Introduction to Surface Area Analysis - Horiba

1 2014 Horiba , Ltd. All rights to Surface area AnalysisJeffrey Bodycomb, Pejcinovic, Amy HouHORIBA 2014 Horiba , Ltd. All rights Why determine Surface area ? Surface area and size Determining Surface area 2014 Horiba , Ltd. All rights Surface area ? Surface area directly correlates with desired properties. Reactivity Dissolution Catalysis Separation 2014 Horiba , Ltd. All rights Catalysts Adsorbents Pigments Pharmaceutical products Chromatographic carriers Sintered materials Building materials Ceramics Filters 2014 Horiba , Ltd. All rights reactionsWhen a solid is involved in a chemical reaction, either as a reagent or a catalyst, the Surface area is the only accessible area for the example: dust explosions! 2014 Horiba , Ltd. All rights Dissolution of materials ( , API s) depends on Surface area .

2 Noyes-Whitney Equation bsCCdDAdtdm m = mass dissolved materialt = timeA = Surface area of interfaceD = Diffusion coefficientd = Boundary layer thicknessCs= Concentration of substance on surfaceCb= Concentration of substance in solvent 2014 Horiba , Ltd. All rights Why determine Surface area ? Surface area and size Determining Surface area 2014 Horiba , Ltd. All rights a particle of a given volume is broken into two parts as shown in the figure, total volume does not change. The total Surface area , however, does change. It INCREASES by the amount of the two newly-exposed simple illustration demonstrates relationship between Surface area and particle size. As ratio of Surface area to volume increases, Surface phenomena come into play. For this reason, measurement of Surface area becomes much more important for small volume Smaller size -- greater Surface area Surface area vs.

3 Particle size 2014 Horiba , Ltd. All rights size -> Large Surface area 2014 Horiba , Ltd. All rights Size -> Large Surface area 2014 Horiba , Ltd. All rights 20 30 40 50 Particle size in microns15%25%30%20%10%Volume % in binSurface area mean size can be arithmetically calculated from a measured volume based particle size area and Size iiiVVdVD )/()/6()/6(iiiiiiiiiiiiiiSdVVdVddVSdSSdS D2)2/(4dS 3)2/(34dV 2014 Horiba , Ltd. All rights PARTICLE PARTICLEWITH SOME IRREGULARITY PARTICLEWITH DEEP INTERSTICES Surface area measurement using nitrogen adsorption detects total Surface area of the particles. Conventional particle sizing detects only the overall structure of the particles. All of these particles will produce same result using conventional particle size measurement techniques.

4 Nitrogen adsorption methods will yield progressively higher results for particles with greater irregularities. Surface roughness 2014 Horiba , Ltd. All rights area and shape We can use a size analyzer, but eventually prefer to measure Surface area directly. Specific Surface area for a given size changes according to shape Another way to think about determining particle shape or Surface roughness 2014 Horiba , Ltd. All rights Why determine Surface area ? Surface area and size Determining Surface area 2014 Horiba , Ltd. All rights adsorptionTo find Surface area , simply determine amount of N2adsorbed to the Surface in a single layer. Use the projected Surface area of each molecule times the number of molecules to find Surface area . 2014 Horiba , Ltd. All rights a single layer, but how do we find a single layer?

5 Need to look at adsorbed N2as a function of pressure. 2014 Horiba , Ltd. All rights surfaces EQUIVALENT MONOLAYER Type 2W tWmP/P0 Surface area 2014 Horiba , Ltd. All rights reserved. Used for unknown materials to determine behavior of the material. Measure multiple points to two parameters (a material constant and the Surface area ).Amount Adsorbed 0 p/p0 Relative PressureMulti-point method 2014 Horiba , Ltd. All rights reserved. Once that determination has been accomplished, a SINGLE POINT MEASUREMENT is quite satisfactory for many (90-95%) practical Adsorbed p/p0 Relative Pressure Single-point method 2014 Horiba , Ltd. All rights volumeBET equationCWPPCWCPPWPPmm111000 P = N2partial pressureP0= N2equilibrium vapor pressureW = mass adsorbed N2Wm= mass of N2monolayerC = BET constantSlope mIntercept bY = m x + b 2014 Horiba , Ltd.

