CS265607B1 - High- temperature method of double kobalt calcium cyclo-tetraphosphates preparation - Google Patents

Abstract

The solution concerns special inorganic chemistry substances and solves the high temperature process double-cyclo-tetraphosphate synthesis cobalt-lime-calcium c-CO2_xCaxP4012, where x fe (0; 1> mixtures consisting of cobalt compounds; \ t calcium dihydrogen phosphate, respectively starting phosphoric acid / hydrogen phosphate blends or cobalt phosphate a calcium, or with oxide, hydroxide, carbonate, or cobalt (II) hydroxide calcium in amounts corresponding to moles. ratio Co / Ca = (2 - x) / x and P2O 5 / (Co + Ca) equal 0.99 to 1.1, at temperatures above 1060 ° Celsius when the melt is formed. The one is sharp by cooling it to a vitreous intermediate, which is reheated to a temperature of at least 560 ° C and less than 885 ° C crystallized from cobalt-calcium double-cyclo-tetraphosphates microcrystalline character.

Description

The present invention relates to a high temperature process for the preparation of cobalt calcium calcium double cyclotetrophosphates.

Cobalt-calcium double cyclo-tetraphosphates of the formula o-CO 2 _x Ca _x P ^ O ^ 2 r where χ β (0; 1> are compounds of the cyclic anion condensed phosphate type consisting of four interconnected tetrahedra (PO ^). blue-violet compounds with high thermal and chemical stability with a crystal structure in a monoclinic system These compounds are designed for use as anti-corrosion thermally stable pigments.

The method of their synthesis is based on the thermal treatment of a mixture of cobalt and calcium carbonate, hydroxide, carbonate or bicarbonate and phosphoric acid, whereby only melting temperatures of up to 885 ° C can be used. The process is advantageous from an energy and technological point of view, but it is sometimes necessary to prepare products with regular, well-formed particles of well-developed c-Co 2 _{x x} C _x P 2 O 2, which are preferred for some applications. These include, for example, the use of products for experimental research work, for preparative purposes and also for some agrochemical applications.

According to the invention, the preparation of a product with the above-mentioned particle properties allows a high-temperature process for the preparation of cobalt-calcium-calcium double cyclotetraphosphates of the formula c-COjjj and Ca PPjOjj where xfi (0; 1>). , hydrogen phosphates, phosphates, or oxides, hydroxides, carbonates or hydroxide-carbonates of cobalt and calcium in such amounts that mol. the Co / Ca ratio corresponds to (2 - x) / x and on the one hand from phosphoric acid in such an amount that the phosphorus anions are in moles relative to the divalent cations in the mixture. a P ₂ O ₅ / (Co + Ca) ratio of 0.99 to 1.1, preferably 1 to 1.01, is heated, preferably such that the heating rate is less than 20 ° C / min and the water pressure the vapor in the calcine space is 40 to 100 kPa, to a temperature greater than 1060 ° C, preferably greater than 1100 ° C, when the previously formed intermediates are melted and then the melt is cooled, preferably by pouring into water or a cold plate of inert material, to form a further intermediate product in the form of a homogeneous amorphous glassy material which is further preferably reheated after grinding to a temperature of at least 560 ° C and below 885 ° C, preferably above 630 ° C and below 850 ° C, when recrystallization of the intermediate takes place together with the rearrangement of the tetrahedra (PO4) in the anions to form double cobalt calcium calcium phosphates, which is ultimately still finely divided into fine-grained microcrystalline particles.

In the high temperature process for the preparation of cobalt-calcium double cyclo-tetraphosphates, it is possible to start from raw materials in which the content of phosphorus anions and the corresponding divalent cations is expressed in moles. a ratio of P 10 / (Co + Ca) equal to one, or is in the vicinity of one - 0.99 to 1.1, preferably 1 to 1.01.

