Machinable Glass Ceramics - Chemical Durability and Resistance of Macor Machinable Glass Ceramics by Precision Ceramics

Precision Ceramics, a division of McGeoch Technology, is a company dedicated to the engineering of technical ceramics. From procurement and supply through to technical design and specialist machining, we offer a complete service.

Our reputation for quality and service is truly international with specialist ceramic components engineered by Precision Ceramics finding their way into an ever-widening array of worldwide applications in industries as diverse as aerospace, opto-electronics and nuclear power.

Precision Ceramics is a Macor Distributor. Precision Ceramics is a Macor Expert. In fact, there is no other Macor Supplier who knows more about this unique machinable glass ceramic than Precision Ceramics. We're also experts in Macor Metallization and publishers of the Macor Technical Bulletin.

Macor Machinable Glass Ceramic

Macor is an outstanding engineering material and is machinable with ordinary metalworking tools. Macor is also a problem solving material combining the performance of a technical ceramic with the versatility of a high performance plastic.

Macor has a high use temperature (800°C continuous to 1,000°C peak). It has a low thermal conductivity and is a useful high temperature insulator as well as an excellent electrical insulator. Macor has no porosity and when properly baked out, will not outgas. It is strong and rigid and, unlike high temperature plastics, will not creep or deform. Macor is also radiation resistant.

Macor is pure white and can be highly polished. It can be thick or thin film metallised, brazed and epoxy bonded. Another major advantage of this unique material is that, even in small quantities, components are economical to manufacture.

Chemical Durability of Macor Machinable Glass Ceramic

The chemical durability of fluorphlogopite (magnesia mica) glass (code 9658) was studied through the pH range from 0.1 to 13. The effects of time, temperature and pH were examined.

This study showed that Macor® machinable glass ceramic code 9658 glass ceramic has poor acid and alkali resistance relative to other Corning glass ceramics as demonstrated in the following comparison:

Table 1. Acid/alkali resistance of macor machinable glass ceramic

Acid/Alkali Resistance

Weight Loss (mg/cm2/day) at 95°C

Major Phase

Code

pH 0.1

pH 7

pH 13

Phlogopite
(Machinable)

9658

110

0.01

40

Cordierite
(Radomes)

9606

10

0.02

10

B-Spodumene
(Corning-ware)

9608

0.1

0.01

4

Chemical Durability Test on Macor Machinable Glass Ceramic

Poor acid and alkali durability are attributed to the poorly resistant borosilicate glassy phase. The glass was found to be ten times more acid leachable than the mica crystals. Throughout the entire pH range, the crystalline phase appeared to be stable against attack, while B2O3 was so readily leached from the glassy phase that the entire structure was more vulnerable to attack.

Table 2. Test results on the chemical durability of macor machinable glass ceramic

Test Results

Weight Loss (mg/cm2)

Solution

pH

Time

Temp

Calculated

Gravimetric

5%

0.1

24 hrs

95°C

149

110

0.002N HNO3

2.8

24 hrs

95°C

0.53

0.56

0.1N NaHCO3

8.4

24 hrs

95°C

0.36

0.32

0.02N Na2CO3

10.9

24 hrs

95°C

0.47

0.52

5% NaOH

13.2

6 hrs

95°C

11.2

12.0

Effect Over Time

pH

Time

Temp

Calculated

Gravimetric

0.002N HNO3

2.8

1 days

95°C

0.53

0.56

 

 

3 days

95°C

2.7

1.7

 

 

7 days

95°C

5.3

4.3

Effect of Temperature

pH

Time

Temp

Calculated

Gravimetric

0.002N HNO3

2.8

3 + Days

25°C

0.03

0.03

 

 

 

50°C

0.16

0.10

 

 

 

75°C

0.59

0.48

 

 

 

95°C

2.7

1.7

Resistance to Water Over Time

pH

Time

Temp

Calculated

Gravimetric

H2O

7.6

1 day *

95°C

0.02

0.01

 

 

3 days *

95°C

0.2

0.07

 

 

7 days *

95°C

11.6

9.4

 

 

3 days **

95°C

-

0.06

 

 

6 days **

95°C

-

0.11

 

This information has been sourced, reviewed and adapted from materials provided by Precision Ceramics.

For more information on this source, please visit Precision Ceramics.

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