Henry Louis Le Châtelier Biography (1850-1936)


Henry Louis Le Châtelier grew up in a family steeped in scientific andtechnological traditions. Young Henry's relatives and close family friends included engineers and scientists involved in lime and cement production, railway construction, mining, and aluminum and steel manufacturing. France's leading chemists often visited the Le Châtelier home, and all of the Le Châtelier children pursued science-related careers. In later life, Le Châtelier said that his family had strongly influenced his research pursuits.

After interrupting his studies to serve as an army lieutenant in the Franco-Prussian War of 1870-71, Le Châtelier returned to college at the École Polytechnique and earned a degree in science and engineering in 1875. Two years later, he became a chemistry professor at the École des Mines, where he began research on cements, ceramics, and glass. Some of his experiments with cements required the measurement of very high temperatures, for which the equipment available at the time was inadequate.

Le Châtelier invented a thermocouple that gave more accurate, reproducible results when measuring high temperatures. Thermocouples consist of two metal wires, of differing composition, welded together. When the junction is heated, an electric current is created, and the temperature at the junction ofthe thermocouple is computed by analyzing the difference in voltage between the two wires. Le Châtelier's thermocouple used one platinum wire and one platinum-rhodium alloy wire. He also introduced the use of known boiling and melting points as standards for calibrating thermocouples. Around the sametime, Le Châtelier developed an optical pyrometer. These devices measure temperature by comparing the light emitted from hot objects against a knownstandard. Although other methods have replaced the pyrometer, Le Châtelier's equipment was useful at the time, and scientists continue to employ thermocouples in high-temperature research.

In the early 1880s, a series of mining disasters spurred the French government to investigate their cause and prevention. As an École des Mines professor, Le Châtelier took part in research on gas explosions. This workinvolved studying the ignition temperature, flame speed, and other conditions affecting explosions of methane, carbon monoxide, and hydrogen mixtures. LeChâtelier's results, applied to acetylene combustion, enabled other chemists to develop the oxyacetylene welder now used for cutting and welding steel. During this period, Le Châtelier also assisted in the developmentof safer explosives and improved the miner's safety lamp, which had been invented in the early 1800s by Humphry Davy.

Le Châtelier pursued further applications through his investigation ofchemical reactions occurring in blast furnaces, which are used to manufacturesteel. Engineers could not determine why carbon monoxide was present in theexhaust gases because, they believed, the compound should have reacted with iron oxides in the furnace to produce carbon dioxide. Le Châtelier realized that the iron oxides were catalyzing the reverse reaction, which createdcarbon monoxide. By clearing up this confusion, Le Châtelier enabled industrial engineers to develop blast furnaces that could reach higher temperatures by preheating the combustion air with hot exhaust gases.

Le Châtelier's scientific experience culminated in the discovery for which he is best known today-- Le Châtelier's principle. Announced in 1884, the principle states that when a system is in equilibrium and one of the factors affecting it is changed, the system will respond by minimizing the effect of the change. Essentially, the principle predicts the direction that a chemical reaction will take when pressure, temperature, or any other conditionis altered. Using Le Châtelier's principle, scientists were able to maximize the efficiency of chemical processes. For example, Fritz Habermade use of the principle to develop a practical process for ammonia synthesis using nitrogen and hydrogen. Le Châtelier himself had tried this, butgave up when his gas mixture exploded.

For the rest of his career, Le Châtelier continued teaching. In addition to his position at the École des Mines, he held posts at the Collegede France and at the Sorbonne. After working for the French government during World War I, he retired from the École des Mines in 1919 at age 69.

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