It is therefore possible to start from a mixture of dihydrogen phosphates (dihydrates or anhydrides), or a mixture of hydrogen phosphates or phosphates (tertiary) (again in hydrate or anhydride form) and phosphoric acid. However, starting materials of the phosphate type are less suitable for wider technological use, since they require preparation in advance which is not in itself a simple operation, so that it is more suitable only for preparing smaller quantities of the product c-Co _{2 x} Ca _x P in completely pure form. For technological applications, such as the synthesis of double cyclotetaphosphates for pigmentary or agrochemical purposes, it is preferable to start from a mixture of oxides or hydroxides, or carbonates, or hydroxide-carbonates of cobalt and calcium (or mixtures thereof) and phosphoric acid. The acid can be used at any concentration, however, it is to be understood that dilute acids are preferable for efficient reaction of the starting mixture, whereas higher concentrations of acid are preferable for energy requirements for evaporating dilution water from the acid.

The acid concentration should therefore be selected individually according to the reactivity of the starting cobalt compound (the calcium compounds are more reactive to the acid) and the energy possibilities of the manufacturer. When using a high concentration acid at high heating rates, there may be a risk of separate condensation of phosphoric acid to higher polyphosphoric acids and at high temperatures even to phosphorous pentoxide, which may then volatilize from the mixture and thereby adversely affect the ratio of phosphate anions and bivalent respectively. melt.

The first condensed phosphate type intermediate formed during calcination is dihydrogen diphosphate at temperatures of about 200 ° C. At temperatures of about 100 ° C to 200 ° C, it is converted to a product which, to a greater or lesser extent, corresponds to double cobalt-calcium-calcium cyclophosphates. In order to minimize the proportion of double cyclo-tetraphosphates, which are also an intermediate in this phase, and to minimize the risk of separate condensation of the phosphorous component and, consequently, its volatilization losses, it is advantageous to conduct heating at less than 20 ° C / min. in the presence of water vapor at a pressure of 40 to 100 kPa.

Maintaining a water vapor pressure in the calcinate space of at least 40 kPa is advantageous to prevent the formation of undesirable by-products, in particular to prevent cleavage and separate condensation of the phosphorus component. The water vapor present in the individual condensation reaction slows down the formation of intermediates somewhat, allowing them to be more quantitative; it also prevents the formation of undesirable non-porous crusts on the surface of the particles in the calcined mixture, which would prevent the course of dehydration reactions. The final calcination temperature at this stage of the preparation of the product according to the invention must be higher than 1060 ° C, as this is the highest temperature at which the respective intermediates melt. Because of the need for rapid melting of the calcinate, which may also contain other starting materials, it is preferred to select a temperature of at least 1100 ° C. The intermediate melts non-congruently, with the disintegration of the tetraphosphate cycles and the coupling of the resulting short phosphate chains into long chains, to which the presence of at least trace amounts of water vapor in the melt area also contributes.

Thereafter, the melt should be quenched, preferably by pouring it into water or onto a cold plate of inert material (metal or ceramic). This produces a further intermediate product which is a homogeneous amorphous mass of glassy character, containing anions in the form of long chains. The piece of glass obtained in this way, after cooling and, if necessary, after cooling. preferably, the dry drying is ground and reheated to recrystallize the intermediate to rearrange the tetrahedra (PO ^) in the anions to form double-calcium cyclo-tetraphosphate cobalt microcrystals of c-Co _{2 x x} Ca _x P 4 O ₃₂ ( ^χ 6 1?) · This releases small amounts of chemically bound water in the glassy intermediate. Therefore, it is easier to conduct the process of thermal recrystallization if the glassy intermediate is dry ground in advance.

The lower temperature of this reheat is 560 ° C and corresponds to the lowest recrystallization temperature of the cobalt intermediates. While this temperature can only be achieved, since the recrystallization process is exothermic and once it starts, it continues to run spontaneously, however, the preferred temperature range for recrystallization is above 630 ° C and below 850 ° C, where recrystallization of the glassy intermediate always occurs. at any heating rate and any consistency of the intermediate (powdered, lumpy or completely compact) and there is no risk of melting the final product, which, due to its non-congruity, would again lead to the formation of a glassy intermediate. Thus, in recrystallization, it is not possible to exceed the limit of 885 [deg.] C., which corresponds to the lowest melting point of double cyclotetaphosphates, namely the melting point of c-CoCaP2O4.

