Process for providing a defined surface topography to at least a portion of a ceramic body

Abstract

A Process for providing a defined surface topography to at least a portion of a ceramic body, the process comprising the subsequent steps of a) applying a layer of a calcium containing substance comprising at least one calcium compound onto the surface of at least a portion of the ceramic basic body; b) thermally treating the ceramic basic body with the layer applied thereon at an elevated temperature, whereby a calcium compound or a calcium component based on the calcium compound diffuses into the basic body to form an intermediate body, said intermediate body comprising in its outermost surface region a calcium containing crystalline phase; and c) chemically treating the outermost surface region of the intermediate body with an inorganic acid or base to partially remove the calcium containing crystalline phase, thereby obtaining the surface topography.

Claims

1. Process for providing a defined surface topography to at least a portion of a ceramic body, the process comprising the subsequent steps of a) applying a layer of a calcium containing substance comprising at least one calcium compound onto the surface of at least a portion of the ceramic basic body; b) thermally treating the ceramic basic body with the layer applied thereon at an elevated temperature, whereby a calcium compound or a calcium component based on the calcium compound diffuses into the basic body to form an intermediate body, said intermediate body comprising in its outermost surface region a calcium containing crystalline phase; and c) chemically treating the outermost surface region of the intermediate body with hydrofluoric acid, an inorganic acid other than hydrofluoric acid, or an inorganic base to partially remove the calcium containing crystalline phase, thereby obtaining the surface topography, wherein when the hydrofluoric acid is used, it is diluted in water in a volume ratio of water to hydrofluoric acid of at least 4:1.

2. Process according to claim 1, wherein the ceramic basic body is made of a ceramic material comprising alumina and/or zirconia.

3. Process according to claim 1, wherein the calcium containing crystalline phase is a CaZrO phase.

4. Process according to claim 3, wherein the calcium containing crystalline phase is a CaOZrO.sub.2 phase.

5. Process according to claim 1, wherein the calcium compound contained in the calcium containing substance is selected from the group consisting of a calcium salt, calcium oxide, calcium hydroxide, metallic calcium, and mixtures thereof.

6. Process according to claim 1, wherein the thermal treatment of step b) is carried out at a temperature of at least 500 C.

7. Process according to claim 1, wherein an inorganic acid selected from the group consisting of HNO.sub.3, HCl, HF diluted in water in a volume ratio of water to hydrofluoric acid of at least 4:1, H.sub.3PO.sub.4 and H.sub.2SO.sub.4 and mixtures thereof, is used for the chemical treatment of step c).

8. Process according to claim 1, further comprising a step of roughening at least a part of the surface of the basic body by a subtractive mechanical treatment.

9. Process according to claim 1, wherein the surface topography is defined by the arithmetic mean height Sa being in a range from 0.1 m and 1.7 m.

10. Process according to claim 1, wherein the surface topography is further defined by a developed surface area Sdr being in a range from 5% to 40%.

11. Process according to claim 1, wherein step c) is carried out with an inorganic acid other than hydrofluoric acid.

12. Process according to claim 1, wherein step c) is carried out with hydrofluoric acid diluted in water in a volume ratio of water to hydrofluoric acid of at least 80:1.

Description

EXAMPLES

1. Sample Preparation; First Set

(1) 1.1. Blanks

(2) Discs of yttria-stabilized zirconia (Y-TZP) having a polished surface, a thickness of about 2 mm and a diameter of about 14 mm were cleaned with a cleaning solution (Deconex by Borer Chemie AG, Zuchwil, Switzerland) in a standard cleaning procedure.

(3) 1.2. Preparation of Intermediate Body

(4) First, the blanks were subjected to oxygen plasma cleaning.

(5) 100 l of a CaCO.sub.3 slurry (having a weight ratio of CaCO.sub.3 to H.sub.2O of 1:2) were pipetted onto the surface of the cleaned blanks before drying the samples at 90 C. for 30 minutes.

(6) The dried samples were then subjected to a thermal treatment at 1100 C. for 48 hours.

(7) After the thermal treatment, the samples were cleaned from residual material using a brush, and washed by rinsing with ultrapure water (5 minutes under sonication, then by pivoting (shaking) for 5 seconds each in two water filled beakers).

(8) The washed samples were then blow-dried under a stream of argon.

