bluuebunny/crossref_metadata_2025 huggingface dataset:
Introducing innovative farming methods in the adjacent territories of Russia and Kazakhstan
Authors: Artamonova T , Bondarenko S , Kaliyeva K
Published: November 2019

Attitude to nature is the basic value of the peoples of Eurasia. This is especially clearly manifested in the example of land use. The development of virgin lands in the adjacent territories of Russia and Kazakhstan led to the solution of the food problem, but with social and environmental consequences. Violation of the traditional integrity of human and natural being lies at their core. The authors argue that it is possible to restore the proportionality of their coexistence, including through the introduction of innovative farming methods as the basis for sustainable development of agricultural territories.
Low-Temperature Preparation of α-Si3N4 Powder via Combined High-Energy Ball Milling and Molten Salt Nitridation Method
Authors: Zhang Jing , Liu Guoqi , Li Hongxia , Sun Feng
Published: November 2019

In this work, α-Si3N4 powder was synthesized by a combined high-energy ball milling and molten salt nitridation method using silicon powder as raw materials, and NaCl-NaF binary molten salt as reaction medium and diluents. The effects of nitridation temperature, soaking time, and NaF content in the molten salt on the formation of α-Si3N4 were investigated. The results show that the nitridation of silicon powder was completed at NaF content of 10wt% in the molten salt after nitridation at 1200°C and held for 4 h. The α-Si3N4 content in the as synthesized powder is 96wt%. The α-Si3N4 whiskers with 40-280 nm in diameter and several microns to tens of microns in length appear in the final products. The crystal growth process of α-Si3N4 whiskers follows vapor-crystal (VC) mechanism.
Preparation and Characterization of Magnetic Gd3+Doped Hydroxyapatite Nanoparticles
Authors: Ruan Zhuozhi , Zhang Xiaojun , Xing Qingguo , Han Yingchao
Published: November 2019

Hydroxyapatite (HAP), the major inorganic composition of mammal bones, has good biocompatibility, biological activity and osteoconductivity. Gadolinium(Gd) with seven unpaired electron on 4f orbit can be used for MRI contrast agent due to its large electron spin magnetic moment and relaxivity. In this study, the magnetic Gd3+doped HAP nanoparticles (Gd-nHAP) were synthesized via coprecipitation method. Results showed that the magnetization of Gd-nHAP was gradually enhanced along with the increase of doping content of Gd3+, which indicated magnetic property depended on doping content. Moreover, with a fixed doping content of Gd3+, the increase of reaction temperature (60°C-280°C) did not generate significant effect on magnetization of synthesized Gd-nHAP. The result showed that magnetization of Gd3+has no strong correlation with crystallinity and crystalline size of HAP.
Preparation and SERS Study of Triangular Silver Nanoplates
Authors: Xu Runxiang , Yan Luting
Published: November 2019

Metal nanostructures have unique properties that differ from their bulk structures. Of the metals, silver has probably play the most important role in the development of plasmonics, and its unique properties make it well-suited for most of the next-generation plasmonic technologies. Among the various silver nanostructures, silver nanoplates have attracted considerable attention because of their shape-dependent optical properties, which have been applied in surface enhanced Raman spectroscopy (SERS). In this study, the direct chemical reduction route was used to prepare silver nanoplates. Then the influence of experimental conditions on the morphologies of silver nanoplates has been studied. The results has been proved by the UV-vis spectrum and the transmission electron microscope images of the triangular silver nanoparticle. Finally, the silver nanoplates have been applied in SERS properties with Rhodamine 6G as the probe molecules. It was found that the SERS enhancement ability of the silver nanoplates is remarkable. By comparing the advantages and disadvantages of solid Raman and liquid Raman tests, Liquid Raman test is considered to be simpler and more convenient, with high performance price ratio and extremely high application value in the future.
Preparation of Al2O3-SiO2 Aerogel by Supercritical Drying
Authors: Sui X.Y. , Xu J. , Zhang L. , Liu R.X. , Zhou C.L. , Wang K.Y.
Published: November 2019

Al2O3-SiO2 aerogel was prepared through sol-gel process and ethanol supercritical drying technology using aluminum chloride hexahydrate (AlCl3•6H2O) and tetraethoxysilane (TEOS) as precursors. Structures and properties of Al2O3-SiO2 aerogel were investigated by means of BET, XRD, SEM, FTIR, TG-DTA. At room temperature, the specific surface area of Al2O3-SiO2 aerogel was 574m2•g−1, and the average pore size was 26.34nm. The three-dimensional network skeleton was composed of leaf shape particles. Al2O3-SiO2 aerogel went through the transformation process of γ-AlOOH + amorphous SiO2 → γ-Al2O3 + amorphous SiO2 → Mullite (3Al2O3•2SiO2) when heat treatment temperature increased from room temperature to 1200°C. At 1200°C, the specific surface area was 162m2•g−1, the average pore size was 59.91nm.It was indicated that Al2O3-SiO2 aerogel possessed excellent high temperature stability and heat insulation performance.
Stress Responses of Polycarbosilane Melt under an Oscillating Shear Straining
Authors: Huang Liuying , Wang Hongyu , Cheng Xuan , Zhang Ying
Published: November 2019

