Know More About Positive Material Identification

There are so many ways to assess properties and composition of a material without causing damage. Collectively, such procedures are classified as nondestructive testing or NDT. Nondestructive testing methods are important because they do not change the material being tested. NDT procedures are liquid penetrant, radiographic, ultrasonic, and magnetic-particle testing. NDT is usually an important aspect of mechanical engineering, civil engineering, forensic engineering, and arts.

Positive material identification is an NDT process that involves determining of metal alloys present in a material. It is one of the various nondestructive methods employed in determining metal composition of a material. PMI is a reliable method because it can be done in controlled laboratory setting or on the site. Identification of metallic elements in materials is important for various industrial, engineering, and chemical purposes. Because there are more than eighty metals known in chemistry, appropriate identification is a must. There is a wide range of application within which material assessment is of crucial importance. Manufacturing industries see composition analysis of a material as an essential process. As it is essential in the technical aspects of manufacturing and production, so its relevance in key processes cannot be undermined. Indeed, many industrial activities cannot proceed without apt material testing. PMI is not something that can be postponed or skipped. Material evaluation is vital and that's why it is part of the standard procedure.

Anyway, not all businesses and industries need PMI as a process. People who deal with many types of metals and utilize them in making alloys or those people who deal with alloys find material identification as an important process in manufacturing. Industries that depend on PMI testing are aerospace manufacturing, pharmaceutical manufacturing, and electric power industry. PMI is a reliable method when the material that needs to be tested cannot be altered, dented, or scratched. It is also relied upon when the material is part of a bigger equipment or mass. When the material for testing is enormous, transporting it to a lab testing facility may be extremely cumbersome. There are also materials that cannot be cut for examination purposes. Cutting or scraping materials cause a change in mass or may even alter the aesthetic value of the material. Another instance when cutting a material for testing is inapplicable is when it is too expensive or rare. Also, PMI will be of much use when the subject for testing is hazardous.

Precision is important in any kind of testing and PMI inspectors should be able to carry out tests on materials that would yield accurate results even if no amount of material is extracted. This is because many subsequent processes will rely on the test. Inaccurate results will greatly affect inspection, manufacturing, and production. Engineers doing tests should therefore be qualified professionals. They should have enough knowledge in operating testing equipment and interpreting results.

PMI is one of the most effective means in material recognition and is one of the most trusted methods of identifying metals on the site. It is used in a variety of applications that involve identification of metallic elements, particularly for nondestructive analysis. Inspection of ferrous and non-ferrous metals may require this process and this has something to do with quality control, manufacturing, and engineering.

Today, metal analysis involves the use of sophisticated technology such as X-Ray Fluorescence (XRF). XRF is unlike mass spectrograph, which is a process relying on wavelengths emitted by a sample of test object. An XRF equipment detects the metal elements present in a material by collecting and analyzing X-Ray emission data. The portable testing device is used to fire X-Ray radiation to the object. Each type of metal or element will emit characteristic X-Rays. Hence, the elements present in a sample can be determined by analyzing the X-rays emitted.

Understanding the Different Roofing Materials

The choice for your roofing material is very crucial to the beauty, durability, and overall appearance of your property. Therefore, whether you are building a new house or doing a home renovation, you need to understand the different roofing materials available in the market.

The roof protects your from the environment. It protects you from the wind, snow, and rain. It also serves as an insulator of the structure. This can have a significant effect on your heating bills. This is just one of the things you need to consider with the choice of material for your roof.

The Location and the Choice of Roofing Materials

In the market, there are many types of materials available. But the type of material you choose may depend on your requirements, taste, and budget. You also need to consider where your property is located. The location will determine the best roofing material you will use.

Try to take a look at your neighborhood. If you are quite familiar with your locality, then you are most likely aware of the roofing material used in the houses nearby. This is a great starting point in searching the right type of roofing material to use.

If you do not have any clue on what is the best material to use that will best suit your location, ask for the advices of the experts. It is really worth your time to speak to professional roofers in your area. They are most likely knowledgeable of the best material for the climate you have.

