Do you know what factors affect the performance of low cement refractory castables?

The performance of low cement refractory castables is influenced by various factors, mainly including raw material ratios, process parameters, and environmental conditions. The following are the key influencing factors and their mechanisms of action:

1、 The core function of ultrafine powder

Dispersion and compaction functions

Ultra fine powders (such as SiO ₂, α - Al ₂ O3) fill the gaps between aggregates, reduce porosity, and significantly improve the density and strength of castables through their high specific surface area (about 20 m ²/g) and nanoscale particle size (0.1-5 μ m).

SiO ₂ micro powder has higher activity and reacts with calcium aluminate cement to form needle shaped mullite (3Al ₂ O ∝· 2SiO ₂), enhancing high temperature toughness and thermal shock resistance, but excessive (>3%) will reduce fire resistance.

Cohesive binding mechanism

Ultra fine powder adsorbs Al ³ ⁺ and Ca ² ⁺ ions through surface charge, reaches the "isoelectric point", and undergoes agglomeration to form a binding network, reducing cement consumption (CaO content<2.5%).

2、 Selection and influence of binders

Aluminum salt cement type

CA-70 cement (Al ₂ O3 ≥ 70%) has better performance than CA-50 cement (Al ₂ O3 ≥ 50%): the drying compressive strength can reach 74 MPa (1100 ℃), but the cost is higher.

The amount of cement used needs to balance the strength at room temperature and high temperature performance. Excessive use can lead to a decrease in strength at medium temperatures (due to hydrate decomposition).

No cement system

Using ρ - Al ₂ O3 or sol binder (CaO<0.2%) to avoid the formation of low melting point phases, suitable for ultra-high temperature scenarios such as steel refining.

3、 Grading and Material of Aggregates

Particle size distribution optimization

Adopting a three-level or four level grading system (such as 10-40% for 10-5mm and 20-30% for 5-3mm).

White corundum aggregate (porosity 3.4%) is denser than third grade alumina clinker (porosity 7.2%), and the drying strength is increased by 37% (123 MPa vs 90 MPa).

Aggregate purity

High purity raw materials (such as fused alumina) reduce impurity phases (Fe ₂ O ∝, TiO ₂), improve slag resistance and high temperature stability.

4、 Water usage and additives

Water addition control

The water content should be ≤ 7%. Excessive water content can lead to an increase in porosity (visible porosity increases from 15% to 25%) and a decrease in strength (compressive strength decreases by 30%).

Low water content accelerates cement hydration, reduces bound water content, and enhances early strength.

Water reducing agent and explosion-proof agent

Organic water reducing agents (such as sodium humate) are more effective than inorganic agents (sodium tripolyphosphate), reducing water by 20-30%.

Add metal aluminum powder or organic fibers to improve baking breathability and prevent explosion.

5、 Process and environmental factors

Baking system

Low breathability requires strict temperature control (such as 50 ℃/h heating) to avoid water vapor accumulation and peeling.

Time variation

Ultra fine powder is prone to moisture absorption and requires sealed packaging; The mixture should be used up within 30 minutes to prevent a decrease in fluidity.

Performance improvement effect of factor optimization scheme for ultrafine powder type SiO ₂ micro powder (3-5%)+α - Al ₂ O Ⅲ micro powder. High temperature strength increased by 30%, thermal shock resistance increased by 20%. Cement variety CA-70 replaced CA-50. 100 ℃ compressive strength increased by 20%. Aggregate gradation: white corundum tertiary gradation. Volume density increased by 15%, apparent porosity increased by 40%. Water reducing agent: sodium humate (0.3%). Water addition: 25%, flowability maintained

summary

The performance optimization of low cement refractory castables requires comprehensive consideration of the ultrafine powder cement aggregate water quaternary system. Through scientific grading, water reducer adaptation, and strict process control, the goal of low porosity, high strength, and high temperature resistance can be achieved. The specific selection needs to be adjusted according to the operating temperature, erosion environment, and cost budget.