Philips tech. Rev. 33, 21-24,1973, No. 1

Plasma-MIG welding

Through the years a variety of techniques have beendeveloped for joining metals together. An importantgroup among these techniques is that of the arc-weld-ing processes. Recently Philips Research Laboratorieshave extended this group by a new method, whoseessential feature is that the filler wire and its are aresurrounded by a thermally ionized gas stream. Thisenables the welding process to be controlled accurately,and makes possible a number of interesting appli-cations, such as overlay welding of stainless steel onmild-steel plates at a relatively high speed and high-speed welding of thin sheet. The process may be re-garded as a combination of plasma welding and gas-metal are (MIG) welding (MIG standing for MetalInert Gas). To make this clear, we shall first brieflydescribe these two processes.

In plasma welding the work is heated by means ofan are discharge between a non-consumable tungstenelectrode and the workpiece in an atmosphere of argonor of some other gas. In plasma welding the energydensity is made greater than in ordinary are weldingwith a non-consumable electrode (argon-are welding)by reducing the diameter of the are. This is done bypassing the are through a cooled copper nozzle. Theare stays clear of the wall of the nozzle, because thegas near the wall is not ionized, owing to the lowtemperature, and does not therefore conduct electri-cally. Between the nozzle - which is part of the weld-ing torch - and the workpiece there is very littledivergence of the are. Because the are is thinner at thesame current, the temperature ofthe plasma is higher [1]

than it would otherwise be.In plasma welding it is sometimes necessary to add

filler metal to the weld pool. Since the tungsten elec-trode, the copper nozzle and the are are all coaxial it isusual to introduce the filler wire into the are sideways.

21

Filler wire introduced in this way is not very intensivelyheated, and the deposition rate is therefore low. Thefeed rate of the wire also has to be very accuratelycontrolled. Lt would be better if the wire travelled alonger distance through the plasma.

M IC welding is also carried out with an are dischargein a shielding-gas atmosphere (argon or C02). In thiscase, however, a consumable electrode of filler wire isused. The wire is fed continuously from a reel througha guide tube, which conducts the welding current tothe wire.

Like plasma welding, M[G welding has its limi-tations. In MIG welding at low current the limit isfound where the are becomes unstable and the metal istransferred to the work in very large molten drops fromthe filler wire. At very high currents the tip of the fillerwire and the are begin to rotate rapidly, and moltendrops are spattered from the are to land well awayfrom the heated part of the workpiece [2].

Experiments have shown that combining these twowelding methods gives an entirely new situation. Toindicate the close relationship we have called the newmethod plasma-MIC welding [3]. In this method thereis no lower limit to the current through the filler wirebelow which the welding process becomes unstable,while the upper current limit is much higher than inMIG welding.

rn H. Maecker, Z. Physik 141, 198, 1955.[2J To some extent the behaviour of the wire tip is comparable

with that of a running hose clamped at a distance from thenozzle; when the flow of water exceeds a certain strength, thereaction causes the dangling end to start twisting. See forexample the article by A. Lesnewich, Welding J. 37, Res.Suppl., 418-s, 1958.

[3J W. G. Essers, A. C. H. J. Liefkens and G. W. Tichelaar, Proc.Conf. on Advances in Welding Processes, 1970, p. 216, publ.The Welding Institute, Cambridge 1971.

22 w. G. ESSERS el al. Philips tech. Rev. 33, No. 1

The methods could be combined by offsetting thetungsten electrode that generates the plasma are fromthe axis of the copper nozzle (see fig. J). Although theare is then slightly curved between the electrode Tandthe nozzle R, this presents no difficulties. The fillerwire F can now be introduced into the plasma axially,and the length of wire in the plasma are can now bemuch greater than with a side feed. In this way thelower part of the wire F and the are M, between thewire tip and the workpiece W, are surrounded by theplasma P, thus ensuring efficient heating of the wireand consequently a high deposition rate. The deposi-tion rate is of course largely determined by the currentin the filler wire. The presence of the plasma also givesbetter control of metal and heat transfer to the work-piece than in conventional MIG welding. Fig. 2 showsthe experimental arrangement in our laboratory.