The Implication to Insurance

Another consideration with the choice of the material for your roof is the implication to your insurance. If you have a thatched roof, expect to pay higher costs in insurance than when you choose a tile roof.

Doing the Job Yourself or Hiring a Professional?

Based on the choice of the roofing material, you can decide whether to do the job on your own or to hire a roofing professional. The success with your project depends on the quality of the material and the expertise of the people to install it. Even if you have the most expensive roofing materials in the world, installing it sloppily will only waste your time and money.

Is there someone in the area that can properly fit the material to your house? This is something you need to take into account before choosing the material to use for your roof.

Conclusion

To end this article, understanding the roofing material is very important. It is one of the basic decisions you need to do correctly because this will dramatically affect your budget, your time, and your overall success later.

Construction Materials

Building a house will never happen without the right materials for construction. Despite having a grandiose design, it will never transpire without the proper materials that you can use so that you can bring out that design from the papers to the real thing. Most people who want to build a house of their own only rely on contractors when it comes to buying the right materials for construction, but if you want to be hands on when it comes to the construction of your house then you can actually be the one to look and purchase the materials that would suit the construction needs of your house.

The construction materials that you need would first be based on the design that you have. Everything starts with the kind of house that you want to build. It's not enough that you know the materials that can be used for construction. The problem in just simply buying materials without putting the design in mind is that unnecessary purchases can be made which will just put your spare construction essentials to waste. To avoid unnecessary expenses on the materials which you can't use, it would be best to know what you need and what you don't need based on the design plan for the house. If you happen to design a brick house, then invest more on cement and bricks. As another example, if your design plan gives you a house that is oriental in nature, then you might want to invest on wood that you find appealing for your house. Aside from these, you should also buy the right amount of the essential materials for construction like nails and other necessary equipment that you can use for your construction.

Another important that you should consider when buying materials for your construction would be your budget. Again, your budget must also be based on the design that you have, or both can be adjusted in one way or another. If you have a great design but your budget is limited, then you can make adjustments on the materials and the equipment that you can use for your construction. You might want to look for materials that look like the one that you need but are cheaper than the original ones. You might want to consider buying the basic and simple versions of the expensive construction materials. You don't have to worry much about it because there are so many materials in the market that you can choose to have depending on the budget that you have. There are some materials that are more expensive than the others because these are known brands, but there are also some that are cheaper but can still guarantee quality. Thus, you just have to be wiser and more inquisitive in terms of looking for materials if you have a tight budget.

If you're looking for construction materials, you can always go to your nearest home depot or do-it-yourself shops. The best thing about these stores is that they can assist you in choosing the best materials for your needs.

Know If a Material Is According To Its Standard Using Positive Material Identification

Positive material identification or PMI is a nondestructive test method that is used to examine alloys and other materials to determine the presence of impurity. This is done in order to find out if the material is authentic based on the grade name it bears and to find out whether an alloy possesses unneeded elements. It is a process that shall serve as a gauge whether to accept or reject a material. There is no way that this process will be used to adjust the quality of the material to make it suitable for usage.

Engineers generally push the borderline of the capacity of any material to limits that make it efficient for the purpose and design. Hardly ever does a material come pure as it is typically alloyed or mixed with other elements to make it sturdier and more durable. However, several issues arise and we should take into account that with modification of composition comes the change in material specification. The durability of a material shall be determined by the proportions of the elements present in it. The wrong ratio can render the material futile. To complicate matters, the presence of impurities can limit the usefulness of a material. There is no other way for engineers to find out if a material is going to be suitable for particular purpose than doing methodical tests and it is just one of those standard tests employed to verify aptness of a material.

Positive material identification determines the alloy composition and grade of a material whether it comes with a certificate or not. The objective is to find out whether the grade as mentioned on the label is truthful. The process is generally used for premium metals like precious alloys and stainless steel. Because it is a non destructive test (like dye penetrant inspection or radiography), it is an excellent method of examination without altering the material physically or chemically.

