I would like to ask **all of you** about the physical property parameters of lubricating oil

Overview of lubricating oil: Lubricating oil is a non-volatile oily lubricant. Based on their source, they are divided into three categories: animal and vegetable oils, petroleum lubricants, and synthetic lubricants. Petroleum-based lubricants account for over 97% of the total usage, so lubricants often refer to petroleum-based lubricants. It is primarily used to reduce friction between the surfaces of moving parts, and it also serves to cool machinery, provide sealing, offer corrosion protection, prevent rust, provide insulation, transmit power, and remove impurities. Primarily using lubricating oil fractions and residue fractions from crude oil distillation units as raw materials, processes such as solvent deasphalting, solvent dewaxing, solvent refining, hydrorefining or acid-base refining, and clay refining are employed to remove or reduce components that cause the formation of free carbon, substances with low viscosity indices, materials with poor oxidation stability, paraffins, and chemicals that affect the color of the finished oil. This yields qualified lubricating oil base oils, which, after blending and the addition of additives, become lubricant products. The most important properties of lubricating oil are viscosity, oxidation stability, and lubricity, which are closely related to the composition of its fractions. Viscosity is an important quality indicator that reflects the fluidity of lubricating oil. Different operating conditions require different viscosity levels. Mechanisms that operate under heavy loads and at low speeds require lubricants with high viscosity. Oxidation stability refers to the anti-oxidation capacity of oils in their operating environment, as influenced by temperature, oxygen in the air, and metal catalysis. After oil oxidation, fine carbonaceous substances primarily composed of asphaltenes are formed depending on the operating conditions; these substances take the form of viscous pitch-like materials or coatings, or viscous aqueous substances, thereby reducing or eliminating the oil’s performance properties. Lubricity refers to the anti-friction property of lubricating oil. I. Functions of lubricating oil: Lubricating oil is a liquid lubricant used in various types of machinery to reduce friction and protect the machinery as well as the components being processed. Its main functions include lubrication, cooling, rust prevention, cleaning, sealing, and cushioning. Lubricating oils account for 85% of all lubricant materials, with a wide variety of types and grades; the global annual consumption is currently around 38 million tons. The overall requirements for lubricating oils are: (1) to reduce friction and wear, thereby lowering frictional resistance to save energy, reducing wear to extend the service life of machinery, and improving economic efficiency ； (2) Cooling: It is necessary to remove the friction heat from the machine at all times ； (3) Sealing: must be leak-proof, dust-proof, and airtight ； (4) Corrosion and rust resistance, to protect the friction surface from oil degradation or external erosion ； (5) Clean rinsing: it is necessary to remove the dirt accumulated on the friction surface ； (6) Stress dispersion buffering, load distribution, and impact mitigation as well as shock absorption ； (7) Kinetic energy transmission, hydraulic systems, remote-controlled motors, and frictional continuously variable transmissions, etc. II. Composition of lubricating oil Lubricating oil generally consists of two parts: base oil and additives. Base oil is the main component of lubricants and determines their basic properties, while additives can compensate for and improve the shortcomings of the base oil’s performance, endowing it with certain new properties; they are an important part of lubricants. 1. Lubricant base oils: Lubricant base oils are mainly divided into two categories: mineral base oils and synthetic base oils. Mineral base oils are widely used and account for a large proportion (over 95%), but in some applications products formulated with synthetic base oils are necessary, which has led to the rapid development of synthetic base oils. Mineral base oil is derived from crude oil. The main production processes for lubricant base oils include: atmospheric and vacuum distillation, solvent deasphalting, solvent refining, solvent dewaxing, and clay or hydrogenation-based further refining. In 1995, China’s current standards for lubricant base oils were revised, primarily by changing the classification method, and standards for two specialized types of base oils—those with low freezing points and those that have undergone advanced refining—were added. In the production of mineral-based lubricants, the most important thing is to select the best crude oil. The chemical composition of mineral base oils includes high-boiling-point, high-molecular-weight hydrocarbons and non-hydrocarbon mixtures. Its composition generally includes alkanes (straight-chain, branched, highly branched), cycloalkanes (monocyclic, bicyclic, polycyclic), aromatics (monocyclic aromatics, polycyclic aromatics), cycloalkyl aromatics, as well as oxygen-containing, nitrogen-containing, and sulfur-containing organic compounds, along with non-hydrocarbon compounds such as resins and asphaltenes. 