Ceramic, digestion

S. L. Swart2, "Topics iu Electronic Ceramics," IEEE Trans. Elect. Insul Digest on Dielectrics 25, 935—987 (Oct. 1990). 

Digestion of clay samples with perchloric acid led to 3 explosions, each of which destroyed a ceramic hotplate used as heat source. There seems a good case for using metal hotplates for reactions involving risk of explosion. 

Open vessel digestion (HF HC104) for ceramics, glass, rocks, and soil These acids should completely dissolve most materials. HF removes the silica (as volatile SiF4), which reduces the total dissolved solid content and therefore reduces interferences, and C104 produces perchlorates, which are soluble (but explosive if dried out). The use of hydrofluoric and perchloric acids therefore has considerable safety risks and requires specialized fume hoods, handling equipment, and safety equipment. The hydrofluoric and perchloric acids are removed by a later evaporation stage unless the analytical instmment and safety considerations have been specially adapted. 

Bismuth subcarbonate [(BiOl CO ] is used to make other bismuth compounds, cosmetics, enamel, and ceramic glazes. Its major use is as an opaque substance placed in the digestive tract to show up on X-rays. The bismuth blocks X-rays, and thus the physician can see patterns inside the stomach and intestines. 

Iron(III) oxide or alumina is refined from bauxite. Approximately 175 million tons of bauxite are mined annually worldwide, with virtually all of this processed into alumina. Alumina is a white crystalline substance that resembles salt. Approximately 90% of all alumina is used for making aluminum, with the remainder used for abrasives and ceramics. Alumina is produced from bauxite using the Bayer process patented in 1887 by Austrian Karl Josef Bayer (1847-1904). The Bayer process begins by grinding the bauxite and mixing it with sodium hydroxide in a digester. The sodium hydroxide dissolves aluminum oxide components to produce aluminum hydroxide compounds. For gibbsite, the reaction is Al(OH)3 + NaOH —> Al(OH)4 + Na+. Insoluble impurities such as silicates, titanium oxides, and iron oxides are removed from the solution while sodium hydroxide is recovered and recycled. Reaction conditions are then... 

Inductively coupled plasma-mass spectrometry (ICP-MS) has seen increasing use in trace element studies of ceramics in the last two decades. While early work using weak acid extraction proved problematic (/), recent work by Kennet et al. using microwave digestion (2) and by Larson et al. using laser ablation (3) have yielded considerable advances in the application of this technique. 

Inductively coupled plasma-mass spectrometry (ICP-MS) has been utilized as a bulk technique for the analysis of obsidian, chert and ceramic compositional analyses 12-14). However, due to the high level of spatial variation of ceramic materials, increased sample preparation is necessary with volatile acids coupled with microwave digestion (MD-ICP-MS) to properly represent the variability of ceramic assemblages IS, 16). Due to the increased sample preparation and exposure to volatile chemicals, researchers have continued to utilize neutron activation analysis (INAA) as the preferred method of chemical characterization of archaeological ceramics (77). 

Typically, these will be alloys, rocks, fertilisers, ceramics, etc. These materials are taken into solution using suitable aqueous/acid media, according to solubility hot water, dilute acid, acid mixtures, concentrated acids, prolonged acid digestion using hydrofluoric acid if necessary, alkali fusion (e.g. using lithium metaborate), Teflon bomb dissolution. Fusion and bomb methods are usually reserved for complex siliceous materials, traditionally reluctant to yield to solubilisation. 

Microwave-assisted digestion has been applied to other types of samples such as ceramics [198,199], air particulate matter [200-202], polymers [203,204], lithographic materials [205], coal and ash [206], among others. As with the previous samples, the main purpose was the determination of their metal contents. The results provided by microwave-assisted digestion are similar to those obtained with conventional methods. 

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