FR2796064A1 - CLINKER OF CALCIUM PHOSPHATES, COMPOSITION AND REINFORCED MATERIAL OBTAINED FROM THE CLINKER AND METHODS OF MAKING THE SAME - Google Patents

Abstract

The invention concerns calcium phosphate clinker, comprising at least 10 wt. % of tetracalcium phosphate (C4P), at least 5 wt. % of hydroxyapatite (HAp) and between 0.5 and 5 wt. % of free lime (C), and preferably also tricalcium phosphate (C3P) or a C3P-C2S solid solution, in an amount not more than 25 wt. %. The invention also concerns a method for making such a clinker, a cement composition comprising such a ground clinker and a reinforced material as well as a method for making such reinforced material by hydrating such a composition.

Description

The present invention relates to a clinker of calcium phosphates and to a process for producing such a clinker, as well as to a cementitious composition comprising such a crushed clinker, to a reinforced material obtained from the hydration of such a composition and a method of manufacturing such a reinforced material.

In what follows, we use the standard abbreviated notation: - C for CaO, - P for P205, - HAp for hydroxyapatite, of formula Calo (P04) 6 (OH) 2, substituted or not, - H for H20 .

These ratings will be systematically used later, unless explicitly stated otherwise.

To reinforce certain materials, such as, for example, dental cement or cement for prosthesis, it is known to use a mixture of synthesized pure tetracalcium phosphate and other suitable constituents, by hydration. The hydrated tetracalcium phosphate has the property of generating hydroxyapatite and Portiandite CH, according to the reaction: 3 (C4P + H) <B> -> PAH + 2CH, The addition of the constituents mixed with the C4P is necessary because C4P alone would not achieve a satisfactory reaction rate. This technique, however, requires precise preparation of the mixture and requires the handling of several products.

The subject of the invention is a product based on calcium phosphates, capable of forming, by hydration, a mineral micro-self-hardening within a matrix, so as to make it possible to obtain a reinforced material having improved mechanical properties. The invention relates to such a product having good reactivity, which can be used as such directly without the need to resort to other constituents.

The product of the invention can have the following advantages: - good reactivity: kinetics and progress of the reaction, - good reproducibility of the hydration, - satisfactory rheology and durability, - easy manufacture to implement, - reproducibility of manufacture of the product, and - low sensitivity to variations of a few percent of the constituents used to make this product.

The product of the invention is useful not only in cementitious compositions, but also in other materials such as, for example, plastics. The improvement of the mechanical properties of the material may relate in particular to its resistance in bending and possibly in compression.

The invention also relates to a method of manufacturing the above product, as well as a cementitious composition containing it, a reinforced material obtained from the hydration of such a composition and a method of manufacturing such a reinforced material. .

The product of the invention consists of a clinker of calcium phosphates, comprising by weight: at least 10% of tetracalcium phosphate (C4P), at least 5% of hydroxyapatite (HAp) and between 0.5% and 5% of free lime (C).

Although the term "clinker" usually refers to the product of the baking of constituents at the exit of the furnace, before grinding, we will understand by this term also the crushed product. Thus, the appropriately milled clinker is introduced into a matrix to obtain a reinforced material after hydration.

Such a clinker makes it possible to obtain astonishing performances and, used independently of any other constituent, produces a very effective mineral micro-self-support. This clinker, which has the advantages mentioned above, notably constitutes a reactive clinker making it possible to manufacture in situ hydroxyapatite fibers.

The introduction of the clinker of the invention into a cementitious composition makes it possible to create, after mixing with water, a very cohesive matrix and a good adhesion of the fibers to the matrix. The clinker of the invention is also found to have very beneficial effects in plastics, forming cohesive organo-mineral interfaces.

The clinker of the invention offers the advantages traditionally obtained with tetracalcium phosphate: - low consumption of water necessary for hydration, - chemical stability of the hydroxyapatite fibers, including at high pH (above 12.5) .

