Benelux Scientific Technology Days Ghent, May 6th 2015

Transcription

1 Benelux Scientific Technology Days Ghent, May 6th 2015 Dr. Peter Paplewski, Dipl. Chem. Product Manager, CS/ONH-Analyzers, Kalkar, Germany May 6, 2015

2 Bruker Elemental CS, ONH, dh Analyzers Fundamentals, Overview & Applications (Do s & Don ts) of CS & ONH Analysis (by Combustion & IGF) 1. Carbon & Sulfur by combustion (induction furnace) 1. Introduction & Principles 2. Related Standards & Norms 3. Sulfur recovery & moisture, flowpath inertness 4. Possible Difficulties (in general) 5. Tips 2. ONH by Inert Gas Fusion 1. Principles of IGF 2. The Chemistry behind IGF: possible side reactions and how to avoid them 3. IGF related Standards & Norms May 6,

3 Bruker Elemental CS, ONH, dh Analyzers Fundamentals, Overview & Applications (Do s & Don ts) of CS & ONH Analysis (by Combustion & IGF) 2. ONH by Inert Gas Fusion continued 4. Some special Applications: a) ON in Al samples b) ONH in Ti c) H in high purity Al d) Ar in HIP samples by MS 5. Carrier gas selection May 6,

4 1. Carbon & Sulfur by Combustion Facts about Sulfur Sulfur Occurs in elemental form, as sulfidic minerals/ores (e.g. FeS 2, PbS, ZnS) and sulfate minerals Sulfur is an essential element for all life (e.g. amino acids) and present in coal, crude oil and other organic metabolites Burning of coal, coke and petroleum sets free large amounts of SO 2 and in presence of water & oxygen, SO 3. These react further to sulfurous acid (H 2 SO3) and sulfuric acid (H 2 SO 3 ) acid rain Sulfur is a strong poison to catalysts and highly unwanted in most intermediate & final products. Environmental restrictions for the emission of sulfur compounds are getting lower every few years. May 6,

5 1. Carbon & Sulfur by Combustion Why Carbon and Sulfur? Sulfur Undesirable in steel Influences brittleness, conductivity, workability, formability, etc. Carbon Typical concentration in steel: ~ ppm S Most alloying element in steel Influences hardness, wear resistance, workability, etc. Typical concentrations: Carbon steel: ~0.05-2% C Cast iron: ~2-3% C Tungsten carbide: ~6.1% C May 6,

6 1. Carbon & Sulfur by Combustion 1. Operation Principle Simultaneous determination of carbon and sulfur by combustion of a solid sample in a ceramic crucible within a pressurized oxygen flow in a high frequency induction furnace (under presence of a conductive accelerator). Transport of the formed CO 2 and SO 2 with the carrier gas oxygen through selective NDIR detectors Integration of the signals and calculation of results D M n {C x,s y } m n M + m{x C + y S} O 2 + {C} D O 2 in excess CO 2 (+ CO) 350 C Pt cat., O 2 CO 2 O 2 + {S} D O 2 in excess SO 2 ( but ) 350 C Pt cat., O 2 SO 2 + SO 3 order of detection matters: SO 2 first, then CO 2 May 6,

7 Differential Pressure Sensor - H 2 O 1. Carbon & Sulfur by Combustion 1. Operation Principle SO 2 HIGH IR SO 2 LOW IR Particle Filter MV2 Autocleaner assembly 3 μm Dust filter nom. 5.5 bar 6-10 bar 8888 ΔP U Air Catalyst Heater (350 C) converts CO to CO 2 and part. SO 2 to SO 3 Pressure / Flow Regulator Nozzle Crucible Sample HF-Coil 8888 P U - H2O - CO2 MV1 Free of Oil nom. 3.5 bar 3-4 bar O 2 - SO3 Crucible lift Digital pressure sensor 99,996 % CO 2 LOW IR CO 2 HIGH IR Digital Flow Sensor 8888 Q U MV3 EXHAUST IR Carrier Gas O 2 SO 2 Analysis Flow SO 3 Analysis Flow CO Analysis Flow CO 2 Analysis Flow Infrared Flowcell May 6,

