Graphite intercalation compound with iodine as the major intercalate

Halogenated graphite CBr_xI_y (1 < y/x < 10) was made by exposing graphite materials to either pure Br₂ or an I₂/Br₂/HBr mixture to initiate the reaction, and then to iodine vapor containing a small amount of Br₂/HBr/IBr to complete the intercalation reaction. Wetting of the graphite materials by the I₂/Br₂/HBr mixture is needed to start the reaction, and a small amount of Br₂/HBr/IBr is needed to complete the charge transfer between iodine and carbon. The interplanar spacings for the graphite materials need to be in the 3.35 to 3.41 Å range. The X-ray diffraction data obtained from the halogenated HOPG indicate that the distance between the two carbon layers containing intercalate is 7.25 Å. Electrical resistivity of the fiber product is from 3 to 6.5 times the pristine value. The presence of a small amount of isoprene rubber in the reaction significantly increased the iodine-to-bromine ratio in the product. In this reaction, rubber is known to generate HBr and to slowly remove bromine from the vapor. The halogenation generally caused a 22% to 25% weight increase. The halogens were found uniformly distributed in the product interior. However, although the surface contains very little iodine, it has high concentrations of bromine and oxygen. It is believed that the high concentrations of bromine and oxygen in this surface cause the halogenated fiber to be more resistant to structural damage during subsequent fluorination to fabricate graphite fluoride fibers.     

Electrochemical reactions of stage 1 sulfuric acid—Graphite intercalation compound

By means of cyclic voltammetry, a study of the redox reactions has been made on stage 1 sulfuric acid-graphite intercalation compound (H₂SO₄-GIC) prepared by anodic oxidation of graphite in sulfuric acid electrolyte. It was found that further oxidation of the stage 1 GIC gives rise to the reversible ionization reaction of carbon atoms in the graphite basal plane and also of sulfuric acid molecules produced in the interlayer spacing. This ionization reaction and the reverse deionization reaction are responsible for plateaus observed in the current vs. potential curve. These redox reactions between the stage 1 GIC and its ionized state were analyzed in situ by means of X-ray diffractometry.     

Preparation,structure and electrical conductivity of graphite intercalation compound with titanium fluoride

The graphite intercalation compound (GIC) of titanium fluoride has been prepared in a fluorine atmosphere. The GICs prepared from natural graphite and pitch-based carbon fiber were mostly stage-2 compounds with repeat distance 11.28–11.59 Å and composition C_11–15TiF_4.5–6.2. The ESCA spectrum indicates that intercalated TiF₆²⁻ anions are mainly in a bridged state. The slight decrease in the repeat distance with increasing fluorine pressure is ascribed to the nestling of TiF₆²⁻ anions in benzene rings of carbon layers due to the increase in nonbridging TiF₆²⁻ anion. X-ray powder diffraction data indicate the high regularity in the orientation of intercalated species between carbon layers. The highest electrical conductivity was 2.4 × 10⁵ Scm⁻¹, which is 13 times higher than that of pristine HOPG.     

Graphite intercalation compounds as PEMFC electrocatalyst supports

Intercalation of metal chlorides into fine natural graphite flakes of 2 × 10⁻⁶ m in diameter was attempted. CuCl₂ was satisfactorily intercalated from the vapour phase. NiCl₂ and PdCl₂ were also intercalated from the liquid phase using chloroform solvent. The reduction products of the obtained graphite intercalation compounds were used as carbon supports of the platinum electrocatalyst for a proton exchange membrane fuel cell. Oxygen reduction activity was evaluated and it can be seen that natural graphite flakes treated using the intercalation technique provide different levels of activity from that of pristine natural graphite flakes. In particular, the catalytic activity was enormously improved when CuCl₂ was used as the intercalate.     

Electrochemical behavior of graphite intercalation compounds of fluorine and metal fluorides

Ternary intercalation compounds, C_xF(AlF₃)_y and C_xF(MgF₂)_y containing active fluorine atoms adsorbed on carbon layers of host graphite were used as a cathode material of lithium cell. The discharge potentials are 2.8–2.5 V at current densities 40–400 μA cm^?2, being higher than that for graphite fluoride below 300 μA cm^?2. X-ray diffraction analysis and ESCA measurement of the discharge products indicate the formation of a new intercalation compound C_x(LiF) (MF_n)_y, (M = Al or Mg, n = 3 or 2).     

