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1.
Ultrafine zirconium diboride (ZrB2) powders have been synthesized by sol-gel process using zirconium oxychloride (ZrOCl2·8H2O), boric acid (H3BO3) and phenolic resin as sources of zirconia, boron oxide and carbon, respectively. The effects of the reaction temperature, B/Zr ratio, holding time, and EtOH/H2O ratio on properties of the synthesized ZrB2 powders were investigated. It was revealed that ultrafine (average crystallite size between 100 and 400 nm) ZrB2 powders can be synthesized with the optimum processing parameters as follows: (i) the ratio of B/Zr is 4; (ii) the solvent is pure ethanol; (iii) the condition of carbothermal reduction heat treatment is at 1550°C for 20 min. 相似文献
2.
为了降低ZrB_2粉体的合成温度,并在此基础上合成粒径细小、纯度高的ZrB_2粉体,以ZrO2及B4C为原料,以Mg粉为还原剂,以NaCl-KCl为熔盐介质,研究熔盐镁热还原法低温合成ZrB_2超细粉体的工艺。探讨了反应温度、B/Zr物质的量比及Mg粉用量对合成ZrB_2超细粉体的影响,并对粉体的物相组成及显微结构进行了表征。结果表明合成ZrB_2的起始温度为1 173K,最佳合成温度为1 473K。合成纯相的ZrB_2粉体最佳工艺条件为:B/Zr物质的量比为2.2,Mg过量50%(质量分数),1 473K反应3h。所合成ZrB_2粉体的晶粒尺寸为30~300nm。 相似文献
3.
《Advanced Powder Technology》2014,25(3):910-915
High-purity zirconium diboride nano-powders were synthesized by carbothermal reduction reaction at a relatively low temperature from a novel sorbitol modified sol–gel method. Phase composition and morphology of the ZrB2 nano-powders were characterized by X-ray diffraction and transmission electron microscopy, respectively. The effect of sorbitol on sol–gel process and the formation mechanism of ZrB2 powders were investigated by fourier transform infrared spectroscopy and thermo gravimetric/differential thermal analysis. Sorbitol, used as bridging and chelating ligand, led to the formation of chelate complex through its polyhydroxy opening reaction with H3BO3, and then induced the condensation of zirconia forming Zr–O–C–B network, which promoted the carbothermal reduction reaction to complete at 1450 °C for 1 h. The synthesized powders exhibited near-spherical morphology with a small average crystalline size of about 100 nm. With respect to the conventional solid state method, the sorbitol modified sol–gel method route guaranteed a faster, easier and energy-saving process for obtaining single-phase nano-powders. 相似文献
4.
V. S. Sulyaeva V. A. Shestakov Yu. M. Rumyantsev M. L. Kosinova 《Inorganic Materials》2018,54(2):133-139
Using mechanochemical synthesis, we have prepared zirconium borohydride, Zr(BH4)4, as a precursor for ZrB2 film growth by chemical vapor deposition. We have carried out the thermodynamic modeling of phase formation processes in the Zr–B–(N)–H and Zr–B–(N)–H–O systems in a wide temperature range, from 100 to 2500°C, at various p(H2)/p(Zr(BH4)4) and p(NH3)/p(Zr(BH4)4) partial pressure ratios in the starting gas mixtures. A process has been proposed for the growth of zirconium diboride films by Zr(BH4)4 decomposition using two techniques: chemical vapor deposition and plasma-enhanced chemical vapor deposition. We also developed a process for the growth of multilayer ZrB2-and BC x N y -based structures. 相似文献
5.
Hailei Zhao Jianlin Wang Zhiming Zhu Jian Wang Wei Pan 《Journal of Materials Science》2006,41(6):1769-1773
ZrB2-ZrN1−x composites were in situ synthesized from Zr and BN powders by hot-pressing at high temperatures. Thermodynamic calculation indicates that ZrN will
be formed preferentially than ZrB2 in Zr-BN system. Three samples with Zr/BN molar ratios of 3:2, 3.5:2 and 2:1 were investigated at temperatures above 1650°C.
