The quasi‐isentropic loading technique allows investigation of material properties in a high‐pressure, low‐temperature regime that is inaccessible by conventional shock wave experiments. In the present paper, the l...
The quasi‐isentropic loading technique allows investigation of material properties in a high‐pressure, low‐temperature regime that is inaccessible by conventional shock wave experiments. In the present paper, the layered flier‐plate and graded density flier‐plate, which have different variations in the density gradient along the thickness direction but the same density range, were designed and fabricated. Impact experiments were then performed on a two‐stage light gas gun. VISAR‐measured results show that wave profiles with an initial jump followed by a slowly‐rising front to the peak velocity amplitude are generated by using both types of the flier‐plate, indicating that quasi‐isentropic loading to the targets have been successfully realized. The process of quasi‐isentropic loading can be seen as the successive overlap of a series of small shock waves by the transient layers in the flier‐plate. It is obvious that the graded density flier‐plate creates a more smoothly rising front, and the compression effect must be closer to isentropic loading than that of the layered flier‐plate with the same density range.
Sintering behavior, microstructure and microwave dielectric properties of Ba1+x(Mg1/3Nb2/3)O3 (-0.01 [less-than or equal to] x [less-than or equal to] 0.01) were investigated. An improvement of the degree of 1:2 order...
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Sintering behavior, microstructure and microwave dielectric properties of Ba1+x(Mg1/3Nb2/3)O3 (-0.01 [less-than or equal to] x [less-than or equal to] 0.01) were investigated. An improvement of the degree of 1:2 ordering and sinterability was found in Ba-deficient Ba(Mg1/3 Nb2/3)O3 because there existed Ba vacancies. Excessive Ba inhibits the sintering and the degree of 1:2 ordering. It was proposed that excessive Ba exist in grain boundary and inhibit the movement of grain boundary. Therefore, the sintering was restrained. Ba-deficiency had little effect on dielectric constant of Ba(Mg1/3Nb2/3)O3 ceramics. With Ba-deficiency increasing, Qf value decreased drastically.
The precursor of M-type barium hexaferrite with iron excess, which the nominal composition was BaFe12.4O19.6, was prepared by a so-called co-dump coprecipitation method. The crystallization behavior of the precursor u...
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The precursor of M-type barium hexaferrite with iron excess, which the nominal composition was BaFe12.4O19.6, was prepared by a so-called co-dump coprecipitation method. The crystallization behavior of the precursor under the spark plasma sintering (SPS) conditions and the magnetic properties of the SPS samples were investigated. The results show that the samples obtained at 700-850°C were composed of single-phase M-type barium hexaferrite, and that the crystallization of intermediates such as BaFe2O4 and Y-Fe2O3 did not occur. The distribution of crystal grains obviously changed with the increase of temperature;the distribution was random at 700°C and became preferential orientation when the temperature was more than 700°C. The saturation magnetization significantly increased at 700°C and remained almost constant in the range of 750°C to 850°C. This accorded with the evolution characteristics of the phase composition of the SPS samples with the increase of temperature. The coercivity first increased and then decreased with the increase of the temperature, which was attributed to the corresponding increases in the content of M-type barium ferrite and the degree of preferential orientation of crystal grains.
Tin dioxide based ceramics doped with ZnO, Sb2O3 and ZnO-Sb2O3 were prepared by the pressureless sintering. The relative density (ρr) was measured by the Archimedes method, the resistivity (R) was measured by the van...
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Tin dioxide based ceramics doped with ZnO, Sb2O3 and ZnO-Sb2O3 were prepared by the pressureless sintering. The relative density (ρr) was measured by the Archimedes method, the resistivity (R) was measured by the van der Pauw method, and the mi-crostructure and crystal structure were measured by scanning electron microscope. Then the internal relationship between the material and structure were analyzed. The results indicate that ZnO can improve the sintering characteristics of the material;the ρr increases and then decreases with the increase of ZnO, and the optimal content of ZnO is 1.0% (mole fraction, the same below). However, the ρr decreases with the increase of Sb2O3;the R decreases at first, and then increases and decreases at last. The ρr and R of the material are good when Sb2O3 content is 0.5%. The SnO2 based ceramic doped with 1.0% ZnO-0.5% Sb2O3 and sintered at 1400°C has high performance;the ρr is 97% and the R is 0.1099 Ω·cm.
Ga dopping GaxPb1-xTe(x=0.01-0.05) compounds were prepared by melting reaction method, and the in-c fluence of Ga content on the thermoelectric properties were investigated. The results showed that temperature dopende...
