SE463493B - SEATED IN PREPARATION OF A CHEMICAL BONDED CERAMIC PRODUCT AND ALSO SEATED MANUFACTURED PRODUCT - Google Patents

Abstract

The present invention relates to a method for the production of a chemically bonded ceramic product by a reaction between one or several pulverulent binding agents as well as a liquid reacting with said binding agents. The ceramic product can also include one or several aggregate materials, which essentially do not participate in the chemical hardening reactions. According to the invention a powder body is compacted, which comprises said binding agent(s) and possibly aggregate materials without an addition of said liquid, by subjecting, before said raw compact is impregnated with said liquid, said powder body to such a high external pressure that a thoroughly integrated raw compact is obtained, in which the filling density has increased to at least 1.3 times the initial filling density, which is defined as that filling density, which is obtained by shaking, vibrating and/or carefully packing the loose powder in a container.

Description

Another example of a material which can be defined as a CBC material is the "cement" used in dentistry and which is based mainly on zinc oxide and orthophosphoric acid. This cement has been used for temporary fillings, for fixing crowns, etc., but its strength has so far been insufficient to enable its use for permanent fillings. Another type of material for dental applications is so-called glass polyalkeno cement and similar materials. Examples of this type of material are given, for example, SE-B-381 808, EP-A-0024056 and EP-A-0115058.

In general, a number of requirements are imposed on stiffening masses for dental or general orthopedic applications (implants), which must be met for permitted and accepted use, eg hygienic and in the dental area also aesthetic properties. Furthermore, these materials must not contain components which are toxic or which in their environment may give rise to toxic constituents. Furthermore, they must be functional, have adequate mechanical properties for the purpose, be corrosion resistant, comfortable to use, be biologically compatible, have an acceptable appearance, and not be too expensive to use. An essential property of a stiffening material for dental applications on a person is also that it solidifies slowly enough for the intended application to be performed without haste. On the other hand, such a stiffening material must relatively quickly become hard and sufficiently firmly anchored to allow the treated person to eat within a reasonable time after application. The above-mentioned hydrating materials, zinc oxide-based materials, glass polyolefinate cement materials, etc. materials meet the requirements imposed on dental materials with regard to, among other things, hygienic and aesthetic properties, toxicity etc. However, the strength of these materials has not been considered sufficient in comparison with amalgam.

It is known that the strength properties of CBC materials can be improved by various treatments of the components included in the material or by additives of various kinds. Reinforcement of concrete by rebar is a macro-scale example of this technique. It is also known to reinforce advanced CBC materials with the aid of reinforcing fibers, which may, for example, consist of steel fibers, carbon fibers, glass fibers, organic fibers, etc. However, possible dimensions and processing limitations set physical limits for which reinforcement materials and - methods that can be used in dentistry and surgery.

Requirements for the surface material of the stiffening material, flowability during preparation and application, and - for use as a cementing compound, ie as an adhesive, - a joint thickness of less than 50 μm, also sets an upper limit for the physical extent of reinforcement particles in connection with dental and surgical applications. In addition, reinforcing fibers in the usual sense would, in dental applications, provide a possible attachment for bacteria, if they protrude from the surrounding matrix material and / or do not wear down in step with this.

It is known that the strength of at least some cements can be increased by packing the paste of the powdered binder and the reacting liquid, which can be achieved by means of a dispersant, more specifically with a so-called super plasticizer, Science, February 1987, pages 235-236, and US-4 363 667. In the preparation, which is carried out in connection with the application, the pulp is homogenized and blisters are expelled by repeated kneading. The method is statistical and individual strength-determining air bubbles (pores) can remain. The homogenization in connection with the application can also be a practical problem.

The degree of tightness and thus the strength can also be increased by the powder being composed of well-balanced grain size fractions; US-4,353,746 and US-A-4,353,747. Although this technique per se can also be integrated into the technique of the present invention, it is not sufficient to achieve the desired results. Thus, only moderate increases in strength are achieved.