Interesting results can be obtained with plasma-MIGwelding, especially when the electrodes are connectedto the positive pole of the current source and the work-

T

F

PG_j

+ +

lp

Fig. 1. Diagram of the plasma-MIG welding process. An arc Mis maintained between the filler wire F and the workpiece W.This are is located at the axis of a plasma arc P between a non-consumable tungsten electrode T and the workpiece. The plasmaarc is constricted by a copper nozzle R located at the end of awater-cooled double-walled housing. The plasma gas PG issupplied through this housing. SG is a stream of shielding gasaround the plasma arc. The are M and the plasma are Pareeach fed from a separate d.c. source (h! and Jp).

Fig. 2. Experimental welding torch for plasma-M IG welding. Thereel carrying the supply of filler wire can be seen at the top. Thewire is automatically fed at the desired speed into the weldingtorch, which also contains the tungsten electrode.

piece to the negative pole. Just as in ordinary MIGwelding, the current in the welding wire in plasma-MIG welding has a critical value above which themolten wire tip and the are are made to rotate by theaction of electromagnetic forces and mechanicalreaction forces. The process of metal transfer fromwelding wire to workpiece when the are is stationary isquite different from the process when it is rotating, butin plasma-MIG welding both processes are completelycontrolled. We shall illustrate this with a few exampleswhich show that the two situations lead to entirelydifferent welding results.

Fig. 3 shows a photograph of a plasma are with aW thin stationary are in the centre; this situation holds as

long as the current in the wire remains below thecritical limit. The welding process can be very effec-tively demonstrated by taking high-speed films andshowing them in slow motion. The title photographshows a frame from such a film (2500 frames persecond) of the same are as in fig. 3. The molten dropscan be seen to be moving vertically in a straight line tothe workpiece, about 500 drops per second with an

Philips tech. Rev. 33, No. I PLASMA-MIG WELDING

Fig.3. Photograph of the plasma-MIG process with a thinstationary are. The brighter are between the tip of the fillerwire and the workpiece can be seen at the centre of the plasmaarc.

average diameter of 0.9 mm, travelling at an approximate velocity of 2.2 mis.The high energydensity in the are causes the molten zone to penetrate deeply intothe workpiece, producing welds like those in fig. 4 (see page 24). The stationarytype of are can also be used for high-speed welding of sheet steel: [ mm stainlesssteel sheet can be welded at a speed of 10 m/min.

Fig. 5a is a photograph of the rotating are obtained when the critical current isexceeded. The fluid end of the wire assumes the form of a conical helix androtates very rapidly within the almost unchanged plasma are. The are extendsfrom the fluid wire tip to the workpiece and describes a vertical cylindrical sur-face as it rotates. Here this surface has a diameter of 8 mm. Fig. 5b gives a clearpicture of the rotating fluid part of the wire and of the droplets detaching from it.High-speed films like this - in this case taken at a speed of 4000 frames persecond - enable useful quantitative data to be derived. For example, the fre-quency of rotation at a given wire thickness is found to be related to the currentin the filler wire and to lie between 130 and 270 revolutions per second. Anotherexample relates to the transfer of the filler metal. If the conditions are the same asthose in the stationary process illustrated in fig. 3, apart from the current in thewire and the wire feed, then at least 3000 droplets with a mean diameter ofO.6 mm

a

Fig. 5. a) Photograph of theplasma-MIG process with ro-tating arc. The contours of thesurface of the molten wire tipcan be seen inside the plasma.b) Series of frames from ahigh-speed film (4000 frames persecond) of the rotating arc.