But, compared to the use of pure C4P, this clinker considerably improves the reactivity and cohesion force produced by hydration (mechanical resistance). The significant acceleration of the hydration kinetics of clinker compared to pure C4P can be explained by the following factors: - presence of HAp seeds already contained in the clinker: seeding effect and also the recovery of C4P grains at a rate of higher rate of progress, - presence of free lime which rapidly hydrates in CH, which also produces germs for CH.

Moreover, it can be seen that the clinker of the invention makes it possible to generate quasi-amorphous fibers of HAp (1 to 4 gym), whereas with pure C4P, the size of the hydroxyapatite fibers is generally less than 1 μm. because of higher supersaturations.

Preferably, the clinker also comprises tricalcium phosphate (C3P) or a solid solution C3P-C2S, in an amount at most equal to 25% by weight.

The C3P-C2S solution is obtained in a system containing silica.

In a preferred embodiment, the clinker comprises by weight: at most 75% of tetracalcium phosphate (C4P), at most 50% of hydroxyapatite (HAp), and at most 25% of tricalcium phosphate (C3P); of a solid solution C3P-C2S. The invention also relates to a clinker of calcium phosphates which, according to the invention, comprises a distribution of mineralogical phases such as during a hydration at 20 C of milled clinker with a fineness of 25 lm for 50% by weight of passing by sieve (d50 = 25 Eum), with equal masses of water and clinker, the heat flux released as a function of time has: - a first initial exothermic peak and a second exothermic peak observed before 1 h 30 from the beginning hydration, and a progress rate of the hydration reaction at least equal to 30% at the end of the appearance of this second exothermic peak.

The reactivity of such a clinker is particularly good, particularly in comparison with pure tetracalcium phosphate. This clinker may be of the type defined previously by its mineralogy, and it is moreover advantageously in accordance with the preceding definitions.

Preferably, the clinker according to the invention is in milled form, with a particle size preferably between 5 .mu.m and 200 .mu.m for 50% by weight of passing through the sieve.

The invention also relates to a method of manufacturing a clinker according to the invention. According to this process: - a raw material is prepared from a source of phosphate and a source of calcium adapted to the desired mineralogy, and - it is cooked with at least one temperature level having a level and a suitable duration to obtain this clinker.

According to different forms of implementation, the raw material includes already purified products or natural ores. In an advantageous form of implementation, the raw material is a stoichiometric tetracalcium phosphate (C4P) crude with respect to the CIP ratio of C4P.

Preferably, the temperature stages comprise an upper stage having a level of between 1300 ° C. and 1500 ° C. and a duration of between 0 h 30 and 15 hours. In a particularly advantageous embodiment, the upper plateau has a level of about 1400 C and a duration of about 3 hours.

Another particularly advantageous form, using or not this upper bearing, is such that cooking comprises: a first rise at 600 Clh up to 900 ° C., an intermediate bearing of 1 hour at 900 ° C., a second rise at 600 Clh to the upper bearing, - the upper bearing, - cooling to 1000 Clh up to 1100 C, and - air quenching or slow cooling.

In a preferred form of implementation, the raw material is obtained by means of a mixture of CaCO 3 and calcium phosphate. The raw material is then advantageously obtained using a mixture of CaCO 3 and CaHPO 4. This mixture may in particular be homogenized by the wet route.

The invention also relates to a cementitious composition comprising a ground clinker according to the invention and a hydraulic binder. This composition is advantageously obtained by mixing or co-grinding.

Preferably, the clinker and the hydraulic binder are such that the hydration kinetics of the clinker is faster than the hydration kinetics of the hydraulic binder.

It can be seen that the mechanical properties of the material formed are considerably improved when this characteristic is verified. This is explained by the fact that the micro-self-harm produced by the ground clinker is created before the setting induced by the hydraulic binder.

Advantageously, the cementitious composition of the invention is used to produce mortars or concretes.

