JPS5924726B2 - Production method of hydroxyapatite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to synthetic bone ash used in the production of bone china and a method for producing the same.

Bone porcelain (otherwise known as English china) has long been of great importance in the ceramic industry, and its high degree of whiteness, reflectivity, and translucence contribute to its aesthetic appearance as well as its characteristic sound. It is something that has properties.

This material weighs approximately 140.62 kg/i (2000 Ib/1
It has a large strength that produces a firing strength of up to n2).

The high strength of bone china is apparently due to the good thermal expansion coefficient match between the glass bond and the crystalline matrix and the relatively small grain size.

Bone porcelain is made from bone ash (made by calcining bone from which gelatin has been removed, such as that produced in glue manufacturing factories), kaolin (chi
na clay) and Stone Flux (5tone
f 1ux).

The traditional composition of bone ash porcelain is 50% bone ash by weight. 25% by weight
Kaolin and 25% by weight Cornitsch stone (co
rnish 5tone).

Increasing the bone ash concentration makes porcelain more expensive.

Whiteness, translucency and firing strength are improved.

Increasing the bone ash content thickens the mixture to the extent that it also becomes plastic before firing.

However, reducing the bone ash percentage below 50% generally impairs color and reduces translucency, strength, and plasticity.

Bone ash accounts for the majority of the cost of bone porcelain mixtures.

The price of bone ash has increased in recent years for various reasons.

The quality and availability of bone ash also varies, creating difficulties in obtaining standard products.

Replacing some of the bone ash with other materials such as bentonite and ball clay produces clearly inferior products.

Color is affected by trace metal components in additives, and translucency is significantly impaired.

There is therefore a need for synthetic alternatives so that bone porcelain can be produced economically and without substandard standards.

. Bone ash, as used in the ceramic industry, consists of a sintered form of hydroxyapatite.

This compound is necessary for bone ash magnetic production.

Because it combines with clay and stone to produce the necessary translucent vitrified bodies, the sintered structure is necessary to provide the necessary physical structure.

Apatite-type phosphate rock is mined in large quantities in various locations around the world and is commonly used in fertilizer production.

Calcining this rock, however, yields tricalcium phosphate, which reduces the processability of the system, requires the addition of plasticizers, and is much less effective in imparting the necessary structure in the calcined product, making the bone ash magnetic mixture less effective. It cannot be easily contained in the inside.

It has been proposed to produce synthetic bone ash using pure phosphoric acid and calcium carbonate (Rao & Boehm*J,
DenLRes, 1351-1354 (1974)
), but such methods are considered uneconomical and cannot compete favorably with bone ash.

In a previous study (Gee, Rroc-Tech, 5es
s, Bone Char, 337-352 (1953
) show that hydroxyapatite can be formed over a wide range of pH values and temperatures by the reaction of very dilute lime solutions with phosphate-calcium solutions.

In addition, to reduce the formation of pyrophosphates due to calcination,
It is also shown that the ratio of calcium to phosphate ions needs to be higher than that of pure hydroxyapatite.

In fact, hydroxyapatite itself has even been shown to yield β-tricalcium phosphate upon calcination (Neuman
& Neuman, Chemical Dy-r n
amics of Bone Mineral).

Furthermore, hydroxyapatite must have a suitable crystal structure and grain size to give the desired vitrified ceramic material, and the crystals of the material obtained by the hydroxyapatite manufacturing method tend to be too small. There is.

, the grain size can be increased, for example, by sintering the material at a temperature of at least 700°C.

However, in order to provide a hydroxyapatite material suitable for inclusion in bone china, the content of orthophosphate in the hydroxyapatite must be kept as low as possible, ensuring that the
It has been found that the weight percentage must be kept below.

A high proportion of orthophosphates leads to the formation of β-tricalcium phosphate upon sintering, and the presence of this substance has been found to be disadvantageous in the production of bone porcelain.

It has now been discovered that pure hydroxyapatite can be produced by the first method.

Thus, the controlled reaction of lime and phosphoric acid produces a material containing less than 5% by weight of orthophosphate.

