共查询到20条相似文献,搜索用时 31 毫秒
1.
Reaction synthesis mechanism of Calcium hexaboride (CaB6) powder was investigated by using CaCO3-B4C-C system. Micron-scale CaCO3 and B4C powders were used as main raw materials. The synthesized powder was determined by X-ray diffraction, showing no left reactants if enough CaCO3 was added to compensate the evaporation of calcium atoms at high temperature. The powder morphology was observed through SEM. The synthesized CaB6 powder formed hard agglomerates which consisted of cubic CaB6 crystallites when the reaction completely finished. Reaction process was illustrated indicating it was a solid-state reaction occurred from B4C surface to the centre. The dry high-energy ball milling was used to investigate the influence of ball-milling time on the shape and size of powder particles. The particle granularity was measured by laser size analysis method. It is obvious that the particles were refined greatly after ball milling for 8 h. However, the CaB6 powder could not been refined markedly after 16 h. Finally, optimized parameters for size controlling were given in this paper. 相似文献
2.
In this study, PVA-CaB6O10·5H2O precursor mixtures were prepared by coating the ceramic powders with PVA to synthesize CaB6 via carbothermal reduction. Boron loss, the main problem in the synthesis of borides, was reduced by the use of metastable CaB6O10 as a transitional phase which is stable until the critical temperature ranges where the boron sub-oxides have higher volatilities. To minimize boron loss, due to the high hydrophilicity and ability to form cross-linked PVA-borate gels, PVA was used as a carbon source and carbon coating process was carried out via pyrolysis of the PVA - CaB6O10·5H2O mixed gels. The effect of the molecular weight of PVA on the CaB6 synthesis was also studied. Because of highly efficient interaction of CaB6O10·5H2O with the PVA60-water solution, PVA60 was found to be the optimal carbon source. The CaB6O10·5H2O-PVA60 composite powder was characterized by using Fourier transform infrared spectroscopy (FTIR) and the effect of molecular weight of the PVA’s on the thermal characteristics of mixed powders were analyzed by using simultaneous thermal analysis (STA). The effect of carbothermic reduction temperature and dwell time on the phase formation were examined via x-ray diffractometer (XRD) and scanning and transmission electron microscopy (SEM and TEM) techniques. The optimum synthesis conditions were determined for the formation of CaB6 as 1450ºC for 12 h under an Argon flow by using the CaB6O10·5H2O-PVA60 mixed precursor. 相似文献
3.
《Ceramics International》2020,46(6):7223-7234
This study investigates the formation of B4C in the B2O3–Mg–C ternary system via a magnesiothermic reduction process using two kinds of boron oxide (B2O3) ‒ the commercial B2O3 and that synthesized from boric acid via the coupled chemical-thermal process. In addition to the raw materials, the products were subjected to XRD, FTIR, SEM, and FESEM analyses to determine the effects of microstructural and morphological properties of boron oxide as an important raw material, on B4C formation in the combustion synthesis process. For this purpose, powder mixtures of B2O3:Mg:C were prepared at a stoichiometric molar ratio of 2:6:1 and compacted into pellets using a uniaxial hydraulic press, which were subsequently subjected to the combustion synthesis process based on the self-propagating high-temperature synthesis (SHS). Finally, the samples thus obtained were leached in an aqueous hydrochloric acid solution. Analysis of the commercial B2O3 revealed the presence of large amounts of such by-products as magnesium borate (Mg3B2O6) and magnesium oxide (MgO) along with relatively small amounts of boron carbide after the leaching process, while those obtained for the chemically-thermally synthesized B2O3 showed a relatively large amount of B4C (from micron-sized particles to nanoparticles) together with a remaining carbon phase and very small amounts of magnesium borate as by-products. It can be, therefore, concluded that the changes in chemical composition and introduction of a hydrous HBO2 phase in the boron oxide in the B2O3–Mg–C mixture as well as its varied microstructure, morphology, and particle size have significant effects on the efficiency of B4C production through the SHS process. 相似文献
4.
《Ceramics International》2019,45(12):14749-14755
Boron carbide submicron powder was synthesized with boron oxide and graphene as starting materials by gas-solid reaction method using two different apparatuses. The effects of calcination temperature and holding time, apparatus type and B2O3/C ratio of the starting materials on the phase composition and morphology of the synthesized powders were evaluated. A newly formed residual carbon morphology distinct from original graphene were present in samples synthesized at a higher B2O3/C ratio or temperature. The synthesis temperature of ∼1500 °C was found to be more suitable to obtain boron carbide powder without the existence of residual carbon. The new type of apparatus enabled the synthesis of boron carbide phase at a relatively lower temperature, due to its more efficient use of B2O3 vapor. 相似文献
5.
