Structure of gallium chalcogenide cubane compound, where E = S, Se, and R = CMe
3 , CMe
2 Et, CEt
2 Me, CEt
3 .
Data collection
In a typical experiment 5 - 10 mg of sample is used with a heating rate of ca. 5 °C/min up to under either a 200-300 mL/min inert (N
2 or Ar) gas flow or a dynamic vacuum (
ca . 0.2 Torr if using a typical vacuum pump). The argon flow rate was set to 90.0 mL/min and was carefully monitored to ensure a steady flow rate during runs and an identical flow rate from one set of data to the next.
Once the temperature range is defined, the TGA is run with a preprogrammed temperature profile (
[link] ). It has been found that sufficient data can be obtained if each isothermal mass loss is monitored over a period (between 7 and 10 minutes is found to be sufficient) before moving to the next temperature plateau. In all cases it is important to confirm that the mass loss at a given temperature is linear. If it is not, this can be due to either (a) temperature stabilization had not occurred and so longer times should be spent at each isotherm, or (b) decomposition is occurring along with sublimation, and lower temperature ranges must be used. The slope of each mass drop is measured and used to calculate sublimation enthalpies as discussed below.
A typical temperature profile for determination of isothermal mass loss rate.
As an illustrative example,
[link] displays the data for the mass loss of Cr(acac)
3 (
[link] a, where M = Cr, n = 3) at three isothermal regions under a constant argon flow. Each isothermal data set should exhibit a linear relation. As expected for an endothermal phase change, the linear slope, equal to m
sub , increases with increasing temperature.
Plot of TGA results for Cr(acac)
3 performed at different isothermal regions. Adapted from B. D. Fahlman and A. R. Barron,
Adv. Mater. Optics Electron ., 2000,
10 , 223.
Samples of iron acetylacetonate (
[link] a, where M = Fe, n = 3) may be used as a calibration standard through ΔH
sub determinations before each day of use. If the measured value of the sublimation enthalpy for Fe(acac)
3 is found to differ from the literature value by more than 5%, the sample is re-analyzed and the flow rates are optimized until an appropriate value is obtained. Only after such a calibration is optimized should other complexes be analyzed. It is important to note that while small amounts (<10%) of involatile impurities will not interfere with the ΔH
sub analysis, competitively volatile impurities will produce higher apparent sublimation rates.
It is important to discuss at this point the various factors that must be controlled in order to obtain meaningful (useful) m
sub data from TGA data.
The sublimation rate is independent of the amount of material used but may exhibit some dependence on the flow rate of an inert carrier gas, since this will affect the equilibrium concentration of the cubane in the vapor phase. While little variation was observed we decided that for consistency m
sub values should be derived from vacuum experiments only.
The surface area of the solid in a given experiment should remain approximately constant; otherwise the sublimation rate (i.e., mass/time) at different temperatures cannot be compared, since as the relative surface area of a given crystallite decreases during the experiment the apparent sublimation rate will also decrease. To minimize this problem, data was taken over a small temperature ranges (
ca . 30 °C), and overall sublimation was kept low (
ca . 25% mass loss representing a surface area change of less than 15%). In experiments where significant surface area changes occurred the values of m
sub deviated significantly from linearity on a log(m
sub ) versus 1/T plot.
The compound being analyzed must not decompose to any significant degree, because the mass changes due to decomposition will cause a reduction in the apparent m
sub value, producing erroneous results. With a simultaneous TG/DTA system it is possible to observe exothermic events if decomposition occurs, however the clearest indication is shown by the mass loss versus time curves which are no longer linear but exhibit exponential decays characteristic of first or second order decomposition processes.
Bacteria doesn't produce energy they are dependent upon their substrate in case of lack of nutrients they are able to make spores which helps them to sustain in harsh environments
_Adnan
But not all bacteria make spores, l mean Eukaryotic cells have Mitochondria which acts as powerhouse for them, since bacteria don't have it, what is the substitution for it?
Assimilatory nitrate reduction is a process that occurs in some microorganisms, such as bacteria and archaea, in which nitrate (NO3-) is reduced to nitrite (NO2-), and then further reduced to ammonia (NH3).
Elkana
This process is called assimilatory nitrate reduction because the nitrogen that is produced is incorporated in the cells of microorganisms where it can be used in the synthesis of amino acids and other nitrogen products
There are nothing like emergency disease but there are some common medical emergency which can occur simultaneously like Bleeding,heart attack,Breathing difficulties,severe pain heart stock.Hope you will get my point .Have a nice day ❣️
_Adnan
define infection ,prevention and control
Innocent
I think infection prevention and control is the avoidance of all things we do that gives out break of infections and promotion of health practices that promote life