A typical oligomers material, polycarbosilane (PCS) melt, was tested by using the advanced rheumatic expansion system (ARES) with a supplemental data acquisition card and an analog-to-digital converter (ADC). The stress response of the sample at 295 °C to the oscillating shear straining deformation with a 50% shear and an angular frequency of 3.142 rad/s were collected, processed by using the fast Fourier transformation (FFT) technique, and compared to the conventional dynamic stress response of the melt provided by ARES. It was found that the stress response of the melt was no longer sinusoidal and that the main frequency and the amplitude of the stress response were consistent with those provided by the conventional testing method. The PCS at 295 °C behaved like a typical yield fluid when it under the oscillating shear straining deformation with a 50% shear and an angular frequency of 3.142 rad/s.
Preparation of Silicon Carbide Reinforced Aluminium Matrix Composites (SiC/Al) by Selective Laser Melting
Authors: Zhang Jialian , Li Faliang , Zhu Qing , Zhang Haijun
Published: November 2019

Silicon carbide reinforced aluminium matrix composites (AMCs) attracted a lot of attention owing to their low density, high specific strength and specific stiffness, and good wear resistance. Selective laser melting (SLM) technique has been widely used in the preparation of complex structural product with high precision, short production cycle and low cost. In this paper, silicon carbide (SiC) powders and aluminium (Al) powders were mixed together firstly with a weight ratio of 15:85 and then used to prepare AMCs by SLM technology. The effects of laser power on the microstructures, microhardness and flexural strength of formed AMCs were studied. The results show that the relative density, microhardness and flexural strength of the as-prepared samples can be improved with increasing the laser power. Meanwhile, the samples prepared at higher laser power exhibit lower friction coefficient.
A Novel ZrO2 Ceramic Suspension for Ceramic Stereolithography
Authors: Han Zhuoqun , Wang Zaiyi , Liu Shihao , Wang Yingying , Zhou Yuanyuan , Li Ling , Liu Futian
Published: November 2019

Stereolithography have been widely applied in multiple fields. In this paper, we developed a highly filled, low viscosity stereolithography-based zirconia suspension, and successfully used to fabricate a complex shaped zirconia parts by DLP process. After debinding and sintering, the sintered bodies showed significant shrinkage, with the shrinkage between 27.28% and 29.64%.XRD, SEM and other methods were used to test the composition, microstructure and flexural strength. The XRD pattern shows that the crystalline phase of the part is the t-ZrO2 phase, while SEM characterization revealed that the sintered bodies were composed of submicron-grade grains. The relative density measured by the Archimedes’ water displacement method was 96.59%.Additionally, the measured maximum flexural strength was 650MPa.These values are close to the structural properties of common zirconia ceramics prepared by conventional approaches. Hence, a novel DLP-stereolithography-based ZrO2 suspension for the fabrication of complex and dense zirconia ceramic parts has been proposed in this work.
Study on Diffusive Reaction Between C-Si System and Mo Metal
Authors: Li C Q , Liu B L , Zhao C X , Feng X Y
Published: November 2019

Diffusive reaction layer on Mo metal covered by C powder (Si powder or SiC powder, i.e. C-Si system) and heat treated in vacuum ranging from 600°C to 1600°C for 2 h was investigated. Microstructure of interfacial reaction layer between C-Si system/Mo metal were characterized by XRD, SEM, and mechanical properties were compared between reaction layer based on Mo and Mo. The results show: after Si diffusing into Mo, Mo3Si phase appears after heat treatment higher than 1000°C, Mo5Si3 phase forms at 1400°C, even MoSi2 phase appears; after C diffusing into Mo, Mo2C phase appears firstly, then MoC forms at 1400°C; after SiC diffusing into Mo, Mo2C appears first, Mo3Si then forms at 1200°C, Mo5Si3(Mo2C and Mo5Si3C) mutiphase coexist on Mo surface after heat treatment high than 1400°C. Tensile and specific elongation of C-Si system/Mo vary little, but Vickers hardness of Mo diffused by C or Si comparing with Mo enhance distinctly.
A Novel Technique for the Measurement of the Effective Thermal Conductivity of Thermal Insulating Materials up to 1000°C
Authors: Gao Zenghua , Wang Yang , Zhou Jinshuai , Yuan Tao , Wu Xian
Published: November 2019

A novel large temperature gradient steady-state technique for the measurement of the effective thermal conductivity of thermal insulating materials up to 1000°C has been developed. With the incorporation of a vacuum system, the mean effective thermal conductivity of thermal insulating materials under certain temperature gradient in air and/or inert atmospheres with the gas pressure range of 10−2 Pa to 105 Pa can be measured. A transforming method was proposed to derive the true effective thermal conductivity from the as-measured mean effective thermal conductivity. By evaluating the measurement uncertainty of the constructed testing apparatus as well as comparing experimentally with the guarded hot plate test results, the measurement accuracy of this technique was determined to have an accuracy of less than 8.5%.
Determining Structural Damage of Stone Curtain Walls by Dynamic Method
Authors: Zheng Dezhi , Bao Yiwang , Liu Xiaogen
Published: November 2019

Dry hanging stone curtain wall is widely used in the building envelopes, but it was of ten deemed as a safety risk. The damage of the back anchorage structure may result in the urban disaster accident due to the falling down of the tone panel. There is no yet effective detection method because the damage part is hidden behind the panel. In this paper, a dynamic detection method is presented to monitor the damage degree of the anchorage structure on the back of the panel and to determine the damage location. Experiments indicate that the first three steps of natural frequency of the stone panel declined, with the increase of the damage degree of the anchorage structure. The degradation of the natural frequency can be used to identify the degree of back connection damage. In addition, the relationship between the damage position of the back connection and the modal parameters of the stone was investigated. It was found that the change of the damaged location significantly affected the modal vibration of the stone panel and the relative discriminant method is proposed to determine the damage position.
Fabrication and Properties of 3D Mullite Fiber-Reinforced Al2O3 Matrix Composites Prepared by Sol-Gel Process
Authors: Geng Guangren , Zhou Changling , Zhou Yuanyuan , Wang Kaiyu , Yang Fanghong , Cheng Zhiqiang , Liu Futian
Published: November 2019