23

b

24 PLASMA-MIG WELDING Philips tech. Rev. 33, No. 1

Fig. 4. Square-butt weld in plate of 8 mm stainless steel welded bythe plasma-MIG method using a thin are. The filler wire (PZ 6061)had a diameter of 1.2 mm and was also of stainless steel. Theplasma gas was argon (6.5 I/min), the shielding gas a mixture ofargon (lOl/min) and C02 (5 I/min). The diameter of the plasmaexit was 6 mm, and its distance to the workpiece was 15 mm.Plasma-are current 100 A at 50 V. Current in the filler wire 180Aat 40 V. Both electrodes were positive with respect to the work-piece. The rate of travel was 40 cm/min at a deposition rate of95 grams of filler metal per minute. Under these conditions thecritical current through the wire at which the arc starts to rotateis approximately 250 A.

Fig. 6. Weld bead of stainless steel (filler wire PZ 6061, diameter1.2 mm) on a 10 mm steel plate. Plasma gas 6.5 I argon perminute, shielding gas 121 argon + 3 I C02 per minute. Nozzlediameter 10 mm, distance from torch to workpiece 22 mm.Plasma-are current 100 A at 45 V. Current in the filler wire 400 Aat 40 V, both electrodes are positive with respect to the work-piece. Travel rate 23 cm/min, deposition rate 300 g/min, beadwidth 40 mm.

are transferred per second. The detached droplets movein an almost vertical path to the workpiece, with avelocity of about 2.6 mis.

With the rotating are there is no question of the deeppenetration shown in fig. 4, since the electrical andthermal energy is spread over a larger surface of theworkpiece. In this case a relatively wide weld bead isformed (in fig. 6 nearly 40 mm) with shallow penetra-tion in the metal sheet.

This welding method appears to be very suitable forcladding chemical storage tanks and nuclear reactorvessels with a corrosion-resisting layer of stainless steel.The high deposition rate is an economic advantage insuch work. With a single welding torch a depositionrate of 30 kilograms per hour has already beenobtained in our laboratory. This rate is high comparedwith that obtainable with other methods.

w. G. EssersG. JelmoriniG. W. Tichelaar

W. G. Essers, G. Jelmorini and Dr Ir G. W. Tichelaar are withPhilips Research Laboratories, Eindhoven.

Philips tech. Rev. 33, No. 1 25

Recent scientific publicationsThese publications are contributed by staff of laboratories and plants which form partof or co-operate with enterprises of the Philips group of companies, particularly by staffof the following research laboratories:

Philips Research Laboratories, Eindhoven, Netherlands EMullard Research Laboratories, Redhill (Surrey), England MLaboratoires d'Electronique et de Physique Appliquée, Limeil-Brévannes (Val-

de-Marne), France . LPhilips Forschungslaboratorium Aachen GmbH, WeiBhausstraBe, 51 Aachen,

Germany APhilips Forschungslaboratorium Hamburg GmbH, Vogt-Kölln-StraBe 30,

2000 Hamburg 54, Germany HMBLE Laboratoire de Recherches, 2 avenue Van Becelaere, 1170 Brussels(Boitsfort), Belgium. B

Reprints of most of these publications will be available in the near future. Requests forreprints should be addressed to the respective laboratories (see the code letter) or to PhilipsResearch Laboratories, Eindhoven, Netherlands.

v. Belevitch: Dissipative filters.Aspects of network and system theory, pub!. Holt-Rinehart-Winston, New York 1971, pp. 267-285. B

G. Bergmann: Polarisationseigenschaften von Glüh-licht.Math. naturwiss. Unterricht 25, 133-139, 1972(No. 3).

A

J. Bloem & A. H. Goemans (Philips SemiconductorDevelopment Laboratory, Nijmegen): Slip in siliconepitaxy.J. app!. Phys. 43, 1281-1283, 1972 (No. 3).