SUMMARY OF THE INVENTION The object of the invention is generally to offer a way of improving the strength of chemically bonded ceramic products, so-called CBC products or CBC materials. In particular, an object is to prepare the binder (s) together with any aggregate to be included in the CBC product, so that the user can work with a binder product processed for adequate strength, which the user completes by soak the finished, prepared binder with the liquid before application or in situ.

According to one aspect of the invention, an object is to be able to offer a material suitable for dental applications, in particular for permanent fillings.

According to one aspect of the invention, it is an object to be able to provide a material suitable as a prosthetic material (implant) for general orthopedic applications.

According to another aspect of the invention, an object is to facilitate the in situ addition of hydration fluid (eg in the form of seawater) for underwater structures.

These and other objects can be achieved by compacting a powder body consisting of said binder and any aggregate material without the addition of said liquid by exposing the powder body to such a high external pressure and at such a low temperature before the liquid is brought to soak. sintering reactions during compaction obtain a well-cohesive crude body, in which the filling density has increased to at least 1.3 times the initial filling density, which is defined as the filling density obtained by shaking, vibrating and / or lightly packing the loose powder in a container. Preferably, the powder body is subjected to such a high pressure that the filling density increases to at least 1.5 and suitably to at least 1.7 times the initial filling density.

According to a first preferred embodiment of the invention, 1.4 said binder consists of one or more hydraulic binders, the hydrating phases of which belong to the group of compounds consisting of aluminates, silicates and phosphates, the liquid consisting of a hydrating liquid consisting of water and optionally dissolved therein. 20 25 30 35 465 495 substances. Among aluminates, calcium aluminate may be mentioned in the first instance, which may occur in varying proportions between CaO and Al2O3. Among silicates, there is mainly calcium silicate with varying proportions between CaO and SiO2, which is the main constituent of Portland cement, but which also contains other constituents, including Al2O3. Other phases may be, for example, 3CaO 'Al2O3 and 4CaO' Al2O3 and 4CaO AlO2 3 'Fe2O3. Combinations of silicates and aluminates with a higher proportion of aluminate than in ordinary Portland cement are also conceivable. An example of phosphate that can be used as a binder in these contexts can be mentioned calcium phosphate and zinc phosphate.

The above substances can occur naturally as minerals or be produced synthetically. Regardless of origin, they are subjected to a preparatory treatment which belongs to conventional technology and which does not form any part of this invention. As a result of this treatment, a powder is obtained, in which the powder grains have a size ranging from submicron size up to a maximum of 100 μm in the longest distribution of the grains. A normal average grain size can amount to about 15 μm, ie 50% by weight of the grains have a size larger than about 15 μm. The shape is very irregular.

In addition, the powder grains generally form larger, porous agglomerates. For these reasons, and also due to electrostatic interaction between the powder grains, with this type of powder very low filling density of the loose powder is achieved. A normal so-called TAP density also called Bulk density or Loose density for calcium aluminate cement, for example of type SECAR 71, is 32%. This can be increased to about 39% by shaking, vibrating or subjecting the powder to light packing in the container in which the powder is stored. It is the filling density in the latter state, ie after vibration, shaking or light packing which is to be regarded as the initial filling density. in the method according to the invention. Incidentally, this can be increased a little further by soaking the powder with a non-reacting liquid, which is then removed before the very powerful compaction according to the invention.

Although the invention has been developed for hydrating materials of the aluminates, silicates and phosphates type, it is likely that its basic features can be used for other systems as well. In the dental field, and also in other fields, the invention could be used, for example, in case the binders consist mainly of one or more oxides, for example zinc oxide, while the liquid consists of one or more acids, for example some phosphorus-based acid, preferably and mainly orthophosphoric acid.