8 1. Carbon & Sulfur by Combustion 1. Operation Principle: Reagents The order in which things are done matters also during carrier gas precleaning! To remove CO 2 and moisture traces from pure Oxygen stream, traps/scrubbers filled with reagents are used. RT 2 NaOH + CO 2 Na 2 CO 3 + H 2 O CO 2 scrubbing releases water! Always put a moisture trap after the CO 2 scrubber. When using combi-tubes verify correct order. Some permanent gases (CO, CH 4 ) cannot be scrubbed. If these exist as contaminants in the Oxygen, they can react in the hot zone to CO 2 (and water). The amount of oxidation varies depending on the temperature of sample & crucible and cannot be calibrated away. Watch your gas quality! Check CO 2 baseline returning to zero while crucible is hot (e.g. when running conditioners ). May 6,

9 1. Carbon & Sulfur by Combustion 1. Operation Principle: HF-Generator Induction Heating: Heating of an electrically conducting material (usually metal) by electromagnetic induction Application of AC power with high voltage and high frequency The alternating electromagnetic field induces eddy currents in the sample inside a coil The resistance leads to Joule heating of the metal Short interaction times to reach the required temperature May 6,

10 1. Carbon & Sulfur by Induction Accelerators I Why do we need accelerators at all? Accelerators are a conductive metal and needed to provide a handle (an interaction coupling) to the HF field coming from the HF-generator. Otherwise nothing will happen with a nonconductive sample. Another purpose of the accelerator is to ignite or set fire to the sample. The combustion of the accelerators used is exothermic what means it sets free additional energy. Accelerators can also double as a flux to dissolve oxide skins and make the melt thoroughly fluid. Note: A completely fluid melt is essential in order to oxidize the carbon and sulfur in the sample in a short time. ALWAYS watch your melt and follow the one cannot find too much rule May 6,

11 1. Carbon & Sulfur by Induction Accelerators II Tungsten Good general purpose accelerator for plain carbon steels providing excellent combustion characteristics when combined with tin. Tin Typically used as an additive to tungsten, copper and iron. Burns readily, producing a lot of heat. It can lower the liquefaction temperature of the melt, acting as a flux. Iron chip Used for both carbon and sulfur determination in some ferroalloys as well as nonferrous materials. Usually combined with tungsten or tin. Copper chip Excellent accelerator/flux for carbon determination (particularly in ultra low carbon determination) in steel, nonferrous metals and alloys. Usually combined with iron chip when nonferrous materials are analyzed. Copper accelerator is normally not recommended for sulfur determination in ferrous materials. May 6,

12 1. Carbon & Sulfur by Induction Principle of a NDIR Detector Molecules absorb infrared radiation under excitation to specific levels of higher rotational and vibrational (rovibrational) energy IR-Source Sample Gas Optical narrowband filter IR-Sensor NDIR = non-dispersive IR: Wavelength is selected by narrow-band filters to the specific molecule, here to CO 2 and SO 2, resp. Due to the absorption by the particular molecule, the transmission of the IR light is attenuated, which is registered by the sensor IR sensors used (e.g. Pyroelectric) require choppering of the source May 6,

13 1. Carbon & Sulfur by Induction 1. Operation Principle: Quantification Peak areas = integrals I correspond to the concentration of the element in the sample: c = (I x F)/m F = calibration factor or function m = sample mass I No absolute method F must be determined by calibration with CRM Lambert-Beer law is an ideal law. Deviations are compensated by linearization May 6,

14 1. Carbon & Sulfur by Induction 2. Applications Applications Metals Steel, cast iron Copper, brass Iron, nickel, cobalt alloys Ferroalloys Titanium and alloys Zirconium and alloys Tungsten and alloys Precious metals Minerals Lime, limestone, gypsum Cement Ceramics Markets Aerospace Automotive Casting Ceramics and cement industry Chemical plants and refineries Contract laboratories Marie and military Research labs, universities Primary-metal production industry Steel, iron, copper, etc. Foundries Metal processing and machining industry Forging plants Rolling mills May 6,