There are usually two ways to carry out positive material inspection and these are x-ray fluorescence and spark emission spectrography. X-ray fluorescence (XRF) is usually more reliable than spark emission spectrography because it leaves no traces on the surface of the material being tested. The x-ray flourescence equipment consists of radioactive sources that emit low voltage x-rays. As the theory speaks, atoms of materials exposed to x-rays become excited and emit energy. The energy emitted by an excited atom is unique. As a result, this method is an effective way of identifying what elements are present in a material. X-ray flourescence does not only detect what elements are present but also determines how much of each element is present.

Much of positive material identification test is done with the use of x-ray flourescence, which is suitable when the integrity of the material being tested should be preserved. Some material analysis require taking a piece of the test subject for laboratory analysis but this is not applicable in many instances. Positive material identification is just one of the many nondestructive testing methods, like acoustic emission, leak detection, and hydrotesting.

A Safer Approach To Moving Handling And Storing Materials

"Precaution is better than cure", this proverb goes true not only in the health-care industry but in all industries, including those of heavy machineries. In addition to acquisition of raw materials, the efficient handling and storing of materials are vital to the heavy industry. The improper handling and storing of materials often result in costly injuries. To avoid such unwanted workplace hazards, the right material handling equipment is essential in more or less all heavy industries.
Weight and bulkiness of objects are major contributing factors to the injuries at workplace in many industries. Bending, followed by twisting and turning, are also more commonly cited movements that caused back injuries. Other hazards include falling objects, improperly stacked materials, and improper use of the various types of equipment. Manual material handling involves potential risks of injuries that can be among the following:

• Strains and sprains from lifting loads improperly or from carrying loads that are either too large or too heavy,
• Fractures and bruises caused by being struck by materials or by being caught in pinch points, and
• Cuts and bruises caused by falling materials that have been improperly stored or by incorrectly cutting ties or other securing devices.

It is essentially important to provide important safety information on handling, lifting, loading, storing and installing in heavy industries. Efficient flow and proper handling of materials is essential to a high production operation. A systematic approach should be used to reduce the total amount of required manual material handling and minimize the hazards associated with these activities during the planning and construction phases, by creating a unified material handling system.
Material handling equipment selection is a complex task and there is usually more than one good solution for any particular situation. The choice of material handling equipment depends on the product and process requirements. For this reason, material handling equipment can only be selected according to the product and process specifications. The entire material handling equipment process can be divided into three stages:

• Material Handling Equipment selection
• Rationalization of the selected Material Handling Equipment.
• Utilization and detailed design of the Material Handling Equipment

The types of material handling equipment are most often based on one of the following categories:

• Load Type
• Load Capacity
• Size
• Nature
• Speed
• Accumulation Required
• Distance
• Frequency Of Movement
• Flexibility of Path
• Loading and Unloading ability

An effective management always works towards worker safety and health protection. It is a decisive factor in reducing the extent and severity of work-related injuries and illnesses and their related costs.

Have You Selected Wrong Materials for Chemicals?

Chemicals are very much a part of our lifestyles. Every household detergent, solvent, and bleach that you use in your homes is a result of some production efforts from manufacturing plants somewhere in the world around you. Fertilizer, automobile radiator coolant, shampoo, soap, insecticide, paint solvent, lubricants, fuel oil are just a few that I can name right now. I'm sure you can find more around you, but you get the point. We use chemicals everywhere.

Anyone who has visited a chemical processing plant is sure to notice the many pumps, agitators, tanks, piping, and valves that are installed there. Liquid have to be transferred from one place to another. Pumps are therefore very important in a chemical processing plant. Without them the chemical processing plant will literally come to a halt!

One of the main jobs for Plant Engineers is to maintain the numerous pumps installed at their plant. These pumps can count into the hundreds or even thousands, depending on the size of the plant. So you should realize that to do a proper preventive maintenance, it is no mean task. There must be regular schedules, proper tracking of jobs done, available manpower and skills, suitable tools, replacement parts, materials and a proper system of administration of all these.

