Figure 2. The SEM images of hydroxyapatite (HAp) ( a ) 7ZnHAp ( b ), and 20ZnHAp ( c ) and their Figure 2. The SEM images of hydroxyapatite (HAp) ( a ) 7ZnHAp ( b ), and 20ZnHAp ( c ) and their corresponding particle size distribution ( d – f ). ZnHAp: zinc-doped hydroxyapatite. corresponding particle size distribution ( d – f ). ZnHAp: zinc-doped