High quality boron carbide powder without free carbon is desired for many applications. In this study, the factors that influence free carbon content in boron carbide powders synthesized by rapid carbothermal reduction reaction were evaluated. The dominant factors affecting free carbon contents in boron carbide powder were reaction temperature, precursor homogeneity, the particle size of reactants, and excess boron reactant amount. The reaction temperature at 1850 °C was sufficient to synthesize boron carbide with low free carbon content. Depending on process conditions, precursor homogeneity was also affected by the calcination temperature and time. Smaller particle size of reactants contributed to less carbon content and more uniformity in synthesized boron carbide. Excess boric acid effectively compensated for B2O3 volatilization. In the optimal sample, using 80 mol% excess nano boric acid and calcined at 500 °C, the free carbon in the synthesized boron carbide was negligible (0.048 wt.%). 相似文献
6.
Mahnaz GahremanDerakhshan Leila Nikzad Mohammad Farvizi Touradj Ebadzadeh 《International Journal of Applied Ceramic Technology》2021,18(1):32-39
Composite powders containing titanium diboride and boron carbide have been prepared by sol-gel method at 1450°C using titanium isopropoxide (titanium precursor), boric acid (Boron precursor), sucrose (carbon source), and acetic acid (AcOH) as a solvent. The effect of boron source (trimethyl borate and boric acid) and B2O3/TiO2, C/B2O3 mole ratios of starting materials on the final phases has been studied. The progress of reactions was determined using thermal analysis (TGA-DTA). The resultant powders were characterized by X-ray diffraction (XRD) analysis and field-emission scanning electron microscope (FESEM). XRD patterns confirmed the formation of TiB2, B4C, and TiC phases after heat treatment at 1450°C at mole ratio of B2O3/TiO2 = 4.5, C/B2O3 = 2.4. With increasing the content of boron oxide, the unwanted phases such as TiC and C were reduced. TiB2 and B4C composite powders (~5 µm diameter) containing residual carbon (<4 wt%) were synthesized using the mole ratio of B2O3/TiO2 = 10 and C/B2O3 = 1.9 at low temperature of 1450°C. 相似文献
7.
Yi Zeng Huilin Lun Xiang Xiong Ziming Ye Tianxiao Qian Wei Sun Yalei Wang Zhaoke Chen 《Journal of the American Ceramic Society》2020,103(1):23-27
Multicomponent boron-containing carbide (ie, Zr-Ti-C-B) composites show good ablation resistance. The present work is the first report to introduce the powder fabrication of Zr-Ti-C-B using a new method for solid-state diffusion of boron atoms. First, the nonstoichiometric carbide (ie, Zr0.8Ti0.2C0.8) with carbon vacancies was fabricated by free-pressureless spark plasma sintering. Different boron sources such as B2O3, B, and B4C were used to react with the nonstoichiometric carbide. The Zr0.81Ti0.19C0.86B0.14 can be finally generated through the solid-state diffusion of boron atoms using the B2O3 boron source at 1300°C followed by carbon thermal reduction using the phenolic resins at 1600°C. 相似文献
8.
Thermal properties and formation mechanism of h‐BN nanoneedles synthesized via carbothermic reduction reaction
下载免费PDF全文
![点击此处可从《International Journal of Applied Ceramic Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yasser Momtaz Zak Ahmed Said Moawad El‐Sheikh Asmaa Abd‐El‐Baset Abd Allah Said Anwar 《International Journal of Applied Ceramic Technology》2018,15(1):42-52
Hexagonal boron nitride (BN) was synthesized through the carbothermic reduction reaction (CRR) of boric acid using lactose as a carbon source under the nitrogen atmosphere at 1500°C for 3 hours. The boron/carbon (B/C) molar ratio was controlled during the CRR, and the produced samples were investigated by XRD diffraction pattern, FTIR analysis, and Raman spectra. Boron carbide (B4C) was formed in samples that have a higher carbon content, in addition to boron nitride. While boron nitride pure sample was produced from lower carbon content samples. Formation of B4C was found to depend on the B/C molar ratio. The morphology of the produced powder was also investigated by SEM and TEM, which revealed that the samples consist of nanoneedles of BN and hexagonal particles of B4C. The vapor‐solid (VS) reaction mechanism was processed greatly with increasing boron amount, producing boron nitride nanoneedles, which compete with the liquid‐solid (LS) reaction mechanism. The physicochemical properties of the produced samples were studied by DTA, UV, PL, and AC impedance measurements, and revealed that the samples are promising to many proper applications. 相似文献
9.