In this case, the setting produced by the cement often takes place between 2 and 3 hours from the beginning of the hydration. The clinker of the invention makes it possible to obtain a faster hydration kinetics and thus obtain particularly effective reinforcements. The invention also applies to a reinforced material obtained from the hydration of a composition according to the invention.

It also relates to a process for manufacturing such a reinforced material, in which: - a crushed clinker of calcium phosphates according to the invention is produced, - this crushed clinker is mixed with at least one other component, so as to form a composition according to the invention, and - this composition is hydrated.

The invention will be better understood and illustrated by means of particular embodiments and implementations which are in no way limitative, with reference to the appended figures in which: FIG. 1 represents a histogram giving the mineralogy of a clinker obtained by a process of manufacture according to the invention, for an upper temperature step of a duration of 3 hours and as a function of the temperature of this bearing; FIG. 2 represents a histogram of the mineralogy of a clinker obtained by a manufacturing method according to the invention, with an upper temperature level equal to 1400 ° C. and having a duration of 3 hours or 15 hours; FIG. 3 shows the reactivity, in the form of the heat flux (in mWlg) as a function of time (in minutes) during hydration at 20 ° C., pure C4P and two clinkers obtained by the manufacturing process according to FIG. invention with an upper temperature step of 3 hours and respectively worth 1300 C and 1400 C, for a grinding corresponding to d50 = 25 #tm; - Figure 4 and Figure 5 are photographs respectively showing a non-hydrated grain and a hydrated grain of a clinker according to the invention.

Calcium phosphate clinker is manufactured, for example, as follows.

In a first step, a stoichiometric mixture is made with C4P in CaCO3 and wet homogenized CaHPO4. In a second step, this mixture is dried at 90 ° C. in an oven.

In a third step, a muffle furnace is baked in a crucible of Pt. This third stage comprises the following phases: - rise to 600 Clh up to 900 C, - step of 1 hour at 900 ° C, - rise at 600 Clh up to a higher temperature value, - higher temperature step at the higher temperature value; - cooling to 1000 Clh up to 1100 C and - quenching in air or slow cooling.

The clinker mineralogy thus obtained depends on the level and duration of the upper temperature stage. Preferably, the upper tier has a level between 1300 C and 1500 C and a duration between 0 h 30 and 15 hours.

The main constituents present in the clinker formed are as follows: C, HAp, aC3P, PC3P (the latter two constituents are particular crystallographic forms of C3P) and C4P. These phases are respectively referenced 1 to 5 in FIGS. 1 and 2. The reactions in progress for a level of the upper temperature stage of between 1200 and 1500 C are essentially the following: aC2P + C - + UC3P a.C3P + C C4P aC2P + 2C -> C4P a.C3P + C + H -> HAp HAp -> 2aC3P + C4P HAp + 2C -> 3C4P + H Clinker mineralogy was thus obtained for a duration of 3 hours and levels were of 1,200 C, 1,300 C, 1,400 C and 1,500 C of the upper temperature plateau (Figure 1), the percentage by weight of each phase (axis 12) being given as a cumulative histogram as a function of the temperature in C (axis 11). The histogram bars corresponding to the temperatures 1 200, 1 300, 1 400 and 1 500 C are respectively referenced 41 to 44. The bar 44 is not strictly speaking a clinker, but a reference product containing pure C4P. The mineralogy of a clinker formed with an upper temperature level equal to 1400 C and a duration of this stage equal to 15 hours was also obtained. The results appear in a histogram giving the percentage of each phase (axis 12) as a function of time (axis 13, in hours), and showing the bar 45 corresponding to these manufacturing conditions to the side of the bar 43 associated with a level 1400 C and 3 hours of the upper temperature plateau (Figure 2).

To obtain the desired clinker, cooking conditions are defined which make it possible to produce, by weight, in the clinker: at least 10% of C4P, at least 5% of HAp, and between 0.5% and 5% of C.

