title: Chemical modulation of crystalline state of calcium oxalate with nickel ions.
abstract: BACKGROUND
  We explored that the presence of nickel ions in the precipitation medium affected size, shape and crystalline phase of the precipitated particles of calcium oxalate, whereas the applied synthesis conditions strongly influenced their uniformity.
  
  
  METHODS
  Aqueous solutions of oxalic acid and calcium chloride, containing varying amounts of nickel sulfate, were mixed at room temperature and allowed to sonicate for various periods of time. The obtained particles were characterized by SEM, XRD, TG/DTA, and FTIR.
  
  
  RESULTS
  Results revealed that particle morphology of calcium oxalate and their hydration states were dependent upon the chemical composition of the reactant solutions. For instance, the particles precipitated out in the form of dihydrate and having prismatic, and discs shaped particle morphology, when nickel ions were introduced in the starting reactant solution in different amounts. In contrast, the calcium oxalate particles precipitated under identical conditions in the absence of nickel ions were in the form of flakes with corrugated edges. Obvious variations were also found in the XRD patterns and crystallite size of these three solids. Heat treatment produced changes in the surface morphology of these particles due to loss of material and converted them calcium oxide.
  
  
  CONCLUSIONS
  Gentle mixing of aqueous solutions of calcium chloride and oxalic acid in the absence and presence of nickel ions produced precipitated particles of calcium oxalate. Chemical composition of the reactant solutions and their order of mixing were found to be the key parameters in controlling the particle morphology and their hydration/crystalline state. Heat treatment at the elevated temperature transformed the as-prepared calcium oxalate to calcium oxide with visible changes in surface features of the particles.
authors.affiliation: National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar-25120, Khyber Pakhtoonkhwa, Pakistan. khalida_akhtar@yahoo.com
authors.forename: Khalida
authors.initials: K
authors.lastname: Akhtar
authors.forename: Ikram Ul
authors.initials: IU
authors.lastname: Haq
mesh_terms: D002129:Calcium Oxalate / Q000737:chemistry*; D003460:Crystallization; D007477:Ions / Q000737:chemistry; D009532:Nickel / Q000737:chemistry*; D019815:Oxalic Acid / Q000737:chemistry; D010316:Particle Size; D013499:Surface Properties; D013696:Temperature
chemical_list: D007477:Ions; D002129:Calcium Oxalate; C029938:nickel sulfate; D009532:Nickel; D019815:Oxalic Acid