Site search References Helander, Herbert F. Scand J Gastroenterol Arch Biochem Biophys
Zinc oxide can be called a multifunctional material thanks to its unique physical and chemical properties. The first part of this paper presents the most important methods of preparation of ZnO divided into metallurgical and chemical methods.
The mechanochemical process, controlled precipitation, sol-gel method, solvothermal and hydrothermal method, method using emulsion and microemulsion enviroment and other methods of obtaining zinc oxide were classified as chemical methods. In the next part of this review, the modification methods of ZnO were characterized.
The modification with organic carboxylic acid, silanes and inroganic metal oxides compounds, and polymer matrices were mainly described.
Finally, we present possible applications in various branches of industry: This review provides useful information for specialist dealings with zinc oxide.
Introduction Zinc oxide, with its unique physical and chemical properties, such as high chemical stability, high electrochemical coupling coefficient, broad range of radiation absorption and high photostability, is a multifunctional material [ 12 ].
In materials science, zinc oxide is classified as a semiconductor in group II-VI, whose covalence is on the boundary between ionic and covalent semiconductors.
A broad energy band 3. The piezo- and pyroelectric properties of ZnO mean that it can be used as a sensor, converter, energy generator and photocatalyst in hydrogen production [ Chem 202 notes6 ]. Because of its hardness, rigidity and piezoelectric constant it is an important material in the ceramics industry, while its low toxicity, biocompatibility and biodegradability make it a material of interest for biomedicine and in pro-ecological systems [ 7 — 9 ].
The variety of structures of nanometric zinc oxide means that ZnO can be classified among new materials with potential applications in many fields of nanotechnology.
Zinc oxide can occur in one- 1Dtwo- 2Dand three-dimensional 3D structures. One-dimensional structures make up the largest group, including nanorods [ 10 — 12 ], -needles [ 13 ], -helixes, -springs and -rings [ 14 ], -ribbons [ 15 ], -tubes [ 16 — 18 ] -belts [ 19 ], -wires [ 20 — 22 ] and -combs [ 23 ].
Examples of 3D structures of zinc oxide include flower, dandelion, snowflakes, coniferous urchin-like, etc. ZnO provides one of the greatest assortments of varied particle structures among all known materials see Figure 1.
In this review, the methods of synthesis, modification and application of zinc oxide will be discussed. The zinc oxide occurs in a very rich variety of structures and offers a wide range of properties. The variety of methods for ZnO production, such as vapour deposition, precipitation in water solution, hydrothermal synthesis, the sol-gel process, precipitation from microemulsions and mechanochemical processes, makes it possible to obtain products with particles differing in shape, size and spatial structure.
These methods are described in detail in the following sections Table 1. Metallurgical Process Metallurgical processes for obtaining zinc oxide are based on the roasting of zinc ore.
According to the ISO standard [ 68 ], zinc oxide is classified either as type A, obtained by a direct process the American process ; or type B, obtained by an indirect process the French process.
The direct American process involves the reduction of zinc ore by heating with coal such as anthracitefollowed by the oxidation of zinc vapour in the same reactor, in a single production cycle. This process was developed by Samuel Wetherill, and takes place in a furnace in which the first layer consists of a coal bed, lit by the heat remaining from the previous charge.
Above this bed is a second layer in the form of zinc ore mixed with coal. Blast air is fed in from below, so as to deliver heat to both layers and to carry carbon monoxide for zinc reduction. The resulting zinc oxide of type A contains impurities in the form of compounds of other metals from the zinc ore.
The resulting ZnO particles are mainly needle-shaped, and sometimes spheroidal. To obtain a product with a permanent white color, the oxides of lead, iron and cadmium that are present are converted to sulfates.
Increasing the permanence of the color is linked to increasing the content of water-soluble substances, and also increasing the acidity of the product. Acidity is desirable in the case of rubber processing technology, since it lengthens prevulcanization time and ensures the safe processing of the mixtures [ 69 ].
In the indirect French process, metallic zinc is melted in a furnace and vaporized at ca. The immediate reaction of the zinc vapour with oxygen from the air produces ZnO.
The particles of zinc oxide are transported via a cooling duct and are collected at a bag filter station. The indirect process was popularized by LeClaire inand since then has been known as the French process.
The product consists of agglomerates with an average particle size ranging from 0. The ZnO particles are mainly of spheroidal shape. The French process is carried out in vertical furnaces, with an original vertical charge, vertical refining column, vaporizer with electric arc, and rotary combustion chamber [ 71 ].
Type B zinc oxide has a higher degree of purity than type A. Chemical Processes Because of its interesting properties, zinc oxide has been the subject of study by many researchers.
This has led to the development of a great variety of techniques for synthesizing the compound. Unfortunately, methods that work in the laboratory cannot always be applied on an industrial scale, where it is important for the process to be economically effective, high yielding and simple to implement.
Mechanochemical Process The mechanochemical process is a cheap and simple method of obtaining nanoparticles on a large scale. It involves high-energy dry milling, which initiates a reaction through ball—powder impacts in a ball mill, at low temperature.CHEM introduces the students to the fundamental principles of organic chemistry including relationships between the molecular structure of organic compounds and their macroscopic properties.
Some of the principles are illustrated with a variety of examples from nature and everyday life. A period 2 element is one of the chemical elements in the second row (or period) of the periodic table of the chemical initiativeblog.com periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases; a new row is started when chemical behavior begins to repeat, creating columns of elements with similar properties.
Laser Physics Letters is an international journal publishing Letters dealing with the fundamental and applied aspects of laser science. Published by IOP Publishing on behalf of Astro Ltd.
Submit an article.
Download the best CHEM class notes at University of Louisville to get exam ready in less time! The mechanochemical method was proposed by Ao et al. , they synthesized ZnO with an average crystallite size of 21 initiativeblog.com milling process was carried out for 6 h, producing ZnCO 3 as the zinc oxide precursor.
Calcination of the precursor at °C produced ZnO with a hexagonal structure. View crowdsourced SDSU CHEM General Chemistry course notes and homework resources to help with your San Diego State CHEM General Chemistry courses.