J. van den Boomgaard: Stability of the high-tempera-ture phase FeSh.J. Iron and Steel Inst. 210, 276-279, 1972 (No. 4). E

L. Boonstra & F. L. J. Sangster: Analog functions fitneatly onto charge transport chips.Electronics 45, No. 5, 64-71, Feb. 28, 1972. E

J. Borne: Analysis of the educational system.Acta Electronica 14, 289-293, 1971 (No. 3). (Also inFrench, pp. 283-287.) L

c. J. Bouwkamp: Note on an asymptotic expansion.Indiana Univ. Math. J. 21, 547-549, 1971 (No. 6). E

J. R. Brandsma & B. L. A. Waumans: A common busswitch.Proc. Int. Computing Symp., Venice 1972,pp. 446-454.

E

P. Branquart, J. Lewi, M. Sintzoff & P. L. Wodon:The composition of semantics in ALGOL 68.Comm. ACM 14,697-708, 1971 (No. 11). B

C. H. J. van den Brekel & P. J. Severin: Controlof thedeposition of silicon nitride layers by 2537A radiation.J. Electrochem. Soc. 119, 372-376, 1972 (No. 3). E

E. Bruninx: The evaluation of errors caused by flux in-homogeneities in thermal neutron activation analysis.Ana!. chim. Acta 60,207-217, 1972 (No. I). E

K. H. J. Buschow & H. J. van Daal: Comparison ofanomalies observed in U- and Ce-intermetallics.AlP Conf. Proc. 5, 1464-1477, 1971 (No. 2). E

M. Cazabat, C. Schiller, D. Dlguet (R.T.C. La Radio-technique Compelec, Caen) & J. C. Lefèvre (R.T.C.etc., Caen): Etude par microscopie à balayage descorrélations entre images de cathodoluminescence etde conduction des jonctions dans GaAs.A.V.I.SEM 71, ColI. int. Versailles 1971 (Supp!. LeVide No. 152), pp. 401-406. L

T. Chisholm, J. Hubregtse (Groningen University),G. F. Weston & E. E. Windsor: The use of a-channelelectron multiplier with a residual gas analyser.Residual gases in electron tubes, Proc. 4th int. Conf.,Florence 1971, pp. 165-173; 1972. M

J. B. Clegg: Reduction in secondary ion fogging onphotographic plates used in mass spectrography.Anal. Chem. 44,1100-1101,1972 (No. 6).' M

J. Cornet & D. Rossier: Technique d'évaporation etcaractérisation physique de couches minces amorphesde chalcogénures semi-conducteurs.A.V.I.SEM 71, ColI. int. Versailles 1971 (Supp!. LeVide No. 152), pp. 443-453. L

C. Crevecoeur & H. J. de Wit: The preparation of .C(-As2Se3crystals.J. Crystal Growth 12, 334-336, 1972(No. 4). E

P. Delsarte: Bounds for unrestricted codes, by linearprogramming.Philips Res. Repts. 27, 272-289, 1972(No. 3). B

P. Delsarte, J. M. Goethals & J. J. Seidel (EindhovenUniversity of Technology): Orthogonal matrices withzero diagonal, Il.Canad. J. Math. 23, 816-832, 1971 (No. 5). B

P. A. Devijver: A generalorder Minkowski metricpattern classifier.AGARD Conf. Proc. No. 94, 18.1-18.11, 1971. B

26 RECENT SCIENTIFIC PUBLICATIONS Philips tech. Rev. 33, N.o. 1

A. M. van Diepen, K. H. J. Busehow & J. S. van Wie-ringen: Study of the Mössbauer effect, magnetization,and crystal structures of the pseudobinary compoundsThC05-5zFe5z and ThNi5-5zFe5z.J. appl, Phys. 43, 645-650, 1972 (No. 2). E

A. M. van Diepen & R. P. van Stapele: Mössbauereffect of 57Fe in cubic Cdo.9sFeo.o2Cr2S4.Phys. Rev. B 5, 2462-2466, 1972 (No. 7). E

