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Benzidine, (4,4'-diaminobiphenyl), is the solid organic compound with the formula (C6H4NH2)2.  It is a manufactured chemical that does not occur naturally. Benzidine is a crystalline (sandy or sugar-like) solid that may be greyish-yellow, white, or reddish-grey. It will evaporate slowly from water and soil. Its flammability, smell, and taste have not been described. In the environment, benzidine is found in either its "free" state (as an organic base), or as a salt (for example, benzidine dihydrochloride or benzidine sulphate). In air, benzidine is found attached to suspended particles or as a vapour.  Benzidine has been linked to bladder and pancreatic cancer. Since August 2010 benzidine dyes are included in the EPA's List of Chemicals of Concern.
Safety data sheets (SDSs) for several bulk flavourings failed to list hazardous substances, according to National Institute for Occupational Safety and Health (NIOSH) findings. Out of 26 bulk liquid flavourings obtained from two U.S. coffee roasting and packaging facilities, 21 contained diacetyl, and 15 contained 2,3-pentanedione. Inhalation of diacetyl may lead to obliterative bronchiolitis, a debilitating lung disease. Animal studies of 2,3-pentanedione, a common substitute, have found evidence of similar inhalational hazards. Of the 26 flavourings tested, 24 came from a single manufacturer. None of the SDSs listed diacetyl and 2,3-pentanedione.
Chemical manufacturers, distributors, and importers must provide employers with SDSs under the Occupational Safety and Health Administration’s (OSHA) hazard communication standard. SDSs notify employers of hazardous substances in the chemicals they purchase so they can implement appropriate controls to protect the health and safety of their employees. However, some substances may not be listed on an SDS for reasons that include:
Employers at the two coffee-roasting and packaging facilities asked NIOSH to perform a Health Hazard Evaluation out of concern about occupational exposure to flavouring chemicals and possible risks for respiratory impairment. One facility representative told NIOSH investigators the manufacturer said there was no added diacetyl or 2,3-pentanedione in its flavourings. The manufacturer later clarified to the facility that diacetyl may occur as a natural by-product of acetoin, which is added to almost all coffee flavours used by the facility. Workers in food-processing facilities face respiratory hazards due to inhalation of diacetyl and 2,3-pentanedione, which are emitted from bulk materials, especially at elevated temperatures.
Food Industry Hazards Identified
In August 2000, NIOSH investigated cases of obliterative bronchiolitis among former workers of a microwave popcorn plant. The institute determined that artificial butter flavourings added to the popcorn were responsible for causing the disease. NIOSH later found that flavourings used to produce flavoured whole-bean and ground-roasted coffee led to the same lung disease among workers employed in coffee roasting and packaging. There are no OSHA permissible exposure limits for diacetyl and 2,3-pentanedione. NIOSH has recommended exposure limits be set at an 8-hour time-weighted average (TWA) of 5 parts per billion (ppb) for diacetyl and 9.3 ppb for 2,3-pentanedione in workplace air. It also has recommended 15-minute TWA short-term exposure limits of 25 ppb for diacetyl and 31 ppb for 2,3-pentanedione.
Recommended Precautions for Employers
NIOSH recommends a series of controls and practices for food-processing employers to prevent or limit diacetyl and 2,3-pentanedione exposures:
Scientists from Tohoku University and the High Energy Accelerator Research Organisation have developed a new complex hydride lithium superionic conductor that could result in all-solid-state batteries with the highest energy density to date. The researchers say the new material, achieved by designing structures of hydrogen clusters (complex anions), shows markedly high stability against lithium metal, which would make it the ultimate anode material for all-solid-state batteries. All-solid-state batteries incorporating a lithium metal anode have the potential to address the energy density issues of conventional lithium-ion batteries. But until now, their use in practical cells has been limited by the high lithium ion transfer resistance, caused mainly by the instability of the solid electrolyte against lithium metal. This new solid electrolyte that exhibit high ionic conductivity and high stability against lithium metal can therefore be a real breakthrough for all-solid-state batteries that use a lithium metal anode. "We expect that this development will not only inspire future efforts to find lithium superionic conductors based on complex hydrides, but also open up a new trend in the field of solid electrolyte materials that may lead to the development of high-energy-density electrochemical devices," said Sangryun Kim of Shin-ichi Orimo's research group at Tohoku University. All-solid-state batteries are promising candidates for resolving the intrinsic drawbacks of current lithium-ion batteries, such as electrolyte leakage, flammability and limited energy density. Lithium metal is widely believed to be the ultimate anode material for all-solid-state batteries because it has the highest theoretical capacity (3860 mAh g-1) and the lowest potential (-3.04 V vs. standard hydrogen electrode) among known anode materials. Lithium-ion-conducting solid electrolytes are a key component of all-solid-state batteries because the ionic conductivity and stability of the solid electrolyte determine battery performance. The problem is that most existing solid electrolytes have chemical/electrochemical instability and/or poor physical contact against lithium metal, inevitably causing unwanted side reactions at the interface. These side reactions result in an increase in interfacial resistance, greatly degrading battery performance during repeated cycling. As revealed by previous studies, which proposed strategies such as alloying the lithium metal and interface modification, this degradation process is very difficult to address because its origin is the high thermodynamic reactivity of the lithium metal anode with the electrolyte. The main challenges to using the lithium metal anode are high stability and high lithium ion conductivity of the solid electrolyte. "Complex hydrides have received a lot of attention in addressing the problems associated with the lithium metal anode because of their outstanding chemical and electrochemical stability against the lithium metal anode," said Kim. "But because of their low ionic conductivity, using complex hydrides with the lithium metal anode have never been attempted in practical batteries. So, we were very motivated to see if developing complex hydride that exhibit lithium superionic conductivity at room temperature can enable the use of lithium metal anode. And it worked."