This material is then calcined to produce a sintered product free of β-tricalcium phosphate.

The method comprises combining a stream of water lime slurry with a stream of at least 60% by weight phosphoric acid and 10 Ca(OH)2 to 6H.
It consists of continuously contacting approximately stoichiometric proportions of 3PO4 at a temperature of 80-85[deg.]C and an adjusted reaction mixture pH of 9.0-11.0.

A slurry of about 10-30% by weight hydrated lime is preferred G1
A pH of less than or equal to 10.5 is advantageous.

If the pH value is lower than 9.0, the amount of hydroxyapatite produced will be low (and if the pH value is too high, it will be difficult to control the pH value, and the purity of hydroxyapatite will be low.

Also, if the phosphoric acid concentration is lower than a predetermined concentration, the reaction will produce an undesirable gelatinous product.

The separated material can then be calcined at a temperature of at least 1000° C. to produce a sintered granular product that can be used to replace ground bone ash in bone porcelain objects.

The reaction step is most conveniently carried out as a continuous addition method, whereby lime and phosphoric acid are introduced simultaneously and continuously into the reactor in the required proportions and with vigorous stirring.

This method keeps the pH at the required constant value.

This is in contrast to the situation that occurs when adding one reactant into an amount of another reactant causes the pH to change significantly over a period of time.

Lime is conveniently added as a suspension at a concentration of about 15-20% by weight, while phosphoric acid is preferably used at a concentration of 80-90% by weight.

It is convenient to maintain a constant flow of lime slurry and to control the flow of acid to adjust the pH.

Residence time for the reaction is important.

It is desirable that the amount of free Ca'' (C, i'c'0H)2 in the product is kept as low as possible and that crystals are formed with the required particle size.

Residence times of up to 90 minutes are generally advantageous;
It has been found that 0 minutes is advantageous.

It is also important to stir the mixture very effectively and to check the pH at the reaction site itself.

The temperature at which hydroxyapatite is calcined is very important.

As mentioned above, temperatures of at least 1000° C. are required; higher calcination temperatures are preferred.

Generally, the calcination temperature is 3 higher than 1000°C. It can be said that shrinkage during material firing is reduced.

Calcination temperatures of at least 1150° C., preferably at least 1200° C. are generally desirable.

In traditional bone ash production, the bones are kept at a much lower temperature.

It will be appreciated that calcination may take place at a temperature of, for example, 800°C.

The hydroxyapatite can be calcined by any suitable method as long as the correct temperature is obtained.

A preferred specific example of the method is as follows. The hydroxyapatite is calcined by passing it through a rotating cylinder or porcelain lined with a refractory material, tilted to the horizontal.

A residence time of about 1 hour has been found to be suitable, although longer times may be used.

It is particularly preferred if the heating of the material is carried out gradually and not abruptly.

It has been found that the longer the time to reach the calcination temperature, the larger the resulting particles or crystallites.

A preferred method is to heat the material to 1050°C at 200°C/hour.
℃ and then kept at this temperature for 1 hour.

The hydroxyapatite covered by the present invention is prepared in a conventional bone porcelain mixture by incorporating kaolin and Cornitsch stone together at 25% by weight each to account for 50% by weight of the mixture. It is then possible to provide an object capable of producing ceramic bone porcelain whose properties are equal to the translucency and general aesthetic appearance of traditional materials.

Moreover, open pores are reduced to virtually zero at a firing temperature of 1240°C.

At higher temperatures, it remains at that level.

Closed pores are extremely constant over a wide temperature range.

Typically a range of 51°C can be obtained.

This range is very large compared to ordinary bone porcelain materials and is highly desirable.

Another characteristic that bone porcelain made from a mixture containing calcined hydroxyapatite according to the invention is superior to traditional products is the so-called firing range.

Ceramic bulk density force j from its maximum value 0.5flAc
The temperature range that decreases by is known as the firing range,
Use of calcined hydroxyapatite in mixtures can provide a range of 30°C.

This is 20 degrees, which is the lowest value that can be normally achieved with conventional bone china.
This is much more preferable than the C firing range.