Another among several possible application areas is the production of so-called glass polyalkeonate cement, wherein the binder may consist of a mixture of glass powder and a freeze-dried acid according to per se known technology, while the liquid may consist of water.

In addition to binder and liquid, which after reaction with the binder form a solid phase, ballast materials can be added in a manner which is generally known, by which is meant materials which do not participate in the chemical reactions between the binder and the liquid, but which exist as a solid phase. in the finished, solid end product. For certain application areas, such ballast materials can consist of reinforcements or reinforcements of various kinds, such as fibers of metal, carbon, glass or organic materials, etc. The reinforcement can advantageously also take place by introducing elongated crystals, so-called shiskers, of for example SiC, Si3N4 and / or Al 2 O 3. Also for dental applications or as prosthetic material for general surgical applications, the CBC material according to the invention may contain ballast material, provided that they meet certain requirements. Thus, they must not be toxic, they must be biocompatible, not cause irritation in the oral cavity in the case of dental applications, do not corrode, etc. For example, boron nitride can be added at a low level to serve as a solid lubricant in connection with compaction. of the dry powder material, preferably in a content of 5-15% by volume of the dry substance before compaction and soaking with the liquid in question.

In case the binder consists of one or more hydrating materials, the ballast may also consist of, for example, hydroxylapatite or solid solutions thereof and / or oxides of one or more of titanium, zirconium, zinc and aluminum. It is particularly advantageous if the ballast consists of outwardly directed, needle-shaped crystals, preferably of titanium dioxide, which are biocompatible and chemically inert in all the systems in question here, ie both against hydrating liquids and in phosphoric acid, etc. The titanium dioxide ballast preferably consists of three-dimensional ballast. and star-shaped, acicular crystals, which may be a few tenths of a micrometer thick but normally several times longer in length. These crystals are agglomerated into larger particles or agglomerates with a size of several micrometers. The reinforcing effect that the agglomerates exert in the cured product also depends on the nature of the agglomerates. The bond between the hardening phase and the agglomerates of titanium dioxide crystals is thus improved and strengthened when the agglomerates are etched, for example in 0.5-10 M, especially 1-3 M sodium hydroxide, or in another etching solution, eg mineral acid, such as phosphoric acid.

According to the invention, the superplasticizer can also be mixed in dry or via an anhydrous solution, after which the crude body is manufactured. An example of a superplasticizer is 79% hydrolyzed polyvinyl acetate.

When soaking the crude press body with liquid, it is important that you not only have a high but also regular filling density, so that you do not have larger pockets which are filled with liquid when soaking. Thus, not only the average value of the liquid content in the moistened crucible body must be low, but also within each small sub-volume a low liquid number must be present. On the other hand, the liquid content must be sufficient to be able to dissolve the binder to such an extent that this will not be present in large continuous strips in the finished CBC material. If the binder consists of an aluminate or other hydrating material, and if the material is used for dental fillings, longer continuous strips of unreacted calcium aluminate would cause the aluminate, as the filling wears down, to react with water in the oral cavity in an undesirable manner. The ballast material can play a role not only as mainly reinforcing material, but also to contribute to an optimal distribution, so that in each subvolume there is a sufficient but not too high content of liquid which can react with the binder. , so that longer, continuous streaks of unreacted binder are substantially avoided. The ballast particles or agglomerates of ballast material preferably have a particle size of 0.5-10 μm. It is particularly advantageous if their average particle size is substantially smaller than the average grain size of the binder, whereby a slightly higher initial filling density can be achieved. Preferably, the aggregate material amounts to between 3 and 25% by weight of the finished CBC material or to between 4 and 30% by volume of the mixture of binder powder and aggregate material in the crucible body.

