A Comparsion of Dot-counting and Mercury immersion Methods for Determing Density

Transcription

1 Intern rapport Nr 39/96 A Comparsion of Dot-counting and Mercury immersion Methods for Determing Density Girma Kifetew Dick Sandberg Stockholm 996 Internrapport Inst. for Produktionssystem avd. Trateknologi Kungl Tekniska Hogskolan Stockholm TRA

2 CONTENT Summary Introduction Literature survey Materials and method Results Conclusion References Appendix Measurement and calculated density values Statistics analysis for pine Statistics analysis for spruce Page A BI B2

3 A Comparison of Dot-counting and Mercury immersion Methods for Determining Density Summary This paper describes two wood density determination techniques, one using the dotcounting and the other Mercury immersion and discuses the correlation between the methods. The paper includes also a short literature survey on some other wood density determination methods. Introduction The determination of density is quite difficult for porous solids. Closed voids, air bubbles, swelling and other obstacles make the determination of density a somewhat laborious and contribute to questionable results. Density is a macroscopic property and can be defined only by ignoring the microporosity. At the same time within the field of wood quality research it is becoming evident to make an objective assessment of wood density to obtain a more detailed information using special instruments and technique. The methods used are non-destructive and are regarded to be accurate. Among the techniques been used today to determine wood density, this paper deals primarily with the application of Dot-counting and Mercury immersion. Secondly a literature survey is presented for Beta-ray, X-ray, dual-linear traversing micrometer and microphotometric techniques. Literature Survey A scanning microphotometric technique to determine ring width, per cent of earlywood and latewood and cross-sectional dimensions of tracheids has been developed by Green and Worrall (964). Elliott and Brook (967) applied the microphotometric technique to determine the cell-wall area; lumen area ratio from thin wood section. They also outlined that the technique be possible applied to study packing density and compression wood development Smith (965) using a dual-linear transverse micrometer measured cell diameter and thickness and based on that he determined the density of wood. To estimate wood density he has used the measurements on the cross-sections of isolated earlywood and latewood with a micrometer and compared with the maximum moisture method and found a high degree of correlation. Two radiation techniques for measuring density of wood were compared by Harris and Polge (967) using a small series of test. Both the Beta ray and X -ray are compared

4 with regard to quality of record, speed of operation, direction of radiation, cost and finally density measurement. In a concluding remark they suggested that the Beta ray has the capability of examining the fast grown conifers, while in its present form it would be not suitable for detailed studies of slow grown conifers. The X-ray apparatus is considered to have a more refined capabilities even though it is relatively expensive. In connection with issues describing different techniques for the accurate determination of density Dinwoodie (968) discussed whether or not the cost and effort in obtaining additional information on density be justified. He concluded that the development and use of refined techniques for measuring density is important for deeper understanding of the factors controlling density in the tree and how density may be controlled in the future to the advantage of the timber user. Materials and Methods The materials used for the investigation are eleven and thirteen specimens of Pinus silvestris L. and Picea abies Karst. respectively. Mercury immersion and dot-counting methods are used to determine the density. The degree of correlation have been determined by a simple linear regression analysis. Mercury immersion: Specimens of size 20 x 20 x 20 mm were cut with a band saw machine. Specimens were oven dried at 03 C to a moisture content of about 0% and the oven-dry weight and volume were determined. The volume was determined by fixing the specimen with the help of a needle and immerse it in to the mercury bath. The volume of the displaced weight of the mercury is determined using Archimedes principle. The density was then calculated according to: pwood= PSg mo ltihg PHg= 3538,5 Kglm 3 at 23 C Dot-counting: From the 20 x 20 x 20 mm 3 specimens, microtomed specimens of 50 micrometers in thickness were prepared for dot counting in a light microscope. The microscope is equipped with a scale on the ocular which is used to count the number of dots the cell wall occupied. Ten random counts were taken from each specimen and the mean value calculated. The density of each specimen was calculated using the formula: L(dots the cell walls occupy) pwood pwood substance Total dots on the scale pwood substance= 500 Kglm3 2

5 Results The results of the measurements and calculated values are shown in Appendix A. While the statistics analysis is shown in Appendix B. For simplicity the density determination discussion of Pinus silvetris and Picea abies are taken separately. Pinus silvetris: As shown, there is a significant difference between the calculated values of density with the two methods. The Mercury immersion method has a mean value of 537 Kglm3 and a standard deviation of 2 Kglm 3. The calculated mean value for the dot-counting method is 428 Kg/m3 and a standard deviation of 28 Kglm 3. The correlation coefficient R2 = 0,30. As can be observed from the figure the correlation between the two methods is positive. Densite(Dot-countin ) ~----~--~----~----~--~ Densite(Dot -counting) PM. imm=435,39 + 0,238Pdot R2 = 0,30 Picea abies: It can be seen that there is a good correlation between the two methods used, with a coefficient R2 =0,59. The mean value for Mercury immersion is 355 Kglm 3 and the standard deviation of 20 Kglm 3. For the dot-counting method the mean 3

6 value is 357 Kglm3 and the standard deviation of 7 Kglm 3. Compared to pine, spruce has a negative correlation for the two methods used t ::s 360 ~ (l) ~-C 355.;;: s:: (l) 0 Densite(Dot-countin ) Densite(Dot-counting) PM.imm= 455,27-0,276Pdot Conclusion On the basis of this study it is very difficult to give any concluding remark as to which method could be advisable to use for density determination accurately. The Mercury immersion method is simple, cheap and specimen preparation is comparatively easier compared to dot-counting method. While the penetration of mercury into voids affect the accuracy of the measurement and due to the environmental aspect it not advisable to use Mercury. In using the dot-counting method the number of dots that the cell walls cover can vary depending on the person conducting the test. While dot-counting on micrograph will eliminate the problem. We suspect that due to microtoming cell walls deform and the accuracy of the dot-count that the cell walls cover is questionable. Since the specimens were taken out directly from the oven and immersed the density of Mercury variation due to rise in temperature is insignificant. 4

