MAGNESIUM-CONTAINING METAL MATERIAL PROVIDED WITH COATING

Abstract

Provided is a magnesium-containing metal material that includes coatings having excellent corrosion resistance on a surface. Specifically, provided is a magnesium-containing metal material with coating, which is characterized by including: a magnesium hydroxide-containing first coating on a surface of a magnesium-containing metal material composed of magnesium or a magnesium alloy; a hydroxyapatite and/or hydroxyapatite carbonate-containing third coating over the first coating; and a dibasic calcium phosphate-containing second coating between the first coating and the third coating.

Claims

1. A magnesium-containing metal material with coating, comprising: a magnesium hydroxide-containing first coating on a surface of a magnesium-containing metal material composed of magnesium or a magnesium alloy; a hydroxyapatite and/or hydroxyapatite carbonate-containing third coating over the first coating; and a dibasic calcium phosphate-containing second coating between the first coating and the third coating.

2. The magnesium-containing metal material with coating according to claim 1, wherein the second coating is a coating containing monetite and/or brushite.

Description

EXAMPLES

[0071] The present invention will now be described in more detail by way of Examples thereof.

<Magnesium Material>

[0072] In the present Examples, a pure magnesium plate material having a purity of 99.9% or higher was used.

<Production of Magnesium Material with Coating>

(Pretreatment)

[0073] On a surface of the pure magnesium plate material, a degreasing treatment was performed by spraying thereto an alkali degreasing agent [an aqueous solution obtained by mixing FINE CLEANER MG110E (manufactured by Nihon Parkerizing Co., Ltd.) with water at a concentration of 30 g/L] at 65 C. for 120 seconds, followed by washing with water. Subsequently, the thus degreased surface of the pure magnesium plate material was physically polished with sandpaper while applying deionized water thereto, after which the plate material was washed with deionized water and dried with hot air.

[0074] On this pretreated pure magnesium plate material, the below-described steam treatment, surface conditioning treatment, chemical conversion treatment and apatite conversion treatment were sequentially performed, whereby test pieces of Examples 1 to 5 were each produced.

(Steam Treatment)

[0075] Using an autoclave, the pretreated pure magnesium plate material was subjected to a steam treatment at each temperature for each time period as shown in Table 1. Subsequently, the thus steam-treated pure magnesium plate material was taken out of the autoclave, washed with deionized water and then dried with hot air, whereby a pure magnesium plate material having a magnesium hydroxide-containing coating was produced.

TABLE-US-00001 TABLE 1 Steam treatment temperature Steam treatment time Test piece ( C.) (min) Example 1 120 60 Example 2 125 180 Example 3 140 60 Example 4 120 60 Example 5 140 60

<Surface Conditioning Treatment>

[0076] The thus obtained pure magnesium plate material having a magnesium hydroxide-containing coating was immersed in a surface conditioner at 25 C. for 30 seconds to perform a surface conditioning treatment. It is noted here that the surface conditioner was prepared as follows.

[0077] In 55 parts by weight of deionized water, 1 part by weight of carboxymethyl cellulose was dissolved. To this solution, 24 parts by weight of monetite or brushite was added, and the resulting mixture was stirred and then wet-pulverized using a DYNO-MILL pulverizer (1-mm alkali glass beads). The particle size distribution of solids in the thus pulverized mixture (a suspension having a solid concentration of 30%) was measured using a MICROTRAC analyzer UPA-EX150 manufactured by Nikkiso Co., Ltd. to determine the values of D.sub.50 and D.sub.90. As a result, the D.sub.50 and the D.sub.90 were found to be 0.45 m and 0.9 m, respectively.

[0078] To the above-described suspension, sodium pyrophosphate and trisodium phosphate were added to final concentrations of 250 ppm and 200 ppm, respectively, whereby a surface conditioner was prepared.

<Chemical Conversion Treatment>

[0079] The pure magnesium plate material having a magnesium hydroxide-containing coating, which had been subjected to the above-described surface conditioning treatment, was immersed in a chemical conversion treatment agent at 50 C. for 5 minutes to perform a chemical conversion treatment. Subsequently, the thus treated pure magnesium plate material was washed with deionized water and dried with hot air, whereby a pure magnesium plate material having a dibasic calcium phosphate-containing coating formed on a magnesium hydroxide-containing coating was produced. It is noted here that the chemical conversion treatment agent was prepared as follows.

[0080] In deionized water, 75% phosphoric acid and calcium nitrate tetrahydrate were dissolved to final concentrations of 7 g/L and 12 g/L, respectively, and the pH of the resultant was adjusted to be 3.5 with sodium hydroxide, whereby a chemical conversion treatment agent was prepared.