In a special embodiment of the invention, a fine-grained binder phase and a slightly coarser ballast material phase in the powder body are used instead. According to this embodiment, the majority of the powder grains in the binder phase may have grain sizes between 1 and 20 μm, while the majority of the grains in the aggregate material phase have an order of magnitude between 5 and 50 μm. This choice of particle size distribution between the binder phase and the aggregate material phase facilitates an almost total "consumption", ie reaction between the binder phase and the liquid during soaking. The final CBC product will then be present as relatively large ballast material particles surrounded by fully hydrated and correspondingly reacted areas, respectively. Such a material may be particularly suitable for wear applications in wet - preferably in a hydrating environment. If unhydrated areas are exposed to this wet, abrasive environment, wear can be accelerated by the fact that release from the unhydrated phase is greater than for the fully hydrated phase. Corresponding conditions may also exist when the binder consists of a non-hydrating binder and the final product is to be used in an environment containing liquid of the same kind used as reaction liquid in the curing of the product.

The initial filling density, ie the filling density before the compaction according to the invention in the dry state, normally amounts to a maximum of 40%. By special pretreatment methods, for example by centrifugation in a non-chemically reactive liquid, the filling density can be increased to a maximum of 50 to 55%.

According to a preferred embodiment of the invention, the compaction according to the invention is carried out by callisostatic compaction, whereby callisostatic means isostatic compaction at such a low temperature that no sintering reactions take place, normally at room temperature. However, other mechanical pressing, such as, for example, cold rolling or forging, preferably step forging, is also conceivable.

During compaction, the agglomerates are broken by binder grains and possibly or preferably also the agglomerates of existing aggregate material are broken or crushed, and the fragments are redistributed, so that the porosity is reduced and the material is homogenized. The process is facilitated by treating the constituent powder in a non-polar liquid, eg petroleum ether (light petrol), whereby the binding force of the resulting agglomerates after evaporation of the liquid becomes low, ie results in the formation of soft agglomerates.

In cold isostatic compaction, the powder body is arranged in a tight housing, preferably in a plastic housing, after which the enclosed powder body is subjected to an external pressure in a volume of liquid surrounding the housing, preferably a pressure exceeding 200 MPa, preferably at least 250 MPa. Another way of achieving the cold compaction of the binder and the possible ballast according to the invention is by injection molding or extrusion, the powder also containing a solid lubricant, for example a polymer in a content substantially corresponding to the pore volume in the crude press body. After compaction, the polymeric lubricant is evaporated, preferably by gasification by heating.

Regardless of the compaction method, the compaction is carried out so as to obtain 10 10 crucible bodies with a geometric shape adapted to the intended area of use. For example, the crucible body, when intended for dental applications, may consist of a narrow strand, possibly divided into easily separable sections, or of smaller granules. If the compaction is carried out as callisostatic compaction in a plastic casing, it is advisable for the crude compact to remain encapsulated in this casing until the time of use, especially if the crucible contains hydrating adhesives which would otherwise require packaging to avoid unintentional exposure to moisture during transport and storage. Some suitable product shapes are shown in the accompanying drawing figures, in which Fig. 1 shows a strand of a crude body in a plastic casing according to a first embodiment, Fig. 2 shows a series of granular crucible bodies in an elongate continuous plastic casing, Fig. 3 constitutes a section III -III in Fig. 2, and Fig. 4 is a longitudinal section through a third conceivable embodiment of a crude press body in a tight plastic casing.

In the embodiment according to Fig. 1, the raw compression body 1 simply consists of a straight even rod, which may have a circular or other cross-section and a thickness of, for example, 3 to 7 mm, in the case of a material for dental applications. The cover consists of a folded plastic foil 2 which is sealed longitudinally along one side, at 3a, and at the ends have end seals Sb. The length of the rod 1 can amount to, for example, between 30 and 200 mm.

The granules 4 according to Figs. 2 and 3 may have a more or less spherical shape 10 J: CF 2 (JJ 11 and be arranged in a plastic casing 5, which can, for example, be shrink-sealed around the granules 4 before the callisostatic compaction.