《Ceramics International》2022,48(22):33400-33411
The effects of reactant proportions were investigated on features (phase composition, micromorphology and crystal development) of B4C (boron carbide) powder synthesized by in-situ magnesiothermic SHS (self-propagating high temperature synthesis) method, which was based on the perspective of thermodynamic design. The results showed that the reactant proportions were the fundamental reasons affecting the phase composition of the products during the reaction process. Mg addition could decrease the Mg3B2O6/MgO mass ratio of the SHS products. Moreover, C addition would increase the C/B mass ratio of the leached products. When the C molar ratio was 0.2, free boron appeared in the leached products, and the composition of boron carbide was B13C2. When the C molar ratio ≥0.6, the composition of boron carbide changed into B4C, while free carbon began to appear. The lattice parameters a and c of boron carbide crystal dropped with the increase of the C/B mass ratio from 0.1 to 0.3. Meanwhile, carbon atoms gradually entered the boron carbide unit cell. When the C/B mass ratio exceeds 0.3, the lattice parameters tended to be constants of a = 5.608 Å, c = 12.039 Å, while free carbon began to appear in the leached products. 相似文献
10.
《Ceramics International》2017,43(18):16787-16791
Three-dimensional (3D) network nanostructure boron carbide was successfully synthesized via the carbothermic method. The carbon source and template was carbonized bacterial cellulose (CBC) with a 3D network nanostructure, and the boron source was B2O3 and amorphous B powder. X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) were used to study the morphology and structure of the samples. XRD and Raman spectra confirm that they belong to the B4C crystalline phase. The FESEM images show that the synthetic B4C retains the 3D network nanostructure of the template CBC well and consists of B4C nanosheets with an average thickness of less than 100 nm. The analytical results of high-resolution TEM (HRTEM) and Selected Area Electron Diffraction (SAED) indicate that the B4C takes the shape of hexagonal single crystals with a rhombohedral structure. These B4C single crystal nanosheets alternate, forming the 3D network nanostructure. The mechanism of formation can be accounted for by in situ reduction reactions along the carbon nanofibers of CBC. 相似文献
11.
《Ceramics International》2019,45(15):18795-18802
Within this work, the preparation of yttrium tetraboride (YB4) in the form of powder as well as bulk material was investigated.Powders were synthesized via four different reaction methods, including direct synthesis from elemental powders, reduction of yttrium oxide with boron, boron carbide reduction, and combined boron carbide/carbothermal reduction at 1500 °C, 1700 °C and 1900 °C. Pure YB4 powder was successfully synthesized using the combined boron carbide/carbothermal reduction method. Secondary phases, especially Y2O3, YB2 or YBO3, were found in powders prepared using the other three methods.Bulk material was prepared using direct synthesis from elements by reactive hot-pressing. Influence of temperature and boron content on densification and phase evolution of samples was studied. In situ reaction sintering was performed using conventional hot-pressing at temperatures from 1100 °C to 1800 °C in vacuum. The amount of boron varied from the stoichiometric content to 5 and 10 wt% excess (with respect to the reaction from elemental powders). Stoichiometric reactions led primarily to the formation of YB2 and YB4 and several secondary phases such as Y2O3, YBO3 and Y16.86B8O38. YB4 as a main phase was formed only at elevated temperatures (1700 °C and 1800 °C) but certain content of impurities was still present. Excess of B resulted in the formation of YB4 as a primary phase in all prepared samples with a small content of YBO3 and/or Y16.86B8O38. Moreover, SEM analysis revealed the presence of unreacted boron. 相似文献
12.
《Ceramics International》2022,48(9):11940-11952
In this study, a polymeric precursor was synthesized from industrial raw materials by the sol-gel method. The organic components in the polymeric chain structure were separated with the calcination process, and a reactant consisting of carbon and B2O3 was obtained. Mechanically modification process was applied to the reactant by a ball milling, which changed the structure of the reactant. It was observed that this process promoted the crystallinity and decreased the particle size of the reactant. In addition, the bimodal structure of the reactant was transformed to a bicontinuous structure. The reactant and a mechanically modified carbon-based reactant (MMCBR) were applied to heat treatment at 1400–1700 °C for 5 h under argon gas to investigate the effect of mechanically modification process on final products. A non-uniform powder morphology with polyhedral and rod-shaped B4C particles was obtained from reactant and MMCBR. While the B4C powder obtained from the reactant was agglomerated, no agglomeration was observed at the B4C powder obtained from MMCBR. As a result, the B4C powder synthesized in this fashion contained less free carbon as compared to that prepared with MMCBR. 相似文献
13.
