CHEMICAL ETCHING AS ANTI-SLIP TREATMENT ON PORCELAIN STONEWARE TILES

Transcription

1 CHEMICAL ETCHING AS ANTI-SLIP TREATMENT ON PORCELAIN STONEWARE TILES B. Mzznti, E. Rmldi, F. Prete Centro Cermico Bologn, Itly ABSTRACT Commercil cid-sed nti-slip tretments re useful to reduce the risk of slipping on cermic tiles. Severl works del with this topic in terms of consumer sfety, without studying in-depth the cermic surfce chrcteristics nd y mesuring the slip resistnce with empiricl methods (not stndrdized). In the present work, the impct of chemicl nti-slip tretment on the surfce properties of glzed cermic tiles ws investigted in terms of microstructurl chrcteristics, gloss vritions, nd chemicl nd stin resistnce. Slip performnces were evluted ccording to the most widespred stndrds. By the comprison of the treted nd untreted surfces of the sme product, it ws possile to nlyse the effects in terms of visul ppernce, clenility nd nti-slip performnce. 1

2 1. INTRODUCTION Porcelin stonewre is product in which the synergy etween mnufcturing technology nd physicl-mechnicl properties is prticulrly well developed with excellent results. Since this product hs excellent technicl chrcteristics, such s good flexurl strength, resistnce to surfce rsion nd stins, surfce hrdness nd, in comprison with other clsses of tiles, high frcture toughness, it cn e used in those environments where high performnce nd reliility re required. For these resons, porcelin stonewre tile production is still quite high. For exmple in Itly, in 2012, on totl tile production of out 367 million m 2, more thn 288 million m 2 ws porcelin stonewre (192 million m 2 glzed nd 96 million m 2 unglzed) [1]. With the im to reduce the risk of slipping on cermic tiles, severl tretments hve een introduced to the mrket. Most of these tretments consist of cid sed pplictions on the cermic surfces (hydrofluoric cid, mmonium ifluoride), which re le to produce chemicl etching. In the literture, some works on chemicl etching s nti-slip tretment re ville only for glzed cermic tiles [2,3]. These works fce the prolem from consumer point of view, in terms of sfety, without considering the cermic surfce chrcteristics. Nevertheless, studies to ssess the effectiveness of the tretment in ccordnce with stndrdized methods for slip resistnce re still unville. Systemtic investigtions from the stndpoint of the mnufcturer, y studying in-depth the cermic surfce, re lcking. It is induitle tht deep knowledge of the tile chrcteristics, in terms of composition nd microstructure, plys key role in ssessing whether the cid tretment will give rise to n nti-slip surfce without dmging the cermic product. In the literture, mny works del with the microstructurl modifiction of glzed tiles in cid or sic environment [4,5,6,7,8] nd it is known tht some kinds of crystls, such s wollstonite, re corroded y hydrofluoric cid [5,9]. When commercil hydrofluoric cid- or mmonium ifluoride-sed tretments re pplied on the cermic surfce, severl effects could e produced, such s microstructurl modifictions, decresed gloss, colour chnges nd, mye, lower clenility. In the present work two commercil glzed porcelin stonewre tiles were considered nd nlysed efore nd fter the nti-slip tretment, in order to correlte their performnce (slip resistnce, chemicl nd stin resistnce, wettility nd gloss) with their minerlogicl composition nd microstructurl chrcteristics. 2

3 2. EXPERIMENTAL Two glzed tiles hving different surfce finishes were considered: smple A, chrcterized y heterogeneous nd textured surfce, nd smple B with homogeneous nd smooth surfce. The commercil nti-slip tretment consists of hydrofluoric cid-sed solution, which ws pplied following the mnufcturer s instructions: y hnd, 1 minute for smple A nd 30 seconds for smple B. The photogrphs of oth the smples efore nd fter the cid etching re shown in Fig. 1. Minerlogicl composition nd microstructurl chrcteristics of the tile surfces hve een investigted in-depth y X-ry diffrction (PW 3830; Philips, NL) nd scnning electron microscope (SEM, Zeiss EVO 40, D) equipped with n energy dispersive X-ry ttchment (Inc, Oxford Instruments, UK). Surfce metrology of the tiles hs een studied y confocl profiler (Leic, DCM 3D,D). To evlute the tretment effectiveness, on oth the treted nd untreted surfces, slip resistnce ws determined ccording to severl stndrdized methods: rmp (DIN nd DIN 51097), pendulum (EN ), dynmometer (ASTM C1028) nd Tortus (B.C.R.). The effects cused y the tretment on the surfce were studied in terms of stin resistnce (ISO ), chemicl resistnce (ISO ), wettility (mesurements of contct ngle) nd gloss vritions (ASTM C346). figure 1. Photos of smple A (), untreted (AU) nd treted (AT) of 30x60 cm sizes, nd smple B () untreted (BU) nd treted (BT) of 60x60 cm sizes. 3

