These coatings arerecommended for use in the presence of hot concentrated
sulfuric acid.Theyare also used for weak acid conditions up to apHof7.
9.2C alcium Aluminate
Coatings of this type consist of calcium aluminate-based cement and various
inert ingredients and are supplied in powder form to be mixed with water
when used.Theymay be appliedbycasting, pouring, or guniting. Calcium
aluminate-basedcoatings are hydraulic and consume water in their reaction
mechanism to form hydrated phases.T his is similar to portland cement
compositions; however,t heir rates of hardening are very rapid.E ssentially,
full strength is reached within 24 hat7 3 8 F( 238 C).
They have better acid resistance than portland cement, but they are not
useful in acids below pH 4.5–5. They are not recommended for alkali service
aboveapH of 10, nor are they recommended for halogen service. Refer to
Table9 .2 fort he chemicalr esistance of calciuma luminate and
portland cement.
9.3P ortlandC ement
Portland cement is made from limestoneorother natural sources of calcium
carbonate, clay( as ource of silica), alumina, ferric oxide, and minor
impurities. After grinding, the mixture is fired in ak iln at approximately
25008 F( 11378 C). The final product is ground to afi neness of about 10 m m,
TABLE 9.2
Chemical Resistance of Calcium Aluminate and Portland Cement
Cement Type
Calcium
Aluminate
Portland
Cement
pH range
4.5–10
7–12
Water resistance
EE
Sulfuric acid
XX
Hydrochloric acid
XX
Phosphoric acid
PX
Nitric acid
XX
Organic acids
FF
Solvents
GG
Ammonium hydroxide
FG
Sodium hydroxide
FF
Calcium hydroxide
FG
Amines
FG
Note:E,e xcellent; G, good; F, fair; P, poor; X, not recommended.
Corrosion of Linings and Coatings
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