Focus on Cellulose ethers

Haɓaka novel HEMC cellulose ethers don rage agglomeration a cikin gypsum-tushen inji-fesa filastar

Haɓaka novel HEMC cellulose ethers don rage agglomeration a cikin gypsum-tushen inji-fesa filastar

Ana amfani da filasta na tushen gypsum (GSP) a Yammacin Turai tun shekarun 1970.Bayyanar feshin inji ya inganta ingantaccen aikin aikin plastering tare da rage farashin gini.Tare da zurfafa kasuwancin GSP, ether cellulose mai narkewa da ruwa ya zama babban ƙari.Cellulose ether yana ba GSP kyakkyawan aikin riƙe ruwa, wanda ke iyakance ɗaukar danshi a cikin filasta, don haka samun ingantaccen lokacin saiti da ingantattun kayan aikin injiniya.Bugu da kari, takamaiman rheological lankwasa cellulose ether iya inganta sakamakon inji spraying da muhimmanci sauƙaƙa m turmi matakin da karewa matakai.

Duk da fa'idodin ethers na cellulose a cikin aikace-aikacen GSP, yana kuma iya ba da gudummawa ga samuwar busassun kullu yayin fesa.Wadannan kullun da ba a ji ba ana kuma san su da dunƙulewa ko caking, kuma suna iya yin illa ga daidaitawa da ƙare turmi.Agglomeration na iya rage haɓakar rukunin yanar gizon da haɓaka farashin aikace-aikacen samfuran gypsum masu girma.Don ƙarin fahimtar tasirin ethers cellulose akan samuwar lumps a cikin GSP, mun gudanar da bincike don ƙoƙarin gano ma'auni na samfurin da ya dace wanda ke rinjayar samuwar su.Dangane da sakamakon wannan binciken, mun haɓaka jerin samfuran ether cellulose tare da raguwar haɓakar haɓakawa da kuma kimanta su a aikace-aikace masu amfani.

Mabuɗin kalmomi: ether cellulose;gypsum inji fesa filastar;adadin rushewa;kwayoyin halittar jiki

 

1.Gabatarwa

An yi nasarar amfani da ethers na cellulose mai ruwa mai narkewa a cikin gypsum-tushen injin-fasa filasta (GSP) don daidaita buƙatun ruwa, inganta riƙewar ruwa da haɓaka halayen rheological na turmi.Sabili da haka, yana taimakawa wajen inganta aikin rigar turmi, don haka tabbatar da ƙarfin da ake bukata na turmi.Saboda kaddarorin sa na kasuwanci da abokantaka na muhalli, busassun hadaddiyar giyar GSP ya zama kayan gini na ciki da ake amfani da su a ko'ina cikin Turai cikin shekaru 20 da suka gabata.

An yi nasarar sayar da injuna don haɗawa da fesa busasshiyar GSP na shekaru da yawa.Ko da yake wasu fasalolin fasaha na kayan aiki daga masana'antun daban-daban sun bambanta, duk injunan feshi da ake samu na kasuwanci suna ba da damar iyakanceccen lokacin tashin hankali don ruwa ya haɗu da cellulose ether mai ɗauke da gypsum bushe-mix turmi.Gabaɗaya, gabaɗayan tsarin hadawa yana ɗaukar 'yan daƙiƙa kaɗan kawai.Bayan hadawa, jikar turmi ana yin famfo ta cikin bututun isar da sako kuma a fesa bangon da ke ƙasa.An kammala dukan tsari a cikin minti daya.Duk da haka, a cikin irin wannan ɗan gajeren lokaci, cellulose ethers suna buƙatar narkar da su gaba ɗaya don haɓaka dukiyoyinsu a cikin aikace-aikacen.Haɗa samfuran ether ɗin cellulose mai kyau zuwa ƙirar turmi na gypsum yana tabbatar da cikakken rushewa yayin wannan aikin feshin.