4 3. RESULTS The chemicl (Fig. 2 of EDS spectr) nd minerlogicl (Tle I) compositions of the untreted smples A nd B do not show significnt differences even if their surfce finish is quite different: heterogeneous nd textured for smple A nd homogeneous nd smooth for smple B. Plgioclse nd zircon re the min crystls emedded in glssy phse. Smple A, the textured one, shows the presence of rium in the morphous phse nd Smple B, the smoother one, shows the presence of -lumin crystls, in trces. After the cid tretment, the glzes still hve the sme overll chemicl nd minerlogicl composition. In smple A, the textured one, t reltively high mgnifiction (50x ojective), oth the SEM microgrphs (Fig. 3) nd the confocl 3D imges (Fig. 4 -), show different microstructure efore nd fter the tretment. The cid tretment cuses chemicl etching on the cermic surfce: the morphous phse is corroded [7,8,1] nd plgioclse crystls re clerly visile on the surfce. Oserving lrger res of oth the surfces, treted nd untreted, with the confocl profiler y using 10x ojective, only few differences re visile (Fig. 4 c-d). In prticulr, the treted surfce seems to hve lower peks. In ny cse, the 3D prmeters do not clerly show tendency to higher or lower vlues (Tle II). It is proly due to the heterogeneity nd texture of the surfce which could mitigte the tretment effects in terms of roughness. Also in smple B, the smoother one, oth the SEM imges (Fig. 5) nd the surfce mpping (Fig. 6 -) revel chemicl ttck induced y the tretment. The cid corrodes the morphous phse leving zircon nd plgioclse crystls clerly evident [7,8]. The surfce mpping of lrger res cquired y 10x ojective (Fig. 6 c-d), revels some morphologicl differences fter the tretment, which re once gin confirmed y SEM microgrphs (Fig. 5) due to the corrosion of the morphous phse. This is highlighted y the contour digrms (Fig. 7), in which the coloured lines join the points t the sme level. The 3D roughness prmeters (Tle III) confirm some differences: for the treted surfce, BT, ll the vlues re lower with respect to those of the untreted surfce, BU. Smple AU BU Minerlogicl phses Plgioclse nd zircon (trces) in morphous phse Plgioclse, zircon nd -lumin (trces) in morphous phse Tle I. minerlogicl composition of the untreted smples A nd B. 4

5 CASTELLÓN (ESPAÑA) Figure 2. EDS spectr of surfce res for the untreted smples A () nd B (). Figure 3. SEM microgrphs of the untreted () nd treted () smple A. 5

6 c d Figure 4. Confocl 3D imges of smple A y using 50x ojective, untreted () nd treted (); nd y using 10x ojective, untreted (c) nd treted (d). ISO Height Prmeters - AU AT S P (mm) Mximum pek height of the Scle Limited Surfce (SLS) S v (mm) Mximum pit height of the SLS S z (mm) Mximum height of the SLS (sum of S P nd S v ) S A (mm) Arithmeticl men height of the SLS Tle II. 3D roughness prmeters of the untreted nd treted smple A. 6

7 CASTELLÓN (ESPAÑA) Figure 5. SEM microgrphs of the untreted () nd treted () smple B. c d Figure 6. Confocl 3D imges of smple B y using 50x ojective, untreted () nd treted (); nd y using 10x ojective, untreted (c) nd treted (d). 7

8 Figure 7: Contour digrms of the confocl 3D imges of smple B untreted () nd treted () reported in Fig. 6 c-d, respectively. ISO Height prmeters - BU BT S P (mm) Mximum pek height of the Scle Limited Surfce (SLS) S v (mm) Mximum pit height of the SLS S z (mm) Mximum height of the SLS (sum of S P nd S v ) S A (mm) Arithmeticl men height of the SLS Tle III. 3D roughness prmeters of the untreted nd treted smple B. The slip resistnce results determined following the stndrd for the rmp method for workrooms with rised slip dnger (Tle IV), shows tht smple A, the textured one, does not improve fter the tretment, mintining the clssifiction R9, even if the slip ngle increses y 1. Smple B, the smoother one, is not suitle for workrooms with high risk of slipping, not even fter the tretment. In refoot res nd in wet conditions (Tle V) oth the smples, fter tretment, AT nd BT, rech the est clssifiction, A+B+C, while the untreted smples, AU nd BU, re unclssifile. Slip resistnce, ccording to stndrd for pendulum (Tle VI), is evluted y mesuring the loss of energy due to friction etween ruer nd the smple surfce. Results show tht the slip resistnce is clerly improved in oth the smples fter the tretment. Using the dynmometer method (Tle VII), the sttic coefficient of friction is mesured, oth in dry nd wet conditions. In generl, vlues higher thn 0.60 re considered good. For these kinds of smples, fter tretment, the slip resistnce improves especilly in wet conditions. 8