Sometimes, even with all the maintenance activities being carried out, pumps do fail. And when they do, plant engineers will have to find out what causes them to fail. Especially with new pumps where there is very little record trend of breakdown, engineers will be hard pressed into finding solutions for this. This is when experience helps in pinpointing the cause(s) of the failure.

Pumps or other machinery will give tell-tale signs when they are not working properly. An observant pump user will be able to avoid major breakdowns or damage if the problem is corrected early.

In order to solve any pump problem, we need to notice the symptoms carefully so as to determine the most likely causes. Instruments like pressure gauges are very helpful and should be installed in the pumping system.

Very often we do have to rely on our 5 senses to determine the exact symptom. Normally, pump problems can be classified into:

1) Suction Related,

2) System Related, or

3) Mechanical Related.

It can also be a combination of these.

Most of the system related problems occur because of design flaw. For example, the designer may have chosen the wrong pump whose characteristic does not match the system requirement. Suction related problems are usually caused by air locks that are due to a variety of reasons. I will not mention them here.

The effects of mechanical related problems could manifest themselves as suction related problems - air leaks in the system, worn out impellers, and mouth rings - but the most common symptom is the presence of vibration and abnormal noise in the equipment.

However, there is one area where we seldom focus on - the effect of chemicals. Was the material selected able to withstand the chemicals? If you have done all your designing right and you still find that leaks are occurring so frequently, chances are that the materials are failing due to chemical reaction. Signs of corrosion at the seals are a strong indication of material failure due to wrong usage.

Nowadays, waste treatment plants or even process plants are called upon to process strong acids, alkalis, oxidizers, solvents, waste, slurry and other corrosive and abrasive chemicals. And it is not only pumps that are affected. Agitators, storage tanks, and piping need to be compatible to these chemicals. If the wrong material is selected, it can lead to dangerous and widespread consequences of chemical spills, emergency evacuation, pollution, environmental damage and other disruptions to the production facility.

Engineers in such chemical processing plants need to know what materials are suitable to be used for their process. It is much more complex than just selecting materials for water pumps. Much detailed and careful selection choices based on the chemicals, the temperatures (because some of the plastic materials can weaken at temperatures that are considered normal for metals), chemical reactions, safety, spills and many others have to be taken.

The aim of any maintenance personnel is to lengthen the lifespan of equipment under his care. Selection of chemical resistant materials is not a one-cure-fits-all solution. Some materials are not affected by certain chemicals but can be damaged by others. Some have good mechanical strength while others cannot last long without reinforcement. Usually, materials that can withstand many types of chemicals are very expensive.

Cost considerations need to be taken into account when choosing a material for a certain application. If there is a choice of materials for a certain application, it makes better sense to choose cheaper materials if they can perform just as well.

There are several components to check for when selecting suitable materials:

1) Elastomers for flexible parts like seal rings and gaskets

2) Metal parts like shafting, springs, holders, bolts & nuts, and pressure gauges

3) Plastic parts like housing, piping, impellers, and covers

Metals have good mechanical strength that can last very long in operation. In fact some parts need to be made of metal, e.g. bearing housing and shafts. Pump housing made of metal can be casted and machined easily. They are able to withstand abrasive fluids and rough handling without any other reinforcement. One very important characteristic of metals is heat conduction. If the chemical to be pumped is hot, metal is always the choice.

Plastics have become the better choice for many corrosive chemical applications because it is more resistant to chemical action than metals. When using plastics to replace metals, you have to compromise on the mechanical strength of the pump. If the pump does not encounter much rough handling or abrasion, plastics can be used. Sometimes plastics are used to coat metal parts. These are fine as long as the plastic coating remains intact.

Elastomers are the flexible materials that are needed for sealing the pump parts. There should not be any compromise here. Laboratory tests on the suitability of elastomers with certain chemicals should be followed. Unsuitable material used can cause leaks that can lead to other failures in other parts.

