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Dehydrogenation Catalysts
Published in Alvin B. Stiles, Theodore A. Koch, Catalyst Manufacture, 2019
Alvin B. Stiles, Theodore A. Koch
Safety Note: Chromium trioxide is a toxic material, and inhalation of the fumes should be strictly avoided. Protective clothing must be used, and ventilation must be well designed. The dried extrudates or pellets are now calcined in equipment such as that shown in Figs. 22, 23, or 26 in air at a temperature of 500–700°C. This brings about some decomposition and some interaction between chromium oxide and aluminum oxide. At this point the catalyst is ready for use. It must first be reduced, but this is usually carried out in place as part of the start-up procedure.
Oxidation Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
The basic structure of chromium trioxide is CrO3, but this reagent is generally considered to be a polymer, (CrO3)n where n is a large number. Chromium trioxide is a Cr (VI) reagent. What species are present in solution when chromium trioxide is dissolved in water?
Electrodeposition: three steps towards sustainability
Published in Transactions of the IMF, 2020
A. Mulone, J. Hildenbrand, U. Klement
These compounds are included in the Annex XVII of the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulation (i.e. European ‘Restriction List’ that limits the import and the use of a compound under very strict rules) because it is highly carcinogenic. Among the compounds containing Cr6+, chromium trioxide, chromic and dichromic acids are also listed in the Annex XIV as substances that need authorisation. Authorisation periods are limited and can be also refused or reduced from the requested authorisation period. For example, in February 2019, for a group of companies led by Gerhardi Kunststofftechnik GmbH, the authorisation period to use chromium trioxide for the automotive industry has been reduced from 12 to 7 years.9 Such reduction is applied to incentivise the development of innovative substitutes for electrodeposited chromium.9
Spectrophotometric study of corrosion inhibition of aluminium in orthophosphoric acid aqueous solutions by using sodium molybdate
Published in Corrosion Engineering, Science and Technology, 2019
Marek Wojnicki, Przemysław Kwolek
Aluminium and its alloys are corrosion resistant in near neutral environment due to the presence of air formed oxide. Such air-formed film can be thickened significantly to form anodic film by anodising in acid solution, which further enhances their corrosion resistance or adhesion with paint. In some circumstance, the anodic film needs to be stripped for different applications. In this case, a mixed acid solution of orthophosphoric acid and chromium trioxide is used to strip the anodic film traditionally. Since aluminium is not corrosion resistant in acid solution, the presence of chromium trioxide in orthophosphoric acid ensures that the metallic substrate remains intact in the corrosive environment during stripping process. The mixed acid solution is commonly applied in industry for gravimetric determination of the weight of anodic coating [1]. The major drawback of this solution is its high toxicity and carcinogenicity due to the presence of Cr(VI) species [2]. Therefore, the efficient and non-toxic inhibitor of corrosion of aluminium and its alloys in the acidic solutions should be found.
A new orientation relationship between cementite and austenite and coexistence of pseudo-primary and secondary dislocations in the habit plane
Published in Philosophical Magazine, 2018
A high-purity Fe-1.29C-13.9Mn steel was produced by vacuum induction melting. The sample was solution treated at 1100 °C for 30 min and then quenched to room temperature to retain austenite. The sample was kept at 650, 700 and 750 °C for 10 min, 3 h and up to 3 days in the final heat treatment for the growth of cementite precipitates in the austenite matrix. The sample for EBSD measurement was prepared first by mechanical and vibratory polishing, and then electro-polished for 5 s to remove the contamination and residual strain on the surface. The TEM sample was prepared first by mechanical thinning and then the samples of 3 mm diameter discs were thinned in a Struers TenuPol-5 twin-jet electropolisher with applied parameters of 35 V and 52 mA at room temperature. The composition of the electrolyte for twin-jet polishing was composed of 120 g chromium trioxide, 750 ml glacial acetic acid and 50 ml distilled water [2]. The morphological and crystallographic information of the cementite precipitates was characterised by a Tecnai G2–20 TEM and a ZEISS Merlin SEM equipped with the EBSD module from Oxford.