French process

The zinc is boiled, and the resulting vapor is oxidized by combustion in air under defined conditions. The crystallographic and physical properties of the ZnO can be controlled by adjustment of the combustion conditions (e.g., flame turbulence and air excess). The chemical composition of the ZnO is solely a function of the composition of the zinc vapor. 

Muffle Furnaces or Retorts of Graphite or Silicon Carbide. The metal is fed into the furnace either batchwise as a solid or continuously as a liquid. The heat of vaporization is supplied by heating the outside of the retort with a burner. In a muffle furnace the vaporizing section is separated by a silicon carbide arch from the heating chamber. The heat from burning gas or oil in the heating chamber is transferred to the zinc bath from the arch by radiation. 

The nonvolatile residues (iron, lead and aluminum in the case of dross from smelting and casting) accumulate in the retort or in the muffle furnace and must be removed at intervals. This is facilitated by tipping the retorts. 

Fractional Distillation. The vapor, containing Cd, Pb, Fe, Al, and Cu, can be purified by fractional distillation in columns (New Jersey Zinc Co.) with silicon carbide plates. Oxidation takes place at the exit of the column. 

Furnaces with Two Separate Chambers. The metallic raw material, which can be in large pieces, is fed into the first chamber where it melts. This is connected to the second, electrically heated chamber where distillation takes place in the 

---

Historically, ZnO is an older pigment than Ti02. In France, the industrial production of zinc oxide started in 1840. In the French process, zinc... 

Indirect (French) Process. Ziac metal vapor for burning is produced ia several ways, one of which iavolves horizontal retorts. Siace all the vapor is burned ia a combustion chamber, the purity of the oxide depends on that of the ziac feed. Oxide of the highest purity requires special high grade ziac and less-pure products are made by blending ia Prime Western and even scrap ziac. 

Zinc oxide is made either by the oxidation of the metal in oxygen (the indirect, IP, or French process), by the direct decomposition of zinc ores in air (the direct or American process) or by the thermal decomposition of zinc salts (TD zinc oxide). IP zinc oxides differ from TD zinc oxides in that their surfaces do not contain absorbed water. Also, whereas TD zinc oxide reacts with plain eugenol, IP zinc oxide hardly reacts unless activated by an acetic add or zinc acetate accelerator (Table 9.2). 

French process material, in general, tends to have a blockier particle shape with a relatively narrow particle size range in comparison with the American process product. The French process oxides also exhibit a finer particle size and hence have a higher surface area. 

French Also known as the Indirect process. A process for making zinc oxide, in the form of a white pigment, from metallic zinc. The zinc is melted and vaporized in a current of carbon monoxide. The vapor is oxidized with air in a second chamber, forming zinc oxide and carbon dioxide. The fume passes through a settling chamber, where oversized particles settle out, and from there go to a bag house, where the product is collected. Confusingly, the French process has been operated by North American Oxide Company, at Clarksville, TN. See also American. 

Indirect An alternative name for the French process for making zinc oxide. 

PIVER A French process for vitrifying nuclear waste. 

A French process proposes the fermentation of wood sugars for the production of butyric and acetic acids that may be converted into... 

Zinc oxide is obtained as an intermediate in recovering zinc from minerals (See Zinc, Recovery). The oxide is prepared by vaporizing zinc metal and oxidation of the zinc vapors with preheated air (French process). The oxide can be produced by other processes. Another method involves roasting franklinite and other ores with coal and then oxidizing the product in air. 

Zinc oxide [1314-33-2], ZnO, Mr 81.38, was formerly used only as a white pigment, and was named zinc white (C.I. Pigment White 4), Chinese white, or flowers of zinc. The term zinc white now denotes zinc oxide produced by the combustion of zinc metal according to the indirect or French process. 

In the indirect French process, metallurgically refined zinc metal is boiled and the generated vapors combust with air to form zinc oxide. Metallic zinc is the starting material of this latter process, making it more expensive than the American one. The French process is the preferred production method, however, because it yields a purer product. Volatile metals, such as lead and cadmium, are again the main impurities that can be found in zinc white. Complex purification methods, such as fractional distillation, have been devised to reduce the amount of these impurities to acceptable levels. 

PI VER [Pllote VErre] An early French process for vitrifying nuclear waste. It was a batch process, used between 1969 and 1973 and then from 1979, until it was decommissioned in 1990. Superseded by the continuous AVH and AVM processes. 

ZnO powder is produced from the combustion of vapors coming from the distillation of metallic zinc according to the so-called French process or dry process. Using vapors coming from fractionated distillation, extra-pure oxide powders are produced, as illustrated from the chemical analysis data of two kinds of powder produced by two different companies ... 

The term zinc white now denotes zinc oxide produced by the combustion of zinc metal according to the indirect or French process. 

In the mid-18th century, the German chemist Cramer discovered that cadmia could be obtained by the combustion of metallic zinc. Courtois began to produce zinc white in 1781 in France, but it was not until 1840 that industrial production was started by Leclaire (indirect or French process). The use of this white pigment spread rapidly. 

R. P. Pavlik, Latest Developments of French Process Equipment, presented at AOCS meeting, 1992, Toronto, Canada. 

In the manufacture of zinc white by the French process, metallic zinc is melted, evaporated and oxidized in the vapor state to zinc oxide with air. If the starting material is insufficiently pure, the zinc has to be purified by evaporation and condensation prior to the oxidation step. The size and shape of the zinc oxide crystals can be controlled by the oxidation conditions. After combustion the ZnO is precipitated from the ZnO/air mixture in settling chambers, in which classification of the zinc oxide particles takes place according to their size. 

The raw materials for the manufacture of zinc oxide by the American process are roasted ores, concentrates of zinc ores or more recently zinc hydroxide or zinc carbonate from the processing of scrap. These are reduced with coal and directly reoxidized to ZnO in the same reaction chamber. The purity of the zinc oxide is normally somewhat inferior to that from the French process. Grades of various purities can be produced by fractionation. 

Derivation (1) Oxidation of vaporized pure zinc (French process), (2) roasting of zinc oxide ore (franklinite) with coal and subsequent oxidation with air, (3) similar treatment starting with other ores, (4) oxidation of vapor-fractionated die castings. 

Grade American process, lead-free French process lead-free green seal red seal white seal (according to fineness) leaded (white lead sulfate) USP single crystals. 

---