According to Fig. 4, the blank press body 6 instead has the shape of a rod divided into sections 7 and between them weakenings 8. A tight plastic cover is denoted 9. Instead of covers 3, 5 and 9 of plastic, it is also conceivable that covers of another polymer, such as rubber.

After compaction, the intermediate thus formed has acquired a considerable bending strength and compressive strength. It is therefore not entirely easy to crush or break off pieces of the blank press body, so it is important that it has a size corresponding to the volume of the desired end product or that the individual blank press bodies are so small, or that the blank press body is designed with break instructions, so that less pieces can be broken off, so that the end product can easily be built up by a number of smaller crude compacts after the liquid has been added.

These possibilities are met by the embodiments shown with reference to the drawing figures 1-4.

The soaking with the liquid which is to react with the binder is carried out only when the CBC product is to be completed.

The crude press body is then soaked with the intended liquid by wetting it or by immersing it in the liquid. The pores in the crude body act as capillaries, which suck in an adequate amount of liquid. Due to the partial dissolution of the binder, the strength of the crude compact decreases drastically; from a compressive strength of the order of 10 MPa to a compressive strength of the order of 3 MPa. The wet raw press body can therefore now be broken up and formed into smaller pieces, if desired. Thus, through the initial dissolution, it acquires an acceptable formability in order to be able to be used, for example, as a dental filling material.

If larger structures are to be erected, a plurality of raw press bodies can be soaked in so that, after soaking with the liquid, 10 15 20 25 30 35 12 are joined together into larger units. In particular, the invention facilitates in-situ addition of liquid, in particular hydrating liquid in case the binder consists of one or more hydrating binders. fl For example, the liquid in this case may consist of seawater or of water in lakes and watercourses for underwater structures, whereby the soaking with water can take place directly at the application site.

If the powder in the crude body consists entirely of binder, for example cement, 30 to 60% of the binder is dissolved by the liquid and hardens by known reactions. The total dissolved amount depends on a number of factors, such as the size, shape and distribution of the powder grains, but the degree of compaction and the size of the crude compact are also important in this case, since the hydrates that are formed will form diffusion barriers for additional water. The ballast material can be actively used to maximize the hydration and the corresponding reaction in cases where binders other than hydrating are used. For example, if one assumes that the filling density in the crude body is 67% or 2/3, with 1/3 consisting of pores, and if one assumes that 1/3 of the binder is "consumed", ie dissolved by the liquid during soaking, one could theoretically achieve a total hydration, if half of the binder was replaced by an equal volume of ballast material.

In case the invention is to be used for the production of material for permanent dental fillings, the ballast material preferably consists of acicular titanium dioxide crystals agglomerated into larger particles of the order of 1-5 μm, as described above. This ballast material has a very high whiteness opacity and albedo. In addition, it is completely lightfast, chemically resistant, biocompatible and does not cause irritation or other discomfort in the oral cavity in the case of a dental application. Fig. 5 shows in magnification particles of pure titanium dioxide consisting of three-dimensional and star-shaped Å acicular crystals. This material can be obtained from, for example, TIL Central Laboratories, Stockton-on-Tees in the United Kingdom, under the trade name "Tilcom". The crystals are a few hundredths of a nanometer thick but 10 15 20 30 35 465 4923 13 several times larger in length. They are agglomerated into particles with a grain size of 0.5-10 μm.

Additional aspects of the invention will become apparent from the following examples.

EXAMPLE 1 A calcium aluminate cement of type Secar 71 (manufacturer Lafarge) was used as the binder phase. Secar 71 consists of a mixture of CaO'Al2O3 and CaO'2Al2O3. The average grain size was about 15 μm.

An approximately 5 cm 2 volume of the binder powder was cold-pressed at 300 MPa in a dense plastic casing to form a parallelepiped. In this, a fill density of 67.5% was measured after the callisostat compaction. The plastic casing was removed and distilled water was added, after which the sample was stored at 35 ° C and 100% relative humidity (RH) for 24 hours. The strength determined as a three-point bending sample was measured to be about 70 MPa. Open porosity measured according to the ASTN method before porosity measurement amounted to 1.7%.

