7 preparation methods for expandable graphite

Expandable graphite is an interlayer compound that uses physical or chemical methods to insert foreign materials of a different nature from graphite into the layer of graphite sheets, and high temperature and heat can expand rapidly to expand graphiteas a new type of carbon functional material,has many special properties, can be widely used in electrode materials, petrochemicals, fire retardants, oil-absorbing materials, environmental protection, medical dressings, military smoke and anti-static coatings and other fieldstherefore, the study of its preparation is particularly importantchemical oxidation method
chemical oxidation method is a traditional method of preparing expandable graphite, this method will be natural scale graphite and the appropriate amount of oxidants and layering agents evenly mixed, control a certain temperature, constantly stirring, by washing, filtration, drying to obtain expandable graphitechemical oxidation method has become a relatively more and more mature method in industry, such as simple equipment, convenient operation and low costchemical oxidation process steps include oxidation and insertionThe oxidation of graphite is the basic condition for the formation of expandable graphite, because whether the layer reaction can be carried out smoothly depends on how open the graphite layer isNatural graphite has excellent stability and acid-resistant alkaline at room temperature, so it does not react with acid-base, so the addition of oxidants becomes a key component that must not be lacking in chemical oxidationthere are many types of oxidants, the general use of oxidants are solid oxidants (such as potassium permanganate, potassium chromium, chromium trioxide, potassium chlorate, etc.), can also be some oxidizing liquid oxidants (such as hydrogen peroxide, nitric acid, etc.)Through recent studies, it is found that the main oxidants commonly used in the preparation of expandable graphite are potassium permanganateunder the action of oxidant, graphite is oxidized to make the neutral mesh macromolecule of the graphite layer into a flat macromolecule with positive charge, due to the repulsion of the same positive charge, the distance between graphite layers increases, which provides channels and space for the layer ingester to smoothly enter the graphite layerThe preparation process of expandable graphite is mainly acid-based, and in recent years researchers mainly have sulfuric acid, nitric acid, phosphoric acid, perchloric acid, mixed acid and ice acetic acidthe process of preparing expandable graphite
electrochemical method
electrochemical method is the electro-
solution of the inserted water solution, the graphite and metal material (stainless steel material, platinum plate, lead plate, titanium plate, etc.) constitute a composite anode, insert edges the metal material in the electrolyte as a cathode, forming a closed circuit; The surface of graphite is oxidized into carbon positive ions, and under the combined effect of electrostatic gravity and differential diffusion of concentration, acid root ions or other polar insertion ions are embedded in the graphite layer to form expandable graphite relative to chemical oxidation method, electrochemical method to prepare the whole process of expandable graphite does not need to use oxidants, large amount of treatment, corrosion residue is small, after the reaction electrolyte can be recycled, reduce the amount of acid, save costs, reduce environmental pollution, damage to equipment is lower, extend the service life In recent years, electrochemical method by virtue of many advantages gradually into a large number of enterprises for the preparation of expandable graphite preferred method gas phase diffusion method (two-chamber method) gas phase diffusion method is the interpolator in the form of gaseous contact with graphite to produce an intubation layer reaction, the preparation of expandable graphite The graphite and insert are generally placed at both ends of the heat-resistant glass reactor, and the vacuum is sealed, so it is also known as the two-chamber method This method is often used in industry to synthesize halide -EG, alkali metal-EG advantages : the structure and order can be controlled, and its reactants and products are easily separated shortcomings : the reaction device is more complex, the operation is difficult, thus limiting the output, and the reaction should be carried out at high temperature conditions, the time required is longer, and the reaction conditions are very high, its preparation environment must be vacuum, so that its production costs are relatively high, not suitable for large-scale production applications the mixture liquid phase method the mixture liquid phase method is to mix the inserted substance directly with graphite, under the protection of the liquid inert gas or sealing system for heating reaction preparation of expandable graphite Generally used in the synthesis of alkali metal - graphite interlayer compounds (GICs) advantages : the reaction process is simple, the reaction speed is fast, by changing the ratio of graphite raw materials and inserts can reach a certain structure and composition of expandable graphite, more suitable for mass production shortcomings : the resulting product is unstable, it is difficult to deal with the free insertion substance attached to the surface of GICs, and it is difficult to ensure the consistency of the graphite layer compounds when large numbers of synthesis melting method
melting method is to mix graphite with the layer material and heat the preparation of expandable graphite Based on the nature of the component cocrystalline that can reduce the melting point of the system (lower than the melting point of each component), it is a method that can simultaneously insert two or more substances (must be able to form a molten salt system) into the preparation of terasimatora or multi-GICs between the graphite layer Generally used in the preparation of metal chlorides - GICs advantages : the stability of synthetic products is good, easy to wash, the reaction device is relatively simple, the reaction temperature is lower, the time is short, suitable for large-scale production shortcomings : it is difficult to control the order structure and composition of the product during the reaction process, and it is difficult to guarantee the consistency of the order structure and composition of the product in large quantities of synthesis pressure the pressure method is to mix graphite substrates with alkaline and rare earth metal powders, and under pressurized conditions, the reaction generates M-GICs disadvantages: the insertion reaction can only be carried out when the steam pressure of the metal exceeds a certain threshold, however, the temperature is too high, it is easy to cause the metal and graphite to produce carbide, negative reaction, so the reaction temperature must be regulated within a certain range Rare earth metals have to be inserted at a very high temperature, so they must be pressurized to reduce the reaction temperature This method is suitable for the preparation of metal-GICs with low melting point, but the device is more complex, the operation requirements are strict, and it is now rarely used rare earth metals need to reach the temperature (C) explosion method under different steam pressure
the explosion method generally uses graphite and expansion agents such as KClO4, Mg (ClO4) 2 nH2O, Zn (NO3)2 nH2O and other pyrotechnics or mixtures, when heated graphite will be simultaneously oxidizing and intubation layer formation compounds, which are then "explosion" layer expansion When the product is more complex when using metal salt as expansion agent, which not only expands graphite, but also metal oxides, which can make the surface of the expansion graphite modified, but the expansion agent is HClO4 when the product is relatively single, which only expands graphite The method is simple to operate, the reaction time is short, the design can be carried out, but the purity of the product is low, and the experimental process is dangerous, so in practice, this method is generally not used to prepare expandable graphite in addition to the preparation methods mentioned above, synthetic GICs methods also have catalyst methods, photochemical methods, etc , these synthesis methods, each has its advantages and disadvantages, synthetic objects are not the same, rarely used At present, chemical oxidation and electrochemical method spree are the most commonly used preparation methods In particular, electrochemical method, by virtue of small environmental pollution, low cost, large processing capacity, acid can be recycled and other advantages, in recent years has attracted much attention Statement: This number is neutral for reproduction, sharing, representation and opinion, for the sole purpose of industry exchanges, copyright is owned by the original author If involved in copyright and intellectual property rights and other infringement issues, please contact the background of this number, immediately delete the content processing