Effect of TiO2 addition and high magnetic field sintering on properties of vitrified bond CBN composites

Vitrified bond CBN composites, with different amounts of TiO₂ doping, were prepared by conventional sintering and high magnetic field sintering processes. Mechanical properties, cross-sectional morphology, refractoriness, fluidity and structural characterization have been carried out to understand the role of TiO₂ addition and sintering conditions. Results show that TiO₂ addition significantly affected bending strength, refractoriness and fluidity of vitrified bonds. In addition, high magnetic field sintering improved bending strength and the microstructure of vitrified bond CBN composites. Due to high magnetic field sintering, CBN grains were completely covered by vitrified bond and exhibited fewer pores. In addition, high magnetic field promoted the growth of specific grains, such as SiO₂, whereas suppressed grain growth of other crystal phases, such as NaAlSi₃O₈.     

Effects of Ni addition on properties of vitrified bond CBN composites in strong magnetic field

Properties of vitrified bond with varying Ni doping amounts were extensively investigated. Effects of Ni addition on microstructures and properties of vitrified bond cubic boron nitride (CBN) composites prepared in strong magnetic field were investigated for applications in CBN grinding tools. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction and other methods. The refractoriness, fluidity, and bending strength of vitrified bond were evaluated. Bending strengths, microstructures, and phase compositions of vitrified bond CBN composites achieved using conventional and strong electromagnetic sintering techniques were compared. Results show that the addition of Ni to vitrified bond CBN composites improved the fluidity and bending strength of the vitrified bond. Strong electromagnetic sintering improved the mechanical strength and pore structure of vitrified bond CBN composites. Moreover, the introduction of the strong magnetic field facilitated Ni migration and aggregation in vitrified bond, rotated abrasives, and formed new substances, thus increasing the stability of vitrified bond CBN composite thermal material. Also, strong magnetic field inhibit grain growth of non-magnetic and ferromagnetic materials with fine-grain effect.     

Effects of Y2O3 addition on structure and properties of LZAS vitrified bond for CBN grinding tools application

The effects of Y₂O₃ addition on the structure and properties of Li₂O–ZnO–Al₂O₃–SiO₂ (LZAS) vitrified bonds were firstly investigated for CBN grinding tools application. Glasses and glass-ceramics were characterized using differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy and infrared spectroscopy. The thermal expansion coefficient (TEC), microhardness, bending strength and chemical durability of the obtained products were also evaluated. Results showed that Y₂O₃ acted as the network former in the track of SiO₄ tetrahedrals. Introducing Y₂O₃ in the glasses increased the glass transition temperature and crystallization temperature. The crystallization of the main β-quartz_ss phase increased with increase of Y₂O₃ content. The morphology of the crystals was dependent on the Y₂O₃ content. The TEC (5.15×10⁻⁶/°C) of vitrified bond containing 1.0 mol% Y₂O₃ (Y1.0) was very close to the TEC (5.0×10⁻⁶/°C) of CBN grains. Moreover, Y1.0 vitrified bond exhibits a high microhardness (5.98 GPa), a high bending strength (202 MPa) and a good chemical durability (20 days, DR=2.8×10⁻⁹ g/cm² min), suggesting that it would be a promising material for CBN grinding tool.     

Effect of polycrystalline mullite fibers on the properties of vitrified bond and vitrified CBN composites

The effect of polycrystalline mullite fibers (PMFs) on the properties of vitreous bonds and vitrified CBN composites was investigated. The results show that the addition of PMFs can increase the porosity of composites and reduce the fluidity of binders. The vitrified composites incorporating 6.4 wt% PMFs display excellent mechanical strength, which is enhanced by 21.2% compared with that of composites without PMFs sintered at the optimal sintering temperature. Meanwhile the thermal expansion coefficient of vitrified bond reduces from 6.256×10⁻⁶ °C⁻¹ to 4.805×10⁻⁶ °C⁻¹ with increasing fraction of PMFs. The improvement of mechanical strength is associated with the change of cracking mechanisms of the composites with fibrous crystals and the existence of several observed mechanisms, including fiber pull-out, fiber bridging and rupture.     

