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is about 10-15% of the purchase price for a new instrument of the same capability without an integrator and somewhat more if an integrator were purchased.
ri
ACKNOWLEDGMENT We wish to thank Alan Fredericks, formerly of Oceanography International Corp., and Edward Milukas of Beckman Instruments for their cooperation and technical advice and Richard Kerr for critically reading the manuscript.
SUPPLY
3- WAY VALVE AT ANALYZER
LITERATURE CITED (1) Menzel, D. W.: Vaccaro, R. F. Limnol. Oceanogr. 1964, 9 , 138-142. (2) van Steenderen, R. A.; Basson, W. D.; van Duuren, F. A. Water Res. 1979, 13, 539-543. (3) Kerr, R. A.; Quinn, J. G. Deep-sea Res. 1975, 22, 107-116. (4) Sharp, J. H. Mar. Chem. 1973, I , 211-229.
I L
Figure 1. Schematic representation showing how the Dow-Beckman carbonaceous analyzer Is interfaced with an ampule analyzing unit and
an improved read-out system. carbon, the determination of particulate organic carbon, sediment carbon, inorganic carbon, and even microbial biomass is also possible. The cost of the modification including the calibration gas arid catalytic furnace for O2 purification
RECEIVED for review February 26, 1981. Accepted April 6, 1981. This work was supported by National Science Foundation Grant No. OCE-74-01537-A02.
Dissolution of Elulk Specimens of Silicon Nitride Warren F. Davis" and Emery J. Merkle Natlonal Aeronautics anid Space Administration, Lewis Research Center, Cleveland, Ohio 44 135
Efforts currently being made to incorporate silicon nitride components into advanced heat engines have emphasized the need for accurate chemical characterization of this ceramic material. Recently research on this material has progressed to fabrication of turbline components. Chemical analysis of bulk specimens is made difficult or impossible because there are no suitable methods for dissolving solid silicon nitride. Grinding procedures result in serious contamination which cannot be compensated by a blank. This contamination is in addition to that contributed by reagents used to effect dissolution. Silicon nitride powder can be dissolved by fusion with 10-15 parts of various alkaline fluxes or by acid mixtures in a Teflon-lined pressure vessel at 150 "C. Parker and Healy (I) used a (1 1)mixture of concentrated hydrofluoric and hydrochloric acids. Feirraro and Strauss (2) used mixtures of hydrofluoric and nitric acid to decompose silicon nitride powder. Particle sizes were minus 44-mesh and minus 160mesh, respectively. Reference 2 mentions that a magnet was passed through the pulverized samples several times to remove iron contaminant picked up from the mortar and pestle. However, none of the above procedures is applicable to bulk silicon nitride. Furthermore, grinding media of steel, tungsten carbide, silicon carbide, or boron nitride are quickly scratched or destroyed due to the diamondlike hardness of silicon nitride. Our results show that up to at least 0.6 g solid pieces of various samples of hot pressed and reaction bonded silicon nitride can be decomposed in a mixture of 3 mL hydrofluoric acid and 1mL nitric acid overnight at 150 "C in a Model 4745 Parr bomb (Parr Instrument Co., Moline, IL). This result is advantageous for determinations of trace elements but seems contrary to what has lbeen reported in the literature. For this reason we further evduated this dissolution procedure using solid materials obtained by a variety of processing methods. Table I lists the types and size of samples which were successfully dissolved or decomposed in the Parr vessel.
+
Table I. Dissolution of Solid Silicon Nitride and Sialon Materials" sample wt , source/description mg Norton NC-132 (Norton Co., Worcester, MA) 147 Norton hot pressed Si,N, 269 Wesgo sintered ball (Western Gold and 462 Platinum Div. GTE, Belmont, CA) A M E Reaction Bonded Si,N, (Advanced 214 Materials Engineering, Ltd., Durham, England ) Reaction bonded Si,N,, vibratory milled 437 Polished Si,N,, wet milled 657 Avco billet 1016, hot pressed Si,N, 145 (Avco Corp., Wilmington, MA) Plessey hot pressed Si,N, 169 (Plessey, Inc., Frenchtown, NJ) Norton NCX-34, Lewis billet 27 217 Norton NCX-34, Lewis billet 28 178 Sialon 8F* 193 Sialon 8SL 192 a All of the Si,N, samples and the two sialon samples were decomposed by using 3 mL of hydrofluoric acid and 1mL of nitric acid in the Parr bomb overnight at 150 'C. Sialon is a generic name for ceramic containing silicon nitride, aluminum nitride, and aluminum oxide,
*
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High-purity silicon nitride is completely soluble in nitric acid after treatment in the bomb. However, materials of silicon nitride usually contain sintering additives, such as oxides of calcium, magnesium, and yttrium, in addition to impurities introduced by grinding with steel or tungsten carbide prior to consolidation. For these materials, additional sample preparation is necessary. Following decomposition, silicon and hydrofluoric acid are volatilized and insoluble fluorides are converted to a soluble form. Tungsten is kept
This article not subject to US. Copyright. Published 1981 by the American Chemical Soclety
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Table 11. Typical Concentration Ranges and Blanks for Impurity and Additive Elements element A1 Ca co
cr
cu Fe Mg Mn Ni Ti Y
w
concn, range, PPm 1400-2000 30-200 1500-4000 100-400 30-150 2000-3000 50-100 200-300 50-100
blank values, PPm 45, 45,45 2.9, 2.9, 2.9 4.3, 6.5, 4.3