(9) 1.3. Preparation of the Ceramic Body with the Desired Surface Topography

(10) In order to prepare the ceramic body with the desired surface topography (samples 1.1. to 1.4.), acid treatment of the intermediate body was performed using the following inorganic acids under the following conditions:

(11) Sample 1.1: treatment with concentrated hydrochloric acid (HCl; 32%) in water in a volume ratio of 1:1 at 90 C. for 5 minutes;

(12) Sample 1.2: treatment with concentrated phosphoric acid (H.sub.3PO.sub.4; 85%) at 90 C. for 5 minutes;

(13) Sample 1.3: treatment with concentrated phosphoric acid (H.sub.3PO.sub.4; 85%) in water in a volume ratio of 1:1 at 90 C. for 10 minutes;

(14) Sample 1.4: treatment with concentrated phosphoric acid (H.sub.3PO.sub.4; 85%) in water in a volume ratio of 1:1 at 90 C. for 5 minutes;

(15) Sample 1.5: treatment with concentrated sulphuric acid (H.sub.2SO.sub.4; 98%) in water in a water/H.sub.2SO.sub.4 volume ratio of 2:1 at 90 C. for 5 minutes.

(16) After the acid treatment, the samples were rinsed with ultrapure water (three times under ultra-sonication for 5 minutes) and then blow-dried with argon.

2. Sample Preparation; Second Set

(17) 2.1 Blanks

(18) Discs of yttria-stabilized zirconia (Y-TZP) having a machined surface, a thickness of about 1.5 mm and a diameter of about 5 mm were cleaned with a cleaning solution (Deconex by Borer Chemie AG, Zuchwil, Switzerland) in a standard cleaning procedure.

(19) The machined discs were sandblasted using corundum with an average grain size from 0.25 mm to 0.5 mm and again subjected to Deconex cleaning.

(20) 2.2. Preparation of Intermediate Body

(21) The discs were then subjected to oxygen plasma cleaning.

(22) 110 l of a CaCO.sub.3 slurry (having a weight ratio of CaCO.sub.3 to H.sub.2O of 1:2) were pipetted onto the surface of the cleaned blanks before drying the samples at 80 C. to 90 C. for 30 minutes.

(23) The dried samples were then subjected to a thermal treatment at 1100 C. for 48 hours.

(24) After the thermal treatment, the samples were cleaned from residual material using a brush, and washed by rinsing with ultrapure water (5 minutes under sonication, then by pivoting (shaking) for 5 seconds each in two water filled beakers).

(25) The washed samples were then blow-dried under a stream of argon.

(26) 2.3. Preparation of the Ceramic Body with the Desired Surface Topography

(27) In order to prepare the ceramic body with the desired surface topography (samples 1.6), acid treatment of the intermediate body was performed using the following inorganic acid under the following conditions:

(28) Sample 1.6: treatment with concentrated sulphuric acid (H.sub.2SO.sub.4; 98%) in water in a water/H.sub.2SO.sub.4 volume ratio of 3:1 at 90 C. for 5 minutes.

3. Sample Preparation; Third Set

(29) 3.1 Blanks

(30) Discs of yttria-stabilized zirconia (Y-TZP) having a machined surface, a thickness of about 1.5 mm and a diameter of about 5 mm were cleaned with a cleaning solution (Deconex by Borer Chemie AG, Zuchwil, Switzerland) in a standard cleaning procedure.

(31) 3.2. Preparation of Intermediate Body

(32) First, the blanks were subjected to oxygen plasma cleaning.

(33) 15 l of a CaCO.sub.3 slurry (having a weight ratio of CaCO.sub.3 to H.sub.2O of 1:2) were pipetted onto the surface of the cleaned blanks before drying the samples at 80 C. for 15 minutes.

(34) The dried samples were then subjected to a thermal treatment at 1100 C. for 48 hours.

(35) After the thermal treatment, the samples were cleaned from residual material using a brush, and washed by rinsing with ultrapure water (5 minutes under sonication, then by pivoting (shaking) for 5 seconds each in two water filled beakers).

(36) The washed samples were then blow-dried under a stream of argon.

(37) 3.3. Preparation of the Ceramic Body with the Desired Surface Topography

(38) In order to prepare the ceramic body with the desired surface topography (samples 1.7 to 1.8), acid treatment of the intermediate body was performed using hydrofluoric acid (HF) under the following conditions:

(39) Sample 1.7: treatment with concentrated hydrofluoric acid (HF; 40%) in water in a water/HF volume ratio of 4:1 at room temperature for 5 minutes; and

(40) Sample 1.8: treatment with concentrated fluoric acid (HF; 40%) in water in a water/HF volume ratio of 80:1 at room temperature for 5 minutes.

