RU2795866C1 - Ceramic material with low sintering temperature based on tetragonal zirconia for additive manufacturing - Google Patents

Abstract

FIELD: obtaining products from high-density ceramics.

SUBSTANCE: obtaining products from high-density ceramics based on zirconium dioxide of complex shape using additive manufacturing by digital light processing (Digital Light Processing, DLP). Developed materials can be used to obtain dental implants, bone structures, high-temperature machine parts and electronics. The ceramic material contains tetragonal zirconium dioxide stabilized with yttria, additives of silicon oxide and aluminum oxide at the following ratios of components in the material, in % by weight: silicon oxide - 2-5, tetragonal zirconium dioxide (yttria content 3-9 mol.%) - 90-96, aluminum oxide - 2-5. The resulting material is characterized by a bending strength of at least 515 MPa during sintering at 1150°C, not less than 800 MPa during sintering at 1450°C, uniform homogeneous structure with a crystal size of 50-70 nm during sintering at 1150°C, 50-100 nm during sintering at 1250°C, 100-300 nm during sintering at 1450°C and open porosity not more than 1%.

EFFECT: adaptation of ceramic powders to obtain ceramic objects of complex shape with high strength, and a decrease in the sintering temperature.

1 cl, 1 tbl, 1 ex

Description

The invention relates to the field of obtaining products from high-density ceramics based on zirconium dioxide of complex shape using additive manufacturing by digital light processing (Digital Light Processing, DLP). Strong ceramic materials based on tetragonal zirconia have high resistance to chemical and biological media, high mechanical properties, which allows them to be used as wear-resistant products, various cutting tools, including medical scalpels, ceramic bearings, as well as implants for replacement of bone defects. The possibility of obtaining complex geometric shapes of the final product significantly expands the scope of these materials.

The main disadvantage of ceramic technology based on zirconium dioxide is the high sintering temperature of 1700-1750°C [Andrianov, N.T., Balkevich, V.L., Belyakov, A.V., Vlasov, A.S., Guzman, I. Ya., Lukin, E.S., … & Skidan, B.S. Chemical technology of ceramics: textbook. manual for universities / Ed. IYA Guzman // M.: Reef LLC "Building Materials", 2012. - 496 p. - 2012].

It is possible to obtain strong ceramic materials based on ZrO ₂ while simultaneously lowering the sintering temperature by using special methods, such as hot or isostatic pressing. However, these methods involve the use of complex expensive equipment and cannot be used in additive manufacturing to obtain objects of complex shape using digital light processing (DLP).

So, ceramic materials of tetragonal modification are known:

1M. Trunec and K. Maca Compaction and Pressureless Sintering of Zirconia Nanoparticles // J. Am. Ceram. Soc., 90 [9] 2735-2740 (2007)] with a sintering temperature of about 1100°C and a relative density of 99.1%. The low sintering temperature and the achievement of a relative density of 99.1% is a consequence of the use of nanodispersed powders with a high specific surface area of 123 m ³ /g. The disadvantage of this material is the use of expensive equipment for isostatic compaction when pressing samples, as well as the relatively low density of the material, which leads to a decrease in strength.

2. [Fu L. et al. Transparent single crystalline ZrO ₂ -SiO ₂ glass nanoceramic sintered by SPS //Journal of the European Ceramic Society. - 2016. - T. 36. - No. 14. - P. 3487-3494.] with a sintering temperature of 1050–1230°C, consisting of 35 mol. % ZrO ₂ and 65 mol. % _SiO2 . The resulting materials are transparent ceramics and obtained by spark plasma sintering under pressure from 30 to 70 MPa. The final bending strength is from 227 to 268 MPa.

The closest technical solution and the achieved effect is a ceramic material of tetragonal modification [patent No. 2572101 "Ceramic material with a low sintering temperature based on tetragonal zirconium dioxide"] with a sintering temperature of about 1150°C. Low sintering temperature, achievement of relative density (open porosity no more than 0.01%) and strength of 350 MPa in bending is achieved through the use of ultrafine powders 150 m ² /g and the use of additives - sodium silicate in the amount of 2-5 wt. %. The disadvantage of this material is the low strength of the material. This is a consequence of the content of low-strength amorphous glass phase in the material. As well as a ceramic material of tetragonal modification [patent No. 2665734 "Ceramic material with a low sintering temperature based on tetragonal zirconium dioxide"] with a higher sintering temperature of 1300-1350 ° C, and, therefore, less active for sintering, but having higher mechanical strength properties for 3-point bending 500 MPa.

