China Aluminum Network Aluminum and its alloys interact with virtually all gases except for inert gases: hydrogen, oxygen, nitrogen, water vapor, carbon dioxide, carbon monoxide, and various hydrocarbons. As a result of the reaction, aluminum and aluminum alloys are contaminated with gases and reaction products of gases and aluminum alloys. However, in these non-metallic inclusions, only the amount of hydrogen and solid metal oxide is sufficient to affect the structure and properties of the alloy. In the smelting process, the composition of the furnace gas that interacts with the aluminum charge for a long time varies with the specific conditions. Qb Led Grow Light,Quantum Board Grow Light,Grow Light Quantum Board,Quantum Board Led Shenzhen Pvison Technology Co., Ltd. , https://www.pvisunggrowlight.com
1. The dissolution process of hydrogen in aluminum is within the smelting temperature range, aluminum and hydrogen do not actually form chemical compounds, but hydrogen can produce very significant dissolution in aluminum. The dissolution of hydrogen in aluminum is carried out in three consecutive processes of "adsorption-dissolution-dissolution". First, hydrogen molecules in the furnace gas or atmosphere hit the metal surface. Under the influence of chemical affinity, hydrogen molecules condense on the metal surface and dissociate into atoms. This is the so-called chemical adsorption process. It should be pointed out here that according to the affinity of gas and metal elements, adsorption can be divided into physical adsorption and chemical adsorption. Physisorption occurs because the force field formed by the unbalanced forces in the upper and lower directions of the metal surface atomic layer causes attraction to the gas molecules that collide with the metal surface. More physical adsorption can only cover the thickness of a single molecule, and the gas is still in a stable molecular state, and therefore can not be absorbed by the metal, that is, physical adsorption can not be dissolved. Chemisorption occurs at a temperature higher than zero, and its driving force reflects the chemical affinity of the electronic coupling of the constituents, so that only the gas with a certain affinity for the metal atom (for aluminum, such as hydrogen, nitrogen, oxygen, water vapor, carbon dioxide) Etc., etc. can occur chemical adsorption, or active adsorption. In chemical adsorption, some of the activation energy is consumed, but no new phase is produced, so it is not a chemical process. The result of chemical adsorption is that gas molecules agglomerate on the metal surface, and gas molecules dissociate into atoms on the surface. In the smelting temperature range of aluminum, the chemisorption rate increases with increasing temperature, and the adsorption slows down until a certain temperature, and depends largely on the surface state.
The metal surface layer continuously adsorbs and dissociates gases. For hydrogen, when the partial pressure of hydrogen on the surface of the metal is greater than the partial pressure of hydrogen inside the metal, the hydrogen atoms adsorbed on the surface of the metal will be promoted by the partial pressure difference and affinity with the metal. Under the action of diffusion into the metal. This is the so-called diffusion process. Obviously, the greater the differential pressure of hydrogen within and outside the metal (ie, the greater the concentration difference), the higher the temperature, the faster the diffusion rate. In addition, the physicochemical state of the melt surface also has an important influence on the diffusion rate. If the result of adsorption on the surface of the melt is the formation of a compound, the diffusion rate is no longer dependent on the pressure. In this case, the diffusion rate depends on the ability of the gas to diffuse in the already formed compound layer.
As the diffusion process continues, hydrogen dissolves in the aluminum liquid in an atom-ion state, forming a hydrogen-containing aluminum "solution." This is the so-called dissolution process. In the process of hydrogen absorption in the aluminum melt, the dominant process is the diffusion process, which determines the rate at which the aluminum melt absorbs hydrogen gas. For Ti, Zr, V, Li, Na, Si and other metal elements in the aluminum melt, they react with hydrogen to form hydrides that are endothermic, but decompose with increasing temperature.
2. The existence of hydrogen in aluminum can be seen from above. In aluminum and aluminum alloys, there are four possible forms of hydrogen: 1 Atomic hydrogen in the form of “solution†or “solid solutionâ€, which is hydrogen in aluminum The main form of presence in the melt; 2 Molecular hydrogen that evolves as a bubble after the hydrogen content exceeds its solubility; 3 Hydrogenated in the form of hydride; 4 The network in the form of γ-Al 2 O 3 ·χH, which will be described below Hydrogen. In the aluminum melt, the distribution in other parts is relatively uniform except that the hydrogen is enriched near the surface of the melt and the inclusions. In solid aluminum and its alloys, dissolved atomic hydrogen fills in the solid solution and the metal matrix of the intermetallic compound to form interstitial solid solution; molecular hydrogen is concentrated in pores and loose pores; hydrogen and complex hydrogen and its compounds Together, they are mainly distributed at grain boundaries and dendritic boundaries.
3. The solubility of hydrogen in aluminum and the gas content in aluminum have been extremely contradictory in the literature on the solubility of hydrogen in aluminum and aluminum alloys, especially data published thirty to forty years ago. These contradictions arise from two aspects: 1 The method for determining the content of gas in metals is not perfect, and 2 the concept of solubility used is inaccurate. In the past, people used to understand the solubility as the total amount of gas absorbed by the metal, regardless of the form of the gas in the metal. If this concept is allowed before the existence of the gas in the metal is very clear, it is unacceptable in modern times. Because this leads to a series of errors, the solubility of the gas in the metal deviates from the West's law (square root law), and in many cases the true value of the solubility is not obtained. Under certain conditions of temperature and pressure, the saturated concentration of a gas present in a metal in the form of a solution or solid solution is called the solubility of the gas in the metal under this condition. Obviously, the temperature is different, the pressure is different, and the solubility of the gas in the metal is also different. The gas content in the metal refers to the total amount of gas absorbed in the metal under certain conditions, regardless of the presence of the gas in the metal, or whether it reaches saturation. Gas solubility and gas content are commonly expressed in two ways: One is the volumetric representation, which is expressed as the volume of gas contained in each 100 g of metal in the standard state (one atmosphere and zero degrees Celsius) and the unit is mL/100g. The other is the mass representation, which is represented by the mass ratio of the gas content in the metal, and the unit is ppm (ie x10-6).