The finely ƙasa cellulose ether gina up daidaito da sauri a kan lamba tare da ruwa a lokacin tashin hankali a cikin sprayer.Yunƙurin ɗankowar da ke haifarwa ta hanyar rushewar ether cellulose yana haifar da matsala tare da jikawar ruwa na gypsum siminti na kayan abu guda ɗaya.Yayin da ruwan ya fara kauri, ya zama ƙasa da ruwa kuma ba zai iya shiga cikin ƙananan pores tsakanin sassan gypsum ba.Bayan an katange damar shiga ramuka, tsarin jika na simintin siminti ta hanyar ruwa yana jinkirta.Lokacin hadawa a cikin mai fesa ya fi guntu lokacin da ake buƙata don cikakken jika barbashi na gypsum, wanda ya haifar da samuwar busassun foda a cikin turmi mai laushi.Da zarar an kafa waɗannan kullun, suna hana haɓakar ma'aikata a cikin matakai masu zuwa: daidaita turmi tare da dunƙule yana da matukar damuwa kuma yana ɗaukar ƙarin lokaci.Ko da bayan turmi ya saita, ƙullun da aka kafa na farko na iya nunawa.Misali, rufe ƙullun da ke ciki yayin ginin zai haifar da bayyanar wuraren duhu a mataki na gaba, wanda ba ma son gani.

Ko da yake an yi amfani da ethers cellulose azaman ƙari a cikin GSP shekaru da yawa, tasirin su akan samuwar lumps ɗin da ba a daɗe ba ya zuwa yanzu.Wannan labarin yana gabatar da tsarin tsari wanda za'a iya amfani dashi don fahimtar tushen dalilin agglomeration daga yanayin ether cellulose.

 

2. Dalilan samuwar dunkulewar da ba a yi ba a GSP

2.1 Jika na filasta na tushen

A cikin matakan farko na kafa shirin bincike, an tattara wasu dalilai masu yawa na tushen abubuwan da ke haifar da kullun a cikin CSP.Na gaba, ta hanyar bincike ta hanyar kwamfuta, matsalar ta fi mayar da hankali kan ko akwai hanyar fasaha mai amfani.Ta hanyar waɗannan ayyukan, mafi kyawun mafita ga samuwar agglomerates a cikin GSP an fara tantance shi da farko.Daga duka la'akari da fasaha da kasuwanci, hanyar fasaha na canza jika na gypsum barbashi ta hanyar jiyya ta saman an cire shi.Daga ra'ayi na kasuwanci, ra'ayin maye gurbin kayan aiki na yanzu tare da kayan aikin feshi tare da ɗakin da aka tsara na musamman wanda zai iya tabbatar da isasshen hadawar ruwa da turmi an kawar da shi.

Wani zaɓi shine a yi amfani da ma'aikatan jika azaman ƙari a cikin ƙirar plaster gypsum kuma mun sami takardar shaidar wannan riga.Koyaya, ƙari na wannan ƙari babu makawa yana yin mummunan tasiri ga aikin filasta.Mafi mahimmanci, yana canza halayen jiki na turmi, musamman taurin da ƙarfi.Don haka ba mu yi zurfi a ciki ba.Bugu da kari, ana kuma la'akari da ƙarin abubuwan jika don yuwuwar yin tasiri mara kyau ga muhalli.

Idan akai la'akari da cewa ether cellulose ya riga ya kasance wani ɓangare na tsarin plaster na tushen gypsum, ƙaddamar da ether cellulose kanta ya zama mafi kyawun bayani wanda za'a iya zaba.A lokaci guda, ba dole ba ne ya shafi kaddarorin riƙewar ruwa ko kuma ya yi illa ga kaddarorin rheological na filastar da ake amfani da su.Dangane da hasashen da aka yi a baya cewa samar da foda ba a jika ba a cikin GSP shine saboda karuwar saurin wuce haddi a cikin danko na ethers cellulose bayan haɗuwa da ruwa yayin motsawa, sarrafa halayen rushewar ethers cellulose ya zama babban burin binciken mu. .

2.2 Lokacin narkar da ether cellulose

Hanya mai sauƙi don rage yawan narkar da ethers cellulose ita ce amfani da samfuran granular.Babban hasara na amfani da wannan hanyar a GSP shine cewa barbashi da suke da yawa ba sa narkewa gaba ɗaya a cikin gajeriyar taga tashin hankali na daƙiƙa 10 a cikin injin fesa, wanda ke haifar da asarar riƙewar ruwa.Bugu da ƙari, kumburin ether cellulose wanda ba a narkar da shi ba a mataki na gaba zai haifar da kauri bayan plastering kuma yana rinjayar aikin ginin, wanda shine abin da ba mu so mu gani.

Wani zaɓi don rage yawan narkar da ethers cellulose shine a sake haɗe saman ethers cellulose tare da glioxal.Duk da haka, tun da abin da ke tattare da haɗin kai yana sarrafa pH, yawan rushewar ethers cellulose ya dogara sosai akan pH na maganin ruwa mai kewaye.Ƙimar pH na tsarin GSP da aka haɗe tare da lemun tsami yana da girma sosai, kuma haɗin haɗin gwiwar glioxal a saman yana buɗewa da sauri bayan tuntuɓar ruwa, kuma danko ya fara tashi nan take.Don haka, irin waɗannan magungunan sinadarai ba za su iya taka rawa wajen sarrafa adadin narkar da GSP ba.

