1. Density and Relative Density
Density refers to the mass contained in a unit volume of a substance; simply put, it is the ratio of mass to volume. Its unit is megagrams per cubic meter (Mg/m³), kilograms per cubic meter (kg/m³), or grams per cubic centimeter (g/cm³).
Relative density, also known as the density ratio, refers to the ratio of the density of a substance to the density of a reference substance under their respective specified conditions. Alternatively, it can be described as 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, expressed as Dt1/t2 or t1/t2, which is a dimensionless quantity (a physical quantity without units).
2. Melting Point and Freezing Point
The temperature at which a substance reaches equilibrium between its liquid and solid states under its vapor pressure is called its melting point or freezing point.
The melting point is a phenomenon where atoms or ions in a solid, initially arranged in a regular pattern, become disordered and activated due to increased temperature, resulting in a liquid with an irregular arrangement. There is also a melting point range, which refers to the measured temperature range from when the substance begins to melt until it is completely melted.
The opposite process is solidification. The temperature at which a liquid changes to a solid is often called the freezing point, ice point, or crystallization point (the phase transition temperature from liquid to solid). The difference between the freezing point and the melting point is that the freezing point releases heat rather than absorbs it. In fact, the melting point and freezing point of a substance are the same.
3. Vapor Pressure, Evaporation Rate, and Ash Content
Vapor pressure is short for saturated vapor pressure. At a certain temperature, a liquid and its vapor reach equilibrium. The equilibrium pressure at this point changes only due to the properties of the liquid and the temperature; this is called the saturated vapor pressure of the liquid at that temperature. Evaporation refers to the vaporization phenomenon that occurs at the surface of a liquid.
The evaporation rate, also called the rate of vaporization, is generally determined by the boiling point of the solvent. The fundamental factor determining the evaporation rate is the vapor pressure of the solvent at that temperature, followed by the molecular weight of the solvent.
Ash content, also known as ignition residue, refers to the residue of oxides and salts formed from mineral components after evaporation and ignition, expressed as a percentage.
4. Pour Point, Boiling Point, Boiling Range, Azeotrope, Sublimation
Pour point is one of the indicators of the properties of liquid petroleum products. It refers to the temperature at which a sample begins to stop flowing when cooled under standard conditions; that is, the lowest temperature at which the sample can still be poured after cooling.
Boiling point is the temperature at which a liquid boils and turns into a gas when heated. Alternatively, it can be described as the temperature at which the liquid and its vapor are in equilibrium. Generally, the lower the boiling point, the greater the volatility.
Boiling range refers to the volume of liquid distilled under standard conditions (1013.25 hPa, 0℃) within the temperature range specified in the product standard.
Sublimation refers to the phenomenon of a solid (crystalline) substance directly transforming into a gaseous state without passing through a liquid state. Examples include ice, iodine, sulfur, naphthalene, camphor, and mercuric chloride, all of which can sublimate at different temperatures.
Azeotropy is a mixture of two (or more) liquids that reaches an azeotropic point. It refers to a solution in equilibrium where the gas and liquid phases have identical compositions. The corresponding temperature is called the azeotropic temperature or azeotropic point.
5. 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 depending on the medium. When light travels from one transparent medium to another transparent medium of different density, its direction of travel changes due to the change in speed; this is called refraction.
The ratio of the sine of the angle of incidence to the sine of the angle of refraction, or the ratio of the speed of light passing through a vacuum to its speed passing through a medium, is the refractive index. The refractive index *n* generally refers to the value of light traveling from air into any medium. The refractive index usually refers to sodium yellow light (D line), such as *n20D* measured at 20°C.
6. Flash Point, Ignition Point, Autoignition Point
The flash point, also known as the ignition point, is one of the indicators of the flammability of liquids. Flash point is the lowest temperature at which a flammable liquid, when heated to its surface, will ignite upon contact with a flame, as the vapor pressure of the liquid and the air mixture will immediately ignite.
Flash point typically produces a pale blue spark that extinguishes quickly and cannot continue burning. Flash point is often a precursor to a fire. There are two methods for determining flash point: the open-cup method and the closed-cup method. Generally, the open-cup method is used for liquids with high flash points, while the closed-cup method is used for liquids with low flash points.
Ignition point, also known as ignition temperature, is one of the indicators of the properties of flammable liquids. It is the lowest temperature at which a flammable liquid, when heated to its surface, will ignite immediately upon contact with a flame and continue burning. The ignition point of flammable liquids is 1–5°C higher than their flash point. The lower the flash point, the smaller the difference between the ignition point and the flash point.