EXAMPLE 2 Secar 71 according to Example 1 was cold-compacted as a block with the dimension 4 x 4 x 8 cm at 320 MPa, so that a crude press body with a density of 2.10 g / cnf, corresponding to 70% filling density, was obtained.

The callisostat-compacted block was cut into a number of test rods with a geometry of 40 x 3 x 3 mm. Distilled water was added, after which half of the samples were stored in a humid environment (100% RH - Relative Humidity) and the rest in water at 37 ° C for varying times. Results with respect to the achieved average flexural strength expressed in MPa, open porosity (OP) and shrinkage (K) are reported in the table below.

TABLE l Samples 1 day 7 days 120 days MPa öP% K% MPa 69% K% MPa _öP% K% 100% RH 66 1.4 <0.1 58 1.4 <0.1 64 1.0 <0.1 water 65 1.9 I <0.1 58 1.3 <0.1 65 1.0 <0.1 10 15 20 25 30 35 14 EXAMPLE 3 In this example, a cement designated OPC stands for Ordinary Portland Cement. The cements thus consisted mainly of calcium silicates, CaO ° SiO2 with a small amount of alumina, iron oxide mlTl.

The cement powder had an average grain size of about 10 microns. The powder was callisostat compacted at 300 MPa to a body having the shape of a parallel pipe and a volume of 30 cma. The crude body was soaked with ordinary tap water. The sample was stored in water for 24 hours, after which density and flexural strength were determined. The result is given below.

TABLE 2 Sample Density g / en? öP% Flexural durability MPa oPc 2.63 0.9 40 ¿_4 EXAMPLE 4 In this example, calcium aluminate of a kind known under the trade name Fondu was used. The powder was called callisostat in the same manner as in Example 3. However, the storage time in water was 7 days. In this case, the crude body was soaked with tap water, after which the sample was treated in the same manner as in Example 3. In this case, the following results were obtained.

TABLE 3 Sample Density g / en? OP% Flexural strength MPa Fondu 2.81 0.5 42 i_2 EXAMPLE 5 Cement powder of type Secar 71, ie of the same type as in Example 1, was compacted at 300 MPa into a cube with a side of 1 cm. water 10 15 20 25 30 35 15 Water was allowed to be sucked up by the test powder, which could then be decomposed into granules of the order of 1-2 mm. The granules were stamped within two minutes at a pressure of 5 MPa to a new pellet which was allowed to hydrate for 1 day at 35 ° C and 100% RH, after which the compressive strength was determined in a universal testing machine, type Instron. The compressive strength was measured at 270 MPa.

EXAMPLE 6 Synthesized calcium aluminate cement, CaO 'Al 2 O 3 was ground in petroleum ether and sieved through a 100 μm mesh screen. A powder amount of about 40 g of callisostat was compacted at 300 MPa. Water and superplasticizer dissolved therein (ÜYD Gohsenol; 79% hydrolyzed polyvinyl acetate) were added to one part of the sample pellet, while another part of the sample pellet was centrifuged in the solution of water and superplasticizer at 6000 RPM. Without centrifugation, the test pellet is not wetted satisfactorily. The centrifuged sample was crushed into smaller granules and then treated as in Example 5. The resulting compressive strength of the final sample vessel was measured to be 230 MPa.

EXAMPLE 7 To an aluminate according to Example 6 was added a superplasticizer (type Gohsenol), and mixing took place partly in the dry state and partly in a light petrol solution. The powders were prepared from raw powders by cold isostatic pressing in a polymer hose. Water was then forced through the hose. After the hose was removed, the moist mass was stamped into the parallelepiped 40 x 3 x 3 mm. The flexural strength obtained in the cured samples was measured to be 49 i_7 MPa in both cases.

