Desiccants calcium oxide

Zinc oxide is a common activator in mbber formulations. It reacts during vulcanization with most accelerators to form the highly active zinc salt. A preceding reaction with stearic acid forms the hydrocarbon-soluble zinc stearate and Hberates water before the onset of cross-linking (6). In cures at atmospheric pressure, such as continuous extmsions, the prereacted zinc stearate can be used to avoid the evolution of water that would otherwise lead to undesirable porosity. In these appHcations, calcium oxide is also added as a desiccant to remove water from all sources. 

Calcium Oxide. Also called lime or quicklime (4,5), calcium oxide [1305-78-8] (Class 1, nonregenerative), is relatively iaexpensive. It is prepared by roasting calcium carbonate (limestone) and is available ia a soft and a hard form according to the way ia which it was burned. For desiccant service, soft-burned lime should always be used. Calcium oxide is most commonly used to dehydrate Hquids and is most efficient when it can be heated to speed the reaction rate. The reaction product is calcium hydroxide, which cmmbles as it picks up moisture. 

Desiccating agents used in corrosion prevention must be cheap, easy to handle and non-corrosive. These requirements rule out many of the familiar laboratory desiccants, and in practice the most common packaging desiccants are silica gel, activated alumina and quicklime (calcium oxide). Activated... 

Five common desiccant materials are used to adsorb water vapor montmorillonite clay ([(Na,Cao.5)o.33(Al,Mg)2Si40io(OH)2 H20], silica gel, molecular sieves (synthetic zeolite), calcium sulfate (CaS04), and calcium oxide (CaO). These desiccants remove water by a variety of physical and chemical methods adsorption, a process whereby a layer or layers of water molecules adhere to the surface of the desiccant capillary condensation, a procedure whereby the small pores of the desiccant become filled with water and chemical action, a procedure whereby the desiccant undergoes a chemical reaction with water. 

Thioureas mainly find use for the vulcanisation of CR, epichlorohydrin (ECO) and some ethylene propylene diene terpolymer (EPDM) compounds. They show high crosslinking activity, with usually adequate compound flow time before onset of the crosslinking. In EPDMs, the thioureas are used as activators for low activity third monomer types and, in the presence of calcium oxide desiccants, in free state vulcanisation of extrudates, etc. The use of thioureas can overcome the retardation caused by the desiccant. In this case some care must be taken otherwise overcompensation may occur. Thioureas are not used in food product applications and are a known health hazard, particularly for pregnant women. 

Lac sulfur 1s prepared by boiling a suspension of 33 g of calcium oxide and 50 g of sublimed sulfur (Fisher Scientific Company) in 200 mL of water for 30 min, then filtering the hot solution and acidifying the clear filtrate to pH 5 with hydrochloric acid. The precipitated sulfur is collected, washed with water, and dried in a vacuum desiccator. 

The use of these efficient reagents should usually be confined to the drying of amines (soda lime, barium oxide or calcium oxide may also be employed), potassium hydroxide is somewhat superior to the sodium compound. These bases react with many organic compounds (e.g. acids, phenols, esters and amides) in the presence of water, and with some common solvents (e.g. chloroform) so that their use as desiccants is very limited. 

Preparation of Fremy s salt a freshly prepared sodium bisulfite solution (100 ml) is added to a mixture of sodium nitrite (345 g) and ice (200 g) in a 1-1 beaker. On addition of 20 ml of glacial acetic acid, the reaction mixture turns black. Concentrated ammonium hydroxide (25 ml) is added and the mixture is cooled in an ice bath. A 0.2 M solution (400ml) of potassium permanganate is added dropwise over 1 h and the black precipitate which forms is immediately removed by filtration. A saturated solution of potassium chloride (250 ml) is added slowly over a 45-min period while the filtrate is gently stirred in an ice water bath. The precipitate that forms is collected by filtration and washed successively with a saturated solution of potassium chloride and methanol, each containing 5% of concentrated ammonium hydroxide and, finally, with acetone. Fremy s salt should be stored in a desiccator over calcium oxide. A small amount of ammonium carbonate in a desiccator is also very effective in protecting Fremy s salt against deeomposition. 

Special considerations calcium oxide is used as acid scavenger and desiccant zinc oxide is a curing agent in vulcanization processes calcium oxide and hydroxide are used as acid scavengers... 

Desical . [Harwick] Calcium oxide dis-pesions desiccants. 

Rhenosorb. [Rhein Chemie] Calcium oxide desiccant for seals, molded and extruded robber goods, conveyor belts. 

Table 2.5 lists some commonly used desiccants and then properties. Aluminum oxide, magnesium perchlorate, calcium oxide, calcium chloride, and silica gel can be regenerated by heating at 150, 240, 500, 275, and 150°C, respectively. 

A sample of (10)3804 H3O obtained from HIO3 nd H3SO4 (see above) is tested to see whether iodine separation takes place when it is shaken with a small amount of H3O. If any I3 separates, the substance is left in the desiccator for a little longer time if the test shows no iodine, the entire quantity is quickly washed several times with small amounts of water in a fritted glass suction filter until the wash water is free of sulfate. Suction is applied after each washing. The material is then washed with small amovints of absolute alcohol and then with absolute ether. The substance is dried at room temperature on a clay dish placed in a desiccator over calcium oxide. 

Silica, amorphous hydrated Strontium oxide Zeoiite Zeolite synthetic desiccant, extruded rubber Calcium oxide... 

Surfactant level varies from 10-15% in low-priced bars to 20-30% in premium bars. Where a combination of surfactants is used, as in the Philippines, typically a mixture of alcohol sulfate and LAS is used in a ratio of 50 50-85 15. Bars containing only AS as the surfactant are very brittle and need a high amount of humectants such as glycerine or addition of hydrotropes to reduce the brittleness. STPP/TSPP level ranges from 0-3% in low-priced bars to 15-30% in premium bars. The moisture level in the bars varies from 3 to 12%, carbonates typically from 10 to 25%, and fillers such as calcite, talc, and clay fill the rest of the formulation. Because the presence of free water in the bars can lead to mushiness during production or use, a variety of desiccants and adsorbent materials have also been added to bars to control the moisture. Examples include phosphorous pentoxide, sulfuric acid, boric acid, and calcium oxide as well as a variety of clays. 

Use of desiccant additives based on calcium oxide can have important cost-effective benefits in processing plastics and rubber, eliminating the need for... 

Handling, Storage, and Precautions in solid form, this reagent is rather unstable. It sometimes undergoes spontaneous decomposition which occasionally results in a violent explosion attributed to impurities such as chloride ion, manganese dioxide, or nitrite ion. Stored in a desiccator over calcium oxide in the presence of ammonium carbonate to provide an ammoniacal atmosphere, it is stable for several months. 

Cement contains calcium oxide which acts both as a desiccant and an alkaU. Injury results from the action of the hydroxyl ion, originated when calcium oxide is exposed to water, becoming calcium hydroxide. 

Good water resistance of polychloroprene vulcanisates relies on the absence of water-soluble components. Obvious ones such as calcium oxide desiccants and glycols may be omitted. However, water-soluble chlorides can be formed during vulcanisation. For this reason calcium carbonate fillers should always be avoided and magnesia/zinc oxide excluded from compounds needing maximum resistance. 

In all continuous processes vulcanisation is carried out at normal atmospheric pressure which gives rise to problems of porosity due to moisture and occluded air. The air in the compound is removed by applying vacuum to the barrel of the extruder which is always of the cold feed type. The moisture in the compound is controlled by adding calcium oxide (6-10 phr) as a desiccant. 

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