Phosphate-bonded high alumina bricks use a phosphoric acid or aluminium phosphate binder instead of a fired ceramic bond, and carry 75-77% Al2O3. The phosphate bond gives the brick high strength at moderate temperature and a low-expansion bond phase, so the material resists thermal shock and can...
Phosphate-bonded high alumina bricks use a phosphoric acid or aluminium phosphate binder instead of a fired ceramic bond, and carry 75–77% Al2O3. The phosphate bond gives the brick high strength at moderate temperature and a low-expansion bond phase, so the material resists thermal shock and can be cured rather than fired — properties that suit burner blocks, port structures and repair work.
XZK Group supplies the phosphate series in first-class and qualified grades — XZK-P75, XZK-P75-Q, XZK-PA77 and XZK-PA77-Q — pressed from high-alumina aggregate with a controlled phosphate addition.
In a conventional fired brick the bond is ceramic: the grains are held together by a glass or mullite phase that matures in the kiln. A phosphate-bonded brick works differently. Aluminium phosphate reacts with the alumina surface of the aggregate to form a network of aluminium orthophosphate that hardens as the brick dries and cures, and that develops further strength in service. The bond is formed chemically, not thermally.
That has two consequences. First, the brick reaches useful strength without a high-temperature firing, so phosphate-bonded shapes are often supplied as cured bricks or as rammed-and-cured linings; this is why they are common in complex shapes and in repairs. Second, the bond phase softens at a lower temperature than a mullitic ceramic bond, which is why the refractoriness under load of the series is 1250–1350°C, lower than a fired high alumina brick of the same alumina content.
What the phosphate bond buys in return is strength and thermal shock resistance. Cold crushing strength reaches 60–75 MPa, and the low-expansion bond handles rapid heating and cooling far better than a rigid ceramic bond. Phosphate-bonded bricks are therefore specified where thermal cycling, mechanical load and complex geometry matter more than the highest possible load-softening temperature.
| Technical Properties | XZK-P75 (First-class) | XZK-P75-Q (Qualified) | XZK-PA77 (First-class) | XZK-PA77-Q (Qualified) |
| Al₂O₃ (%) | ≥ 75 | ≥ 75 | ≥ 77 | ≥ 77 |
| Fe₂O₃ (%) | ≤ 3.2 | ≤ 3.2 | ≤ 3.2 | ≤ 3.2 |
| Cold Crushing Strength (MPa) | ≥ 70 | ≥ 60 | ≥ 75 | ≥ 65 |
| Bulk Density (g/cm³) | ≥ 2.70 | ≥ 2.65 | ≥ 2.75 | ≥ 2.70 |
| Refractoriness Under Load (0.2MPa, ℃) | ≥ 1350 | ≥ 1300 | ≥ 1300 | ≥ 1250 |
Test methods follow GB/T and ISO practice; ASTM equivalents and full certificates of analysis are issued with every shipment.
The series is split into a 75% alumina group (XZK-P75 and XZK-P75-Q) and a 77% group (XZK-PA77 and XZK-PA77-Q), and within each group into a first-class and a qualified grade.
Choose the first-class grade (XZK-P75, XZK-PA77) where the highest strength is required: cold crushing strength of 70–75 MPa and bulk density of 2.70–2.75 g/cm3. Choose the qualified grade (XZK-P75-Q, XZK-PA77-Q) for positions where slightly lower strength is acceptable and cost matters, such as backing courses. The 77% group gives both higher strength and a modest uplift in refractoriness under load over the 75% group.
Because the phosphate bond develops in service, the grade should be matched to the actual temperature of the position, and XZK confirms this against the furnace data rather than by rule of thumb.
Extensively used in critical zones subject to thermal cycling and material abrasion, including:
Phosphate-bonded bricks are chosen for the parts of a glass furnace that combine thermal cycling with mechanical duty, in particular:
Manufacturing is controlled from raw material through to finished brick. Four automatic batching lines feed 20 CNC presses ranging from 630 to 2000 tonnes, so density is set by press force rather than operator judgement, and firing runs through four 108-metre fully automatic tunnel kilns and five ultra-high-temperature shuttle kilns for a uniform soak.
Every batch is tested for bulk density, apparent porosity, cold crushing strength and refractoriness under load, and ships with a certificate of analysis. XZK Group holds ISO 9001, ISO 14001, ISO 45001 and ISO 50001 certification and operates the Henan Provincial Engineering Technology Research Center for Sintered Refractories for Glass Furnaces.
Phosphate-bonded bricks are supplied with SK series high alumina bricks, low porosity fire clay bricks, high alumina castables and refractory mortars. See the alumina-silicon bricks range or browse all refractory products.
Acid Resistance, %:＞99.8;
Bulk Density, g/cm3:2.3-2.4;
Water Absorption, %:≤0.5;
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