Instruct: Given a question, retrieve documents that can help answer the question.
Query: Why is tar used to seal cracks?
Oakum can be used to seal cast iron pipe drains. After setting the pipes together, workers pack oakum into the joints, then pour molten lead into the joint to create a permanent seal. The oakum swells and seals the joint, the "tar" in the oakum prevents rot, and the lead keeps the joint physically tight. Today, modern methods, such as rubber seals (for example, gaskets or o-rings) are more common.[5]
Just before World War II, the PJ & MS Co found that using coal tar as fuel was much cheaper than bunker oil. The PJ & MS Co obtained its coal tar from the North Shore Gas Company, which had nothing else to do with it. At the time it cost two pence a gallon, and the three big steamers of the fleet, "Dee Why", "Curl Curl" and "South Steyne"; were all converted to burn coal tar instead of oil. However, soon other users found that coal tar was useful, and to remain competitive, the North Shore gas Company upped its prices to an unmanageable rate, and so the three steamers were reconverted to oil. It was the price of oil that led to their demise.
Sottos helped developed the first polymeric self-healing material with colleagues including Jeffrey Moore and Scott White. The work was completed in 2000, and published in "Nature" in 2001. They have shown that microencapsulated healing agents can polymerize to heal areas of damage such as cracks smaller than a human hair. 
Their approach was to develop a polymeric matrix which involved both a reactive liquid healing agent and a catalyst. While undamaged, these were kept structurally separate. The liquid agent was contained inside non-reactive reservoirs within the material, while the catalyst was dispersed throughout the polymer. Once the material was damaged and a crack occurred, the reservoirs broke open, and capillary action caused the liquid agent to disperse into the damaged area, where it reacted with the catalyst and solidified to seal the crack. They have studied both the use of a contained healing agent and a dispersed catalyst, and the use of a dispersed healing agent and a contained catalyst. Using dicyclopentadiene (DCPD) and Grubbs' catalyst in an epoxy matrix, polycyclopendiene was formed to seal cracks, recovering up to 75% of the original fracture toughness.
The Native American Chumash and Tongva people living in the area built boats unlike any others in North America prior to contact by settlers. Pulling fallen Northern California redwood trunks and pieces of driftwood from the Santa Barbara Channel, their ancestors learned to seal the cracks between the boards of the large wooden plank canoes by using the natural resource of tar. This innovative form of transportation allowed access up and down the coastline and to the Channel Islands. 
"E. cordata" uses resin to seal cracks and joints, and to seal the entrance hole inside the nest. To leave the nest, an individual creates a small round hole in the resin, big enough for one to pass through. The hole is never sealed when leaving the nest, even when leaving for the last time, but sealed many times during the day while working inside the nest, as well as in the evening. Before a new cell is made, the current cell is provisioned and sealed.
The boat dock also featured a toilet (earth closet) and a stable to house the working horses. Horses provided "hosmuck an' tar" (manure and tar) that was used to seal the wooden boats.
Diaphragm seals (also known as chemical seals or gauge guards) are also used to protect a process fluid from the pressure sensor. Examples of this use are:Diaphragm seals are susceptible to failure via several mechanisms, including cracking. Ozone cracking can occur in many elastomers for example used in pneumatic systems. If the gas contaminates the air supply, then many rubber diaphragms are at risk from the problem.
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Later on, they did not hold up to higher-speed motor vehicle use. Methods to stabilise macadam roads with tar date back to at least 1834 when John Henry Cassell, operating from "Cassell's Patent Lava Stone Works" in Millwall, patented "Pitch Macadam".
This method involved spreading tar on the subgrade, placing a typical macadam layer, and finally sealing the macadam with a mixture of tar and sand. Tar-grouted macadam was in use well before 1900, and involved scarifying the surface of an existing macadam pavement, spreading tar, and re-compacting. Although the use of tar in road construction was known in the 19th century, it was little used and was not introduced on a large scale until the motorcar arrived on the scene in the early 20th century.
Ozone attack will occur at the most sensitive zones in a seal, especially sharp corners where the strain is greatest when the seal is flexing in use. The corners represent stress concentrations, so the tension is at a maximum when the diaphragm of the seal is bent under air pressure.