15 1. Carbon & Sulfur by Induction 2. Related Standards/Norms I ASTM E 1019 Standard Test Methods for Determination of Carbon, Sulfur, Nitrogen and Oxygen in Steel and in Iron, Nickel, and Cobalt Alloys ASTM E 1587 Standard Test Methods for Chemical Analysis of Refined Nickel ASTM G 79 Standard Practice for Evaluation of Metals Exposed to Carburization Environments ASTM C 1494 Standard Test Methods for Determination of Mass Fraction of Carbon, Nitrogen, and Oxygen in Silicon Nitride Powder ASTM E 1941 Standard Test Method for Determination of Carbon in Refractory and Reactive Metals and their Alloys ASTM E 1915 Standard Test Methods for Analysis of Metal Bearing Ores and Related Materials by Combustion Infrared Absorption Spectrometry May 6,

16 1. Carbon & Sulfur by Induction 2. Related Standards/Norms II ASTM D 1552 Standard Test Method for Sulfur in Petroleum Products (High-Temperature Method) ASTM C 25 Std. Test Methods for Chemical Analysis of Limestone, Quicklime and Hydrated Lime ASTM C 1408 Standard Test Method for Carbon (Total) in Uranium Oxide Powders and Pellets By Direct Combustion-Infrared Detection Method UOP 703 Carbon on Catalysts by Induction Furnace Combustion and Infrared Detection as well as many ISO Methologies Carbon: ISO 9556 (steel & iron), (soil), (steels & iron), ([U, Gd]O 2, [U, Pu]O 2 ), 9891 (UO2), (unalloyed steel) Sulfur: ISO 4935 (steel & iron), (steel &iron), 4689 (iron ores), 7524, 7526 (Ni, Ni alloys, Fe-Ni), (steel & iron: C&S) May 6,

17 1. Carbon & Sulfur by Induction 3. Sulfur Recovery & Water SO 2 losses do often occur after the combustion In combination with moisture SO 2 forms highly corrosive species, that tend to stick on the wall and thus retard or retain SO 2 delivery to the detectors. Possible sources of moisture are: Carrier gas (e.g. medical grade Oxygen); the capacity of the build-in pre-cleaning is limited Organic matter present in the sample (or carrier gas) that combust to CO 2 and H 2 O Non dried samples or samples that contain Hydroxides or Hydrides (minerals, (hydrated) lime, etc.) or samples that contain water in form of crystal water will release high amounts of water during combustion Ambient Air Humidity: Especially when the analyzer is cold or during breaks Close the furnace and use standby mode. Active heating of the dust filter over the dwell point helps to overcome pause effects. May 6,

18 1. Carbon & Sulfur by Induction 3. Sulfur Recovery & Inertness How to overcome or minimize Sulfur Recovery Problems? Verify chemical inertness of the entire analytical flow path! Prefer PFA (or PTFE) lines over stainless steel (high Mn) lines for the analysis gases. Remove moisture immediately, check moisture scrubber if in doubt. When running samples like limestone, minerals and Hydroxides, use a build-in membrane dryer (Nafion polymer) directly after the furnace. This dramatically improves Sulfur on this samples (and reduces moisture scrubber consumption with no add. operation costs) May 6,

19 1. Carbon & Sulfur by Induction 4. Difficulties (General) Problems due to MO X dust build up {M} + n O 2 D MO 2n Not only the carbon & sulfur in the sample is oxidized but also the metallic sample (partially) and the accelerator. These MO X can leave the crucible as fine dust. This fine dust can act as a column to retard or retain analyte delivery to the detetctors depending on the amount and type of dust. Dust handling is important! Analyzers shall use automatic cleaning and reduce dust layer in the cold furnace room to a minimum. This applies especially to the dust filter area. May 6,

20 1. Carbon & Sulfur by Induction 4. Difficulties (Dust Handling) Gas extraction nozzle design ensures Perfect combustion tube integrity Makes the combustion tube (and nozzle) a real spare part, not a wear part or consumable Efficient combustion & dust handling Ring slit between crucible and nozzle ensures high interaction of Oxygen, gas extraction through nozzle ensures low dead volume, eliminates lance clogging. Minimizes dust contamination of combustion tube Allows most advanced cleaning & dust handling: May 6,

21 1. Carbon & Sulfur by Induction 4. Difficulties (Dust Handling) Pneumatic cylinder precharged Oxygen volume [1] Sintered metal filter (3µm) [2] [3] sharp edges wipers to clean the system Plunger with tip for nozzle cleaning Unique vacuum-free Autocleaner Fast, efficient, quiet cleaning One stroke to clean dust filter and nozzle; noise free. Dust disposal into spent crucible Cleaning works with crucible in place. Integrated System No maintenance intensive add-on components required; no vacuum cleaners, dust boxes, pinch vales, etc. Extraction nozzle Quartz combustion tube May 6,