2. Additives: Additives are the essence of modern high-performance lubricants. By selecting and adding them appropriately, it is possible to improve their physicochemical properties, endow the lubricants with new special characteristics, or enhance certain existing properties, thereby meeting higher requirements. Carefully selecting additives, balancing them meticulously, and formulating them appropriately based on the required quality and performance of the lubricant is key to ensuring its quality. Commonly used additives include: viscosity index improvers, pour point depressants, antioxidants, detergents and dispersants, friction modifiers, oiliness agents, extreme pressure agents, antifoam agents, metal passivators, emulsifiers, corrosion inhibitors, rust inhibitors, and demulsifiers. III. Basic properties of lubricating greases Lubricating oils are technology-intensive products that are mixtures of complex hydrocarbons, and their actual performance in use is the result of a combination of complex physical or chemical processes. The basic properties of lubricating oils include general physical and chemical properties, special physical and chemical properties, and bench test simulations. General physical and chemical properties: Each type of lubricant has its common general physical and chemical properties, which indicate the inherent quality of that product. For lubricating oils, these general physical and chemical properties are as follows: (1) Appearance (colority) – The color of the oil often reflects its degree of refinement and stability. For base oils, generally the higher the degree of refinement, the more thoroughly the hydrocarbon oxides and sulfides are removed, and the lighter the color becomes. However, even under the same refining conditions, the base oils produced from crude oils of different sources and parent categories may vary in color and transparency. For new finished lubricants, due to the use of additives, color has lost its original significance as an indicator of the degree of refinement of the base oil. (2) Density Density is the simplest and most commonly used physical property indicator for lubricants. The density of lubricating oil increases as the amount of carbon, oxygen, and sulfur in its composition rises; therefore, at the same viscosity or the same relative molecular mass, lubricating oils with a high content of aromatics, as well as those with high levels of gums and asphalts, have the highest density, those with a high content of naphthenes have an intermediate density, and those with a high content of alkanes have the lowest density. (3) Viscosity: Viscosity reflects the internal friction of an oil and is an indicator of its viscosity and fluidity. Without the addition of any functional additives, the higher the viscosity, the greater the strength of the oil film and the poorer its fluidity. (4) Viscosity index: The viscosity index indicates the degree to which the viscosity of a oil changes with temperature. The higher the viscosity index, the less the viscosity of the oil is affected by temperature, indicating better viscosity-temperature performance; conversely, it is worse. (5) Flash point: The flash point is an indicator of the volatility of oils. The lighter the fraction of the oil, the greater its volatility, and the lower its flash point as well. Conversely, the heavier the distillate of the oil, the lower its volatility, and the higher its flash point. At the same time, the flash point is an indicator of the fire hazard of petroleum products. The hazard level of oils is determined based on their flash point: oils with a flash point below 45°C are considered flammable, while those with a flash point above 45°C are considered combustible. It is strictly prohibited to heat oils to their flash point temperature during storage and transportation. At the same viscosity, the higher the flash point, the better. Therefore, when selecting lubricating oil, users should choose based on the operating temperature and the working conditions of the oil. It is generally believed that a flash point 20–30°C higher than the operating temperature ensures safe use. (6) Freezing point and pour point: The freezing point refers to the highest temperature at which the oil stops flowing under specified cooling conditions. The solidification of oils differs greatly from that of pure compounds. Oils do not have a definite freezing temperature; the so-called “freezing” simply means that the oil as a whole loses its fluidity, but not all of its components turn into solids. The freezing point of lubricating oil is an important quality indicator that reflects its flowability at low temperatures. It is of great significance for production, transportation, and use. Lubricants with a high freezing point cannot be used at low temperatures. On the contrary, in areas with higher temperatures, there is no need to use lubricants with a low freezing