In the examples shown, these conditions are verified by bar 43 (upper temperature level of 1400 C and 3 hours) and (to an insignificant amount regarding the percentage of C4P) by the bar 42 (upper temperature step of 1,300 C and 3 hours).

With regard to the reproducibility of the syntheses, one notes that: - for one. 3 hours, the reproducibility is very good at 1500 C and, below 1500 C, the percentage of different phases varies by 3% depending on the cooking, and - with a 15 hour stage, the reproducibility is very good at 1400 C and 1500 C.

In a fourth step, the clinker obtained is milled, advantageously with a fineness of 25 μm for 50% by weight of sieve pass (d50 = 25 μm). This milled clinker makes it possible to carry out reactivity measurements, in which the progress of the hydration reaction of the milled clinker at 20 C, with equal masses of water and clinker, is followed. Thus, the flow of heat released (axis 16, in mWlg) as a function of time (axis 15, in minutes) was drawn (Figure 3) for three products corresponding, respectively, to the bars 44 (pure C4P), 43 (upper level temperature of 1400 C and 3 hours) and 42 (upper temperature level of 1300 C and 3 hours). The curves obtained, respectively referenced 20, 21 and 22, make it possible to follow the progress of the hydration, in particular by the observation of the exothermic peaks.

The curve (pure C4P) has a first steep exothermic peak for the first few minutes, then negligible heat release until about 100 minutes from the start of hydration. Slow heat growth with slow growth and decay then occurs, defining a "second exothermic peak" 60.

For curves 21 and 22 (clinkers at 1400 ° C and 1300 ° C respectively), we also observe first exothermic peaks respectively referenced 51 and 52 during the first minutes, but also second exothermic peaks. respectively referenced 61 and 62, having high values of heat flow released relative to the curve 20 (of the order of 15 mWlg) and appearing much earlier than for the curve 20, these second peaks culminating at times close to 60 minutes from the start of hydration.

It is noted that the level of C4P consumed is worth, respectively for curves 20, 21 and 22: after 50 minutes: 5, 15 and 20%, and after 300 minutes: 10, 65 and 75%.

Thus, it is verified that pure C4P has a low degree of advancement and, in particular, kinetics that are too slow compared with that of Portland cement (the onset of setting of Portland cement being close to 2 hours). In contrast, clinkers corresponding to bars 42 and 43 have a significantly accelerated hydration kinetics compared to pure C4P. We have investigated the reproducibility of the reactivity of clinker manufactured with an upper temperature level of 1400 C and 3 hours. On ten firings, variations in the following ranges were observed: - intensity of the first peak 51: 40 to 42.5 mWlg, - intensity of the second peak 61: 12.5 to 17.5 mWlg, - time at the summit of the second peak 61: 60 to 75 minutes. Thus, the kinetics of hydration of the clinker is relatively insensitive to variations of a few percent of the constituents for making it.

In an alternative embodiment, instead of seeking to achieve a specific clinker mineralogy, it is ensured that the clinker has a desired reactivity. Thus, advantageously, the clinker comprises a distribution of mineralogical phases such that, during a 20 C hydration of clinker milled at d50 = 50 μm, with equal masses of water and clinker, the heat flux released as a function of time represents a first initial exothermic peak and a second exothermic peak observed before 1 h 30 from the start of hydration, and a progress rate of the hydration reaction of at least 30% at the end of the onset of this second exothermic peak. These conditions are verified by the clinkers associated with the bars 42 and 43 (FIG. 3).

A preferred embodiment is that associated with the bar 43 (upper temperature level of 1400 C and 3 hours): - good reproducibility of cooking despite a fairly short landing; good reactivity: kinetics and progress of the reaction, good reproducibility of the hydration and satisfactory rheology and durability.

The hydroxyapatite fibers formed by hydration from such a clinker can be observed on scanning electron micrographs. It is thus possible to see, in FIG. 4, an unhydrated grain and, in FIG. 5, a hydrated grain.