All mixtures of Zr and BN transformed to ZrB2-Zr1−x composites completely without any other detectable phases. Nonstoichiometric zirconium nitride, Zr1−x, is supposed to be formed in 3.5:2- and 2:1-samples. The microstructural morphology of well-sintered ZrB2-Zr1−x composites is characterized by quadrate column-shaped ZrB2 distributed evenly in the interwoven acicular Zr1−x matrix. A certain amount of hollow rectangular-shaped ZrB2 with open ends is found in 3.5:2-sample hot-pressed at 1700°C, while some large spherical particles with lots of acicular
Zr1−x sticked on its surface are observed in 2:1-sample hot-pressed at 1800°C. Excessive Zr compared to the stoichiometric Zr/BN
molar ratio of 3:2 will facilitate the densification process. Acicular Zr1−x is apparently beneficial to the improvement of bending strength and fracture toughness of ZrB2-Zr1−x composites. 相似文献
6.
Mustafa Baris Tuncay Simsek Telem Simsek Sadan Ozcan Bora Kalkan 《Advanced Powder Technology》2018,29(10):2440-2446
The present work provides a new insight into the high purity synthesis of zirconium diboride (ZrB2) powders and a method of controlling impurity during the synthesis process. The single phase ZrB2 nano-powder was synthesized by a combined ball milling and carbothermal method using zirconium oxide (ZrO2), boron oxide (B2O3) and carbon (C) as starting materials. The reaction pathway, phase purity, and morphology of the ZrB2 produced are elucidated from X-ray diffraction (XRD) and scanning electron microscopy studies. The details of the impure phases generated during synthesis were obtained from multi-phase Rietveld refinements of XRD data. Experiments revealed that the method of synthesis carried out at 1750?°C involving ZrB2:B2O3:C at a molar ratio of 1:4.5:7.5 could produce highly pure ZrB2 nano-powders of 67?nm average crystallite size. The magnetometry studies on such pure form of ZrB2 nano-powders indicated that both paramagnetic and diamagnetic characteristics coexisted in ZrB2, which could be attributed to its polycrystallinity. 相似文献
7.
《材料与设计》2015
High dilution of transition metals was employed as a new idea for in situ synthesis of Ni–Zr/Zr–Si(B, C) reinforced composite coatings by high power diode laser (HPDL) cladding Ni–Cr–B–Si powders on zirconium substrate. Microstructure, phase composition, the mechanism of in situ synthesis reinforcement and the microhardness of coatings were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-sclerometer. The results reveal that the morphologies and phase constituents are related to the content of alloying elements in powders. In low alloy coatings, the matrix was mainly composed of intermetallic compounds including NiZr and Ni10Zr7, while the reinforcements consisted of Zr5Si4, β-ZiSi, α-ZrSi and ZrC. At the top of high alloy coatings, the matrix was partially comprised of Zr-based amorphous phase with the reinforcements containing ZrB2. It is thermodynamically favorable for ZrB2 ceramic reinforcement to form compared to ZrC phase. The microstructure evolution was dependent on the contribution of the high dilution zirconium alloy substrate to the in situ reinforcement synthesis. The microhardness of the coating showed clear improvement compared with zirconium alloy substrate, although high variability was also found. 相似文献
8.
A.K. Khanra 《Materials Research Bulletin》2007,42(12):2224-2229
In the present investigation, the ZrB2 powder is produced by SHS of mixture containing H3BO3, ZrO2 and Mg. The thermal analysis and XRD study reveal the reaction mechanism of ZrB2 formation by SHS process. Synthesis of H3BO3-Mg system results in formation of Mg3(BO3)2 and MgB4 phases, whereas ZrO2 is partially reduced to Zr3O and Zr during synthesis of ZrO2-Mg system. The reaction between elemental Zr and MgB4 results in ZrB2 formation. The particle size of ZrB2 is found to decrease with the addition of SHS diluent. 相似文献
9.
