Vapour curing

S2C12, a by-product in the manufacture of carbon tetrachloride from carbon disulphide. Was used, dissolved in solvent naphtha, in the vulcanising of mbber by the cold cure process and the vapour cure process. The process was fraught with health and safety problems and has been superseded by low temperature accelerators and room temperature vulcanising (RTV) systems for silicone and polyurethane. 

The principle of keeping the paint stable by having one reactant outside the can is quite general. Chemicals not normally in the air can be introduced into air in a confined drying chamber. This technique is used in the vapour curing of isocyanate paints (Chapter 15). 

Vapour curing has been shown to work successfully in small industrial painting installations and has potential benefits on metal castings, which absorb heat intended for curing, and on some plastic substrates (e.g. 

Furthermore, there are significant variations in the properties of fly ash due to different conditions of combustion temperature, duration, kinds of fuel and the type of fluidal boiler. The pozzolanic activity of fly ash may be increased by different processing heat (autoclaving with vapour cure), chemical (adding alkalies) or mechanical (grinding) (Fu et al. 2008). 

Organic materials Corrosive vapours are sometimes emitted by organic materials used either in packaging or in the manufactured article, and may be troublesome in confined spaces. Some woods, particularly unseasoned oak and sweet chestnut, produce acetic acid (see Section 18.10), and certain polymers used in paints, adhesives and plastics may liberate such corrosive vapours as formic acid and hydrogen sulphide . It may be necessary to carry out exposure trials, particularly where materials capable of liberating formaldehyde or formic acid are involved. Most corrosion problems of this kind can be prevented by using desiccants, and in many cases they are confined to imperfectly cured materials. For an excellent review see Reference 9. 

The equilibrium relationships found by Sorrell (1977) were valid only for room temperature (22+2 °C) and, because samples were allowed to cure in sealed containers, for equilibrium water vapour pressures determined by the assembly of phases present. The phases which exist under such conditions were quite unequivocally found to be 4 1 5 and 1 1 2. However Sorrell pointed out that it is entirely possible that lower hydration states of either phase could be stable at higher temperatures or lower humidities. In particular the 4 1 4 phase (Feitknecht, 1933) may well be such a phase, particularly as one of the five waters of hydration is known to be held only loosely in the structure. Indeed, Sorrell reported that he observed a slight shoulder on the larger dehydration peak of the DTG curve of the 4 1 5 phase that might be assigned to the loss of this first water molecule. He did not, however, succeed in isolating or characterizing a 4 1 4 phase. 

An obsolescent variation of the cold cure. The articles are vulcanised by exposing them to the vapour of sulphur monochloride in a closed chamber. 

Immersion according to Hempel Method. Half the panel immersed in fresh water and half the panel exposed to vapour. Possible weak adhesion is hereby provoked. The panels are applied, cured for 7 days and immersed in potable water for 2 weeks. After exposure the panels are immediately examined for blistering and adhesion (Knife test, X-cut, -cut). 

The Royal (or Royale) process was originally developed as a method for drying timber, in which the wood is heated in oil under vacuum. The temperatures used are low (60-90 °C) compared to other thermal oil treatments, and although sufficient to lead to some curing of the oil itself, there is no direct modification of the wood as a result of this process. The oil does not penetrate the cell wall. In this process, wet timber is placed in a treatment vessel and oil is then introduced, which is heated to the desired temperature, whilst a vacuum is applied. Water is removed from the timber and the vapour is transported away by the vacuum system. When the wood has reached the desired MC, the oil is removed from the treatment vessel. After this, a vacuum is applied to removed excess oil from the wood. Some dimensional stability is imparted to the timber due to the water repellency of the oil. This treatment is marketed by Osmose as the Royale process. 

Thin articles may be vulcanized by treatment with sulphur monochloride by dipping in a solution or exposure to its vapours. This process has been replaced by using ultra accelerators which are capable of curing at room temperature. 

Pretreatment primers. In this method of use the silane may be applied from a solvent solution, by vapour phase deposition or by plasma deposition although solvent application is the more usual. The solution usually contains water and silane at a concentration of 1-2 wt%. The applied film may be water washed before subsequent coating/bonding and/or heat cured. The solvent(s) used may be important in both the stability of the solution and the performance, particularly in the wet adhesion. It has been shown that the presence of water either in the solution or as a final rinse is important, particularly in the case of AAMS and presumably other silanes [1]. Other factors which are important include the concentration of silane the pH of the solution the thickness of the silane film deposited. 

For the modification of silica with aminosilanes, the liquid phase procedure is usually applied. Only few studies have described the vapour phase APTS modification.6,7 The modification proceeds in three steps, (i) A thermal pretreatment of the silica determines the degree of hydration and hydroxylation of the surface, (ii) In the loading step, the pretreated substrate is stirred with the silane in the appropriate solvent, (iii) Curing of the coating is accomplished in a thermal treatment. On industrial scale ethanol/water is used as a solvent, on lab-scale an organic solvent is used. The reasons for this discrepancy is the increased control on the reaction processes, possible in an organic solvent. This will be clarified by the discussion of the modification mechanism in aqueous solvent and the effect of water in the different modification steps. 

The content of non-evaporable water, relative to that in a fully hydrated paste of the same cement, was used as a measure of the degree of hydration. Portland cement paste takes up additional water during wet curing, so that its total water content in a saturated, surface dry condition exceeds the initial w/c ratio. Evidence from water vapour sorption isotherms indicated that the properties of the hydration product that were treated by the model were substantially independent of w/c and degree of hydration, and only slightly dependent on the characteristics of the individual cement. The hydration product was thus considered to have a fixed content of non-evaporable water and a fixed volume fraction, around 0.28, of gel pores. 

Demanding process, including moisture control, ammonia vapour treatment and oxidation Extra washing after curing including drying costs... 

Due to this water condensation, such adhesives have to be cured at high temperature and under high pressure in so-called autoclaves, when impermeable materials are bonded, to avoid an increase in volume of the adhesive layer caused by the water-vapour expansion. 

For example, when submitted to mustard gas vapours (25 mg/m3 for 30 min rats do not develop signs of general toxicity or of respiratory distress simply, in the following days, they exhibit irritation of the accessible mucosae (eyes, nose, ears, rectum) and are all completely cured after three weeks. On the other hand, when submitted for the same length of time (30 min) to a concentration of vesicant vapours of 5 mg/m3 only (instead of 25 mg/m3) in the presence of... 

Investigation of the released vapours during the cure of epoxy resin system by TGA -... 

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