide. The micro-structural, mechanical and ablative properties of the 3D C/ZrC composite were studied. The flexural strength of the composite was 107.6 MPa, the elastic modulus was 28.8 GPa, and the fracture toughness was 7.03 MPa m^1/2. The mass lose rate and linear recession rate of the 3D C/ZrC composite during oxyacetylene torch test was 0.012 g/s and -0.002 mm/s, respectively. The formation of ZrO₂ melt on the surface of the composite contributed mainly the excellent ablative property.     

Modified hydrothermal treatment route for high-yield preparation of nanosized ZrO2

Nanosized ZrO₂ particles are applied in high-performance thermal barrier coatings and catalyst carriers. To synthesize nanosized zirconia, precipitation from aqueous solutions followed by hydrothermal treatment is widely conducted. In this work, a modified hydrothermal treatment route is described for high-yield fabrication of well-dispersible nanosized t–ZrO₂. Zirconium oxychloride and sodium hydroxide were used as the precursor and precipitant, respectively. N, N-bis(2-hydroxyethyl) glycine (bicine) was used as surface stabilizer to inhibit the early agglomeration of nuclei, and ultrasonication was used to enhance the dispersion of ZrO₂ nanocrystals. The hydrothermal treatment was optimized for reaction temperature, time, fill fraction, and solid content. The synthesized zirconia was characterized using X-ray diffraction, dynamic light scattering, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The yield of zirconia increased to 134 g/L after hydrothermal. Tetragonal ZrO₂ obtained with hydrothermal treatment at 200 °C for 8 h at a fill fraction of 80% has a good dispersibility, with an average particle size of 20 nm and a narrow size distribution.     

Comparative hydrothermal synthesis of hydroxyapatite by using cetyltrimethylammonium bromide and hexamethylenetetramine as additives

Comparative synthesis ways for preparing HA (Ca₁₀(PO₄)₆(OH)₂) nanoparticles in presence of hexamethylenetetramine (HMTA) and cetyltrimethylammonium bromide (CTAB) were carried out. The reactions were performed in a Teflon-lined stainless-steel reactor at 120 °C during 12 h. The effects of the additive concentration and the cooling mode (fast and slow) were analyzed. The obtained powders were characterized by X-ray Diffraction (XRD), Raman Spectroscopy, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). The two hydrothermal ways carried out for preparing HA nano powders produced a pure crystalline phase of HA. When the fast cooling mode was used, the obtained particles exhibited smaller mean particle sizes. The highest concentrations of used additives (HTMA or CTAB) resulted in opposite effect on the obtained mean particle size of HA particles. These observations were associated to the different behavior of these additives in the HA formation processes.     

High-temperature properties and interface evolution of C/SiBCN composites prepared by precursor infiltration and pyrolysis

C/SiBCN composites with a density of 1.64 g/cm³ were prepared via precursor infiltration and pyrolysis and the bending strength and modulus at room temperature was 305 MPa and 53.5 GPa. The precursor derived SiBCN ceramics showed good thermal stability at 1600 °C and the SiC and Si₃N₄ crystals appeared above 1700 °C. The bending strength of the composites was 180 MPa after heat treatment at 1500 °C, and maintained at 40 MPa-50 MPa after heat treatment for 2 h at 1600 °C–1900 °C. In C/SiBCN composites, SiBCN matrix could retain amorphous up to 1500 °C and SiC grains appeared at 1600 °C but without Si₃N₄. The reason for no detection of Si₃N₄ was that the carbon fiber reacted with Si₃N₄ to form an interface layer (composed of SiC and unreacted C) and a polycrystalline transition layer (composed of B and C elements), leading to the degradation of the mechanical properties.     

Low temperature polymer assisted hydrothermal synthesis of bismuth ferrite nanoparticles

BFO nanoparticles were successfully synthesized by a polymer assisted hydrothermal method at a temperature as low as 160 °C. The as-prepared powders, characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), exhibited a pure BFO phase about 10 nm size and uniform sphere-like shape. It was found that the added polymer played a key role in decreasing the growing speed of BFO nuclei and resulted in the formation of BFO nanoparticles.     

A meltable precursor for zirconium carbide ceramics and C/C-ZrC composites

For process simplification and rapid densification of ceramic composites, a meltable single-source ZrC precursor was prepared by condensing zirconium acetylacetonate (Zr(acac)₄) at 190?°C for 40–150?min. The preparation of ZrC precursor and the conversion from precursor to ceramics were investigated by using FTIR and NMR spectroscopies, GPC, DSC-TGA, XRD, SEM, EDS and TEM. The precursor had low viscosity (~ 10?mPa?s) and proper processing window (60?min) for precursor infiltration and pyrolysis (PIP). The ceramic yield at 1650?°C was 29.6%, and EDS revealed that the composition was (ZrC)_0.337(HfC)_0.0025(ZrO₂)_0.044C_0.1865. The ceramics were composed of 0.2–0.5?µm grains which aggregated to form a stacked structure surrounded by amorphous carbon. The preparation processes were designed, and C/C-ZrC composites with the density of 2.45?g/cm³ were successfully fabricated through 11 cycles of PIP with Zr(acac)₄. In conclusion, the synthetic method provides a simple and cheap route for precursors, and allows combined composite preparation with high efficiency.     