Laves phases of the type AB2, where A is zirconium, have potential for use as hydrogen storage materials. These Laves phases have one of two different crystal structures, namely the C15 (cubic MgCu2-type) or the C14 (hexagonal MgZn2-type) Strukterbericht types. Data are presented on the lattice parameters for the two phases and relationships are developed between the lattice parameters of the two phases both for the binary (ZrB2) and the pseudobinary (Zr(B′xB″1?x)2) Laves phases. Electron-to-atom ratios are calculated for both the binary and pseudobinary Laves phases and these are related to hydrogen storage capacity (hydrogen-to-metal ratio, H/M). The hydrogen-to-metal ratio is shown to decrease with increasing electron-to-atom ratio. 相似文献
10.
《Materials Science & Technology》2013,29(1):19-23
AbstractZrB2/Fe composite coating was in situ synthesised by gas tungsten arc welding cladding process on AISI 1020 steel. Zr, B4C and Fe–B alloy powders were used as precursor powders. The phase composition and microstructure were investigated by X-ray diffraction analysis, optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. Microhardness of ZrB2/Fe composite coating at room temperature was examined. Main phases obtained from Zr and B4C precursor are ZrB2 and α-Fe, and those obtained from Zr and Fe–B precursor are ZrB2 and FeB. In the upper part of these composite coatings, ZrB2 phase mainly grows along temperature gradient direction. The middle part of these composite coatings has the highest ZrB2 content and highest microhardness. Gradient dispersions of ZrB2 reinforcements appeared in the composite coating from the middle to the bottom, leading to gradient dispersions of microhardness. With decreasing dilution rate, ZrB2 content and microhardeness increase. 相似文献
11.
Noelia Guillén-Hurtado Agustín Bueno-López Avelina García-García 《Journal of Materials Science》2012,47(7):3204-3213
Ce
x
Zr1−x
O2-mixed oxides with three different Ce/Zr ratios (Ce0.8Zr0.2O2, Ce0.5Zr0.5O2 and Ce0.2Zr0.8O2) along with pure cerium and zirconium oxides were prepared by coprecipitation of the metal hydroxides in alkali media and
subsequent calcinations at 500 °C, using two different cerium precursors (Ce(NO3)3·6H2O or (NH4)2Ce(NO3)6). These samples were characterised by N2 adsorption at −196 °C, XRD, Raman spectroscopy, XPS and H2-temperature programmed reduction. Besides, the two mixed oxides with higher cerium content were calcined at higher temperature
(1000 °C) with the additional purpose of studying their thermal stability and phase homogeneity. XRD and Raman spectroscopy
confirm a significant improvement in the insertion of zirconium cations into the ceria lattice when the samples Ce0.8Zr0.2O2 and Ce0.5Zr0.5O2 are synthesised with (NH4)2Ce(NO3)6 instead of Ce(NO3)3·6H2O. This is attributed to a more homogeneous coprecipitation of cerium and zirconium hydroxides, leading to mixed oxides with
better bulk oxygen mobility and smaller lattice parameter. Moreover, the mixed oxides prepared with the (NH4)2Ce(NO3)6 precursor and calcined at 1000 °C exhibit a single phase whereas phase segregation occurs in the counterpart mixed oxides
prepared with the Ce(NO3)3·6H2O precursor. XPS analysis reveal correlations among O/(Ce + Zr) surface atomic ratio and total cerium content for both cerium
precursors. Among the samples calcined at 1000 °C, Ce0.8Zr0.2O2 synthesised with Ce(NO3)3·6H2O is the only one that preserves the low-temperature surface reduction peak, and also shows a BET surface area slightly higher
than those of the rest of samples calcined at high temperature. 相似文献
12.
