CA1090531A - Stabilization of calcium phosphate dihydrate - Google Patents
Stabilization of calcium phosphate dihydrateInfo
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- CA1090531A CA1090531A CA288,991A CA288991A CA1090531A CA 1090531 A CA1090531 A CA 1090531A CA 288991 A CA288991 A CA 288991A CA 1090531 A CA1090531 A CA 1090531A
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- phosphate dihydrate
- precipitated
- dimagnesium
- dicalcium phosphate
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61Q—SPECIFIC USE OF COSMETICS OR SIMILAR TOILETRY PREPARATIONS
- A61Q11/00—Preparations for care of the teeth, of the oral cavity or of dentures; Dentifrices, e.g. toothpastes; Mouth rinses
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K8/00—Cosmetics or similar toiletry preparations
- A61K8/18—Cosmetics or similar toiletry preparations characterised by the composition
- A61K8/19—Cosmetics or similar toiletry preparations characterised by the composition containing inorganic ingredients
- A61K8/24—Phosphorous; Compounds thereof
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
- C01B25/327—After-treatment
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
- C01B25/34—Magnesium phosphates
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Abstract
STABILIZATION OF CALCIUM HYDROGEN PHOSPHATE
DIHYDRATE.
ABSTRACT OF THE DISCLOSURE:
Dicalcium phosphate dihydrate is stabilized with the use of dimagnesium phosphate trihydrate, the dicalcium phosphate dihydrate being precipitated by reacting a calcium compound with an aqueous solution of orthophos-phoric acid or a phosphoric acid salt. More specifically, 1 to 50 weight% based on dicalcium phosphate dihydrate, of dimagnesium phosphate trihydrate is co-precipitated with the dical-cium phosphate dihydrate, or subsequently on precipitated di-calcium phosphate dihydrate by reacting a magnesium salt with a solution of orthophosphoric acid or of a phosphoric acid salt in the presence of a basic compound.
DIHYDRATE.
ABSTRACT OF THE DISCLOSURE:
Dicalcium phosphate dihydrate is stabilized with the use of dimagnesium phosphate trihydrate, the dicalcium phosphate dihydrate being precipitated by reacting a calcium compound with an aqueous solution of orthophos-phoric acid or a phosphoric acid salt. More specifically, 1 to 50 weight% based on dicalcium phosphate dihydrate, of dimagnesium phosphate trihydrate is co-precipitated with the dical-cium phosphate dihydrate, or subsequently on precipitated di-calcium phosphate dihydrate by reacting a magnesium salt with a solution of orthophosphoric acid or of a phosphoric acid salt in the presence of a basic compound.
Description
105~0S31 This invention relates to an improved process for stabilizing dicalcium phosphate dihydrate -- briefly termed DCP hereinafter -- with the use of dimagnesium trihydrate -- briefly termed DMP hereinafter --, wherein DCP is precipitated in known manner by reacting a cal-cium compound with an aqueous solution of orthophosphoric acid or a phosphoric acid salt, if desired in the pre-sence of a basic compound.
To be suitable for use as a polishing ingredient for tooth paste, it is necessary for DCP to be stabilized against the separation of water of hydration which is known by experience to take place prior to the hydroly-tic decomposition into hydroxyl apatite and orthophos-phoric acid. The useful stabilizers which have been used heretofore comprise, e.g. the following compounds: -1) Alkali metal or alkaline earth metal salts of condensed phosphoric acids, such as tetrasodium pyrophosphate, disodium-calcium pyrophosphate, calcium pyrophosphate, magnesium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate (cf. German Patent Specification No. 1,259,861).
To be suitable for use as a polishing ingredient for tooth paste, it is necessary for DCP to be stabilized against the separation of water of hydration which is known by experience to take place prior to the hydroly-tic decomposition into hydroxyl apatite and orthophos-phoric acid. The useful stabilizers which have been used heretofore comprise, e.g. the following compounds: -1) Alkali metal or alkaline earth metal salts of condensed phosphoric acids, such as tetrasodium pyrophosphate, disodium-calcium pyrophosphate, calcium pyrophosphate, magnesium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate (cf. German Patent Specification No. 1,259,861).
2) Magnesium orthophosphates, e.g. trimagnesium orthophosphate (cf. German Patent Specifications Nos. 1,277,222 and 1,259,861).
As described in the literature, one or more of these stabilizers may be added during the precipita-tion of DCP, or later during a wet-processing phase.
In a further process, which is widely used, the stabilizer is added during a dry-processing stage, i.e.
dry DCP is intimately blended with an a~propriate lOS0531 quantity of stabilizer which is homogeneously distribu-ted tllerein, especially when the resulting blend of DCP
and stabilizer is subsequently ground.
Use is also made of processes, wherein DCP is stabi-lized both during the wet and dry-processing stages (cf. German Patent Specification No. 1,259,861).
DCP stabilized by one of the processes described above is actually ~uitable for use in tooth pastes which are left free from fluorine as a prophylactic agent against caries. In the presence of a fluorinating agent, however, DCP does not present the stability to hydrolysis necessary to avoid cleavage into hydroxyl - apatite and orthophosphoric acid, which is unsatisfac-tory. Fluoride ions are known to accelerate the hydro-lysis of DCP and hence the formation of orthophosphoric acid which invariably results in an undesirable decrease of the pH.
The fact that the hydrolysis occurs more rapidly in the presence of fluoride ions may be explained as being a result of the formation initially of fluorine apatite, which tends to be favored over that o~ hydroxyl apatite, because of the marked electronegative nature of fluorine.
Affsociated with this hydrolytic cleavage is an acidifi-cation phenomenon which adversely affects the compatibi-lity with fluorine in the tooth paæte.