With so many chemicals in use today, how do we know what materials can be used for what chemicals? Sometimes liquids to be pumped contain chemicals that are both corrosive and abrasive. Should we choose a plastic or a metal housing? Sometimes chemicals may become hot either through the process or through mis-operation of the system - perhaps, somebody forgot to open a valve. Plastic parts can weaken at high temperatures.

It's only through the result of test and actual operation that we are able to know what materials to use. It is good to know what to expect when we make a decision for a choice of materials to use. A good choice may involve some compromise.

Chemistry - Various Raw Materials

Natural Gas, Coal

Fossil fuels and many other raw materials are the remains of plants and animals which lived millions of years ago. They are composed of hydrocarbons, so we call them fossil carbon compounds. Fossil fuels and other raw materials can occur as solids, usually in stratified layers of earth. Or, these materials can be liquids, as with oil. Natural gas, which is found in underground caves in often great quantities, occurs sometimes in kilometre-wide supply. Because coal is usually deposited near the surface of the Earth, it was the first fossil fuel to be used as an energy provider by our distant ancestors. Oil and natural gas have gained their importance as fuels mostly as raw materials for industry, and that in more recent times.

Coal is a flammable material made from the remains of plants and other organic substances, which during millions of years of geological history has been charred, or carbonised, to a brown or black colour in a sedimentary layer. Coal can be divided into various kinds based on its degree of carbonisation: brown, black and anthracite.

While brown coal contains about 60-70% carbon and has a relatively high water content, with ash matter and bitumen making up around (asi 7-20% ), hard, black coal is much richer in carbon (75-92% ), while being lower in water content, ash and bitumen. This makes it more expensive, of course. Anthracite is coal with a high degree of carbonisation (containing more than 91.5% carbon). Its water and ash content are negligible.

Carbonisation, or charring, is a process by which fossilised compounds become coal. In the process of this long-term geochemical change, plant material (cellulose and lignite) are transformed into peat, then to brown coal, hard coal and anthracite. One of the prerequisites for carbonisation is a large amount of matter containing carbon. A damp environment is also needed, as is a moderate climate. The organic material has to be covered with a thick layer of mineral sediment (in a depression in the earth). Carbonisation begins at high temperature and pressure in the absence of air, leading to the decrease of the concentrations of hydrogen and oxygen in the material. On the other hand, the relative concentration of carbon in the material increases.

The degree of carbonisation in a material rises from peat material, to brown coal, to black coal, to anthracite.

The various types of coal, with their differing degrees of carbonisation, have variable heat, or calorific, value, with the least amount in peat. Calorific value is the amount of heat energy which is released when 1 kg of material is burned. The calorific value of the individual fossil fuels is given in units of kilojoules per kilogram (KJ/kg)

wood 16 800 KJ/kg

peat 16 380 KJ/kg

brown coal 21 000 KJ/kg

black coal 34 860 KJ/kg

anthracite up to 36 120 KJ/kg

benzene 44 520 KJ/kg

Coal is used in a number of industrial processes, and in households, mostly as a fuel.

Natural gas is a naturally-occurring gas which is often found in caverns in the earth, often together with oil. Natural gas can also be found in porous layers of sand. Natural gas is a mixture of gases composed mostly of methane. Other gases which can be found in natural gas are other hydrocarbons (ethane, propane, butane), nitrogen, hydrogen, water and helium. It is formed by the transformation of fossil compounds by long geological processes. Natural gas can be won by digging natural gas wells. Natural gas need not be taken from the surface of the earth, because the internal pressure of the layer where it is found is sufficient to push it up to the surface of the earth. It is used today as a propulsion and heating material. It is also widely used in many chemical processes.