point. Because the lower the freezing point of the lubricating oil, the higher its production cost, resulting in unnecessary waste. Generally, the freezing point of lubricating oil should be 5–7°C lower than the lowest temperature of the operating environment. It is particularly important to note that when selecting a lubricant for low temperatures, comprehensive consideration should be given to the oil’s freezing point, viscosity at low temperatures, and viscosity-temperature characteristics. Because oils with low freezing points may also have low-temperature viscosity and viscosity-temperature properties that do not meet the requirements. Both the freezing point and the pour point are indicators of the low-temperature flowability of oils; there is no fundamental difference between them, only slight variations in the methods of measurement. The freezing point and pour point of the same oil product are not exactly equal; generally, the pour point is 2–3°C higher than the freezing point, though there are exceptions. (7) Acid value, alkali value, and neutralization value. The acid value is an indicator of the acidic substances contained in lubricating oil, with the unit being mgKOH/g. The acid value is divided into strong acid value and weak acid value; the sum of the two constitutes the total acid value (abbreviated as TAN). What we usually refer to as the “acid value” actually means “Total Acid Number (TAN)”. The alkalinity value is an indicator of the content of basic substances in lubricating oil, with the unit being mgKOH/g. Alkalinity is also divided into strong alkalinity and weak alkalinity; the sum of the two constitutes the total alkalinity (abbreviated as TBN). What we usually refer to as “alkalinity” actually means “Total Base Number (TBN)”. The neutralization value actually includes the total acid value and the total base value. However, unless otherwise specified, the so-called \"neutralization value\" generally refers only to the \"total acid value\", which is also expressed in mgKOH/g. (8) Moisture: Moisture refers to the percentage of water contained in the lubricant, usually expressed as a weight percentage. The presence of water in lubricating oil can destroy the oil film formed by the lubricant, reducing its lubricating efficiency, accelerating the corrosion of metals by organic acids, causing equipment to rust, and leading to the formation of sediment in the oil. In short, the less water in the lubricant, the better. (9) Mechanical impurities: Mechanical impurities refer to precipitates or gelatinous suspensions present in lubricating oil that are insoluble in solvents such as gasoline, ethanol, and benzene. Most of these impurities are sand, gravel, iron filings, and other such substances, as well as some organometallic salts that are insoluble in solvents and result from additives. Generally, the mechanical impurities in lubricant base oils are kept below 0.005% (levels below 0.005% are considered to be absent). (10) Ash and sulfuric ash: Ash refers to the non-combustible substances that remain after burning under specified conditions. The composition of ash is generally considered to be various metal elements and their salts. Ash content has different meanings for various types of oils; for base oils or oils without additives, ash content can be used to determine the degree of refinement of the oil. For oils with metal salt additives (new oils), ash content becomes a means to quantitatively control the amount of additives added. Abroad, sulfuric acid ash is used in place of ash. The method is to add a small amount of concentrated sulfuric acid before burning the oil sample and then carrying out ashing, so as to convert the metal elements of the additive into sulfates. (11) Residue: The charred black residue formed after the heating, evaporation, and combustion of oils under specified experimental conditions is called residue. Residue is an important quality indicator for lubricant base oils; it is a parameter specified to determine the properties of the lubricant and the degree of its refining. In lubricant base oils, the amount of carbon residue is related not only to its chemical composition but also to the degree of refining of the oil. The main substances that cause carbon residue to form in lubricants are gums, asphalts, and polycyclic aromatic hydrocarbons present in the oil. Under conditions of insufficient air, these substances undergo decomposition and condensation under high heat to form residue carbon. The greater the degree of refining of the oil, the lower its residue value. Generally speaking, the lower the carbon residue value of the base oil, the better. Today, many oils contain additives such as metals, sulfur, phosphorus, and nitrogen, which result in high carbon residue values; as a result, the carbon residue value of oils with additives loses its original meaning in carbon residue testing. Mechanical impurities, moisture, ash, and residue are all quality indicators that reflect the purity of oils, and they indicate the degree of refinement of the lubricant base oil. You can design it according to the most stringent requirements