Sodium monofluophosphate is the fluorinating agent most commonly used in combination with DCP. This compound and the calcium ions of DCP are capable of ~orming saltæ of satisfactory solubility which enable the prophylactic efficiency against caries to be preserved. In those cases, 109053~
however, in which a fluoride is used as the fluorinating agent, the latter undergoesreaction with the calcium ions of DCP and substantially insoluble calcium fluoride is obtained, which is an inefficient caries-preventive agent.
In view of the fact that sodium monofluophosphate undergoes rapid hydrolysis in an acid medium with the resultant formation of orthophosphate and fluoride, it is highly desirable to have DCP of optimum stability per-mitting the prophylactic efficiency against caries to be preserved. Tooth pastes containing sodium monofluophosphate have often been found, even after a period as short as 6 months, to have lost more than 50% of their initial soluble and caries-prophylactic fluorine content, due to the formation of calcium fluoride.
The present invention now unexpectedly provides a process which permits the stability to hydrolysis of DCP and its compatibility with sodium monofluophosphate to be improved.
According to the present invention, a process for stabilizing di-calcium phosphate dihydrate with the use of dimagnesium phosphate trihydrate;
wherein the dicalcium phosphate dihydrate is precipitated by reacting a calcium compound with an aqueous solution of orthophosphoric acid or a phosphoric acid salt, in the presence of a basic compound, comprises: precipitating jointly with the dicalcium phosphate dihydrate, or precipitating subsequently, directly on to the newly precipitated dicalcium phosphate dihydrate, 1 to S0 weight %, preferably 2 to 20 weight %, based on dicalcium phosphate dihydrate, of di-magnesium phosphate trihydrate by reacting a magnesium salt solution with a solution of orthophosphoric acid or of a phosphoric acid salt in the presence of a basic compound; and separating the two precipitation products jointly from the resulting reaction mixture.
A preferred version of the present process provides for the reactants, which are necessary for the formation 10~053~.
of dimagnesium phosphate trihydrate, to be added in approximately stoichiometric proportions with thorough agitation so as to initially maintain, during the pre-cipitation, a pH-value of 2.5 to 6.5, pre~erably 3.0 to 4.5 by the preferential addition of reactants under-going an acid reaction, and after the addition is com-plete, to increase the pH to 6.5 to 9 by the addition of the residual reactants undergoing a basic reaction.
It is also preferable to precipitate the dimagne-æium phosphate trihydrate at temperatures of 20 to 60C, preferably 30 to 45C.
The starting materials which may more preferably be used comprise 25 to 35 weight% magnesium chloride or magnesium nitrate æolutions,5Q to 80 weight% solutions of orthophosphoric acid or acid alkali metal phosphates, as well aæ 20 to 50 weight% æolutions of an alkali metal hydroxide or carbonate aæ a basic reactant.
The dimagnesium phosphate trihydrate, which is added to DCP as a stabilizer, may be used in combination with further known stabilizeræ, especially in combination with tetrasodium pyrophosphate.
Various processes for making DCP have already been described which are all based on the reaction of ~arious calcium compounds with orthophosphoric acid or a phos-phoric acid æalt, if deæired with the addition of an alkali metal hydroxide. The useful calcium compoundæ
comprise, e.g.: CaO and Ca(OH)2; CaC03; CaCl2; Ca(N03)2 (cf. German Patent Specifications Nos. 1,216,264 and 1,224,716).
As described in the literature, one or more of these stabilizers may be added during the precipita-tion of DCP, or later during a wet-processing phase.
In a further process, which is widely used, the stabilizer is added during a dry-processing stage, i.e.
dry DCP is intimately blended with an a~propriate lOS0531 quantity of stabilizer which is homogeneously distribu-ted tllerein, especially when the resulting blend of DCP
and stabilizer is subsequently ground.
Use is also made of processes, wherein DCP is stabi-lized both during the wet and dry-processing stages (cf. German Patent Specification No. 1,259,861).
DCP stabilized by one of the processes described above is actually ~uitable for use in tooth pastes which are left free from fluorine as a prophylactic agent against caries. In the presence of a fluorinating agent, however, DCP does not present the stability to hydrolysis necessary to avoid cleavage into hydroxyl - apatite and orthophosphoric acid, which is unsatisfac-tory. Fluoride ions are known to accelerate the hydro-lysis of DCP and hence the formation of orthophosphoric acid which invariably results in an undesirable decrease of the pH.
The fact that the hydrolysis occurs more rapidly in the presence of fluoride ions may be explained as being a result of the formation initially of fluorine apatite, which tends to be favored over that o~ hydroxyl apatite, because of the marked electronegative nature of fluorine.
Affsociated with this hydrolytic cleavage is an acidifi-cation phenomenon which adversely affects the compatibi-lity with fluorine in the tooth paæte.
Sodium monofluophosphate is the fluorinating agent most commonly used in combination with DCP. This compound and the calcium ions of DCP are capable of ~orming saltæ of satisfactory solubility which enable the prophylactic efficiency against caries to be preserved. In those cases, 109053~
however, in which a fluoride is used as the fluorinating agent, the latter undergoesreaction with the calcium ions of DCP and substantially insoluble calcium fluoride is obtained, which is an inefficient caries-preventive agent.
In view of the fact that sodium monofluophosphate undergoes rapid hydrolysis in an acid medium with the resultant formation of orthophosphate and fluoride, it is highly desirable to have DCP of optimum stability per-mitting the prophylactic efficiency against caries to be preserved. Tooth pastes containing sodium monofluophosphate have often been found, even after a period as short as 6 months, to have lost more than 50% of their initial soluble and caries-prophylactic fluorine content, due to the formation of calcium fluoride.
The present invention now unexpectedly provides a process which permits the stability to hydrolysis of DCP and its compatibility with sodium monofluophosphate to be improved.