22 1. Carbon & Sulfur by Induction 4. Difficulties (General) Some MO X are known to interact with SO 2 Certain metals and their oxides are known to create sulfur recovery problems. These include: Mn, Cu, Sn, Pb, Pt, Ir, Pd Although the exact reasons are unknown, two possible reasons exist: 1. Absorption/scrubbing of SO 2 (by MnO 2, PbO 2, CuO, ) will happen generally in the cold zone of the furnace (dust filter, combustion tube, etc.) by the dust produced during combustion Possible check with porous crucible covers 2. Catalytic Oxidation of SO 2 to SO 3 will happen in the hot zone (crucible itself) Possible check by adding material to a CRM May 6,

23 1. Carbon & Sulfur by Induction 5. Tips Light particles might be partially drawn away by a high lance or purge flow. Check by weighing back the crucible (without combusting). If a problem (showing up in C&S) either use capsules or cover powder by a layer of quartz sand. Very little sample mass with non-conductive material can also represent a problem (not enough melt to be homogeneous) use quartz sand Sn accelerator even when used in combination reduces the SO 2 response factor (compared to W, Fe). It is stable but you need other S-calibration Cu accelerator is the preferred accelerator for carbon only analysis. Manual cleaning of any CuO is required before measuring low S again. What channel (C, S or both) is affected? when trouble shooting - always - ask yourself this question May 6,

24 1. Carbon & Sulfur by Induction 5. Tips Problems related only to Carbon are most likely due to residual carbon in the consumables (crucible, accelerator, gas) or contaminations in the system (e.g. silicon grease) bake out the system while watching carbon baseline. Sometimes a different blank due to different sample mass (and therefore heat to the crucible) can conrtribute Problems related only to Sulfur are most likely due to moisture or dust. Check gas & sample for moisture; verify moisture scrubber is fresh, use membrane dryer. Check for dust build up and clean. Check sample for sulfur recovery problems (e.g. Cu) Problems related to both check for leaks and losses of samples. If not successful call service (and report your findings) May 6,

25 2. ONH by Inert Gas Fusion 1. Facts about Gases in Metals Oxygen forms oxidic inclusion with Al, Si, Ca, in steel inclusions degrade mech. properties (e.g. impact strength, aging brittleness) Oxygen entering steel while forging causes red shortness Nitrogen forms inclusions which reduce toughness, aging stability and increase risk due to segregation (> 120 ppm) alloying of N, (e.g. 0.4%) for stabilizing of austenitic grades (CrNiMn steel) and improving the hardness of Mn steels Hydrogen strong influence on mechanical properties of steel: forming pores and crackings Can lead to most diverse form of damage: flake formation, pickling blistering, hydrogen-induced embrittlement and crack formation May 6,

26 2. ONH by Inert Gas Fusion 1. Operation Principle The Principle: Inert Gas Fusion Method Also referred to as Gas Fusion Analysis (GFA) or Carrier Gas Hot Extraction (CGHE) methods. Sample is fused in a high-purity graphite crucible at temperatures up to 3000 º C Oxygen reacts with Carbon (from graphite) to CO and will be measured with IR-Cells Nitrogen appears as N 2 and will be measured with TC-cell Hydrogen appears as H 2 and will be measured with TC-cell Thermal conductivity: He/H 2 and N 2 /Ar have similar TC. Thus N 2 or Ar is used for determination of Hydrogen; He for determination of Nitrogen May 6,

27 2. ONH by Inert Gas Fusion 1. Operation Principle May 6,

28 2. ONH by Inert Gas Fusion 2. The Chemistry Inert gas atmosphere/carrier gas (He, Ar) Presence of elemental carbon (e.g. graphite crucible) in excess High Temperatures >>2500 C needed to decompose refractories The ideal reactions would release only CO, H 2 and N 2 : M n {O x,n y,h z } m O 2 + {C} CO 2 + {C} T >> m.p. inert gas atm. T > 1800 C inert gas atm. T > 1000 C n M + m{x/2 O 2 + y/2 N 2 + z/2 H 2 } 2 CO (+ CO 2 ) 2 CO (Boudouard Equilibrium) But the yield of equilibrium reactions depend on: T, p, c 0 and when heterogeneous (s/g) reactions are considered on the dwell/contact time There are some well known, reactions that destroy this ideal world