Fiber toughening is an effective method to improve the brittleness of ceramic materials. In this paper, three-dimensional mullite fiber reinforced alumina ceramic matrix (3D mullitef/Al2O3) composites were prepared by sol-gel process. Alumina sol was prepared by two ways in the inorganic aluminium salt method, and the alumina sol with good fluidity and high solid content was used as a precursor. The preparation process of alumina sol was studied by XRD and TGA-DSC. The results show that the sol is transformed into Al2O3 at about 1100°C, and the crystal phase is α-Al2O3 phase. The mechanical properties of the sample were analyzed by three-point bending test. The microstructure of the fractures was observed by scanning electron microscopy. The results show that with the increase of the immersion cycles, the density of composites increases continuously, and the toughening mechanism of continuous fiber extraction, interfacial debonding and crack deflection is fully utilized during fracture, which is characterized by ductile fracture behavior and achieved the purpose of toughening.
Processing and Properties of Oxide Fiber Reinforced Alumina Composites
Authors: Yang Rui , Qi Zhe , Gao Ye , Yang Jinhua , Zhou Yiran , Liu Hu , Jiao Jian
Published: November 2019

A simple, low-cost processing method involving slurry infiltration, hot pressing and subsequent densification was developed to manufacture NextelTM 440fiber reinforced alumina (N440/A) composites. The influence of alumina sol on the densification of alumina matrix was investigated through XRD and SEM. Results showed that the introduction of alumina sol into slurry promoted the densification of alumina matrix. Then the effect of sintering temperature from 1100°C to 1300°C on mechanical properties of N440/A composites was investigated. The optimized composite material exhibited a tensile strength > 140MPa and flexural strength > 170MPa.The analysis of the fracture surface suggested that the porous matrix played a vital role in the toughening mechanism of N440/A composites. Numerous matrices attach to pullout fibers of N440/A composites, indicating that matrix cracks propagate through micro-pores in the matrix and deflect at the fiber/matrix interface effectively.
Effect of Microwave Sintering on Morphology and Structure of Porous Al2O3-SiO2 Ceramics
Authors: Yue Xian , Chen Junyong , Li Huaxin , Yu Xianbo , Xiang Junhui
Published: November 2019

Mesoporous Al2O3-SiO2 ceramics were prepared by one-pot method. In this process, aluminum chloride hexahydrate (AlCl3·6H2O) and tetraethyl orthosilicate (TEOS) acted as the common precursors, and then the composite porous ceramics were obtained by vacuum freeze-drying (FD). Subsequently, the samples were sintered at 800°C, 1000°C and 1200°C by muffle furnace and microwave sintering device (MSD) respectively, and the crystalline transformation process has been characterized by X-ray powder diffraction (XRD). Furthermore, the properties of porous materials were characterized by Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the sintered samples still retain super high specific surface area (over 200m2/g), and microwave sintering can greatly reduce the crystallization temperature of porous alumina ceramics. This rapid sintering method also transforms porous ceramics from leaf-like structure to granular structure, and finally forms nanorod structure. The sintering mechanism was explained from the point of view of crystal growth law.
Effect of Different Crystal Form Nanometre Zirconia on Thermal Shock Resistance of Magnesia Ceramic
Authors: Wu Feng , Xue Zongwei , Li Xinwei , Xu Na , Sheng Kaixun , Luo Xudong
Published: November 2019

The magnesia ceramic specimens were prepared using high purity magnesia powder, monoclinic nanometre zirconia, tetragonal nanometre zirconia, cubic nanometre zirconia as starting materials in order to improve thermal shock resistance of magnesia ceramic. The specimens were sintered at 1550°C for 2 hours under air atmosphere. The thermal shock resistance and sintering property of magnesia ceramics with different crystal nanometre zirconia additives were investigated. The results show that density of the specimens with zirconia is improved due to the dispersal distribution of zirconia in periclase grain boundary. The sintering property of magnesia with zirconia additives are considerably promoted. The thermal shock resistance of the specimens with tetragonal zirconia or cubic zirconia is improved due to second crystalline phase toughening mechanism of zirconia.Thermal shock resistance of specimens with monoclinic zirconia is improved due to phase transformation toughening mechanism and second crystalline phase toughening mechanism of zirconia.
Preparation and Heat Transfer Mechanism of ZrO2 Fiber Flexible Heat-Insulating Materials
Authors: Han Ding , Wang Chunpeng , Sun Xiankai , Zhang Shichao , Sun Haoran , Fang Kai , Chen Yufeng
Published: November 2019

The high temperature insulation material of zirconia fiber and carbon fiber (CZ) was prepared by wet molding process using chopped carbon fiber and zirconia fiber as raw materials. The thermal conductivity of the block was measured by high temperature flat plate thermal conductivity instrument. The effects of content of zirconia fiber, diameter of zirconia fiber and material density on CZ thermal conductivity were studied. The heat transfer mechanism of CZ was also studied. The results showed that the heat conductivity of CZ insulation material could be reduced with the reducing the diameter of zirconia fiber. The heat conductivity of CZ insulation material also could be reduced with increasing the content of zirconia fiber.
The Effect of Particle Size of Silicon Nitride Powder on Properties of Silicon Nitride Ceramic Balls
Authors: Li Honghao , Sun Feng , Dong Tingxai , Xu Xuemin
Published: November 2019