Influence of TiO2 amount on the interfacial wettability and relevant properties of vitrified bond CBN composites

The influence of TiO₂ amount on the microstructure and relevant properties of SiO₂-Al₂O₃-B₂O₃-Na₂O-Li₂O-BaO vitrified bond and vitrified bond CBN composites were systematically studied via SEM, EDS, FTIR, and XPS. Results indicated that adding TiO₂ could regulate the quantity of β-quartz solid solution and rutile crystals in the vitrified bond and considerably affect the thermal properties and mechanical strength of this bond. Under sintering temperature, the dense B₂O₃ oxide layer on the CBN surface diffused into vitrified bond and reacted with Ti⁴⁺ enriched at the interface to form a strong chemical Ti-B bond. This reaction extensively improved the interfacial wettability between the CBN and the vitrified bond. When the TiO₂ amount was 6wt.%, the interfacial wettability significantly improved, and the wetting angle decreased from 68° to 43°. The flexure strength and hardness of the composites were 116.18 MPa and 128 HRB, which were 48.49% and 34.74% higher than those of the basic-formula composites, respectively.     

Preparation of a novel vitrified bond CBN grinding wheel and study on the grinding performance

The vitrified bond CBN grinding wheels are characterized by high efficiency, high precision, and low environmental pollution. In recent years, the vitrified bond CBN grinding wheel has been widely used in manufacturing industries such as aerospace, automotive, and machine tools. In this study, a novel vitrified bond formulation containing nano SiO₂ and nano CeO₂ is selected to prepare the grinding wheel. The grinding experiments on 45# steel and YG20 alloy indicate that the grinding performance of the nano vitrified bond grinding wheel is significantly better than that of the conventional vitrified bond grinding wheel. The introduction of nano SiO₂ and nano CeO₂ greatly improves the machining performance of the vitrified bond CBN grinding wheel.     

Variations in structure and properties of vitrified bonds and vitrified diamond composites prepared by sol-gel and melting methods at different sintering temperature

Differences in structure and properties of Na₂O–Al₂O₃–B₂O₃–SiO₂ vitrified bonds and vitrified diamond composites prepared by sol-gel and melting methods were methodically discussed. Results showed that the vitrified bond prepared by sol-gel method contained more [AlO₄] tetrahedron and owned higher bending strength, with the maximum value reaching 137 MPa, 31.73% higher than that prepared by melting method (104 MPa). As the sintered temperature rose, coefficient of thermal expansion of the vitrified bond prepared by sol-gel method increased first and then decreased, acquiring a maximum value of 5.75 × 10⁻⁶ °C ⁻¹ at 720 °C, which was still much lower than the minimum value of vitrified bond prepared by melting method (7.02 × 10⁻⁶ °C ⁻¹). The vitrified diamond composite prepared by sol-gel method possessed lower sintering shrinkage than that prepared by melting method, and could be applicable to the production of grinding tools with high dimensional accuracy. What's more, the maximum bending strength of vitrified diamond composites obtained by sol-gel method was 106 MPa, 24.7% higher than that of vitrified diamond composites prepared by melting method (85 MPa).     

Effects of Al2O3 addition on sintering behaviour,microstructure, and physical properties of Al2O3/vitrified bond CBN composite

The effects of Al₂O₃ content on the sintering behaviour, microstructure, and physical properties of Al₂O₃/vitrified bonds (SiO₂–Al₂O₃–B₂O₃–BaO–Na₂O–Li₂O–ZnO–MgO) and Al₂O₃/vitrified bond cubic boron nitride (CBN) composites were systematically investigated using X-ray diffraction, differential scanning calorimetry, dilatometry, scanning electron microscopy, and X-ray photoelectron spectroscopy. Various amounts of Al₂O₃ promoted the formation of BaAl₂Si₂O₈ and γ-LiAlSi₂O₆, increasing the relative crystallinity of the Al₂O₃/vitrified composite from 85.0 to 93.2%, resulting in residual compressive stress on BaAl₂Si₂O₈, thereby influencing the thermal behaviour and mechanical properties of the Al₂O₃/vitrified composite. The bulk density, porosity, flexural strength, hardness, and thermal conductivity of 57.5 wt% Al₂O₃ sintered at 950 °C were 3.12 g/cm³, 6.1%, 169 MPa, 90.5 HRC, and 4.17 W/(m·K), respectively. The coefficient of thermal expansion of the bonding material was 3.83 × 10^?6 °C^?1, which was comparable to that of CBN, and the number of N–Al bonds were increased, which boosted the flexural strength of the Al₂O₃/vitrified CBN composite to 81 MPa. The excellent mechanical properties, compact structure, and suitable interfacial bonding state with the CBN grains of the Al₂O₃/vitrified composite make it a promising high-performance bonding material for superhard abrasive tools.     