Lokacin narkarwar ethers cellulose shima ya dogara da yanayin halittarsu.Duk da haka, wannan gaskiyar ba ta sami kulawa sosai ba ya zuwa yanzu, kodayake tasirin yana da mahimmanci.Suna da adadin narkar da kai tsaye [kg/(m2s)], don haka rushewarsu da haɓakar ɗankowarsu sun yi daidai da saman da ke akwai.Wannan ƙimar na iya bambanta sosai tare da canje-canje a cikin ilimin halittar jiki na ƙwayoyin cellulose.A cikin lissafin mu an ɗauka cewa an kai cikakken danko (100%) bayan 5 seconds na haɗuwa da motsawa.

Lissafi na nau'ikan kwayoyin halitta daban-daban sun nuna cewa barbashi mai siffar zobe suna da danko na 35% na danko na karshe a rabin lokacin hadawa.A cikin lokaci guda, ƙwayoyin ether cellulose mai siffar sanda na iya isa kawai 10%.Barbashi mai siffar diski sun fara narkewa bayan2.5 seconds.

Hakanan an haɗa su da kyawawan halaye masu narkewa don ethers cellulose a cikin GSP.Jinkirta gina dankon farko na sama da daƙiƙa 4.5.Bayan haka, danko ya karu da sauri don isa danko na karshe a cikin dakika 5 na lokacin hadawa.A cikin GSP, irin wannan lokaci mai tsawo da aka jinkirta yana ba da damar tsarin don samun ƙananan danko, kuma ruwan da aka kara da shi zai iya cikakken jika ƙwayoyin gypsum kuma ya shiga cikin pores tsakanin sassan ba tare da damuwa ba.

 

3. Barbashi ilimin halittar jiki na cellulose ether

3.1 Ma'auni na kwayoyin halitta

Tun da siffar cellulose ether barbashi yana da irin wannan gagarumin tasiri a kan solubility, da farko wajibi ne don ƙayyade sigogi da ke kwatanta siffar cellulose ether barbashi, sa'an nan kuma gano bambance-bambance tsakanin wadanda ba wetting samuwar agglomerates ne musamman dacewa siga. .

Mun sami ilimin halittar ɗan adam na cellulose ether ta hanyar fasahar nazarin hoto mai ƙarfi.Za'a iya siffanta yanayin halittar kwayar halitta ta cellulose ethers ta amfani da SYMPATEC mai nazarin hoto na dijital (wanda aka yi a Jamus) da takamaiman kayan aikin bincike na software.An samo mafi mahimmancin sigogin sifofin sifofi sune matsakaicin tsayin filaye da aka bayyana azaman LEFI(50,3) da matsakaicin diamita da aka bayyana azaman DIFI(50,3).Matsakaicin bayanan tsayin fiber ana ɗaukar su cikakken tsayin wani nau'in kwayar halitta ce ta ether.

Yawanci bayanan rarraba girman barbashi kamar matsakaicin fiber diamita DIFI ana iya ƙididdige su bisa adadin barbashi (wanda aka nuna ta 0), tsayi (wanda aka nuna ta 1), yanki (wanda aka nuna ta 2) ko ƙara (wanda aka nuna ta 3).Duk ma'aunin bayanan barbashi a cikin wannan takarda sun dogara ne akan ƙara don haka ana nuna su tare da kari 3.Misali, a cikin DIFI(50,3), 3 yana nufin rarrabuwar girma, 50 kuma yana nufin cewa 50% na ɓangarorin girman rabon rabon ya yi ƙasa da ƙimar da aka nuna, kuma sauran 50% ya fi girma fiye da ƙimar da aka nuna.Ana ba da bayanan siffar sifar ƙwayoyin ether cellulose a cikin micrometers (µm).

3.2 Cellulose ether bayan barbashi ilimin halittar jiki ingantawa

Shan la'akari da sakamakon barbashi surface, da barbashi narkar da lokaci na cellulose ether barbashi tare da sanda-kamar barbashi siffar karfi ya dogara da matsakaicin fiber diamita DIFI (50,3).Dangane da wannan zato, aikin haɓakawa akan ethers cellulose yana nufin samun samfurori tare da matsakaicin matsakaicin matsakaicin fiber DIFI (50,3) don inganta solubility na foda.