Preparation of novel carborane-containing boron carbide precursor and its derived ceramic hollow microsphere

High melting point and hardness of boron carbide make it extremely difficult to be directly prepared as hollow microsphere. However, precursor derived method is an effective approach to prepare ceramic materials with complex shape. Therefore, in this work a novel boron carbide precursor, poly[1,7-bis(4-chlorophenyl)-m-carborane] (P4CB), was synthesized. The ceramic yield of the precursor P4CB reached as high as 90.25% at 900 °C in nitrogen. Oxidation of P4CB in air was barely observed below 500 °C, and a passive oxidation was exhibited beyond 700 °C. The P4CB/PAN slurry was prepared and coated on a polyoxymethylene (POM) ball substrate. After air crosslinking, substrate decomposition and heat-treatment at 1100 °C in Ar atmosphere, boron carbide hollow microsphere with diameter of approximate 1.34 mm and average shell thickness of 30 μm was finally obtained. The novel precursor could be also utilized to fabricate boron carbide ceramics with different shapes due to its high ceramic yield.     

Linear organodecaborane block copolymer as a single-source precursor for porous boron carbide ceramics

Boron carbide is one of the most widely used non-oxide ceramics as it possesses excellent physical and chemical properties. Much attention has been paid to prepare boron carbide ceramics via precursor derived method. In this work, poly(6-norbornenyldecaborane)-b-poly(6-cyclooctenyldecaborane) (PND-b-PCD) block copolymer was synthesized by the ruthenium-catalyzed ring-opening metathesis polymerization (ROMP) of 6-norbornenyldecaborane with 6-cyclooctenyldecaborane. The synthesized boron carbide preceramic polymer had good solubility and film-forming ability with a high ceramic yield of 75% at 850 °C. TGA, XRD and TG-IR-GC–MS were used to investigate the ceramization process of the precursor. Boron carbide ceramic foams were prepared by the precursor via replicating polyurethane foam template. The component, crystalline and morphology were investigated in detail. The ceramic foams showed a good high temperature performance and could keep their structure even up to 1800 °C.     

碳化锆陶瓷有机前驱体的热解过程

合成了碳化锆陶瓷有机前驱体,研究了其在热解过程中化学成分和物相组成变化,探讨了从有机高分子向无机陶瓷转化的机理,对碳热还原反应进行了热力学分析。结果表明,前驱体在600℃以下完成了有机结构的断裂、裂解碎片的重排与挥发,600℃以上裂解产物不再具备有机特征;随热解温度升高,无定型碳和单斜相ZrO2逐渐生成,大于1200℃时可检测到立方相ZrC,1400℃时单斜相ZrO2基本消失;1500℃时完成碳热还原反应,在远低于热力学反应温度的条件下生成了高度结晶的纳米尺寸的立方相碳化锆陶瓷。     

Synthesis,characterization and use of synthesized fine zirconium diboride as an additive for densification of commercial zirconium diboride powder

Zirconium diboride (ZrB₂) was synthesized by a solution-based technique using zirconyl chloride (ZrOCl₂·8H₂O, ZOO), boric acid (H₃BO₃, BA) and gum karaya (GK) as the sources of zirconium, boron and carbon, respectively. The initial formation temperature of ZrB₂ was 1200 °C and complete conversion was achieved by 1400 °C. Preceramic precursors and as-synthesized ZrB₂ powders were characterized by XRD, TG-DTA, SEM, TEM, EDX and compared with commercial ZrB₂ powder made by carbothermic reduction. FT-IR of as-synthesized dried preceramic precursor revealed the formation of Zr–O–C and Zr–O–B whereas SEM showed agglomerated spherical particles with mean diameter of <1 µm. Commercial ZrB₂ and as-synthesized fine ZrB₂ powder were spark plasma sintered (SPS) at 1900 °C for 10 min. Addition of 10 wt% of synthesized fine powder improved the fired density from 87% to 93% of theoretical. A significant cost benefit arises for the utilization of cheap synthesized fine powder as an additive for the densification of the more expensive commercial powder.     

Fabrication of SiC ceramic architectures using stereolithography combined with precursor infiltration and pyrolysis

Stereolithography based additive manufacturing provides a new route to produce ceramic architectures with complex geometries. In this study, 3D structured SiC ceramic architectures were fabricated by stereolithography based additive manufacturing combined with precursor infiltration and pyrolysis (PIP). Firstly, photosensitive SiC slurry was prepared. Then, stereolithography was conducted to fabricate complex-shaped green SiC parts. Polymer burn-out was subsequently performed, and porous SiC preforms were produced. After that, precursor infiltration and pyrolysis was used to improve the density and strength. Finally, 3D-structured SiC ceramic architectures with high accuracy and quality were obtained. It is believed that this study can give some fundamental understanding for the additive manufacturing of SiC ceramic structures.     