9 With the Tortus method (Tle VIII), the dynmic coefficient of friction is mesured, oth in dry nd wet conditions. The Itlin regultion estlishes tht floors in pulic uildings must hve friction coefficient higher thn 0.40 [1]. After tretment, oth the smples re suitle for this kind of intended use. Smple Averge slip ngle Group AU 6 R9 AT 7 R9 BU 0 UC BT 0 UC Tle IV. Results of slip resistnce with the rmp method with footwer (DIN 51130). Smple Averge slip ngle Group AU 8 UC AT 33 A+B+C BU 11.7 UC BT 35 A+B+C Tle V. Results of slip resistnce with the rmp method refoot (DIN 51097). Smple Wet surfce- PTV AU 17 AT 25 BU 15 BT 30 Tle VI. Results of slip resistnce with the pendulum method in wet conditions (EN ). Smple Dry surfce - µ Wet surfce - µ AU AT BU BT Tle VII. Results of slip resistnce with the dynmometer method in dry nd wet conditions (ASTM C1028). 9

10 Smple Dry surfce with lether - µ Wet surfce with ruer - µ AU AT BU BT Tle VIII. Results of slip resistnce with the Tortus method in dry nd wet conditions (B.C.R.). The stin resistnce (Tle IX) ws determined ccording to the interntionl stndrd ISO , y using three different stining gents nd removing them from the cermic surfce fter 24 hours y using different methods: hot wter, wek or strong detergent, or proper solvent. Results show tht, in oth the smples, the stin resistnce is not compromised fter the tretment, nd stins re removed y flowing hot wter (clss 5) or y clening with wek detergent (clss 4). The chemicl resistnce (Tle X) ws determined ccording to the interntionl stndrd ISO y using household chemicls (mmonium chloride solution), swimming pool slts (sodium hypochloride), cid nd lklis solutions in low nd in high concentrtions (hydrochloric cid, citric cid, potssium hydroxide nd lctic cid). After their removl, the clss determintion is mde y visul exmintion. The treted smples (AT nd BT) mintin the sme clss even if in smple BT it ws not possile to perform the pencil test ecuse the pencil lines cnnot e removed y wet cloth. This is proly due to the gloss decresing fter the tretment in oth the smples, ut especilly in smple B, cused y the chemicl corrosion of the morphous phse (Tle XI) The wettility decreses (Tle XI) in oth the smples fter the tretment, especilly in smple BT, in which the wter contct ngle increses y out 50 with respect to the untreted smple. Smple Chrome green in light oil Iodine (lcoholic solution 13 g/l) Olive oil AU AT BU BT Tle IX. Results of stin resistnce ccording to the stndrd ISO

11 Smple Ammonium Chloride 100 g/l Sodium Hypochloride 20 mg/l HCL 3% V/V Citric Acid 100 g/l KOH 30 g/l HCL 18% V/V Lctic Acid 5% V/V KOH 100 g/l AU GA GLA GHA AT GA GLA GHA BU GA GLA GHA BT GA(V) GLA(V) GHA(V) Tle X. Results of chemicl resistnce ccording to the stndrd ISO (G=glzed surfce; L=low concentrtion of chemicl gent, H=high concentrtion of chemicl gent. Resistnce clsses: A=no visile effect, B=definite chnge in ppernce, C=prtil or complete loss of the originl surfce; (V)=pencil nd reflection test not possile). Smple Gloss, GU Wter contct ngle, Θ AU ± 1.5 AT ± 1.5 BU ± 1.5 BT ± 1.5 Tle XI. Gloss vlues nd wter contct ngle of the untreted nd treted smples A nd B. 4. CONCLUSION In the investigted glzed tiles, the hydrofluoric cid-sed nti-slip tretment cuses chemicl corrosion of the morphous phse, while crystls (plgioclse, zircon nd -lumin) re unchnged. Similr glzes in terms of composition ut with different surfce finish, textured or smooth, give rise to quite different results, especilly for the micro-roughness. In oth the glzes, the slip resistnce ws improved fter tretment, minly in wet conditions. The mintennce of performnces fter tretment ws verified in oth the smples, even if decrese of gloss (out 30%) ws detected. 11

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