Duk da haka, karuwa a cikin matsakaicin matsakaicin fiber tsawon DIFI(50,3) ba a sa ran za a kasance tare da karuwa a cikin matsakaicin girman adadin.Haɓaka sigogi biyu tare zai haifar da barbashi waɗanda suka yi girma don narke gaba ɗaya a cikin lokacin tashin hankali na 10 na biyu na inji.

Saboda haka, manufa hydroxyethylmethylcellulose (HEMC) ya kamata ya sami mafi girma matsakaicin fiber diamita DIFI(50,3) yayin da rike da matsakaicin fiber tsawon LEFI (50,3).Muna amfani da sabon tsarin samar da ether cellulose don samar da ingantaccen HEMC.Siffar barbashi na ether cellulose mai narkewa da ruwa da aka samu ta wannan tsarin samarwa ya sha bamban da nau'in kwayar halitta da ake amfani da shi azaman albarkatun ƙasa don samarwa.A takaice dai, tsarin samarwa yana ba da damar ƙirar siffar sigar cellulose ether ta zama mai zaman kanta daga samar da albarkatun ƙasa.

Hotunan sikanin microscope guda uku: ɗayan ether cellulose da aka samar ta hanyar daidaitaccen tsari, da ɗayan ether cellulose wanda sabon tsari ya samar tare da diamita mafi girma na DIFI(50,3) fiye da samfuran kayan aiki na al'ada.Har ila yau, an nuna yanayin halittar cellulose mai laushi da aka yi amfani da shi wajen samar da waɗannan samfurori guda biyu.

Idan aka kwatanta micrographs na lantarki na cellulose da cellulose ether da aka samar ta hanyar daidaitaccen tsari, yana da sauƙi a gano cewa su biyun suna da halaye iri ɗaya.Yawan adadin barbashi a cikin hotuna biyu suna nuna yawanci dogayen sifofi masu sirara, suna nuna cewa ainihin sifofin halittar halittar jikinsu ba su canza ba ko da bayan halayen sinadaran sun faru.A bayyane yake cewa halayen halayen halayen halayen halayen halayen halayen suna da alaƙa sosai tare da albarkatun ƙasa.

An gano cewa morphological halaye na cellulose ether samar da sabon tsari ne muhimmanci daban-daban, shi yana da ya fi girma matsakaita diamita DIFI (50,3), kuma yafi gabatar zagaye gajere da lokacin farin ciki siffofi, yayin da hankula bakin ciki da kuma dogon barbashi. a cikin albarkatun cellulose Kusan bacewa.

Wannan adadi ya sake nuna cewa ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar ƙwayar cuta ba ta wanzu ba.

 

4. Tasirin ilimin halittar jiki na HEMC akan samuwar kututtukan da ba a daɗe ba a cikin GSP.

An gwada GSP a ƙarƙashin yanayin aikace-aikacen filin don tabbatar da cewa hasashenmu game da tsarin aiki (cewa yin amfani da samfurin ether cellulose tare da mafi girman ma'anar diamita DIFI (50,3) zai rage haɓakar da ba a so) daidai ne.HEMCs tare da ma'anar diamita DIFI(50,3) jere daga 37 µm zuwa 52 µm an yi amfani da su a cikin waɗannan gwaje-gwajen.Don rage tasirin abubuwan ban da ilimin halittar ɗan adam, tushen plaster gypsum da duk sauran abubuwan ƙari ba su canza ba.An kiyaye danko na ether cellulose akai-akai yayin gwajin (60,000mPa.s, 2% bayani mai ruwa, wanda aka auna tare da rheometer HAAKE).

An yi amfani da kayan feshin gypsum na kasuwanci (PFT G4) don fesa a cikin gwajin aikace-aikacen.Mayar da hankali kan kimanta samuwar kututtukan turmi na gypsum da ba a daɗe ba nan da nan bayan an shafa shi a bango.Ƙimar ƙulle-ƙulle a wannan mataki a duk lokacin aiwatar da aikin plastering zai fi bayyana bambance-bambance a aikin samfur.A cikin gwajin, ƙwararrun ma'aikata sun ƙididdige halin da ake ciki, tare da 1 shine mafi kyau kuma 6 shine mafi muni.

Sakamakon gwajin yana nuna alaƙa a fili tsakanin matsakaicin matsakaicin diamita na fiber DIFI (50,3) da maƙiyan aikin clumping.Daidaita da hasashen mu cewa samfuran ether cellulose tare da DIFI mafi girma (50,3) sun fi ƙarancin samfuran DIFI (50,3), matsakaicin maki na DIFI (50,3) na 52 µm shine 2 (mai kyau) , yayin da waɗanda ke da DIFI ( 50,3) na 37µm da 40µm sun zira kwallaye 5 (rasa).