Influence of process conditions on preparation of CBN/Fe-based spherical magnetic abrasive via gas atomization

To meet the demand for high-performance magnetic abrasive particles (MAPs) for finishing of difficult-to-machine materials, CBN/Fe-based spherical composite MAPs were prepared via gas atomization under different process conditions. The effects of nozzle type (single-stage and two-stage), second-stage gas pressure (2, 4, 6, and 8 MPa), and the grain size of the CBN abrasive (W7 and W40) on the MAP quality were studied. The MAPs were analysed through scanning electron microscopy and energy-dispersive spectroscopy. The results indicate that the quality of MAPs prepared using two-stage atomizing nozzles is better than that of MAPs prepared using single-stage nozzles. When the second-stage gas pressure was 6 MPa, the prepared MAPs had the best sphericity, and the CBN abrasive was embedded uniformly and densely on the surface of the iron matrix. For MAPs with the same particle size, the iron matrix wrapped more effectively around CBN abrasives with smaller grain sizes. This research is can serve as a methodological reference for understanding the preparation of ceramic/metal-based spherical composite MAPs via gas atomization.     

Effect of porosity on the grinding performance of vitrified bond diamond wheels for grinding PCD blades

In this paper, the preparation of nano-AlN modified Na₂O–B₂O₃–SiO₂ vitrified bond diamond tools with various porosities is reported. The effects of porosity on the impact strength and grinding properties of the wheels for grinding PCD blades are also discussed. The results show that the porosity not only affects the impact strength of the wheels but also the grinding properties, such as the grinding efficiency, the self-dressing, the service life and the surface roughness of the work pieces. The optimum porosity for nano-AlN modified Na₂O–B₂O₃–SiO₂ vitrified bond diamond wheels for grinding PCD tools is approximately 40.5 vol%.     

Study on the high magnetic field processed ZnO based diluted magnetic semiconductors

Diluted magnetic semiconductors with the unique advantage of simultaneously manipulating the spin and charge of electrons possess potential applications in spintronics and quantum computing, which attracts long-term tremendous attention. It is pivotal and meaningful for practical application that room temperature ferromagnetism has been acquired successively in ZnO based diluted magnetic semiconductors. Although the unclear origin of ferromagnetism hampers their further development, there is a consensus that their magnetic properties are susceptible to materials preparation process. As an extreme condition with high-intensity energy, indirect contact and controllability, high magnetic field has been applied to various materials fabrication. Similarly, high magnetic field is employed in the preparation of ZnO based diluted magnetic semiconductors to adjust microstructural and magnetic properties, such as enhancing Curie temperature, inducing the transition from paramagnetism or diamagnetism to ferromagnetism, and improving ferromagnetism, while exploring the ferromagnetism mechanism from another perspective. In this brief perspective, recent study on the high magnetic field processed ZnO based diluted magnetic semiconductors is reviewed.     

Influence of TiO2 on the physical properties of low-temperature ceramic vitrified bond and mechanical properties of CBN composites

The microstructures and properties of vitrified bond abrasive tools made of CBN grains and advanced vitrified bond systems with different TiO₂ doping amounts were investigated. Based on the experimental observations and analysis, the incorporation of TiO₂ in appropriate amount (4 wt.%) was beneficial to the improvement on flowing ability and thermal expansion property of the vitrified bond systems, and mechanical properties of the CBN composites including bending strength and Rockwell hardness were obviously improved. On the basis of discussion for microstructure, the CBN grains were better covered by vitrified bond and acquired less pores when the content of TiO₂ reached 4 wt.%. These results were related to the role of TiO₂ in the glass network structure which was analyzed by Fourier transform infrared spectroscopy (FTIR).     

Fabrication of c-axis oriented hydroxyapatite ceramics in a rotating high magnetic field using photopolymerization

C-axis oriented hydroxyapatite (HAp) was prepared by colloidal processing using a photopolymerization reaction in a rotating magnetic field with a UV-curable binder as the solvent. This technique achieved a short processing time of 150 s in a magnetic field as a result of rapid solidification induced by the photopolymerization. The slight difference in refractive index between the HAp material and UV curable resin allowed the fabrication of 1.6 mm thick green compacts. The oriented structure in the compact was maintained from the surface down to a depth of 700 μm, but was randomized at depths of 700 μm and beyond. The orientation degree was retained after sintering at 1250 °C, and the relative density of the compact was approximately 97 %. This technique can be effectively utilized for the manufacture of high-performance biomaterials.     