Autoignition point is the lowest temperature at which a flammable substance can ignite without contact with an open flame. The lower the autoignition point, the greater the risk of fire. The autoignition point of the same substance varies depending on pressure, concentration, heat dissipation, and the testing method.
7. Explosion Limits When a flammable gas, vapor of a flammable liquid, or dust of a flammable solid mixes with air or oxygen at a certain temperature and pressure and reaches a certain concentration range, it will explode upon encountering an ignition source. This certain concentration range is called the explosion limit or flammability limit.
If the composition of the mixture is outside this certain range, it will not ignite even with a large supply of energy. The lowest concentration at which vapor or dust mixed with air and reaching a certain concentration range will burn or explode upon encountering an ignition source is called the lower explosive limit; the highest concentration is called the upper explosive limit.
Explosion limits are usually expressed as the volume percentage of vapor in the mixture, i.e., % (vol); dust is expressed as mg/m³ concentration.
If the concentration is below the lower explosive limit, even an open flame will not cause an explosion or combustion because the proportion of air is large, and the concentration of flammable vapor and dust is low.
If the concentration is above the upper explosive limit, although there will be a large amount of flammable material, the lack of oxygen for combustion means that even if it encounters an open flame, it will not explode immediately without air supply. Flammable solvents all have a certain explosive range; the wider the explosive range, the greater the danger.
8. Viscosity and Mooney Viscosity
Viscosity is the internal frictional resistance of a fluid (liquid or gas) during flow. Its magnitude is determined by factors such as the type of substance, temperature, and concentration.
It is generally an abbreviation for dynamic viscosity, and its unit is Pascal-second (Pa·s) or millipascal-second (mPa·s). Viscosity is divided into dynamic viscosity, kinematic viscosity, and relative viscosity; these three are distinct and should not be confused.
Mouney viscosity, also known as rotational (Mouney) viscosity, is a value measured using a Mooney viscometer and essentially reflects the degree of polymerization and molecular weight of synthetic rubber. According to the GB1232 standard, rotational (Mouney) viscosity is represented by the symbol Z100℃14.
Where Z is the rotational viscosity value; 1 represents a preheating time of 1 min; 4 represents a rotation time of 4 min; and 100℃ represents a test temperature of 100℃. It is conventionally expressed as ML100℃14 for Mooney viscosity.
9. Solubility and Solubility Parameters
Solubility refers to the maximum amount of a substance that can dissolve in a given amount of solvent at a certain temperature and pressure.
The solubility of solid or liquid substances is generally expressed as the number of grams of substance that can be dissolved in 100g of solvent. The solubility of gaseous solutes is usually expressed as the number of milliliters of gas dissolved per liter of solvent.
The solubility parameter, also known as the cohesive energy parameter, is a measure of intermolecular forces. The energy that holds molecules together is called cohesive energy. The cohesive energy per unit volume is called cohesive energy density (CED). The square root of CED (CED)/2 is defined as the solubility parameter, denoted by δ or SP.
10. Surface Tension and Surface Energy
The attractive forces between molecules within a liquid cause molecules on the surface to be under an inward force. This force causes the liquid to minimize its surface area, forming a force parallel to the surface, called surface tension.
Alternatively, it can be described as the mutual attraction force per unit length between adjacent parts of the liquid surface; it is a manifestation of molecular forces. The unit of surface tension is N/m.
The magnitude of surface tension is related to the properties, purity, and temperature of the liquid. Surface tension multiplied by the surface area equals surface energy. The greater the surface tension, the larger the surface area, and the greater the surface energy.
11. Specific Heat Capacity and Thermal Conductivity
Specific heat capacity refers to the amount of heat absorbed when the temperature of a substance increases by 1 K per kilogram. The unit is kJ/(kg·K). Under constant pressure, the amount of heat absorbed when the temperature increases by 1 K is called the isobaric specific heat capacity.
Thermal conductivity, formerly known as the thermal conductivity coefficient, reflects a substance’s ability to conduct heat. It is defined as the amount of heat conducted from one plane to the other within 1 second if the temperature difference between two parallel planes 25px apart and with an area of 25px² is 1 K, perpendicular to the direction of heat conduction within the substance. The unit is W/(m·K).
