Select The Most Suitable Ceramic Pump Based On Particle Hardness, Particle Size, And PH Level

Different ceramics react differently. For example, alumina, zirconia and silicon nitride have different values for hardness and wear resistance. The first step is to measure Mohs hardness of the solids in the liquid. For example, quartz or corundum possess Mohs hardness between 7 and 9, and alumina will suffer degradation at much lower hardness. But in real life it will simply ground down quickly due to repeated micro-impact and cutting. Silicon carbide possesses higher hardness-above 9.2-and able to tackle harder particles but at the same time has the disadvantage of being more fragile unlike zirconia. In the cases where only soft solids-like calcium carbonate, aluminum hydroxide or soft sludge-are in the liquid, silicon carbide would be too much. Alumina or zirconia linings are plenty. The real danger is when particle hardness gets close to or passes the ceramic's hardness. That's when wear accelerates fast. You want the ceramic to be at least 1 to 2 Mohs points harder than whatever is flowing through it.

Particle size is what determines the flow path design and how much clearance you leave between moving parts. Fine particles under 50 microns usually work okay with a closed impeller and tight clearances, which helps efficiency. But once you get above 0.5 mm, especially in the 2–5 mm range, closed impellers start trapping solids. A hard particle jammed between the ceramic impeller and the casing can chip the impeller right along its grain boundaries. That's when you need a semi-open or open impeller, plus bigger axial and radial gaps between the impeller, pump cover, and wear rings. Always base the clearance on the biggest particle you expect, not the average. Say you have a D50 of 80 microns but occasionally see 3 mm chunks-your minimum gap should still be at least 4 mm. Wide particle size distributions, irregular shapes, or fibers also mean you should avoid narrow flow channels. They'll clog at the inlet or right in front of the vanes. Ceramic doesn't give like metal. It won't deform to let a particle pass. It either blocks the flow or breaks.

Different ceramics handle acids and bases very differently. Alumina is pretty stable in acidic conditions, but hot, strong alkaline solutions will form soluble aluminates on the surface, making it rough and causing material loss. Zirconia resists alkalis better than alumina, but it's no good with hydrofluoric acid or concentrated sulfuric acid. Silicon carbide stays stable across basically the whole pH range-0 to 14-so it's the most versatile choice for acid and alkali service. The downsides are cost and tighter requirements for seal compatibility. Silicon nitride proves to withstand acids and bases fairly well; however, due to the difficulty of machining it, you'll find it used less in pump components. Remember that there are other materials that come in contact with the fluid. The O-rings, seals, shaft sleeves and adhesives involved will also have to operate under the same temperature and pH level. Moreover, it is important to consider temperatures because any 20-30°C increase in temperature will double the corrosion rate. A ceramic material that is effective at room temperature may completely crumble in the same acid or base above 80°C.