In highly corrosive industrial fields such as chemical industry, metallurgy, and environmental protection, acid-resistant refractory castables are key lining materials, and their performance is directly related to equipment life and production safety. Starting from the principles of materials science and combining engineering practice, this paper systematically explains the configuration technology of acid-resistant refractory castables, providing practitioners with a technical guide that is both professional and operational.
1.Material system construction: the philosophy of balancing acid resistance and fire resistance
The core challenge of acid-resistant refractory castables is to resist both acidic medium erosion and high temperature environment damage. The material system must meet three basic requirements:
Main component selection: SiO₂-Al₂O₃ system as the skeleton, in which silica fume (containing SiO₂≥92%) provides a dense network structure, and alumina clinker (Al₂O₃ content 75%-85%) enhances high temperature stability.
Acid-resistant additives: Phosphates (such as Al(H₂PO₄)₃) or silica sol (SiO₂·nH₂O) are introduced as binders to form a dense Si-O-P or Si-O-Si protective film on the material surface to block the H+ penetration path.
Aggregate grading optimization: adopt the “three-level proportioning method”, that is, coarse aggregate (5-3mm) accounts for 40%-50%, medium aggregate (3-1mm) 30%-35%, fine powder (≤0.088mm) 15%-20%, and the D50 value is verified by the laser particle size analyzer in the range of 8-12μm to ensure that the bulk density is ≥2.65g/cm³.
2.Formulation design: technology transformation from laboratory to industrialization
Typical formula design should follow the “3+2+1” principle:
3 types of basic raw materials: refractory aggregate (60-70%), refractory powder (15-20%), binder (8-12%).
2 types of functional additives: plasticizers (such as methyl cellulose, 0.2-0.5%) to improve construction performance, explosion-proof agents (such as organic fibers, 0.1-0.3%) to control baking cracks.
Category 1 acid-resistant component: Select according to the characteristics of the medium. For example, in a sulfuric acid environment, the ZrO₂ content needs to be increased to 8%-10%, while in a hydrochloric acid environment, SiC (6%-8%) is preferred.
3.Preparation process: full process control from mixing to curing
Premixing stage: use a forced mixer to dry mix the aggregate and powder for 3-5 minutes to ensure uniform distribution of SiO₂ and Al₂O₃.
Binder addition: add the aluminum phosphate solution three times, with an interval of 1 minute each time to avoid local gelation.
Vacuum treatment: remove bubbles for 5 minutes in a vacuum environment of -0.095MPa to eliminate microscopic pores.
Molding process: vibration casting method is recommended, and the vibration frequency is controlled at 2800-3200 times/minute, and the duration is based on the surface slurry.
Curation system: adopt the “three-stage curing method”, that is, 25℃ moisturizing curing for 24h → 110℃ drying for 12h → 600℃ heat treatment for 4h, to ensure full conversion of the phosphate binding phase.
4.Performance optimization: from laboratory testing to field verification
Key performance indicators:
Acid resistance (GB/T 17601-2008): ≥98.5%
Apparent porosity: ≤18%
110℃ drying flexural strength: ≥8MPa
1000℃×3h heat treatment strength retention: ≥85%
Failure mode prevention and control:
Corrosion cracking: Ti-Si-O protective layer is formed by adding TiO₂ (2-3%) to inhibit H+ penetration.
Structural peeling: Fiber reinforcement technology is used to construct a three-dimensional network structure in the matrix to improve fracture energy.
5.Technology Development Trend
Nano modification technology: Nano SiO₂ (particle size 20-50nm) is introduced through the sol-gel method to increase the room temperature strength by 40%, and the 110℃ drying strength exceeds 12MPa.
Bake-free technology: Develop a calcium aluminate cement-phosphate composite bonding system to achieve a demoulding strength of ≥5MPa after 24h of natural curing, shortening the construction period by 60%.
3D printing adaptability: Optimize particle size grading and rheological properties to ensure that the castable meets the printing requirements of extrusion pressure ≤0.3MPa and open time ≥60min.
The configuration of acid-resistant and fire-resistant castables is a deep integration of material science and engineering practice. Through precise material selection, scientific formula design, and strict process control, high-performance products that meet the needs of complex working conditions can be prepared. With the integration of cutting-edge technologies such as nanotechnology and 3D printing, this field is accelerating its evolution towards intelligence and functionalization, providing a more reliable protective barrier for industrial equipment.