Critical thinking skills are one of the 21st century skills that are effectively trained by using the OR-IPA and Problem Based Learning (PBL) Model, therefore this research aims to compare the effectiveness of both. Research design used True Experiment with Randomized Subject Control-group Pre-test and Post-test with 94 pre-service physics teachers. Data collected using the critical thinking skills test and the student response sheet, and then analyzed using t-test and N-gain. The results showed: (1) the teaching instruments of OR-IPA and PBL Model have fulfilled the validity requirements (rα ~ .26) and reliability (α = .96 - .99). (2) Each of OR-IPA, PBL, and Conventional Model can significantly increase critical thinking skills at α = 5%, respectively with average N-gain: medium (.60), medium (.48), and low (.14); with the student response of: very positive, very positive, and less positive. (3) The OR-IPA and PBL Model are effective to improve critical thinking skills, while the Conventional Model is ineffective, and the OR-IPA Model is more effective compared to the PBL Model. Implication of this research is that the OR-IPA Model can be an innovative solution to improve critical thinking skills, but there is still a need for repetitive research like this. Keywords: basic physics, critical thinking skills, OR-IPA model, pre-service physics teachers, and PBL model.

In this study, extraction and synthesis of SiO 2 nanoparticles from silica sands have been conducted by means of two different methods, i.e. dry method (method 1) and hydrothermal process (method 2). The basic difference between the two methods is in the extraction step. The two methods were compared in terms of being more efficient, economical, and superior in obtaining SiO 2 nanoparticles. The SiO 2 nanoparticles were characterized in terms of phase purity, crystallinity, Si-O functional bonding as well as particles size and morphology. The most interesting fact in this study was the formation of both quartz and cristobalite phases within all prepared SiO 2 nanoparticles.

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Indonesia adalah negara dengan potensi alam yang melimpah, khususnya bahan tambang (mineral), diantaranya material-material dengan kandungan oksida yang mempunyai prospek aplikasi sebagai material cerdas (misalnya SiO2, CaCO3, Al2O3,TiO2, dsb). Tujuan dari penelitian ini adalah mencari atau mengidentifikasi kandungan unsur oksida didalam bahan alam jenis batuan atau pasir kuarsa dengan kemurnian tinggi (> 50%), khususnya sebagai sumber oksida SiO2 (silica) dan CaCO3 (calsite). Selanjutnya bahan-bahan tersebut akan diproses dengan milling proses serbuk (ukuran mikron) untuk, peningkatan kemurnian tinggi dan pengecilan ukuran pada orde nanometer. Identifikasi awal adalah melakukan uji difraksi Sinar-X (XRD) dan analisisnya (kualitatif) serta uji flouresensi sinar-X (XRF). Telah dilakukan uji XRD dan XRF pada sampel batuan yang diambil dari daerah Tulungagung, onik dari pulau Bawean-Gresik, dan pasir dari Tuban dan Sumenep. Hasil difraksi sinar X (XRD) bahan alam (batuan dan pasir) yang diambil sebagai sampel yang diambil dari beberapa daerah tersebut, diperoleh bahwa Batu_1(onik) dan Batu_2(putih) menunjukan bahwa sampel tersebut mempunyai fase dominan struktur kristal Calsite (CaCO3), dan untuk pasir dari Tuban dan Sumenep mempunyai fase dominan quartz (SiO2), demikian. Dan hasil XRF menunjukan kandungan CaCO3 pada sampel batuan (onik) cukup tinggi (98,23%), dan untuk sampel pasir (Tuban dan Sumenep) menunjukan kandungan oksida quartz (SiO2) dengan kemurnian yang tinggi (65,9 -76,8 %), dengan impuritas terbanyak CaO dan Fe2O3 (20-28%).