Views: 3 Author: Site Editor Publish Time: 2024-10-10 Origin: Site
In the quality indicators of raw materials, we often encounter some terms. Accurately understanding their meanings will help us better grasp the performance of raw materials. Here are some commonly used terms.
1. Density and relative density
Density and relative density——Density refers to the mass contained in a unit volume of a substance. In short, it is the ratio of mass to volume. Its unit is million grams per meter3 (Mg/m3) or kilograms per meter3 (kg/m3) or grams per centimeter3 (g/cm3). Relative density is also called density ratio. It refers to the ratio of the density of a substance to the density of a reference substance under their respective specified conditions, or the ratio of the mass of a certain volume of a substance at temperature t1 to the mass of an equal volume of a reference substance at temperature t2. The commonly used reference substance is distilled water, and is expressed as Dt1/t2 or t1/t2, which is a dimensionless quantity.
2. Melting point and freezing point
Melting point and Freezing point——The temperature at which a substance reaches equilibrium between liquid and solid under its vapor pressure is called melting point or freezing point. This is a phenomenon in which the regular arrangement of atoms or ions in a solid becomes chaotic and activated due to the rise in temperature, forming an irregularly arranged liquid. The opposite process is solidification. The temperature at which a liquid turns into a solid is often called the freezing point or freezing point. The difference from the melting point is that it releases heat instead of absorbing heat. In fact, the melting point and freezing point of a substance are the same.
3. Melting range
Refers to the temperature range from the beginning of melting to complete melting of the substance measured by capillary method.
4. Crystal point
It refers to the phase transition temperature at which a liquid changes from liquid to solid during the cooling process.
5. Pourpoint
One of the indicators that indicates the properties of liquid petroleum products. It refers to the temperature at which the sample stops flowing when cooled under standard conditions, that is, the lowest temperature at which the sample can still be poured when cooled.
6. Boiling point
The temperature at which a liquid boils and becomes a gas. Or the temperature at which a liquid and its vapor are in equilibrium. Generally speaking, the lower the boiling point, the greater the volatility.
7. Boiling range
The distillation volume under standard conditions (1013.25hPa, 0°C) within the temperature range specified in the product standard.
8. Sublimation
The phenomenon that solid (crystalline) substances are directly transformed into gas without passing through the liquid state. For example, ice, iodine, sulfur, naphthalene, camphor, mercuric chloride, etc. can sublime at different temperatures.
9. Vaporizing velocity
Evaporation refers to the gasification phenomenon that occurs on the surface of a liquid. The evaporation rate is also called the volatilization rate, which is generally determined by the boiling point of the solvent. The fundamental factor that determines the evaporation rate is the vapor pressure of the solvent at that temperature, followed by the molecular weight of the solvent.
10. Vapor pressure
Vapor pressure is the abbreviation of saturated vapor pressure. At a certain temperature, the liquid and its vapor reach equilibrium. At this time, the equilibrium pressure changes only due to the properties and temperature of the liquid, which is called the saturated vapor pressure of the liquid at that temperature.
11. Azeotrope
A constant boiling point mixture formed by two (or more) liquids is called an azeotropic mixture, which refers to a mixed solution in a state of equilibrium with the same composition of the gas phase and the liquid phase. The corresponding temperature is called the azeotropic temperature or azeotropic point.
12. Refractive Index
The refractive index is a physical quantity that represents the ratio of the speed of light in two different (isotropic) media. The speed of light varies with different media. When light enters another transparent medium with different density from one transparent medium, its direction of travel changes due to the change in speed, which is called refraction.
The ratio of the sine of the incident angle of light to the sine of the refraction angle, or the ratio of the speed of light when passing through a vacuum to that when passing through a medium, is the refractive index. The refractive index n generally refers to the value of light entering any medium from air. The refractive index usually refers to the value measured at tC using sodium yellow light (D line), so it is expressed as ntD. If measured at 20°C, it is n20D.
13. Flashing point
Flash point, also known as the burning flash point, is one of the indicators of the properties of flammable liquids. It refers to the lowest temperature at which a flammable liquid is heated to a temperature where the vapor pressure on the liquid surface and the mixture of air come into contact with a flame and a flash occurs. Flash fire is usually a light blue spark that goes out immediately and cannot continue to burn. Flash fire is often a precursor to a fire. There are two methods for measuring flash point: the open cup method and the closed cup method. Generally, the former is used to measure high flash point liquids, and the latter is used to measure low flash point liquids.
14. Ignition Point
The ignition point is also called the fire point, which is one of the indicators of the properties of flammable liquids. It refers to the lowest temperature at which the vapor and air mixture on the surface of the flammable liquid immediately catches fire and continues to burn when it comes into contact with the flame. The ignition point of flammable liquids is 1 to 5°C higher than the flash point. The lower the flash point, the smaller the difference between the ignition point and the flash point.
15. Spontaneous ignition point
The lowest temperature at which a flammable substance can catch fire without contact with an open flame is called its autoignition point. The lower the autoignition point, the greater the risk of ignition. The autoignition point of the same substance varies with pressure, concentration, heat dissipation and other conditions and test methods.
16. Explosive limits
When combustible gas, vapor of combustible liquid or dust of combustible solid is mixed with air or oxygen at a certain temperature and pressure and reaches a certain concentration range, it will explode when it encounters a fire source. This certain concentration range is called the explosion limit or combustion limit. If the composition of the mixture is not within this certain range, no matter how much energy is supplied, it will not catch fire.
When steam or dust is mixed with air and reaches a certain concentration range, the lowest concentration at which it will burn or explode when it encounters a fire source is called the lower explosion limit; the highest concentration is called the upper explosion limit. The explosion limit is usually expressed as the volume percentage of steam in the mixture, that is, % (vol); dust is expressed in mg/m3 concentration.
If the concentration is below the lower explosion limit, it will not explode or burn even with an open flame, because the air accounts for a large proportion at this time, and the concentration of combustible vapor and dust is not high; if the concentration is higher than the upper explosion limit, although there will be a large amount of combustible substances, there is a lack of oxygen to support combustion. In the absence of air supplementation, it will not explode for a while even with an open flame. Flammable solvents have a certain explosion range. The wider the explosion range, the greater the danger.
17. Viscosity
Viscosity is the internal frictional resistance generated by a fluid (liquid or gas) during flow, and its magnitude is determined by factors such as the type of substance, temperature, and concentration. It is generally referred to as dynamic viscosity, and its unit is Pascal-second (Pa·s) or millipascal-second (mPa·s).
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