Mechanical activation-assisted self-propagating high-temperature synthesis (MA-SHS) in air was successfully applied to the
synthesis of the powder mixtures of ZrB2 and ZrC as a precursor of the ZrB2–ZrC composite. When the powder mixtures of Zr/B/C = 4/2/3–6/10/1 in molar ratio were mechanically activated (MA) by ball
milling for 45–60 min and then exposed to air, they self-ignited spontaneously and the self-propagating high-temperature synthesis
(SHS) was occurred to form ZrB2 and ZrC. The ZrB2–ZrC composites were produced from these MA-SHS powders by spark plasma sintering (SPS) at 1800 °C for 5–10 min and showed
the fine and homogeneous microstructure composed of the <5 μm-sized grains. The mechanical properties of the composites evaluated
by Vickers indentation method showed the values of Vickers hardness of 13.6–17.8 GPa and fracture toughness of 2.9–5.1 MPa·m1/2, depending on the molar ratio of ZrB2/ZrC. Thus, the better microstructure and mechanical properties of the ZrB2–ZrC composites were obtained from the MA-SHS powder mixtures, compared with those obtained from the MA powder, the mixing
powder and the commercial powder mixtures. 相似文献
13.
《材料科学技术学报》2019,35(9):1966-1976
Oxide powders of Zr1–xTixO2 (x = 0–1) solid solutions with micron-sized particles were synthesized via a solution combustion method. The synthesis process and Zr/Ti molar ratio were optimized to produce powders with the tetragonal crystal structure. X-ray diffraction, Raman spectroscopy and transmission electron spectroscopy results confirm that a full crystallization microstructure with the single tetragonal phase is obtained after calcination at 600 °C while maintaining the crystallite size <30 nm. Zr/Ti oxide mixtures with Zr ≥ 67 mol% exhibit a tetragonal crystal structure and the embedding Ti in ZrO2 improves the structure stability. The nitrogen sorption results indicate that the powders possess mesoporous morphology with medium specific surface areas (∼10–50 m2/g). Chemical stability tests show that these powders are relatively stable with negligible removal of titanium and zirconium after elution by 0.5 mol/L HCl. Density functional theory was used to calculate the most stable structure with low energy for the selected composition. 相似文献
14.
《Materials Chemistry and Physics》1998,55(2):152-154
The hydrothermal synthesis of a novel layered zirconium arsenate, Zr( AsO4) (H2AsO4) · 2H2O, with γ-type structure and preliminary data on its characterization by chemical and thermal analysis, X-ray diffraction (XRD) and ion exchange are reported. This XRD powder pattern is indexed on a monoclinic cell: a = 5.5699(2) Å, b = 6.8175(4) Å, c= 12.1203(6) Å and β= 103.15(1)°. 相似文献
15.
V. Bolbut I. Bogomol C. Bauer M. Krüger 《Materialwissenschaft und Werkstofftechnik》2017,48(11):1113-1124
Two high temperature alloys, namely Mo‐13Zr‐25.9B and Mo‐17.4Zr‐34.8B (in at. %), which were specified as eutectic compositions according to the literature were produced with a zone melting (ZM) method [1, 2]. Investigations with a scanning electron microscope demonstrated that the microstructures of both alloys are not completely eutectic. The alloy Mo‐13Zr‐25.9B shows well‐aligned arrangements of their microstructural constituents along the crystallization direction. X‐ray diffraction analysis revealed the phases molybdenum solid solution and zirconium monoboride (ZrB) in each alloy and, additionally, in alloy Mo‐13Zr‐25.9B the phases Mo2Zr and dimolybdenum boride (Mo2B) and in alloy Mo‐17.4Zr‐34.8B the phase zirconium diboride (ZrB2). Moreover, the microhardness of the individual phases was measured. The fracture toughness of both materials was determined using the SEVNB method according to DIN EN ISO 23146. Finally, the creep resistance of the alloys was tested at 1100 °C under compressive loading and compared with other molybdenum alloys and a single‐crystalline nickel based superalloy. 相似文献
16.
Some properties of titanium diboride (TiB2) obtained by explosive mechanochemical synthesis and self-propagated high-temperature synthesis (SHS) have been investigated. The properties of zirconium diboride (ZrB2) obtained by SHS have also been studied. There is a general opinion that explosive mechanochemical synthesis proceeds by a SHS mechanism. For that reason, it is of interest to compare the properties of a product synthesized from the same reagents, by both mechanochemical synthesis and SHS. In order to elucidate the peculiarities of mechanochemical synthesis, the changes in shape and size of the titanium particles occurring during their mechanical treatment up to the moment of synthesis have been examined. Titanium and zirconium powders with particles differing drastically in shape and size have been used for the synthesis of TiB2 and ZrB2 by SHS. It has been shown that irrespective of the difference in properties of the reagents, the products obtained have some common properties characteristic of the synthesis method and important with respect to the practical applications of the borides of titanium and zirconium. 相似文献
17.