短纤维取向对其橡胶复合材料性能的影响

通过对比性实验,研究了短纤维取向对其橡胶复合材料综合物理机械性能的影响。结果表明,在短纤维取向方向上,复合材料综合物理机械性能较好,并且表现出了各向异性的特性。     

Effects of NiO nanoparticles on the magnetic properties and diffuse phase transition of BZT/NiO composites

A new composite system, Ba(Zr_0.07Ti_0.93)O₃ (BZT93) ceramic/NiO nanoparticles, was fabricated to investigate the effect of NiO nanoparticles on the properties of these composites. M-H hysteresis loops showed an improvement in the magnetic behavior for higher NiO content samples plus modified ferroelectric properties. However, the 1 vol.% samples showed the optimum ferroelectric and ferromagnetic properties. Examination of the dielectric spectra showed that the NiO additive promoted a diffuse phase transition, and the two phase transition temperatures, as observed for BZT93, merged into a single phase transition temperature for the composite samples.     

磁场对聚丙烯腈原丝及其预氧化的影响

在加热条件下对聚丙烯腈(PAN)原丝施加强磁场,研究了磁场对PAN原丝的影响及经过强磁场预处理后的PAN原丝在预氧化过程中产生的变化;采用红外吸收光谱、X射线衍射、扫描电子显微镜等方法对PAN原丝进行表征。结果表明:经磁场强度为1.9 T,磁化时间为60 min的磁场预处理后,PAN原丝的氰基基团取向度从0.37增大到0.46,微晶尺寸减小12.95%,相同预氧化温度下的相对环化率均大幅提高,纤维密度均有增大,预氧化丝的皮芯结构明显改善。     

电场和磁场对催化剂制备过程的影响

综述了近年来电场和磁场在催化剂制备中的影响。从催化剂的成核和长大过程分析了电场和磁场的加入对催化剂形成过程的影响,系统解释了电场和磁场处理与晶粒细化效果、催化活性之间的关系和规律。     

Polymerization in a magnetic field. XV Some azo‐initiators behavior in a high magnetic field

The effect of a high magnetic field of 7 T on styrene polymerization reactions was taken under study. The intervened magnetokinetic modifications are correlated to the system of radical initiation, respectively: benzoyl peroxide, 2, 2′‐azobis(2‐methylpropionitrile), 4, 4′‐azobis(4‐cyanopentanoic acid), and 1,1′‐azobis (cyclohexan‐1‐carbonitrile). The reaction products are also characterized from the viewpoint of their molecular weights correlated with the reaction conditions, as well as their thermal stability. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1025–1031, 2005     

Microstructures and superconducting properties of MgB2 bulk samples processed by ultra-high pressure-assisted sintering

Nanocrystalline MgB₂ bulk superconductors have been fabricated by ultra-high pressure-assisted sintering (～ 5 GPa) over a range of temperatures (700 °C-1100 °C). Phase evolution and morphology, grain size and lattice defects were systematically investigated. The superconducting performance was measured using magnetization methods and linked to the corresponding microstructural features. A sample processed at 900 °C and 5 GPa achieved a J_c value of 4.5 × 10⁷ A/m² at 4.2 K, 6 T, 30 times and more than 100 times higher than those prepared at 800 and 1100 °C respectively, under similar pressures. Its superior superconducting properties arise from the combination of limited grain growth, retained crystal defects and complete densification achieved in a rapid process by the application of ultra-high pressure. This study reveals the importance of microstructure in controlling the superconducting behavior in sintered MgB₂, especially the sample homogeneity that can affect the length scales over which the supercurrents flow.     

Using the external magnetic field of composites to control fiber orientation and enhancement of electrical conductivity

The industrial developments have led to more applications of various composites. Since fiber orientation and distribution will influence product performance in composites, controlling said orientation and distribution is of critical importance. This study used external magnetic fields to control the fiber orientation and distribution in a polymer. The orientation of the actual fibers under magnetic field control during flowing was observed using a visualization system, which was made by PMMA and transparent epoxy as an upper cover and filling polymer. In order to clearly observe and calculate, 0.1 wt% fiber content was used, and 0.3 wt% fiber content was used to measure conductivity. Fiber distribution angles without a magnetic field concentrate parallel to the flow direction (0° ~ 30° and 151° ~ 180°) while distribution angles under magnetic field control were concentrated along the magnetic field direction, which was perpendicular to the flow direction (61° ~ 120°). The higher the magnetic flux density, the larger the torque of the electromagnetic field on the fibers and the higher the orientation of fibers was with the magnetic field. The electrical conductivity was 12.23 times higher for 1 mm fibers in an external magnetic field versus no magnetic field.