29 2. ONH by Inert Gas Fusion 2. The Chemistry It is know H 2 reacts with {C} beginning at 1600 C; when higher T is applied, significant losses of H 2 appear in form of CH 4 : 2 H 2 + {C} T > 1600 C inert gas atm. CH 4 Severe side reactions appear when even trace levels of moisture are present (e.g. carrier gas, large surface non-dried samples, leaks, ): CO + H 2 O CO 2 + H 2 {C} + H 2 O CO + H

30 2. ONH by Inert Gas Fusion 2. The Chemistry If no stringent Temperature control is applied, the primary products of an IGF analysis are not only CO, N 2 and H 2 but also CO 2, CH 4 Hydrogen can appear as H 2, CH 4 Oxidation of CH 4 (from H 2 ) to CO 2 and H 2 O results in false positive amounts of O (if O is determined via CO 2 ) and losses of H 2 if Hydrogen is only assessed as H 2 In the presence of H 2 O (moisture), the H & O determination problem is simply not solvable due to conversion reactions

31 2. ONH by Inert Gas Fusion 3. Related Standards ASTM E 1019 Standard Test Methods for Determination of Carbon, Sulfur, Nitrogen and Oxygen in Steel and in Iron, Nickel, and Cobalt Alloys ASTM E 2575 Standard Test Method for Determination of Oxygen in Copper and Copper Alloys ASTM E 1409 Standard Test Method for Determination of Oxygen and Nitrogen in Titanium and Titanium Alloys by the Inert Gas Fusion Technique ASTM E 1447 Standard Test Method for Determination of Hydrogen in Titanium and Titanium Alloys by the Inert Gas Fusion Thermal Conductivity Method ASTM E 1937 Standard Test Method for Determination of Nitrogen in Titanium and Titanium Alloys by the Inert Gas Fusion Technique ASTM E 1569 Standard Test Method for Determination of Oxygen in Tantalum Powder May 6,

32 2. ONH by Inert Gas Fusion 2. Related Standard II ASTM E 1587 Standard Test Methods for Chemical Analysis of Refined Nickel ASTM E 2792 Standard Test Method for Determination of Hydrogen in Aluminum and Aluminum Alloys by Inert Gas Fusion as well as many ISO Methologies Steel & Iron: ISO , 10720, 15351, Titanium: ISO UO 2, PuO 2 : ISO May 6,

33 2. ONH by Inert Gas Fusion 4. Appl. a) ON in Al O(N) in Al requires a temperature of ~2300 C to decompose the material When using capsules, no flux is required H in Al is straight forward with T ~1650 C Comparison of m.p. Al: 660 C AlH 3 : 100 C (decomp.) AlN: 2200 C Al 2 O 3 : 2050 C Weight [g] Oxygen [%] Nitrogen [%] Mean: Weight [g] Hydrogen [%] Mean: May 6,

34 2. ONH by Inert Gas Fusion 4. Appl. b) ONH in Ti N(O) in Ti is a high temperature application! Ni-flux (low Oxygen!) required in 1:10 ratio Normally sample (0.1g) is packed into a low Oxygen Ni-basket. Standard Ni needs to be etched. Nibbled Ni can be used as well. Pt flux works better ($$$) and is still reference method Comparison of m.p. Ti: 1668 C TiH 2 : 600 C (decomp.) TiN: 2950 C TiO 2 : 1835 C ASTM dictates addition of carbon black prior to degassing Only when using Ni flux (not with Pt). Graphite prevents dome formation, improves O results with samples > 1000 ppm Oxygen H in Ti is low temperature application N 2 carrier gas reacts with Ti! Use Sn pellets or Ar carrier gas. May 6,

35 Hydrogen in Aluminum Pore Formation In aluminum production and casting Hydrogen can lead to pore and crack formation With welding H 2 dissociates in the arc into H + H (atomic). Liquid aluminum has a high solubility of atomic hydrogen When cooling down (liquid/solid) solubility of hydrogen decreases Solved H atoms in the lattice recombines to H 2 molecules Hydrogen molecules escape from the melt as gas bubbles When gas bubbles are included with solidification, voids filled with H 2 are formed: pores Solubility in the hot zone melting point Solubility, liquid m.p. Solubility, solid m.p. boiling point REM-picture of a pore Source: Internet, MIG WELD, Landau 35