The micron-sized silicon nitride raw powder was ball-milled into submicron powders of different particle sizes, the silicon nitride ceramic balls were prepared by gas pressure sintering with cerium oxide and aluminium oxide as sintering aids. The microstructures and phase composition of the ceramic balls were characterized by SEM and XRD. The effects of particle size of silicon nitride powders on sintering properties and mechanical properties were investigated. The results show that the relative density, hardness and crushing load of silicon nitride ceramic balls increased with the decrease of the particle size of silicon nitride ceramic powder, and the ceramic balls prepared by small particle size have low porosity and uniform grains. The powder with the longest grinding time has a particle size of 0.40 μm, and the density of the silicon nitride ceramic ball is 3.245 g/cm3, the hardness is15.2 GPa, the fracture toughness is 7.6 MPa·m−2, and the crushing load ratio of the steel ball is 51.2%.
Oxidation Behavior of SiC/Si-B-C-N Ceramic Matrix Composites
Authors: Qiu Haipeng , Chen Mingwei , Xie Weijie , Zhang Bingyu , Liu Shanhua , Luo Wendong , Ma Xin
Published: November 2019

Silicon carbide fiber reinforced Si-B-C-N (SiC/Si-B-C-N) ceramic matrix composites were manufactured through polymer impregnation pyrolysis (PIP) process with SiC fiber as disperse phase and Si-B-C-N ceramic as continuous phase. Thermal stability of SiB-C-N ceramic and the high temperature oxidation behavior of SiC/Si-B-C-N ceramic matrix composites were studied. Results showed that the introduction of boron and nitrogen element restrained the growth of SiC grain and the formation of crystalline phase transformation effectively, and could help to keep the amorphous state up to 1400°C. In addition, SiC/Si-B-CN ceramic matrix composites possessed excellent high temperature oxidation resistance with bending strength retention rate of 80.57% after oxidation test at 1200°C for 100 hours due to the formation B2O3 or borosilicate glass from the oxidation of boron element. Liquid B2O3 or borosilicate glass with suitable fluidity could fill the pores and cracks in the interior which acted as a protective layer and lowered oxygen diffusivity according to the morphology and component analysis. Therefore, SiC/Si-B-C-N ceramic matrix composites possessed excellent oxidation resistance for a wide temperature range.
Effect of Boron Carbide Additive on SiC Ceramic Sintered by Solid-Phase Method under Ar Atmosphere
Authors: Zhou Shicong , Chen Changlian , Liang Xin , Ji Jiayou , Huang Zhiliang , Xu Man , Ding Gangqiang , Zhang Hongliang
Published: November 2019

With boron carbide (B4C) as sintering additives, silicon carbide (SiC) ceramics were prepared in 2100°C by solid-phase sintering under argon atmosphere. The change of microstructure, phase composition and density for all sintered samples were studied. The results showed that with the increase of B4C addition, the density of SiC ceramic was significantly increasing between 0-4 wt% of B4C addition and slightly increasing between 4-8 wt%. XRD analysis showed that all the ceramics without B4C were SiC-6H crystal, while those with B4C contained SiC-4H crystal, B4C turned SiC-6H to SiC-4H, and the more B4C added, the more change it made. SiC ceramic particles changed from equiaxial shape without B4C to flake shape with B4C added, and the particle sizes increased significantly with the amount of B4C additive.
Effect of Machining Processes on Mechanical Properties of SiC/SiC Composites
Authors: Xie Weijie , Qiu Haipeng , Guan Hong , Wang Qiming
Published: November 2019

The purpose of this study was to investigate the effects of different machining processes on mechanical properties of SiC fiber reinforced SiC matrix (SiC/SiC) composites. SiC/SiC composites were prepared by polymer impregnation pyrolysis (PIP) progress with polycarbosilane (PCS) as impregnant and SiC fiber as reinforcement. The tensile strength at room temperature and high temperature of the 2.5D braided composites were measured and analyzed after grinding process and laser process. It was found that the tensile strength of the composites with laser cutting was higher than that with grinding cutting, especially at high temperature. While the tensile strength of the composites with laser surface machining was lower than that with grinding surface machining.
The Effect of PyC/SiC Compound Interphase on the Properties of PIP SiC/SiC Composite
Authors: liu Shanhua , Qiu Haipeng , Liu Shijian , Wang Ling , Zhang Bingyu , Chen Mingwei , Xie Weijie , Liang Yanyuan
Published: November 2019

In order to improve the properties of SiC/SiC composite, chemical vapor infiltration (CVI) process was applied for fabricating the PyC/SiC compound interphase. Precursor infiltration and pyrolysis (PIP) process was used to fabricate SiC matrix. Then an investigation was carried out for the effect of PyC/SiC compound interphase thicknesses on the properties of the composites. According to the results, it was found that the mechanical properties of composites with the PyC/SiC compound interphase are much higher than those of composite with only PyC interphase. The flexural strength, flexural modulus, fracture toughness and interlaminar shear strength of the composites increase gradually when the thickness of CVI SiC interphase is lesser than 2 μm. Further increase of the thickness of CVI SiC interphase to 4μm leads to a continuous increase on the modulus of the composites, while a decrease trend occurs on the flexural strength, fracture toughness and interlaminar shear strength of the composites because of the different coefficients of thermal expansion of the CVI SiC interphase and the PIP SiC matrix. SiC/(PyC/SiCx)/SiC composites showed the better properties of oxidation resistance than those of SiC/PyC/SiC composite. It was due to the survived PyC interphase protected by CVI SiC interphase when the oxygen diffuses into the compound PyC/SiCx intherphase.
Preparation of SiCf/SiC Composites with Low Porosity by Liquid Composite Moulding-Pyrolysis Process
Authors: Wang Xiaomeng , Zhang Bingyu , Zhao Yuliang , Wang Ling , Qiu Haipeng
Published: November 2019