Hydroxyapatite must be produced using lime and phosphoric acid of the required purity.

That is, the starting material should be free of metal ions that would color the resulting ceramic object.

Generally speaking, the material being examined should be pure white in color, but it has been found that even very pure samples may exhibit a distinct blue color.

The following examples are illustrative of the invention.

Example 1 A 20% suspension of lime and a 90% solution of phosphoric acid were mixed into 9.
The reaction was carried out at a temperature of 80-85[deg.] C. in two ways: pH 1 was adjusted to 5, and pH 1 was adjusted to 10.5.

The residence times were 88 and 71 minutes, respectively.

5 products were obtained containing 98.5 and 99.5% hydroxyapatite, respectively.

The product obtained by such a reaction step is shown in the attached FIG. 1.

FIG. 1 is a photograph of the reaction product at a magnification of about 78,000x (A4 size) and was captured by an electron micrograph of a thin section of the epoxy block.

The calcined product obtained from such a reaction product at a temperature of about 1050° C. is illustrated in the attached FIG. 2.

This figure is a similar electron micrograph at similar magnification.

It can be seen that the crystal size increases from an initial crystal length of about 0.035 μm to roughly spherical crystallites with a diameter of about 0.5 μm.

Bone porcelain samples obtained by replacing the conventional 50:25:25 bone ash with a calcination material showed good color, translucency and strength, and in particular a very good firing range.

Comparative Example 1 Reactions similar to Example 1 were carried out at pH values of 5.5 and 8.5, yielding products with hydroxyapatite contents of only 45 and 88%.

Experiments were carried out at 25° C., which required very high pH values that were difficult to control and produced products of insufficient purity.

Furthermore, a comparison was made between the present invention and the conventional example as follows.

Hydroxyapatite (Ca5(OH)(PO4)3)
Stoichiometric amounts of lime and phosphoric acid were reacted under various conditions to produce phosphoric acid.

The resulting product was analyzed and sintered.

The lime used was approximately a 20% suspension.

The phosphoric acid was an 81% phosphoric acid aqueous solution.

The reaction temperature was 80°C. The operation was performed in the following three ways.

(1) Lime slurry was gradually added to the acid over 3 hours with stirring.

(2) The acid was gradually added to the lime slurry over a period of 3 hours while stirring.

(3) Acid and lime slurry were added continuously to the reactor in stoichiometric ratios, keeping the pH value constant.

(Invention) In each case, the hot reaction mixture was filtered and the powdered product obtained in the form of a cake was dried overnight at 105°C.

The product was then analyzed by X-ray diffraction and X-ray fluorescence.

A sample of each product was then calcined at 1000°C and again
It was investigated by line diffraction.

The results are shown in Table 1.

Finally, the sample of the Tani calcined product is 50% of this calcined product.

It was placed in a bone porcelain matrix containing 25% Cornitsch stone and China clay.

This material was fired at a normal bone porcelain firing temperature, and its properties were investigated.

The substrates containing each of (1) and (2) above showed considerably more shrinkage than those obtained by (3) above.

Furthermore, the first green body exhibited a shiny surface, indicating that undesirable surface vitrification had occurred.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph of a reaction product of lime and phosphoric acid according to the method of the present invention. FIG. 2 is an electron micrograph of the reaction product of FIG. 1 calcined at a temperature of 1050°C.

Claims (1)

[Claims] 1. A slurry stream of hydrated lime, 10 Ca(OH)2
A flow of at least 60% by weight phosphoric acid in a stoichiometric ratio of 6H3PO4 to 9.0-11.
A process for producing hydroxyapatite, characterized in that the contacting is carried out continuously at a controlled reaction mixture pH of 0. 2. The method according to claim 1, which is carried out as a continuous addition method. 3. The method according to item 1 above, wherein lime is added as a suspension with a concentration of 10 to 30% by weight. 4. The method according to item 1 above, wherein the pH is 10.5 or less. 5. The method according to item 1 above, wherein the phosphoric acid is present at a concentration of 80 to 90% by weight.