36 2. ONH by Inert Gas Fusion 4. Appl. c) H in h.p. Al Al rods from the melt Al wire Before After Before After Removal of the furnace by turning with cooling, cleaning, storage in isopropanol, immediate analysis Sample size max. 16x9 mm Heating cold furnace to about C crucible temperature Automatic melting point detection by pyrometer switches off furnace power Cut off pieces (8 mm length) from cleaned or uncleaned welding wires Sample weight about mg Furnace power switch-off after fixed, programmed time Heating time must be determined by trials, e.g. 18 s, total analysis time approx. 2 min 36

37 2. ONH by Inert Gas Fusion 4. Appl. c) H in h.p. Al Extract from App Note AN1310 (see also ASTM E ) Typical Results: #1: (8) ppm, n = 10 #2: (3) ppm, n = 10 #3: (3) ppm, n = 5 #4: (8) ppm, n = 5 #5: (5) ppm, n = 5 One s STD in brackets May 6,

38 2. ONH by Inert Gas Fusion 4. Appl. d) Ar in HIP by MS MS coupled to IGF analyzer for ppb level LODs High purity (5.0) Ar used as working gas but residual contamination incl. water still present a problem. Ar entering the capsule forms inclusions. Standard Values: < 60 ng/g part can be used without problems ng/g part qualification depends on application ng/g customer release required > 400 ng/g part is scrap Chemical Analysis necessary Light microscopy cannot differentiate between Ar and other non metallic inclusions, values of 400 ng/g are not reliably determined. May 6,

39 2. ONH by Inert Gas Fusion 5. Carrier gas selection Nitrogen Determination by IGF with TCD He shortage the related high prices and availability issues are well known ( no need to stress any further) TCD compares the thermal conductivity of the pure carrier gas (reference) with the analytical gas flow (measure). Sensitivity scales 1:1 with the difference of TC between carrier gas and the analyte. He => Ar for N 2 determination: What do we expect? Gas Type CAS# Molar Mass [kg/kmol] Density [kg/m^3] (0 C, 1.013bar) c p [kj/(kg K)] spec. Heat capacity Therm. Conduct. [W/(m K)] dyn. Viscosity [N s/m^2] H E-06 He E-05 N E-05 Ar E-05 Source: Messer Griesheim ~ 8.5 May 6,

40 2. ONH by Inert Gas Fusion 5. Carrier gas selection Nitrogen Determination by IGF with TCD using Ar He => Ar conversion: Penalty Comparing the 2 carrier gases: Ar has ~8.5 lower TC than He. But we are comparing two carrier gases. What matters is analyte vs. carrier gas: DTC 1 : He N 2 = (DTC 1 / DTC 2 ) = DTC 2 : Ar N 2 = Recent TCD developments improved the stability for long measuring times, introduced on-the-fly programmable amplifiers and polarity switching. Real World performance He vs. Ar out-of-the-box (changed TCD amplification); ppm N range, 1g & 0.5g sample May 6,

41 2. ONH by Inert Gas Fusion 5. Carrier gas selection Helium Carrier Gas Argon Carrier Gas Meas. Sample Code Time in sec N in ppm Integral Time in sec N in ppm Integral 1 CSN , , CSN , , CSN , , CSN , , CSN , , CSN , , CSN , , CSN , , CSN , , CSN , , Average: 28, Average: 29, Factor Area He/Ar : 4,27 Std.Dev.: 0,80 Std.Dev.: 0,67 RSD: 2,85 RSD: 2,24 May 6,

42 2. ONH by Inert Gas Fusion 5. Carrier gas selection Conclusion He => Ar conversion: Penalty? Changing the TCD gain on-the-fly reduces the penalty factor from ~16 to ~4 without further modifications. Real world performance Allows reliable measurement of 20ppm N with 0.5g sample. Switching back to He possible any time. No additional modifications (~30s longer analysis times using Ar). Ready to run on Ar? Ar is good enough for 90% of all measurements in the steel industry, annual savings up to 60k possible. May 6,

43 Copyright Bruker Corporation. All rights reserved.