HF Corrosion Research Articles

Effects of water contamination on the electrical properties of 18650 lithium-ion batteries

Effects of water on the voltage, internal resistance, initial capacity and cycling behavior of 18650-type lithium-ion batteries are studied. The voltage curves of the first charging can be used to judge whether cells are contaminated by water, because the voltage growth rates of cells are obviously different (>100 mV) between water-free batteries and containing water batteries at the first charging period of 10–50 min. The self-discharging performances of water contamination cells are also larger, because water-related side effects happen continuously during aging at high voltage of 4.2 V. Besides, HF corrosion on the cathode materials and Co ion dissolved out from lithium nickel cobalt manganese oxides lead to rapid capacity fading from >90% (100 cycles) to <80% (300 cycles, 0.5 C charging/0.5 C discharging).

Sputtering graphite coating to improve the elevated-temperature cycling ability of the LiMn2O4 electrode

To improve the cycle performance of LiMn2O4 at elevated temperature, a graphite layer is introduced to directly cover the surface of a commercial LiMn2O4-based electrode via room-temperature DC magnetron sputtering. The as-modified cathodes display improved capacity retention as compared to the bare LiMn2O4 cathode (BLMO) at 55 °C. When sputtering graphite for 30 min, the sample shows the best cycling performance at 55 °C, maintaining 96.2% capacity retention after 200 cycles. Reasons with respect to the graphite layer for improving the elevated-temperature performance of LiMn2O4 are systematically investigated via the methods of cyclic voltammetry, electrochemical impedance spectroscopy, X-ray photoelectron spectrometry, scanning and transmission electron microscopy, X-ray diffraction and inductively coupled plasma-atomic emission spectrometry. The results demonstrate that the graphite coated LiMn2O4 cathode has much less increased electrode polarization and electrochemical impedance than BLMO during the elevated-temperature cycling process. Furthermore, the graphite layer is able to alleviate the severe dissolution of manganese ions into the electrolyte and mitigate the morphological and structural degradation of LiMn2O4 during cycling. A model for the electrochemical kinetics process is also suggested for explaining the roles of the graphite layer in suppressing the Mn dissolution.

A graphite functional layer covering the surface of LiMn2O4 electrode to improve its electrochemical performance

Here, we first report the introduction of sputtering a graphite layer covering the surface of the as-fabricated LiMn2O4 cathode to form a protective layer as a solution to solve the rapid capacity fading of LiMn2O4-based lithium ion battery at elevated temperature. Compared with the rapid capacity fading of the bare LiMn2O4 cathode (LMO), the graphite layer modified cathode (G-LMO) possesses excellent cyclic performance at 55°C. It maintains 92% of initial discharge capacity even after 500cycles at 1C. TEM images show that the surface of the bare LiMn2O4 particles in LMO sample is damaged while G-LMO withstands Mn leaching induced by HF corrosion under the protection of graphite layer.

Carbon Nanotubes Supported Pt Catalysts for Ethanol Oxidation in Alkaline Solutions

An efficient method for functionalizing carbon nanotubes (CNTs) is reported, which combined HF corrosion with sulfuric acid and nitric acid for further oxidation. The X-ray diffraction and transmission electron microscopy are employed to investigate the physic-properties of the prepared catalysts. Cyclic voltammetry and chronoamperometry methods are used to study the performance of the prepared catalysts. CNTs further treated with H2SO4 and HNO3 mixed solutions with the volume ratio of 1 to 3, heating at 100 oC for 2 h, used as catalysts supports exhibit significantly improved performance towards ethanol oxidation in alkaline solutions in comparison with other decorated CNTs. The reason could be attributed to the oxygen-contain functional groups on CNTs surface can efficiently improve the interaction between CNTs and metallic particles in catalysts.

The Effect of the Amorphous and Crystalline States on Preferential Corrosion of Hf from a Cu75Hf20Dy05 Alloy

Amorphous solid-solution Cu75Hf20Dy05, which undergoes devitrification without changing composition either locally or globally, was used to examine the effects of structural ordering on corrosion properties in the absence of any accompanying chemical partitioning. Melt spun amorphous Cu75Hf20Dy05 undergoes single-phase devitrification to a Cu51Hf14 phase. The difference in corrosion behavior between these two structures was explored in hydrofluoric acid solutions where preferential dissolution of hafnium occurred. Preferential Hf dissolution occurred more readily in the amorphous alloy compared with its crystalline counterpart. Remaining copper reorganized to form a face-centered cubic (fcc) nanostructure in both conditions, but this process occurred quickly in the amorphous state and more slowly in the crystalline variant. A uniform, nanoporous Cu sponge structure, with a pore diameter of approximately 10 nm, formed after dissolution in the amorphous state. A less uniform, nanoporous structure developed more slowly when occurring from the crystalline state. These differences were traced to the effects of ordering on both dissolution and surface diffusion.