 The surface of the latter is observed quasi-amorphous HAp fibers from 1 to 4 @Lm.

Claims (19)

<U> CLAIMS </ U> 1. Clinker of calcium phosphates, comprising by weight: # at least 10% of tetracalcium phosphate (C4P), # at least 5% hydroxyapatite (HAp) and # between 0.5% and 5% of free lime (C ). 2. Clinker according to claim 1, characterized in that it also comprises tricalcium phosphate (C3P) or a solid solution C3P-C2S, in an amount at most equal to 25% by weight. 3. Clinker according to one of claims 1 or 2, characterized in that it comprises by weight: # at most 75% of tetratricalcium phosphate (C4P), # at most 50% hydroxyapatite (HAp), and # at plus 25% tricalcium phosphate (C3P) or a solid solution C3P-C2S. 4. Clinker of calcium phosphates, characterized in that it comprises a distribution of mineralogical phases such as during hydration at 20 C milled clinker with a fineness of 25 Nm for 50% by weight of sieve pass (d50 = 25 μm), with equal masses of water and clinker, the heat flux released as a function of time exhibits a first initial exothermic peak and a second exothermic peak observed before 1 hour 30 minutes after the start of hydration, and a rate of progress of the hydration reaction at least equal to 30% at the end of the appearance of this second exothermic peak. 5. Clinker according to claim 4, characterized in that it is according to any one of claims 1 to 3. 6. Clinker according to any one of claims 1 to 5, characterized in that it is in ground form, with a particle size preferably between 5 pm and 200 pm for 50% by weight of sieve pass. 7. A method of manufacturing a clinker according to any one of claims 1 to 6, characterized in that: # is prepared a raw material from a source of phosphate and a source of calcium adapted to mineralogy desired, and said cooking is carried out with at least one temperature step having a level and duration suitable for obtaining said clinker. 8. The manufacturing method according to claim 7, characterized in that said raw is a crude tetracalcium phosphate (C4P) stoichiometric vis-à-vis the CIP C4P report. 9. The manufacturing method according to one of claims 7 or 8, characterized in that said temperature steps comprise an upper bearing having a level between 1300 C and 1500 C and a duration between 0 h 30 and 15 hours. 10. The manufacturing method according to claim 9, characterized in that the upper bearing has a level of about 1400 C and a duration of about 3 h. 11. The manufacturing method according to one of claims 9 or 10, characterized in that the cooking comprises: a first rise to 600 Clh up to 900 C, an intermediate bearing one hour at 900 C, a second climb up to 600 Clh to the upper bearing, # the upper bearing, # a cooling to 1000 Clh up to 1100 C, and # an air quench or slow cooling. 12. The manufacturing method according to any one of claims 7 to 11, characterized in that the raw material is obtained by means of a mixture of CaCO 3 and calcium phosphate. 13. The manufacturing method according to claim 12, characterized in that the raw material is obtained by means of a mixture of CaCO 3 and CaHPO 4. 14. Cementitious composition comprising a ground clinker according to claim 6 and a hydraulic binder. 15. Cementitious composition according to claim 14, characterized in that it is obtained by mixing or co-grinding. 16. Composition according to one of claims 14 or 15, characterized in that the clinker and the hydraulic binder are such that the hydration kinetics of the clinker is faster than the kinetics of hydration of the hydraulic binder. 17. Cementitious composition according to any one of claims 14 to 16, characterized in that it is used to make mortars or concretes. 18. Reinforced material obtained from the hydration of a composition according to any one of claims 14 to 17. 19. A method of manufacturing a reinforced material according to claim 17, wherein: ## STR00005 ## is made of a crushed clinker of calcium phosphates according to claim 6, said crushed clinker being mixed with at least one other component, forming a composition according to any of claims 14 to 17, and hydrating said composition.