According to the present invention, a process for stabilizing di-calcium phosphate dihydrate with the use of dimagnesium phosphate trihydrate;
wherein the dicalcium phosphate dihydrate is precipitated by reacting a calcium compound with an aqueous solution of orthophosphoric acid or a phosphoric acid salt, in the presence of a basic compound, comprises: precipitating jointly with the dicalcium phosphate dihydrate, or precipitating subsequently, directly on to the newly precipitated dicalcium phosphate dihydrate, 1 to S0 weight %, preferably 2 to 20 weight %, based on dicalcium phosphate dihydrate, of di-magnesium phosphate trihydrate by reacting a magnesium salt solution with a solution of orthophosphoric acid or of a phosphoric acid salt in the presence of a basic compound; and separating the two precipitation products jointly from the resulting reaction mixture.
A preferred version of the present process provides for the reactants, which are necessary for the formation 10~053~.
of dimagnesium phosphate trihydrate, to be added in approximately stoichiometric proportions with thorough agitation so as to initially maintain, during the pre-cipitation, a pH-value of 2.5 to 6.5, pre~erably 3.0 to 4.5 by the preferential addition of reactants under-going an acid reaction, and after the addition is com-plete, to increase the pH to 6.5 to 9 by the addition of the residual reactants undergoing a basic reaction.
It is also preferable to precipitate the dimagne-æium phosphate trihydrate at temperatures of 20 to 60C, preferably 30 to 45C.
The starting materials which may more preferably be used comprise 25 to 35 weight% magnesium chloride or magnesium nitrate æolutions,5Q to 80 weight% solutions of orthophosphoric acid or acid alkali metal phosphates, as well aæ 20 to 50 weight% æolutions of an alkali metal hydroxide or carbonate aæ a basic reactant.
The dimagnesium phosphate trihydrate, which is added to DCP as a stabilizer, may be used in combination with further known stabilizeræ, especially in combination with tetrasodium pyrophosphate.
Various processes for making DCP have already been described which are all based on the reaction of ~arious calcium compounds with orthophosphoric acid or a phos-phoric acid æalt, if deæired with the addition of an alkali metal hydroxide. The useful calcium compoundæ
comprise, e.g.: CaO and Ca(OH)2; CaC03; CaCl2; Ca(N03)2 (cf. German Patent Specifications Nos. 1,216,264 and 1,224,716).
3 The precipitation velocity, the quantitative yield 109053~
and particle size of the resulting DCP are critically determined by the maintenance of certain conditions during the precipitation. The Ca and P04"-containing reactants used do not affect the present process, but it is an important requirement for it that the DMP
used as the stabilizer should be precipitated in accor-dance with the present invention.
The DMP is formed, e.g. in the manner shown by the following idealized reaction equations:
MgC12 + 2 NaOH + H3P04 + H20 ~ MgHP04 3 H20 + 2 NaCl MgC12 + Na2C03 + H3P04 + 2 H20 MgHP04 3 H20 + C02 + 2 NaCl Mg(N03)2 + NaH2P04 + NaOH + 2 H20 MgHP04 3 H20 + 2 NaN03 The following Examples illustrate the invention:
EXAMPLE 1:
A stainless steel reactor (capacity = approximately 15 liters) provided with an agitator and a double cooling jacket was fed with 3 kg of water which was thoroughly stirred by means of a propeller mixer (2000 rpm.). Next, 3.2 kg of a 35 weight% calcium chloride solution, 3.2 kg of a 25 weight% sodium hydroxide solution and a 75 weight%
orthophosphoric acid were added, the latter in the pro-portions necessary to establish a pH of 3 to 4. ~uring the reaction, the temperature rose from initially 16C
to 40C.
The DMP stabilizer was precipitated by introducing the following reactants in the manner described above, namely 0.075 kg of a 32 weight~ magnesium chloride solution and 0.08 kg of a 25 weight% sodium hydroxide 109~531 solution together with orthophosphoric acid.
In this latter step, the orthophosphoric acid was added in the proportions necessary to maintain a pH of
and particle size of the resulting DCP are critically determined by the maintenance of certain conditions during the precipitation. The Ca and P04"-containing reactants used do not affect the present process, but it is an important requirement for it that the DMP
used as the stabilizer should be precipitated in accor-dance with the present invention.
The DMP is formed, e.g. in the manner shown by the following idealized reaction equations:
MgC12 + 2 NaOH + H3P04 + H20 ~ MgHP04 3 H20 + 2 NaCl MgC12 + Na2C03 + H3P04 + 2 H20 MgHP04 3 H20 + C02 + 2 NaCl Mg(N03)2 + NaH2P04 + NaOH + 2 H20 MgHP04 3 H20 + 2 NaN03 The following Examples illustrate the invention:
EXAMPLE 1:
A stainless steel reactor (capacity = approximately 15 liters) provided with an agitator and a double cooling jacket was fed with 3 kg of water which was thoroughly stirred by means of a propeller mixer (2000 rpm.). Next, 3.2 kg of a 35 weight% calcium chloride solution, 3.2 kg of a 25 weight% sodium hydroxide solution and a 75 weight%
orthophosphoric acid were added, the latter in the pro-portions necessary to establish a pH of 3 to 4. ~uring the reaction, the temperature rose from initially 16C
to 40C.
The DMP stabilizer was precipitated by introducing the following reactants in the manner described above, namely 0.075 kg of a 32 weight~ magnesium chloride solution and 0.08 kg of a 25 weight% sodium hydroxide 109~531 solution together with orthophosphoric acid.
In this latter step, the orthophosphoric acid was added in the proportions necessary to maintain a pH of
4 to 4.5. Towards the end of the reaction, the balance quantities of magnesium chloride and sodium hydroxide solution were added at the rate necessary to establish a final pH-value of 8.3. Next, the whole was filtered and the precipitate was dried and ground as usual.
The quantity of precipitated DMP was 2.5 weight%, based on DCP.
EXAMPLE 2:
The reaction was effected as in Example 1, but the DMP was prepared with the use of 0.24 kg of a 32 weight%
magnesium chloride solution and 0.25 kg of a 25 weight%
sodium hydroxide solution. The quantity of precipitated DMP was 8 weight%, based on DCP.
