UCLES

Plenary 18. Robin J FI Clark, e-mail address r.i.h.clark ucl.ac.uk (RS). Reports on recent diagnostic probing of art works ranging from illuminated manuscripts, paintings and pottery to papyri and icons. Nondestructive NIR microscopic RS is now realistic using CCD detection. Optimistic about new developments. 

The confidence limits for the slope are given by fc where the r-value is taken at the desired confidence level and (A — 2) degrees of freedom. Similarly, the confidence limits for the intercept are given by a ts. The closeness of x to X is answered in terms of a confidence interval for that extends from an upper confidence (UCL) to a lower confidence (LCL) level. Let us choose 95% for the confidence interval. Then, remembering that this is a two-tailed test (UCL and LCL), we obtain from a table of Student s t distribution the critical value of L (U975) the appropriate number of degrees of freedom. 

The average range for the 20 duplicate samples is 0.177. Because two replicates were used for each point, the UWL and UCL are... 

Interpreting Control Charts The purpose of a control chart is to determine if a system is in statistical control. This determination is made by examining the location of individual points in relation to the warning limits and the control limits, and the distribution of the points around the central line. If we assume that the data are normally distributed, then the probability of finding a point at any distance from the mean value can be determined from the normal distribution curve. The upper and lower control limits for a property control chart, for example, are set to +3S, which, if S is a good approximation for O, includes 99.74% of the data. The probability that a point will fall outside the UCL or LCL, therefore, is only 0.26%. The... 

Rule 1. A system is considered to be out of statistical control if any single point exceeds either the UCL or the LCL. 

BeCl2, CdCl, ZnCl2, BF, BCl, BBr, GaCl, GaBr, TiCl, ZrCl, SnCl, SnBr, SbCl, SbCl, BiCl, FeCl, and UCl. ... 

Fig. 3. Confidence limits for exposure levels. A, noncompliance B, possible overexposure C, compliance. STD is the standard value, LCL and UCL represent lower and upper confidence levels, between which it is 95% certain that the tme exposure Hes, and and correspond to two separate...

Fig. 2. An SPC control chart of the purity analysis of a reference standard where (—) represents the average value and UCL and LCL are the upper and...

Uranium [7440-61-17 is a naturally occurring radioactive element with atomic number 92 and atomic mass 238.03. Uranium was discovered in a pitchblende [1317-75-5] specimen ia 1789 by M. H. Klaproth (1) who named the element uranit after the planet Uranus, which had been recendy discovered. For 50 years the material discovered by Klaproth was thought to be metallic uranium. Pnligot showed that the uranit discovered by Klaproth was really uranium dioxide [1344-57-6] UO2, and obtained the tme elemental uranium as a black powder in 1841 by reduction of UCl [10026-10-5] with potassium (2). 

Preparation of Uranium Metal. Uranium is a highly electropositive element, and extremely difficult to reduce. As such, elemental uranium caimot be prepared by reduction with hydrogen. Instead, uranium metal must be prepared using a number of rather forcing conditions. Uranium metal can be prepared by reduction of uranium oxides (UO2 [1344-59-8] or UO [1344-58-7] with strongly electropositive elements (Ca, Mg, Na), reduction of uranium halides (UCl [10025-93-1], UCl [10026-10-5] UF [10049-14-6] with electropositive metals (Li, Na, Mg, Ca, Ba), electro deposition from molten... 

The electromagnetic separation plant built during World War 11 at Oak Ridge, involved two types of calutrons, alpha and beta. The larger alpha calutrons were used for the enrichment of natural uranium, and the beta calutrons were used for the final separation of U from the pre-enriched alpha product. For the electromagnetic separation process, UO was converted into UCl [10026-10-5] with CCl. The UCl was fed into the calutron for separation. The calutron technique has been used to separate pure samples of and stable isotopes of many other elements. The Y-12 calutron... 

Chlorides. The oHve-green trichloride [10025-93-1], UCl, has been synthesized by chlorination of UH [13598-56-6] with HCl. This reaction is driven by the formation of gaseous H2 as a reaction by-product. The stmcture of the trichloride has been deterrnined and the central uranium atom possesses a riine-coordinate tricapped trigonal prismatic coordination geometry. The solubiUty properties of UCl are as follows soluble in H2O, methanol, glacial acetic acid insoluble in ethers. 

Uranium tetrachloride [10026-10-5], UCl, has been prepared by several methods. The first method, which is probably the best, involves the reduction/chlorination of UO [1344-58-7] with boiling hexachloropropene. The second consists of heating UO2 [1344-57-6] under flowing CCl or SOCI2. The stmcture of the dark green tetrachloride is identical to that of Th, Pa, and Np, which all show a dodecahedral geometry of the chlorine atoms about a central actinide metal atom. The tetrachloride is soluble in H2O, alcohol, and acetic acid, but insoluble in ether, and chloroform. Industrially the tetrachloride has been used as a charge for calutrons. 

The reddish brown pentachloride, uranium pentachloride [13470-21 -8], UCl, has been prepared in a similar fashion to UCl [10026-10-5] by reduction—chlorination of UO [1344-58-7] under flowing CCl, but at a lower temperature. Another synthetic approach which has been used is the oxidation of UCl by CI2. The pentachloride has been stmcturaHy characterized and consists of an edge-sharing bioctahedral dimer, U2CI2Q. The pentachloride decomposes in H2O and acid, is soluble in anhydrous alcohols, and insoluble in benzene and ethers. 

The hexachloride, uranium hexachloride [13763-23-0], UCl, is best prepared by chlorination of UCl [10026-10-5] with SbCl. An alternative preparative approach is the disproportionation UCl [13470-21 -8] to UCl and UCl under reduced pressure. The obvious disadvantage of the second method is contamination by UCl, however, sublimation is a possible purification technique. Isostmctural with the hexafluoride, the hexachloride is monomeric with an octahedral arrangement of the chlorine atoms around the uranium center. 

Tetrakis-Cp uranium complexes are readily prepared via metathesis of UCl and KCp in refluxing benzene. These complexes are a relatively rare example of a pseudotetrahedral complex with four Tj -Cp rings, (rj-ring) (25). The Cp derivative has been shown to react with CO and CO2 to give acyl and carboxylato complexes. This complex also reacts with alkyl haUdes to afford the U(IV) complex, Cp UX (X = halide). 

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