热压多晶氟化镁研究

热压多晶氟化镁是一种良好的红外光学材料，尤其在l～7μm的红外波段上透过率达90％以上，在国内外广泛用于红外目标探测器。介绍了氟化镁粉料的合成工艺、技术参数、物象分析及应用效果。     

氟化镁的制备方法

氟化镁是一种重要的无机化工原料,其用途广泛,市场广阔。介绍了目前中国制备氟化镁的方法,包括碳酸镁法、硫酸镁（或硝酸镁）法、氧化镁法、氯化镁法,简要分析了这些方法的优缺点。不同的氟化镁生产企业,所采用的生产工艺有所不同,大都依据自身的优势,如氟资源优势。中国萤石资源储量有限、分布不均,且富矿含量偏低。针对此种情况,提出了开发利用磷矿伴生的氟资源,扩大氟的来源,提升氟化镁的市场竞争能力。     

Graphite intercalation compounds as positive electrodes in galvanic cells

A systematic investigation of the anodic intercalation of the anions HSO^?₄, ClO^?₄ and BF^?₄ into natural graphite (as composite electrodes “CPP” with polypropylene binder) and its cathodic redissolution is presented. Slow cyclic voltammetry (1 mV/s) is the method used. The anions were provided as aqueous acid solutions in the concentration range of 0.1–12 M.At a critical potential of intercalation E_K, which decreases linearly with anion concentration (60 Vcm³/mol), an anodic intercalation current rises steeply. Current limitation occurs due to a diffusion process into the bulk of the electrode. From potentiostatic transients, a diffusion coefficient of about 4.10^?9 cm²/s is derived. In a potential range of only about 200 mV, the different intercalation stages up to C₂₄A are represented as anodic peaks, which are refound as cathodic peaks of low overvoltage (<50 mV) upon redissolution. Current efficiencies up to 100 per cent are found in spite of the high water concentration.A new model of electrochemical intercalation, based on anion adsorption on the graphite electrode, is presented.Due to the very positive potentials (up to 1.9 V vs nhe) and the high reversibility, the electrodes should be useful as positives in galvanic cells.     

Preparation and electrical conductivity of fluorine-graphite fiber intercalation compound

Fluorine-graphite fiber intercalation compounds were prepared in the presence of copper fluoride, and their electrical conductivities and stability were evaluated. Major products were a mixture of the 2nd and 3rd stages or the 3rd stage with intercalate 12–16 wt% corresponding to C_8–12F. A mixture of the 3rd and 4th stages contained 8–12 wt% intercalate corresponding to C_12–18F. No 1st and pure 2nd stage compounds were prepared under the present condition (F₂:1 atm, 10 days). The highest electrical conductivities at room temperature were 1.1 × 10⁵ 2.0 × 10⁴ and 7.0 × 10³ Scm⁻¹ for VGCF, pitch fiber and PAN fiber-based GIC's, respectively. They were 8.5, 8 and 6 times those of the pristine fibers. The decrease in the conductivity in air was less than 18% after 100 days for PAN fiber-based GIC, and 30% after 130 days for pitch fiber-based GIC. However, VGCF-based GIC decomposed to graphite after 1 month. DTA and TG analyses showed that the decomposition of GIC to a high stage compound started at 150°C, and the high stage GIC started to decompose to graphite at 360–390°C for PAN and pitch fiber-based GIC's. VGCF-based GIC decomposed at lower temperatures than those of other two fibers.     

Graphite intercalation compounds of lanthanide metals prepared in molten chlorides

Graphite intercalation compounds of several lanthanide metal donors (Nd, Sm, Dy, Er and Yb) have been prepared by interacting graphite and metals in molten chlorides. These lanthanide metals are suspended in molten chlorides at lower than 400 °C in the presence of their trichlorides via disproportionation equilibrium: 3Ln(II) = Ln(0) + 2Ln(III). In this condition, one can avoid the formation of carbides in the reaction product. The X-ray powder diffraction patterns for all the lanthanide GICs prepared suggest they belong to the hexagonal EuC₆-structure type.     

氟化铝产品氟含量的测定研究

介绍了工业氟化铝产品的来源与组成,对氟化铝产品中氟含量的测定方法进行了简单分析,同时提出了氟含量检测过程中需要注意的几个问题。     

高岭石有机插层反应的影响因素

利用高岭石的层状结构特征,将有机分子插入高岭石层间形成的高岭石有机复合物,兼具粘土矿物和有机物的特性,是一种新型矿物材料,在功能填料、陶瓷材料、催化剂、择吸附剂、环境修复材料等方面具有广泛的应用前景。高岭石层间氢键作用较强,有机分子的插层作用比较困难,合理控制插层条件是插层作用完成的关键。评述了高岭石特征、插层有机分子性质、水、温度、压力、PH值等因素对高岭石有机插层作用的影响。