EXAMPLE 3:
The reaction was e~fected as in Example 1, but the DMP was prepared with the use of 0.45 kg of a 32 weight%
magnesium chloride solution and 0.47 kg of a 25 weight%
sodium hydroxide solution. The quantity of precipitated DMP was 15 weight%, based on DCP.
EXAMPLE 4:
A stainless steel reactor (capacity _ approximately 15 liters) provided with an agitator and a double cooling ~acket was fed with 2 kg of water which was thoroughly stirred by means of a propeller mixer (2000 rpm). Next, 2.6 kg of a 38 weight% aqueous calcium carbonate suspen-sion and a 85 weight% orthophosphoric acid were added in substantially stoichiometric proportions, the latter in lO9~S31 the proportions necessary to establish a pH o~ 2 to 3.5.
Following the reaction of the calcium carbonate, the tem-perature was at 35C.
The DMP stabilizer was precipitated by introducing the necessary starting materials in the manner described above, namely 0.1 kg of a 38 weight% magnesium nitrate solution and 0.08 kg of a 25 weight% sodium hydroxide solution to-gether with orthophosphoric acid, the latter being added at a rate necessary to esiablish a pH of 4 to 4.5. To-wards the end of the reaction, the balance quantities of magnesium nitrate and sodium hydroxide solution were added at the rate necessary to establish a final pH-value of 8.5.
The quantity of precipitated DMP was 2.5 weight%, based on DCP.
The reaction mixture was then admixed with 0.1 weight%, based on DCP, of fine particulate tetrasodium pyrophosphate as an additional stabilizer, and the whole was stirred for a further 10 minutes.
The precipitate was filtered off, dried and ground as usual.
EXAMPLE 5:
The reaction was effected as in Example 4, but the DMP
was prepared with the use of 0.32 kg of a 38 ~reight% mag-nesium nitrate solution and 0.25 kg of a 25 weight~ sodium hydroxide solution. The quantity of precipitated DMP was 8 weight%, based on DCP.
EXAMPLE 6:
The reaction was effected as in Example 4, but the DMP
was prepared with the use o~ 0.6 kg of a 38 weight~ mag-109~:~i31 nesium chloride solution and 0.47 kg of a 25 weight% so-dium hydroxide solution. The quantity of precipitated DMP was 15 weight%, based on DCP.
EXAMPLE 7:
The reaction was effected as in Example 4, but the dry precipitate was dry-blended with 0.6 %, based on DCP, of tetrasodium pyrophosphate as an additional stabilizer, and the resulting blend was ground.
EXAMPLE 8:
The reaction was effected as in Exa~ple 5, but the dry precipitate was dry-blended with 0.6 ~, based on DCP, of tetrasodium pyrophosphate as an additional stabilizer, and the resulting blend was ground.
EXAMPLE 9:
The reaction was effected as in Exa~ple 6, but the dry precipitate was dry-blended with 0.6 %, based on DCP, of tetrasodium pyrophosphate as an additional stabilizer, and the resulting blend was ground.
A stainless steel reactor (capacity = approximately 15 liters) provided with an agitator and a double coo-ling Jacket was fed with 3 kg of water which was tho-rough~y stirred by means of a propeller ~ixer (2000 rpm).
Next, 2.25 kg of a 38 weight% aqueous calcium carbonate suspension and a 75 weight% orthophosphloric acid were added simultaneously, the latter in the proportions nec-essary to establish a pH of 2 to 3.5. During the reaction, the temperature of the reaction mixture rose to 38C.
After all o~ the calcium carbonate was found to have reacted, the balance of the orthophosphoric acid in ex-lQ9(~S31 cess was caused to react until a pH of 8.2 by the con-current addition, in stoichiometric proportions, a) of a mixture consisting of 0.4 kg of a 35 % calcium chloride solution and 0.07 kg of 32 % magnesium chloride solution, and b) of a 24 % sodium hydroxide solution (ratio of (CaCl2 + MgC12) : NaOH = 1 : 2).The whole was filtered, dried and ground, and DCP containing 2.5 weight% of DMP was obtained.
10 ~ EXAMPLE 11:
The procedure was as in Example 10, but the reaction of the residual phosphoric acid was effected by the addi-tion, in stoichiometric proportions, a) of a mixture consisting of 0.2 kg of a 32 % magnesium chlo~ide solution and 0.13 kg of a 35 % calcium ohloride solution, and b) of a 25 % sodium hydroxide solution. The whoIe was filtered, dried and ground, and DCP containing 8 weight%
of DMP was obtained.
EXAMPLE 12:
A stainless steel reactor (capacity = 15 liters) provided with an agitator and a double cooling jacket was fed with 3 kg of water which was thoroughly stirred by means of a propeller mixer (2000 rpm). Next, the water was admixed a) with a mixture consisting of 3.2 kg of a 35 X calcium chloride solution and 0.44 kg of a 32 ~ magnesium chloride - solution, and b) with 3.7 kg of a 25 % sodium hydrox'ide solution to-gether with a 75 % orthophosphor$c acid, the latter being 109~531 added in the proportions necessary to establish a pH o~
3 to 4. During the reaction, the temperature rose to about 40C.
Towards the end of the reaction, the balance quanti-ties of magnesium chloride/calcium chloride solution and sodium hydroxide solution were added and a final pH
of 8.2 was established. The whole was filtered, dried and ground, and D~P containing 15 weight% of DMP was obtained.
EXAMPLE 1~ (Comparative Example) A stainless steel reactor (capacity = approximately 15 liters) provided with an agitator and a double coo-ling jacket was fed with 3 kg of water which was tho-roughly stirred by means of a propeller mixer (2000 rpm).
