Chapter 4 Chemistry of fire retardancy,4.1 Preface4.2 The chemistry of pyrolysis and combustion 4.3 Mechanisms of fire retardancy4.4 Fire-retardant formulations 4.5 Future researches,4.1 Preface,Wood and its products are closely related to peoples lives. More and more people like to decorate their room with wood, and woody buildings draw more and more attentions. But as we known wood are combustible materials, which not only threat to peoples lives and possessions, but also limited their application areas.With the increase of high buildings and large mansions, fire becomes the main trouble needing to be solved.,indoor decoration, building, gardening, and so on,The charming wood,in,The modern wooden building is very popular in most of the countries.,In 2000, 90 percent of the American new villa(别墅) was built up of wood. And Among the 330,000 high rise residences, 275,000 was built up of wood.,In Canada, wood industry is the mainstay industry, the techniques of manufacture and installation are quite mature.,At present, more than half of the new houses in Japan are built up of wood or wood products.,Except for wooden houses, most of the public buildings such as factory, school, hotel , gymnasium and so on are built up of wood or wood products.,will you believe that wooden building can grow up in China in the future?,The chief criminal of fire,Wood,Wood is the criminal of fire.,Wooden building should be limited or discarded.,Is it right?,Its a false and unadvisable idea. why?,Wood,Steel,cement,plastic,the extensively applied materials,the only renewable material,In fact, wood especially large scale of wooden products are fireproof material. Why? P108,In our mind, reinforced concrete is a kind of fireproof material, and strong enough to resist violent collision(猛烈撞击). But reinforced concrete has a mortal defect(致命的缺点).,Would you tell me whats the fatal defect to reinforced concrete at higher temperature ?,Reinforced concrete turns soft when undergoing high temperature. Normally, the strength of steel reduces by half when the temperature exceeded 300C, and falls down when the temperature exceeded 500C. Therefore, fire retarding is of the utmost importance.,Coffer (or safe)保险柜: 制作材料？金属金属和木（竹）材其它,1.Is it necessary to preventing wood from fire, why?2.According to your opinion, which kind of wood (assorted by their application areas) should be protected from fire?3.From the pictures above, please tell me the most serious threats in a fire.,Questions,4.2 The chemistry of pyrolysis and combustion,Including four stages:,(1) The temperature of wood is improved under the heat.,(2) Wood gradually degrades and pyrolyzes, the following material produces: CO2, CO, CH4, CH2=CH2, R-CHO, R-CO, and so on,Tar (including phenol(酚类),aldehyde(醛类),carbonyl chemicals(羰基化合物),Flammable gases,heat,Low molecular chemicalsAnd flammable gases,(3) Flammable gases,heat,Catch fire and combustion,There are four necessary conditions for the flammable combustion of wood: combustible gases, heat, oxygen and radical groups。,(4) Combustion continues,Heat conducts to the adjacent wood,Combustion provide large amount of heat,Wood temperature improved,Pyrolysis begins, then ignition, combustion, fire spread, and so on,Large amount of smoke also produced during the combustion of wood, the composition of the smoke is listed in the follows:,Combustible gases: CO, CH4, H2, CH2=CH2, R-CHO, R-CO, and so on,Noncombustible gases: CO2, H2O,Tar: phenol, aldehyde(醛类), carbonyl chemicals,Charcoal: combustible residue.,Pyroligneous acid(木醋液): mainly formic acid(蚁酸) or acetic acid(乙酸),Some terms of combustion,Flame combustion(有焰燃烧)： luminous burning at the gas state. 木材进行发光的气相燃烧。,Smoulding(有焰燃烧)： nonluminous burning with smog. 木材燃烧时处于一种无可见光而有烟雾的燃烧。,Flameless combustion(红热燃烧)：aphlogistic(无焰) combustion at a solid state. 木材处于固相状态 而没有火焰的燃烧，也叫无焰燃烧。,4.3 Mechanisms of fire retardancy,Prevent the escape of volatile products by forming a glassy barrier. Prevents oxygen from reaching the substrateInsulates the wood surface from high temperatures,(1) Barrier theories(障碍理论),(2) Thermal theories(热理论),Fire-retardants may increase the thermal conductivity of wood to dissipate the heat from the surface faster than it is supplied by the igniting source; Affect chemical and physical changes so that the heat is absorbed by the chemical. For example :chemicals content crystal water.,(3) Dilution by noncombustible gases theories(不燃气体稀释理论),Noncombustible gases released by the decomposition of the fire-retardant Chemicals, which dilute the combustion gases, and form a non flammable Gaseous mixture.,(4) Free radical trap theories(自由基捕集理论),Fire-retardant chemicals release free radical inhibitors at pyrolytic temperatures that interrupt the chain propagation mechanism of flammability.,CO，CO2，H2O，HO和其它成分(1) HO十COCO2+H (2) H十O2HO十O (3) O+ H2HO+ H,