Current filament

Settings. X-ray tube primary voltage, 65.3 volts filament current, 10 ma detector voltage, 73 volts per stage. 

Adjust the filament current and voltage to their recommended values (as provided by your teacher) and allow the filament to warm up for several minutes. When the electron beam is strong and steady, darken the room. 

Thus, reducing the potential from 50.0 to 34.9 kV will reduce the intensity of the desired radiation ("Mo-Ka) by 68%. Although some of this loss in intensity may be recovered by increasing the filament current, this is not a convenient solution for most experiments. For samples which are strongly diffracting, e.g. minerals, this is a... 

Figure 15.8 Thermal conductivity bridge electronic circuit. 12 V dc power supply, stable to 1 mV. Ripple is not significant due to thermal lag of the filaments. Pj, 100 ohms for filament current control Mj, milliamp meter, 0-250 mA P2, 2 ohms for coarse zero. Filaments 1 and 4 are detector 1 2 and 3 are detector 2. P3,1 ohm for fine zero Ri j, R12, padding resistors 64 ohms Rj-Rio, attenuator resistors 1, 2, 4. .. 512 ohms Si (DPDT) switch for polarity. Attenuator resistors are 0.25 %w/w, lowest temperature coefficient all others are 1 %.

Gas Chromatography-Mass Spectrometry. A Finnigan 4500/Incos instrument with a 30-m X 0.32-mm i.d. capillary column coated with SP-B-5 was used. The GC parameters were as follows injector, 270 °C column oven temperature programmed, 50 °C (0.1 min, hold) 15 °C/min to 100 °C, 5 °C/min to 270 °C internal standard, anthracene-djo helium flow, 3.0 mL/min sample size, 3.0 /xL. MS conditions were as follows El, 70 eV scan (m/z), 35-650 daltons source temperature, 250 °C filament current, 0.5 A sensitivity, 10-8 A/V. (NOTE When the name of a compound is followed by (confirmed) , it means that the standard material was analyzed for confirmation under conditions identical to those of the sample when the name is followed by (tentative) , it means that the mass fragmentography showed the best fit (>80 ) based on the National Bureau of Standards [NBS] library computer search.)... 

It is common to split the carrier gas into two streams, sending part through the analytical column and part through a matched reference column. Each stream is passed over a different filament or alternated over a single filament. The resistance of the sample filament is measured with respect to that of the reference filament. The reference column minimizes flow differences when temperature is changed. Sensitivity increases with the square of the filament current. However, the maximum recommended current should not be exceeded, to avoid burning out the filament. The filament should be off when carrier gas is not flowing. 

Don t run out of carrier gas with the filament current on. As the air diffuses into the detector, the filaments will literally burn up. Some instruments have sensors that turn off the filaments if the carrier flow in interrupted, but it is safer not to rely on this feature. 

All samples were analyzed in an AllTech 1/8"I.D, 20 foot column, packed with VZ-7 resin, using helium as the carrier gas. This column proved more effective for the measurement of the C4 components than the Poropak- N column. Ammonia was not detected by this column and as a result some of the assumptions employed to treat the solvent phase are described in a later paragraph. The G.C. was run with the injector chamber set at 115 C, the column oven temperature at 60 C and the filament current set at 150 ma. Column analyses were performed by an Autolab Integrator. A Leeds and Northrup strip chart recorder was used to plot the output of the integrator and to... 

For instance, the 12AX7 twin triode tube has a 6.3-V filament voltage that produces a filament current of 0.3 A for a fixed plate voltage Eh = 250 and a grid voltage Ec = —2 V, one gets a plate current 4 = 1.2 mA, an amplification factor n = 100, a plate resistance rp = 62,500 Q, and a transconductance of 1.6 millisiemens. 

Fig. 8.—Acetylated Hydro(hydroxymethyl)ation Product of Tetra-O-acetyl-3-deoxy-a-D-eryf/iro-hex-2-enopyranose. (Column 12 x 3/8" 10% silicone gum rubber SE-52 on Chromosorb Wj column temp., 280 helium flow, 200 ml./min. detector temp., 310° injection temp., 280° filament current 150 mA.).

Spring connectors for filament current and accelerating potential... 

In your notebook record all information relevant to this analysis column diameter and length, column packing, carrier gas and its flow rate, filament current, temperature of column, detector and injection port, sample size, attenuation, and chart speed. 

Fig. 4-6. Detector circuits for vapor-phase chromatography, (a) Thermistor detector Di, D=, Victory Eng. Corp. 32A12 thermistors Ri, Ri, 1,0000 wire wound resistors Rz, 1,0000 Helipot Rt, 10,0000 1% carbon film resistor Rs, 5,0000 1 % carbon film resistor Rt, Rj, 2,5000 1 % carbon film resistor Sw, single-pole four-position switch, (b) Hot-wire detector Rz, filament current control, to adjust filament current between 150—300 ma ( 20 ohm 5w) Ri, R4, reference detectors Rs, R, sample detectors Re, zero control 20 Re, 600 1 % carbon film resistor R, 300 1 /, carbon film resistor R, 150 1% carbon film resistor Rse, 7.5Q 1 % carbon film resistor Rs, 7.SCI 1 % carbon film resistor M, 300 ma meter,- S, single-pole six-position sv/itch.

Attempts to produce boron fibers in a pure state have been frustrated by the brittleness of the material, which has hindered the manufacture of continuous filaments. Currently boron fibers are produced by chemical vapor deposition (CVD) in which boron is deposited by reducing BCI3 in a hydrogen-containing atmosphere at 1127 to 1177°C, according to the overall reaction ... 

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