添加碳须的阀控式密封铅蓄电池性能的改进

将长碳须(长度与直径之比甚大)加于阀控式铅酸蓄电池的正、负极活物质中。发现它有助于活物质颗粒之间形成高电子导电网络。添加在涂膏式正极板中可以减小欧姆电阻并提高化成充电效率,从而减少化成所需的时问和充电所需的电量。添加在正极板内的碳须有一半在化成过程中分解,导致大孔径的大孔隙体积形成,从而使放电时活物质利用率有所提高。当碳须加于涂膏式的负极板(负极铅膏),可以减小阀控式铅酸蓄电池的容量损失,并能延长其深放电循环寿命。据认为,由于导电网络的形成,碳须减小了活物质在放电终期的电阻,使其易于再充电,PbSO_4的积存也更少。实际上,添加碳须的负极活物质在电池寿命终止时,很少有PbSO_4积存下来。

Increasing both the electromagnetic shielding and thermal conductive properties of three-dimensional graphene-CNT-SiC hybrid materials

During the operation of electronic devices,a considerable amount of heat and electromagnetic radiation is emitted.Therefore,the investigation of materials with electromagnetic shielding and thermal management abilities has significant importance.Hybrid materials of three-dimensional graphene networks containing both carbon nanotubes(CNTs)and SiC whiskers(3D graphene-CNT-SiC)were synthesized.Using an aqueous-phase reduction method for the self-assembly of the graphene oxide,a three-dimen-sional porous graphene structure was fabricated.SiC whiskers,inserted between the graphene layers,formed a framework for longit-udinal thermal conduction,while CNTs attached to the SiC surface,created a dendritic structure that increased the bonding between the SiC whiskers and graphene,improving dielectric loss and thermal conductivity.It was found that the thermal conductivity of the hybrid material reached 123 W·m^(-1)·K^(-1),with a shielding effectiveness of 29.3 dB when the SiC addition was 2%.This result indic-ates that 3D graphene-CNT-SiC has excellent thermal conductivity and electromagnetic shielding performance.

Reduced graphene oxide porous films containing SiC whiskers for constructing multilayer electromagnetic shields

Developing lightweight and flexible thin films for electromagnetic interference(EMI)shielding is of great importance.Porous thin films of reduced graphene oxide containing SiC whiskers(SiC@RGO)for EMI shielding were prepared by a two-step reduction of graphene oxide(GO),in which the two steps were chemical reduction by HI and the solid phase microwave irradiation.A significant increase of the film thickness from around 20 to 200μm was achieved due to the formation of a porous structure by gases released during the 3 s of solid phase microwave irradiation.The total shielding effectiveness(SET)and the reflective SE(SE_(R))of the SiC@RGO porous thin films depended on the GO/SiC mass ratio.The highest SET achieved was 35.6 dB while the SE_(R) was only 2.8 dB,when the GO/SiC mass ratio was 4∶1.The addition of SiC whiskers was critical for the multi-reflection,interfacial po-larization and dielectric attenuation of EM waves.A multilayer film with a gradient change of SE values was constructed using SiC@RGO porous films and multi-walled carbon nanotubes buckypapers.The highest SET of the multilayer films reached 75.1 dB with a SE_(R) of 2.7 dB for a film thickness of about 1.5 mm.These porous SiC@RGO thin films should find use in multilayer or sand-wich structures for EMI absorption in packaging or lining.

Preparation of MgO whisker from magnesite tailings and its application

Magnesium carbonate whisker as precursor was prepared from the low-grade magnesite tailings by the route of calcination, hydration, carbonation and thermal decomposition, and then MgO whisker was prepared by calcining the precursor. In addition, the effect of MgO whisker addition on sintering and thermal shock resistance of refractory was also investigated. The results show that the thermal decomposition product is MgCO3·3H2O and its morphology is remarkably influenced by the types of additives, and magnesium carbonate whisker with the length of 10-60 μm and length-diameter ratio of 10-20 is successfully prepared when a type of soluble magnesium salt is added. MgO whisker with the length of 10-40 μm is derived from precursor with the heating rate of 1 ℃/min. The thermal shock resistance of refractory is significantly improved by the addition of MgO whisker due to its effect on binding and preventing crack expanding, and the proper amount of whisker addition is around 3%.

Mechanical properties of calcium carbonate whisker-reinforced high-strength cement mortar

In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural strength,split tensile strength and work of fracture are measured.Microstructures and micromechanical behaviors are investigated using scanning electron microscopy.The strengthening and toughening mechanisms and the efficiency of whisker-reinforced high-strength cement mortar are discussed.The results show that the addition of CaCO3 whiskers brings positive effects on the high-strength cement mortar.The strengthening and toughening mechanisms are whisker-cement coalition debonding,whisker peeling,whisker impact breakage and whisker bridging.Crack deflection is one efficient mechanism,but it is hard to be achieved in high-strength cement mortar.And the interfacial bonding strength between whiskers and the cement mortar matrix should be appropriately weak to introduce more crack deflection mechanisms to strengthen and toughen the cement mortar efficiently.

Grinding Characteristics Of Directionally Aligned SiC Whisker Wheel - Comparison With A12O3 Fiber Wheel

A unique SiC whisker wheel was invented,in which the whiskers were aligned normally to the grinding wheel surface.In this paper,grindabilities of the SiC whisker wheel are investigated and compared with those of other wheels of SiC grains,Al2O3 grains,as well as Al2O3 long and short fibres which were also aligned normally to the grinding wheel surface,respectively.The main research contents concern grinding characteristics of a directionally aligned SiC whisker wheel such as material-removal volume,wheel-wear rates,integrity of the ground surfaces,grinding ratios and grinding efficiency.Furthermore,grinding wheels of whiskers and fibres have a common disadvantage:they tend to load easily.The authors have proposed a simple method of loading-free grinding to overcome this propensity and investigate some related grinding characteristics under loading-free grinding conditions.

The synthesis of micro-sized silicon carbide whiskers and the application for heat transfer enhancement

This paper presents a simple and cost-effective method for the production of micro-sized silicon carbide whiskers at high yield and the effect on heat transfer enhancement for the whisker laden fluids. For SiC whisker synthesis, the starting powder mix- ture is obtained by milling short carbon fibers with the white ashes of rice hulls. Calcina：ion in argon, together with the subse- quent purification process, results in a high yield of SiC whiskers, which possess a diameter of 200-400 nm and a length of several tens of microns. The formation of the whiskers is discussed according to VS growth mechanism. Convective heat transfer performance in small channel tubes is then studied for fluid systems mixed with those micro-sized SiC whiskers at different concentrations. The heat transfer coefficient of SiC containing fluid can be significantly improved in comparison to the base fluid.