Next, 2.25 kg of a 38 weight% aqueous calcium carbonate suspension and a 75 weight% orthophosphoric acid were added concurrently, the latter in the proportions nec-essary to establish a pH of 2 to 3.5. During the reac-tion, the temperature rose to 38C.
After all of the calcium carbonate was found to have reacted, the balance of the orthophosphoric acid in ex-cess was caused to react until a pH of 8.3 by the con-current stoichiometric addition of a 35 weight% calcium chloride solution and a 25 weight% sodium hydroxide solu-tion (CaCl2 : NaOH = 1 : 2). To stabilize the wet phase, 1.0 weight% of fine particulate tetrasodium pyrophos-phate and 2.5 weight~ of fine particulate DMP, the per-centages being based on DCP, were added, and the reac-tion mixture was stirred *or a *urther 10 minutes. The precipitate was filtered and dried, and the dry material lQ9aS3~
was dry-blended with 0.6 weight% of tetrasodium pyro-phosphate. The resulting blend was ground.
EXAMPLE 14: (Comparative Example) The procedure was as in Example 13, but 8 weight% of DMP, based on DCP, was added.
EXAMPLE 15: (Comparative Example) The procedure was as in Example 13, but 15 weight% of DMP, based on DCP, was added.
The products prepared as described in Examples 1 through 15 were tested for their stability to hydrolysis and compatibility with sodium monofluophosphate by the following methods.
I. Testing stability to hydrolysis:
25 g of the DCP to be tested is suspended in a solu-tion of 1.63 g of sodium fluoride in 1Q0 ml of water, which is heated to 60C and maintained at that tèm-perature. The DCP is kept in suspension by means of a stirrer. The pH-value is measured at regular inter-vals and themoment at which the pH falls below 4 i8 determin~d. The period of time until a pH of 4 is reached is an index of the stability to hydrolysis of DCP.
II. Testing compatibilitv with sodium monofluoPhosPhate:
10 g of the DCP to be tested is suspended in 90 g of water and the suspension is heated to 80C. Next, the suspension is admixed with 76 mg of sodium mono-- fluophosphate (1000 ppm of fluorine, based on DCP) and the whole is maintained for exactly 1 hour at 80C with agitation. ~ollowing this, the material is cooled in an ice bath to room temperature, filtered lQ9(3531 by means of a frit, and the content of fluorine is determined in an aliquote portion of the filtrate.
The content of soluble fluorine is an index of the compatibility of DCP with sodium monofluophosphate. This is expressed as a percentage of the in~tial value.
The Table hereinafter shows that the products made in accordance with this invention have an improved stability as compared with DCP stabilized in customary manner which has long been held to afford an optimum stabilization effect. With reference to the Table:
The products of this invention described in working Examples 1, 4, 7 and 10, and the comparative product described in Example 13 each contained 2.5 weight% of DMP stabilizer. With respect to the present products, they were found to have the lowest compatibility with fluorine at 70 % and the lowest stability to hydrolysis at 8 hours. In the comparative Example, the correspon-ding values were 66 % and 0.3 hour, respectively.
In each of working Examples 2, 5, 8 and 11, and in comparative Example 14, use was made o~ DCP containing 8 weight% of DMP stabilizer. With respect to the pre-sent products, they were found to have the lowest stabi-lity to fluorine at 80 % and the lowest sta~ility to - hydroIysis at 24 hours. In the comparative Example, the corresponding values were 72 % and 10.5 hours, respec-tively.
In each of working Examples 3, 6, 9 and 12, and in comparative Example 15, use was made of DCP containing 15 weight% of DMP stabilizer. With respect to the pre-sent products, they were found to have the lowest compa-10~531 tibility with fluorine at 76 % and the lowest stability to hydrolysis at 22 hours. In the comparative Example, the corresponding values were 73 % and 12 hours, respec-tively.
As can be seen, DCP which is stabilized in accordance with this invention with 8 % of DMP compares favorably even with DCP stabilized in conventional manner with 15 % of DMP.
T a b 1 e :
_ _ Ex. Stability to fluorine, Stability to hy-No. in weight% water-solu- drolysis, expressed in hour~
ble fluorine, based on until pH 4 is reached.
initial values _ 1 71 8.3 2 81 :' 24 3 80 ~ 24 -~ 24 6 81 ~ 24 7 74 10.4 8 84 ~ 24 9 85 ~ 24 11 82 ' 24 13 66 o.3 14 72 10.5
The quantity of precipitated DMP was 2.5 weight%, based on DCP.
EXAMPLE 2:
The reaction was effected as in Example 1, but the DMP was prepared with the use of 0.24 kg of a 32 weight%
magnesium chloride solution and 0.25 kg of a 25 weight%
sodium hydroxide solution. The quantity of precipitated DMP was 8 weight%, based on DCP.
EXAMPLE 3:
The reaction was e~fected as in Example 1, but the DMP was prepared with the use of 0.45 kg of a 32 weight%
magnesium chloride solution and 0.47 kg of a 25 weight%
sodium hydroxide solution. The quantity of precipitated DMP was 15 weight%, based on DCP.
EXAMPLE 4:
A stainless steel reactor (capacity _ approximately 15 liters) provided with an agitator and a double cooling ~acket was fed with 2 kg of water which was thoroughly stirred by means of a propeller mixer (2000 rpm). Next, 2.6 kg of a 38 weight% aqueous calcium carbonate suspen-sion and a 85 weight% orthophosphoric acid were added in substantially stoichiometric proportions, the latter in lO9~S31 the proportions necessary to establish a pH o~ 2 to 3.5.
Following the reaction of the calcium carbonate, the tem-perature was at 35C.
The DMP stabilizer was precipitated by introducing the necessary starting materials in the manner described above, namely 0.1 kg of a 38 weight% magnesium nitrate solution and 0.08 kg of a 25 weight% sodium hydroxide solution to-gether with orthophosphoric acid, the latter being added at a rate necessary to esiablish a pH of 4 to 4.5. To-wards the end of the reaction, the balance quantities of magnesium nitrate and sodium hydroxide solution were added at the rate necessary to establish a final pH-value of 8.5.