EXAMPLE 8 Cement raw material of type Secar 71, see Example 1, was added with 5% by volume of boron nitride of a kind marketed under the name HC Starck.

The boron nitride was in the form of a very fine powder with a grain fineness corresponding to a specific surface area of 3 mg / g. The mixture was callisostat compacted at 300 MPa. The crude body obtained was allowed to soak up distilled water below 30 ° C. The moistened crude press body could then be removed.

LN 493 GN 16 is crushed by subjecting it to a pressure of approximately 2 MPa. The granules thus obtained were stamped into a test tube at low pressure. This pressure was measured with a load sensor connected to the piston, which consisted of a cylinder with a diameter of 2.5 mm. The formability expressed as the required pressure to obtain an open porosity of up to a maximum of 2% in a sample hydrated for 1 day at 35 ° C and 100% RH was found to be about 2 MPa lower than for the corresponding sample without the addition of boron nitride. The example shows that boron nitride acts as a lubricant in forming the wetted crude compact.

EXAMPLE 9 Secar 71 type cement raw material, according to Example 1, was mixed with 12% by volume of fine-grained hydroxylapatite having a particle size of less than 5 μm, in a ball mill with petroleum ether and silicon nitride cylpebs as grinding environment. (Cylpebs = oylindrical pebles; small cylindrical grindstones.) A volume of 8 cnf of the powder mixture was called callisostat compact at 300 MPa. The obtained crude press body was allowed to absorb hydration liquid consisting of distilled water, tap water or water added with 0.5% soluble salt of chlorides. The hydration was allowed to proceed for 24 hours at 35 ° C and below 100% RH, after which flexural strength testing was performed according to Example 1. The average strength of seven test rods was 61 MPa (minimum value 42 MPa, maximum 93 MPa) indicating a significant amount of a fine-grained ballast phase can be added without significant reduction of the flexural strength, compare Example 1, and that the resulting strength is substantially independent of the purity of the water, as far as this has been tested.

EXAMPLE 10 To a calcium aluminate cement of the same type Secar 71 as in Example 1 was added 35% by volume of a polymeric binder for injection molding consisting of a mixture of polyethylene and ethyl vinyl acetate. The mixture of aluminate cement and polymer powder was homogenized in a Brabender mixer and injection molded at a pressure of 1200 bar to form a parallelepiped. The polymer was then evaporated by heating to 400 ° C. The filling density then amounted to 65.5%. The porous crude body thus formed was then allowed to soak up distilled water supplemented with 0.035 molar of a chloride salt, after which the moistened body was placed in room temperature water. After 24 hours it had a compressive strength of 210 MPa. The fracture toughness of the material was determined by the Vickerdiamant impression method to 2.8 MPame.

It will be appreciated that the invention may be varied within the scope of the appended claims, and that substances other than those described in the foregoing description may also be added. Thus, it is conceivable to add accelerators or retarders to the mixture of binder, liquid and any aggregate in order to accelerate or dampen the curing reaction.

Claims (25)