Traditionally, Polymer infiltration and pyrolysis (PIP), chemical vapor infiltration (CVI) and melt infiltration (MI) are main processes to fabricate continuous silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites, one of attractive potential high temperature structural materials. However, long preparation period and high porosity are still problems for further applications. Especially, porosity is crucial to the mechanical properties. Liquid composite moulding-pyrolysis (LCMP) used liquid SiC precursor to decrease the open porosity to 5% with no more than 11 cycles of infiltration and pyrolysis. Mechanical properties like bending strength was investigated with different thickness of pyrolitic carbon (PyC) interface and pyrolysis cycles. The bending strength reached 585 MPa with 200 nm PyC interface under 1200°C pyrolysis temperature. Thus, LCMP process offers exciting opportunities to improve performance of SiCf/SiC composites.
Effect of Si Content on Melt Infiltration Method of SiCf/SiC-Ti3SiC2
Authors: Zhou Y R , Jiao J , Jiang Z Y , Lv X X , Yang R , Qi Z
Published: November 2019

SiCf/SiC composites have attracted wide attention as thermo-structural materials owing to its extraordinary properties at elevated temperature. To further improve the toughness of SiCf/SiC, Ti3SiC2 is used as the reinforcement of SiC matrix. In this study, the effect of Si content on the formation of Ti3SiC2 was discussed. The melt Si infiltration method was used to prepare the SiC matrix, whichTi3SiC2phase was in-situ formed from the reaction between TiC, C and Si during the infiltration process. X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were determined to characterize the phase constitution and microstructure of the matrix. The results demonstrate that the synthesis of Ti3SiC2 was depended on the amount of Si during the molten Si infiltration. The small amount of Si could resulted in the incomplete infiltration reaction. TiSi2 was obtained at the presence of excessive Si. Thus appropriate amount of Si promotes the formation of Ti3SiC2 and improves the purity.
BN/SiC Coating on SiC Tows Prepared by Chemical Vapor Infiltration
Authors: Qi Zhe , Lv Xiaoxu , Zhao Wenqing , Zhu Shizhen , Jiao Jian
Published: November 2019

Boron nitride (BN) and silicon carbide (SiC) coatings were prepared in sequence on desized SiC tows by chemical vapor infiltration (CVI) at the temperature of 950°C. BN was synthesized by the reaction between boron trichloride (BCl3) and ammonia (NH3) while SiC was from the thermal decomposition of methyl trichlorosilane (MTS). The thickness of the coatings was uniform on a certain cross section of a monofilament, and the thickest/thinnest ratio is less than ∼2 across the whole SiC tows for both SiC and BN coatings, as observed by scanning electron microscopy (SEM). Distinct β-SiC powder X-ray diffraction (XRD) pattern was obtained for as-prepared CVI SiC while as-prepared BN coating only showed a bump and a tiny peak corresponding to hexagonal BN (h-BN). This result was verified by transmission electron microscopy (TEM) images, in which CVI BN only had curved diffraction fringes within small pockets, known as turbostractic structures(t-BN). However, t-BN possesses similar short-range structure to h-BN as demonstrated by 11B solid-state NMR spectrum. SiCf/SiC minicomposites using the interphase coating mentioned above is currently under investigation.
Influence of the content of ZrxAlyCz on properties of ZrB2-ZrxAlyCz Composite Ceramics Fabricated by Spark Plasma Sintering
Authors: Guo Qilong , Pang Jianli , Gan Jizhong , Junguo LI , Zhang Lianmeng
Published: November 2019

ZrB2/ZrxAlyCz composite ceramics with different volume contents of ZrxAlyCz were fabricated by the spark plasma sintering. The sintering behavior, microstructure, mechanical properties and oxidation resistance were studied. The results indicated that sinterability of the composites was remarkably improved by addition of ZrxAlyCz compared to the single-phase ZrB2 ceramic. As the content of ZrxAlyCz increased, both the Vickers hardness and Young’s modulus of the composites first increased and then decreased. The fracture toughness of the ZrB2-40vol% ZrxAlyCz composite was 3.56 MPa·m1/2, which increased by approximately 70% compared to the monolithic ZrB2 ceramic. As increasing the content of ZrxAlyCz, the oxidation resistance of composite ceramics was obviously enhanced. The oxidation-resulted increase in weight of composite ceramic with 20vol% ZrxAlyCz was the best performance in oxidation resistance at 1500 °C. The high-temperature oxidation resulted in dense and stable Al-B-O glass due to adding ZrxAlyCz into the composite ceramics, those resulting products effectively blocked the oxygen atoms entering into the ceramic matrix.
Effect of Oxidation Exposure on Flexural Strength of Hot-Pressed ZrB2-SiC Composites with Cr3C2 Additives
Authors: Guo Shuqi
Published: November 2019