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Ga dopping GaxPb1-xTe(x=0.01-0.05) compounds were prepared by melting reaction method, and the in-c fluence of Ga content on the thermoelectric properties were investigated. The results showed that temperature dopendent carrier concentration increased and the hall mobility decreased with increasing Ga content, which indicated that the carrier scattering mechanism gradually changed from an acoustical scattering to the interaction between an acoustical phone and an ionized impurity scattering as x increased. All samples show n-type conduct and the absolute Seebeck coefficient values and the electric conductivity increase significantly with increasing Ga content.
The layered perovskite-type organic-inorganic hybrids (CnH2n+1NH3)2 MnCl4 (n=2, 4, 6, 8, 10, 12) were synthesized in solution and their structures were characterized. The results showed that the structures of the prod...
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The layered perovskite-type organic-inorganic hybrids (CnH2n+1NH3)2 MnCl4 (n=2, 4, 6, 8, 10, 12) were synthesized in solution and their structures were characterized. The results showed that the structures of the products were independent on the reaction initial temperature. The X-ray diffraction (XRD) patterns and the scanning electron microscopy (SEM) images of the products demonstrated that the hybrids crystallize very well and had typical layered structures. The interlayer distance of each hybrid was obtained from the XRD patterns. It was linear dependent on the carbon atom number in the organic chain and the organic chains interdigitated between the two adjacent inorganic sheets.
The solubility of layered perovskite-type organic-inorganic hybrids (CnH2n+1 NH3)2MCl4 (where M = Mn, Co, Cu, Zn;n = 2, 4, 6, 8, 10, 12) in seven kinds of solvent are obtained by atomic absorption spectrometry and tit...
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The solubility of layered perovskite-type organic-inorganic hybrids (CnH2n+1 NH3)2MCl4 (where M = Mn, Co, Cu, Zn;n = 2, 4, 6, 8, 10, 12) in seven kinds of solvent are obtained by atomic absorption spectrometry and titration method. The solvents are sherwood oil, cyclohexane, acetone, trichloromethane, DMF, methanol and water. The results show that the hybrids are prone to dissolve in polar solvent. This is attributed to the polarity of the hybrids. The hybrids disassembly dissolve when the interaction between the ammonium and the electron-donating group of the solvent is stronger than that between the organic and the inorganic parts in the hybrids. The series of M = Zn and Co have better solubility in the polar solvent than that of M = Mn and Cu and this is presumably because there are weaker interactions between the organic and inorganic parts in hybrids of M = Zn and Co.
A novel process was introduced in this paper for the diameter-controlling synthesis of carbon nanofibers (CNFs) in the ethanol flames. The carbon nanofibers were grown on a nanocrystalline Fe layer, which was electro-...
A novel process was introduced in this paper for the diameter-controlling synthesis of carbon nanofibers (CNFs) in the ethanol flames. The carbon nanofibers were grown on a nanocrystalline Fe layer, which was electro-deposited on a substrate using periodic reverse (P.R.) pulse plating. It was found that the quality of the plating nanocrystalline and the corresponding carbon nanofibers was related with two plating parameters: output pulse frequency ( f ) and duty cycle ( r ). In addition to that the straight and helical carbon nanofibers were selectively synthesized by addition of different additives in plating bath. In this paper, the base-growth mechanism of carbon nanofibers was clearly discussed.
Using the microwave sintering technology, the effects of phosphorus （P） additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only ...
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Using the microwave sintering technology, the effects of phosphorus （P） additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only 0.3wt% P additions, full density WC-10Co cermets were obtained at temperature of 1250℃, which is 70 ℃ lower than that of the undoped counterparts. Lower sintering temperature can result in finer WC grain growth; therefore, the P-doped WC-10Co alloys exhibited higher hardness than the undoped ones. But at the same time, P doping could lead to sacrifice of fracture toughness ofWC-10Co cemented carbides.
A new niobate Ba3Nd2Ti2 Nb2O15 was synthesized by high temperature solid state reaction in the BaO-Nd2O3-TiO2- Nb2O5 system. The chemical compositions, crystal structure, microstructure, and microwave dielectric prope...
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A new niobate Ba3Nd2Ti2 Nb2O15 was synthesized by high temperature solid state reaction in the BaO-Nd2O3-TiO2- Nb2O5 system. The chemical compositions, crystal structure, microstructure, and microwave dielectric properties of the new compound were characterized. Ba3Nd2Ti2 Nb2O15 crystallizes in trigonal system with space group P3 ml (164) and lattice constants a=5.6532(1) A, c=11.6117(2) A, V=321.377(6) A3, Z=1. The Ba3Nd2Ti2 Nb2O15 ceramic exhibits a high dielectric constant of 40.1, high quality factors (Q) 3390 (at 5.7542 GHz), and low temperature variation of resonant frequency (τf)+12 × 10-6 K-1. Ba3Nd2Ti2 Nb2O15 might be a suitable candidate of high εr microwave dielectric ceramics.
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