Oil, Fossil Fuels and Raw Materials

Composition and Uses of Oil and Natural Gas

Oil begins to be formed when microorganisms decompose plant and animal matter in the absence of air. This previously organic material is amassed thousands of meters below the surface of the Earth, in porous caverns in sedimentary rock formations. Oil is a brown to black liquid. It is more or less viscous, thanks to its chemical composition. Oil is a mixture of materials, but it is primarily composed of normal or cyclic hydrocarbons (up to 80-90% ) and water (10-14% ). Oil can be burned when it is in its liquid state, as a heating oil, but it is also a raw material in the production of other fuels, lubricants, paraffins and bitumens. Besides these uses, it is a geochemical raw material which is used in other special processes which produce various powders, plastics and synthetic fibres, among others.

Separation of Individual Oil Fractions Using Distillation

Oil is composed of a mixture of linear and cyclic hydrocarbons. These can be separated by taking advantage of their different boiling points, using distillation to separate the components. When oil is heated, its fractions, or components, with the lowest boiling point vaporise first. If the distillation is carried out gradually and slowly, a fraction can be cooled, and the gas will condense. In this way, one liquid fraction can be isolated, and this fraction should be fairly pure. This separation of the individual fractions of oil is called a fractional distillation. Of course, each individual fraction separated contains a mixture of materials. Each mixture has its own special uses as well.

Approximate Boiling Point (° C) Fraction Uses

500 bitumen asphalt products, freeway materials

From a practical point of view, fractional distillation means that when oil is heated, it vaporises, its fumes rising up a column from its liquid origin in the bottom of the column to the top. These fumes are horizontally divided into individual columns. The temperature of each fraction decreases as the column rises away from the original liquid material. The fractions condense and can be divided out. Before a fractional distillation of oil is carried out, the original oil sample must be cleaned, which means removing the salts it contains, and removing any water which might be present.

Mineral Oils and Motor Oil

Fuels contain alkanes and cyclic hydrocarbons in their liquid form, with two main groups which can be distinguished. Motor oils are products with low boiling points (30-200° C). These can be used in the propulsion systems of Otto motors. Diesel oil is separated from a boiling fraction at temperatures of 200-300° C. It is used in diesel motors and has a higher burning temperature than petrol. When the fuel is completely burned, water and carbon dioxide are produced. If there is insufficient oxygen available during the burning process, carbon monoxide, a very poisonous and reactive gas, is produced. The release of excessive carbon monoxide into the air can result in problems in the atmosphere. To help solve this problem, modern cars are equipped with catalytic converters, in order to decrease the amount of carbon monoxide and other harmful gases into the atmosphere. Catalytic converters change carbon monoxide into the less harmful carbon dioxide, as well as transforming harmful nitrogen oxides into less harmful compounds.

Environmental Consequences of Burning Fossil Fuels

Besides water, carbon dioxide is formed when fossil fuels are burned. This gas is released into the atmosphere. Atmospheric concentration of carbon dioxide rises, and the result is the we have to be concerned about possible changes to the Earth's climate. Carbon dioxide is not the only harmful gas released in burning reactions: Nitrogen-containing oxides and sulphur oxides are also released. The latter are easily dissolved in water, which makes them a main ingredient in rain, which falls on both land and water, acidifying our environment and bringing even more consequences to bear. The burning of fossil carbon sources, then, has significant effects on the Earth's climate, nature, agriculture and of course, our health. The use of alternative sources of energy, therefore, is the only possible answer to this dilemma. Only in this way can the negative effects of the release of these harmful gases be limited. Another possibility, of course, is using less energy, especially that derived from fossil fuels.

The significance of the above-mentioned alternative sources of energy has grown and continues to grow, on the one hand because of the pollution of our environment which is the result of the burning of fossil fuels. Not to be underestimated, however, is the reasoning that the stocks of these fuels are bound to be used up at some point in the not so distant future. Fossil fuels are one type of exhaustible energy source. There is only a certain amount of fossil fuels found on Earth; once this amount is gone, there is no way to produce more. As these stocks are used up, it will become more and more important to generate the energy humanity needs from alternative sources which can be regenerated and can therefore be used in a practically unlimited way. Wind energy, solar energy, hydroelectric energy and geothermic energy are only some of the possibilities.

