Problem 88 - Chemistry: The Central Science in SI Units, Global Edition

Question

Ultrapure germanium, like silicon, is used in semiconductors. Germanium of "ordinary" purity is prepared by the high-temperature reduction of \(\mathrm{GeO}_{2}\) with carbon. The Ge is converted to \(\mathrm{GeCl}_{4}\) by treatment with \(\mathrm{Cl}_{2}\) and then purified by distillation; \(\mathrm{GeCl}_{4}\) is then hydrolyzed in water to \(\mathrm{GeO}_{2}\) and reduced to the elemental form with \(\mathrm{H}_{2}\). The element is then zone refined. Write a balanced chemical equation for each of the chemical transformations in the course of forming ultrapure Ge from \(\mathrm{GeO}_{2}\).

Step-by-Step Solution

Answer

The balanced chemical equations for the chemical transformations in the course of forming ultrapure Ge from GeO₂ are: 1. \( GeO_{2}(s) + C(s) \rightarrow Ge(s) + CO(g) \) 2. \( Ge(s) + 2Cl_{2}(g) \rightarrow GeCl_{4}(g) \) 3. \( GeCl_{4}(g) + 2H_{2}O(l) \rightarrow GeO_{2}(s) + 4HCl(aq) \) 4. \( GeO_{2}(s) + H_{2}(g) \rightarrow Ge(s) + H_{2}O(g) \)

Step 1: Reduction of GeO₂ with Carbon

In this step, germanium dioxide (GeO₂) reacts with carbon (C) to produce germanium (Ge) and carbon monoxide (CO). The balanced chemical equation for this reaction is: \[ GeO_{2}(s) + C(s) \rightarrow Ge(s) + CO(g) \]

Step 2: Conversion of Ge to GeCl₄ using Chlorine

In this step, germanium (Ge) reacts with chlorine gas (Cl₂) to produce germanium tetrachloride (GeCl₄). The balanced chemical equation for this reaction is: \[ Ge(s) + 2Cl_{2}(g) \rightarrow GeCl_{4}(g) \]

Step 4: Hydrolysis of GeCl₄ in Water and Reduction with Hydrogen

This step can be broken down into two substeps: Substep 4.1: Hydrolysis of GeCl₄ in water In this substep, germanium tetrachloride (GeCl₄) reacts with water (H₂O) to produce germanium dioxide (GeO₂) and hydrochloric acid (HCl). The balanced chemical equation for this reaction is: \[ GeCl_{4}(g) + 2H_{2}O(l) \rightarrow GeO_{2}(s) + 4HCl(aq) \] Substep 4.2: Reduction of GeO₂ with Hydrogen In this substep, germanium dioxide (GeO₂) reacts with hydrogen gas (H₂) to produce germanium (Ge) and water (H₂O). The balanced chemical equation for this reaction is: \[ GeO_{2}(s) + H_{2}(g) \rightarrow Ge(s) + H_{2}O(g) \] So, the balanced chemical equations for the chemical transformations in the course of forming ultrapure Ge from GeO₂ are as follows: 1. \( GeO_{2}(s) + C(s) \rightarrow Ge(s) + CO(g) \) 2. \( Ge(s) + 2Cl_{2}(g) \rightarrow GeCl_{4}(g) \) 3. \( GeCl_{4}(g) + 2H_{2}O(l) \rightarrow GeO_{2}(s) + 4HCl(aq) \) 4. \( GeO_{2}(s) + H_{2}(g) \rightarrow Ge(s) + H_{2}O(g) \)

Key Concepts

Germanium Purification

Producing ultrapure germanium (Ge) for semiconductor manufacturing involves several stages of purification. Each of these stages is crucial to remove impurities and produce high-quality germanium. The process starts with germanium dioxide (\( \text{GeO}_{2} \)), a common germanium compound. Germanium dioxide is combined with carbon in a high-temperature reduction process. This step yields germanium and carbon monoxide, setting the stage for further purification.

The germanium obtained is then transformed into germanium tetrachloride (\( \text{GeCl}_{4} \)) by introducing chlorine gas. Germanium tetrachloride is favored due to its volatility, which allows it to be purified through distillation. Once purified, it's hydrolyzed back to germanium dioxide and then reduced with hydrogen gas, finally leading to the desired pure elemental germanium. This multi-step process ensures the removal of contaminants, making germanium suitable for use in advanced electronic components.

Chemical Equations

Chemical equations succinctly illustrate the transformations that substances undergo in chemical reactions. Each step in the germanium purification process is defined by a specific equation that balances atoms and charge.

• The equation \( \text{GeO}_{2}(s) + \text{C}(s) \rightarrow \text{Ge}(s) + \text{CO}(g) \) describes the initial reduction of germanium dioxide with carbon.
• Next, \( \text{Ge}(s) + 2\text{Cl}_{2}(g) \rightarrow \text{GeCl}_{4}(g) \) represents the conversion of elemental germanium into germanium tetrachloride using chlorine.
• This is followed by hydrolysis: \( \text{GeCl}_{4}(g) + 2\text{H}_{2}\text{O}(l) \rightarrow \text{GeO}_{2}(s) + 4\text{HCl}(aq) \).
• Finally, \( \text{GeO}_{2}(s) + \text{H}_{2}(g) \rightarrow \text{Ge}(s) + \text{H}_{2}\text{O}(g) \) captures the reduction of germanium dioxide with hydrogen.

Each equation reflects conservation of mass and elements, crucial for understanding the sequence of reactions in this purification process.

Zone Refining

Zone refining is a unique purification technique essential for achieving ultrapure germanium. This method harnesses the principle of melting and solidification to effectively segregate impurities.

In zone refining, a narrow region of the germanium rod is heated to create a molten zone. As this molten zone is slowly moved along the length of the rod, the impurities preferentially remain in the molten part. As the pure germanium recrystallizes from the trailing edge of the molten zone, impurities are pushed toward one end of the rod. Repeatedly passing the molten zone across the rod results in highly purified germanium.

This technique is indispensable in semiconductor manufacturing, as even trace impurities can significantly affect electronic properties. Zone refining transforms germanium into an ideal material with exceptional purity for electronic applications.

High-Temperature Reduction

High-temperature reduction is the critical initial step in germanium purification, where germanium dioxide (\( \text{GeO}_{2} \)) is reduced to elemental germanium (\( \text{Ge} \)) using carbon as the reducing agent. This process occurs at elevated temperatures, essential for achieving adequate reaction completion and efficiency.

Within this high-temperature environment, carbon removes oxygen from \( \text{GeO}_{2} \), converting it to carbon monoxide (\( \text{CO} \)) and producing pure, elemental germanium. Such reduction is vital because it lays the foundation for subsequent processing steps by ensuring the initial removal of oxygen, one of the main impurities.

Elemental germanium obtained from this process can then be further refined and processed into the ultrapure form needed for semiconductor applications. Understanding this high-temperature reduction is fundamental to grasping how elemental germanium is initially prepared before entering further purification phases.