Unit 12 Conduction in Liquids and Gases

Transcription

1 Conduction in Liquids and Gases

2 Objectives: Define positive and negative ions. Discuss electrical conduction in gases. Discuss electrical conduction in a liquid. Discuss several of the ionization processes.

3 Ions An ion is a charged atom. Positive ions have a deficiency of electrons. Negative ions have extra electrons.

4 Conduction in Liquids An electrolyte is a solution that will conduct electricity. An electrolytic solution may be created from distilled water by adding salt. A wide range of electrolytes can be created from acids, alkalies, and metallic salts.

5 Conduction in a liquid.

6 Electrolysis Electrolysis is the process of separating elements electrically.

7 Electroplating Electroplating uses electricity to deposit atoms of one type of metal onto a different metallic surface. DC current is passed from a power source, through an electrode immersed in an electrolyte, to the object to be plated and back to the power source.

8 Electroplating Factors 1. The electrolyte solution must contain ions of the metal to be plated. 2. Metal ions are always positively charged. 3. The plated object must be connected to the negative power terminal. 4. Direct current is used as the power source. 5. The positive electrode is the same metal as the new coating of the plated object.

9 The electroplating process.

10 Conduction in Gases Conduction in gases occurs when an arc is established across a gap between two electrodes. The initial voltage required to start the arc is very high. A reduced amount of voltage is required to sustain an arc.

11 Conduction in Gases Current flow across the gap is aided by an ion trail caused by ionized gas. An arc welder is an example of a practical application.

12 Ionization in Gases Ionization potential is the amount of voltage, or potential, an electron must possess to cause ionization. Conduction in a gas occurs as a result of electron impact from molecule to molecule. The pressure of the ionized gas affects the required ion potential for current flow.

13 Electron impact frees electrons from gas molecules.

14 Please insert Figure Electron impact under high gas pressure.

15 Electron impact under low gas pressure.

16 The cathode ray tube is another application for conduction in gases.

17 Review: 1. An electrolyte is a solution that will conduct electricity. 2. An electrolytic solution may be created from distilled water by adding salt. 3. Solutions of acids, alkalies, and metallic salts are referred to as electrolytes.

18 Review: 4. Electroplating is the process of depositing the atoms of one type of metal onto another. 5. Electroplating uses electricity to deposit atoms from one metal onto a different metallic surface. 6. DC current passes from a power source, through an electrolyte, to the object to be plated, and back to the power source.

19 Review: 7. Factors affecting electroplating of metals: a. The electrolyte solution must contain ions of the plating metal. b. Metal ions are always positively charged. c. The object to be plated must be connected to the negative power terminal. d. The power source is direct current. e. The positive terminal and the coating must be of the same metal.

20 Review: 8. The term electrolysis refers to the process of separating elements electrically. 9. Conduction through a gas depends on the ionization of gas molecules. 10. The amount of voltage required to cause ionization of a gas is called the ionization potential.

21 Review: 12. Gas can be ionized more easily when it is at a low pressure than when it is at a high pressure. 13. The ionization potential is different for different gasses. 14. The most important factor in the ionization of a gas is electron impact.