<Apatite Conversion Treatment>

[0081] The thus obtained pure magnesium plate material having a magnesium hydroxide-containing coating and a dibasic calcium phosphate-containing coating was immersed in each aqueous alkaline solution at the respective treatment temperatures for the respective treatment times as shown in Table 2 to perform an alkali treatment. Subsequently, the thus alkali-treated pure magnesium plate material was washed with deionized water and dried with hot air, whereby a pure magnesium plate material with coating, in which dibasic calcium phosphate on the surface of the dibasic calcium phosphate-containing coating was partially or entirely substituted with hydroxyapatite and/or hydroxyapatite carbonate (pure magnesium plate material with coating which had a magnesium hydroxide-containing coating, dibasic calcium phosphate-containing coating, and a hydroxyapatite and/or hydroxyapatite carbonate-containing coating; each test piece of Examples 1 to 5) was produced.

TABLE-US-00002 TABLE 2 Aqueous alkaline solution Treatment Treatment Aqueous alkaline concentration temperature time Test piece solution (g/L) ( C.) (min) Example 1 sodium hydroxide 40 60 1 Example 2 sodium carbonate 50 80 5 Example 3 sodium carbonate 15 90 5 Example 4 potassium carbonate 100 80 5 Example 5 potassium hydroxide 50 60 1

[0082] As a Comparative Example, a pure magnesium plate material subjected to only the above-described pretreatment (test piece of Comparative Example 1) was prepared. In addition, a chemical conversion-treated pure magnesium plate material (test piece of Comparative Example 2) was prepared by immersing a pretreated pure magnesium plate material in a mixture, which was obtained by adjusting the pH of an aqueous solution containing 50 mM of Ca-EDTA and 50 mM of KH.sub.2PO.sub.4 to be 6.4 with an addition of a 1/40-amount of a 1 NNaOH aqueous solution, at 95 C. for 8 hours. Moreover, a chemical conversion-treated pure magnesium plate material (test piece of Comparative Example 3) was also prepared by immersing a pretreated pure magnesium plate material in a mixture, which was obtained by adjusting the pH of an aqueous solution containing 50 mM of Ca-EDTA and 50 mM of KH.sub.2PO.sub.4 to be 7.3 with an addition of a 1/20-amount of a 1N-NaOH aqueous solution, at 95 C. for 8 hours.

<Identification of Coating Crystal System>

[0083] The coatings formed on the surfaces of the test pieces of Examples 1 to 5 and Comparative Examples 1 to 3 were measured by an X-ray diffraction method, and the crystal systems thereof were identified. As a result, crystalline magnesium hydroxide and dibasic calcium phosphate crystals were detected from the test pieces of Examples 1 to 5. Hydroxyapatite crystals were detected from the test pieces of Examples 1 and 5, hydroxyapatite carbonate crystals were detected from the test pieces of Examples 2 and 4, and hydroxyapatite crystals and hydroxyapatite carbonate crystals were detected from the test piece of Example 3. In the test pieces of Examples 1 to 5, it was thus confirmed that a dibasic calcium phosphate-containing coating was formed on a magnesium hydroxide-containing coating, and a hydroxyapatite and/or hydroxyapatite carbonate-containing coating was formed on the dibasic calcium phosphate-containing coating. On the other hand, none of these crystals was detected from the test piece of Comparative Example 1, while crystalline magnesium hydroxide and hydroxyapatite crystals were detected from the test pieces of Comparative Examples 2 and 3.

<Evaluation of Corrosion Resistance>

[0084] The test pieces of Examples 1 to 5 and Comparative Examples 1 to 3 were immersed in an aqueous solution containing the ions shown in Table 3 at the respective concentrations, at 38 C. for 24 hours. Subsequently, the test pieces were washed with deionized water and dried with hot air, after which the test pieces were each irradiated with a light and the projected area was measured. Thereafter, the disappeared area was determined by comparing before and after the immersion treatment in the aqueous solution, and the corrosion resistance was evaluated based on the below-described criteria. The results thereof are shown in Table 4.

TABLE-US-00003 TABLE 3 Contained ion species Ion concentration (mol/L) Na.sup.+ ion 0.14 K.sup.+ ion 0.006 Ca2.sup.+ ion 0.0013 Mg2.sup.+ ion 0.0008 Cl ion 0.14 HCO.sub.3.sup.2 ion 0.004 HPO.sub.4.sup.2 ion 0.0008

(Evaluation Criteria)

[0085] 5: The disappeared area was 0.

[0086] 4: The disappeared area was smaller than 5%.

[0087] 3: The disappeared area was 5% or larger but smaller than 50%.

[0088] 2: The disappeared area was 50% or larger but smaller than 90%.

[0089] 1: The disappeared area was 90% or larger.

TABLE-US-00004 TABLE 4 Test piece Corrosion resistance Example 1 4 Example 2 5 Example 3 5 Example 4 4 Example 5 5 Comparative Example 1 1 Comparative Example 2 2 Comparative Example 3 3

[0090] The present invention has been described above in detail referring to concrete examples thereof; however, it is obvious to those skilled in the art that various modifications and changes can be made without departing from the gist and the scope of the present invention.