Kamar yadda muka yi tsammani, ɗabi'ar ƙulle-ƙulle a aikace-aikacen GSP ya dogara sosai akan matsakaicin diamita DIFI(50,3) na ether cellulose da aka yi amfani da shi.Bugu da ƙari, an ambata a cikin tattaunawar da ta gabata cewa a cikin dukkanin sigogi na morphological DIFI (50,3) ya shafi tasirin lokacin rushewar cellulose ether powders.Wannan yana tabbatar da cewa lokacin rushewar ether cellulose, wanda ke da alaƙa sosai tare da ilimin halittar ɗan adam, a ƙarshe yana rinjayar samuwar kumbura a cikin GSP.Babban DIFI (50,3) yana haifar da tsawon lokacin rushewar foda, wanda ke rage yawan damar haɓakawa.Duk da haka, tsayin lokacin rushewar foda zai sa ya yi wahala ga ether cellulose don narke gaba ɗaya a cikin lokacin motsawa na kayan aikin feshin.

Sabuwar samfurin HEMC tare da ingantaccen bayanin martabar rushewa saboda girman matsakaicin matsakaicin fiber diamita DIFI (50,3) ba wai kawai yana da mafi kyawun wetting na gypsum foda (kamar yadda aka gani a cikin kimantawar clumping), amma kuma baya shafar aikin riƙe ruwa na samfurin.Riƙewar ruwa da aka auna bisa ga EN 459-2 ba a bambanta da samfuran HEMC na danko iri ɗaya tare da DIFI (50,3) daga 37µm zuwa 52µm.Duk ma'auni bayan mintuna 5 da mintuna 60 sun faɗi cikin kewayon da ake buƙata wanda aka nuna a cikin jadawali.

Duk da haka, an kuma tabbatar da cewa idan DIFI (50,3) ya zama babba, ƙwayoyin ether cellulose ba za su sake narke gaba ɗaya ba.An samo wannan lokacin gwajin DIFI(50,3) na samfurin 59 µM.Sakamakon gwajin riƙewar ruwan sa bayan mintuna 5 kuma musamman bayan mintuna 60 ya kasa cika mafi ƙarancin da ake buƙata.

 

5. Takaitawa

Cellulose ethers sune mahimman abubuwan ƙari a cikin tsarin GSP.Ayyukan bincike da haɓaka samfura a nan suna duban alaƙar da ke tsakanin ƙwayoyin halittar ethers na cellulose da samuwar ƙullun da ba a taɓa gani ba (wanda ake kira clumping) lokacin da aka fesa ta hanyar injiniya.Ya dogara ne akan zato na tsarin aiki cewa lokacin rushewar cellulose ether foda yana rinjayar wetting na gypsum foda ta ruwa kuma ta haka yana rinjayar samuwar clumps.

Lokacin narkarwar ya dogara da ilimin halittar ɗan adam na ether cellulose kuma ana iya samun su ta amfani da kayan aikin bincike na hoto na dijital.A cikin GSP, ethers cellulose tare da babban matsakaicin diamita na DIFI (50,3) sun inganta halayen rushewar foda, suna ba da damar ƙarin lokaci don ruwa don jika ƙwayoyin gypsum sosai, don haka yana ba da damar anti-agglomeration mafi kyau.Ana samar da irin wannan nau'in ether cellulose ta hanyar amfani da sabon tsarin samarwa, kuma nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'in nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i nau'i)) don samar da sabon tsarin samarwa.

Matsakaicin diamita na fiber DIFI (50,3) yana da tasiri mai mahimmanci akan clumping, wanda aka tabbatar ta hanyar ƙara wannan samfurin zuwa wurin gypsum ɗin da aka fesa na'ura na kasuwanci don fesa a kan shafin.Bugu da ƙari, waɗannan gwaje-gwajen feshin filin sun tabbatar da sakamakon gwajin mu: mafi kyawun samfuran ether na cellulose tare da manyan DIFI (50,3) sun kasance masu narkewa gaba ɗaya a cikin taga lokacin tashin GSP.Sabili da haka, samfurin ether na cellulose tare da mafi kyawun kayan anti-caking bayan inganta siffar barbashi har yanzu yana kula da aikin riƙe ruwa na asali.


Lokacin aikawa: Maris 13-2023
WhatsApp Online Chat!