6 All rights volumeBET equationSlope mIntercept bY = m x + bmbWm 1bbmC We use Wmto get Surface 2014 Horiba , Ltd. All rights volume Measuring for BET equationP = N2partial pressure = controlled by instrument (MFC)P0= N2equilibrium vapor pressure = knownW = mass adsorbed N2= measured from desorbed volume of nitrogenWm= mass of N2monolayer = found from equationC = BET constant = found from equationCWPPCWCPPWPPmm111000 2014 Horiba , Ltd. All rights reserved. The single-point method method is applicable to many, but not all samples. For unknown materials, the multi-point method is best. However, for most materials, the single point method applies. Single point is preferred because it is much simpler and faster to use. Measure at a single N2pressure.

7 References: Brunauer,S., Emmett, P., and Teller, E., J. Amer. Chem. Soc. 60, 309 (1938) Gregg, , and Sing, , Adsorption, Surface area & Porosity, Academic Press, (1967)Single Point Measurement 2014 Horiba , Ltd. All rights mass, Single PointBET equation CCWPPCWCPPWPPmm111000 01 CWmCC )1(mWPPW 01 Measure W at one value of P/P0and obtain Wm. 2014 Horiba , Ltd. All rights Surface area from Wm We obtain Wmfrom linear plot (multipoint) or single point. Use Wm(quantity of N2) and cross sectional area of N2to determine Surface area :wxAmtMANWS St=Total Surface areaWm= Mass of N2monolayerMw= Molecular weight of N2= 28 g/molNA= Avagadro s Number = x 1023molecules/molAx= x 10-20m2/molecule 2014 Horiba , Ltd. All rights point measurement errorsIf we know c, we can predict error in single point results.

8 2014 Horiba , Ltd. All rights method offers the advantage of simplicity and speed,with acceptable accuracy. oamPPVV Vm= 1/slopeA relative pressure of gives good general agreement with the multi-point of single point error at P/P0= by multiplying the single point BET value by C/C-2 decreases the BET(m2/g)Uncorrected single-point(m2/g)Uncorrecteddifference( %)Corrected single point(m2/g)Correcteddifference(%) + to single point when life is bad 2014 Horiba , Ltd. All rights matters! Not all of sample brought to lab is analyzed Must sub-divide sample How to introduce representative sample into instrument?Bulk or process streamGrosssampleLaboratory sampleTest sample Measurementsample10nkg>kg<kggmg 2014 Horiba , Ltd. All rights from Drums 2014 Horiba , Ltd.

9 All rights Sampling from Bottle When a powder is stored in a container, it can be mixed by rolling and tumbling the container. The container should not be more than half to two-thirds full. It is important to perform this action before grabbing a sample with a spatula. Then pull sample with a image cannot currently be display ed. 2014 Horiba , Ltd. All rights : Coning & Quartering Pile of powder is divided into 4 sections. Two diagonal sections are discarded, and two are retained and mixed together. Mixture is again divided into 4 sections, and two diagonal sections are mixed. Process is repeated until remaining sample is correct amount for Analysis . Can be carried out with very small sample amount or very large samples. 2014 Horiba , Ltd. All rights : Chute Riffling Chute splitting allows sample to vibrate down a chute to vanes which separate the mass into two portions.

10 Each portion moves further where they each are divided into two parts, now giving four parts. This may be continued until usually 8 or 16 portions are obtained. 2014 Horiba , Ltd. All rights Technique Error Levels Standard Deviation ( ) in % Sugar-Sand Mixture SCOOP TABLE CHUTE SPINNING Density of sand and sugar respectively and g/ml Reference: Allen, T. and Khan, (1934), ChemEng, 238, CE 108-112 2014 Horiba , Ltd. All rights out sample Frequent source of error. Use a balance with four places. Carefully determine and record mass of empty sample cell. You will need this value after measurement. 2014 Horiba , Ltd. All rights sample Record mass of cell+sample 2014 Horiba , Ltd. All rights reserved. Material in Sample Cell must be OUTGASSED Sample cell containing sample must be heated to over 100 C for at least 20 to 30 minutes to drive off impurities that adhere to 2014 Horiba , Ltd.