(41) The surface topography and the surface composition of samples 1.1, 1.2 and 1.5 as well as of samples 1.7 and 1.8 is shown in the figures, of which FIG. 1 shows scanning electron micrograph (SEM) images of sample 1.1 (A), sample 1.2 (B) and sample 1.5 (C) together with SEM images of the polished blank forming the basic body (D) and of the intermediate body (E) for comparative reasons; FIG. 2 shows EDX (energy-dispersive X-ray spectroscopy) spectra of sample 1.1 (A), sample 1.2 (B) and sample 1.5 (C) together with EDX spectra of the polished blank forming the basic body (D) and of the intermediate body (E) for comparative reasons; and FIG. 3 shows scanning electron micrograph (SEM) images of sample 1.7 (A) and sample 1.8 (B).

(42) As shown in FIG. 1, the samples obtained by a chemical treatment with HCl, H.sub.3PO.sub.4 and H.sub.2SO.sub.4 showed a distinctly different surface topography compared to the reference sample, i.e. the polished blank forming the basic body as well as the intermediate body obtained after thermal treatment. Particularly, the sample obtained by H.sub.3PO.sub.4 treatment as well as the sample obtained by H.sub.2SO.sub.4 treatment showed a clearly increased roughness. In these samples, the grooves originating from the polishing of the surface are no longer visible. In case of the H.sub.3PO.sub.4 treatment, an etching structure on the level of grains is achieved, while in case of the H.sub.2SO.sub.4 sample cavities in the range of about 1 m were additionally formed.

(43) Analysis of the samples obtained by different concentrations of H.sub.3PO.sub.4 (sample 1.2/1.3 and 1.4) and different treatment times (sample 1.2 and 1.4/1.3) showed that on the level of individual grains, the structures are comparable, but with the mildest conditions (sample 1.4; volume ratio 1:1, treatment duration of 5 minutes) resulting in the lowest overall roughness.

(44) The EDX spectra according to FIG. 2 show that calcium is present for all examples except for the ZrO.sub.2 reference sample, but with distinct differences between the samples. The respective amount of Ca, O, Zr and optionally Pd is given in mass-% (Massen %) in the upper right corner. (Low amounts of Pd or Pt were detected due to the presence of a thin Pt/Pd coating on the sample surface in order to make the surface conductive and thus imagable by the SEM.)

(45) The EDX spectrum of sample 1.1 (HCl) showed only very little calcium, whereas the calcium content of sample 1.2 (H.sub.3PO.sub.4) and sample 1.5 (H.sub.2SO.sub.4) is comparable to the CaZrO.sub.2 reference sample.

(46) Further tests showed the following in addition to the above findings: In comparison to sample 1.5, the surface topography of which is shown in FIG. 1C, lower concentration of H.sub.2SO.sub.4 according to sample 1.6 led to an even more pronounced formation of microstructures as well as nanostructures. Also for sample 1.6, EDX spectra revealed the presence of calcium, indicative of a partial removal of the calcium containing crystalline phase.

(47) The samples obtained by a chemical treatment with HF (samples 1.7 and 1.8) showed the formation of pits having a lateral dimension of about 0.5 m. This was found both by treatment with HF in a dilution of 1:4 (shown in FIG. 3A) as well as by treatment with HF in a dilution of 1:80 (shown in FIG. 3B). Also for samples 1.7 and 1.8, EDX spectra (not shown) confirmed that the calcium containing crystalline phase was only removed partially.

(48) Samples 1.7 and 1.8 thus give clear evidence that a desired surface topography of the ceramic body can be achieved when using highly diluted HF, in particular HF at a concentration low enough to circumvent elaborate safety requirements and further low enough to avoid attack of the yttria-stabilized zirconia. If a more pronounced surface topography than the ones shown in FIGS. 3A and 3B is to be achieved, a longer treatment duration and/or a higher treatment temperature may be chosen.

(49) In summary, the results prove that by the process according to the present invention a rough surface topography is obtained and that the desired roughness can be set by appropriately adjusting the type and concentration of inorganic acid or base as well as by the treatment conditions, in particular the treatment duration and the temperature.