Carboxylic Acids and Eesters

Nomenclature of Carboxylic Acids

Carboxylic acids are organic acids which contain a functional carboxylic group (-COOH). Aliphatic, saturated monocarboxylic acids which contain one carboxylic group in the molecule form a homologous group with the general chemical formula (CnH2a+1COOH). In naming of these acids, the compound name of the corresponding alkane is taken as an adjective, with the name of the acid added on. The first acids in the homologous group carry their traditional names:

formic acid (HCOOH)

acetic acid (CH3COOH)

propionate acid (CH3CH2COOH)

butyl acid (CH3CH2CH2COOH)

When the salts of carboxylic acids are named, the base name of the corresponding alkane is taken and an -ate suffix is added to the end. The cation of the salt is indicated by an adjective of the name of the element.

The hydrocarbon portion of the molecule of carboxylic acids is named according to how the corresponding alkane would be named. This is characterised by the main symbol of the carboxylic acid - for example the carboxylic group (-COOH), which is the functional group.

Physical Properties and Reactivity

Molecules of carboxylic acid are polar. The carboxylic groups contained on the molecules form hydrogen bonds with neighbouring molecules. Thanks to these weak intermolecular forces, carboxylic acids have high melting and boiling points. With increasing size of the hydrocarbon rest of the molecule, the polar character of the functional group is masked by the non-polar character of the hydrocarbon chain. The first homologous members of the series are liquids which are soluble in water. As the series continues, however, its members become solid at room temperature, and begin dissolving in non-polar solvents. Because of their acidic character, carboxylic acids form salts with impure metals.

The acid reactions which take place among carboxylic acids are caused to a great degree by the presence of their carboxylic group. Its oxygen atom increases the polar character of bonds formed with oxygen and hydrogen, making it very easy for it to release an electron - to form a carboxylic ion.

Acetic Acid

Acetic acid is the base ingredient of common table vinegar. Acetic acid is a clear liquid with an acrid odour. It is corrosive, and combined with indicators, it reacts in an acidic manner. Concentrated acetic acid is known as icy acetic acid, because below 16.6° C, its melting point, it hardens into a metal-like structure. Acetic acid is easily soluble in water and ethanol. When it is reacted with impure metals, hydrogen, metal salts and acetic acids known as octanes (acetates) are formed. Acetic acid is used in the food service industry. It is used as a preservative in the production of some groceries.

In industry, acetic acids are used to produce acetic acid esters. These are good solvents. In addition, acetic acids can be used in the production of plastics, artificial silks, some medicines and paints and other colourings.

The acids which are found in vinegar are produced with the help of the bacteria found in alcoholic wine. This reaction has as its mechanism the oxidation of ethanol by oxygen contained in the air, to acetic acid. This process is called acetic fermentation.

bacteria

CH3CH2OH + O2 ¾ ¾ ¾ ® CH3COOH + H2O

Ethanol acetic acid

Production of Esters and their Reactivity

Esters are produced when carboxylic acids are allowed to react with alcohols. Esters have the functional group -COO-. Water is also produced as a by-product in the reaction which produces esters.This is a reversible reaction, sometimes also called an equilibrium reaction. The break-up of an ester (reversible reaction) is called the hydrolysis of an ester. The synthesis of an ester is a multi-step reaction, with additions and eliminations included.

Significance of Esters

One of esters' most distinguishing characteristics is their intense odour, similar in some cases to fruits and other plants. For this reason, they are often used in the food service industry, especially in the production of certain delicacies or additives which tend to intensify some tastes in foods. Esters are good solvents. They are ingredients in some glues and paints. In the production of an ester from an acid derived from an alkane bonded to glycerin (glycerol), fats and oils are produced. The oils contain

unsaturated carboxylic acids of ester glycerin. The fats contain saturated acids. Waxes are esters of higher aliphatic alkanols with carboxylic acids. They have 16-32 carbon atoms in each molecule. Fats and oils are very significant for living organisms, because important materials necessary for living systems can dissolve in them.