The surface layer is blasted off the white dwarf, increasing luminosity by a factor on the order of 50, The white dwarf and companion remain intact, however, so the process can repeat. Analogous to the process leading to novae, degenerate matter can also accumulate on the surface of a neutron star that is accreting gas from a close companion. If a sufficiently thick layer of hydrogen accumulates, ignition of runaway hydrogen fusion can then lead to an X-ray burst.
As with novae, such bursts tend to repeat and may also be triggered by helium or even carbon fusion. A type Ia supernova results from runaway carbon fusion in the core of a carbon-oxygen white dwarf star. If a white dwarf, which is composed almost entirely of degenerate matter, can gain mass from a companion, the increasing temperature and density of material in its core will ignite carbon fusion if the star's mass approaches the Chandrasekhar limit.
This leads to an explosion that completely disrupts the star. Luminosity increases by a factor of greater than 5 billion. One way to gain the additional mass would be by accreting gas from a giant star or even main sequence companion. A pair-instability supernova is believed to result from runaway oxygen fusion in the core of a massive , — solar mass, low to moderate metallicity star. As the core heats further, the gamma rays eventually begin to pass the energy threshold needed for collision-induced decay into electron - positron pairs, a process called pair production.
This causes a drop in the pressure within the core, leading it to contract and heat further, causing more pair production, a further pressure drop, and so on. The core starts to undergo gravitational collapse. At some point this ignites runaway oxygen fusion, releasing enough energy to obliterate the star. These explosions are rare, perhaps about one per , supernovae. Not all supernovae are triggered by runaway nuclear fusion. Type Ib, Ic and type II supernovae also undergo core collapse, but because they have exhausted their supply of atomic nuclei capable of undergoing exothermic fusion reactions, they collapse all the way into neutron stars , or in the higher-mass cases, stellar black holes , powering explosions by the release of gravitational potential energy largely via release of neutrinos.
It is the absence of runaway fusion reactions that allows such supernovae to leave behind compact stellar remnants. From Wikipedia, the free encyclopedia. December Abrupt Climate Change. A Report by the U. Geological Survey. March Retrieved 9 January Learning from Accidents 3rd ed. Oxford U. And Then the Catastrophe". Archived from the original on Retrieved 16 April Science Translational Magazine.
American Association for the Advancement of Science. November Solid-State Electronics. Bibcode : SSEle. IAEI Magazine. Retrieved Microelectronics Reliability. Archived from the original PDF on May 2, Nature Communications. Bibcode : NatCo CNN Money. Consumer Product Safety Commission. The Inquirer. National Transportation Safety Board. September 26, Stellar Structure and Evolution lecture notes.
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The Astrophysical Journal. Bibcode : ApJ Retrieved 15 August The Astrophysical Journal Letters. To ensure optimization and safety of Grignard reactions in research, development and production, in situ monitoring and understanding reaction heat flow is important. Hydrogenation reactions are used in the manufacturing of both bulk and fine chemicals for reducing multiple bonds to single bonds. Catalysts are typically used to promote these reactions and reaction temperature, pressure, substrate loading, catalyst loading, and agitation rate all effect hydrogen gas uptake and overall reaction performance.
Thorough understanding of this energetic reaction is important and PAT technology in support of HPLC analysis ensure safe, optimized and well-characterized chemistry. These chemistries often involve highly exothermic reactions which require specialized equipment or extreme operating conditions such as low temperature to ensure adequate control.
Ensuring safe operating conditions, minimizing human exposure, and gaining the maximum amount of information from each experiment are key factors in successfully designing and scaling-up highly reactive chemistries. Particularly challenging is the fact that sampling the reactor contents during the reaction is often impractical or impossible under the desired operating conditions. In addition, as highly reactive materials are often unstable, the accuracy of any possible offline analysis is often limited. Handling of reagents can be minimized through the use of synthesis workstations, a new generation of technology, that are designed to provide high quality synthetic conditions such as control over temperature and pH , a degree of automation of methods, and importantly greatly reduce the amount of material that comes into contact with the operator.