Xiumin Xie Ying Wang Jianqi Qi Shanshan Wang Zhao Feng Gu Hou Wei Liu Wei Zhang Qiang Xu Tiecheng Lu 《Journal of the American Ceramic Society》2016,99(8):2601-2606
Fluffy and homogenous sucrose‐coated‐γ‐Al2O3 structured precursor was prepared by drying ethanol‐water sucrose/Al2O3 suspension, in which the ethanol content of 85 vol% was optimized. Using the C/Al2O3 mixture pyrolyzed from such precursor with 23.2 wt% sucrose, single‐phase AlON powder was synthesized by two‐step carbothermal reduction and nitridation method at 1550°C for 2 h and 1700°C for another 1.5 h. The particle size of the AlON powder was around 0.6–1.0 μm. Compared with those synthesized by the traditional approaches with mechanical C/Al2O3, Al/Al2O3, or AlN/Al2O3 mixtures, the synthesis temperature was reduced about 50°C, and the AlON powder was fine and exhibited good dispersity. Such superiority of this method was attributed to that the pyrolyzed carbon film on Al2O3 particle greatly restrained Al2O3 coalescence during the thermal treatment. 相似文献
14.
Combined Effects of Boron Carbide,Silicon, and MWCNTs in Alumina‐Carbon Refractories on Their Microstructural Evolution
下载免费PDF全文
![点击此处可从《Journal of the American Ceramic Society》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ning Liao Yawei Li Shengli Jin Yibiao Xu Shaobai Sang Zhaojun Deng 《Journal of the American Ceramic Society》2017,100(1):443-450
The phase and microstructure evolutions of multiwalled carbon nanotubes (MWCNTs) in B4C‐ and Si‐containing Al2O3–C specimens under elevated temperatures were investigated by means of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results show that the incorporation of B4C decreases the partial pressure of SiO(g) in Al2O3–C specimens due to the oxidation of B4C prior to Si at lower temperature, which prevents the transformation of MWCNTs at 1000°C and suspends the transformation under higher temperature. B2O3 vapor resulting from oxidation of B4C powder reacts with C sources to generate nanoscaled B4C droplets, which facilitate the catalytic formation of new MWCNTs and nano onion‐like carbon. In addition, B‐doped MWCNTs and BN tubes with the coexistence of B2O3, MWCNTs, and N2 are obtained under evaluated temperatures. 相似文献
15.
Carbothermal reduction using B2O3 and carbon black was applied for synthesis of B4C powder and the effects of heat-treatment temperature and starting composition of raw mixture on morphology of B4C particles were investigated. Morphology of B4C particles synthesized at 1450 °C was mainly spherical shapes. The B4C powder synthesized at 1550 °C was large and changed in morphology from polyhedral to skeletal shape, and particle size of B4C increased with an increase in the amount of B2O3 in the starting mixtures. The B4C powder synthesized beyond 1650 °C consisted from dendrite-like particles aggregated by small primary particles. Morphology of the primary B4C particles synthesized at 1750 °C changed from polyhedral to rounded shape with increasing the amount of B2O3 in the starting mixtures. It is clarified that heat-treatment temperature and the starting compositions of raw mixtures mainly affected B4C nuclei number along with primary particle size and morphology of primary B4C particles, respectively. 相似文献
16.
Özge Balcı Duygu Ağaoğulları İsmail Duman M. Lütfi Öveçoğlu 《Ceramics International》2012,38(3):2201-2207
Zirconium diboride (ZrB2)-zirconium dioxide (ZrO2) ceramic powders were prepared by comparing two different boron sources as boron oxide (B2O3) and elemental boron (B). The production method was high-energy ball milling and subsequent annealing of powder blends containing stoichiometric amounts of ZrO2, B2O3/B powders in the presence of graphite as a reductant. The effects of milling duration (0, 2 and 6 h), annealing duration (6 and 12 h) and annealing temperature (1200–1400 °C) on the formation and microstructure of ceramic powders were investigated. Phase, thermal and microstructural characterizations of the milled and annealed powders were performed by X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and transmission electron microscope (TEM). The formation of ZrB2 starts after milling for 2 h and annealing at 1300 °C if B2O3 is used as boron source and after milling for 2 h and annealing at 1200 °C if B is used as boron source. 相似文献
17.