In this study, the effect of oxidation exposure on room temperature flexural strength was examined in 3 and 5 wt% Cr3C2-containing ZrB2-20 vol% SiC composites exposed to air at different temperatures between 1100°C and 1300°C, for up to 100 h. The oxidation products determined by X-ray diffraction consisted of ZrO2, SiO2, Cr2O3 and ZrSiO4. After 100 h of oxidation, the flexural strength of the two compositions was evaluated at room temperature by four-point bending test. The results show that the strength retention displayed by the two compositions depended on the amount of Cr3C2 additives. For 3 wt% Cr3C2composition, the flexural strength slightly increased after 100 h of oxidation at 1100°C, however, the strength substantially degraded after 100 h oxidation at 1200°Cand 1300°C. For 5 wt% Cr3C2 composition, on the other hand, the flexural strength decreased after 100 h of oxidation between 1100°Cand 1300°C. Additionally, the flexural strength was higher for 3 wt%Cr3C2 composition than for 5 wt%Cr3C2one in the oxidation temperature range 1100°C to 1300°C. The strength decrease was associated with the formation and coarsening of defects in the oxidized layer and the delamination of the outermost thinner dense oxide layer.
Processing and Properties of Laminated ZrB2-Mo5SiB2 Ceramic Composites Fabricated by Tape Casting and Hot Pressing Sintering
Authors: Zhao Pengbo , Zhao Xiaotong , Wang Hailong
Published: November 2019

The slurry of ZrB2-Mo-Si-B have been prepared using the polyethylene glycol-800 (PEG800) and polyvinyl butyral (PVB) as dispersant and binder respectively. The effects of different additive concentration on the fluidity of the slurry were studied. When the amount of dispersant and binder were 0.2wt%, 4wt% and R value were 1.0, the slurry was most suitable for casting, and the green tape were smooth and flexible. ZrB2-Mo-Si-Blaminated structure ceramics have been successfully prepared by tape casting and hot-pressure sintering at 1900°C for 1h under a pressure of 30 MPa in argon gas. The highest flexural strength and fracture toughness of sintered samples at room temperature were 490±10 MPa and 7.73 ± 0.56 MPa·m1/2, respectively.
Effect of SiC Content on the Microstructure and Properties of Zr2Al4C5/SiC Composites in situ Fabricated by Spark Plasma Sintering
Authors: Guo Qilong , Wang Jing , Pei Junjun , Li Junguo , Zhang Lianmeng
Published: November 2019

Zr2Al4C5/SiC composite ceramics were successfully fabricated from the powder mixture of Zr, Al, C and SiC by spark plasma sintering method. The composition-dependent densification, phase evolution, microstructure and mechanical properties of the composite ceramics were studied. With increasing the SiC content in the starting powder mixture, the densification behavior of sintered samples was promoted. It is found that the as-sintered products are mainly composed of Zr2Al4C5 matrix and SiC reinforcement, and the fine SiC particles tend to disperse on the matrix grain boundaries. Besides, the addition of SiC particles can evidently hinder the coarsening of Zr2Al4C5 grains. Both the Vickers hardness and Young’s modulus of composites ceramics gradually increase as increasing the SiC content. The fracture toughness of the composites decreases first then increases with the increase in the SiC and the Zr2Al4C5/30vol%SiC sample possesses the maximum value of 4.4MPa·m1/2.
Effect of He2+ Ion Irradiation on the Crystal Structure of Non-stoichiometric Sm2+xZr2-xO7-x/2 (x = 0, 0.2, 0.4, 0.6)
Authors: Feng Hanghang , Qu Zhixue , Sun Yuan , Ji Yarou
Published: November 2019

In this paper, a series of non-stoichiometric Sm2+xZr2-xO7-x/2 (x=0, 0.2, 0.4, 0.6) were synthesized by chemical co-precipitation method. He2+ ion irradiation experiments were carried out with irradiation energy of 500 KeV and irradiation flux of 5×1016 ions/cm2. Effect of He2+ ion irradiation on the crystal structure was characterized by XRD, GIXRD, and Raman spectroscopy. The XRD patterns show that all the peaks shift to lower diffraction angles and the characteristic peaks of pyrochlore structure weaken after irradiation, which suggests an expansion of the lattice and the degeneration of pyrochlore structure. Moreover, the GIXRD patterns reveal the existence of an irradiated layer on the surface of the sample.
Preparation and Thermal Stability of Quartz Fiber Reinforced Silicon Doped Aluminum Aerogel Composites
Authors: Wang K Y , Liu R X , Zhang L , Yan Y H , Sui X Y , Zhou C L , Cheng Z Q
Published: November 2019

Aerogel composites have drawn great attention as innovative thermal insulation materials in the field of thermal protection. In this study, quartz fiber reinforced silicon doped aluminum aerogel composites were synthesized using aluminum chloride hexahydrate (AlCl3·6H2O) and tetraethoxysilane (TEOS) co-precursor by sol-gel and supercritical fluid drying. The composites were characterized by FTIR, BET, SEM and Quartz lamp simulation test. The results showed that quartz fiber reinforced aerogel composites exhibited low density, low thermal conductivity and high temperature thermal stability. The thermal conductivities of composites increased from 0.025 W·m−1·K−1 at 150°C to 0.121 W·m−1·K−1 at 1200°C. The as-prepared composites exhibited high specific surface area (515 m2/g) with low density of 0.23 g/cm3. After being heated to 1000°C and 1200°C for 2 h, the surface area of composites reached to 217 and 68 m2/g, respectively. The aerogel composites with 25mm thickness was evaluated by quartz lamp at 1200°C for 1500 seconds. The back surface temperature of 732.7°C demonstrated excellent heat insulation performance of the aerogel composites.
Toughening of WC-Co Cemented Carbides by In-stiu Transformed Carbon Fiber
Authors: Lv Changchun , Ren Xiaoyong , Wang Chengbiao , Peng Zhijian
Published: November 2019

