What are the structural properties of refractories? What does it contain?
The structural properties of refractories include bulk density, porosity, permeability, water absorption, true density, pore size distribution, etc. The structural properties of refractories are closely related to the raw materials used and their manufacturing processes, including the type, proportion, particle size, mixing, molding, drying and firing conditions of raw materials.
Structural Properties of Refractories 1: Bulk density of refractory
Bulk density refers to the ratio of the mass of porous materials (excluding free water) to the total volume (including the volume of solid phase and all gases), expressed in g/cm.
Bulk density（ ρ b) The calculation formula is as follows:
ρ b=m1/（m3－m2） ×ρ mg
Where: M1 – mass of dry sample
M2 — mass of saturated sample suspended in liquid
M3 – mass of saturated sample in air
ρ Mg – density of impregnating liquid at test temperature
Bulk density directly reflects the compactness of dense refractory products and is an important index to measure their quality level. In addition, it also enables the basic data of material consumption calculation in engineering.
Structural Properties of Refractories 2: Porosity of refractory
Pores are divided into open pores, closed pores and through pores. In the refractory monitoring standard, the ratio of the volume of all open pores to the total volume is regarded as the apparent porosity, expressed in%. The calculation formula of apparent porosity (is as follows:
λ a（%）=（m3－m1）/（m3－m2） × one hundred
The calculation formula of true porosity is as follows:
λ t（%）=（ ρ t－ ρ 1）/ ρ one × one hundred
Where: ρ T — true density of sample (g/cm)
ρ 1 – density of impregnating liquid at test temperature (g/cm)
Closed porosity（ λ f) The calculation formula of is as follows:
λ f= λ t－ λ a
The size of the pores of the refractory determines its ability to resist external erosion under high temperature conditions. Since the open pores and through pores account for the vast majority of the total pore volume and play a decisive role in its service performance, the size of the apparent porosity of the material can reflect its compactness and whether the particle grading, molding and firing in the manufacturing process are reasonable. Therefore, it is important to detect the apparent porosity of dense refractory products.
Structural Properties of Refractories 3: True density of refractory
True density refers to the ratio of the mass of a sample under completely dry conditions (excluding free water) to its true volume. Refractory products reflect the purity of their materials or the degree of crystal transformation, which can be speculated about the possible changes in use.
Structural Properties of Refractories 4: Water absorption of refractory
Water absorption refers to the ratio of the mass of water absorbed by all open pores when they reach the saturated state to the mass of the sample in the completely dry state (excluding free water). This index is often used to identify the calcination quality of raw materials.
Structural Properties of Refractories 5: Permeability of refractory
Permeability refers to the ability of gas to pass through a certain area and thickness sample under a certain pressure difference. The size of air permeability is mainly determined by the size, number and structure of through pores.