Dry-seal gas holders have a static cylindrical shell, within which a piston rises and falls. As it moves, a grease seal, tar/oil seal or a sealing membrane which is rolled out and in from the piston keeps the gas from escaping. The MAN ("Maschinenfabrik Augsburg-Nürnberg AG") was introduced in 1915: it was polygonal and used a tar/oil seal. The Klonne dry seal gas holder was circular: it used a grease seal. The "Dry-seal Wiggins gas holder" was patented in 1952: it used a flexible curtain that was suspended from the piston. The largest low-pressure gas holders built was the Klonne gas holder built in 1938 in Gelsenkirchen. It was high and in diameter, which gave it a capacity of . There was a MAN type, built in 1934 in Chicago with a capacity of . 
The objectives of visbreaking are:The term coil (or furnace) visbreaking is applied to units where the cracking process occurs in the furnace tubes (or "coils"). Material exiting the furnace is quenched to halt the cracking reactions: frequently this is achieved by heat exchange with the virgin material being fed to the furnace, which in turn is a good energy efficiency step, but sometimes a stream of cold oil (usually gas oil) is used to the same effect. The gas oil is recovered and re-used. The extent of the cracking reaction is controlled by regulation of the speed of flow of the oil through the furnace tubes. The quenched oil then passes to a fractionator where the products of the cracking (gas, LPG, gasoline, gas oil and tar) are separated and recovered.
Oakum is a preparation of tarred fibre used to seal gaps.[1] Its main traditional applications were in shipbuilding, for caulking or packing the joints of timbers in wooden vessels and the deck planking of iron and steel ships;[1] in plumbing, for sealing joints in cast iron pipe; and in log cabins for chinking. In ship caulking, it was forced between the seams using a hammer and a caulking iron, then sealed into place with hot pitch.[2]
Carbon black (subtypes are acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, or ethylene cracking tar. Carbon black is a form of paracrystalline carbon that has a high surface-area-to-volume ratio, albeit lower than that of activated carbon. It is dissimilar to soot in its much higher surface-area-to-volume ratio and significantly lower (negligible and non-bioavailable) PAH (polycyclic aromatic hydrocarbon) content. However, carbon black is widely used as a model compound for diesel soot for diesel oxidation experiments. Carbon black is mainly used as a reinforcing filler in tires and other rubber products. In plastics, paints, and inks, carbon black is used as a color pigment.
Native Americans were keenly aware of oil reserves in California, and they relied on its utility for thousands of years, albeit not for energy sources. The most abundant oil seep in the ancient California territory was the La Brea tar pits, in present-day Los Angeles. Native Americans used oil from La Brea and other seeps primarily as a lubricant, but they also used it as a sealant to waterproof canoes. When Spanish explorers arrived in California in the 1500s, they also used oil to seal cracks in their ships and the roofs of their homes.
Outside cities, roads were dirt or gravel; mud in the winter and dust in the summer. Early organizers cited Europe where road construction and maintenance was supported by national and local governments. In its early years, the main goal of the movement was education for road building in rural areas between cities and to help rural populations gain the social and economic benefits enjoyed by cities where citizens benefited from railroads, trolleys and paved streets. Even more than traditional vehicles, the newly invented bicycles could benefit from good country roads.Later on, they did not hold up to higher-speed motor vehicle use. Methods to stabilise macadam roads with tar date back to at least 1834 when John Henry Cassell, operating from "Cassell's Patent Lava Stone Works" in Millwall, patented "Pitch Macadam".
This method involved spreading tar on the subgrade, placing a typical macadam layer, and finally sealing the macadam with a mixture of tar and sand. Tar-grouted macadam was in use well before 1900 and involved scarifying the surface of an existing macadam pavement, spreading tar, and re-compacting. Although the use of tar in road construction was known in the 19th century, it was little used and was not introduced on a large scale until the motorcar arrived on the scene in the early 20th century.