WC-2Co cemented carbides toughened by in situ transformed carbon fibers were prepared by hot-press sintering at 1450°C using pre-oxidized polyacrylonitrilefibers (PANf) as the precursor. The phase composition, microstructure and mechanical properties of the samples with different added fractions of PANfwere investigated. The results show that the PANftransformed in situ into carbon fibers at 1450°C during the hot-press sintering. The formed carbon fiber could supply carbon to the sintering system, suppressing the formation of η phase and improving the relative density of the samples. With the increase in the added fraction of PANf, the Vickers hardness of the samples initially increased and then slightly decreased, reaching its maximum of about 1900 HV10with 0.5 wt.% PANf. The flexural strength and fracture toughness of the samples gradually increased from 530 MPa and 5.5 MPa·m1/2to 700 MPa and 7.5 MPa·m1/2with the increase in the added fraction of PANffrom 0 to 2 wt.%. The toughening mechanisms were cracks deflection, fiber pull-out and crack bridging.
Preparation and Thermal Properties of LaPO4 Ceramics
Authors: Dong Hongying , Chen Xiaodong , Li Jianguo , Jia Pengwei , Shuang Yingchai , Sun Qinghong , Ma Wen
Published: November 2019

Ceramic thermal barrier coatings (TBCs) are widely used on the gas turbine engine. As one of the candidate TBC materials, LaPO4 has attracted much attention. In the present study, the bulk LaPO4 was prepared by spark plasma sintering (SPS). The effect of different preparation conditions on the properties of the obtained LaPO4 ceramic was studied. The phase composition, microstructure, thermal expansion and thermal conductivity of the LaPO4 ceramic with heat treatment at 1450°C for different time were studied by XRD and SEM.
Study on Scintillation Properties of Several Non-fluoride Halides under Low Energy241 Am radiation
Authors: Liu S , Hou Y , Yuan H , Gui Q , Zhang C , Fang Z , Zhang M
Published: November 2019

A few of halide inorganic scintillation crystals have been applied as radiation detection materials and are playing important roles in nuclear medicine, high energy physics, security inspection, petroleum logging and so on, but most of them are on the way of research and development. In this paper, a series of novel halide scintillation crystals, LaBr3(Ce), LaCl3(Ce), SrI2(Eu), Cs2LiYCl6(Ce) and NaI(Tl) were studied using low energy 241Am radioactive source. The effect of reflective film thickness on low-energy ray transmittance and light output of encapsulated scintillators was investigated, Teflon thickness of 0.48 mm as reflective film is best choice to obtain higher light collection and better radiation transmittance. Among all these crystals, LaBr3(Ce) crystal has excellent energy resolution above 25keV gamma ray radiation, 9.3% at 26.34 keV, 8.4% at 59.54 keV and2.6% at 661.66 keV. Only NaI (Tl) crystal works fine below 25 keV X-rays radiation, with energy resolution of 17.68% at 13.9 keV, 14.16% at 17.8 keV and 13.42% at 20.8 keV.
Study on High-Temperature Performance of LaBr3(Ce) Scintillators
Authors: Hou Y , Liu S , Yuan H , Gui Q , Zhang C , Fang Z , Zhang M
Published: November 2019

In this paper, the relative light output, energy resolution and count rate of encapsulated LaBr3 (Ce) crystals were tested under the temperature from 25 °C to 175 °C using 137Cs γ radioactive source. The variation of high temperature scintillation performance of LaBr3 and NaI(Tl) crystal packages was measured and analyzed. The results show that the decline of light output of LaBr3(Ce) scintillation crystal is about 80% of that of NaI(Tl) at 175 °C. The energy resolution of LaBr3(Ce) at high temperature 175 °C is approximately 8%, which is better than the 9.9% energy resolution of NaI(Tl) scintillation crystals at room temperature 25 °C. The count rate of LaBr3(Ce) is about 5-6 times more than that of the NaI(Tl) crystal.
Compressive Creep Prediction of Corundum-Mullite Refractories Based on BP Neural Network
Authors: Deng Lina , Yi Shuai , Zeng Luju , Xue Fei , Pan Chuancai , Lin Guowei , Liu Yueqiang , Zhang Hang , Liu Xiaochen , Xie Jinli
Published: November 2019

Compressive creep of corundum-mullite refractories is an important performance to measure whether they can be used stably for a long time at high temperature. Therefore, a compressive creep prediction method of corundum-mullite refractory based on BP neural network is proposed. The inputs of the BP neural network are the content of Al2O3, SiO2, Fe2O3 and the time of high temperature whereas creep rate is the output. The results show that the predicted results can correspond well with the experimental results. The developed BP neural network model can efficiently and accurately predict the creep rate of corundum-mullite refractories.
Investigation on Preparation of Al0.52Zr0.48O1.74 by Microwave Pyrolysis
Authors: Gao Qiancheng , Chen Yongqiang , Zhang Ning , Chu Songzhu , Tao Zhichuang , Zhang Rui , Li Hongxia
Published: November 2019

ZTA composite powder was prepared by muffle furnace heating and microwave heating respectively. The effect of pyrolysis on the preparation of ZTA composite powder was investigated. Zirconium chloride (ZrOCl2•(8H2O)), aluminium sulfate and ammonia were used as raw materials. Heating temperatures were at 600°C, 700°C, 800°C, 900°C, 1000°C for 20 min respectively. XRD and SEM were carried out to characterize samples. Results showed that microwave heating completed the preparation of ZTA composite powder at an excellent lower temperature (600°C) with an optimum size (211 nm). It is mainly due to the rapid coupling between microwave and materials. The different of crystal phase of the samples by muffle furnace heating and microwave heating is mainly due to the selective response between microwave and ZTA composite materials. Microwave plasma is the main factor leading to grain refinement of ZTA ceramic powder.
Research on Corrosion Resistance of Al2O3-MgAl2O4 Refractories and SiC-MgAl2O4 Refractories to Gasifier Slag
Authors: Sun Honggang , Li Hongxia , Zhao Shixian , Du Yihao , Wang Lan , Si Yaochen
Published: November 2019

