ball mills |
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Ball mills, also known as centrifugal or planetary mills, are devices used to rapidly grind materials to colloidal fineness (approximately 1 micron and below) by developing high grinding energy via centrifugal and/or planetary action. |
bar |
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Bar (bar) is a unit of pressure equal to 105 Pa. Its use is temporarily maintained with the SI. The milibar (100 Pa) is commonly used in meteorology. |
barrel |
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Barrel (US, petrol) is an American unit of capacity usually employed in the petroleum industry and trading in fuels (barell = 158.9872949 L). |
base |
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Historically, base is a substance that yields an OH - ion when it dissociates in solution, resulting in a pH>7. In the Brønsted definition, a base is a substance capable of accepting a proton in any type of reaction. The more general definition, due to G.N. Lewis, classifies any chemical species capable of donating an electron pair as a base. Typically, bases are metal oxides, hydroxides, or compounds (such as ammonia) that give hydroxide ions in aqueous solution. |
becquerel |
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Becquerel (Bq) is the SI derived unit, with a special name, for radioactivity, equal to s-1. It describes a radioactivity of an amount of radionuclide decaying at the rate, on average, of one spontaneous nuclear transition per second. The unit is named after the French scientist A. H. Becquerel (1852-1908) (disintegrations per unit time), equal to s-1. |
Beer's law |
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Beer's law is the functional relationship between the quantity measured in an absorption method (A) and the quantity sought, the analyte concentration (c). As a consequence of interactions between the photons and absorbing particles, the power of the beam is attenuated from P0 to P. Beer's law can be written
A = log (P0/P) = abc
where a is a proportionality constant called the absorptivity and b is the path length of the radiation through the absorbing medium. Also called the Beer-Lambert law. |
beta particles |
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Beta particle is a charged particle emitted from a radioactive atomic nucleus either natural or manufactured. The energies of beta particles range from 0 to 4 MeV. They carry a single charge; if this is negative, the particle is identical with an electron; if positive, it is a positron.
An unstable atomic nucleus changes into a nucleus of the same mass number but different proton number with the emission of an electron and an antineutrino (or a positron and a neutrino)
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beta radiation |
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Streams of beta particles are known as beta ray or beta radiation. Beta rays may cause skin burns and are harmful within the body. A thin sheet of metal can afford protection to the skin. |
biogas |
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Biogas is a mixture of methane and carbon dioxide resulting from the anaerobic decomposition of such waste materials as domestic, industrial, and agricultural sewage. Methanogenic bacteria carry out the decomposition; these obligate anaerobes produce methane, the main component of biogas, which can be collected and used as an energy source for domestic processes, such as heating, cooking, and lighting. |
black body radiation |
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Black body radiation is the radiation emitted by a perfect black body, i.e., a body which absorbs all radiation incident on it and reflects none. The wavelength dependence of the radiated energy density ρ (energy per unit volume per unit wavelength range) is given by the Planck formula
where λ is the wavelength, h is Planck's constant, c is the speed of light, k is the Boltzmann constant, and T is the temperature. |
blackbody |
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In radiation physics, an ideal blackbody is a theoretical object that absorbs all the radiant energy falling upon it and emits it in the form of thermal radiation. Planck's radiation law gives the power radiated by a unit area of blackbody, and the Stefan-Boltzman law expresses the total power radiated. |
Bohr magneton |
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Bohr magneton (μB) is the atomic unit of magnetic moment, defined as
μB = eh/4πme = 9.274×10-24 A m2
where h is Planck's constant, me the electron mass, and e the elementary charge. It is the moment associated with a single electron spin. |
boiling point |
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Boiling point is the temperature at which the liquid and gas phases of a substance are in equilibrium at a specified pressure. The normal boiling point is the boiling point at normal atmospheric pressure (101.325 kPa). |
Boltzmann constant |
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Boltzmann constant (k) is the molar gas constant R divided by Avogadro's constant. It has the value 1.380658×10-23 J/K. |
Born-Haber cycle |
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Born-Haber cycle is a cycle of reactions used for calculating the lattice energies of ionic crystalline solids. For a compound MX, the lattice energy is the enthalpy of the reaction
M+(g) + X-(g) → M+X-(s) ΔHL
The standard enthalpy of formation of the ionic solid is the enthalpy of the reaction
M(s) + 1/2X2(g) → M+X-(s) ΔHf
The cycle involves equating this enthalpy (which can be measured) to the sum of the enthalpies of a number of steps proceeding from the elements to the ionic solid. The steps are:
1) Atomization of the metal
M(s) → M(g) ΔH1
2) Atomization of the nonmetal
1/2X2(g) → X(g) ΔH2
3) Ionization of the metal
M(g) → M+(g) + e- ΔH3
This is obtained from the ionization potential.
4) Ionization of the nonmetal
X(g) + e- → X-(g) ΔH4
This is electron affinity.
5) Formation of the ionic solids
M+(g) + X-(g) → M+X-(s) ΔHL
Equation the enthalpies gives
ΔHf = ΔH1 + ΔH2 + ΔH3 + ΔH4 + ΔHL
from which ΔHL can be found. |
Boyle's law |
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Boyle's law is the empirical law, exact only for an ideal gas, which states that the volume of a gas is inversely proportional to its pressure at constant temperature. |
Bragg angle |
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Bragg angle (θ) is defined by the equation
nλ = 2dsinθ
which relates the angle θ between a crystal plane and the diffracted x-ray beam, the wavelength λ of the x-rays, the crystal plane spacing d, and the diffraction order n (any integer). |
Brownian motion |
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Brownian motion is the continuous random movement of small particles suspended in a fluid, which arise from collisions with the fluid molecules. First observed by the British botanist R. Brown (1773-1858) when studying pollen particles. The effect is also visible in particles of smoke suspended in a still gas. |
buffer |
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Buffer is a solution designed to maintain a constant pH when small amounts of a strong acid or base are added. Buffers usually consist of a fairly weak acid and its salt with a strong base. Suitable concentrations are chosen so that the pH of the solution remains close to the pKa of the weak acid. |