This technology allows scientists to design and develop better and safer processes through the delivery of information regarding the behavior of reaction species such as starting materials, intermediates and products, allowing them to gain a greater understanding of the reaction being studied. Continuous flow chemistry opens options with exothermic synthetic steps that are not possible in batch reactors, and new developments in flow reactor design provide alternatives for reactions that are mixing limited in batch reactors.
This can often result in better product quality and higher yield. When coupled with Process Analytical Technology PAT , flow chemistry allows for rapid analysis, optimization, and scale-up of a chemical reaction. Measuring and understanding polymerization reactions, mechanisms, kinetics, reactivity ratios, and activation energies lead researchers to employ in situ infrared spectroscopy as a routine technique to gain comprehensive, information-rich data that is used to advance research in a shorter time frame.
Optimization and scale-up of crystallization and precipitation to produce a product that consistently meets purity, yield, form and particle size specifications can be one of the biggest challenges of process development. Scientists and engineers eliminate risks of explosions in a chemical plant with a comprehensive safety study.
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The safety study is applied to develop a process that eliminates uncontrolled heat or gas generation, flammable vapor release, or an over-pressurization of the reactor leading to rupture and loss of contents, which may be flammable. In order to avoid the risk of uncontrolled heat generation, reaction calorimetry determines the heat of reaction and the rate of heat release, so that a process can be designed that minimizes the risk of loss of control. Essential measurements and calculations are necessary to model runaway scenarios and establish the ideal reaction procedure.
Measuring, calculating, and understanding the parameters are essential to assess and avoid risk in a chemical process. This allows scientists to make predictions about the temperature profiles, maximum operating temperature, and dosing. The heat of reaction, or reaction enthalpy, is an essential parameter to safely and successfully scale-up chemical processes.
The heat of reaction is the energy that is released or absorbed when chemicals are transformed in a chemical reaction. Transport and Logistics. Expertise Library.
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Develop a Safe Chemical Process Prevent Runaway Chemical Reactions Analyzing reaction dynamics allows scientists to model runaway reaction scenarios and establish the ideal reaction procedure. From the view point of thermochemistry, the key information is: 1.
Accumulation and Heat Evolution During a Chemical Reaction Accumulation usually refers to either material being dosed during a semi-batch reaction, which does not react right away, or energy that is accumulated because the heat production is larger than the heat removal capacity. Adiabatic Temperature Rise The Adiabatic Temperature Rise is a property which is calculated for any given reaction to indicate the potential severity of a cooling failure or other process upset.
Heat Capacity Heat Capacity or Specific Heat Capacity of a material describes the amount of energy required to increase the temperature of one kilogram of the material by one degree Celsius. Reaction Enthalpy The reaction enthalpy of a chemical reaction is the enthalpy change that occurs when substances are transformed by a chemical reaction.
Desired Reaction, Undesired Reaction Decomposition, Thermal Runaway A thermal runaway or thermal explosion may be the consequence of an adiabatic process of a reaction or series of reactions. Using Reaction Calorimeters Reaction Calorimeters determine a range of safety-related parameters with high accuracy.
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Heat Transfer and Process Scale-up. Mass Transfer and Reaction Rate. Chemical Reaction Kinetics Studies. Grignard Reaction Mechanisms. Hydrogenation Reactions. Highly Reactive Chemistry. Flow Chemistry. Polymerization Reactions. Crystallization and Precipitation. Prevent Runaway Chemical Reactions. Heat of Reaction. See details. Overview Publications Related Products. See less. Overview Applications Publications Related Products. Overview Applications Publications. Sustain a Culture of Safety. Insight for Every Reaction. Deliver From Lab to Plant. Resources to help design processes for manufacturability early in the process.
Guide to Chemical Process Safety. Guide to Process Safety discusses challenges to consider when designing a safe process including thermal hazard analysis in chemical production, runaw Risks From Rising Temperature. Harvey norman business plan. Peer pressure case study Peer pressure case study. Tips on how to write the best essay. Presenting results of literature review. Sdsu honors college essay examples. Narrative descriptive essay tips. Case study for international business management.
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