CaHPO4・2H2Oの結晶の安定性について
1969 年 5 巻 p. 59-65
詳細
1969 年 5 巻 p. 59-65
Among several investigated methods on the stability of CaHPO4⋅2H2O crystal for polishing agent of dentifrice, TGA No. 46 method (Set Test) adopted by Toilet Goods Association of United States is the most popular way.
When a thin slurry of CaHPO4⋅2H2O in glycerine-water solution is heated in test tube, if the CaHPO4⋅2H2O used is unstable against the dehydration, there is a tendency for the powder to become partially dehydrated on aging, thereby causing the paste to become gritty, stiffen or no free flowing.
Then, Set Test observed on condition of the slurry or paste, is ready method for determination of stability of the polishing agent CaHPO4⋅2H2O.
Moreover, there is another method which determines the extent of the dehydration when CaHPO4⋅2H2O transits to CaHPO4.
However, they have several drawbacks. One of the difficulties is that the composition is the different from dentifrice composition and another is that the operation is troublesome. Now authors have carried on study on crystalline transformation of CaHPO4⋅2H2O by X-ray diffraction method.
It was found that transformation of CaHPO4⋅2H2O crystal was accelerated by addition of CaCO3. X-ray diffraction method using CaHPO4⋅2H2O-CaCO3 mixture is satisfactory way, because the composition is similar to dentifrice composition and is able to be determined under the condition of paste or slurry.
In this paper, the effects of several components of dentifrice on the stability of CaHPO4⋅2H2O crystal, have been studied by above mentioned method.
Paste sample was filled into sealed glass bottle and placed in the 50°C thermostat. The value of 2.79A/3.87A increased proportional to apatite growing.
The time needed to reach until 2.79A/3.87A=50 was measured and converted to its logarithmic value, which the authors named as “Index of Apatite Growing Time.”
Effects of several components in dentifrice against index of apatite growing time are as follows:
(A) Anionic surface active agent:
CH3(CH2)11OSO3Na[SDS]>CH3(CH2)10CON(CH3)-CH2COONa[SLSa]
(B) Solvent (Liquid): Glycerine>Pure water
(C) Grade of CaHPO4⋅2H2O: Grade treated with crystalline stabilizer at its manufacturing>>No treated Grade
(D) Crystalline stabilizing Agent: Addition>>No addition
Influence of kinds of magnesium phosphate on stability of CaHPO4⋅2H2O are very much different with kinds of them. In case of addition of Mg (H2PO4)2, it was accelerated to dissolve Mg (H2PO4)2 itself and CaHPO42H2O.
On the other hand, in case of addition of MgHPO4⋅3H2O or Mg3(PO4)2⋅8H2O, solubilities of magnesium phosphates added are small and therefore they have inhibitive effect against the dissolution of CaHPO4⋅2H2O.
Inhibitive effect of magnesium phosphates was as follows: Mg3(PO4)2⋅8H2O>MgHPO4⋅3H2O.