12. Moisture, Water Absorption, and Oil Absorption
Water content refers to the amount of water contained in a substance, excluding water of crystallization and associated water. It is usually expressed as the percentage of the original mass of the sample compared to the mass after water loss.
Water absorption is a measure of the degree to which a substance absorbs water, that is, the percentage increase in mass of a substance when immersed in water for a certain period of time at a certain temperature.
Oil absorption is the amount of oil required to completely wet the absolute surface of a given mass of pigment (filler) particles.
13. Penetration and Penetration Comparison
Penetrating depth is expressed as the depth to which a standard needle penetrates vertically into an asphalt sample under specific load, time, and temperature conditions, measured in 1/10 mm.
Unless otherwise specified, the combined weight of the standard needle, needle rod, and additional weights is 100 ± 0.1 g, the temperature is 25℃, and the time is 5 s. A higher penetration indicates a softer material, i.e., lower consistency; conversely, a lower penetration indicates a harder material, i.e., higher consistency.
The percentage obtained by multiplying the penetration of the sample after determining evaporation loss by 100 is the ratio of the original penetration to the current penetration.
14. Hardness
Hardness is the material’s resistance to external forces such as indentation and scratches. Depending on the testing method, there are Shore hardness, Brinell hardness, Rockwell hardness, Mohs hardness, Barcol hardness, and Vichers hardness, among others.
The numerical value of hardness depends on the type of hardness tester. Among commonly used hardness testers, the Shore hardness tester has a simple structure and is suitable for production inspection. Shore hardness testers are classified into Type A, Type C, and Type D. Type A is used to measure soft rubber, while Types C and D are used to measure semi-hard and hard rubber.
15. Aniline Point and Volume Resistivity The aniline point is the lowest temperature at which equal volumes of petroleum alkanes and aniline dissolve together, used to indicate the content of saturated hydrocarbons such as alkanes. The aniline point is related to the chemical composition; the higher the aniline point, the higher the alkane content; the lower the aniline point, the higher the aromatic hydrocarbon content.
Volume resistivity, also called volume resistance or volume resistivity coefficient, is an important indicator characterizing the electrical properties of dielectric or insulating materials. The volume resistivity represents the resistance of a 25px³ dielectric to leakage current, measured in Ω·m or Ω·cm. Higher volume resistivity indicates better insulation performance.
16. Acid Value, Hydroxyl Value, and Iodine Value
Acid value, also known as acid number, is an indicator of organic matter. It represents the number of milligrams of potassium hydroxide (KOH) required to neutralize the free acid in 1g of non-volatile organic matter, expressed as mgKOH/g.
Hydroxy value refers to the number of milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl groups in 1g of sample, expressed as mgKOH/g.
Iodine value is an indicator of the degree of unsaturation of organic matter. It is the percentage by mass of iodine that 1g of sample can absorb. Higher unsaturation results in a higher iodine value.
17. Epoxy Value, Epoxy Equivalent, and HLB Value
Epoxy value represents the equivalent number of epoxy groups in 100g of epoxy resin, i.e., epoxy value = epoxy equivalent / 100 = number of epoxy groups / molecular weight of epoxy resin * 100%.
A higher epoxy value corresponds to a smaller molecular weight and lower viscosity. Epoxy equivalent represents the molecular weight of the resin corresponding to each epoxy group.
Epoxy equivalent = Epoxy resin molecular weight / Number of epoxy groups. HLB (Hydrophilic-lipophilic balance) is an abbreviation for hydrophilic-lipophilic balance, used to measure the relative strength of the polar and non-polar groups in a surfactant molecule. Stronger polar groups result in a larger HLB value and stronger hydrophilicity; longer non-polar groups result in a smaller HLB value and weaker hydrophilicity.
18. Critical Micelle Concentration (CMC) Critical micelle concentration, also known as critical micelle concentration, is the concentration range at which the properties of an emulsifier solution undergo a sudden change. After reaching the critical micelle concentration, many emulsifier molecules aggregate to form micelles. The unit of CMC is mol/L.
19. Baumé Degree The value given by a Baumé meter using a special calibration method in a glass tube float meter is called the Baumé degree, symbolized as °B′e. Used to indirectly indicate the density of a liquid.
20. Solid Content Solid content, also known as non-volatile matter content or total solids (TS), represents the ratio of the mass of the residue remaining after heating the sample at a certain temperature to the mass of the sample, expressed as a percentage.
Post time: Dec-20-2025