Also the mechanical design of a glass-to-metal seal has an important influence on the reliability of the seal. In practical glass-to-metal seals cracks usually start at the edge of the interface between glass and metal either inside or outside the glass container. If the metal and the surrounding glass are symmetric the crack propagates in an angle away from the axis. So, if the glass envelope of the metal wire extends far enough from the wall of the container the crack will not go through the wall of the container but it will reach the surface on the same side where it started and the seal will not leak despite the crack.
Ozone cracks form in products under tension, but the critical strain is very small. The cracks are always oriented at right angles to the strain axis, so will form around the circumference in a rubber tube bent over. Such cracks are very dangerous when they occur in fuel pipes because the cracks will grow from the outside exposed surfaces into the bore of the pipe, so fuel leakage and fire may follow. 
Seals are also susceptible to attack, such as diaphragm seals in air lines. Such seals are often critical for the operation of pneumatic controls, and if a crack penetrates the seal, all functions of the system can be lost. Nitrile rubber seals are commonly used in pneumatic systems because of its oil resistance. However, if ozone gas is present, cracking will occur in the seals unless preventative measures are taken.
In the early stages, sealing cracks with crack sealant limits further deterioration of the subgrade due to moisture penetration. Small areas may be repaired by removal of the affected area, and replacement with new base and asphalt surface. Once the damage has progressed or the affected area is large and extensive, a structural asphalt overlay or complete reconstruction is necessary to ensure structural integrity. Proper repair may include first sealing cracks with crack sealant, installing paving fabric over a tack coat, or milling the damaged asphalt. An overlay of hot mix asphalt is then placed over the completed repair.
There were two purposes to the liquid seal: first, to draw off some of the tar and liquor, as the gas from the retort was laden with tar, and the hydraulic main could rid the gas of it, to a certain degree; further tar removal would take place in the condenser, washer/scrubber, and the tar extractor. Still, there would be less tar to deal with later. Second, the liquid seal also provided defense against air being drawn into the hydraulic main: if the main had no liquid within, and a retort was left open with the pipe not shut off, and air were to combine with the gas, the main could explode, along with nearby benches.
In a matched seal the thermal expansion of metal and glass is matched. Copper-plated tungsten wire can be used to seal through borosilicate glass with a low coefficient of thermal expansion which is matched by tungsten. The tungsten is electrolytically copper plated and heated in hydrogen atmosphere to fill cracks in the tungsten and to get a proper surface to easily seal to glass. The borosilicate glass of usual laboratory glassware has a lower coefficient of thermal expansion than tungsten, thus it is necessary to use an intermediate sealing glass to get a stress-free seal.
In its early years as a colony, North Carolina settlements became an important source of the naval stores of tar, pitch, and turpentine, especially for the British navy. Tar and pitch were largely used to paint the bottom of wooden British ships both to seal the ship and to prevent shipworms from damaging the hull.
Penetrating sealants typically must be applied some time after curing. Sealants include paint, plastic foams, films and aluminum foil, felts or fabric mats sealed with tar, and layers of bentonite clay, sometimes used to seal roadbeds.
Pioneered by Scottish engineer John Loudon McAdam in the 1820s, macadam roads are prone to rutting and generating dust. Methods to stabilize macadam surfaces with tar date back to at least 1834 when John Henry Cassell, operating from "Cassell's Patent Lava Stone Works" in Millwall, patented "lava stone".
This method involved spreading tar on the subgrade, placing a typical macadam layer, and finally sealing the macadam with a mixture of tar and sand. Tar-grouted macadam was in use well before 1900, and involved scarifying the surface of an existing macadam pavement, spreading tar, and re-compacting. Although the use of tar in road construction was known in the 19th century, it was little used and was not introduced on a large scale until the motorcar arrived on the scene in the early 20th century.
There are many factors when considering what type of road surfacing is necessary. Most advantages to Otta seal over other inexpensive surfacing techniques spring from its ability to use a wide range of materials and material sizes during construction. Pros and cons are listed here:
Otta seal is more durable than many alternative seals. It is impermeable and resistant to cracking from the sun’s radiation. Cracks form in all roads due to changes in temperature, but Otta seal performs better than other seals. Overall, Otta seal can be expected to last 50 to 60 percent longer than a chip seal. This results in a lifespan between 6 and 12 years if properly maintained, and even longer if a sand seal is used on top of the Otta seal.