Table 2: XPS-determined binding energies (eV) of Ca 2p, P 2p, and (Ca 2p, P 2p), and Ca/P ratios for hydroxyapatite (HAP), HAP treated with 30% phosphoric acid (HAP—30% PA), and HAP—30% PA in storage for 12 hours (HAP—30% PA—12 h) at each incidence angle of the X-ray (90, 75, 60, 45, 30, or 15 degrees).

SampleAngle of incidence (degrees)Binding energy (eV)Ca/P
Ca 2pP 2p (Ca 2p, P 2p)

HAP
Mean 214.08a1.65b
SD

HAP—30% PA
Mean346.85132.78214.08a1.45b
SD

HAP—30% PA—12 h
Mean 1.09b
SD

indicates no significant difference between the samples.
indicates significant differences among the samples.