Lecture 3: Ceramics

Question 1

1. Cite some elements (no less than 3) that you would expect to be present in ceramics and explain why based on the properties of the periodic table.

Answer 1

A ceramic is a non-metallic solid material comprising an inorganic compound of metal, non-metal or metalloid atoms primarily held in ionic and covalent bonds.

Na⁺, Ca²⁺,Mg²⁺,F^-,O^2-,…

As they are on the far ends of the periodic table they are more likely to form ionic bonds.

Question 2

What are a crystal lattice, unit cell, and crystal planes? Is the distribution of elements in the crystal lattice relevant for the properties of that compound? Give at least one example.

Answer 2

A crystal lattice is the arrangement of these atoms, or groups of atoms, in a crystal.

The unit cell is defined as the smallest repeating unit having the full symmetry of the crystal structure.

Crystal planes are defined as some imaginary planes inside a crystal in which large concentration of atoms are present.

Diamond has a crystal structure of carbon bonds in 6 directions, which causes it to be very rigid and strong.

Graphite has a structure of planes of atoms which can slide over eachother, which is why it is very soft.

Question 3

3. How are the elements distributed in a glass crystal? What would you expect an x-ray diffractogram acquired from glass to look like?

Question 4

4. On the ternary diagram below, chose one point and give the composition of that point.

Answer 4

The first method is an estimation based upon the phase diagram grid. The concentration of each species is 100% (pure phase) in each corner of the triangle and 0% at the line opposite it. The percentage of a specific species decreases linearly with increasing distance from this corner, as seen in figures 3–8. By drawing parallel lines at regular intervals between the zero line and the corner (as seen in the images), fine divisions can be established for easy estimation of the content of a species. For a given point, the fraction of each of the three materials in the composition can be determined by the first.

Question 5

5. On the ternary diagram below, identify the concentration of the elements that will not give a yellow (or yellowish) colour.

Answer 5

40% < conc_copper

30% > conc_gold > 95%

4% > conc_silver > 60%

Question 6

6. Explain what a colloid is and give an example.

Answer 6

State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm, or that in a system discontinuities are found at distances of that order.

An example is a solution such as milk.

Question 7

7. What might the ζ-potential tell you about the particles in a solution?

Answer 7

Zeta potential is a scientific term for electrokineticpotential in colloidaldispersions.

Question 8

8. Is it possible to have ζ-potential in any kind of solution? And how about surface charge on the particle?

Answer 8

Only colloidal solutions.

Diagram showing the ionic concentration and potential difference as a function of distance from the charged surface of a particle suspended in a dispersion medium. The zeta potential can be seen on the slipping plane.

Question 9

9. Given the plot below, what is the best pH to have sedimentation in the suspension of both particles? And the worst? How you would modify the alumina surface to obtain a better suspension with the rutile?

Answer 9

6.2 - the best

11 - the worst

Question 10

10. To make a ceramic, what would be the characteristics that you would choose for your material to obtain the best amount of material in the suspension?

Answer 10

large difference in zeta potential? viscous glaze?

Question 11

11. How many phases of calcium phosphate exist are and what would be the main differences between them of relevance for implants?

Answer 11

-

Question 12

12. Why do some of the calcium phosphates dissolve in acid solutions and others in basic solutions?

Answer 12

some contain anions and some contain cations.

Question 13

13. Why would you expect a good affinity of calcium phosphates with proteins and amino acids and why are calcium phosphates used to decontaminate soils from heavy metals?

Answer 13

calcium phosphate can take in anions and cations and neutralise them.

Question 14

14. Why are calcium phosphates used in implants? What kind of implants?

Answer 14

osteointegration implants. because they can attract proteins and other molecules and induce bone growth.

Question 15

What are the most typical ceramics in biomaterials?

Answer 15

Alumina

Zirconia

Calcium phosphate

Bioactive glasses

Silicates