7 References J. M. Dinwoodie (968). Why Measure Density Critically. J. Inst. Wood Sci., 2,3-5. G. K. Elliot and S. E. G. Brook (967). Microphotometric Technique for Growth-Ring Analysis. J. Inst. Wood Sci., 3 (6), H. V. Green and J. Worrall (964). Wood Quality Studies. A Scanning Microphotometer for Automatically Measuring and Recording Certain Wood Characteristics. T. A. P. P. I., 47 (7), J. Harris and H. Polge (967). A Comparison of X-ray and Beta-ray Techniques for Measuring Wood Density. J. Inst. Wood Sci., 4 (), D. M. Smith (965). Rapid Measrirment of Tracheid Cross-Sectional Dimensions of Conifers: Its Application to Specific Gravity Determination. Forest Products Journal 5 (8),

8 Density APPENDIX A I Mercury! Dot-counting Spec. mo mhg Dens. pine ens. pine no. [g] [g] [Kg/m3] 2 -~ ean [Kg/m3] 3,93 99,2 536, ,9 48,5 2 3,88 0,45 58,6 24! ,4. 4,0 3 4,3 549,3 3,2539 ~~.~22 : 0, , 42,5 4 4,08 0,43 545, ,2 453, ,9 0,90 520, 22! , 25,5 382,5 6 3,90 98,38 536,3 48,5 j~~ 3. 3~ltillr 7 4, 00,82 55, ,6 429,0 8 3,92 99,63 532,6 23: ! 29,3 439,5 9 3,94 ~83 535, : ,0 O 3,96 0,63 532,8 34\ !39: , 406,5 4,6 0,30 556, ,6 459,0 f-!.._.. Mercury I Dot-counting Spec. mhg Dens. spruce, _. : Dens. spruce m : l [g] [Kg/m3] [Kg/m3] 7! 8 363, ,2 38, ,3 363, I9 23! 20 27! 7 32 \ 23,5 352,5 3 3,05 7,2 352, ' ?5,3 379,5 f ! 4 3,04 I 6, 354, , ,06 7,5 352,6 '302225\ ,9 373,5 6 3,3 4,8 369, 7' 20 23!28~ ,2 333,0 7 3,06 7,9 35, : ,3 379& - 8 3,05 7,9 350, , 36,5 9 3,07 7,5 353, ~ 36,5 0 3,3 6,2 364,7 W30!2"22,9,922',9,.2, 22,S 337,5 3,02 5,2 354,9, ,20 I 24,9 373,5 2 3,05 I 8,8 347, _~ !23 23,9 358,5 3 3,3 5,9 365, ,4 336,0 I

9 APPENDIX B Density pine "0 Cl <Ii c: Q) Cl / -.. ~ ~----. (Power Details Dialog Dens. Hg Click and Enter Values: Alpha N [Sample Size] s [std dey error] IDeltal Inflationl 0,050 24,6425 4,6379 0,007 (Effect '(power Test Test J Sum of Squares F Ratio OF Prob>F 2356,9502 3,883 0,0803 Dens. Hg Details 375 -I-~~--r--r--.---r-..., j AI p ha Number Sig ma De Ita P ower ~=0~.0=5=0=0============2=4=,6=4=2=5====4=,=6=37=9===0=,=4=2=09== Dens. Hg Leverage P~!l.~.~...oot I?l:!.~.!J.~...tt.g r ~-----, 560 r ,----, (auantiles maximum quartile median quartile minimum (Moments J Mean Std Dev Std Err Mean upper 95% Mean lower 95% Mean N Sum Wgts 00.0% 99.5% 97.5% 90.0% 75.0% 50.0"/0 25.0% 0.0% 2.5% 0.5% 0.0% 48,50 48,50 48,50 477,00 453,00 42,50 4,00 387,30 382,50 382, , , maximum quartile median quartile upper 95% Mean lower 95% Mean N 00.0% 99.5% 97.5% 90.0% 75.0% 50.0% 25.0% 0.0% 2.5% 0.5% 0.0% 556,60 556,60 556,60 555,62 549,30 536,30 532,60 58,90 58,60 58, ,0000,0000

10 APPENDIX B 2 Density spruce (5 Cl ui t: <l> Cl ~---'----r---'---~---'4"' I I I I I Dens. Hg Leverage [(power Details Dialog I Dens. Hg Click and Enter Values: Alpha N [Sample Size] s [std dey error] IDeltal Inflatlonl 0, , , , """.. " ".. _-_ (Effect Test J Sum of Squares F Ratio OF Prob>F 279,9536 5,8642 0,002 [power Details ) Test Dens. Hg (power ) Alpha Number Sigma Delta power 0, , , , (Quantiles maximum 00.0% 99.5% 97.5% 90.0% quartile 75.0% median 50.0% quartile 25.0% 0.0% 2.5% 0.5% minimum 0.0% (Moments ) Mean Std Dev SId Err Mean upper 95% Mean lower 95% Mean N Sum Wgts 369,0 369,0 369,0 367,70 364,20 354,50 35,85 348,64 347,60 347,60 347,60 357,223 7,0500, , ,9628 3,0000 3, % 379, % 379, % 379, % 379, % % 358, % 336,75 0.0% 324,00 2.5% 38,00 0.5% 38,00 0.0% 38,00 354,5769 9,595 5, , ,7379 3,0000 3,0000