H. Dötseh: Magnetoelastic YIG delay lines withlinear dispersion.J. appl. Phys. 43, 1923-1927, 1972 (No. 4). H

H. C. van den Elzen & P. van der Wurf: A ,simplemethod of calculating the characteristics of FSK signalswith modulation index 0.5.IEEE Trans. COM-20, 139-147, 1972 (No. 2). E

P. van Engelen, W. Boon & J. Dieleman: Electronnuclear double resonance of cobalt doped cadmiumsulphide.J. Phys. Chem. Solids 33, 1041-1050, 1972 (No. 5). E

P. van Engelen & R. P. van Stapele: ENDOR of C02+in CdS.J. magn. Resonance 7, 122-123, 1972 (No. 2). E

M. Favreau (Thomson-CSF), R. Genève, L. Goussot(ORTF), S. Laeharnay (ORTF), A. Laurens (TRT) &J. Polonsky (Thomson-CSF): La radiodiffusion sonoreet visuelle.Onde é1ectr. 51, 594-604, 1971 (No. 7). L

N. E. Goddard: Instantaneous frequency-measuringreceivers.IEEE Trans. MTT-20, 292-293, 1972 (No. 4). M

J. J. Goedbloed: Determination of the intrinsic re-sponse time of semiconductor avalanches from micro-wave measurements.Solid-State Electronics 15, 635-647, 1972 (No. 6). E

G. Groh, G. S. Hayat (SUNY, Stony Brook, N.Y.,U.S.A.) & G. W. Stroke (SUNY, Stony Brook): X-rayand y-ray imaging with multiple-pinhole cameras usinga posteriori image synthesis.Appl. Optics 11, 931-933, 1972 (No. 4). H

P. Guétin & G. Sehréder: Band-structure effects III

metal-GaSb tunnel contacts under pressure.Phys. Rev. Letters 27, 326-330, 1971 (No. 6). L

P. Guétin & G. Sehréder: Influence d'un bombarde-ment ionique de faible énergie sur les caractéristiquesdes barrières Schottky.A.V.I.SEM 71, ColI. int. Versailles 1971 (Suppl. LeVide No. 152), pp. 80-85. L

G. J. van Gurp: Precipitation of Si in evaporated AI/Sifilms.Scripta metall. 6, 361-366, 1972 (No. 5). E

P. Hansen: Ferromagnetic resonance in ruthenium-doped gadolinium iron garnet.Phys. Rev. B 5, 3737-3746, 1972 (No. 9). H

K. H. Härdtl & D. Hennings: Distribution of A-siteand B-site vacancies in (Pb,La)(Ti,Zr)Oa ceramics.J. Amer. Ceramic Soc. SS, 230-231, 1972 (No. 5). A

H. Haug & K. Weiss: Reduced density-matrix equa-tions and superfl.uid hydrodynamics.Physica 59, 29-46, 1972 (No. I). E

E. E. Havinga (Ill, IV), H. Damsma (Ill, IV) & J. M.Kanis (Iv): Compounds and pseudo-binary alloys withthe CuAh(CI6)-type structure, Ill. Stability and com-petitive structures, rv. Superconductivity.J. less-common Met. 27, 269-280 & 281-291, 1972(No.3). E

J. H. C. van Heuven & T. E. Rozzi: The invarianceproperties of a multivalue n-port in a linear embedding.IEEE Trans. CT-19, 176-183, 1972 (No. 2). E

K. R. Hofmann: Stability theory for thin Gunn diodeswith dielectric surface loading.Electronics Letters 8, 124-125, 1972 (No. 5). E

K. R. Hofmann & H. 't Lam: Suppression of Gunn-domain oscillations in thin GaAs diodes with dielectricsurface loading.Electronics Letters 8, 122-124, 1972 (No. 5). E

E. P. Honig: Theory and measurement of the suspen-sion effect.J. electroanal, Chem. interf. Electrochem. 37, 249-266,1972. E