The quantity of precipitated DMP was 2.5 weight%, based on DCP.
The reaction mixture was then admixed with 0.1 weight%, based on DCP, of fine particulate tetrasodium pyrophosphate as an additional stabilizer, and the whole was stirred for a further 10 minutes.
The precipitate was filtered off, dried and ground as usual.
EXAMPLE 5:
The reaction was effected as in Example 4, but the DMP
was prepared with the use of 0.32 kg of a 38 ~reight% mag-nesium nitrate solution and 0.25 kg of a 25 weight~ sodium hydroxide solution. The quantity of precipitated DMP was 8 weight%, based on DCP.
EXAMPLE 6:
The reaction was effected as in Example 4, but the DMP
was prepared with the use o~ 0.6 kg of a 38 weight~ mag-109~:~i31 nesium chloride solution and 0.47 kg of a 25 weight% so-dium hydroxide solution. The quantity of precipitated DMP was 15 weight%, based on DCP.
EXAMPLE 7:
The reaction was effected as in Example 4, but the dry precipitate was dry-blended with 0.6 %, based on DCP, of tetrasodium pyrophosphate as an additional stabilizer, and the resulting blend was ground.
EXAMPLE 8:
The reaction was effected as in Exa~ple 5, but the dry precipitate was dry-blended with 0.6 ~, based on DCP, of tetrasodium pyrophosphate as an additional stabilizer, and the resulting blend was ground.
EXAMPLE 9:
The reaction was effected as in Exa~ple 6, but the dry precipitate was dry-blended with 0.6 %, based on DCP, of tetrasodium pyrophosphate as an additional stabilizer, and the resulting blend was ground.
A stainless steel reactor (capacity = approximately 15 liters) provided with an agitator and a double coo-ling Jacket was fed with 3 kg of water which was tho-rough~y stirred by means of a propeller ~ixer (2000 rpm).
Next, 2.25 kg of a 38 weight% aqueous calcium carbonate suspension and a 75 weight% orthophosphloric acid were added simultaneously, the latter in the proportions nec-essary to establish a pH of 2 to 3.5. During the reaction, the temperature of the reaction mixture rose to 38C.
After all o~ the calcium carbonate was found to have reacted, the balance of the orthophosphoric acid in ex-lQ9(~S31 cess was caused to react until a pH of 8.2 by the con-current addition, in stoichiometric proportions, a) of a mixture consisting of 0.4 kg of a 35 % calcium chloride solution and 0.07 kg of 32 % magnesium chloride solution, and b) of a 24 % sodium hydroxide solution (ratio of (CaCl2 + MgC12) : NaOH = 1 : 2).The whole was filtered, dried and ground, and DCP containing 2.5 weight% of DMP was obtained.
10 ~ EXAMPLE 11:
The procedure was as in Example 10, but the reaction of the residual phosphoric acid was effected by the addi-tion, in stoichiometric proportions, a) of a mixture consisting of 0.2 kg of a 32 % magnesium chlo~ide solution and 0.13 kg of a 35 % calcium ohloride solution, and b) of a 25 % sodium hydroxide solution. The whoIe was filtered, dried and ground, and DCP containing 8 weight%
of DMP was obtained.
EXAMPLE 12:
A stainless steel reactor (capacity = 15 liters) provided with an agitator and a double cooling jacket was fed with 3 kg of water which was thoroughly stirred by means of a propeller mixer (2000 rpm). Next, the water was admixed a) with a mixture consisting of 3.2 kg of a 35 X calcium chloride solution and 0.44 kg of a 32 ~ magnesium chloride - solution, and b) with 3.7 kg of a 25 % sodium hydrox'ide solution to-gether with a 75 % orthophosphor$c acid, the latter being 109~531 added in the proportions necessary to establish a pH o~
3 to 4. During the reaction, the temperature rose to about 40C.
Towards the end of the reaction, the balance quanti-ties of magnesium chloride/calcium chloride solution and sodium hydroxide solution were added and a final pH
of 8.2 was established. The whole was filtered, dried and ground, and D~P containing 15 weight% of DMP was obtained.
EXAMPLE 1~ (Comparative Example) A stainless steel reactor (capacity = approximately 15 liters) provided with an agitator and a double coo-ling jacket was fed with 3 kg of water which was tho-roughly stirred by means of a propeller mixer (2000 rpm).
Next, 2.25 kg of a 38 weight% aqueous calcium carbonate suspension and a 75 weight% orthophosphoric acid were added concurrently, the latter in the proportions nec-essary to establish a pH of 2 to 3.5. During the reac-tion, the temperature rose to 38C.
After all of the calcium carbonate was found to have reacted, the balance of the orthophosphoric acid in ex-cess was caused to react until a pH of 8.3 by the con-current stoichiometric addition of a 35 weight% calcium chloride solution and a 25 weight% sodium hydroxide solu-tion (CaCl2 : NaOH = 1 : 2). To stabilize the wet phase, 1.0 weight% of fine particulate tetrasodium pyrophos-phate and 2.5 weight~ of fine particulate DMP, the per-centages being based on DCP, were added, and the reac-tion mixture was stirred *or a *urther 10 minutes. The precipitate was filtered and dried, and the dry material lQ9aS3~
was dry-blended with 0.6 weight% of tetrasodium pyro-phosphate. The resulting blend was ground.
EXAMPLE 14: (Comparative Example) The procedure was as in Example 13, but 8 weight% of DMP, based on DCP, was added.
EXAMPLE 15: (Comparative Example) The procedure was as in Example 13, but 15 weight% of DMP, based on DCP, was added.
The products prepared as described in Examples 1 through 15 were tested for their stability to hydrolysis and compatibility with sodium monofluophosphate by the following methods.