Spinel-containing refractory is a kind of potential chromium-free refractory for coal gasification because MgAl2O4 spinel has good slag resistance. Corundum-spinel refractories with w(Al2O3)=94%, w(MgO)=5% and SiC-spinel refractories with w(SiC)=64%, w (Al2O3)=5% were prepared. The crucible specimens were tested for slag corrosion with commercial gasifier slag at 1 500°C for 1 h in reducing atmosphere. XRD analysis were researched on the sidewall of the crucible after slag test. Microstructure and chemical composition of samples in slag corrosion zone were analyzed by SEM and EDS. The results show that the slag resistance of SiC-MgAl2O4 refractory was significantly better than Al2O3-MgAl2O4 refractory. The corundum particles were decomposed into fine particles by the slag, and the microstructure was destroyed. The oxidation of the surface of the silicon carbide particles formed a high-viscosity glass phase with the infiltrated slag, which was benefit to prevent the slag penetration into the interior. And a solid solution of (Mg, Fe)O·Al2O3 composite spinel was formed in matrix of the sample after slag penetration because MgAl2O4 absorbed FeO in the slag. It is speculated that the spinel solid solution repairs and strengthens the structure of the matrix, which improves the slag resistance.
Influence of Sucrose Binder on the Oxidation Resistance of MgO-C Refractory
Authors: Lv Zhenfei , Zhu Ling , Zhang Weiyi , Shi Tengteng , Min Xin , Wu Xiaowen , Liu Yan-gai , Fang Minghao , Huang Zhaohui
Published: November 2019

In this study, novel MgO-C refractories using environmentally friendly sucrose as binder were prepared. To solve the harmful effects of formaldehyde and phenolic compounds that cause serious harm to the environment and human health released during the development, production and use of phenolic resin binders for MgO-C refractories, MgO-C refractories using environmentally friendly sucrose instead of phenolic resins as binders were prepared. The phase, microstructure, oxidation resistance and the antioxidant mechanism of MgO-C refractories prepared by adding sucrose as binder at different temperatures were analyzed. The formula between the weight loss of the material and the temperature is y=1.6225x+0.215 (600°C ∼ 1200°C). The addition of aluminium resulted in the formation of Al2O3 inside the refractories. Meanwhile, MgAl2O4 crystals were synthesized by Al2O3 and MgO at high temperature. The formation of Al2O3 and MgAl2O4 played an important role in improving the oxidation resistance property of MgO-C refractories using sucrose as binder.
The Behavior of Slag Resistance of MgO-C Refractory Prepared by Sucrose as Binder
Authors: Shen Xiulin , Zhu Ling , Lv Zhenfei , Shi Tengteng , Yin Zhaoyu , Min Xin , Wu Xiaowen , Liu Yan-gai , Fang Minghao , Huang Zhaohui
Published: November 2019

The harmful components such as formaldehyde and phenolic compounds released during the development, production and use of MgO-C refractories prepared by using phenolic resin as a binder can cause serious harm to the environment and human health. In this paper, MgO-C refractory material with sucrose as binder and metal aluminium powder as antioxidant is prepared. Different slag temperature and time factors have a largely influence on the slag corrosion resistance of as-prepared samples. By analyzing the microstructure and composition of the samples, it is found that under the condition of constant time, the higher the temperature, the more obvious the slag corrosion phenomenon; under isothermal conditions, the longer the time, the more obvious the slag corrosion phenomenon. At the same time, it is revealed that the main corrosion process of MgO-C refractories prepared by adding sucrose as a binder is carbon oxidation and slag corrosion, which provides a theoretical basis for optimizing the slag resistance of MgO-C refractories.
Optimization and Application Technology of Reflective Foils Using in Zirconia Fiber Insulation Materials
Authors: Ai Bing , Zhang Shichao , Sun Xiankai , Sun Haoran , Chen Yufeng , Fang Kai , Yan Dachen
Published: November 2019

Graphite paper was used as reflective foils in the zirconia fiber insulation materials system, the effects of the number, spacing and emissivity of reflective foils on the thermal insulation properties of zirconia fiber insulation materials were studied. It was found that when the number of reflective foils is 10, interlayer spacing was 1 mm, the minimum thermal conductivity of the insulation materials was obtained. Zirconia superfine powder was used to reduce the emissivity of reflective foils, the modified reflective foils was used in the zirconia fiber insulation materials system, it was found that when the emissivity of the modified reflective foils was 0.37, the minimum thermal conductivity of insulation materials was obtained.
Erosion Mechanism of Li-Ion Batteries Cathode Materials on Si3N4-SiC and SiO2-SiC Refractories
Authors: Duan X K , Qian F , Chen Y Q , Li H X , Guo A , Si Y C , Wang X F , Liu G Q
Published: November 2019

The erosion mechanism of Li-ion ternary cathode material on Si3N4-SiC and SiO2-SiC refractory slabs was studied at 780 °C for 20h. The results show that the erosion resistance of Si3N4-SiC is much better than that of SiO2-SiC refractory slab after heat treatment for 20h. Erosion mechanism of the two kinds of refractory slabs are different. Inward diffusion of Li2O reacts with a large amount of SiO2 in the SiO2-SiC system. This leads to a large number of reaction products, so that the incompletely reacted SiC particles fall off along with the reaction product, causing the erosion of SiO2-SiC. For Si3N4-SiC, it is mainly because the dense SiO2 protective layer produced by oxidation of Si3N4 prevents further oxidation of Si3N4 and SiC in the system, giving the material excellent erosion resistance.