F. A. de Jonge & W. F. Druyvesteyn: Calculations andexperiments related to the magnetostatics of bubbledomains.Festkörperprobleme 12, 531-597, 1972. E

B. A. Joyee & J. H. Neave: Reply to comments on theinteraction of oxygen with Si(111) surfaces.Surface Sci. 30, 710-711, 1972 (No. 3). M

H.-G. Junginger & W. van Haeringen: Calculation ofthree-dimensional refractive-index field using phaseintegrals.Optics Comm. 5, 1-4, 1972 (No. I). A, E

D. Kasperkovitz: An integrated 11 MHz p-n-p-n shiftregister.Solid-State Electronics 15, 501-504, 1972 (No. 5). E

A. Klopfer: Recent studies on electronic desorptionfrom metals used in vacuum systems.J. Vacuum Sci. Techno!. 9, 301, 1972 (No. I). A

M. Koek & G. Rabe (Elektro Spezial, Bremen): Paralleland time sequential optical multiplex systems for pat-tern recognition.Optics Comm. 5, 73-77,1972 (No. 2). H

G. Landvogt: A novel frequency analog force trans-ducer with vibrating plate.VDI-Berichte No. 176,99-105, 1972. H

S. Leblane: Enseignement assisté par ordinateur pourIe recyclage des techniciens.Acta Electronica 14, 379-399, 1971 (No. 4). L

P. E. Leuthold (Federal Institute of Technology,Zürich): A new concept for the realization of datamodems with integrated digital filters and modulators.Philips Res. Repts. 27, 223-243, 1972 (No. 3).

Philips tech. Rev. 33, No. 1 RECENT SCIENTIFIC PUBLICATIONS 27

R. Loppes, R. Matagne (both with Université deLiège) & P. J. Strijkert: Complementation at thearg-7 locus in Chlamydomonas reinhardi.Heredity 28, 239-251, 1972 (No. 2). E

R. Loppes (Université de Liège) & P. J. Strijkert:Arginine metabolism in Chlamydomonas reinhardi.Mol. gen. Genet. 116, 248-257, 1972 (No. 3). E

M. Martin: Analyseur de réponses pour expérimen-tations pédagogiques.Acta Electronica 14, 341-359, 1971 (No. 4). L

D. Mateika: Growth of MnTe single crystals fromnonstoichiometrie melts by liquid encapsulation.J. Crystal Growth 13/14,698-701, 1972. H

L. J. Meuleman: Injection frequency locking of theavalanche transit-time oscillator.Philips Res. Repts. 27, 201-222, 1972 (No. 3). E

R. F. Mitchell: Generation and detection of sound bydistributed piezoelectric sources.Thesis, London 1971. M

F.L. van Nes (Institute for Perception Research (IPO),Eindhoven): Determining temporal differences withanalogue and digital time displays.Ergonomics 15, 73-79, 1972 (No. I).

H. W. Newkirk & A. J. R. de Kock: Crystal perfectionof tetraphenyl tin and its isomorphs.Phys. Stat. sol. (a) 11, K 101-102,1972 (No. 2). A, E

K. H. Nicholas, B. J. Goldsmith, J. H. Freeman(AERE, Harwell), G. A. Gard (AERE), J. Stephen(AERE) & B. J. Smith (AERE): The evaluation of theHarwell-Lintott industrial ion implantation machineby making silicon planar resistors.J. Physics E 5, 309-310, 1972 (No. 4). M

A. van Oostrom: Requirements for partial pressureanalysers from the user's point of view.Vacuum 22, 15-17, 1972 (No. I). E

A. E. Pannenborg (Philips Board of Management,Eindhoven): Solid state physics.Indian & Eastern Engr. Nov. 1971, 527-533.

D. H. Paxman, R. J. Tree & C. E. C. Wood: Unstabledomains in solution-grown epitaxial InP.Electronics Letters 8,241-243, 1972 (No. 9). M

