Toward a better understanding of multifunctional cement-based materials: The impact of graphite nanoplatelets (GNPs)

The impact of graphite nanoplatelets (GNPs) on the physical and mechanical properties of cementitious nanocomposites was investigated. A market-available premixed mortar was modified with 0.01% by weight of cement of commercial GNPs characterized by two distinctively different aspect ratios.The rheological behavior of the GNP-modified fresh admixtures was thoroughly evaluated. Hardened cementitious nanocomposites were investigated in terms of density, microstructure (Scanning Electron Microscopy, SEM and micro–Computed Tomography, μ-CT), mechanical properties (three-point bending and compression tests), and physical properties (electrochemical impedance spectroscopy, EIS and thermal conductivity measurements). At 28 days, all GNP-modified mortars showed about 12% increased density. Mortars reinforced with high aspect ratio GNPs exhibited the highest compressive and flexural strength: about 14% and 4% improvements compared to control sample, respectively. Conversely, low aspect ratio GNPs led to cementitious nanocomposites characterized by 36% decreased electrical resistivity combined with 60% increased thermal conductivity with respect to the control sample.     

Effect of Zr addition on the interfacial reaction of the SiC joint brazed by Inconel 625 powder filler

Ni-based alloys are believed to be the most suitable brazing fillers for SiC ceramic application in a nuclear environment. However, graphite, which severely deteriorates the mechanical property of the joint, is inevitable when Ni reacts with SiC. In this paper, Different amounts of Zr powders are mixed with Inconel 625 powders to braze SiC at 1400 °C. When Zr addition reaches 40 wt%, the brazed seam confirms the absence of graphite. This research proves that Zr can avoid the graphite’s formation by suppressing Ni’s activity. The room-temperature shear strength of the joint with graphite’s absence is tested to be 81.97 MPa, which is almost three times higher than that of the joint with graphite. The interfacial reaction process and mechanism of the SiC joint are investigated and explained in this paper using thermodynamic calculations.     

Superior hydrogen evolution electrocatalysis enabled by CoP nanowire array on graphite felt

Renewable electricity-powered hydrogen production is an attractive alternative to unsustainable industrial processes, but the large-scale implantation of such sustainable technology still requires efficient and noble-metal-free electrocatalysts for driving cathodic hydrogen evolution reaction (HER), especially under alkaline conditions. In this paper, CoP nanowire array was in-situ developed on porous graphite felt (CoP/GF) as a new 3D electrocatalyst in facilitating hydrogen evolution electrocatalysis. This CoP/GF presents outstanding HER activity, requiring a low overpotential of 130 mV to deliver a current density of 20 mA cm^?2 as tested in 1.0 M KOH. Furthermore, this free-standing catalyst exhibits impressive long-term durability of up to 50 h under working conditions.     

汽车密封件双料一体旋转模具设计

针对PP+TPE汽车密封件设计了大型双料一体旋转注射模,介绍了二次合模的精确定位、可控注射系统、顶出平衡设计。该模具技术能够使两种性能完全不同的材料按照指定区域分布,并且达到塑件尺寸的精度需求,实现同时与钣金、玻璃、塑件等不同材质的零件进行复合配套。本项目实施后,在模具精度、寿命等方面接近或部分达到国外同类产品先进水平,而价格仅为国外产品的40%,性价比优势明显。     

Structure and crystallization behavior of complex mold flux glasses in the system CaO-Na2O-Li2O-CaF2-B2O3-SiO2: A multi-nuclear NMR spectroscopic study

The structure of mold flux glasses in the system CaO-(Na,Li)₂O-SiO₂-CaF₂ with unusually high modifier contents, stabilized by the addition of ∼4 mol% B₂O₃, is studied using ⁷Li, ²³Na, ¹⁹F, ¹¹B, and ²⁹Si magic-angle-spinning (MAS), and ⁷Li{¹⁹F} and ²³Na{¹⁹F} rotational echo double-resonance (REDOR) nuclear magnetic resonance (NMR) spectroscopy. When taken together, the spectroscopic results indicate that the structure of these glasses consists primarily of dimeric [Si₂O₇]⁻⁶ units that are linked to the (Ca,Na,Li)-O coordination polyhedra, and are interspersed with chains of corner-shared BO₃ units. The F atoms in the structure are exclusively bonded to Ca atoms, forming Ca(O,F)_n coordination polyhedra. This structural scenario is shown to be consistent with the crystallization of cuspidine (3CaO·2SiO₂·CaF₂) from the parent melts on slow supercooling. The progressive addition of Li to a Na-containing base composition results in a corresponding increase in the undercooling required for the nucleation of cuspidine in the melt, which is attributed to the frustrated local structure caused by the mixing of alkali ions.     

汽车加油口双色注射模设计

分析了汽车加油口塑件结构,确定了注射成型方案、进胶方式,并介绍了通过滑块与开模动作配合实现塑件脱模的过程。     

带斜孔的U形支座注塑模具设计

根据某品牌汽车U形支座结构特点设计了模具的浇注系统、成型零件、推出机构以及斜孔抽芯机构等关键部件。其中采用热流道系统与普通流道系统相结合的复合结构,解决塑料材料流动性差的工艺问题;采用二级滑块抽芯机构解决斜孔成型与抽芯的结构难题。生产实践表明:该模具结构紧凑,动作可靠。     

Effects of graphite nano-flakes on thermal and microstructural properties of TiB2–SiC composites

In the last decades, the production of ultra-high temperature composites with improved thermo-mechanical properties has attracted much attention. This study focuses on the effect of graphite nano-flakes addition on the microstructure, densification, and thermal characteristics of TiB₂–25 vol% SiC composite. The samples were manufactured through spark plasma sintering process under the sintering conditions of 1800 °C/7 min/40 MPa. Scanning electron microscopy images demonstrated a homogenous dispersion of graphite flakes within the TiB₂–SiC composite causing a betterment in the densification process. The thermal diffusivity of the specimens was gained via the laser flash technique. The addition of graphite nano-flakes as a dopant in TiB₂–SiC did not change the thermal diffusivity. Consequently, the remarkable thermal conductivity of TiB₂–SiC remained intact. It seems that the finer grains and more interfaces obstruct the heat flow in TiB₂–SiC–graphite composites. Adding a small amount of graphite nano-flakes enhances the densification of the mentioned composite by preventing the grain growth.     

铸造3D喷墨打印砂型尺寸精度测量评定方法研究

随着铸造行业的转型发展,3D打印技术已经成熟的应用于制造铸造砂型,所制作的砂型不再单单作为铸造过程中的半成品,而是可以作为产品面向各铸造厂进行销售。但是目前对于砂型的检验标准存在缺失,对于砂型质量的把控和评定缺少依据。针对铸造砂型的尺寸精度,通过设计制作测量试块,给出了一种3D喷墨打印砂型的测量方法及评定标准,填补了目前铸造行业中这一领域在标准上的空白,对推动3D打印技术在铸造行业的应用以及砂型的产品化有着重要的意义。