The final products - cobalt-calcium double cyclotetaphosphates - after cooling are preferably further comminuted (grinding, comminution) to regular fine-grained particles of microcrystalline nature. If the glass product was ground prior to recrystallization, the final comminution of the products is very easy.

Furthermore, the process according to the invention consists in treating the product after calcination with hydrochloric, sulfuric, nitric or phosphoric acid, preferably by mass. This operation is carried out as ev. cleaning of the obtained products in their pure form, for example for analytical or preparative purposes. The treatment of the above-mentioned rinse 260607 liner removes all unwanted by-products and ev. residues of the starting mixture which thus pass into solution. The cobalt-calcium double cyclo-tetraphosphates resist the action of these acids.

Advantages of the process according to the invention are the high yield and high purity of the products, which can be further purified by leaching. Another advantage is the microcrystalline fine-grained character of the product particles, which are regular and very surface-developed. They are therefore suitable for some special applications.

Example 1

A mixture of 100 g of cobalt dibasic phosphate (45,8% ^Ρ 2θ5 * Co) ^and 87,9 g of calcium dibasic phosphate (52,2% ^P 2 ° 5 ^'29,4 * ^Ca ) together with 150 g of phosphoric acid. the 85% ^H 3 ^PO 4 concentration was calcined at a rate of 12 ° C / min while maintaining the water vapor pressure in the calcined space up to a temperature of 500 ° C above 85 kPa to a temperature of 1100 ° C. The resulting melt was quenched by pouring into water. The resulting glassy intermediate was separated and dried and dry ground. It was then heated to 650 ° C and, after cooling, triturated. The product contained 99.0% cobalt calcium calcium c-CoCaP2O4 double cyclotetraphosphates and 270 g were obtained; it was in the form of regular fine microcrystals.

Example 2

A mixture of 100 g of cobalt carbonate (49% Co) and 27.8 g of calcium carbonate (40% Ca) together with 547 g of phosphoric acid. the concentration of 40% H 2 PO 4 was calcined at a rate of 10 ° C per minute while maintaining the water vapor pressure in the calcined space up to a temperature of 550 ° C above 80 kPa, at a temperature of 1100 ° C. The resulting melt was quenched by pouring onto a corundum plate. The cooled, glassy intermediate was dry ground and then heated to 680 ° C and then triturated after cooling. 240 g of product were obtained, which contained more than 98% of cobalt-calcium-calcium double cyclotetraphosphates of the formula c-Co4 ₅ Ca _{Q 5} ^P 4 ° ^ 2 in microcrystalline fine-grained form.

Claims (2)

A high-temperature process for the preparation of cobalt-calcium double cyclo-tetraphosphates of the formula c-Co _{2 x x} Ca _x P 2 O ₂ , wherein x ₆ (0; 1 2), characterized in that the starting mixture consists of dihydrogen phosphates, hydrogen phosphates, phosphates or cobalt and calcium oxides, hydroxides, carbonates or bicarbonates in such amounts that the Co / Ca · molar ratio corresponds to (2 - x) / x and from phosphoric acid in such an amount that the phosphorus anions are mixed with divalent cations the molar ratio of P ₂ O 4 (Co + Ca) equal to 0.99 to 1.1, preferably 1 to 1.01, is heated, preferably such that the heating rate is less than 20 ° C / min and the tension the water vapor in the calcine space is 40 to 100 kPa, to a temperature greater than 1060 ° C, preferably greater than 1100 ° C, when the previously formed intermediates thaw and then the melt is quenched, preferably by pouring into water or cold of an inert material, to form another intermediate product in the form of a homogeneous amorphous glassy material which is further heated, preferably after grinding, to a temperature of at least 560 ° C and below 885 ° C, preferably above 630 ° C and below 850 ° C, when recrystallization of the intermediate takes place together with the rearrangement of the tetrahedra (PO / v anions to form double cobalt calcium calcium phosphates), which is ultimately still finely divided into fine-grained microcrystalline particles. 2. Process according to claim 1, characterized in that the product, after calcination, is treated with hydrochloric, sulfuric, nitric or phosphoric acid, preferably a concentration by weight of 0.5 to 10%. Severography, n. P., MOST Price 2,40 Kčs