C. Piaget & Ph. Jarry: Applications des semiconduc-teurs à la photoémission et à l'émission secondaire.A.V.I.SEM 71, ColI. int. Versailles 1971 (Suppl. LeVide No. 152), pp. 427-442. L

Ph. Piret: Structure and error probability of burst-correcting convolutional codes.Philips Res. Repts. 27, 244-256, 1972 (No. 3). B

Ph. Piret: Convolutional codes and irreducible ideals.Philips Res. Repts. 27, 257-271, 1972 (No. 3). B

J. E. Ralph & J. M. Woodcock: A new filamentarymodel for voltage formed amorphous óxide films.J. non-cryst. Solids 7, 236-250, 1972 (No. 3). M

H. Rau: Apparatus for measurement of high vaporpressures and densities at high temperatures underisothermal conditions.Rev. sci. Instr. 43, 831-832, 1972 (No. 5). A

K. Rennicke: Drehzahlregelung mit einphasig gestelltenInduktionsmotoren. .Elektrotechn. Z. B 24, 222-225, 1972 (No. 9). H

F. Rondelez & H. Arnould: Déformations de la textureplanaire d'un cholestérique à grand pas sous l'actiond'un champ électrique.C.R. Acad. Sci. Paris 273B, 549-552, 1971 (No. 13). L

D. J. Schipper & Th. W. Lathouwers: Bromine incor-poration in sodalite.Inorg. nuel. Chem. Letters 8, 449-452, 1972 (No. 5). E

P. J. Severin: Interpretation of the infrared thicknessmeasurement of epitaxiallayers.Appl. Optics 11, 691-692, 1972(No. 3). E

J. A. G. Slatter: Fundamental modelling of cylindrical-geometry bipolar transistors.Electronics Letters 8, 222-223, 1972 (No. 9). M

M. J. Sparnaay: Ion-size corrections of the Poisson-Boltzmann equation.J. electroanal. Chem. interf. Electrochem. 37, 65-70,1972. E

W. T. Stacy & W. Tolksdorf: Growth-induced mag-netic anisotropy in yttrium iron garnet.AlP Conf. Proc. 5, 185-189, 1971 (No. I). E, H

A. Stegherr: Korrosion von hochdispersen, aus Eisen-,Chrom- und Kobaltsalzlösungen reduzierten Metall-pulvern.Werkstoffe und Korrosion 23, 180-186, 1972 (No. 3).

A

B. D. H. Tellegen: Stability of negative resistances.Int. J. Electronics 32,681-686,1972 (No. 6). E

M. J. J. Theunissen: Etch channel formation duringanodic dissolution of n-type silicon in aqueous hydro-fiuoric acid.J. Electrochem. Soc. 119, 351-360, 1972 (No. 3). E

J.-P. Thiran: Recursive digital filters with maximallyfiat group delay.IEEE Trans. CT-18, 659-664, 1971 (No. 6). B

J.-P. Thiran: Equal-ripple delay recursive digital filters.IEEE Trans. CT-18, 664-669, 1971 (No. 6). B

W. Tolksdorf & F. Welz: The effect of local coolingand accelerated crucible rotation on the quality ofgarnet crystals.J. Crystal Growth 13/14, 566-570, 1972. H

J. van der Veen, W. H. de Jeu, A. H. Grobben & J.Boven: Low melting liquid crystalline p,p'-di-n-alky1-azoxy- and azobenzenes.Mol. Cryst. liq. Cryst. 17,291-301, 1972 (No. 3/4). E

M. L. Verheijke: A computer program in ALGOL-60forthe location and evaluation of peaks in Ge(Li) gammaray spectra. .J. radioanal. Chem. 10,299-314, 1972 (No: 2). .. E

28 RECENT SCIENTIFIC PUBLICATIONS Philips tech. Rev. 33, No.l

Q. H. F. Vrehen & A. J. Breimer: Spectral propertiesof a pulsed dye laser with monochromatic injection.Optics Comm. 4, 416-420, 1972 (No. 6). E

