The hottest oxide coating material IV

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Oxide coating material (IV)

in the experiment, we adopt the following measures to stabilize the flux of reaction gas:

(1) use bottled oxygen as the source of reaction gas

(2) use needle valve to control the amount of reaction gas

(3) adjust the vacuum degree to a certain value (5 ~ 7) after adding oxygen into the reaction chamber × PA) to balance with the vacuum holding system

(4) introduce the reaction gas at different positions, compare the final effect, and find out the best reaction area

5. generation and function of plasma gas

the introduced reaction gas reacts with the evaporates to form a coating, which must provide appropriate energy. This task is completed by the joint action of high-voltage electrode and evaporation source electron beam. The energy carried by high-energy electrons in the electron beam is extremely high (thousands to tens of thousands of electron volts). It can not only dissolve and vaporize the plating material with new computerized substances, but also excite secondary electrons on the surface of the plating material, which are accelerated by the electric field of the built-in high-voltage electrode. The plating vapor and reaction gas above the evaporation raw material container are excited and ionized by high-energy electrons in the electron beam, accelerated secondary electrons and a part of primary electrons intercepted by the high-voltage electrode, forming plasma gas above the evaporation area. The excited and ionized plating atoms and reaction gases have increased chemical activity, combined and neutralized in the evaporation area, deposited on the surface of the substrate, formed a solid bond with the substrate, and improved the quality of the coating at the same time

experiments show that the formation of plasma gas is very important to improve the quality of coating. Plasma cannot be formed in the evaporation area without high-voltage electrode during evaporation. At this time, the obtained film will be separated from the surface of the substrate after being removed from the vacuum chamber by slight friction. At the same time, in order to obtain good plasma gas, the vacuum degree in the vacuum chamber is better below PA, so that the electron splashing, ionization, chemical reaction and deposition can proceed smoothly. However, too low vacuum will affect the normal operation of the electron gun. Therefore, we can only give consideration to each other during production

6. Beam intensity

the evaporation source of the experimental equipment adopts the electron gun evaporation system. It is characterized by high evaporation temperature (up to 6000 ℃), which can evaporate any substance (metal, non-metallic substances, compounds), fast evaporation speed, good film-forming quality and good adhesion. The working voltage of the electron gun used in the experiment is divided into 6kV and 10kV, and the beam current can be adjusted in the range of 300mA. Theoretically, the output power of the electron gun can reach 3KW, and the beam spot area is 0.15cm2. The power density of this electron beam on the surface of the evaporation raw material can reach 20kw/cm2. In the experiment, it can melt all kinds of oxides involved in the gas rapidly. Control for different evaporation raw materials, but if the feeding is insufficient, it is impossible to maintain the beam intensity with different pressure, and a coating with excellent barrier performance can be obtained

Using SiO as raw material, adding an appropriate amount of reaction gas, and controlling the beam current at 35 ~ 50mA (working voltage 6kV), a good coating can be prepared; If the beam current is controlled below 35mA, the bonding strength between the evaporated non-metallic film and the substrate is low, and the barrier performance is poor; When the beam current is higher than 50mA, the melting (sublimation) and gasification of the plating material are rapid. Sparks splashed and hit the substrate, causing it to melt through and form pinholes

when SiO2 is used as raw material for evaporation, its melting point and gasification heat are higher than that of SiO, so the power of evaporation source will not produce splash, and the coating has good stability, colorless and transparent

when using Al2O3 and MgO as raw materials for evaporation, on the one hand, it is necessary to carry out general preparation under low beam current, although the configuration is not longer than the preheating of high-end configuration, otherwise, it is easy to burst (large pieces of plating material are broken into small pieces and splashed); On the other hand, because of its high melting point and high gasification heat, the power of evaporation source must be greater than 8kw/cm2. Under such a high evaporation power, the evaporated raw materials placed in the beam spot area of the crucible are vaporized at a high speed, and the surrounding parts are very hot and extremely hot. Its radiant heat causes the substrate on the top of the crucible to soften, and thermal extension deformation occurs, which ultimately affects the appearance and quality of the product. Therefore, when using the above evaporation raw materials, strong measures must be taken to strengthen the cooling of the substrate evaporation area and reduce the thermal deformation to the allowable range

tio2, MgF2, Y2O3 and other evaporation raw materials have high gasification energy. Therefore, melting and gasification in high vacuum air consumes a lot of energy, which seems not to be suitable for evaporation of low heat-resistant plastic films

7. Evaporation rate

under the condition of constant process conditions, the evaporation rate is inversely proportional to the coating thickness. Theoretically, the thicker the evaporation film, the better its barrier performance. However, in order to get the "1035" development plan of the industry formulated by the China Polyurethane Industry Association, which is too thick, it is clearly proposed that the coating layer must maintain a low evaporation rate, which will lead to the decline of production efficiency. At the same time, the influence of the coating thickness on the barrier is not linear. When the coating thickness is less than 500 a, the barrier performance will be significantly improved with the increase of the coating thickness; However, when the coating thickness is greater than 500 a, increasing the coating thickness is no longer very obvious to improve the barrier performance of the material

when the evaporation materials are non-metallic substances such as SiO, SiO2, Al2O3, MgO, etc., because the flexural softness after film formation is inversely proportional to the film thickness, that is, the thicker the film, the higher the stiffness. When subjected to external forces such as folding and rubbing, the film is prone to break and form cracks, resulting in the decline of barrier performance. Therefore, the coating thickness should be controlled within the range of good barrier performance and favorable processing operation during use. According to the experiment, the production speed should be kept within the range of 100~500 angstroms of film thickness, which is ideal. (to be continued)

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