Synthesis of vanadium carbide nanopowders by thermal processing and their characterization

Vanadium carbide (V₈C₇) nanopowders were successfully prepared by thermal processing the precursor which originated from the mixture of ammonium vanadate (NH₄VO₃) and nanometer carbon black. The products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) methods. The single phase V₈C₇ powders can be prepared at ∼ 1100 °C for 1 h with the average crystallite size of 32.6 nm and the powders show good dispersion and are mainly composed of uniformly-sized spherical particles with a mean diameter of ∼ 100 nm.     

Effects of the number of benzene rings on the properties of single-source ZrC-based liquid precursors and nano zirconium carbide powders thereof

Effects of carbon source in single-source ZrC-based liquid precursors on the properties of the precursors and precursor-derived nano ZrC powders were investigated. The liquid precursors were prepared by directly blending and heating zirconium n-butoxide with either 2,4-pentanedione, benzoyl acetone or 1,3-diphenyl-1,3-propanedione additives which have the same chemical composition and structure except for the number of benzene rings (0, 1 and 2, respectively) in order to control the carbon content in the precursors. The ceramic yield of the precursor decreased as the number of benzene rings in the precursors increased. The stability of the precursors in air and the carbon content of the ceramic powder increased when using 1,3-diphenyl-1,3-propanedione additive. X-ray pure nano zirconium carbide powders with ultra-fine size (30 nm), isotropic shape and homogeneous particle size distribution were synthesized from the liquid precursors containing two benzene rings in the structure. Compared with ZrC powders derived from the precursors containing zero or one benzene ring, the powder from the precursor containing two benzene rings was finer and more homogeneous in size distribution.     

Mechanical properties and grain orientation evolution of zirconium diboride-zirconium carbide ceramics

The effect of ZrC on the mechanical response of ZrB₂ ceramics has been evaluated from room temperature to 2000 °C. Zirconium diboride ceramics containing 10 vol% ZrC had higher strengths at all temperatures compared to previous reports for nominally pure ZrB₂. The addition of ZrC also increased fracture toughness from $～3\text{.5}\text{MPa}\sqrt{\text{m}}$ for nominally pure ZrB₂ to $～4\text{.3}\text{MPa}\sqrt{\text{m}}$ due to residual thermal stresses. The toughness was comparable with ZrB₂ up to 1600 °C, but increased to $4\text{.6}\text{MPa}\sqrt{\text{m}}$ at 1800 °C and 2000 °C. The increased toughness above 1600 °C was attributed to plasticity in the ZrC at elevated temperatures. Electron back-scattered diffraction analysis showed strong orientation of the ZrC grains along the [001] direction in the tensile region of specimens tested at 2000 °C, a phenomenon that has not been observed previously for fast fracture (crosshead displacement rate = 4.0 mm min^?1) in four point bending. It is believed that microstructural changes and plasticity at elevated temperature were the mechanisms behind the ultrafast reorientation of ZrC.     

Synthesis and characterization of zirconium silicalite-1

Zirconium silicalite-1 (ZS-1) catalysts with MFI structure were prepared using a hydrothermal synthesis method. XRD, SEM, IR,²⁹Si MAS NMR, UV-VIS DRS, physical adsorption of nitrogen, and elemental analysis were then performed to evaluate its physico-chemical properties, and evidences of Zr⁴⁺ incorporation into the zeolite framework were provided : The unit cell volume of zirconium silicalite-1 increased linearly with increases in zirconium content, and the characteristic framework i.r. spectra shifted to lower frequencies as Zr⁴⁺ was incorporated into the silicalite-1 lattice. For its catalytic reaction test, liquid phase 2-butanol oxidation using hydrogen peroxide as an oxidant was carried out. All of the zirconium silicalite-1 samples synthesized were active for the 2-butanol oxidation, but activities obtained using ZS-1 catalysts were lower than TS-1 catalyst. Zirconium in the zeolite frameworkwas found to be the active site for the 2-butanol oxidation.     

Thermal properties of Cf/HfC and Cf/HfC-SiC composites prepared by precursor infiltration and pyrolysis

Ultra-high temperature ceramic infiltrated carbon-fibre composites were prepared by precursor infiltration and pyrolysis (PIP) using a laboratory synthesized precursor. Microstructures and thermal properties including thermal expansion, thermal diffusivity, specific heat capacity and oxidative stability are correlated. XRD reveals the presence of C_f-HfC and C_f-HfC-SiC phases without formation of oxides. The CTE observed at 1200?°C is slightly higher for C_f-HfC (3.36?×?10^?6?K^?1) compared to C_f-HfC-SiC (2.95?×?10^?6?K^?1) composites. Lower thermal diffusivity of the C_f-HfC-SiC compared to C_f-HfC composites is attributed to a thermal barrier effect and cracks in the composites which formed due to the CTE mismatch between carbon fibre and the matrix as well as CO generated during graphitization. The thermal conductivity of C_f-HfC (4.18?±?0.14?Wm^?1?K^?1) is higher than that of C_f-HfC-SiC composite (3.33?±?0.42?Wm^?1?K^?1). Composites microstructures were coarse with some protruding particles (5?μm) with a homogeneous dense (～70%) matrix (HfC and HfC-SiC) for both composites.