F. W. de Vrijer: Proposal for an integrated videophonesignal.Proc. Int. Zürich Seminar on Integrated Systems forSpeech, Video and Data Communications, 1972, pp.F 7 (1)-(5). E

K. Weiss: Doppelschicht und Gleichstrompolarisationvon AgBr.Ber. Bunsen-Ges. phys. Chemie 76, 379-384, 1972(No.5). E

H. W. Werner, H. A. M. de Grefte & J. v.d. Berg: Themeasurement of small ion currents with the aid ofphotomultipliers.Int. J. Mass Spectrom. Ion Phys. 8, 459-474, 1972(No.5). E

H. J. de Wit: Hall effect ofan inhomogeneous material.J. appl. Phys. 43, 908-913, 1972 (No. 3). E

S. Wittekoek & D. E. Lacklison: Investigation of theorigin of the anomalous Faraday rotation ofBixCa3-xFe3.5+0.5xV1.5-0.5x012 by means of the mag-neto-optical Kerr effect.Phys. Rev. Letters 28, 740-743, 1972 (No. 12). E, M

J. Wolter: Experimental study of nonlinear inter-action between Bleustein-Gulyaev waves in a piezo-electric plate and an adjacent semiconductor.Physics Letters 38A, 479-480, 1972 (No. 7). E

C. E. C. Wood, R. J. Tree & D. H. Paxman: Solution-grown epitaxial InP for high-efficiency circuit-con-trolled microwave oscillators.Electronics Letters 8, 171-172, 1972 (No. 7). M

Contents ofPhilips Telecommunication Review 30, No. 4, 1972:

J. Mulder: 1 kW all-solid-state HF communications transmitter RZ 500 (pp. 137-146).J. P. A. Aarts: The professional communications receiver RO 150 (pp. 147-155).J. P. A. Aarts: PARCS, Automatic Remote Control System for HF radio stations (pp. 156-166).M. M. Jung & J. deBoer: Comparison of the traffic handling capacity of subscriber transpositions (pp. 167-172).R. Bodart: Telegraph distortion introduced by TDM systems (pp. 173-181).W. Stimpel: TV transmission equipment at Munich Olympics (p. 182).

Contents of Electronic Applications Bulletin 31, No. 4, 1972:

E. XanthouIis: ~en-bit digital-to-analog converter with thin-film ladder network (pp. 207-217).J. Mulder: Large-signal behaviour of r.f. power transistors, Part 2. Computer program (pp. 218-233).L. J. G. Berière: Measurement of a.m. suppression in an intercarrier sound channel (pp. 234-243).R. W. Cooper: Infra-red intensity modulators using Faraday rotation in YIG (pp. 244-257).

Contents of Mullard Technical Communications 12, No. 116, 1972:

M. Michaelides : Microstrip transmission lines: impedance matching, coupling and filtering (pp. 170-196):Tapered transmission lines for impedance matching sections (pp. 170-176);Microstrip directional couplers (pp. 177-187);Interdigital filters and experimental microstrip filter design at 470 MHz (pp. 188-192);Microstrip bandpass filter for 0.7 to 1.4 GHz (pp. 193-196).

J. Gerritsen: A newmethod of colour purity adjustment (pp. 197-200).

Contents ofValvo Berichte 17, No. 1, 1972:

W. Kühl: Fernsehaufnahmeröhren für niedrige Strahlungsleistungen in LLL TV-Systemen (pp. 1-16).D. Schwabe & J. Wüstehube: Digitale Teiler mit integrierten Schaltungen zur Untersetzung von Impulsfolgen(pp. 17-42).W. Golombek: Verzerrungen elektronischer Verstärker (pp. 43-60).

Volume 33, 1973, No.1 pages 1-28 Published 1,9th February, 1973