Maryam Erfani Elias Saion Nayereh Soltani Mansor Hashim Wan Saffiey B. Wan Abdullah Manizheh Navasery 《International journal of molecular sciences》2012,13(11):14434-14445
Calcium borate nanoparticles have been synthesized by a thermal treatment method via facile co-precipitation. Differences of annealing temperature and annealing time and their effects on crystal structure, particle size, size distribution and thermal stability of nanoparticles were investigated. The formation of calcium borate compound was characterized by X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and Thermogravimetry (TGA). The XRD patterns revealed that the co-precipitated samples annealed at 700 °C for 3 h annealing time formed an amorphous structure and the transformation into a crystalline structure only occurred after 5 h annealing time. It was found that the samples annealed at 900 °C are mostly metaborate (CaB2O4) nanoparticles and tetraborate (CaB4O7) nanoparticles only observed at 970 °C, which was confirmed by FTIR. The TEM images indicated that with increasing the annealing time and temperature, the average particle size increases. TGA analysis confirmed the thermal stability of the annealed samples at higher temperatures. 相似文献
18.
Soja K. Vijay R. Krishnaprabhu V. Chandramouli S. Anthonysamy 《Ceramics International》2018,44(5):4676-4684
Nanocrystalline boron carbide powder was synthesized by a precursor method using B2O3 as the source of boron and sucrose as the source of carbon. Precursor was prepared at different temperatures ranging from 300 to 800 °C. The optimum temperature for the precursor preparation was found to be 600 °C. All the precursors were heat treated at different temperatures from 1000 to 1600 °C for different duration of heating, ranging from 5 to 240 min under vacuum. The products thus obtained after heat treatment were characterized using X-ray diffraction. The boron carbide obtained was nanocrystalline and the average X-ray crystallite size was found to be ~ 33 nm. Boron, total carbon and free carbon contents also were determined. The free carbon content was found to be less than 3% for samples heated at 1600 °C for 10 min. Effect of heat treatment temperature on the morphology of the synthesized product was studied using scanning electron microscope. 相似文献
19.
《Ceramics International》2019,45(13):16097-16104
A precursor (PBSZ) for SiCw-ZrC-ZrB2 hybrid powder was synthesized by chemical reaction of phenol, paraformaldehyde, zirconium oxychloride, boric acid and tetraethylorthosilicate. Results show that zirconium, silicon and boron atoms have been successfully introduced into the branched structure. Decomposition of PBSZ is completed at 800 °C, and it gives amorphous carbon, SiO2, B2O3 and ZrO2 with a yield of 38% at 1200 °C. During the pyrolysis process, ZrB2 and SiC form at about 1500 °C, followed by the appearance of ZrC when the amount of B2O3 is limited. Highly crystallized ZrB2–ZrC–C powder with ZrB2 and ZrC grains evenly distributed in the carbon matrix together with randomly distributed SiC whiskers are obtained after heat-treated at 1800 °C. Further heated at 1900 °C, ZrB2 and ZrC grains grow from 200 to 500 nm, while SiC whiskers show a much smaller diameter size and tend to grow on the ZrB2–ZrC–C block surface. The morphology difference is caused by the larger gas supersaturation and accommodation coefficient of the pore channels on the block surface. In addition, defects of the carbon matrix are cumulated to the highest at 1500 °C and the structure-ordered carbon is obtained after heat treated at 1900 °C. 相似文献
20.
Ömer Yildiz 《Powder Technology》2004,142(1):7-12
Boron oxide (B2O3), water content, particle size, and specific surface area are important parameters in colemanite (2CaO3B2O35H2O) in the production of glasses especially of E-glass, boron carbide (B4C) and borides (CaB6, LaB6, SiB6, LiB6, MgB2, TiB2, and TaB2 etc.) which are used in ceramics applications. Calcination, a thermal treatment method, is known to affect these parameters significantly. In this study, differential thermal analysis (DTA)-TG, X-ray diffraction (XRD), SEM, BET and chemical analysis were performed on Turkish colemanites before and after calcination. The results are compared in order to elucidate the influence of calcination on processing. An application in the ceramic industry for the production of CaB6 is demonstrated. Results indicate that the raw colemanite could be processed through calcination in the temperature range of 400 and 600 °C without milling. Calcination is shown to have a significant impact on colemanite similar to that of the milling process. As a result, colemanite was upgraded to ∼58 wt.% B2O3 for <250 μm yielding a specific surface area of 2.8 m2/g. This is higher than that of milled colemanite. Because of the crystal water of colemanite, CaB6 is not produced from uncalcined colemanite, but easily produced from colemanite calcined at 600 °C. 相似文献