Functionalized Carbon Nanotubes as Pt Catalyst Supports in Methanol Oxidation

An efficient method for the functionalization of carbon nanotubes (CNTs) is presented, which uses the HF corrosion and intermittent microwave heating (IMH) H 2 O 2 solution. The Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy are used to investigate the physicochemical properties of the CNTs and the prepared catalysts thereof. Cyclic voltammetry, liner current sweeping measurements, chronoamperometry measurements are employed to study the performance of the prepared catalysts. CNTs further treated with IMH H 2 O 2 solution (10s-on/20s-off, over five cycles) can be used as catalyst support, and exhibit significantly improved performance towards the methanol oxidation in comparison with other modified CNTs. The results represent a novel approach to functionalize CNTs in a simple and economic way. The method can also be applied in the mass production of nanosized materials. 采用 HF 刻蚀及交替微波加 H 2 O 2 相结合的方法进行快速功能化碳纳米管 (CNTs), 应用红外光谱、拉曼光谱和透射电镜等方法详细考察了 CNTs 及其载 Pt 催化剂的物化性质, 并采用循环伏安法、线性电流扫描法和计时电流法考察了所得催化剂的电化学性能. 结果表明, CNTs 经过HF刻蚀和交替微波 H 2 O 2 双重处理后更适合用作催化剂载体, 以 10s-on/20s-off 加热 5 次所得 CNTs 载 Pt 催化剂显示出最佳的催化性能. 这可归因于处理后的 CNTs 表面含有丰富的微孔及含氧官能团, 能有效增强 Pt 颗粒及 CNTs 间的相互作用. This work report an efficient method to decorate CNTs by combining HF corrosion and intermittent microwave heating H 2 O 2 solution, and it could be easily scaled-up in synthesizing nanomaterials.

Intra-level voltage ramping-up to dielectric breakdown failure on Cu/porous low- k interconnections in 45 nm ULSI generation

The degradation of reliability for intra-level voltage-breakdown in the 45 nm generation node has become an increasingly important issue with the introduction of porous low- k dielectrics. The dominant failure mechanism for lower voltage ramping-up to dielectric breakdown and higher leakage current was that more electrons easily transported through the percolation path in intra-level porous low- k interconnections damaged from HF corrosion. An optimal ultraviolet curing process and a less NH 3 plasma pre-treatment on porous low- k dielectrics before the SiCN capping layer are developed to improve performance in both of these cases. The stiff configuration of the reconstruction of Si–O network structures and less HF corrosion is expected to have high tolerance to electrical failure. As a result, the proposed model of this failure facilitates the understanding of the reliability issue for Cu/porous low- k interconnections in back-end of line (BEOL) beyond 45 nm nodes.

Synthesis of carbon nanocoils on surface morphology changed silicon substrates

By the controlled corrosion of HF, silicon substrates appeared to be in a state of concavo-convex morphology. Carbon nanocoils were synthesized on these silicon substrates by the pyrolysis of acetylene with catalytic thermal chemical vapor deposition (CVD). Scanning electron microscopy and transmission electron microscopy were carried out to observe the regular morphology of carbon nanocoils, while Raman spectra was used to characterize the graphitization degree. The growing process of the nanocoils was regarded as the anisotropic activity of catalyst particles resulting from the different thicknesses of FeO layer.

Corrosion of Ceramics in Aqueous Hydrofluoric Acid

A variety of commercially available ceramic‐based oxides, carbides, nitrides, and borides were evaluated for chemical attack in an azeotropic aqueous hydrofluoric acid (HF) test protocol at 90°C. Weight change measurements and microstructure analysis showed that HF corrosion in polycrystalline ceramics generally occurred at grain boundaries by the dissolution of grain boundary phases although the bulk single crystal may inherently resist attack. Virtually all commercially prepared polycrystalline oxide ceramics (i.e., Al2O3, TiO2, ZrO2) and nonoxide ceramics (i.e., Si3N4, AlN, BN) were extensively corroded while polycrystalline pure carbides (i.e., SiC, TiC, B4C, WC) resisted corrosion. Equilibrium thermodynamic calculations show that these materials are soluble in HF; however, the kinetics of dissolution are slow enough in some cases to permit useful engineering lifetimes.

Corrosion of Alumina in Aqueous Hydrofluoric Acid

A variety of alumina‐based ceramics were evaluated for dissolution in an azeotropic aqueous hydrofluoric acid test protocol at temperatures up to 200°C. Weight change measurements and microstructure analysis showed that HF corrosion in polycrystalline aluminas generally occurred at grain boundaries by the dissolution of silicate‐based, glass grain boundary films that segregate to grain boundaries. These materials often have useful service lifetimes even though thermodynamic calculations indicate high solubilities. It is proposed that corrosion rates are controlled by chemical reactions at the solid/liquid interface, the physical structure of the solid, and microstructure. The addition of MgO to alumina greatly increased corrosion resistance by removing silicate‐based glassy grain boundary films.

Baffled by HF or Caustic Corrosion?

Baffled by HF or Caustic Corrosion?