CS246345B1 - Tetragonal potassium phosphate's single crystals' growth method with determinated deuteration degree - Google Patents

Description

The invention relates to a process for the cultivation of single crystals of tetragonal potassium phosphate of the formula

K (D 1 _; H 1 _{x x 2} PO ₄₎ with a predetermined degree of deuteration x.

The cultivation of single crystals of tetragonal potassium phosphate, especially with a high degree of deuteration, is complicated by the formation of monoclinic potassium dideuterophosphate. This isotopic effect causes both the spontaneous dropping of the parasitic monoclinic phase from the culture solution, whose solubility is lower than the tetragonal phase, and recrystallization of the tetragonal embryo to monoclinic, making it difficult to grow perfect tetragonal monocrystals.

The method of growing tetragonal potassium phosphate monocrystals of the formula eliminates these difficulties

K (D _x H _{1 x} ) ₂ PO ₄ having a predetermined degree of deuteration x according to the invention, characterized in that it is grown in a stable tetragonal phase defined by invariant points of the state in the presence of trideuterophosphoric acid up to 2 M, wherein the degree of deuteration of the culture solution X _r is determined according to the requirement for the degree of deuteration of the single crystal X _k according to

X _r = V0,328 + 2,146 X _k - 0,573 and the dependence of temperature of invariant points on the degree of deuteration corresponds to the relation n

t = Σ A ,. what with . i. x i = 0 where t is the temperature in ° C,

A coefficients for i = 0 to 4, which is A _o = 38.40, A! = 12.57, A ₂ = 0.45, A ₃ = -1.05, A ₄ = -0.85 and x corresponds to x = (Xr-86) where

X _r is the degree of deuteration of the solution.

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In this method of cultivation, there are no common complications with the possibility of the formation of parasitic monoclinic crystals and it is possible to use lower quality seeds without the risk of recrystallization of both the seed and the growing single crystal.

The relationship of temperature and degree of deuteration in mol% D is shown in the attached graph, where the stability region of the monoclinic phase I and the stability region of the tetragonal phase II are indicated.

Example 1

From the requirement of growing a single crystal of tetragonal potassium phosphate with a degree of deuteration of 85 mol% D, the required deuterium content in the foaming solution was calculated to be 89.4 mol% D. By comparing this value with the invariant point position the single crystal can be reproducibly grown below 50 ° C. For this case, a saturation temperature of 45 ° C was chosen sufficient to grow the single crystal of the desired size.

The spent growing solution from the previous growing cycle was adjusted to the desired degree of deuteration by the addition of redistilled water. wherein the deuterium content was measured by a method of measuring the absolute refractive index of a 3 ml sample. The saturation of the mother liquor was carried out with a slight excess of solid potassium phosphate raw material of known degree of deuteration for 3 h with stirring in a thermostat at 45 ° C. After transfer to the crystallizer, the solution was stabilized for 1 week at 60 degrees Celsius and accurately measured the saturation point for the tetragonal potassium phosphate phase, which was 44.80 ° C. The saturation point was measured by the shadow method. The trideuterophosphoric acid content was not adjusted due to the satisfactory content from the previous growing cycle of 1.362 M. Single crystal cultivation was not complicated by the isotopic effect, although a seed with mild defects was used and a perfect single crystal was grown.

Example 2

For the cultivation of tetragonal potassium phosphate monocrystal with the required degree of deuteration of 93% mol D, the necessary deuterium content in the solution was calculated

95.2 mol% D. The delimited region of stability of the tetragonal phase is delimited by a maximum temperature of 32.2 ° C.

In this case, a larger volume crystallizer was required for cultivation so that, due to the possibility of cooling the solution from 30 to 20 ° C, the amount of salt precipitated corresponded to the required single crystal size.

The growth solution was prepared by dissolving a solid potassium phosphate feedstock of known degree of deuteration in heavy water D ₂ O with the addition of trideuterophosphoric acid to a concentration of 1.651 M in the solution at 30 ° C. Here too the cultivation was not complicated by isotopic etect and a perfect single crystal was grown.

Claims (1)

A method of growing single crystals of tetragonal potassium phosphate of the formula with a predetermined degree of deuteration (x), characterized in that it is grown in a stable tetragonal phase defined by invariant points of the system in the presence of trideuterophosphoric acid up to 2 M; is determined according to the requirement for the degree of deuteration of the single crystal (Xr) according to X _r = V0.328 + 2,146 X _k - 0,573 and the temperature dependence of invariant points on the degree of deuteration corresponds to the relation n t - Σ Aj. what with . i. xi = O where (ie temperature in ° C, (A) coefficients for (ij = 0 to 4, which is A _o = = 38,40, A _t = 12.57, A ·,, - 0, 45, A ₃ = —1.05, A ₄ = 0.85 and (xj corresponds to x = ...... (X _r - 86) where (X _r ) is the degree of deuteration of the solution. 1 sheet of drawings