To obtain parts of complex geometry, consisting of ZrO ₂ ceramics, it is necessary to take into account a number of technological parameters. Today, 3D printing with ceramic materials is already actively used, but it requires high-tech expensive equipment that allows you to work with viscous ceramic suspensions, which limits the possibility of using this technology. A decrease in viscosity allows the use of these suspensions in DLP technology, however, insufficient filling of powder particles does not provide an acceptable green density, which ultimately leads to the formation of cracks and deformations in the sintered product. In the case of using highly active ceramics, the effect of baking at low temperatures of pyrolysis of the organic binder is observed, which makes it possible to preserve the structure without deformations and cracks.

The technical result of the invention is to create a material based on a tetragonal modification of zirconium dioxide, sintering at a low temperature of 1150°C and characterized by high mechanical characteristics: bending strength of at least 515 MPa.

The technical result is achieved by the fact that the ceramic material with a low sintering temperature based on tetragonal zirconium dioxide contains an additive of silicon oxide, which promotes sintering at a temperature of 1150°C, and a strengthening additive of Al ₂ O ₃ at the following ratios of components in the material, wt. %: tetragonal zirconium dioxide (yttria content 3-9 mol.%) - 90-96 wt. %, addition of aluminum oxide 2-5 wt. % and the addition of silicon oxide in the amount of 2-5 wt. %. The resulting material is characterized by a bending strength of at least 515 MPa, a uniform homogeneous structure with a crystal size of about 50-70 nm and an open porosity of not more than 4%.

The ceramic material of this composition is unknown. As a result of the action of the SiO ₂ additive, numerous defects appear in the lattice of the ZrO ₂ crystalline material, which contribute to the intensification of sintering due to the introduction of the Si ⁴⁺ cation (ionic radius 42 pm). High strength of 515 MPa is achieved by a fine grain size of 50-70 nm. As the temperature increases, grain growth and structure compaction occur, these two processes cancel each other, so the bending strength readings do not change up to 1450°C. Upon reaching 1450°C, the open porosity was no more than 0.01%, and the bending strength of the ceramic increased to 800–930 MPa. At sintering temperatures above 1450°C, further crystal growth occurs, without an increase in density, which leads to a decrease in strength. At a temperature of 1100°C, the drop in strength occurs due to an increase in porosity (open porosity 26%), however, the material still has a high bending strength of 251 MPa. When the content of yttrium oxide is less than 2 mol. %, a monoclinic modification is formed, and at more than 9 mol. % cubic modification, the content of which also reduces the strength of the material. Due to its high sintering activity, this ceramic powder does not require high filling in 3D printing, which makes it possible to use it using a budget DLP printing method.

Example. Ceramics were obtained from nanodispersed powders of the composition 93 wt.% ZrO ₂ (zirconium dioxide contained 9 mol.% yttrium oxide) 2 wt.% Al ₂ O ₃ - 5 wt.% SiO ₂ , the specific surface of the powders was not less than 55 m ² /g . To obtain samples, powder samples were pressed in the form of beams 30 × 3 × 3 mm in size. The resulting samples were sintered at a temperature of 1150°C. The result was a ceramic material consisting of 100% tetragonal phase. The material was characterized by a homogeneous fine-grained structure with a crystal size of 50–70 nm, an open porosity of no more than 4%, and a bending strength of 515 MPa.

Were made samples of ceramics with compositions within the declared, and determined their properties in comparison with the prototype.

The results obtained are summarized in the table.

Sample Content
Y ₂ O ₃ in relation to ZrO ₂ ,
mol.% Contents
nie
zirconia,
wt.% Contents
nie
alumina,
wt.% Content
silicon oxide,
wt.% Sintering temperature,
°С Crystal size, nm Strength
when bending
MPa open porosity,
% Note 1 9 90 5 5 1250 50-200 250 No more than 5 2 3 96 2 2 1150 50-70 515 No more than 4 3 6 93 2 5 1250 50-100 320 No more than 1 4 (prototype) - 90 5 5 1300 - 95 40 crackling 5 2 93 2 5 1450 100-300 300 4

Claims (3)

A ceramic material with a low sintering temperature based on zirconium dioxide of a tetragonal modification, characterized in that it contains additives of silicon oxide and aluminum oxide at the following ratios of components in the material, wt. %: silica additive 2-5 tetragonal zirconia (yttria content 3-9 mol.%) 90-96 aluminium oxide 2-5, the resulting material is characterized by a bending strength of at least 515 MPa during sintering at 1150°C, at least 800 MPa during sintering at 1450°C, a uniform homogeneous structure with a crystal size of 50-70 nm during sintering at 1150°C, during sintering at 1250 °С 50-100 nm, during sintering at 1450°С 100-300 nm and open porosity not more than 1%.