I. Testing stability to hydrolysis:
25 g of the DCP to be tested is suspended in a solu-tion of 1.63 g of sodium fluoride in 1Q0 ml of water, which is heated to 60C and maintained at that tèm-perature. The DCP is kept in suspension by means of a stirrer. The pH-value is measured at regular inter-vals and themoment at which the pH falls below 4 i8 determin~d. The period of time until a pH of 4 is reached is an index of the stability to hydrolysis of DCP.
II. Testing compatibilitv with sodium monofluoPhosPhate:
10 g of the DCP to be tested is suspended in 90 g of water and the suspension is heated to 80C. Next, the suspension is admixed with 76 mg of sodium mono-- fluophosphate (1000 ppm of fluorine, based on DCP) and the whole is maintained for exactly 1 hour at 80C with agitation. ~ollowing this, the material is cooled in an ice bath to room temperature, filtered lQ9(3531 by means of a frit, and the content of fluorine is determined in an aliquote portion of the filtrate.
The content of soluble fluorine is an index of the compatibility of DCP with sodium monofluophosphate. This is expressed as a percentage of the in~tial value.
The Table hereinafter shows that the products made in accordance with this invention have an improved stability as compared with DCP stabilized in customary manner which has long been held to afford an optimum stabilization effect. With reference to the Table:
The products of this invention described in working Examples 1, 4, 7 and 10, and the comparative product described in Example 13 each contained 2.5 weight% of DMP stabilizer. With respect to the present products, they were found to have the lowest compatibility with fluorine at 70 % and the lowest stability to hydrolysis at 8 hours. In the comparative Example, the correspon-ding values were 66 % and 0.3 hour, respectively.
In each of working Examples 2, 5, 8 and 11, and in comparative Example 14, use was made o~ DCP containing 8 weight% of DMP stabilizer. With respect to the pre-sent products, they were found to have the lowest stabi-lity to fluorine at 80 % and the lowest sta~ility to - hydroIysis at 24 hours. In the comparative Example, the corresponding values were 72 % and 10.5 hours, respec-tively.
In each of working Examples 3, 6, 9 and 12, and in comparative Example 15, use was made of DCP containing 15 weight% of DMP stabilizer. With respect to the pre-sent products, they were found to have the lowest compa-10~531 tibility with fluorine at 76 % and the lowest stability to hydrolysis at 22 hours. In the comparative Example, the corresponding values were 73 % and 12 hours, respec-tively.
As can be seen, DCP which is stabilized in accordance with this invention with 8 % of DMP compares favorably even with DCP stabilized in conventional manner with 15 % of DMP.
T a b 1 e :
_ _ Ex. Stability to fluorine, Stability to hy-No. in weight% water-solu- drolysis, expressed in hour~
ble fluorine, based on until pH 4 is reached.
initial values _ 1 71 8.3 2 81 :' 24 3 80 ~ 24 -~ 24 6 81 ~ 24 7 74 10.4 8 84 ~ 24 9 85 ~ 24 11 82 ' 24 13 66 o.3 14 72 10.5
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Process for stabilizing dicalcium phosphate dihydrate with the use of dimagnesium phosphate trihydrate, wherein the dicalcium phosphate dihydrate is precipitated by reacting a calcium compound with an aqueous solution of orthophosphoric acid or a phosphoric acid salt, in the presence of a basic compound, which comprises: precipitating jointly with the dicalcium phosphate dihydrate, or precipitating subsequently, directly on to the newly precipitated dicalcium phosphate dihydrate, 1 to 50 weight %, based on dicalcium phosphate dihydrate, of dimagnesium phosphate trihydrate by reacting a magnesium salt solution with a solution of orthophosphoric acid or of a phosphoric acid salt in the presence of a basic compound; and separating the two precipitation products jointly from the resulting reaction mixture.
2. Process as claimed in claim 1, wherein the reactants, which are necessary for the formation of dimagnesium phosphate trihydrate, are added in approximately stoichiometric proportions with thorough agitation so as to initially maintain, during the precipitation, a pH-value of 2.5 to 6.5 by the preferential addition of reactants undergoing an acid reaction, and after the addition is complete, to increase the pH to 6.5 to 9 by the addition of the residual reactants undergoing a basic reaction.
3. Process as claimed in claim 2, wherein a pH-value initially of 3.0 to 4.5 is maintained during the precipitation.
4. Process as claimed in any of claims 1 to 3, wherein the dimagnesium phosphate trihydrate is precipitated at a temperature of 20 to 60°C.
5. The process as claimed in claim 4, wherein the precipitation is ef-fected at a temperature of 30 to 45°C.
6. The process as claimed in claim 1, wherein a 25 to 35 weight %
magnesium chloride or magnesium nitrate solution is used as the magnesium salt.
magnesium chloride or magnesium nitrate solution is used as the magnesium salt.
7. The process as claimed in claim 1, wherein a 50 to 80 weight % solu-tion of orthophosphoric acid or of an acid alkali metal phosphate is used.
8. The process as claimed in claim 1, wherein a 20 to 50 weight %
solution of an alkali metal hydroxide or carbonate is used as the basic com-pound for the precipitation of dicalcium phosphate dihydrate and for the precipitation of dimagnesium trihydrate.
solution of an alkali metal hydroxide or carbonate is used as the basic com-pound for the precipitation of dicalcium phosphate dihydrate and for the precipitation of dimagnesium trihydrate.
9. The process as claimed in claim 1, which comprises the further step of admixing the precipitated dicalcium phosphate dihydrate and dimagnesium phosphate trihydrate with an additional known stabilizer.