10 15 20 25 30 35 18 PATENT REQUIREMENTS A process for the preparation of chemically bonded ceramic product by reaction between one or more powdered binders and a liquid reacting with these binders, wherein the ceramic product can also be made to contain one or more aggregate materials which do not substantially participate in the chemical curing reactions, characterized in that a powder body consisting of said binder and any aggregate material without addition of said liquid is compacted by exposing the powder body to such a high external pressure and at such a low temperature that before the liquid is brought to soak that without sintering reactions the compaction obtains a well-cohesive blank press body, in which the filling density has increased to at least 1.3 times the initial filling density, which is defined as the filling density achieved by shaking, vibrating and / or light packing of the loose powder in a container. 2. A method according to claim 1, characterized in that the powder body is compacted by mechanical pressing, preferably cold isostatic pressing. 3. A method according to claim 1, characterized in that the powder body also contains an organic lubricant or binder, that the powder body is formed and compacted by injection molding or extrusion, that the organic lubricant or binder is evaporated, so that a porous raw press body, and that the raw press body thus formed is soaked with the liquid. 4. A method according to any one of claims 1-3, characterized in that the first-mentioned binder consists of one or more hydraulic binders, wherein the hydrating phase belongs to the group of compounds consisting of aluminates, silicates and phosphates and that the liquid consists of a hydrating fluid consisting of water and solutes dissolved therein. (i 10 15 20 25 30 35 19 5. A method according to any one of claims 1-3, characterized in that the first-mentioned binder consists mainly of one or more oxides, preferably mainly zinc oxide, and that the liquid consists of one or more acids, preferably mainly orthophosphoric acid. 6. A method according to claim 1, characterized in that the crude press body or a separated part thereof is soaked with the liquid by allowing the liquid to be sucked in by capillary forces acting in the body. 7. A method according to claim 1, characterized in that the crude press body or a part thereof is soaked by the liquid partly by allowing the liquid to be sucked in by capillary forces acting in the body, partly by centrifuging, shaking, vibrating or exposing the raw press body or said separated part. similar treatment in the liquid. 8. A method according to claim 1, characterized in that in the production of the raw compact the filling density is caused to increase to at least 1.5 and preferably at least 1.8 times the initial filling density. 9. A method according to claim 1, characterized in that the compaction is carried out at a temperature below 100 ° C, preferably at room temperature. 10. A method according to any one of the preceding claims, characterized in that the crude press body is given the shape of a narrow string or thin disc, possibly provided with breaking instructions. 11. ll. A method according to any one of claims 1-9, characterized in that the crude compact is given the shape of granules. 12. A method according to any one of claims 1 to 11, characterized in that the powder body is encapsulated in a plastic casing, and that it is subjected to callisostatic compaction in a liquid in said plastic casing. 10 15 20 25 30 35 20 13. A method according to claim 1, characterized in that the optimum amount and content of liquid is determined by the degree of compaction and the associated amount of liquid which is sucked into the crude press body by capillary action. 14. A method according to claim 1, characterized in that a plurality of soaked crude press bodies are joined together for the construction of larger structures. 15. A method according to claim 2, characterized in that the crude body is hydrated in situ in an aquatic environment, preferably for underwater constructions: 16. A method according to claim 1, characterized in that the powder body is caused to contain up to 50% by volume of aggregate material. 17. A method according to claim 16, characterized in that the powder body contains 5-25% by volume of aggregate material. 18. A method according to claim 1, characterized in that the powder body contains 25-50% by volume of aggregate material. 19. A method according to any one of claims 1-18, characterized in that the binder consists of a hydrating binder and that the aggregate material consists wholly or partly of hydroxylapatite or solid solutions thereof and / or oxides of preferably titanium, zirconium, zinc and aluminum . 20. A method according to any one of claims 1-19, characterized in that the powder body contains 5-15% by volume of boron nitride. 21. A method according to any one of claims 1-19, characterized in that the ballast material is wholly or partly in the form of wipers or fibers. 10 15 20 25 30 35 .rs C? ~ C> l \ & D: _14 21 22. A method according to any one of claims 1 to 19, characterized in that the powder body contains 5-20% by volume of a granulate consisting of outwardly directed, acicular crystals of mainly titanium oxide. 23. A method according to claim 22, characterized in that the titanium oxide is etched. 24. A method according to any one of claims 1 to 23, characterized in that the ballast material consists of a material which is finer-grained than the binder phase and that it preferably has an average grain size of less than 10 μm. 25. A method according to any one of claims 1-23, characterized in that the ballast material is coarser than the binder phase, more particularly that the binder phase in the powder body mainly has a particle size between 1 and 20 μm, while the ballast material consists of a powder with grain sizes mainly between 5 and 50 um.