T. V. Safronova V. I. Putlyaev M. D. Andreev Ya. Yu. Filippov A. V. Knotko T. B. Shatalova P. V. Evdokimov 《Inorganic Materials》2017,53(8):859-868
A calcium phosphate powder has been synthesized from aqueous 0.25, 0.5, and 1.0 M calcium lactate and ammonium hydrogen phosphate solutions atat a Ca/P = 1, without pH adjusting. According to X-ray diffraction data, the as-synthesized powder consisted of brushite (CaHPO4 · 2H2O) and octacalcium phosphate (Ca8(HPO4)2(PO4)4 · 5H2O). After heat treatment in the range 500–700°C, the powders were gray in color because of the destruction of the reaction by-product. The powders heat-treated in the range 500–700°C consisted largely of γ-Ca2P2O7. The ceramics prepared from the synthesized powders by firing at 1100°C consisted of β-Ca2P2O7 and β-Ca3(PO4)2. 相似文献
18.
《Materials Research Bulletin》1987,22(1):99-108
Fine powders consisting of aggregated submicron crystallites of Ba(Ti,Zr)O3 in the complete range of Ti/Zr ratios are prepared at 85–130°C by hydrothermal method, starting from TiO2 + ZrO2 · xH2O mixed gel and Ba(OH)2 solution. The products obtained below 110°C incorporate considerable amounts of H2O and OH− within the lattice. As-prepared BaTiO3 is cubic and converts to tetragonal phase after the heat treatment at 1200°C, accompanied by the loss of residual hydroxyl ions. TEM investgations of the growth features show a transformation of the gel to the crystallite. Ba2+ ions entering the gel produce chemical changes within the gel, followed by dehydration, resulting in a cubic perovskite phase irrespective of Ti/Zr. The sintering properties of these powders to fine-grained, high density ceramics and their dielectric properties are presented. 相似文献
19.
Yan Wang Jinghong Ma Dong Liang Meimei Zhou Fuxiang Li Ruifeng Li 《Journal of Materials Science》2009,44(24):6736-6740
Super-acid catalyst, SO4 2?/ZrO2–SiO2, with high zirconium loading was synthesized and the nature of the surface acid was investigated by FT-IR of pyridine adsorption. With the increasing ZrO2 content, the Lewis and Brønsted acid sites increased and reached the maximum when Zr/Si (molar ratio) = 1.3. The sample with Zr/Si = 1.3 showed the strongest IR adsorption band in the S=O stretching region (1,300–1,400 cm?1). Pyrosulfate and monosulfate species existed on the surface of the catalysts and the acidic strength could be enhanced by induction effect of their S=O groups. And there were two kinds of Brønsted acid sites on the surface of the catalysts. 相似文献
20.
Zhong-Cheng Qiu Jian-Ping Zhou Gangqiang Zhu Peng Liu Xiao-Bing Bian 《Bulletin of Materials Science》2009,32(2):193-197
Pb(Zr0·52Ti0·48)O3 (PZT) powders were prepared by hydrothermal method. The effects of experimental parameters, including Pb/(Zr, Ti) ratio,
alkaline concentration, reaction temperature and time on the product powders were studied in detail. Pure PZT powders were
synthesized at suitable experimental conditions and Raman spectra confirmed the PZT with a perovskite-type structure. The
homogeneous PZT powders with cubic-shaped morphology were formed at alkaline concentration of 1·2 M after reacting at 230°C
for 2 h. The pure PZT powders obtained at low temperature and low alkaline concentration were attributed to precursors, TiCl4, with high activity and mineralizer NaOH with small cation radius. 相似文献