10. The process as claimed in claim 9, wherein tetrasodium pyprophosphate is used as the additional stabilizer.
11. The process as claimed in claim 1, wherein 2 to 20 weight % of dimagnesium phosphate trihydrate, based on dicalcium phosphate dihydrate, is precipitated.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2648061.5 | 1976-10-23 | ||
| DE19762648061 DE2648061C2 (en) | 1976-10-23 | 1976-10-23 | Method for stabilizing di-calcium hydrogen phosphate dihydrate |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1090531A true CA1090531A (en) | 1980-12-02 |
Family
ID=5991226
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA288,991A Expired CA1090531A (en) | 1976-10-23 | 1977-10-19 | Stabilization of calcium phosphate dihydrate |
Country Status (6)
| Country | Link |
|---|---|
| BE (1) | BE859968A (en) |
| CA (1) | CA1090531A (en) |
| DE (1) | DE2648061C2 (en) |
| FR (1) | FR2368440A1 (en) |
| GB (1) | GB1548465A (en) |
| NL (1) | NL184943C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5024825A (en) * | 1989-05-13 | 1991-06-18 | Hoechst Aktiegesellschaft | Process for the preparation of dicalcium phosphate |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0045826A1 (en) * | 1980-08-12 | 1982-02-17 | Monsanto Company | Dicalcium phosphate dihydrate having improved stability and a method for preparing it |
| US4472365A (en) * | 1981-06-15 | 1984-09-18 | Stauffer Chemical Company | Dicalcium phosphate dihydrate having improved monofluorophosphate compatibility and process for the preparation thereof |
| EP0092929B2 (en) * | 1982-04-20 | 1991-05-02 | Beecham Group Plc | Oral hygiene compositions |
| DE3705845A1 (en) * | 1987-02-24 | 1988-09-01 | Hoechst Ag | TOOTHPASES AND CLEANING BODIES FOR TOOTHPASES BASED ON DICALCIUMPHOSPHATE DIHYDRATE AND A METHOD FOR THE PRODUCTION OF SUCH CLEANING BODIES |
| DE69104453T2 (en) | 1990-09-13 | 1995-03-16 | Akzo Nv | Stabilized solid chemical compositions. |
| US5292520A (en) * | 1990-09-13 | 1994-03-08 | Akzo N.V. | Stabilized solid pharmaceutical composition containing acid addition salts of a basic drug and an alkaline stabilizer |
| DE4305276A1 (en) * | 1993-02-20 | 1994-08-25 | Hoechst Ag | Process for the preparation of a dicalcium phosphate dihydrate suitable for use in toothpastes |
| DE4306673A1 (en) * | 1993-03-04 | 1994-09-08 | Hoechst Ag | Process for the preparation of a dicalcium phosphate dihydrate suitable for use in toothpastes |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2133286A (en) * | 1937-05-11 | 1938-10-18 | Rumford Chemical Works | Acid calcium tetraphosphate and method of making the same |
| US2287699A (en) * | 1940-02-15 | 1942-06-23 | Monsanto Chemicals | Stabilized dicalcium phosphate |
| FR1483486A (en) * | 1965-06-16 | 1967-06-02 | Knapsack Ag | Process for the preparation of stabilized dicalcium phosphate dihydrate |
| DE2456692A1 (en) * | 1974-11-30 | 1976-08-12 | Henkel & Cie Gmbh | PROCEDURE FOR STABILIZING CALCIUM HYDROGEN PHOSPHATE DIHYDRATE AGAINST HYDROLYSIS |
| DE2456787A1 (en) * | 1974-11-30 | 1976-08-12 | Henkel & Cie Gmbh | PROCEDURE FOR STABILIZING CALCIUM HYDROGEN PHOSPHATE DIHYDRATE AGAINST HYDROLYSIS |
| DE2456693A1 (en) * | 1974-11-30 | 1976-08-12 | Henkel & Cie Gmbh | PROCESS FOR STABILIZING CALCIUM HYDROGEN PHOSPHATE ANHYDRIDE AGAINST REALIZATION WITH FLUORIONS |
| DE2456667A1 (en) * | 1974-11-30 | 1976-08-12 | Henkel & Cie Gmbh | PROCESS FOR STABILIZING CALCIUM HYDROGEN PHOSPHATE ANHYDRIDE AGAINST REALIZATION WITH FLUORION IONS |
| DE2456808A1 (en) * | 1974-11-30 | 1976-08-12 | Henkel & Cie Gmbh | PROCESS FOR STABILIZING CALCIUM HYDROGEN PHOSPHATE ANHYDRIDE AGAINST REALIZATION WITH FLUORIONS |
| DE2456666A1 (en) * | 1974-11-30 | 1976-08-12 | Henkel & Cie Gmbh | METHOD OF STABILIZING CALCIUM HYDROGEN PHOSPHATE DIHYDRATE AGAINST HYDROLYSIS |
-
1976
- 1976-10-23 DE DE19762648061 patent/DE2648061C2/en not_active Expired
-
1977
- 1977-10-18 GB GB4329377A patent/GB1548465A/en not_active Expired
- 1977-10-18 NL NL7711428A patent/NL184943C/en not_active IP Right Cessation
- 1977-10-19 CA CA288,991A patent/CA1090531A/en not_active Expired
- 1977-10-21 FR FR7731803A patent/FR2368440A1/en active Granted
- 1977-10-21 BE BE181938A patent/BE859968A/en not_active IP Right Cessation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5024825A (en) * | 1989-05-13 | 1991-06-18 | Hoechst Aktiegesellschaft | Process for the preparation of dicalcium phosphate |
Also Published As
| Publication number | Publication date |
|---|---|
| GB1548465A (en) | 1979-07-18 |
| FR2368440B1 (en) | 1982-03-26 |
| FR2368440A1 (en) | 1978-05-19 |
| NL7711428A (en) | 1978-04-25 |
| DE2648061A1 (en) | 1978-04-27 |
| DE2648061C2 (en) | 1982-11-04 |
| BE859968A (en) | 1978-04-21 |
| NL184943C (en) | 1989-12-18 |
| NL184943B (en) | 1989-07-17 |
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